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Neonatal life is a sensitive period of brain plasticity. There are concerns that pre-weaning handling may therefore alter behavioural phenotype in adolescence or adulthood. Since neurodevelopment tests require daily manipulation with pups, later behavioural outcomes might be biased by repeated handling during suckling period. The aim of our study was to assess whether daily neurodevelopmental testing would cause alterations in behavioural phenotype. Sixty-four CD1 mice were randomized to tested and not tested group. In the tested group, maturation of physical features and neurodevelopment were monitored daily from postnatal day 1-21 between 9 and 11 AM. After weaning, battery of behavioural tests to monitor anxiety-like, depressive, or repetitive behaviour was performed in all mice. We revealed no significant between-group differences in performance of these tests. Our data did not confirm the assumption that early neurodevelopment testing during suckling period affects behavioural phenotype in adolescence., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Males as compared to females display increased impulsivity and inefficient inhibitory control and are more frequently diagnosed with disorders characterized by impulsivity. We previously demonstrated male rats make more impulsive action responses (i.e. premature responding) than females on the 5-choice serial reaction time task (5-CSRTT). Furthermore, pre-pubertal male rats make more impulsive choice responses (i.e. choosing an immediate small reward over a delayed larger reward) than females on a delayed-based reward T-maze task. The goal of the current work was to determine if gonadal hormones impact sex differences in impulsivity in adult rats. In an initial experiment, male and female rats underwent sham surgeries or were gonadectomized either pre-pubertally or during adulthood and tested on the 5-CSRTT in adulthood. Males displayed more impulsive action responses than females regardless of hormone status. In a second experiment, females received testosterone or vehicle injections on postnatal days 1 and 2. Males received vehicle injections. All rats were gonadectomized prior to puberty and tested on the 5-CSRTT in adulthood. Females treated neonatally with testosterone and control males made more impulsive action responses than control females. In another set of experiments, manipulation of gonadal hormones led to no differences in performance on the delayed-based reward T-maze task in males and females. Results indicate that no sex difference is apparent in impulsive choice on a delayed-base reward task in adult rats. They also reveal that adult sex differences on a task of impulsive action is mediated by organizational effects of gonadal hormones acting during the neonatal period and not impacted by hormones acting during puberty or adulthood., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Maternal alcohol consumption during pregnancy may cause neurocognitive and behavioral disorders that can persist until adulthood. Epidemiological data has revealed an alarming increase in the frequency of alcohol intake in pregnant women. Nutritional variables may also have an impact on the behavioral alterations occasioned by alcohol during development. Moreover, omega-3, a polyunsaturated fatty acid necessary for normal brain development, is deficient in ethanol-treated animals. Although studies have shown that omega-3 supplementation after prenatal ethanol (EtOH) treatment improves some disorders, there are no reports about acute treatment with omega-3 in binge alcohol neurotoxic models during postnatal development. The goal of this study was to determine whether an administration of omega-3, after an acute ethanol dose in neonates, would be able to attenuate alcohol effects in offspring. Male/ female rats were administered ethanol (2.5 g/kg s.c. at 0 and 2 h) or saline on postnatal day (PND) 7, with a single dose of omega-3 (720 mg/kg) 15 min after the last alcohol injection. It was have found that EtOH-treated animals showed hyperlocomotion on PND 14 (pre-juvenile), and anxiety-like behavior was observed at all the three ages studied. Administration of omega-3 after EtOH treatment reduced hyperlocomotion and the anxiety-like behaviors on PND 14, but did not diminish the anxiety on either PND 20 or 30 (juvenile). In conclusion, acute ethanol exposure produced neurobehavioral alterations that persisted in the offspring, with omega-3 able to ameliorate these effects on PND 14. These data are relevant considering that omega-3 administration may have therapeutic effects through mitigating some of ethanol´s damaging consequences., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In adult rodents, neuroblasts originating from the subventricular zone migrate tangentially through the rostral migratory stream (RMS) toward the olfactory bulb where they differentiate into interneurons. Neuroblasts in the RMS migrate in chains for a long distance along specifically arranged blood vessels which promote their migration. Although blood vessels in the neurogenic region of the forebrain are present early in development, their rearrangement into this specific pattern takes place during the first postnatal weeks. Here we examined the relevance of this rearrangement to the migration-guiding "scaffold" for the neurogenic processes in the RMS such as cell migration and proliferation. To disturb the reorganization of blood vessels, endostatin - an inhibitor of angiogenesis, was administered systemically to rat pups during the first postnatal week. Ten days or three months later, the arrangement of blood vessels, migration and proliferation of cells in the RMS were assessed. As we expected, the inhibition of angiogenesis disrupted rearrangement of blood vessels in the RMS. The rearrangement's failure resulted in a strong disruption of the mode and direction of neuroblast migration. Chain migration failed and neuroblasts migrated out of the RMS. The inhibition caused a slight increase in the number of proliferating cells in the RMS. The consequences were more obvious ten days after the inhibition of angiogenesis, although they persisted partly into adulthood. Altogether, here we show that the process of rearrangement of blood vessels in the RMS during the early postal period is crucial to ensure the regular course of postnatal neurogenesis., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Maternal care plays an important role as an early modeler of neurodevelopment and brain function, and its effects remain until adulthood. Such modeling or programming has shown to influence the stress response and represents a key susceptibility factor in the development of mood disorders. In order to characterize such process which is still not clear, male offspring were classified in animals with low, medium and high licking/grooming (LG) according to the maternal behavior. Juvenile animals were subjected to the open field test (OFT) and the forced swimming test (FST), and offspring of low and high LG mothers were compared. Seven days after the FST, neurochemical and gene expression analyses were carried out in order to identify possible changes on relevant targets. Maternal care did determine locomotor behaviors in the OFT, supporting an anxiogenic effect of low maternal investment. This effect seems to be associated with the serotonergic systems in both nucleus accumbens (NAc) and hippocampus (HPC), since offspring of low LG mothers showed decreased 5-HT neurotransmission in those brain regions compared with animals of high LG mothers. Furthermore, TrkB expression was higher in offspring of high LG compared to the group of low LG mothers, supporting its influence as a mechanistic intermediate of such effect, at least in the NAc. Taken together, these findings strongly support the influence of differential maternal care on the neurodevelopment and responsivity of juvenile rats., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Classical eyeblink conditioning has been used to assess learning and memory impairments in both humans and animal model studies of fetal alcohol spectrum disorders (FASD). Gestational exposure to alcohol in humans and its equivalent in rats severely impairs various eyeblink conditioning tasks, but less is known about how these effects are influenced by variables, such as the timing and dose of alcohol exposure. In a series of four experiments, we systematically examine how varying the timing and dose of alcohol exposure impact long delay and trace eyeblink conditioning in juvenile rats, tasks that both depend on a brainstem-cerebellar circuit but differ in that trace conditioning additionally recruits the hippocampus and prefrontal cortex. Using a "third-trimester-equivalent" alcohol exposure model, rats were exposed to a high binge dose of alcohol at one of two alcohol doses over postnatal days (PD) 4-9 or PD 7-9, windows of exposure thought to differentially target the cerebellum and hippocampus. Sham-intubated and untreated rats served as controls. As juveniles, rats from each treatment condition were trained in either a long delay or trace eyeblink conditioning task. Alcohol-exposed rats demonstrated general conditioning impairments compared to controls during long delay conditioning, with more robust impairments in rats exposed to the higher alcohol dose (5.25 g/kg/day) than those that received the lower dose (4.66 g/kg/day). Alcohol-exposed rats showed trace conditioning impairments compared to controls only when the high dose of alcohol was administered over PD 4-9 or PD 7-9. These findings indicate significant learning and memory impairments following neonatal alcohol exposure at both PD 4-9 and PD 7-9. The pattern of impairments across delay and trace conditioning suggest that alcohol disrupts processes that are common to both tasks. These findings are consistent with studies of delay and trace eyeblink conditioning in children with FASD. Future studies of the mechanisms underlying these deficits will further our understanding of brain injury and memory impairments resulting from developmental alcohol exposure., (Copyright © 2012. Published by Elsevier B.V.)

Environmental enrichment has been shown to have profound effects on the healthy adult brain and as a remedial tool for brains compromised by injury, disease, or negative experience. Based upon these findings and evidence from the prenatal stress literature, we ventured an exploratory study to examine the effects of parental enrichment on offspring development. Using Long Evans rats, paternal enrichment was achieved by housing sires in enriched environments for 28 days prior to mating with a control female. For the maternal enrichment paradigm, female rats were also housed in enriched environments for 28 days (7 days prior to conception and for the duration of pregnancy). Increased size, multiple levels for exploration, an abundance of stimulating toys, and numerous cagemates for social interaction were characteristic of the enriched environments. Offspring were assessed using two early behavioral tests and then sacrificed at postnatal day 21 (P21). Brain tissue from the frontal cortex and hippocampus was harvested for global DNA methylation analysis. Parental enrichment, preconceptionally and prenatally, altered offspring behavior on the negative geotaxis task and openfield exploratory behavior task. Paternal enrichment significantly decreased offspring brain weight at P21. Additionally, both environmental enrichment paradigms significantly decreased global methylation levels in the hippocampus and frontal cortex of male and female offspring. This study demonstrates that positive prenatal experiences; preconceptionally in fathers and prenatally in mothers, have the ability to significantly alter offspring developmental trajectories., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Maternal care is the newborns' first experience of social interaction, which affects their development and social competence throughout life. For the first time, we investigated the involvement of the endocannabinoid system (ECS) in mother-infant interaction in mice. We found that blocking the dam's CB1 receptors (CB1R) by the antagonist/inverse agonist rimonabant (SR141716) during postpartum days 1-8 affected maternal behavior as well as the social and emotional characteristics of the offspring as adults. Pups of rimonabant treated dams (RTD) had lower body weight during the first week of life and emitted fewer ultrasonic vocalizations (USVs) than vehicle treated dams (VTD). RTD crouched less over their pups and exhibited delayed pup retrieval. In Y-maze preference tests conducted at weaning age, females and males of both groups preferred their dam over milk. Males and females of RTD preferred dam over pup and pup over milk as opposed to the control group. At the age of 2.5 months, males of RTD displayed less motor activity. In the social behavior test, RTD male and female offspring were both more active, showing higher levels of active social interaction and rearing. These results indicate that the ECS is crucial for establishment of maternal behavior during the first postpartum week, with a long-term impact on the offspring's socio-emotional development., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Exposure to methamphetamine during brain development impairs cognition in children and adult rodents. In mice, these impairments are greater in females than males. Adult female, but not male, mice show impairments in novel location recognition following methamphetamine exposure during brain development. In contrast to adulthood, little is known about the potential effects of methamphetamine exposure on cognition in adolescent mice. As adolescence is an important time of development and is relatively understudied, the aim of the current study was to examine potential long-term effects of neonatal methamphetamine exposure on behavior and cognition during adolescence. Male and female mice were exposed to methamphetamine (5 mg/kg) or saline once a day from postnatal days 11 to 20, the period of rodent hippocampal development. Behavioral and cognitive function was assessed during adolescence beginning on postnatal day 30. During the injection period, methamphetamine-exposed mice gained less weight on average compared to saline-exposed mice. In both male and female mice, methamphetamine exposure significantly impaired novel object recognition and there was a trend toward impaired novel location recognition. Anxiety-like behavior, sensorimotor gating, and contextual and cued fear conditioning were not affected by methamphetamine exposure. Thus, neonatal methamphetamine exposure affects cognition in adolescence and unlike in adulthood equally affects male and female mice., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The infant stage of rat development is a very important period for potential correction of adverse consequences produced by negative prenatal events. However the age limit for this correction needs to be investigated. The last prenatal and first two weeks after birth are "critical" for maturation of the nociceptive and emotional systems. Clinical observations suggest a correlation between persistent pain response and emotional behavior. In infant male rats of different ages, we studied indices of the inflammatory pain response (the number of flexes+shakes in the formalin test), depression-related behavior (immobility in the forced swim test) and the relations between them, as well as the effects of prenatal stress on these indices. Furthermore, we assessed the trend of body weight and the relations between body weight and the depression- and pain-related behaviors. We demonstrate heterogeneity of the infant stage: control prenatally non-stressed rat pups showed significantly lower immobility at 7 days of age than at 10 days; prenatal stress caused an increase of immobility and the number of flexes+shakes in 7-8-day-old pups but not in 10-11-day-olds. These findings should be taken into account in the treatment of abnormalities of emotional and inflammatory pain-related behaviors produced by prenatal stressful events. The present data and our previous findings indicate that the deficiency of body weight in prenatally stressed newborns may predict the development of abnormalities in inflammatory pain-related responses during postnatal ontogeny.

Mammalian females have long been known to release olfactory attraction in their offspring. Mammary odor cues control infant state, attention and directional responses, delay distress responses, stimulate breathing and positive oral actions, and finally can boost learning. Here, we survey female-offspring odor communication in two mammalian species - European rabbits and humans - taken as representatives of evolutionary extremes in terms of structure and dynamics of mother-infant relations, and level of neonatal autonomy. Despite these early psychobiological differences, females in both species have evolved mammary structures combining multiple sources of endogenous and exogenous odorants, and of greasy fixatives, conferring on them a chemocommunicative function. To process these mammary chemosignals, neonates have co-evolved multiple perceptual mechanisms. Their behaviour appears to be driven by plastic mechanism(s) calibrated by circumstantial odor experience in preceding and current environments (fetal and postnatal induction of sensory processes and learning), and by predisposed mechanisms supported by pathways that may be hard-wired to detect species-specific signals. In rabbit neonates, predisposed and plastic mechanisms are working inclusively. In human neonates, only plastic mechanisms could be demonstrated so far. These mammary signals and cues confer success in offspring's approach and exploration of maternal body surface, and ensuing effective initial feeds and rapid learning of maternal identity. Although the duration of the impact of these mammary signals is variable in newborns of species exposed to contrasting life-history patterns, their functional role in setting on infant-mother interaction in the context of milk transfer can be crucial.

There is increasing evidence for specialised processing of social cues in the brain. This review considers how the main olfactory system of mammals is designed to process social odours and the effects of learning in a social context. It focuses mainly on extensive research carried out on offspring, mate or conspecific learning carried out in sheep and rodents. Detailing the roles of the olfactory bulb and its projections, classical neurotransmitters, nitric oxide, oestrogen and neuropeptides such as oxytocin and vasopressin in mediating plasticity changes in the olfactory system arising from these different social learning contexts. The relative simplicity of the organisation of the olfactory system, the speed and robustness of these forms of social learning together with the similarity in brain regions and neurochemical contributions across the different learning paradigms make them important and useful models for investigating general principles of learning and memory in the brain.

Serotonin (5-HT) is known to play a role in the suppression of the lordosis response in males. We have previously shown that there is a sex difference in the density of 5-HT immunoreactive (5-HT-ir) fibers in the ventrolateral division of the adult ventromedial nucleus of the hypothalamus (VMNvl) and that neonatal administration of estradiol (E2) increases 5-HT-ir in the female VMNvl to male-typical levels. Here we demonstrate that postnatal administration of the ERalpha agonist 1,3,5-tris(4-Hydroxyphenyl)-4-propyl-1H-pyrazole (PPT), but not the ERbeta agonist diarylpropionitrile (DPN), also masculinizes 5-HT-ir in the female VMNvl, suggesting a mechanistic role for ERalpha in this process. Sexual receptivity, as ascertained by the lordosis quotient, was unaffected by either PPT or DPN treatment but nearly abolished by estradiol benzoate (EB), a synthetic estrogen with high affinity for both ERalpha and ERbeta. Collectively, these observations show that postnatal estrogens increase the density of 5-HT projections to the VMNvl via an ERalpha dependent mechanism, but that this increased inhibitory input is not sufficient to suppress the lordosis response.

In both humans and animals, stress experienced during gestation is associated with physiological changes and disruptions in emotional function and cognitive ability in offspring; however, much less is known about the effects of such stress in mothers. In animal models, physical restraint is commonly employed to induce stress during gestation and results in elevated postpartum maternal anxiety and changes in maternal care. The purpose of the current study was to evaluate the consequences of restraint stress applied on gestation days 10 through 19 in mother rats and their juvenile offspring. Progeny were reared by birth mothers. Preterm anxiety was assessed in the elevated plus maze and maternal behavior in the retrieval test. Cognitive (T-maze) and anxiety measures (elevated plus maze and emergence) were applied to a subset of male and female offspring at 30-31 days of age. Weight and litter characteristics were also recorded. Mother rats exposed to stress during gestation had attenuated weight gain, elevated anxiety-like behavior, and reduced maternal care. Stressed mothers also had fewer pups and an elevated offspring mortality rate. The consequences of gestational stress in offspring were subtle and gender-dependent. Only juvenile females displayed marginal effects of gestational stress in the form of elevated anxiety-like behavior and attenuated weight gain. In the current study, although gestational stress had robust effects in the mother rat, these did not translate to similar changes in offspring behavior. The importance of focusing research on maternal responses to gestational stress is highlighted by these findings.

We investigated sleep ontogenesis in the ferret-a placental mammal that is highly altricial compared to other mammalian species. Because altriciality is linked with elevated rapid-eye-movement (REM) sleep amounts during infancy, it was expected that ferret kits would display very high levels of this state. Longitudinal polysomnographic measurements were made from 8 ferret kits from approximately eye-opening (postnatal day [P]30)-P50 using an experimental routine that minimized the effects of maternal separation. These data were compared to values from 8 adult ferrets (>3 months of age) and 6 neonatal cats (mean age: P31.7). We find that the polygraphic features of REM and non-REM (NREM) sleep are present by at least P30. Over the next 2 weeks, REM sleep amounts slightly declined while wakefulness and NREM sleep amounts increased. However, a comparison to published values from developing cats and rats showed that the ferret did not exhibit a disproportionate amount of REM sleep at similar postnatal ages or relative to a common developmental milestone (eye-opening).

Cortical networks in vivo and in vitro are spontaneously active in the absence of inputs, generating highly variable bursts of neuronal activity separated by up to seconds of quiescence. Previous measurements in adult rat cortex revealed an intriguing underlying organization of these dynamics, termed neuronal avalanches, which is indicative of a critical network state. Here we demonstrate that neuronal avalanches persist throughout development in cortical slice cultures from newborn rats. More specifically, we find that in spite of large variations of average rate in activity, spontaneous bursts occur with power-law distributed sizes (exponent -1.5) and a critical branching parameter close to 1. Our findings suggest that cortical networks homeostatically regulate a critical state during postnatal maturation.

Clinical studies show cognitive impairment in depression. However, the neural substrates underlying these remain elusive. Hence, we have examined the effect of neonatal clomipramine treatment on cognition in adulthood. The neonatal clomipramine treated rats displayed a profound impairment in partially baited 8-arm radial maze task. This work provides a novel perspective into neural basis of depression associated cognitive changes and help in development of therapeutic strategies to treat depression related memory dysfunctions.

It is well known that early life events induce long-lasting psychophysiological and psychobiological influences in later life. In rodent studies, environmental enrichment after weaning prevents the adulthood behavioral and emotional disturbances in response to early adversities. We compared the behavioral effect of neonatal isolation (NI) with the effect of NI accompanied by tactile stimulation (NTS) to determine whether NTS could reverse or prevent the effects of NI on the adulthood behavioral and emotional responses to environmental stimuli. In addition, we also examined the sex difference of the NTS effect. Measurements of body weights, an open-field locomotor test, an elevated plus maze test, a hot-plate test, and a contextual fear-conditioning test were performed on postnatal day 60. As compared with rats subjected to NI, rats subjected to NTS showed significantly higher activity and exploration in the open-field locomotor test, lower anxiety-like behavior in the elevated plus maze test, and significantly prolonged latencies in the hot-plate test, and this effect was equal among males and females. In the contextual fear-conditioning test, whereas NTS significantly reduced the enhanced freezing time due to NI in females, no significant difference in the freezing time between NI and NTS was found in males. These findings indicate that adequate tactile stimulation in early life plays an important role in the prevention of disturbances in the behavioral and emotional responses to environmental stimuli in adulthood induced by early adverse experiences.

Intrauterine growth restriction (IUGR) can increase susceptibility to perinatal hypoxic brain injury for reasons that are unknown. Previous studies of the neonatal IUGR brain have suggested that the cerebral mitochondrial capacity is reduced but the glycolytic capacity increased relative to normal weight (NW) neonates. In view of these two factors, we hypothesized that the generation of brain lactate during a mild hypoxic insult would be greater in neonatal IUGR piglets compared to NW piglets. Brain lactate/N-acetylaspartate (NAA) ratios and apparent diffusion coefficients (ADCs) were determined by proton magnetic resonance spectroscopy and imaging of the brain before, during and after hypoxia in seven neonatal piglets with asymmetric IUGR and six NW piglets. During hypoxia, IUGR piglets had significantly higher brain lactate/NAA ratios than NW piglets (P=0.046). The lactate response in the IUGR piglets correlated inversely with apoptosis in the thalamus and frontal cortex of the brain measured 4 h post hypoxia (Pearson's r=0.86, P<0.05). Apoptosis in IUGR piglets with high brain lactate was similar to that in the NW piglets whereas IUGR piglets with low brain lactate had significantly higher apoptosis than NW piglets (P=0.019). ADCs in the high lactate IUGR piglets were significantly lower during hypoxia than in all the other piglets. This signifies increased diffusion of water into brain cells during hypoxia, possibly in response to increased intracellular osmolality caused by high intracellular lactate concentrations. These findings support previous studies showing increased susceptibility to hypoxic brain injury in IUGR neonates but suggest that increased glycolysis during hypoxia confers neuroprotection in some IUGR piglets.

Removal of the medial prefrontal cortex (mPFC) of the rat during the initial 7-12 days of life results in spontaneous filling of lesion cavity that is accompanied by recovery of cognitive and motor functions. To date, it remains uncertain whether tissue filling the lesion cavity is actually supporting the functional improvement. In the present study, we examined whether spontaneous neuronal activity could be recorded in adulthood from the tissue that fills the lesion cavity. We recorded EEG and multiunit activity in adulthood from the mPFC and the motor cortex of rats that had received neonatal mPFC lesions on post-natal day 10 (P10) or their non-lesioned littermate controls. We found similarities in both the firing pattern and firing rate of cells from the filled-in region compared to that of controls, although the power associated with peak frequencies in the delta, alpha, and beta range in the EEG recorded from the filled-in region was lower compared to controls. Overall, our results suggest that the cells found in the lesion cavity have similar neurophysiological properties to those found in normal tissue and thus should be capable of at least partially supporting the observed recovery of function.

The circuits that generate rhythmic locomotor activities are located in the ventromedial area of the lumbar spinal cord and comprise commissural interneurons necessary for left-right alternation during walking movements. In this study we injected biotinylated dextran amine (BDA) into the ventromedial gray matter of the lumbar spinal cord of neonatal rats to label commissural interneurons. Anterogradely labeled axons arose from the site of injection, crossed the midline in the anterior commissure and arborized extensively in the contralateral ventral horn of the spinal cord. The presence of neurotransmitter systems in labeled axon terminals of commissural interneurons was investigated by using antibodies raised against specific transmitter-related proteins. Boutons potentially containing inhibitory amino acids were identified by applying glutamic acid decarboxylase (GAD65/67) and glycine transporter 2 antibodies. Out of 1146 BDA-labeled axon terminals, 663 boutons were assumed on this basis to be inhibitory; 76% of these terminals were immunoreactive for glycine transporter, 53% were immunoreactive for GAD and about 30% of inhibitory boutons might contain both inhibitory amino acids. Boutons potentially containing putative excitatory neurotransmitter were revealed with antibodies raised against vesicular glutamate transporters 1 and 2. Out of 590 BDA-labeled boutons about one fourth (158) were immunoreactive for glutamate transporters. These mammalian commissural interneurons are compared to the glycinergic commissural interneurons in the swimming CPGs of lamprey and the Xenopus tadpole. Our results show that commissural interneurons in the mammalian spinal cord form a heterogeneous group including glutamatergic excitatory and GABAergic and glycinergic inhibitory neurons.

Human depression and anxiety disorders show inherited biases across generations, as do antisocial disorders characterized by aggression. Each condition is preceded in children by behavioral inhibition or aggressive behavior, respectively, and both are characterized by separation anxiety disorders. In affected families, adults and children exhibit different forms of altered autonomic nervous system regulation and hypothalamic-pituitary-adrenal activity in response to stress. Because it is difficult to determine mechanisms accounting for these associations, animal studies are useful for studying the fundamental relationships between biological and behavioral traits. Pharmacologic and behavioral studies suggest that infant rat ultrasonic vocalizations (USV) are a measure of an early anxiety-like state related to separation anxiety. However, it was not known whether or not early ultrasound emissions in infant rats are markers for genetic risk for anxiety states later in life. To address these questions, we selectively bred two lines of rats based on high and low rates of USV to isolation at postnatal (P) 10 days of age. To our knowledge, ours is the only laboratory that has ever selectively bred on the basis of an infantile trait related to anxiety. The High and Low USV lines show two distinct sets of patterns of behavior, physiology and neurochemistry from infancy through adulthood. As adults High line rats demonstrate "anxious"/"depressed" phenotypes in behavior and autonomic nervous system (ANS) regulation to standard laboratory tests. In Lows, on the other hand, behavior and autonomic regulation are consistent with an "aggressive" phenotype. The High and Low USV lines are the first genetic animal models implicating long-term associations of contrasting "coping styles" with early attachment responses. They thus present a potentially powerful model for examining gene-environment interactions in the development of life-long affective regulation.

Rodent models provide a valuable approach to elucidating the pathophysiological mechanisms underlying the deleterious effects of childhood trauma and stress. Neonatal rats and mice emit ultrasonic vocalizations (USVs) when separated from the dam and litter. USVs are suppressed in rat pups by exposure to the putatively infanticidal threat of an adult male. In the present study, C57BL/6J mouse pups were exposed to an anaesthetized (non-sire) adult C57BL/6J male for 3-min/day from postnatal days 2-14, and subsequently tested for anxiety-related behaviors (using the novel open field, elevated plus-maze, light/dark exploration tests) and depression-related behavior (using the forced swim test) at 11 weeks of age. In a separate cohort, hypothalamic-pituitary-adrenal-axis activation was measured via plasma corticosterone levels following either a single male-exposure or separation episode. Results showed that pups exposed to an adult male emitted significantly fewer USVs than separation-only counterparts. Corticosterone levels were significantly lower following single exposure to the adult male than separation alone. Repeated neonatal male-exposure did not lead to significant alterations in anxiety- or depression-related behaviors in adulthood. Taken together, present data suggest that the form of adult male-exposure employed did not act as a significant stressor, at least in this mouse strain. Further studies will be needed to determine whether alternative mouse strains, exposure protocols or adult behavioral assays will produce a different pattern of short-term and long-term effects.

Automated registration of neonatal rat entries in the squares of a testing chamber is suggested for the animal locomotion assessment. This method allows detection of paddling and pivoting activities that are not accompanied by forward movement of the animal. The proposed technique is also relatively insensitive to nonlocomotor changes in a pup's body position, such as breathing and shaking, and thus offers a selective detection of locomotor-related activity. The application of the method permits the evaluation of spontaneous and stimulated motor activity of neonatal rats using relatively short test duration and a minimal number of animals.

This study analysed the long-term consequences of an asphyctic event at birth on maternal behaviour and emotionality in rats. Pregnant Wistar rats were delivered by Caesarean section and the pups, still in the uterus horns, were placed into a water bath at 37 degrees C for periods of 0 (Caesarean delivery, CD) or 20 min (asphyxia, CD+20). Control subjects were born by vaginal delivery (VD). Subsequently, pups were given to surrogate mothers, weaned at 21 days, and mated at adulthood. After giving birth, differences in maternal competence and behavioural arousal were assessed observing: (i) maternal behaviour after reunion with the pups following a 3h separation, on postpartum day (PPD) 4; (ii) behaviour in an elevated plus-maze test, on postpartum day 7; and (iii) performance in a fear conditioning test, in which subjects learned to associate a conditional stimulus with an aversive unconditioned stimulus (postpartum days 7-8). Results indicate that subjects in the CD+20 group showed a deficit in maternal care, taking a longer time to retrieve the whole litter and often failing to retrieve all pups. Both CD and CD+20 groups showed higher behavioural activity in the plus-maze. In addition, when tested in the fear conditioning paradigm, the CD+20 group showed a lower latency to perform freezing behaviour in the auditory cue trial. The changes in behavioural arousal described suggest that the dopaminergic system may be a potential neurochemical target for an early hypoxic insult and indicate maternal behaviour as a useful endpoint to study the effects of early birth insult on brain function.

Hypoxia-ischemia (HI) is associated with premature birth, and injury during term birth. Many infants experiencing HI later show disruptions of language, with research suggesting that rapid auditory processing (RAP) deficits (i.e., impairment in the ability to discriminate rapidly changing acoustic signals), play a causal role in language problems. We recently bridged these lines of research by showing RAP deficits in rats with unilateral-HI injury induced on postnatal days 1, 7, or 10 (P1, P7, or P10. While robust RAP deficits were found in HI animals, it was suggested that our within-age sample size did not provide sufficient power to detect age-at-injury differences within the pooled HI group. The current study sought to examine differences in neuropathology and behavior following unilateral-HI injury on P1 versus P7 in rats. Ages chosen for HI induction reflect differential stages of neurodevelopmental maturity, and subsequent regional differences in vulnerability to reduced blood flow/oxygen (modeling age-related differences in premature/term HI injury). Results showed that during the juvenile period, both P1 and P7 HI groups exhibited significant RAP deficits, but deficits in the P1 HI group resolved with repeated testing (compared to shams), while P7 HI animals showed lasting deficits in RAP and spatial learning/memory through adulthood. The current findings are in accord with evidence that HI injury during different stages of developmental maturity (age-at-injury) leads to differential neuropathologies, and provide the novel observation that in rats, P1 versus P7 induced pathologies are associated with different patterns of auditory processing and learning/memory deficits across the lifespan.

Uteroplacental vascular insufficiency in humans is a common cause of intrauterine growth restriction (IUGR) and is associated with an increased incidence of perinatal asphyxia and neurodevelopmental disorders compared to normal weight newborns. Experimental models that provide an opportunity to analyze the pathogenesis of these relationships are limited. Here, we used neonatal pigs from large litters in which there were piglets of normal birth weight (for controls) and of low birth weight (for uteroplacental vascular insufficiency). Hypoxia was induced in paired littermates by reducing the fraction of inspired oxygen to 4% for 25 min. Brain tissue was collected 4 h post-hypoxia. Cerebral levels of apoptosis were quantified morphologically and verified with caspase-3 activity and TUNEL. Expression of Bcl-2, Bcl-XL and Bax proteins was investigated using immunohistochemistry. Cellular positivity for Bcl-2 was consistently higher in the non-apoptotic white matter of the hypoxic IUGR animals compared with their littermates and reached significance at P < 0.05 in several pairs of littermates. Alterations in Bax showed a trend towards higher expression in the hypoxic IUGR littermates but rarely reached significance. The IUGR piglets showed a significantly greater amount of apoptosis in response to the hypoxia than the normal weight piglets, suggesting an increased vulnerability to apoptosis in the IUGR piglets.

Iron deficiency anemia in early childhood is associated with developmental delays and perhaps, irreversible alterations in neurological functioning. The goals were to determine if dietary induced gestational and lactational iron deficiency alters brain monoamine metabolism and behaviors dependent on that neurotransmitter system. Young pregnant rats were provided iron deficient or control diets from early in gestation through to weaning of pups and brain iron concentration, regional monoamine variables and achievement of specific developmental milestones were determined throughout lactation. Despite anemia during lactation, most brain iron concentrations did not fall significantly until P25, and well after significant changes in monoamine levels, transporter levels, and D2R density changed in terminal fields. The changes in D2R density were far smaller than previously observed models that utilized severe dietary restriction during lactation or after weaning. Iron deficient pups had normal birth weight, but were delayed in the attainment of a number of milestones (bar holding, vibrissae-evoked forelimb placing). This approach of iron deficiency in utero and during lactation sufficient to cause moderate anemia but not stunt growth demonstrates that monaminergic metabolism changes occur prior to profound declines in brain iron concentration and is associated with developmental delays. Similar developmental delays in iron deficient human infants suggest to us that alterations in iron status during this developmental period likely affects developing brain monaminergic systems in these infants.

The role of endogenous opioid system in learning (Pavlovian conditioning) and reinforcement was studied in newborn rats by pairing central injection of dynorphin A (1-13), an endogenous ligand with high affinity for kappa opioid receptors, with a surrogate nipple. For conditioning, the nipple served as the conditioned stimulus and dynorphin as the unconditioned stimulus. Dynorphin was found to elicit an immediate unconditioned, dose-dependent increase in the neonatal responsiveness to a surrogate nipple providing water, an effect apparently mediated through the kappa opioid receptors. This immediate effect of dynorphin was evident in the context of suckling behavior but not in the context of adult-like drinking when water was delivered through an intra-oral cannula. One hour after injection, the unconditioned stimulatory effect of dynorphin had dissipated and no longer affected responsiveness to the nipple. However, pairing of centrally injected dynorphin and suckling on a nipple delivering water substantially enhanced responsiveness to a nipple 1h later. This suggested conditioning, and hence reinforcement, by the centrally injected dynorphin. The conditioned sustained nipple attachment was mediated through both kappa and micro opioid receptors. These experiments confirm a central role for the brain opioid systems in reinforcement of neonatal behavior on the nipple.

According to the neurodevelopmental hypothesis of schizophrenia, early brain damage renders the brain vulnerable to adverse effects during puberty, which precipitate the disease in young adults. Animal models can be used to test this hypothesis. We investigated the potentially independent or interactive effects of neonatal (postnatal day 7) excitotoxic lesions of the rat medial prefrontal cortex (mPFC) and subchronic pubertal phencyclidine (PCP)-treatment on adult rat behaviour. Sham-lesioned (vehicle-injection) and naive (unoperated) rats served as controls. On postnatal days 42-48 rats were systemically injected with 5 mg/kg PCP or vehicle twice daily. Behavioural testing started at postnatal day 70. Rats were tested for locomotor activity (open field), anxiety (elevated plus maze), social behaviour (conditioned place preference for cage-mates), reward-related operant behaviour [progressive ratio (PR)] and spatial learning (four-arm baited eight-arm radial maze task). Nissl-stained sections revealed considerable regeneration of much of the lesioned tissue in the mPFC, however, with disturbed cytoarchitecture. Locomotor activity was increased by neonatal lesions but reduced after pubertal PCP-treatment. Neonatal lesions alone increased operant behaviour in the PR-test and reduced anxiety in the elevated plus maze. In contrast, PCP-treatment disturbed social behaviour while neonatal lesions had no effect. Different aspects of leaning and memory in the radial maze task were independently disturbed after neonatal lesions and PCP-treatment. Neonatal lesions and pubertal PCP-treatment differentially affected adult rat behaviour and no interactions were found.

Birth complications such as perinatal asphyxia are considered risk factors for later neurobehavioural disorders. Behavioural analysis of animal models may help to clarify the contribution of particular patterns of early hypoxia and their combination to psychiatric morbidity. Wistar rats underwent caesarean section (c-section) alone or c-section followed by asphyxia, the latter induced by placing pups still in uterus horns into a water bath at 37 degrees C for 20 min. Vaginally delivered pups were used as controls. Frequency of ultrasound emissions was analysed following isolation at a lower temperature than that of the home nest (23+/-0.5 degrees C) and reunion with their mother (3 min) on postnatal day (PND) 13 (maternal potentiation test). A sex-dependent effect of hypoxia was observed, with higher production of ultrasounds in hypoxic males. Caesarean-delivered pups produced significantly more ultrasounds than those vaginally delivered. At adolescence (PND 35) rats underwent a 25 min social interaction test with a conspecific of the same sex and age. Significant alterations in investigative behaviour (inclusive of: nose, anogenital, body sniffing, and following) were evident in caesarean-delivered rats of both sexes, but not in rats experiencing perinatal asphyxia. At adulthood, auditory, and context conditioned responses, analysed in a fear conditioning test, were not markedly affected either by c-section or c-section plus hypoxia. However, hypoxic rats emitted significantly more 22 kHz ultrasounds than c-section or vaginally delivered rats during the training session. In conclusion, differential effects appear to be brought about by c-section and by hypoxia mainly related to emotional/anxious responses.

Heat shock protein 27 (Hsp27), a molecular chaperone ubiquitously expressed in many cell types, has been shown to play a role in protecting neurons from cellular stresses. Unlike adult DRG neurons in vitro, neonatal DRG neurons require NGF for survival; withdrawal of NGF results in apoptosis of a majority of neonatal neurons. We hypothesized that Hsp27 contributes to the neurotrophin-independent survival of adult DRG neurons. Constitutive Hsp27 expression is higher in adult DRG neurons compared to neonates, although both upregulate Hsp27 expression after heat shock (HS). We found that increasing endogenous Hsp27 by HS in neonatal neurons was able to inhibit NGF withdrawal-induced apoptosis. Heat shock of adult and neonatal neurons also resulted in Akt activation, which could be a mechanism for the increased survival. Hsp27 siRNA treatment of adult neurons effected a decreased expression of Hsp27, which correlated with increased apoptosis in these neurons. Downregulation of Hsp27 via siRNA also blocked the HS-induced rescue of neonatal neurons after NGF withdrawal. These results indicate that physiologically induced upregulation of Hsp27 is sufficient to provide some degree of neuronal protection. Further, this induction appears to be regulated by the transcriptional activation of HSF1 as shown by HSF1 nuclear translocation and by EMSA analyses of HSF1 binding to nuclear protein.

gamma-Aminobutyric acid (GABA) is inhibitory in adult, but excitatory in neonatal, neurons. The switch from excitatory to inhibitory action is due to a negative shift in the equilibrium potential for the GABA(A) receptor-mediated postsynaptic current (E(GABA-PSC)). Here, we report that, in neonatal rat hippocampal CA1 neurons, presynaptic theta-burst activation induces not only a shift in E(GABA-PSC) towards that in adult neurons, but also a recruitment of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor-mediated postsynaptic currents.

Introduction: It is becoming increasingly recognized that CNS immaturity at birth affects ischemic injury and recovery, and that the consequences of neonatal stroke need to be studied using age-appropriate focal stroke models. The inclusion of magnetic resonance imaging (MRI) as a surrogate measure of stroke progression has provided useful information in adult models, but the benefit for neonatal stroke studies is yet to be established., Methods: Postnatal 7-day (P7) rats were subjected to a 3-h transient occlusion of the middle cerebral artery (MCA) which was produced either by inserting a filament via the external carotid artery or via the internal carotid artery. MRI was used to delineate the size and pattern of injury acutely, during MCA occlusion, and 7 days following reperfusion., Results: The size of the diffusion-weighted (DW) MRI-detectable injury during MCA occlusion was similar following both surgical procedures and resulted in histological lesions 7 days later in all animals. The extent of spontaneous recovery in individual animals varied substantially 7 days later within each group, as was depicted by a combination of DW- and T2W-MRI and confirmed by the corresponding histology., Conclusions: The ability of MRI to provide accurate information on the size of histological outcome at 7 days after neonatal focal transient ischemia suggests that MRI is useful as an intermediate surrogate measure of injury progression in long-term neonatal stroke studies.

A population of embryonic rat cortical cells cultured in the presence of FGF2 and having neuronal morphology expressed higher levels of reactive oxygen species (ROS) than did progenitor cells, astrocytes, and several cell lines of neuronal and non-neuronal origin. ROS were assessed using 5-(and-6)-chlormethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H2DCF-DA), and high levels persisted in the presence of antioxidants or lowered levels of ambient oxygen. Greater than 95% of high ROS-producing cells, isolated by fluorescence-activated cell sorting, expressed the neuronal marker beta III tubulin. These cells did not incorporate BrdU or express nestin, unlike low ROS-producing cells, 99% of which exhibited both of these characteristics. Upon growth factor removal, low ROS-expressing cells differentiated into neurons and astrocytes and these neurons expressed high levels of ROS, indicating that ROS accumulation accompanies the differentiation of progenitors into neurons. ROS levels were decreased by added superoxide dismutase and catalase, suggesting that both superoxide and hydrogen peroxide contribute to the ROS signal. High ROS-expressing cells also contained higher levels of several mitochondrial respiratory chain components. Although ROS have been associated with conditions that lead to cell death, our results and recent studies on the role of ROS as regulators of signal pathways are consistent with the possibility that ROS play a role in the development of the neuronal phenotype. Moreover, the differential production of ROS provides a useful method to isolate from mixed populations cells that are highly enriched for either progenitor cells or neurons.

Rodents have been an indispensable tool for the study of the neural mechanisms underlying a variety of emotional, social, and cognitive functions and dysfunctions. Surprisingly, little is known concerning sex difference in rodent social recognition memory and its sensitivity to neonatal stimulation. During the first 3 weeks of life, we exposed male and female neonates to a novel cage for 3-min per day while the matched littermate controls remained in the home cage. At 7 weeks and 7 months of age, we measured frequencies of social investigation over repeated social exposures and found that males showed greater habituation in social investigation than females during both juvenility and adulthood and that neonatal novelty exposure affected changes in the frequency of social investigation across multiple exposures in a sex-dependent manner. We speculate that these observed sex differences may reflect a sex difference in affinity for conspecific novelty rather than memory capability.

Severe perinatal hypoxia-ischemia is an important cause of brain injury in both full-term and premature newborns, with a high risk of future behavioral and neurological deficits. The most commonly used animal model of neonatal hypoxia-ischemia is the unilateral ligation of the common carotid artery followed by exposure to hypoxia in 7-day-old rats. In spite of the wide use of this model, lot of contradictions and discrepancies exist between the results obtained by different laboratories regarding behavioral deficits and there are no data regarding the possible delay of the appearance of neurological reflexes and the time-course of reflex performances following neonatal hypoxic-ischemic injury in rats. In the present study we showed that neonatal hypoxia-ischemia retarded the development of somatic growth and several neurological reflexes (ear twitch, grasping, gait and negative geotaxis). Hypoxic animals also displayed retarded performance in righting, geotaxis and gait reflexes. Although hypoxic pups performed worse in most tests for motor coordination, they reached normal levels by 5 weeks of age except in the footfault test. In the open-field, hypoxic animals were generally more active, except at 3 weeks, when activity of normal pups increased enormously as well. Brain areas were significantly reduced in hypoxic animals, but no close correlation was found with behavioral deficits.

In rats, early life stimulation can enhance learning and memory and induce parallel changes in brain asymmetry. Despite persistent interest in human brain asymmetry, relatively little is known in animal models about developmental stability of early-experience effects on asymmetry and how early-experience may affect males and females differently in asymmetry measures across developmental stages. We exposed male and female neonatal rats to a novel cage for 3min per day during the first 3 weeks of life and measured spontaneous turning behavior at juvenility (7 weeks of age) and adulthood (7 months of age). We found that (1) the effects of such neonatal novelty exposure on turning bias are developmentally stable, and (2) neonatal novelty exposure differentially modulates turning bias in males and females. We briefly discuss implications of these findings in terms of the role of brain asymmetry in modulating cognitive and emotional development.

The aim of this study was to investigate the differential long-term after-effects on the apomorphine-susceptibility in the apomorphine-susceptible (APO-SUS) and apomorphine-unsusceptible (APO-UNSUS) rats of either a saline injection (a mild stressor) or a clonidine-injection (a moderate stressor) applied around the onset of the stress-hypo-responsive-period (SHRP) on postnatal day (PND) 2, 4, 6 or 9. The present study shows that an injection of saline on PND 2 decreases the apomorphine-induced gnawing score in adult APO-SUS rats, but increases this score in adult APO-UNSUS rats; clonidine given on this day has no effect. An injection of saline on PND 4 decreases the apomorphine score in adult APO-SUS rats, but has no effect in adult APO-UNSUS rats. An injection of clonidine on PND 4 counteracts the long-term after-effects of a saline injection on this PND in adult APO-SUS rats, but has no effect in adult APO-UNSUS rats. Finally, an injection of clonidine on PND 9 has no effect on the apomorphine score in adult APO-SUS rats, but increases this score in adult APO-UNSUS rats; saline given on this day has no effect. It is concluded that the long-term after-effects of early postnatal stressors depend on the interrelationship between, rather than the separate impact of, the genetic background of the rat, the nature of the event, and time of exposure to the event, thereby implying that these factors direct the phenotypic expression of a particular genotype at adult age.

Newborn humans are known to show specific facial expressions in response to various kinds of taste stimuli and are presumed to be able to discriminate those kinds of tastes from just after birth. As the closest relatives to humans, the taste reactivity (threshold, preference and taste-elicited facial expression) of non-human primates has long been of great interest. To date, however, there have been few investigations in newborn non-human primates. In the present study, we investigated the facial expressions elicited in response to four basic taste stimuli, sweet, salty, sour and bitter, in the newborns of two non-human primate species, rhesus macaques and chimpanzees. The taste-elicited facial expressions were compared among the kinds of taste stimuli and between the two species. Rhesus macaques of less than 7 days old showed different patterns of facial expressions for water/sweet than for bitter, and chimpanzees less than 30 days old did so for sweet and bitter. The differences between these two species were evident in the presence and absence of certain facial expressions and the emerging patterns of certain components for each stimulus. In particular, chimpanzee response patterns to the bitter stimulus resembled to those of humans rather than rhesus macaques. Overall, rhesus macaques and chimpanzees responded differently to the same kinds of tastes, presumably reflecting differences in their evolutionary backgrounds.

Anatomical, electrophysiological, and behavioral studies implicate extrastriate cortex as a major contributor to the sparing of visually guided behaviors following lesions of primary visual cortex incurred early in life. Here we report considerable sparing of the ability to detect and localize stimuli in the hemifield contralateral to unilateral early lesions of all contiguous visually-responsive primary and extrastriate cortical regions (occipital, visuoparietal, and visuotemporal cortices). In the adult cat this same lesion induces a dense blindness and cats are unable to orient to any visual stimulus introduced into the contralesional hemifield. In the absence of cortical circuits, the neural sparing identified following the neonatal lesion is based on the superior colliculus and it occurs despite massive retrograde transynaptic degeneration of large numbers of retinal ganglion cells.

Human and animal studies indicate that repeated stress during pregnancy can produce long-term biological and behavioural disorders in the offspring. In contrast, although maternal stress is supposed to induce an increase of maternal anxiety, few studies have been conducted to demonstrate it. Therefore, in the present study we examined the emotional reactivity in stressed (chronic restraint stress applied 3 x 45 min per day during the last week of pregnancy) and unstressed females rats after the weaning of their pups. Restraint stress procedure reduced the body weight gain both during pregnancy and up to four weeks after the stress period. Stressed dams presented a reduction of exploration and of corticosterone levels when exposed to a novel environment (25 and 49 days post-stress). They spent less time in the open arms of the elevated plus-maze (26 days post-stress). Finally, they showed no increase in the time spent in immobility after a second exposure to the forced-swim test (35-36 days post-stress). In the contrary, such differences were not observed when the chronic stress procedure was applied on virgin females. Overall, our results show that, chronic stress during gestation induces lasting effects on emotional reactivity of the dams, thus indicating that gestation constitutes a critical period in the vulnerability to stressful events also for the mother.

This study investigated the effects of neonatal handling and maternal separation on the development of anxiety behavior and the hypothalamic-pituitary-adrenal axis of C57BL/6 mice. We hypothesized short periods of neonatal handling would diminish anxiety and secretion of corticosterone, while longer periods of maternal separation would elevate anxiety and plasma corticosterone compared to a nonhandled group. Mice were bred and reared as follows. After birth, each litter was assigned to one of four groups: mother and pups removed from the home cage for 10 min (group 1) or 180 min a day (group 2); mother only removed from home cage 180 min a day (group 3); and no handling until weaning (group 4). All separation occurred on the first 10 days of life. Juvenile males that experienced 10 min of separation/day exhibited decreased anxiety behavior compared to all other mice. A second group of litters were bred and reared according to groups 1, 2, and 4 as described above. Upon adulthood, anxiety behavior was assessed in males, and the corticosterone response to an acoustic stressor was quantified. No effect of differential rearing was observed on behavior, but there was a marked effect on plasma corticosterone secretion between the groups. Adult male mice neonatally handled for 10 min/day exhibited a blunted corticosterone response, and mice that experienced 180 min of maternal separation exhibited a prolonged corticosterone response to the acoustic stimulus compared to the nonhandled group. These results demonstrate the development of the mouse's hypothalamic-pituitary-adrenal axis can be modified by neonatal rearing conditions, and suggest that the mouse could be a viable animal model to determine the genetic-environmental interactions governing brain development.

Visceral pain originates from visceral organs in response to a noxious stimulus which, if prolonged, may lead to chronic changes in the neural network mediating visceral nociception. For instance, colon inflammation enhances the responses of neurons in the thalamus to colorectal distension (CRD), whereas lesion in the dorsal column (DC) reverses this neuronal sensitization, suggesting that the thalamus and the DC play major roles in chronic visceral pain. In this study, we used adult rats sensitized with neonatal painful colon irritation to reveal the contribution of the thalamus and the DC to neuronal hyperexcitability in a model of chronic visceral pain. We recorded the responses of lumbosacral neurons to CRD in control rats and in rats with colon irritation following stimulation or inactivation of the thalamus, and after DC lesion. Our results show that, first, neuronal responses to CRD decreased following thalamic stimulation in control rats, whereas, in rats with colon irritation, responses either decreased or increased; second, DC lesion attenuated or enhanced these effects in the positively or in the negatively modulated group of neurons, respectively; third, lidocaine injection in the thalamus reduced the responses to CRD in some of the neurons recorded in rats with colon irritation, but had no effect on those in control rats. Therefore, it is reasonable to speculate that plasticity in rats with colon irritation that may underlie chronic pain is sustained by feedback loops ascending in the DC and engaging the thalamus., (Copyright 2004 Elsevier B.V.)

Cochlear ablation results in the death of anteroventral cochlear nucleus (AVCN) neurons from birth to approximately postnatal day 14 (P14) in the murine brainstem. It is not known whether microglial activation contributes to AVCN neuronal death following deafferentation. In order to determine whether microglial activation helps to define the period of neuronal susceptibility within AVCN, we performed unilateral cochlear ablation on mice lacking the protein tyrosine phosphatase SHP-1 (me/me). These mice have been shown to have an exaggerated microglial response following ischemic injury. In the present study, the glial and neuronal response to deafferentation within AVCN was examined in wild-type and me/me mice at P5, P14, and P21. Lack of SHP-1 results in robust microglial but not astrocyte activation within the ablated P14 me/me AVCN. These mice also exhibit approximately 28% neuronal death at P14, a time when normal wild-type littermate controls show little cell death. Glial activation and neuronal loss at P5 and P21 were similar between the two phenotypes, suggesting a role of activated microglia in inducing neuronal death beyond P14 but not P21. These results indicate that activated microglia may participate in determining whether neurons in AVCN live or die following deafferentation.

Birth asphyxia accounts for the majority of developmental motor and cognitive deficits. Studies were undertaken to develop a reproducible murine model of perinatal hypoxic-ischemic encephalopathy (HIE) which would permit both anatomic and neurofunctional quantification of injury. Short-term neurofunctional outcomes consisted of three developmental reflexes (righting, cliff aversion and geotaxis) assessed in 7-day-old mouse pups 24 h after unilateral carotid artery ligation followed by inhalation of 8% oxygen. Cerebral infarct volume was dependent on duration of hypoxia, being approximately 2.5-fold greater with longer (60 min) versus shorter (30 min) hypoxia exposure (P=0.001). All three sensorimotor neonatal reflexes assessed at 24 h after HIE injury correlated significantly with long-term neurofunction evaluated using a water-maze test of navigational learning and memory assessed 8 weeks later in the same animals. Cerebral atrophy, a delayed consequence of HIE in this model, also correlated strongly with water-maze performance (r=0.86, P=0.002). These data demonstrate for the first time that murine neonatal sensorimotor reflex performance can be rigorously quantified in the acute phase of perinatal HIE and has strong predictive value not only for anatomic extent of cerebral injury, but also for long-term neurofunctional outcome.

The role of the N-methyl-D-aspartate (NMDA) receptor in cell death was evaluated in the piglet brainstem after exposure to intermittent hypercapnic hypoxia (IHH). Study groups comprised controls (n=6) and piglets exposed to IHH on 2 (n=6) or 4 (n=5) successive days prior to euthanasia. All piglets had the caudal medulla evaluated at 13-14 days of age using double immunohistochemistry for TUNEL and the NMDA receptor 1 (NR1) subunit. The percent of TUNEL positive neurons amongst NR1 (% TUN in NR1) and non-NR1 neurons (% TUN in non-NR1) was determined in eight nuclei. After 2 days of IHH, %TUN in NR1 was increased in the dorsal motor nucleus of the vagus (DMNV, P=0.007) and the inferior olivary nucleus (ION, P=0.05). After 2 days IHH, %TUN in non-NR1 neurons was increased in the lateral reticular nucleus (LRt, P=0.05), nucleus of the solitary tract (NTS, P=0.004) and gracile nucleus (P=0.05). After 4days IHH, the increase of %TUN in NR1 was sustained in the ION (P=0.05), while %TUN in non-NR1 neurons was sustained in NTS (P=0.04) and LRt (P=0.006). Daily IHH exposure induces neuronal death within NR1 and non-NR1 neurons, but the neuronal phenotype is consistent within affected brainstem nuclei. Involvement of the NMDA receptor tended to occur in nuclei with higher basal NR1 expression, and thus occurred in nuclei relevant to cardiorespiratory function. We speculate that IHH exposures, such as occurs during obstructive apnea or facial entrapment in prone sleeping during infancy, can induce abnormalities of cardiorespiratory control.

Increasing data provide support for the hypothesis that inflammatory cytokines mediate inflammation-induced injury to developing white matter. In the present study, roles of tumor necrosis factor-alpha (TNFalpha) and interleukin-1 beta (IL-1beta) in mediating lipopolysaccharide (LPS)-induced brain injury were investigated by co-administration of LPS with IL-1 receptor antagonist (IL-1ra) or TNFalpha antibody in the 5-day-old rat brain. Intracerebral injection of LPS and other agents was performed in a stereotaxic apparatus at the location of 1.0 mm posterior and 1.0 mm lateral to the bregma, and 2.0 mm deep to the skull surface at the left hemisphere. Brain injury was examined in brain sections 3 and 11 days after LPS injection. LPS-induced inflammatory responses were evidenced by great increases in TNFalpha and IL-1beta concentrations in the neonatal rat brain 6 h after LPS injection. White matter rarefaction was observed in 71% (five out of seven) of the rat brains 3 days after LPS injection and bilateral ventricle dilation was found in 71% (five out of seven) of the P8 rat brains and in 100% of the P16 rat brains (four out of four). These alterations were not found in the control rat brains. No apparent histological changes in gray matter were observed in the LPS-injected rat brains. LPS injection also resulted in injuries to oligodendrocytes (OLs) and hypomyelination, as indicated by reduced immunostaining for O4 and myelin basic protein (MBP). Increased astrogliosis, as indicated by increased glial fibrillary acidic protein (GFAP) immunostaining, was also observed in the LPS-injected, but not the control rat brain. Co-administration of LPS with IL-1ra, but not with TNFalpha antibody, significantly attenuated LPS-induced white matter injury, as indicated by decreases in ventricle dilation, white matter rarefaction, GFAP positive staining and by improved O4 and MBP immunostaining. Co-administration of LPS with IL-1ra significantly reduced LPS-induced elevation of caspase-3 activity in the rat brain. While TNFalpha antibody had no effect on LPS-induced elevation of caspase-3 activity, co-administration of LPS with TNFalpha antibody partially, but significantly, decreased LPS-stimulated increase in IL-1beta in the neonatal rat brain. These data suggest that IL-1beta may play an important role in mediating LPS-induced brain injury and TNFalpha may have complicated, probably dual, effects in LPS-induced brain injury.

The involvement of inhibitory transmitters for Ptychodiscus brevis toxin (PbTx)-induced depression of spinal synaptic transmission in neonatal rats was investigated. Stimulation of a dorsal root evoked monosynaptic reflex (MSR) and polysynaptic reflex (PSR) potentials in the segmental ventral root. The PbTx depressed the reflexes in a concentration-dependent manner and the depression was blocked by GABA(A) antagonist, bicuculline (1 microM). GABA also produced depression of the reflexes in a concentration-dependent manner. Simultaneous application of submaximal concentrations of PbTx (28 microM) and GABA (30 microM) enhanced the depression (>75%). In contrast, PbTx alone (28 microM) depressed the MSR and the PSR by 33 and 47%, respectively, and GABA (30 microM) alone depressed the reflexes by 30%. The N-methyl-D-aspartate receptor antagonist, DL-2-amino-5-phosphono-pentanoic acid (10 microM), blocked the PbTx-induced depression of MSR and also the enhancement of GABA response by PbTx. A glycine receptor antagonist, strychnine (1 microM), failed to block the depression by the toxin up to 28 microM; however, the depression was attenuated significantly at 84 microM of the toxin. The results indicate that PbTx depressed the spinal reflexes via GABA(A) receptors. Furthermore, the potentiation of GABAergic action by PbTx requires the N-methyl-D-aspartate dependent mechanism.

We have established an in vitro model of long-time culture of 4-day-old rat utricular maculae to study aminoglycoside-induced vestibular hair-cell renewal in the mammalian inner ear. The explanted maculae were cultured for up to 28 days on the surface of a membrane insert system. In an initial series of experiments utricles were exposed to 1 mM of gentamicin for 48 h and then allowed to recover in unsupplemented medium or in medium supplemented with the anti-mitotic drug aphidicolin. In a parallel control series, explants were not exposed to gentamicin. Utricles were harvested at specified time points from the second through the 28th day in vitro. Whole-mount utricles were stained with phalloidin-fluorescein isothiocyanate and their stereociliary bundles visualized and counted. In a second experimental series 2'-bromo-5'deoxyuridine labeling was used to confirm the antimitotic efficacy of aphidicolin. Loss of hair-cell stereociliary bundles was nearly complete 3 days after exposure to gentamicin, with the density of stereociliary bundles only 3-4% of their original density. Renewal of hair-cell bundles was abundant (i.e. 15x increase) in cultures in unsupplemented medium, with a peak of stereociliary bundle renewal reached after 21 days in vitro. A limited amount of hair-cell renewal also occurred in the presence of the anti-mitotic drug, aphidicolin. These results suggest that spontaneous renewal of hair-cell stereociliary bundles following gentamicin damage in utricular explants predominantly follows a pathway that includes mitotic events, but that a small portion of the hair-cell stereociliary bundle renewal does not require mitotic activity.