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Facultative paedomorphosis in salamanders is a plastic trait that may represent an adaptation to fluctuating environmental conditions. The author compared the timing of reproduction in paedomorphic and terrestrial-morph Ambystoma talpoideum at the same pond. Paedomorphic adults laid eggs approximately 6 wk earlier than terrestrial morphs. Early egg-laying and subsequent growth of hatchlings resulted in a significant size advantage for larvae from paedomorphic parents at the time that terrestrial-morph eggs hatched. These observations suggest that, under certain environmental conditions, facultative paedomorphosis is advantageous. 36 refs.

We address the question of whether individual variation in arrival date of breeding salamanders at a temporary pond is repeatable among years. We present data on variation in the date of arrival of individually marked males and females, and date of pond-filling over 12 years at a breeding site. These data allow us to partition variances within and among individuals, but remove the effects of annual environmental differences by standardizing annual return dates. Date of arrival differed significantly among individual males and females. Repeatability for date of return of individual males was (r = 0.0665), but significantly higher for females (r = 0.1662). Snout-vent length had no effect on the date of return for females, but small males returned earlier than large males

Reciprocal-removal experiments were conducted to test for the occurrence and consequences of interspecific competition between the rodents Mus musculus and Peromyscus leucopus on a large Virginia barrier island (USA). Habitat use and population density of each species were monitored during pre- and post-removal periods. The species exhibited conspicuous differences in pre-removal habitat use, with Mus occupying grassland and peromyscus occupying adjacent shrub thickets

Thirty-two Sprague-Dawley rats were divided into four groups, eight rats per group. Animals were hypophysectomized with removal of both the pars distalis and the neural lobe of the neurohypophysis. Groups of eight rats were euthanized 1, 2, 4 and 8 weeks following hypophysectomy and prepared for routine scanning electron microscopy (SEM) and correlative immunoelectron microscopy employing antisera against arginine vasopressin (AVP). Eight normal rats served as controls. In experimental rats that survived one to eight weeks posthypophysectomy, remarkable neuroanatomical alterations were notable in the median eminence and adjacent third cerebral ventricular lumen. In contrast to normal control rats, large numbers of neuntes were observed with SEM to insinuate from the lateral recess into the cerebral ventricular lumen and as early as one week following hypophysectomy they overgrew the apical surfaces of ependymal cells that constitute the lining of the cerebral ventricle. Immunoelectron microscopy revealed that a significant proportion of these neurites were magnocellular in origin in that they harbored AVP-positive neurosecretory vesicles. In addition to large numbers of invading magnocellular neurites, neuronal perikayria with apparent axosomatic synapses were observed to emerge upon the thick feltwork of invading axons, the latter of which appeared to freely terminate within the ventricular lumen. AVP-positive axon profiles were, in addition, seen to terminate upon the basal lamina of portal perivascular spaces in the zona externa of the median eminence. These data are consistent with the idea that following hypophysectomy (to include high stalk section of the neurohypophyseal system), that there is rapid, and dynamic sprouting and regrowth of AVP-positive axons into the adjacent third cerebral ventricular lumen and to the contact zone of the median eminence as well. This phenomenon may represent a compensatory physiological response to injury of the neurohypophyseal system characterized by a highly plastic neuroanatomical reorganization of magnocellular elements which appear to utilize the CSF of the third cerebral ventricle as a functional terminus for the neurocisternal secretion of AVP which ultimately enters the systemic circulation.

The ontogeny of the rat supraoptic nucleus (SON) has been studied with several different techniques: Microscopic and ultrastructural evaluation of cytodifferentiation of the nucleus, radioimmunoassay of vasopressin (VP) and oxytocin (OT) content of the hypothalamo-neurohypophyseal system, immunocytochemical evaluation of neurophysin (NP) production, and histofluorescence analysis of the noradrenergic innervation of the nucleus. Observations from these varied approaches correlate well and indicate cytodifferentiation of the SON occurring simultaneously with initiation of synthesis and transport of VP and NP. Several phenomena were observed for the first time on 17 days post coitus (dpc). These include identification of the SON as a distinguishable nucleus at the light microscopic level, detection of VP by RIA in the hypothalamo-neurohypophyseal system (HNS), visualization of NP immunocytochemically in the neurons of the SON and in the axons of the hypothalamo-neurohypophyseal tract in the rostral median eminence, and ultrastructurally, observation of developing cytoplasmic apparatus for hormone synthesis. Developing endoplasmic reticulum and Golgi apparatus were observed, and occasional cells possessed dense core granules. Dramatic development was observed in all of the analyzed parameters from 17 dpc to parturition which occurred in the afternoon of 22 dpc. VP content of the HNS increased 3–6 fold daily and NP staining intensity increased concomitantly in the SON. Ultrastructural analysis revealed cellular maturation during this period such that cytodifferentiation was essentially complete by 21 dpc. Evaluation of the development of noradrenergic innervation of the SON was performed simultaneously with the NP studies with alternate sections from the same brains prepared either for immunocytochemical NP visualization or for formaldehyde induced catecholamine (CA) fluorescence. A few CA varicosities were visible in the SON on 17 dpc. The density of CA varicosities increased progressively and by 28 days postnatal an essentially adult-like pattern of varicosity-cell contact was established. At early stages the CA varicosities did not appear to be in juxtaposition to the NP stained cells as is seen in the adult. This observation may correlate with the ultrastructural observation that synaptic contacts were not present on the soma and dendrites of SON neurons until 21 dpc although even at this stage, they were seen infrequently. The appearance of VP and NP in the SON prior to the establishment of CA varicosity-cell contacts may indicate a trophic influence of the neurosecretory neurons on the ingrowing CA axons.

Adjacent tissue sections through the rat median eminence were examined for the distribution of gonadotropin-releasing hormone (GnRH) and catecholamines (CA). A simultaneous visualization technique was employed for this correlative neuroanatomical analysis. At rostral and mid-central levels of the median eminence the majority of GnRH terminals do not appear in coexistence with CA terminals; the latter were confined to the outer-most 10 micrometers of the median eminence while the densest concentration of GnRH terminals was located internal to this layer. However, individual GnRH fibers appeared to penetrate the outer CA zone wherein they were found in juxtaposition to portal capillaries. At caudal levels of the median eminence, there was an extensive overlap of CA and GnRH varicosities adjacent to the tubero-infundibular sulcus. In addition, numerous GnRH terminals were seen adjacent to portal vessels. The differences in the positions of CA and GnRH terminals between rostral and caudal median eminence may provide a morphological basis for the hypothesis of separate regulatory mechanisms for CA upon GnRH secretion at these two levels of the median eminence.

The relationships among timing of metamorphosis, size at metamorphosis, and traits related to adult fitness were studied for 8 yr in the salamander Ambystoma talpoideum at a temporary pond. Among years, the modal time of metamorphosis and mean body size at metamorphosis were positively correlated with the date the pond dried. In years that the pond dried late, one group of larvae metamorphosed well before the pond dried, whereas the other group metamorphosed just before pond drying. Mean body size of late—metamorphosing individuals was not greater than that of individuals metamorphosing early. Early—metamorphosing males and females were larger at first and second reproduction than were late—metamorphosing individuals. Independent of timing of metamorphosis, larger juveniles at metamorphosis were also larger adults at first reproduction. Age at first reproduction for males was not associated with timing of or size at metamorphosis but large early—metamorphosing females reproduced at a younger age than did small early—metamorphosing females. Neither time of metamorphosis nor size at metamorphosis was associated with survival to first reproduction. These results demonstrate a direct relationship between phenotypic variation generated in the larval stage and adult traits closely associated with an individual's fitness.

Nest distribution and nest success (i.e., the proportion of a clutch that successfully hatched to the free-swimming larval stage) of the terrestrial-breeding marbled salamander, Ambystoma opacum, was examined at a breeding site in South Carolina, U.S.A. Females placed nests in areas of high total vegetative cover, and tended to concentrate nests in the lowest portion of the breeding site. Nests placed at high and medium elevations exhibited a nonrandom aggregated pattern, whereas nests at low elevations were randomly distributed. Nest success of 85 nests was highest at low elevations, and was positively correlated with the number of days a female remained with (brooded) the nest. Natural selection may favor nest site selection and nest brooding behavior as mechanisms to reduce embryonic mortality.

A nidus of supraependymal cells was located within the infundibular recess of a rat's third ventricle. Upon transmission electron microscopic analysis, these cells were clearly identified as neurons. Neuronal processes, as well as end-terminals that contained dense-core and clear synaptic-like vesicles, were also observed coursing around these cells. It is suggested that some of the supraependymal cells that have been observed in previous scanning electron microscopic studies could be neurons similar to those described here.

Five male rats were adrenalectomized. Thirty days later 3 were treated with dexamethasone (dex) (100 µg⁄100 g body wt ip and 1 µg⁄ml in the drinking water) for 24 hr. The basal hypothalami were removed and examined after preparation for standard transmission electron microscopy. Attention was directed to the contact zone of the midcentral medianeminence where the ependymal, glial, and tuberoinfundibular elements abut on the portal capillaryperivascular space. The dex treated-adrenalectomized rats showed more than twice as many dense core vesicles (dcv) per axonterminal cross section as the untreated controls. Ether inhalation, dextreatment alone, or adrenalectomy alone had little effect on the dcv counts. (Endocrinology 94: 303, 1974)

Primary cultures of dispersed cells were prepared from 3–5 mg pieces of basal hypothalami of 10–12-day-old rats. The tissue included median eminence, arcuate nucleus and variable amounts of adjacent hypothalamus and preoptic area. The dispersion procedure consisted basically of tissue trypsinization and mechanical dissociation of cells. They were cultured in a modified L-15 medium in an air atmosphere. Neurons survived approximately 3 months. On the basis of morphological characteristics, two basic cell types could be distinguished. One was a larger (50 μm diameter) multipolar cell; microspectrofluorometric analysis revealed that a small percentage of these neurons contained a catecholamine. A second type was smaller, fusiform or ovoid and generally bipolar; a significant number of these were immunoreactive for the releasing hormone LHRH.

This investigation has confronted some very basic questions of neurobiology and specifically deals with the neurovascular and neuroanatomical interactions that occur between graft and host following neural transplantation. Host Long-Evans rats with chronic autosomal diabetes insipidus (DI) received stereotaxic implants of normal 17 day post-coitus fetal hypothalamic fragments from the rostral (anterior) hypothalamus of normal Long-Evans pups. Following stereotaxic surgery DI hosts were killed 60 or 90 days later and their brain prepared for correlative microangiography-immunocytochemistry coupled with transmission electron microscopy. Explants were rapidly invaded by host vessels from several routes. 1. (1) Vessels appeared to arise from portal capillaries in the underlying median eminence and 2. (2) from adjacent vessels from the paraventricular nucleus and surrounding endocrine hypothalamus and 3. (3) possibly from intrinsic vessels of the graft. The former remained fenestrated and established bonafide neurovascular zones in the ventral regions and in actively growing explants. Small clusters of arginine vasopressin-positive fibers and neurophysin positive neurons were noted throughout the parenchyma of explants. Despite the presence of neurosecretory neurons and neurovascular (neurohemal) zones, none of the host rats exhibited a physiological return to normal parameters of water balance. However the active growth and development of explants in the third cerebral ventricle of DI host rats coupled with emergence of neurovascular zones lends support to a potential model for analyzing the development of anatomical substrates for the central delivery of neuropeptide hormones.

An investigayion was made into the status of the Morelet's crocodile Crocodylus moreleti Dumeril & Dumeril in Belize, a Caribbean nation of Central America. Juvenile animals were found to be rather common in isolated areas, but very few adults were observed; we believe this to be an indication of over-exploitation. Certain aspects of the hide-hunting-dealing enterprise are also examined, and it is concluded that if C. moreleti is to survive in any numbers, a policy of protection should be instituted.

Adult male Brattleboro rats with chronic diabetes insipidus underwent stereotaxic surgery wherein minced fragments of anterior hypothalamus from fetal rats, 17 days post-coitus, were stereotaxically positioned into the lumen of the host third cerebral ventricle. Host rats with fetal donor tissue were killed at various times following surgery and were prepared for correlative scanning-transmission electron microscopy. Examination with this technique revealed the presence of large neurografts which grew to occupy the entire lumen of the host third ventricle. Grafts were well vascularized and in addition exhibited remarkable numbers of supraependymal, cerebrospinal fluid-contacting neurons. The physical emergence of this cell line in proximity to viable grafts is discussed with respect to the biochemical influences that a neuropeptide producing fetal transplant has upon a peptide-deficient host.

The main objective of this paper is to present the results of an experimental study relating to the transport of sediment under certain conditions not typical of river sedimentation studies. The area of sediment transport lacks information on the transport down high gradient channels that are typical of streets, construction sites and agricultural land, in addition to mountain torrrents. The study of transport of non-cohesive sediment in high gradient channels includes determination of the transport capacity of shallow flows in high gradient channels with simulated bed roughness and various grain sizes. Regression analysis was performed to relate the dependent and independent variables in functional relationships and revealed good correlation.

This investigation deals with correlative scanning-transmission electron microscopic analysis of the mammalian circumventricular organ system CVO. This specilized system of ancient midline regions throughout the third and fourth cerebral ventricle of the brain share many common structural similarities with respect to their vascular, neuronal and glial organization. Areas of analysis of this investigation have included the median eminence, the neural lobe, the organum vasculosum of the lamina terminalis, the subfornical organ and the area postrema. Ample evidence now suggests that these regions of the brain may play an integrative role between blood, brain and cerebrospinal fluid and because they share so many common features, circumventricular organs have been analogized as ‘windows of the brain’. Regions of the cerebral ventricular wall that do not possess neuroendocrine (either real or suspected), possess a dense nap of cilia throughout their mural walls. However, lining ependymal cells of CVO, the so-called ‘tanycyte’, does not exhibit a major population of cilia and instead exhibits a felt work of microvilli organized in a mosaic pattern. These microvilli appear most prominent along the interface of apically oriented cells that constitute the lining of the family of structures collectively referred to as circumventricular organs. Unlike surrounding brain tissue, circumventricular organs do not exhibit the classical blood-brain barrier but possess instead fenestrated capillaries and specialized epennymal cells (tanycytes) that possess tight junctions at their apical (ventricular) sites. Hence in these specialized regions the blood-brain barrier has been shifted from the vascular to the ventricular side and becomes instead a blood-CSF barrier. Coupled with the fundamental differences in the anatomical appearance of the ventricular lumen of circumventricular organs, numerous individual clusters of cells can be seen to reside upon the ventricular surfaces of circumventricular organs. These cells are identified as either populations of quiescent histiocytes or large dense populations of neurons with extensive neuritic arborizations which extend over the ventricular lumen and appear to represent a system of interconnecting axonal processes that may serve to integrate the various circumventricular organs of the third and fourth cerebral ventricle. This investigation deals with the possible role that supraependymal CSF-contacting neurons may play in the synthesis and secretion of neuropeptides into the brain and into the adjacent cerebrospinal fluid.

A new method is described for producing plastic casts of murine Ventriculosubarachnoid space. Photographs of a representative cast demonstrate the highly detailed tridimensional anatomy obtainable with this method.

Seasonal variation in the elimination rate constants of two radionuclides was examined in the yellow-bellied slider (Pseudemys scripta). Thirty-six turtles from waste ponds contaminated with cesium-137 and strontium-90 were placed in an uncontaminated 18 × 20 m experimental pond and fed ad libitum weekly. Total body burdens of the radionuclides were measured five times at approximately 2-month intervals. These data were used to determine seasonal and overall elimination rate constants. Elimination rate constants differed between radionuclides and among seasons. Seasonal rate constants ranged from 0.002 to 0.029 day−1 for 137Cs, and from −1 for 90Sr. Rate constants were highest, and presumably metabolic activity was greatest, in late April through June. This period corresponds to the spring breeding season in P. scripta. The overall biological half-lives of cesium-137 and strontium-90 were 64 and 365 days, respectively.

This report concerns a light and electron microscopic investigation of the median eminence and dorsal infundibular stem of the rat following surgical isolation (deafferentation). Using a modification of the Halasz technique, the basal hypothalamus, including the arcuate nucleus and median eminence were surgically isolated from surrounding structures. Special attention was directed to the contact (external) zone of the median eminence and rostral infundibulum where tuberohypophyseal axons as well as ependymal cell processes abut upon the abluminal basement membrane of the portal perivascular space. The results of this study to date suggest that 9, 20, and 40 days following surgical isolation, there is a distinct increase in the population of tuberohypophyseal dense core vesicles. It is suggested that deafferentation abolishes inhibitory and excitatory input that serves to modify the cellular dynamics of tuberohypophyseal neurosecretory elements. Comments are also made on the presence of cistern-like structures in the lateral median eminence; the presence of vesicle-like inclusions in terminal ependymal processes is discussed in relationship to the role that ependyma may play in linking the third ventricle with the adenohypophysis.

A light and electron microscopic autoradiographic analysis revealed that H3-valine infused into the lateral ventricle of normal and acutely dehydrated cats is preferentially taken up by the supraoptic (SON) and paraventricular nucleus (PVN) of the hypothalamus. Grain counts for these magnocellular neurons in normal unstressed cats were highest at one hour post infusion with a significant fall off by three hours. Uptake by the SON and PVN at one hour exceeded neighboring nuclear groups by a factor of 7 and 4 fold respectively. Electron microscopic autoradiographs from acutely dehydrated cats revealed the presence of emission grains in association with rough endoplasmic reticulum and large osmiophilic neurosecretory vesicles. In view of statistically significant uptake values and rapid turnover of H3-valine by SON and PVN in normal animals, coupled with emission tracks in direct association with underlying neurosecretory product in acutely dehydrated ones, it is speculated that valine may be an amino acid component of one or both of the neurophysins to which neurohypophyseal hormones are non-covalently linked.

The effects of drive intensity in Sr test and the imposition or withholding of Sr training upon bar pressing were studied in a Zimmerman paradigm. The Ss tested under high drive, with or without Sr training, made significantly more bar presses than satiated Ss. No support was found for an exploratory-manipulatory interpretation of Zimmerman’s results, but the validity of the assumption that intense homeostatic drives interfere with exploratory-manipulatory motivation was questioned. The fact that Ss without Sr training performed as well in test as trained Ss confirmed a previous finding and led to a rejection of Zimmerman’s Sr interpretation of his results.

An in vitro assay for thyrotrophin releasing factor (TRF) is described which is based upon release of TSH from hemi-pituitary glands of normal rats. Pre-incubation of the pituitary gland in rat plasma results in considerable increase in sensitivity to approximately 35 pg of TRF. The content of TRF in median eminence of the hypothalamus of normal rats is estimated to be in the range of 102–140 pg. When median eminence is incubated in vitro with 3H-TRF or when radiolabelled hormone is infused intraventricularly, autoradiographic evidence indicates that the hormone is present in specialized ependyma (tanycytes) of the median eminence.

Scanning electron microscopy was used to assess the ultrastructural differences exhibited by the varigated ependymal lining of the near-term human fetal 4th ventricle. The central portion of the fourth ventricular floor, including the median sulcus is punctuated by numerous clumps of cilia. The density of cilia here is not as great as that described for other regions of the human cerebral ventricular system; accordingly, underlying substructure can be noted. There are distinct differences between ependymas that line the floor of the fourth ventricle with those of the adjacent area postrema. The latter region possesses not cilia, but instead exhibits a dense knap of microvilli. The ultra-architecture of the choroid plexus is relatively similar to that of other circumventricular organs with the exception that it possesses small isolated groups of cilia as well as microvilli. These findings are discussed with respect to the dynamics of local CSF movement and flow, ependymoabsorption and ependymosecretion

A scanning electron microscopic analysis of the adult human third ventricular wall revealed ultra-architectural differences between dorsal and ventral portions. In the brains of thirteen and sixteen week old human fetuses regional differences in the surface organization of lining ependyma were more sharply defined than those of the adult. Alterations in the luminal surfaces of ependyma may reflect differences in the functional capacity of various ventricular areas. The potential role of certain ependyma (tanycytes) and their putative participation in neuroendocrine events is discussed.

Ultrastructural changes in the neural lobe related to lactation and release of oxytocin in response to suckling were observed. Neural lobes of nonlactating controls showed abundant stores of osmiophilic neurosecretion contained in vesicles in the axons. In contrast, the glands of lactating rats sacrificed during suckling by the young displayed extensive depletion as evidenced by decreased numbers of vesicles containing osmiophilic neurosecretion and increased numbers of optically clear neurosecretory vesicles. When a lapse of 15 minutes was allowed between removal of the suckling young and sacrifice of the mother, a high degree of restoration of neurosecretion had taken place, with approximately 50% of the axons filled with neurosecretion. After 1 hour the restoration of neurosecretion was virtually complete. Observations on synaptic vesicles were also made. Relations of these changes to hormonal events and mechanisms of release and restoration of neurosecretion are discussed.

Summary Three patients with unusual patterns of pleural involvement by sarcoidosis are described. Two patients presented with massive recurrent pleural effusions and the third had extensive bilateral pleural thickening. Because of the uncommon presentations, the possibility of sarcoidosis in these patients was initially overlooked. The diagnoses were made only after extensive investigations including multiple biopsies.

Microspectrofluorometry, fluorescence histochemistry and light and electron microscopic autoradiography have established the presence of sub-populations of neurons in the arcuate-periventricular region of the rat hypothalamus that sequester both radiolabeled dopamine and demonstrate formaldehyde-induced fluorescence. These characteristics are consistent with a catecholaminergic function. Selective sequestration of 3H-dopamine at the light and ultrastructural level is discussed in the context of an ultrashort loop autoregulatory mechanism for this neuronal population.

Numbers of successfully metamorphosing juvenile amphibians were tabulated at three wetlands in South Carolina, U.S.A. using terrestrial drift fences with pitfall traps. A relatively undisturbed Carolina bay was studied for eight years, a partially drained Carolina bay for four years, and a man-made borrow pit for three years. Annual production of juveniles at the undisturbed Carolina bay ranged from zero to 75,644 individuals of 15 species. Fewer individuals of fewer species typically metamorphosed at the borrow pit than at the undisturbed bay, with the least numbers at the partially drained Carolina bay. Both total number and species diversity of metamorphosing juveniles at each site each year showed a strong positive correlation with hydroperiod, i.e., the number of days a site contained standing water that year. Data for one common anuran species and the most common salamander species were analyzed separately by multiple regression, in addition to the community analyses. For the mole salamander, Ambystoma talpoideum, hydroperiod was a significant predictor of the number of metamorphosing juveniles, but the number of breeding females was not. For the ornate chorus frog, Pseudacris ornata, the number of breeding females was a significant predictor of the number of metamorphosing juveniles, but hydroperiod was not. Variation in the dates of wetland filling and drying interacts with other factors to determine amphibian community structure and diversity. Either increasing or decreasing the number of days a wetland holds water could increase or decrease the number and species diversity of amphibians in and around a wetland.

The present ultrastructural study proves the existence of nerve terminals closely apposed to the plasmalemmata of tanycytes in the rat median eminence. Several of these “axo-tanycytic” endings display remarkable accumulations of agranular endoplasmic reticulum in the form of pleomorphic vesicles which are closely apposed on either side of the plasma membrane of each cell compartment. Some of these vesicular profiles give the impression of structural continuity across both membrane systems. This phenomenon is discussed in the context of being a potential substratum for communication between both cell compartments.

Light and electron microscopic autoradiography has been employed to define the neuroanatomical patterns of uptake and binding of radiolabelled L-dopa in the endocrine hypothalamus of the rat. A dorsomedial continuum of arcuate and periventricular neurons selectively sequester 3H L-dopa 20 min following its intraventricular infusion. By 40 and 60 min following the infusion labelling of neurons is minimal and supports the notion of rapid degradation. Other cell compartments such as tanycytes demonstrate uptake of 3H L-dopa. The ultrastructural localization and distribution of radiolabelled L-dopa (or its metabolites) in the rodent hypothalamus is discussed with respect to mechanisms and cell compartments involved in neuroendocrine regulatory processes.

Blocks of anterior hypothalamus were transplanted from 19 day-old fetuses of Wistar/Lewis rats into the third ventricle of adult male Brattleboro rats. Physiological changes in graft recipients and in sham-operated animals were monitored daily. Twenty days after surgery, the graft recipients and sham-operated animals were killed and their brains examined by correlative scanning and transmission electron microscopy. Host animals that exhibited both decreased polydipsia and increased urine concentration were found to have viable grafts within the third ventricle. The observed physiological changes suggested that synthesis and release of vasopressin occurred in the transplanted neurons. Grafts were well vascularized by vessels arising from the host hypothalamus. Neurons, with perikarya ranging from 8 to 30 micron in diameter, glial cells, and neurites were located throughout the transplants. A neurohemal contact zone, similar to that normally seen in the median eminence, could not be demonstrated in the grafts. The absence of complete glial and ependymal barriers indicates a relatively close association between cells in the transplants and the cerebrospinal fluid. A large increase in supraependymal neurons and their processes, including an eruption of neurons through the floor of the third ventricle in one animal, was observed in graft recipients but not in sham-operated animals.

The ultrastructural organization of the perinatal hypothalamus and the dynamics of neuronal and ependymal growth and plasticity were examined in this investigation. The brains of fetal rats 16, 17 and 18 days in utero and those of postnatal rats 1–16 days post partum were fixed with aldehyde fixatives and prepared for combined SEM/TEM analysis. By day 17 in utero the ventricular (ependymal) surfaces of the fetal thalamic wall, cerebral vesicle and rhomboid fossa were relatively well differentiated with cilia and microvilli. Type II histiocytes were the first supraependymal cell to appear upon the ventricular lumen and were evident by day 17 in utero. In contrast, the apical surfaces of tanycytes of the infundibular recess as well as those of most other circumventricular organs were poorly differentiated and unremarkable. Tanycytes of the infundibular recess exhibited a simple hexagonal mosaic pattern of apposed plasmalemmata and even by day 1 post partum few cilia or microvilli were evident.

This investigation has combined microangiography, immunocytochemistry, coupled with transmission and scanning electron microscopy to discuss the neuroanatomical interactions that occur in the brains of Brattleboro rats with diabetes insipidus, following stereotaxic placement of normal fetal hypothalamic fragments into the third cerebral ventricle. Following surgical placement of 17 day post-coitus hypothalamic fragments, host rats with chronic autosomal homozygous diabetes insipidus were killed and their brains were prepared for analysis. A significant degree of explants (68%) flourished and grew in the lumen of the third cerebral ventricle of recipient hosts. Explants were rapidly invaded by host vessels from two routes. (1) Vessels arose from the underlying mantle plexus of portal capillaries which remained fenestrated in the lower one-third of the explants and developed neurovascular (neurohemal) zones. (2) The second source of vessels arose from bed capillaries of the adjacent paraventricular nucleus and adjacent hypothalamus. In contrast to vessels arising from the contact zone, these latter vessels remained unfenestrated. Small clusters of immunocytochemically positive neurons (neurophysin positive) were seen throughout the explants. Numerous healthy magnocellular neurons harboring numerous dense core vesicles and exhibiting multiple axosomatic and axodendritic synapses were seen throughout the neuropil of explants. Axon profiles were noted to terminate upon the abluminal basal lamina of perivascular spaces surrounding fenestrated capillaries in the lower one third of explants. None of the host animals exhibited physiological return to normal parameters of urine output, drinking behavior, and/or urine osmolarity. However the growth and development of explants in the third cerebral ventricle of DI hosts coupled with the emergence of bonafide neurovascular zones supports a potential anatomical substrate for the central delivery of neuropeptide hormones in this experimental model.

Light and electron microscopic autoradiographic analysis of the medial basal hypothalamus of rat brains incubated for 30 and 60 minutes in tritiated luteinizing releasing factor (3H-LRF) revealed selective uptake in the form of silver grains over specialized ependyma (tanycytes) and perivascular glial cells in the palisade-contact zone of the median eminence. The functional capacity of tanycytes and glia are discussed in light of these data.

Rats were given a standard scald burn on 60% of the body surface or only a sham burn and were sacrificed at intervals from 6 hr to 14 days later. Serum thyroxine (T 4 ), free thyroxine index (FT 4 I) and triiodothyronine (T 3 ) were depressed compared to values in respective shams as early as 6 hr post-burn. T 4 and FT 4 I were less depressed on post-burn days (PBD) 2–3 than on PBD 1 and then exhibited a further fall. T 3 , remained depressed through PBD 14. Pineal melatonin content was elevated at 6 hr and fell to the normal daytime range in subsequent samples. The ventral portion of the diencephalon was prepared for scanning electron microscopy. Only in the burned rats and beginning on PBD 2, large numbers of supraependymal neurons (SEN) appeared in the ventricular space attached to the inferior walls and floor of the third cerebral ventricle. Transmission electron microscopy was used to confirm the neuronal nature of the SEN. Viewed by scanning electron microscopy, these persisted through PBD 14. SEN were interconnected by cables of their neuntes exhibiting varicosities on individual neuntes as they passed over perikarya of other SEN. Some SEN were seen to be only partially emerged from the underlying tissue and others were seen to send a thick process into the hypothalamic tissue. These observations indicate that after peripheral injury there is marked plasticity of the brain in an area thought to control the endocrine systems that show abnormalities after such a peripheral injury. The timing, location and nature of these anatomic changes indicate the possibility that at least some aspects of central nervous orchestration of the endocrine metabolic response to injury may be related to the emergence of a neuronal system receiving or sending messages through the cerebrospinal fluid and/or through new neurite circuits along the surface of the third ventricular wall. These structures may appear in response to initial primary hormonal changes and/or may play a role in maintaining the post-injury hormonal milieu manifested in part by a subsequent second fall in serum T 4 .

The ultrastructure of the normal median eminence of the male rhesus monkey (Macaca mulatta) is described using high-voltage electron microscopy. Surface specializations of ependymal cells lining the infundibular recess included cilia, apical extrusions, and microvilli. Supraependymal cells were predominantly macrophage-like, but examples of lymphocytic types were also seen. Tanycytes had long, branching, basal processes filled with numerous microtubules, some lipid droplets, and granules. The zona interna was composed of large unmyelinated neurosecretory fibers. A few myelinated fibers were also seen, but their character as neurosecretory fibers could not be established. The zona externa was composed of densely-packed profiles of neuro secretory fibers of small diameter, was well-vascularized and contained the terminations of tanycytes. Perivascular glial cells, vesiculated elements, pituicytes, and cellular elements common to connective tissue were observed. The intricate relationships between both the cellular and fibrous elements of the median eminence can be appreciated with the capability of high-voltage electron microscopy to discern ultrastructure in sections 10 times thicker than those used for low-voltage electron microscopy. The median eminence of this primate species has an ultrastructural organization similar to that described for most other species.

This investigation is one of a series aimed at developing an understanding of the neuroanatomical correlates of neuronal and vascular interactions that occur between heterografts of normal fetal hypothalamic tissue transplanted into the third cerebral ventricle of adult Brattleboro rats with homozygous autosomal diabetes insipidus (DI). Rapid vascular invasion of fetal neurografts occurred within 3 days and arose from the mantle plexus of portal capillaries in the underlying host median eminence. Host vessels also invaded from the periventricular stratum and preoptic area. In the ventral regions of heterografts neurites were observed to terminate upon perivascular spaces that surrounded local capillaries. Despite the development of apparently normal neurovascular zones, none of the DI host recipients demonstrated an amelioration of polydipsia or polyuria characteristic of diabeties insipidus.

This investigation has dealt with a light and electron microscopic autoradiographic analysis of the median eminence of the rat following intraventricular infusion of 3H-dopamine. This study has demonstrated that 3H-dopamine, once infused into the mammalian cerebral ventricular system, is rapidly and selectively absorbed by tanycytes and transported to the contact zone within 5 minutes after ventricular infusion. Certain axon terminals in the ependymal, hypendymal, and palisade-contact zones selectively sequester 3H-dopamine as do subpopulations of arcuate neurons. This picture of intense labelling of neurons and axon terminals is discussed with respect to monoaminergic re-uptake mechanisms. Uptake and transport of 3H-DA by tanycytes is discussed.

With explosively rapid technological advances in the fields of electronics and solid-state physics has emerged a new generation of biomedical instrumentation. In the forefront of these advances is the science and application of scanning electron microscopy (SEM). Despite its relatively recent emergence as a tool for both physical and biological investigations (Thornton, 1 1968; Carr, 2 1971; and Scott et al, 3 1974), conceptually the ideatum behind its evolution as an instrument of practical application can be traced back to the pioneering efforts of Oatly et al 4 in Cambridge in 1965. Unlike optical or transmission electron microscopy (TEM), SEM is restricted to the evaluation of surface structures. However, the sample size available for such analysis exceeds that for TEM by an order of magnitude of greater than 500:1. Furthermore, SEM easily interfaces with TEM and other sophisticated techniques, such as nondispersive x-ray analysis, allowing the investigator a considerably broader

The historic hypotheses postulated by Green and Harris (1947) over a quarter of a century ago have stood the test of time and have clearly established parvicellular neurosecretory neurons and the hypophyseal portal vasculature as the vital linkage in the transduction of bioelectric energy into blood-borne signals, the releasing factors. Recent evidence has suggested, in addition, the presence of parallel mechanisms which may serve as an alternative way in which biologically active molecules reach the portal bed. The purpose of this investigation was to test the distribution of radio-labelled releasing factors in the mammalian hypothalamus with autoradiography.

The lateral ventricles and choroid plexuses of an adult and near-term sheep fetus were examined with scanning electron microscopy. The predominant surface structure of the ependymal cells were cilia arranged in clumps with evidence of metachronic activity. Topographical variations of the ependymal surface are described and discussed according to their role in transport of cerebrospinal fluid and their relation to underlying nervous tissue.

Scanning electron microscopy of the third ventricle of sheep demonstrates areas of ciliated ependymal cells at the dorsal and middle third. The cilia of the dorsal portion of the ventricle have biconcave discs that are attached to each cilium by a slender stalk. The lower third and floor of the ventricular wall, as well as the pineal recess, are largely covered by ependymal cells that possess numerous microvilli with only a few isolated cilia scattered along cell surfaces. The infundibular recess is papillated with apical blebs of the ependymal cells that project into the lumen of the recess. Measurements of these surface elements indicate an average diameter of 0.28 μ for cilia, 0.10 μ for microvilli and 0.50 μ for the apical blebs of the infundibular recess. The functional significance of the regional differences in surface structures is discussed in relation to cerebrospinal fluid movement, ependymoabsorption and ependymosecretion.

The third ventricular walls and floor of male and female mink (Mustela vison) were analyzed with comparative light microscopy, transmission and scanning electron microscopy. Distinct regional fine structural variations were noted in the appearance of the dorsal, middle third and lower portions of the ventricular wall and floor. These variations were characterized by an abrupt decrease in the density of ciliated ependymal surfaces in the middle one-third of the ventricular wall. The ventral walls and floor of the lateral and infundibular recesses displayed smoother contours with numerous bleb-like protrusions and blunt villiform processes. Occasionally multipolar neuron-like cells were observed to lie upon the floor of the infundibular recess. Speculation is raised relative to the differing functional capacities of these various ventricular areas.