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The Chinese tree shrew ( Tupaia belangeri chinensis ), a member of the mammalian order Scandentia, exhibits considerable similarities with primates, including humans, in aspects of its nervous, immune, and metabolic systems. These similarities have established the tree shrew as a promising experimental model for biomedical research on cancer, infectious diseases, metabolic disorders, and mental health conditions. Herein, we used meta-transcriptomic sequencing to analyze plasma, as well as oral and anal swab samples, from 105 healthy asymptomatic tree shrews to identify the presence of potential zoonotic viruses. In total, eight mammalian viruses with complete genomes were identified, belonging to six viral families, including Flaviviridae , Hepeviridae , Parvovirinae , Picornaviridae , Sedoreoviridae , and Spinareoviridae . Notably, the presence of rotavirus was recorded in tree shrews for the first time. Three viruses - hepacivirus 1, parvovirus, and picornavirus - exhibited low genetic similarity (<70%) with previously reported viruses at the whole-genome scale, indicating novelty. Conversely, three other viruses - hepacivirus 2, hepatovirus A and hepevirus - exhibited high similarity (>94%) to known viral strains. Phylogenetic analyses also revealed that the rotavirus and mammalian orthoreovirus identified in this study may be novel reassortants. These findings provide insights into the diverse viral spectrum present in captive Chinese tree shrews, highlighting the necessity for further research into their potential for cross-species transmission.

To achieve surgical anesthesia in animal experimentation, it is important to select the appropriate anesthetic dose. However, few studies have investigated the reasonable anesthetic dose in tree shrew ( Tupaia belangeri ). The aim of the study was to review the literature to determine the most commonly used anesthetic dose in tree shrew and to calculate the reasonable equivalent dose between tree shrew and rat based on the body surface area conversion. Two groups of 10 adult tree shrews each were anesthetized with 1% sodium pentobarbital through intraperitoneal injection separately at doses of 62 mg/kg (equivalent dose) and 40 mg/kg (reported dose). Anesthetic depth and times were assessed in addition to vital signs. The results showed that the dosage was quite different across studies, ranging from 15 mg/kg to 80 mg/kg, with 40 mg/kg being the most frequently reported dose. However, the group of tree shrews anesthetized with the commonly reported dose were unable to meet the requirements of surgery. In contrast, the equivalent dose (62 mg/kg, intraperitoneal injection with sodium pentobarbital) calculated by body surface area conversion could achieve an anesthetic time of 44.28 ± 3.95 min with no serious or fatal effects. During anesthetic monitoring, we found that sodium pentobarbital had an inhibitory effect on the blood pressure, pulse rate, respiratory rate and rectal temperature in tree shrews, especially on the respiratory rate. Thus, our study indicated that the use of the equivalent dose of sodium pentobarbital was effective in anesthetizing tree shrews.

In the present study, liquid chromatography-mass spectrometer (LC-MS) was used to perform untargeted metabolomics analysis of white adipose tissue (WAT) and brown adipose tissue (BAT) in Tupaia belangeri during cold acclimation. Differences in biochemical composition between WAT and BAT were compared. Clarifying how the two adipose tissues respond to the lower temperature in terms of metabolomics, which elucidate the metabolic process and energy homeostasis regulation mechanism in T. belangeri. The results showed that there were 34, 59 and 20 differential metabolites in the WAT, BAT and WAT compared with BAT, respectively. WAT and BAT had significant differences in various metabolic pathways such as sugar metabolism, amino acid metabolism, lipid metabolism, and nucleotide metabolism, which were closely related to the different biological roles of the two tissues. Increasing the concentrations of intermediate products of tricarboxylic acid (TCA) cycle, pyruvic acid, and phosphoenolpyruvic acid (PEP) in WAT and increasing the metabolites in TCA cycle, glyoxylate and dicarboxylate metabolism pathways in BAT, likely to increase the thermogenic capacity in T. belangeri in response to cold stress. There were more differential metabolic pathways in BAT during cold acclimation than that of in WAT. Moreover, compared to WAT, BAT responds to cold stress by adjusting the concentration of nucleotide metabolites., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Tropical ectotherms are generally believed to be more vulnerable to global heating than temperate species. Currently, however, we have insufficient knowledge of the thermoregulatory physiology of equatorial tropical mammals, particularly of small diurnal mammals, to enable similar predictions. In this study, we measured the resting metabolic rates (via oxygen consumption) of wild-caught lesser treeshrews ( Tupaia minor , order Scandentia) over a range of ambient temperatures. We predicted that, similar to other treeshrews, T. minor would exhibit more flexibility in body temperature regulation and a wider thermoneutral zone compared with other small mammals because these thermoregulatory traits provide both energy and water savings at high ambient temperatures. Basal metabolic rate was on average 1.03 ± 0.10 mL O 2 h -1 g -1 , which is within the range predicted for a 65-g mammal. We calculated the lower critical temperature of the thermoneutral zone at 31.0°C (95% confidence interval: 29.3°-32.7°C), but using metabolic rates alone, we could not determine the upper critical temperature at ambient temperatures as high as 36°C. The thermoregulatory characteristics of lesser treeshrews provide a means of saving energy and water at temperatures well in excess of their current environmental temperatures. Our research highlights the knowledge gaps in our understanding of the energetics of mammals living in high-temperature environments, specifically in the equatorial tropics, and questions the purported lack of variance in the upper critical temperatures of the thermoneutral zone in mammals, emphasizing the importance of further research in the tropics.

Background: Tree shrew, as a kind of small and inexpensive animal between insectivores and primates with the general anatomy being similar to human, could be considered as developed animal model for brain ischemia (BI) study. However, there is no neural behavior scores criterion from tree shrew with BI up to now., Methods: To produce BI model of tree shrew, a novel systematic neurobehavioral assessment scale, named as neural behavior scores (NBS) including aggressive behavior, seeking behavior, gait, startle reflex, high jump and warped-tail phenomenon was firstly established and used in this study. Moreover, magnetic resonance imaging (MRI) was performed on the first day after the operation to detect the imaging changes caused by ischemia. Then TTC, HE staining and immunofluorescent staining for GFAP and NeuN, were performed 24 h after surgery respectively., Results: NBS in BI group were significantly higher than that of sham operation group at 1d, 3d, 5d and 7d after ischemia. Meanwhile, compared with the sham operation group, the T2 images demonstrated significant higher signal and local brain swelling after cerebral ischemia in tree shrews. The staining of TTC and HE showed apparent infarction and necrosis of the cerebral region, and most of neurons exhibited a shrink., Conclusion: We have successfully established the BI model of tree shrew, confirmed by NBS (a new developed method), MRI, HE staining, TTC staining and immunofluorescence staining. It is the first time to report a novel neurobehavioral assessment scale for BI in tree shrew., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Pancreatic cancer is one of the most lethal common cancers. The cell of origin of pancreatic ductal adenocarcinoma (PDAC) has been controversial, and recent evidence suggested acinar cells as the most probable candidate. However, the genetic alterations driving the transformation of pancreatic acinar cells in fully mature animals remain to be deciphered. In this study, lentivirus was used as a tool to introduce genetic engineering in tree shrew pancreatic acinar cells to explore the driver mutation essential for malignant transformation, establishing a novel tree shrew PDAC model, because we found that lentivirus could selectively infect acinar cells in tree shrew pancreas. Combination of oncogenic KRAS G12D expression and inactivation of tumor suppressor genes Tp53 , Cdkn2a and Cdkn2b could induce pancreatic cancer with full penetrance. Silencing of Cdkn2b is indispensable for Rb1 phosphorylation and tumor induction. Tree shrew PDAC possesses the main histological and molecular features of human PDAC. The gene expression profile of tree shrew PDAC was more similar to human disease than a mouse model. In conclusion, we established a novel pancreatic cancer model in tree shrew and identified driver mutations indispensable for PDAC induction from acinar cells in mature adults, demonstrating the essential roles of Cdkn2b in the induction of PDAC originating from adult acinar cells. Tree shrew could thus provide a better choice than mouse for a PDAC model derived from acinar cells in fully mature animals., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)

The now classical idea that programmed cell death (apoptosis) contributes to a plethora of developmental processes still has lost nothing of its impact. It is, therefore, important to establish effective three-dimensional (3D) reconstruction as well as simulation techniques to decipher the exact patterns and functions of such apoptotic events. The present study focuses on the question whether and how apoptosis promotes neurulation-associated processes in the spinal cord of Tupaia belangeri (Tupaiidae, Scandentia, Mammalia). Our 3D reconstructions demonstrate that at least two craniocaudal waves of apoptosis consecutively pass through the dorsal spinal cord. The first wave appears to be involved in neural fold fusion and/or in selection processes among premigratory neural crest cells. The second one seems to assist in establishing the dorsal signaling center known as the roof plate. In the hindbrain, in contrast, apoptosis among premigratory neural crest cells progresses craniocaudally but discontinuously, in a segment-specific manner. Unlike apoptosis in the spinal cord, these segment-specific apoptotic events, however, precede later ones that seemingly support neural fold fusion and/or postfusion remodeling. Arguing with Whitehead that biological patterns and rhythms differ in that biological rhythms depend "upon the differences involved in each exhibition of the pattern" (Whitehead in An enquiry concerning the principles of natural knowledge. Cambridge University Press, London, 1919, p. 198) we show that 3D reconstruction and simulation techniques can contribute to distinguish between (static) patterns and (dynamic) rhythms of apoptosis. By deciphering novel patterns and rhythms of developmental apoptosis, our reconstructions help to reconcile seemingly inconsistent earlier findings in chick and mouse embryos, and to create rules for computer simulations.

Spicy foods elicit a pungent or hot and painful sensation that repels almost all mammals. Here, we observe that the tree shrew (Tupaia belangeri chinensis), which possesses a close relationship with primates and can directly and actively consume spicy plants. Our genomic and functional analyses reveal that a single point mutation in the tree shrew's transient receptor potential vanilloid type-1 (TRPV1) ion channel (tsV1) lowers its sensitivity to capsaicinoids, which enables the unique feeding behavior of tree shrews with regards to pungent plants. We show that strong selection for this residue in tsV1 might be driven by Piper boehmeriaefolium, a spicy plant that geographically overlaps with the tree shrew and produces Cap2, a capsaicin analog, in abundance. We propose that the mutation in tsV1 is a part of evolutionary adaptation that enables the tree shrew to tolerate pungency, thus widening the range of its diet for better survival., Competing Interests: The authors have declared that no competing interests exist.

During postnatal refractive development, an emmetropization mechanism uses refractive error to modulate the growth rate of the eye. Hyperopia (image focused behind the retina) produces what has been described as "GO" signaling that increases growth. Myopia (image focused in front of the retina) produces "STOP" signaling that slows growth. The interaction between GO and STOP conditions is non-linear; brief daily exposure to STOP counteracts long periods of GO. In young tree shrews, long-wavelength (red) light, presented 14 h per day, also appears to produce STOP signals. We asked if red light also shows temporal non-linearity; does brief exposure slow the normal decrease in hyperopia in infant animals? At 11 days after eye opening (DVE), infant tree shrews (n = 5/group) began 13 days of daily treatment (red LEDs, 624 ± 10 or 636 ± 10 nm half peak intensity bandwidth) at durations of 0 h (normal animals, n = 7) or 1, 2, 4, or 7 h. Following each daily red period, colony lighting resumed. A 14 h red group had no colony lights. Refractive state was measured daily; ocular component dimensions at the end of the 13-day red-light period. Even 1 h of red light exposure produced some hyperopia. The average hyperopic shift from normal rose exponentially with duration (time constant 2.5 h). Vitreous chamber depth decreased non-linearly with duration (time constant, 3.3 h). After red treatment was discontinued, refractions in colony lighting recovered toward normal; the initial rate was linearly related to the amount of hyperopia. The red light may produce STOP signaling similar to myopic refractive error., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The Chinese tree shrew ( Tupaia belangeri chinensis ), a squirrel-like and rat-sized mammal, has a wide distribution in Southeast Asia, South and Southwest China and has many unique characteristics that make it suitable for use as an experimental animal. There have been many studies using the tree shrew ( Tupaia belangeri ) aimed at increasing our understanding of fundamental biological mechanisms and for the modeling of human diseases and therapeutic responses. The recent release of a publicly available annotated genome sequence of the Chinese tree shrew and its genome database (www.treeshrewdb.org) has offered a solid base from which it is possible to elucidate the basic biological properties and create animal models using this species. The extensive characterization of key factors and signaling pathways in the immune and nervous systems has shown that tree shrews possess both conserved and unique features relative to primates. Hitherto, the tree shrew has been successfully used to create animal models for myopia, depression, breast cancer, alcohol-induced or non-alcoholic fatty liver diseases, herpes simplex virus type 1 (HSV-1) and hepatitis C virus (HCV) infections, to name a few. The recent successful genetic manipulation of the tree shrew has opened a new avenue for the wider usage of this animal in biomedical research. In this opinion paper, I attempt to summarize the recent research advances that have used the Chinese tree shrew, with a focus on the new knowledge obtained by using the biological properties identified using the tree shrew genome, a proposal for the genome-based approach for creating animal models, and the genetic manipulation of the tree shrew. With more studies using this species and the application of cutting-edge gene editing techniques, the tree shrew will continue to be under the spot light as a viable animal model for investigating the basis of many different human diseases.

The tree shrew ( Tupaia belangeri ) is a promising laboratory animal that possesses a closer genetic relationship to primates than to rodents. In addition, advantages such as small size, easy breeding, and rapid reproduction make the tree shrew an ideal subject for the study of human disease. Numerous tree shrew disease models have been generated in biological and medical studies in recent years. Here we summarize current tree shrew disease models, including models of infectious diseases, cancers, depressive disorders, drug addiction, myopia, metabolic diseases, and immune-related diseases. With the success of tree shrew transgenic technology, this species will be increasingly used in biological and medical studies in the future.

While the recent release of the Chinese tree shrew (Tupaia belangeri chinensis) genome has made the tree shrew an increasingly viable experimental animal model for biomedical research, further study of the genome may facilitate new insights into the applicability of this model. For example, though the tree shrew has a rapid rate of speed and strong jumping ability, there are limited studies on its locomotion ability. In this study we used the available Chinese tree shrew genome information and compared the evolutionary pattern of 407 locomotion system related orthologs among five mammals (human, rhesus monkey, mouse, rat and dog) and the Chinese tree shrew. Our analyses identified 29 genes with significantly high ω (Ka/Ks ratio) values and 48 amino acid sites in 14 genes showed significant evidence of positive selection in the Chinese tree shrew. Some of these positively selected genes, e.g. HOXA6 (homeobox A6) and AVP (arginine vasopressin), play important roles in muscle contraction or skeletal morphogenesis. These results provide important clues in understanding the genetic bases of locomotor adaptation in the Chinese tree shrew.

The tree shrew (Tupaia belangeri chinensis) is a squirrel-like lower primate or a close relative of primates, commonly used as an animal model in biomedical research. Despite more than three decades of usage in research, the clear relationships between body weight, fasting blood glucose concentration, sex and age among tree shrews remain unclear. Based on an investigation of 992 tree shrews (454 males and 538 females) aged between 4 months and 4 years old, we found that male tree shrews have significantly higher body weight and fasting blood glucose concentration than female tree shrews (p < 0.001). The concentration of fasting blood glucose slightly increased with body weight in males (r = 0.152, p < 0.001). Meanwhile, in females, the body weight, concentration of fasting blood glucose and waist circumference positively increased with age (p < 0.001). Additionally, 17 tree shrews with Lee index [body weight (g)*0.33*1000/body length (cm)] above 290 had significantly higher body weight, waist circumference and glycated haemoglobin A1c (HbA1c) than non-obese tree shrews with a Lee index score below 290 (p < 0.001). Interestingly, 6 of 992 tree shrews (three males and three females, 2-4 years old) displayed impaired plasma triglycerides, HbA1c, low-density lipoprotein and oral glucose tolerance test, suggestive of the early symptoms of metabolic syndrome. This study provides the first clear relationships between body weight, fasting blood glucose concentration, sex and age in tree shrews, further improving our understanding of this relationship in metabolic syndrome (MetS). Given the similarity of tree shrews to humans and non-human primates, this finding supports their potential use as an animal model in the research of MetS., (© 2013 Blackwell Verlag GmbH.)

Establishing non-human primate models of human diseases is an efficient way to narrow the large gap between basic studies and translational medicine. Multifold advantages such as simplicity of breeding, low cost of feeding and facility of operating make the tree shrew an ideal non-human primate model proxy. Additional features like vulnerability to stress and spontaneous diabetic characteristics also indicate that the tree shrew could be a potential new animal model of human diseases. However, basal physiological indexes of tree shrew, especially those related to human disease, have not been systematically reported. Accordingly, we established important basal physiological indexes of domesticated tree shrews including several factors: (1) body weight, (2) core body temperature and rhythm, (3) diet metabolism, (4) locomotor rhythm, (5) electroencephalogram, (6) glycometabolism and (7) serum and urinary hormone level and urinary cortisol rhythm. We compared the physiological parameters of domesticated tree shrew with that of rats and macaques. Results showed that (a) the core body temperature of the tree shrew was 39.59±0.05 ℃, which was higher than that of rats and macaques; (b) Compared with wild tree shrews, with two activity peaks, domesticated tree shrews had only one activity peak from 17:30 to 19:30; (c) Compared with rats, tree shrews had poor carbohydrate metabolism ability; and (d) Urinary cortisol rhythm indicated there were two peaks at 8:00 and 17:00 in domesticated tree shrews, which matched activity peaks in wild tree shrews. These results provided basal physiological indexes for domesticated tree shrews and laid an important foundation for diabetes and stress-related disease models established on tree shrews.

Recognition memories are formed during perceptual experience and allow subsequent recognition of previously encountered objects as well as their distinction from novel objects. As a consequence, novel objects are generally explored longer than familiar objects by many species. This novelty preference has been documented in rodents using the novel object recognition (NOR) test, as well is in primates including humans using preferential looking time paradigms. Here, we examine novelty preference using the NOR task in tree shrew, a small animal species that is considered to be an intermediary between rodents and primates. Our paradigm consisted of three phases: arena familiarization, object familiarization sessions with two identical objects in the arena and finally a test session following a 24-h retention period with a familiar and a novel object in the arena. We employed two different object familiarization durations: one and three sessions on consecutive days. After three object familiarization sessions, tree shrews exhibited robust preference for novel objects on the test day. This was accompanied by significant reduction in familiar object exploration time, occurring largely between the first and second day of object familiarization. By contrast, tree shrews did not show a significant preference for the novel object after a one-session object familiarization. Nonetheless, they spent significantly less time exploring the familiar object on the test day compared to the object familiarization day, indicating that they did maintain a memory trace for the familiar object. Our study revealed different time courses for familiar object habituation and emergence of novelty preference, suggesting that novelty preference is dependent on well-consolidated memory of the competing familiar object. Taken together, our results demonstrate robust novelty preference of tree shrews, in general similarity to previous findings in rodents and primates., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Study Objectives: In this study the authors characterized sleep architecture and sleep homeostasis in the tree shrew, Tupaia belangeri, a small, omnivorous, day-active mammal that is closely related to primates., Design: Adult tree shrews were individually housed under a 12-hr light/12-hr dark cycle in large cages containing tree branches and a nest box. The animals were equipped with radio transmitters to allow continuous recording of electroencephalogram (EEG), electromyogram (EMG), and body temperature without restricting their movements. Recordings were performed under baseline conditions and after sleep deprivation (SD) for 6 hr or 12 hr during the dark phase., Measurements and Results: Under baseline conditions, the tree shrews spent a total of 62.4 ± 1.4% of the 24-hr cycle asleep, with 91.2 ± 0.7% of sleep during the dark phase and 33.7 ± 2.8% sleep during the light phase. During the dark phase, all sleep occurred in the nest box; 79.6% of it was non-rapid eye movement (NREM) sleep and 20.4% was rapid eye movement (REM) sleep. In contrast, during the light phase, sleep occurred almost exclusively on the top branches of the cage and only consisted of NREM sleep. SD was followed by an immediate increase in NREM sleep time and an increase in NREM sleep EEG slow-wave activity (SWA), indicating increased sleep intensity. The cumulative increase in NREM sleep time and intensity almost made up for the NREM sleep that had been lost during 6-hr SD, but did not fully make up for the NREM sleep lost during 12-hr SD. Also, only a small fraction of the REM sleep that was lost was recovered, which mainly occurred on the second recovery night., Conclusions: The day-active tree shrew shares most of the characteristics of sleep structure and sleep homeostasis that have been reported for other mammalian species, with some peculiarities. Because the tree shrew is an established laboratory animal in neurobiological research, it may be a valuable model species for studies of sleep regulation and sleep function, with the added advantage that it is a day-active species closely related to primates.

Variations in environmental factors instigate significant changes in the physiology and behavior of animals, necessary for their survival. The present study investigated the hypothesis that ambient temperature is a cue capable of inducing changes in body mass, energy intake, and thermogenic capacity. Moreover, the current study determined the potential role of leptin in regulating adaptive thermogenesis in tree shrews (Tupaia belangeri). The tree shrew was chosen as the experimental animal as they inhabit a wide area of Asia and must acclimatize to the cold. Animals were subjected to either 5° C over 28 days to simulate cold acclimation, or maintained under the original climate of room temperature. At 28 days cold-acclimatized shrews had increased body mass by 9.41 g compared to controls. The increase in body mass was found primarily to be due to growth of the digestive organs, combined with significantly increased food intake. Under cold acclimation, uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT) was significantly elevated, while serum leptin concentration was significantly depressed below control levels. Serum leptin concentration was negatively correlated with body mass, energy intake, and thermogenic capacity during cold acclimation. In summary, these findings indicate that tree shrews adjust energy intake, thermogenic capacity, and body reserves in response to the cold, and further suggest that circulating leptin may act as a key signaling protein to regulate these adaptations.

Background: Recent results in birds, marsupials, rodents and nonhuman primates suggest that phylogeny and ecological factors such as body size, diet and postural habit of a species influence limb usage and the direction and strength of limb laterality. To examine to which extent these findings can be generalised to small-bodied rooting quadrupedal mammals, we studied trees shrews (Tupaia belangeri)., Methodology/principal Findings: We established a behavioural test battery for examining paw usage comparable to small-bodied primates and tested 36 Tupaia belangeri. We studied paw usage in a natural foraging situation (simple food grasping task) and measured the influence of varying postural demands (triped, biped, cling, sit) on paw preferences by applying a forced-food grasping task similar to other small-bodied primates. Our findings suggest that rooting tree shrews prefer mouth over paw usage to catch food in a natural foraging situation. Moreover, we demonstrated that despite differences in postural demand, tree shrews show a strong and consistent individual paw preference for grasping across different tasks, but no paw preference at a population level., Conclusions/significance: Tree shrews showed less paw usage than small-bodied quadrupedal and arboreal primates, but the same paw preference. Our results confirm that individual paw preferences remain constant irrespective of postural demand in some small-bodied quadrupedal non primate and primate mammals which do not require fine motoric control for manipulating food items. Our findings suggest that the lack of paw/hand preference for grasping food at a population level is a universal pattern among those species and that the influence of postural demand on manual lateralisation in quadrupeds may have evolved in large-bodied species specialised in fine manipulations of food items.

Relay neurons in dorsal thalamic nuclei can fire high-frequency bursts of action potentials that ride the crest of voltage-dependent transient (T-type) calcium currents [low-threshold spike (LTS)]. To explore potential nucleus-specific burst features, we compared the membrane properties of dorsal lateral geniculate nucleus (dLGN) and pulvinar nucleus relay neurons using in vitro whole-cell recording in juvenile and adult tree shrew (Tupaia) tissue slices. We injected current ramps of variable slope into neurons that were sufficiently hyperpolarized to de-inactivate T-type calcium channels. In a small percentage of juvenile pulvinar and dLGN neurons, an LTS could not be evoked. In the remaining juvenile neurons and in all adult dLGN neurons, a single LTS could be evoked by current ramps. However, in the adult pulvinar, current ramps evoked multiple LTSs in >70% of recorded neurons. Using immunohistochemistry, Western blot techniques, unbiased stereology, and confocal and electron microscopy, we found that pulvinar neurons expressed more T-type calcium channels (Ca(v) 3.2) and more small conductance potassium channels (SK2) than dLGN neurons and that the pulvinar nucleus contained a higher glia-to-neuron ratio than the dLGN. Hodgkin-Huxley-type compartmental models revealed that the distinct firing modes could be replicated by manipulating T-type calcium and SK2 channel density, distribution, and kinetics. The intrinsic properties of pulvinar neurons that promote burst firing in the adult may be relevant to the treatment of conditions that involve the adult onset of aberrant thalamocortical interactions.

The pulvinar nucleus of the tree shrew receives both topographic (specific) and nontopographic (diffuse) projections from superior colliculus (SC), which form distinct synaptic arrangements. We characterized the physiological properties of these synapses and describe two distinct types of excitatory postsynaptic potentials (EPSPs) that correlate with structural properties of the specific and diffuse terminals. Synapses formed by specific terminals were found to be significantly longer than those formed by diffuse terminals. Stimulation of these two terminal types elicited two types of EPSPs that differed in their latency and threshold amplitudes. In addition, in response to repetitive stimulation (0.5-20 Hz) one type of EPSP displayed frequency-dependent depression whereas the amplitudes of the second type of EPSP were not changed by repetitive stimulation of up to 20 Hz. To relate these features to vesicle release, we compared the synapsin content of terminals in the pulvinar nucleus and the dorsal lateral geniculate (dLGN) by combining immunohistochemical staining for synapsin I or II with staining for the type 1 or type 2 vesicular glutamate transporters (markers for corticothalamic and tectothalamic/retinogeniculate terminals, respectively). We found that retinogeniculate terminals do not contain either synapsin I or synapsin II, corticothalamic terminals in the dLGN and pulvinar contain synapsin I, but not synapsin II, whereas tectopulvinar terminals contain both synapsin I and synapsin II. Finally, both types of EPSPs showed a graded increase in amplitude with increasing stimulation intensity, suggesting convergence; this was confirmed using a combination of anterograde tract tracing and immunocytochemistry. We suggest that the convergent synaptic arrangements, as well as the unique synapsin content of tectopulvinar terminals, allow them to relay a dynamic range of visual signals from the SC.

Across mammalian species, comparable morphological and physiological constraints in the production of airborne vocalisations are suggested to lead to commonalities in the vocal conveyance of acoustic features to specific attributes of callers, such as arousal and individual identity. To explore this hypothesis we examined intra- and interindividual acoustic variation in chatter calls of tree shrews (Tupaia belangeri). The calls were induced experimentally by a disturbance paradigm and related to two defined arousal states of a subject. The arousal state of an animal was primarily operationalised by the habituation of the subject to a new environment and additionally determined by behavioural indicators of stress in tree shrews (tail-position and piloerection). We investigated whether the arousal state and indexical features of the caller, namely individual identity and sex, are conveyed acoustically. Frame-by-frame videographic and multiparametric sound analyses revealed that arousal and identity, but not sex of a caller reliably predicted spectral-temporal variation in sound structure. Furthermore, there was no effect of age or body weight on individual-specific acoustic features. Similar results in another call type of tree shrews and comparable findings in other mammalian lineages provide evidence that comparable physiological and morphological constraints in the production of airborne vocalisations across mammals lead to commonalities in acoustic features conveying arousal and identity, respectively.

Tree shrews are small mammals that bear some semblance to squirrels, but are actually close relatives of primates. Thus, they have been extensively studied as a model for the early stages of primate evolution. In this study, subdivisions of cortex were reconstructed from brain sections cut in the coronal, sagittal, or horizontal planes, and processed for parvalbumin, SMI-32-immunopositive neurofilament protein epitopes, vesicle glutamate transporter 2 (VGluT2), free ionic zinc, myelin, cytochrome oxidase, and Nissl substance. These different procedures revealed similar boundaries between areas, suggesting the detection of functionally relevant borders and allowed a more precise demarcation of cortical areal boundaries. Primary cortical areas were most clearly revealed by the zinc stain, because of the poor staining of layer 4, as thalamocortical terminations lack free ionic zinc. Area 17 (V1) was especially prominent, as the broad layer 4 was nearly free of zinc stain. However, this feature was less pronounced in primary auditory and somatosensory cortex. In primary sensory areas, thalamocortical terminations in layer 4 densely express VGluT2. Auditory cortex consists of two architectonically distinct subdivisions, a primary core region (Ac), surrounded by a belt region (Ab) that had a slightly less developed koniocellular appearance. Primary motor cortex (M1) was identified by the absence of VGluT2 staining in the poorly developed granular layer 4 and the presence of SMI-32-labeled pyramidal cells in layers 3 and 5. The presence of well-differentiated cortical areas in tree shrews indicates their usefulness in studies of cortical organization and function.

The responses of neurons in the primary visual cortex (V1) to an optimally oriented grating are suppressed when a non-optimal grating is superimposed. Although cross-orientation suppression is thought to reflect mechanisms that maintain a distributed code for orientation, the effect of superimposed gratings on V1 population responses is unknown. Using intrinsic signal optical imaging, we found that patterns of tree shrew V1 activity evoked by superimposed equal-contrast gratings were predicted by the averages of patterns evoked by individual component gratings. This prediction held across contrasts, for summed sinusoidal gratings or nonsumming square-wave gratings, and was evident in single-unit extracellular recordings. Intracellular recordings revealed consistent levels of suppression throughout the time course of subthreshold responses. These results indicate that divisive suppression powerfully governs population responses to multiple orientations. Moreover, the specific form of suppression that we observed appears to support independent population codes for stimulus orientation and strength and calls for a reassessment of mechanisms that underlie cross-orientation suppression.

In order to gain a better understanding of the ancestral properties of the perivertebral muscles of mammals, this study investigated the fiber type composition of these muscles in six small, extant therians (two metatherians and four eutherians) similar in body shape to early mammals. Despite a few species-specific differences, the investigated species were very similar in their overall distribution of fiber types indicating similar functional demands on the back muscles in mammals of this body size and shape. Deep and short, mono- or multisegmental muscles (i.e., mm. interspinales, intermammillares, rotatores et intertransversarii) consistently showed the highest percentage of slow, oxidative fibers implying a function as local stabilizers of the vertebral column. Superficial and large, polysegmental muscles (i.e., mm. multifidus, sacrospinalis, iliopsoas et psoas minor) were predominantly composed of fast, glycolytic fibers suggesting they function to both globally stabilize and mobilize the spine during rapid non-locomotor and locomotor activities. Some muscles contained striking accumulations of oxidative fibers in specific regions (mm. longissimus et quadratus lumborum). These regions are hypothesized to function independently from the rest of the muscle belly and may be comparable in their functionality to regionalized limb muscles. The deep, central oxidative region in the m. longissimus lumborum appears to be a general feature of mammals and likely serves a proprioceptive function to control the postural equilibrium of the pelvic girdle and lumbar spine. The potential functions of the m. quadratus lumborum during ventilation and ventral stabilization of the vertebral column are discussed. Because representatives of the stem lineage of mammals were comparable in their body proportions and probably also locomotor parameters to the species investigated here, I suggest that the described fiber type distribution is representative of the ancestral condition in mammals. The origin of mammals was associated with a substantial enlargement of the epaxial muscles and the addition of subvertebral muscle mass. Because this novel muscle mass is mainly composed of fast, glycolytic fibers in extant species, it is plausible that these changes were associated with the evolution of increased sagittal mobility in the posterior trunk region in the therapsid ancestors of mammals. The caudally increasing role of sagittal bending in body propulsion is consistent with the overall increase in the percentage of glycolytic fibers in the cranio-caudal direction. The evolution of mammals was also associated with a loss of ribs in the posterior region of the trunk. This loss of ribs is thought to have decreased the stability of the posterior trunk, which may explain the observed greater oxidative capacity of the caudal local stabilizers. The increased need for postural feedback in the more mobile lumbar region may also explain the evolution of the proprioceptive system in the m. longissimus lumborum. Furthermore, the anatomical subdivision of the transversospinal muscle into several smaller muscle entities is suggested to facilitate their functional specialization.

We have investigated the cellular characteristics, especially chromatin condensation and the basic nuclear protein profile, during spermiogenesis in the common tree shrew, Tupaia glis. Spermatids could be classified into Golgi phase, cap phase, acrosome phase, and maturation phase. During the Golgi phase, chromatin was composed of 10-nm and 30-nm fibers with few 50-nm to 60-nm knobby fibers. The latter were then transformed into 70-nm knobby fibers during the cap phase. In the acrosome phase, all fibers were packed into the highest-order knobby fibers, each about 80-100 nm in width. These chromatin fibers became tightly packed in the maturation phase. In a mature spermatozoon, the discoid-shaped head was occupied by the acrosome and completely condensed chromatin. H3, the core histone, was detected by immunostaining in all nuclei of germ cell stages, except in spermatid steps 15-16 and spermatozoa. Protamine, the basic nuclear protein causing the tight packing of sperm chromatin, was detected by immunofluorescence in the nuclei of spermatids at steps 12-16 and spermatozoa. Cross-immunoreactivity of T. glis H3 and protamine to those of primates suggests the evolutionary resemblance of these nuclear basic proteins in primate germ cells.

The developmental life-history of tree-shrews conforms with the general primate pattern. Consequently, elucidation of the tree-shrew's neuroendocrine reproductive axis could shed light on the mechanisms that underlie human pubertal development. In the present study, we examined plasma gonadotropin concentrations in male tree-shrews from birth to sexual maturity, and related them to changes in the androgenic and gametogenic status of the testis. A hypogonadotropic infantile phase, during which a stable population of primordial cells is established, extended from birth to approximately Day 30. Following a short juvenile phase (Days 30-40), a pubertal phase of accelerated reproductive development was initiated between Days 40-55. At this time, FSH and LH levels rose and testosterone concentrations reached peak levels coincident with the descent of the testes, accelerated growth in the reproductive tract and the onset of spermatogenesis. To test whether this developmental peak in testosterone secretion is an important determinant in the normal onset of puberty, we exposed male tree-shrews prematurely to high circulating androgen levels for various periods and then examined the impact on key components of the developing reproductive axis. The testosterone implants failed to initiate spermatogenesis and the testes remained in an infantile state for the duration of the treatment, whereas implant removal led to the development of full spermatogenic activity. In both normal and experimental situations, low levels of FSH were associated with a lack of spermatogenic activity while the progression of germ cell development was precisely correlated with rising FSH levels. Taken together, these data establish a comprehensive picture of reproductive development in the male tree-shrew, and also provide support for the hypothesis that FSH plays a primary role in the initiation of spermatogenesis.

Empirical research on human and non-human primates suggests that communication sounds express the intensity of an emotional state of a signaller. In the present study, we have examined communication sounds during induced social interactions of a monogamous mammal, the tree shrew. To signal their unwillingness to mate, female tree shrews show defensive threat displays towards unfamiliar males paralleled by acoustically variable squeaks. We assumed that the distance between interacting partners as well as the behavior of the male towards the female indicates the intensity of perceived social threat and thereby the arousal state of a female. To explore this hypothesis we analyzed dynamic changes in communication sounds uttered during induced social interactions between a female and an unfamiliar male. Detailed videographic and sound analyzes revealed that the arousal state predicted variations in communication sound structure reliably. Both, a decrease of distance and a male approaching the female led to an increase in fundamental frequency and repetition rate of syllables. These findings support comparable results in human and non-human primates and suggest that common coding rules in communication sounds govern acoustic conflict regulation in mammals.

Muscle fiber type composition of intrinsic shoulder muscles was examined in tree shrews, cotton-top tamarins, and squirrel monkeys with respect to their shoulder kinematics and forelimb loading during locomotion. Enzyme- and immunohistochemical techniques were applied to differentiate muscle fiber types on serial cross-sections of the shoulder. In the majority of the shoulder muscles, the proportions of fatigue resistant slow-twitch fibers (SO) and fatigable fast-twitch fibers (FG) were inversely related to each other, whereas the percentage of intermediate FOG-fibers varied independently. A segregation of fatigue resistant SO-fibers into deep muscle regions is indicative of differential activation of histochemically distinct muscle regions in which deep regions stabilize the joint against gravitational loading. In all three species, this antigravity function was demonstrated for both the supraspinatus and the cranial subscapularis muscle, which prevent passive joint flexion during the support phase of the limb. The infraspinatus muscle showed a high content of SO-fibers in the primate species but not in the tree shrew, which demonstrates the "new" role of the infraspinatus muscle in joint stabilization related to the higher degree of humeral protraction in primates. In the tree shrew and the cotton-top tamarin, a greater proportion of the body weight is carried on the forelimb, but the squirrel monkey exhibits a weight shift to the hind limbs. The lower amount of forelimb loading is reflected by an overall lower proportion of fatigue resistant muscle fibers in the shoulder muscles of the squirrel monkey. Several muscles such as the deltoid no longer function as joint stabilizers and allow the humerus to move beyond the scapular plane. These differences among species demonstrate the high plasticity of the internal muscle architecture and physiology which is suggested to be the underlying reason for different muscle activity patterns in homologous muscles. Implications for the evolution of new locomotor modes in primates are discussed.

During the evolution of therian mammals, the two-segmented, sprawled tetrapod limbs were transformed into three-segmented limbs in parasagittal zig-zag configuration (three-segment limb hypothesis). As a consequence, the functional correspondence of limb segments has changed (now: scapula to thigh, upper arm to shank, fore arm plus hand to foot). Therefore, the scapula was taken into account in the current study of the postnatal growth of the postcranial skeleton in two small mammalian species (Tupaia glis, Galea musteloides). Comparisons were made between the functionally equivalent elements and not in the traditional way between serially homologous segments. This study presents a test of the three-segment limb hypothesis which predicts a greater ontogenetic congruence in the functionally equivalent elements in fore and hind limbs than in the serially homologous elements. A growth sequence, with decreasing regression coefficients from proximal to distal, was observed in both species under study. This proximo-distal growth sequence is assumed to be ancestral in the ontogeny of eutherian mammals. Different reproductive modes have evolved within eutherian mammals. To test the influence of different life histories on ontogenetic scaling during postnatal growth, one species with altricial juveniles (Tupaia glis) assumed to be the ancestral mode of development for eutherians and one species with derived, precocial young (Galea musteloides) were selected. The growth series covered postnatal development from the first successive steps with a lifted belly to the adult locomotory pattern; thus, functionally equivalent developmental stages were compared. The higher number of allometrically positive or isometrically growing segments in the altricial mammalian species was interpreted as a remnant of the fast growth period in the nest without great locomotor demands, and the clearly negative allometry in nearly all segments in the precocial young was interpreted as a response to the demand on early locomotor activity. Different life histories seem to have a strong influence on postnatal ontogenetic scaling; the effects of the developmental differences are still observable when comparing adults of the two species.

We examined masseter and temporalis recruitment and firing patterns during chewing in five male Belanger's treeshrews (Tupaia belangeri), using electromyography (EMG). During chewing, the working-side masseters tend to show almost three times more scaled EMG activity than the balancing-side masseters. Similarly, the working-side temporalis muscles have more than twice the scaled EMG activity of the balancing-side temporalis. The relatively higher activity in the working-side muscles suggests that treeshrews recruit less force from their balancing-side muscles during chewing. Most of the jaw-closing muscles in treeshrews can be sorted into an early-firing or late-firing group, based on occurrence of peak activity during the chewing cycle. Specifically, the first group of jaw-closing muscles to reach peak activity consists of the working-side anterior and posterior temporalis and the balancing-side superficial masseter. The balancing-side anterior and posterior temporalis and the working-side superficial masseter peak later in the power stroke. The working-side deep masseter peaks, on average, slightly before the working-side superficial masseter. The balancing-side deep masseter typically peaks early, at about the same time as the balancing-side superficial masseter. Thus, treeshrews are unlike nonhuman anthropoids that peak their working-side deep masseters early and their balancing-side deep masseters late in the power stroke. Because in anthropoids the late firing of the balancing-side deep masseter contributes to wishboning of the symphysis, the treeshrew EMG data suggest that treeshrews do not routinely wishbone their symphyses during chewing. Based on the treeshrew EMG data, we speculate that during chewing, primitive euprimates 1) recruited more force from the working-side jaw-closing muscles as compared to the balancing-side muscles, 2) fired an early group of jaw-closing muscles followed by a second group of muscles that peaked later in the power stroke, 3) did not fire their working-side deep masseter significantly earlier than their working-side superficial masseter, and 4) did not routinely fire their balancing-side deep masseter after the working-side superficial masseter., (Copyright 2004 Wiley-Liss, Inc.)

Previous studies have demonstrated that stress may affect the hippocampal GABAergic system. Here, we examined whether long-term psychosocial stress influenced the number of parvalbumin-containing GABAergic cells, known to provide the most powerful inhibitory input to the perisomatic region of principal cells. Adult male tree shrews were submitted to 5 weeks of stress, after which immunocytochemical and quantitative stereological techniques were used to estimate the total number of hippocampal parvalbumin-immunoreactive (PV-IR) neurons. Stress significantly decreased the number of PV-IR cells in the dentate gyrus (DG) (-33%), CA2 (-28%), and CA3 (-29%), whereas the CA1 was not affected. Additionally, we examined whether antidepressant treatment offered protection from this stress-induced effect. We administered fluoxetine (15 mg/kg per day) and SLV-323 (20 mg/kg per day), a novel neurokinin 1 receptor (NK1R) antagonist, because the NK1R has been proposed as a possible target for novel antidepressant therapies. Animals were subjected to a 7-day period of psychosocial stress before the onset of daily oral administration of the drugs, with stress continued throughout the 28-day treatment period. NK1R antagonist administration completely prevented the stress-induced reduction of the number of PV-IR interneurons, whereas fluoxetine attenuated this decrement in the DG, without affecting the CA2 and CA3. The effect of stress on interneuron numbers may reflect real cell loss; alternatively, parvalbumin concentration is diminished in the neurons, which might indicate a compensatory attempt. In either case, antidepressant treatment offered protection from the effect of stress and appears to modulate the hippocampal GABAergic system. Furthermore, the NK1R antagonist SLV-323 showed neurobiological efficacy similar to that of fluoxetine.

Spectral-sensitivity functions for large, long-duration increments presented on a photopic white background indicate that wavelength-opponent mechanisms mediate detection in both normal and dichromatic humans. Normal humans exhibit high color-vision sensitivity as they discriminate the color of spectral flashes at detection-threshold intensities. However, dichromatic humans require stimuli up to about 0.4 log units above detection intensity to see certain colors. This low color-vision sensitivity in human dichromats may be an abnormal condition involving a defect in postreceptoral color processing. To test this hypothesis, we determined color-discrimination thresholds in normally dichromatic species: chipmunk, 13-lined ground squirrel, and tree shrew. For comparison, we also tested humans with normal and abnormal (deutan) color vision with the same apparatus and methods. Animals were trained to perform spatial two-choice discrimination tasks for food reward. Detection thresholds were determined for increments of white, 460 nm, 540 nm, 560 nm, 580 nm, 500 nm/long-pass, and 500 nm/short-pass on white backgrounds of 1.25 cd/m2, 46 cd/m2, and 130 cd/m2. Animals were also trained to respond to the colored increments when paired with the white increment when both were at equally detectable intensities. Color-discrimination thresholds were determined by dimming stimulus pairs (colored vs. white) until the subjects could no longer make the discriminations. Results indicated that the normally dichromatic species could discriminate colored stimuli from white at a mean intensity of 0.1 (+/-0.1) log units above detection threshold. The ability of normally dichromatic species to discriminate color near detection-threshold intensity is consistent with increment spectral-sensitivity functions that indicate detection by wavelength-opponent mechanisms. In keeping with previous studies, normal human trichromats discriminated color near detection-threshold intensities but humans with deutan color vision required suprathreshold intensities to discriminate the color of middle and long wavelengths. This high color-vision sensitivity of normally dichromatic species suggest that the low color-vision sensitivity in dichromatic humans is an abnormal condition and indicates a possible defect in their postreceptoral color-vision processing.

The local-global map hypothesis states that locally organized response properties--such as orientation preference--result from visuotopically organized local maps of non-retinotopic response properties. In the tree shrew, the lateral extent of horizontal patchy connections is as much as 80-100% of V1 and is consistent with the length summation property. We argue that neural signals can be transmitted across the entire extent of V1 and this allows the formation of maps at the local scale that are visuotopically organized. We describe mechanisms relevant to the formation of local maps and report modeling results showing the same patterns of horizontal connectivity, and relationships to orientation preference, seen in vivo. The structure of the connectivity that emerges in the simulations reveals a 'hub and spoke' organization. Singularities form the centers of local maps, and linear zones and saddle-points arise as smooth border transitions between maps. These findings are used to present the case for the local-global map hypothesis for tree shrew V1.

Aging is associated with a decreased ability to store and retrieve information. The hippocampal formation plays a critical role in such memory processes, and its integrity is affected during normal aging. We used tree shrews (Tupaia belangeri) as an animal model of aging, because in many characteristics, tree shrews are closer to primates than they are to rodents. Young and aged male tree shrews performed a holeboard spatial memory task, which permits assessment of reference and working memory. Upon completion of the behavioral measurements, we carried out modified stereological analyses of neuronal numbers in various subdivisions of the hippocampus and used the Cavalieri method to calculate the volumes of these subfields. Results showed that the working memory of aged tree shrews was significantly impaired compared with that of young animals, whereas the hippocampus-dependent reference memory remained unchanged by aging. Estimation of the number of neurons revealed preserved neuron numbers in the subiculum, in the subregions CA1, CA2, CA3, and in the hilus of the dentate gyrus. Volume measurements showed no aging-related changes in the volume of any of these hippocampal subregions, or in the molecular and granule cell layers of the dentate gyrus of tree shrews. We conclude that the observed changes in memory performance in aging tree shrews are not accompanied by observable reductions of hippocampal neuron numbers or hippocampal volume, rather, the changes in memory performance are more likely the result of modified subcellular mechanisms that are affected by the aging process., (Copyright 2003 Wiley-Liss, Inc.)

A comparative study of quantitative kinematic data of fore- and hindlimb movements of eight different mammalian species leads to the recognition of basic principles in the locomotion of small therians. The description of kinematics comprises fore- and hindlimb movements as well as sagittal spine movements including displacement patterns of limb segments, their contribution to step length, and joint movements. The comparison of the contributions of different segments to step length clearly shows the proximal parts (scapula, femur) to produce more than half of the propulsive movement of the whole limb at symmetrical gaits. Basically, a three-segmented limb with zigzag configuration of segments is mainly displaced at the scapular pivot or hip joint, both of which have the same vertical distance to the ground. Two segments operate in matched motion during retraction of the limb. While kinematic parameters of forelimbs are independent of speed and gait (with the scapula as the dominant element), fundamental changes occur in hindlimb kinematics with the change from symmetrical to in-phase gaits. Forward motion of the hindlimbs is now mainly due to sagittal lumbar spine movements contributing to half of the step length. Kinematics of small therian mammals are independent of their systematic position, their natural habitat, and also of specific anatomical dispositions (e.g. reduction of fingers, toes, or clavicle). In contrast, the possession of a tail influences 'pelvic movements'.

Animal models for chronic stress represent an indispensable preclinical approach to human pathology since clinical data point to a major role of psychological stress experiences, acute and/or chronic, to the development of behavioral and physiological disturbances. Chronic emotional arousal is a consequence of various types of social interactions, and one major neurohumoral accompaniment is the activation of the classic stress circuit, the limbic--hypothalamic--pituitary--adrenocortical (LHPA) axis. The adrenocortical glucocorticoid hormones cortisol and corticosterone are principal effectors within this circuit since they affect neurotransmission and neuroendocrine control, thus having profound effects on mood and behavior. Using the experimental paradigm of chronic psychosocial stress in tree shrews, we investigated the impact of aversive chronic social encounters on hippocampal structure and function. In chronically stressed animals, we observed dendritic atrophy of hippocampal pyramidal neurons and an impairment of neurogenesis in the dentate gyrus. However, a stress-induced loss of hippocampal neurons was not observed in this animal model. This review summarizes our recent results on structural changes occurring during chronic stress in neurons of the hippocampus and their potential influence on learning and memory. We discuss whether these changes are reversible and to what extent glucocorticoids might be responsible for the stress-induced effects.

The effect of different types of physical stress on brain dopaminergic function has been well established in rodents; however, the role of the dopaminergic system in more naturalistic stress situations is poorly understood. Therefore, the aim of the current study was to investigate the effect of chronic psychosocial stress on the dopamine transporter, which is an important component in the regulation of dopaminergic neurotransmission. For this purpose, we used the well-characterized paradigm of subordination stress in male tree shrews (Tupaia belangeri). In the present study, the animals were subjected to psychosocial stress for 28 days. Animals were daily videotaped and locomotor activity was quantified. In subordinate animals, urinary cortisol and noradrenaline, as well as adrenal weight, were increased, whereas body weight, locomotor activity and testicular function were decreased. Brain dopamine transporter binding sites were quantified by in vitro autoradiography using [3H] WIN 35,428 as ligand. Chronic stress reduced the number of binding sites (Bmax) in the caudate nucleus and the putamen without affecting the affinity (Kd). Stress did not influence the binding parameters in the nucleus accumbens, the substantia nigra or the ventral tegmental area. Furthermore, we found a positive correlation between locomotor activity and the Bmax values for [3H] WIN 35,428 binding in the caudate nucleus, the putamen and the nucleus accumbens. The present study shows that a naturalistic stressor, such as chronic psychosocial conflict, decreases dopamine transporter binding sites in motor-related brain areas, suggesting that the reduction in locomotor activity in subordinate tree shrews is related to the downregulation of dopamine transporter binding sites.

To study the correlation between blood-retinal barrier (BRB) permeability and development of form deprivation (FD) myopia, FD was induced in tree shrews. The refractive error and the axial dimensions of the optical elements were measured. Ocular fluorescence was measured before and after fluorescein-Na injection. The inward permeability (P(in)) of the BRB was measured before and 15, 30, and 45 days after FD was induced. FD eyes became significantly myopic 15 days after FD was induced (P<0.01), and myopia progressed 45 days after FD was induced compared with untreated controls. Neither anterior chamber length nor lens thickness changed significantly. The vitreous chamber in FD eyes, however, was significantly elongated from 15 days after FD was induced (P<0.01) compared with controls. The P(in) ratio (P(in) [FD eye]/P(in) [untreated control]), increased significantly 45 days after FD was induced (P<0.05). In FD myopia in tree shrews, the BRB permeability increases abnormally. Impaired BRB function might be a secondary effect of myopia development rather than the cause of myopia.

According to current hypotheses, in mammals male-specific behavior is organized perinatally, and activated in adulthood by male gonadal hormones. However, this strict differentiation between early organizational and late activational hormone effects has been criticized recently. Around puberty the testosterone levels of male mammals rise far above adult levels. In this study we examined the relevance of this pubertal testosterone peak on marking behavior of adult tree shrews (Tupaia belangeri). Male tree shrews were castrated before puberty and treated with testosterone either around puberty or in adulthood. Several months later, the marking behavior of the castrated adult animals was examined in standard tests in different scent conditions before and after a second testosterone treatment. Males castrated as adults as well as fertile females were used as controls. The testosterone peak during puberty did not influence male marking behavior in the absence of scent from conspecifics (familiarization marking) or in the presence of female scent (sexual marking). However, testosterone during puberty determined both the male-specific reaction patterns to male scent (territorial marking) and the male-specific regulation of this behavior by testosterone. These results indicate that testosterone during puberty specifically organizes male territorial-marking behavior. To our knowledge, these are the first results demonstrating organizational effects of testosterone during puberty on male behavior.

To examine the susceptible period for deprivation-induced myopia, six groups of tree shrew pups (Tupaia glis belangeri) were monocularly deprived for 12 days with an opaque occluder starting 7, 15, 21, 33, 48, or 63 days after natural eyelid opening. Compared to the untreated fellow control eye, significant myopia and vitreous chamber elongation were produced by the deprivation in all six groups. The effect was greater in the middle three groups in comparison with the youngest and the two oldest groups and the amount of induced myopia and axial elongation was not proportional to the normal rate of axial growth. The peak period of susceptibility was between approximately 15 and 45 days after eye opening during the juvenile, slow-elongation phase of ocular development when the eye is within 7% of its adult axial length. Significant myopia and axial elongation were also induced in adult animals by 70 days of monocular deprivation. To examine recovery from deprivation-induced myopia, the occluder was removed at the end of the 12 day deprivation period. After an additional 48 days of binocular visual experience, no significant myopia was present in the previously deprived eyes in any experimental group. During the recovery period, the elongation rate of the previously deprived eyes was reduced in comparison with the control eyes while normal corneal flattening and lens development continued, thus reducing the myopia. No difference in corneal curvature, relative to the untreated control eyes, was found after deprivation or after the recovery period. Data are presented which suggests that changes in the thickness of the choroid may occur in this mammal during deprivation and recovery that are in the same direction, but of smaller magnitude, than those reported in the chicken. The results of this study provide evidence that visually guided emmetropization occurs in this mammalian species during a period of ocular development analogous to the juvenile period in humans.

Existing hypotheses on the mode of disk formation in the photoreceptor cells of mammals appear to be incompatible: (1) plasma membranes of adjacent evaginations form a disk which, subsequently, is internalized by a disk rim; (2) pinocytotic vesicles are pinched off from the plasma membrane and fuse into a larger vesicle, which flattens and forms a disk. We have studied the development of the cone outer segment and the disk formation in Tupaia belangeri by transmission electron microscopy. During the first two postnatal weeks, the distal part of the single cilium, which is inserted apically on the inner segment, becomes balloon-shaped. Apical to the axoneme, it contains tubular and vesicular material, which, most probably, has been detached from the axonemal microtubules. These tubules and vesicles do not contribute to disks. The balloon-shaped expansion, later retained as the ciliary backbone, establishes the contact with the pigment epithelium. Formation of disks, from the 12-day-old Tupaia onwards, occurs between adjacent evaginations at the outer segment base. The initial disk rims are "hooked" to the ciliary axonemal microtubules. The axonemal microtubules are involved in the initiation and in the alignment of the disks. Disk rim formation and, thus, internalization of disks proceeds from the base to the apex of the outer segment, that is, from the younger to the older disks. In the adult Tupaia, an uneven progression of disk rim formation on both sides of the axoneme is found among consecutive disks. The seemingly incompatible hypotheses on the mode of disk formation reflect a heterochrony of the internalization of membranes and of the disk formation among different mammals and, possibly, between cones and rods.

To study the ovarian function of the common tree shrew (Tupaia glis), monoclonal antibodies (MAb) against its ovarian antigen were produced. Several positive hybridomas were cloned and MAb-T2C9 (IgG) was examined for reactivity. Strong immunoreactivity of MAb-T2C9 was localized within the cytoplasm of luteal cells and in the theca interna cells of Graafian follicles. MAb-T2C9 reacted also with testicular interstitial cells and adrenocortical cells, except those of the zona glomerulosa. Similar reactions were seen in the goat and sheep. Western blotting analysis of the ovine corpus luteum after reaction with MAb-T2C9 revealed a single positive band of approximately 60 kDa. These findings suggest that MAb-T2C9 recognized protein molecules related to steroid synthesis.

A number of acrosome reaction (AR) initiators have been found to be effective in inducing AR of human, laboratory and domestic animal sperm. Using an improved simple fluorescence microscopy, effects of gamma-aminobutyric acid (GABA), progesterone and ionophore A23187 on sperm AR of tree shrew, a useful animal model in biomedical research, have been investigated. Spontaneous AR in 4.92-7.53% of viable sperm was observed. Complete AR in 10.31-18.25% of viable tree shrew sperm was obviously induced by 5 microM and 10 microM calcium ionophore A23187, 1 mM GABA, and 5 microM progesterone, and there were no significant differences between their abilities to initiate complete AR. No significant differences of AR percentages between 1- and 2-h treatments with A23187, progesterone and/or GABA were observed. These results suggested that the responses of tree shrew sperm to these AR initiators are similar to that of human and other mammalian sperm.

There is increasing evidence from animal studies in support of the concept of an active emmetropization mechanism which has potentially important clinical ramifications for the management of refractive errors. Recent research into refractive development and emmetropization is reviewed, with emphasis given to work involving the chick, tree shrew and monkey, which represent the three most widely used animal models in this field. The findings of this research are reviewed in a clinical context. Compensatory eye growth responses to focusing errors imposed by lenses represent the most compelling evidence for active emmetropization. These observations are complemented by other evidence showing recovery from induced refractive errors such as form-deprivation myopia. Of the animals listed above, chicks show the most impressive emmetropization, being able to compensate fully (using choroidal and scleral mechanisms) to lens powers ranging from +15 D to -10 D. The range of lens powers eliciting appropriate compensatory responses is narrower in the tree shrew and monkey, and the response patterns generally are also more complex to interpret. These data relate to young animals and together indicate refractive plasticity during development. Extrapolation of these findings to humans predicts that natural emmetropization will be inhibited in neonates by early intervention with prescription lenses, and that refractive correction of myopia will lead to accelerated progression. This convincing evidence for active emmetropization warrants due consideration in developing clinical management strategies for refractive errors.

In the wild, tree shrews (Tupaia belangeri) live in pairs in territories which they defend vigorously against strange conspecifics. The paper gives an overview on some of our laboratory studies with tree shrews, which demonstrate the great relevance the concepts of Jim Henry have in understanding the biological relevance of mammalian social behavior. A basic result of these studies is that the physiological consequences of social relations between mammals depend on the appraisal of the situation by the animals and their coping behavior. Appraisal of a stimulus or a situation, as well as the resulting coping behavior, are basically psychological processes. There are, therefore, no simple relationships between stimuli imposed on individuals and their physiological responses; rather the behavioral, psychological and, thus, the physiological responses of individuals to stimuli differ depending on their genetics, prenatal influences and postnatal learning processes. This means, to understand the consequences of social relations between individuals, an integrated approach is required to assess which factors, including social rank and bonds to conspecifics, interact to affect an individual's fertility and health, as has been so clearly demonstrated in the work of Jim Henry.

Lenticular autofluorescence was measured in vivo in 25 normal tree shrews using a fluorophotometer with a specially designed small animal adapter to assess the usefulness of this model of lens pathology. The average variability in the lenticular autofluorescence measurements was 8.7%. The average ratio between lenticular autofluorescence of the left eye and that of the right eye was 0.99 +/- 0.13 SD. There was a strong correlation between age and mean lenticular autofluorescence in both eyes (correlation coefficient, 0.988; p < 0.001). The calculated annual increase in lenticular autofluorescence was 23.7 ngEq/ml. This method of measurement is reliable, and lenticular autofluorescence in tree shrews varies little among animals other than a variation caused by aging. Moreover, the tree shrew, which is believed to be a primate, is small and easy to breed. This could be a useful animal model to study various lens pathologies in humans.

One of the most persistent problems in the study of the superior colliculus is the relationship between its superficial and deep layers. The superficial tier of layers is considered to be visuosensory in function, whereas the deep tier is multisensory and has premotor functions. This fundamental distinction is the primary basis for the view that a visually triggered shift in the direction of gaze depends on the transfer of information from sensory cells in the superficial tier to premotor cells in the deep tier. The goal of the present experiments was to examine the interlaminar projections of the superficial gray layer in the tree shrew Tupaia belangeri. We used biocytin as the marker for tracing the pathways. The tree shrew was chosen because its large and distinctly laminated superior colliculus facilitates the task of examining connections between the layers. Biocytin was used because of its sensitivity and because it allowed us to place very small injections restricted entirely to the superficial gray layer. The results demonstrated that a prominent pathway originates in the superficial gray layer and terminates in stratum opticum. In comparison, the projection from the superficial gray layer to the layers beneath stratum opticum is extremely sparse. The pathway from the superficial gray layer to stratum opticum has a columnar distribution, extending about 100 microns rostrally and caudally from the center of the injection site. There were no signs of more remote intracollicular connections, nor of patches or bands of terminals. The biocytin injection sites also labeled pathways to nuclei as distant from the superior colliculus as the diencephalon, including the dorsal and ventral lateral geniculate bodies, and the pulvinar. The results suggest that stratum opticum may serve as a link between the superficial gray layer and the deeper layers.

The ventral lateral geniculate nucleus (vLGN) of the tree shrew (Tupaia belangeri) was differentiated into multiple subdivisions (dorsal cap, intergeniculate leaflet, parvicellular segment, and internal and external magnocellular laminae, the latter being further divisible into a lateral and medial division) on the basis of retinal projections, immunochemistry, and histochemistry. Retinal projections traced with intravitreal injections of wheat germ agglutinin conjugated horseradish peroxidase revealed direct bilateral input to all subregions of the vLGN, except for the internal magnocellular lamina (which received only contralateral input) and the parvicellular segment (which was not retinorecipient). Furthermore, retinal inputs clearly distinguished the relatively heavily retinorecipient intergeniculate leaflet from the less prominently labeled dorsal cap. Immunohistochemical localization of Neuropeptide Y (NPY) perikarya revealed their prominence in the intergeniculate leaflet and the external magnocellular laminae with a concentration along the optic tract. NPY immunoreactive fibers were seen in all but the parvicellular subregion. Gamma amino butyric acid immunoreactivity was seen throughout the vLGN, but was most concentrated in the dorsal cap and the magnocellular laminae, followed by the intergeniculate leaflet. Histochemical studies of cytochrome oxidase and nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase localization revealed similar patterns of dense reactivity within the external magnocellular lamina, intergeniculate leaflet and dorsal cap, and somewhat less dense, but substantial reactivity in the internal magnocellular lamina. Within the external magnocellular lamina, cells reactive for cytochrome oxidase were noted in the lateral portion bordering the optic tract, whereas those specific for NADPH-diaphorase were dispersed throughout the lamina. Poor reactivity for both histochemical markers was evident in the parvicellular segment. Overall, the markedly different patterns of retinal input and neurochemical organization between the subdivisions of the tree shrew vLGN suggest their involvement in diverse functions. Furthermore, the basic similarity of the organization of the tree shrew vLGN to that of the taxonomically unrelated ground squirrel may indicate a common mammalian scheme.

In Tupaia belangeri and Galago senegalensis, microelectrode recordings immediately after ablation of the representation of the forelimb in the midportion of the first somatosensory area, S-I, revealed that all parts of the second somatosensory area, S-II, remained highly responsive to cutaneous stimuli. In this way, prosimian primates, close relatives of simian primates, and tree shrews differ markedly from monkeys in which S-II is deactivated by comparable ablations, and resemble such mammals as cats and rabbits in which S-II also remains highly responsive following ablations in S-I. Thus, it appears that the generalized mammalian condition is that S-I and S-II are independently activated via parallel thalamocortical pathways. A dependence of S-II on serial connections from the thalamus to the S-I region and then to S-II apparently evolved with the advent of anthropoid primates, and may be present only in monkeys and perhaps other higher primates.

The wheel-running activity rhythm of tree shrews (tupaias; Tupaia belangeri) housed in constant darkness (DD) phase-advanced following a 3-hr light pulse at circadian time (CT) 21. Dark pulses of 3 hr presented to tupaias in bright constant light (LL) did not induce significant phase shifts of the free-running activity rhythm, irrespective of the CT. In dim LL, tupaias showed simultaneous splitting of their circadian rhythm of wheel-running activity, nest-box activity, and feeding behavior. Light pulses of 6 hr and 2300 lux were presented to 13 tupaias with split wheel-running activity rhythms. These light pulses induced immediate phase shifts in the two components of the split rhythm in opposite directions. No differences were observed between the light-pulse phase response curves of the two components. Equally large immediate phase advances were induced in both components by light pulses of 230 lux, but not by 23 lux. The final phase shifts were small at all CTs. In two tupaias, activity rhythms transiently split and re-fused. Analysis of the relative position of the components in one of these indicates asymmetry in the coupling between the components.