The use of heat-induced hydrolysis in immunohistochemistry on angiotensin II (AT1) receptors enhances the immunoreactivity in paraformaldehyde-fixed brain tissue of normotensive Sprague-Dawley rats.

The research on components of the renin-angiotensin system delivered a broad image of angiotensin II-binding sites. Especially, immunohistochemistry (IHC) provided an exact anatomical localization of the AT(1) receptor in the rat brain. Yet, controversial results between in vitro receptor autoradiography and IHC as well as between immunohistochemical studies using various antisera started a vehement discussion concerning specificity and cross-reactivity of these antisera. In particular the magnocellular subdivision of the paraventricular nucleus (PVN) and the supraoptic nucleus (SON) provided controversial results on the localization of AT(1) receptors. Both areas are known for angiotensin II-induced release of vasopressin (VP) and oxytocin (OXT). To evaluate the significance of the appropriate method of antigen retrieval and its relevance for the detection of AT(1) receptors we performed IHC on AT(1) receptors in paraformaldehyde-fixed and paraffin-embedded brain tissue of Sprague-Dawley rats using either the detergent Triton X-100 or microwave oven heating. This study demonstrates that heat-induced hydrolysis enhances the quality and quantity of immunoreactivity (IR) in IHC on AT(1) receptors. In the organum vasculosum lamina terminalis and in the parvocellular subdivisions of the PVN we report a distribution of AT(1)-like-IR similar to that observed with other methods. However, in addition, we provide evidence that distinct AT(1)-like-IR is also localized in few magnocellular neurons of the PVN and in few parvocellular neurons of the dorsal SON but not in magnocellular neurons of the SON. Moreover, parallel IHC indicates that few magnocellular OXT- or VP-releasing neurons of the PVN as well as parvocellular OXT-releasing neurons of the SON do also contain AT(1) receptors.

Semithin cryosections as a tool to perform high resolution immunofluorescence and in situ hybridization analysis of the nervous tissue: a study in the supraoptic nucleus.

Immunofluorescence and fluorescence in in situ hybridization represent powerful approaches to correlate biochemical and molecular data with the structural organization of cells and tissues. However, the analysis of tissues by fluorescence microscopy is limited by the fact that most methods currently used to preserve the morphological integrity of sectioned samples at high resolution do not allow access of the labeled probes to the target molecules. Here we have made use of semithin cryosections obtained from rat supraoptic nucleus to perform immunofluorescence with antibodies directed against cytoplasmic and nuclear antigens, as well as fluorescence in situ hybridization with antisense oligonucleotide probes complementary to the poly(A) tail of mRNA and to specific mRNAs. In addition, DNA was visualized by incubation of sections with digoxigenin-labeled nucleotides in the presence of Escherichia coli DNA polymerase I. The high resolution of this DNA staining in combination with immunolabeling for nuclear antigens provides a powerful tool to analyze the structural and functional compartmentalization of neuronal cell nuclei. The major conclusion from this study is that performing fluorescence microscopy on 1 micron-thick cryosections provides an important tool to accurately localize proteins, DNA and RNA within nervous tissue in general and particularly in the model of supraoptic nucleus. Moreover, the cryosectioning technique appears particularly suited to the study of the localization of specific mRNA species in the neuronal cytoplasm and represents a useful approach to addressing the functional significance of mRNA localization in protein targeting.

Immunohistochemical localization of corticotropin-releasing factor, [arginine8]-vasopressin and oxytocin neurons in the goat hypothalamus.

Distribution patterns of corticotropin-releasing factor (CRF), [arginine8]-vasopressin (AVP) and oxytocin (OXY) neurons were examined immunohistochemically in the female goat hypothalamus. The majority of the CRF immunoreactive (-IR) cells were located in the parvocellular part of the paraventricular nucleus (PVN) with smaller population found in the magnocellular part of the PVN. CRF-IR cells were also found in the suprachiasmatic nucleus, the preoptic area and around the fornix in the caudal part of the hypothalamus. AVP- and OXY-IR cells were similarly distributed in the hypothalamus. The majority of AVP- and OXY-IR cells were observed in the magnocellular part of PVN and the supraoptic nucleus. Smaller numbers of AVP- and OXY-IR cells were found in the parvocellular part of the PVN and lateral hypothalamic area. AVP-IR but not OXY-IR cells were located in the suprachiasmatic nucleus. CRF-IR fibers were concentrated in the external palisade zone of the median eminence (ME) with a few fibers found in the internal palisade zone of the ME, whereas AVP- and OXY-IR fibers were concentrated in the internal palisade zone of the ME with a few fibers found in the external zone. These results support the view that not only CRF but also AVP and OXY are released into the hypophysial portal blood and involved in the control of pituitary endocrine function in ruminant species.

Vasopressin- and oxytocin-immunoreactive nerve cells in the aging rat hypothalamus.

Immunohistochemistry and morphometry were used to study the age-related changes in the vasopressin (AVP) and oxytocin (OXT) nerve cells in the paraventricular (PVN), supraoptic (SON) and suprachiasmatic (SCN) nuclei of 3-, 11- and 28-month-old rats. The results showed a statistically significant reduction in the mean number of AVP cells in the PVN, SON and SCN, and of OXT cells in the PVN with advancing age. Different age-related changes in the mean size of the immunoreactive cells were found in the three nuclei: a significant and transitory increase in the AVP and OXT cell sizes in the PVN, a tendency towards increasing the AVP and OXT cell sizes in the SON, and a significant and gradual decrease in the AVP cell size in the SCN. The combination of the morphometric data and staining patterns of the AVP and OXT perikarya and fibers in the PVN and SON pointed to an increased transport of AVP and OXT in 11-month-old rats as well as to a decreased production of these peptides in the PVN of 28-month-old rats. Taken together the staining pattern and the morphometric results showed a progressive loss of AVP cells in the SCN in aging.

Ontogeny of arginine vasopressin-immunoreactive neurons in the hypothalamus of fetal and newborn sheep.

Arginine vasopressin (AVP) is a peptide hormone which is found in neurons within the paraventricular (PVN) and the supraoptic (SON) nuclei of the hypothalamus. In fetal sheep, this neuropeptide is involved in maturational processes and adaptive responses to 'stress'. This study examined the effect of age on the total number and distribution of AVP-containing neurons in the PVN and SON of fetal sheep and newborn lambs by quantitative light-microscopic immunocytochemistry. Serial coronal sections of hypothalami from three groups of animals were studied: fetuses at 104-109 days of gestation (n = 6) comprising the early group, fetuses at 130-139 days of gestation (n = 5) comprising the late group and newborn lambs at 12-20 postnatal days (n = 5) comprising the neonatal group. This period of development was chosen since adaptive mechanisms to stress are operative at or near the time of birth. Hypothalamic dimensions were measured to determine if maturation had an effect on the size of the AVP-containing subregions of the hypothalamus during this period of development. Dimensions included: ventricle height, optic chiasm width, distances from the dorsal margin of the ventricle to the lateral and medial margins of the optic tract, and distance between the medial margins of the optic tracts. As expected, with increase in maturational age, overall dimensions of the AVP-containing subregions increased significantly (p < 0.05). When early- and late-gestation fetuses were compared to newborn lambs, there was a significant increase in the total number of immunoreactive neurons in both the PVN (p < 0.01, Anova) and SON (p < 0.001, Anova) with age. With advancing age, we also observed an increase in the density of AVP neurons in the middle subregion of the PVN and in the midrostral subregion of the SON. These data suggest that, during the late gestational and early postnatal period, de novo synthesis of AVP genes occurs in these hypothalamic nuclei. This study provides a baseline for further investigation to study the effects of stress on these neurons in the developing ovine fetus and newborn lamb.

Infrequent cellular coexistence of NADPH-diaphorase and calretinin in the neurosecretory nuclei and adjacent areas of the rat hypothalamus.

Colocalization of the calcium-binding protein calretinin and NADPH-diaphorase activity at the cellular level was studied in the magnocellular secretory nuclei of the rat hypothalamus using sequential immunocytochemical and histochemical staining of the same sections. A low degree of colocalization of these markers was observed in certain cellular subpopulations within all the areas considered (supra-optic, paraventricular, circular and both fornicals nuclei and in the hypothalamic area located between the supraoptic and paraventricular nuclei). However, since in the paraventricular nucleus both markers were expressed by different neuronal populations, the coexistence was almost non-existent in some subdivisions of this nucleus. This rare coexistence strongly suggests that NADPH-diaphorase and calretinin are related to different functions shared by restricted hypothalamic neuronal populations.

Extremely high titre polyclonal antisera against small neurotransmitter molecules: rapid production, characterisation and use in light- and electron-microscopic immunocytochemistry.

We have produced polyclonal antibodies against the small amino acid neurotransmitters, GABA, glutamate, glycine and taurine, with a simple new technique using antigens co-adsorbed with an adjuvant peptide to gold particles, which causes rapid and massive immune responses in all animals that we have studied. These antibodies are all of extremely high titre; they are typically used in immunocytochemistry at dilutions from 1 in 250,000 to 1 in 1,000,000 which represents an increase in titre of at least two orders of magnitude compared to standard antibody production techniques. Such very high dilutions result in minimal background labeling and a high signal-to-noise ratio when applied to sections of aldehyde-fixed, epoxy resin-embedded tissues at both light- and electron-microscopic levels. Each antibody displays minimal cross-reactivity with other neurotransmitter molecules. We suggest that our technique may be broadly applicable for raising antibodies against a wide variety of antigens of interest to neuroscientists, particularly those that normally elicit weak immune responses. The technique may also assist in clonal expansion prior to generation of monoclonal antibodies and may be viable, with modifications, for use in human immunisations.

Distribution of vasopressin and oxytocin cells and fibres in the hypothalamus of the domestic pig (Sus scrofa).

The distribution of vasopressin and oxytocin cells and fibres was studied in the pig hypothalamus by means of monoclonal antibodies, in order to prevent the non-specific staining that is characteristic for the pig. The nucleus circularis is described for the first time in the pig hypothalamus and consists of both oxytocin and vasopressin containing cell bodies. A cell group, characteristic for the pig and horse, lateral and caudal from the vascular organ of the lamina terminalis, was found to be continuous with the supraoptic nucleus. It contained only oxytocin and it is proposed that this group be called pars dorsomedialis of the supraoptic nucleus. In this study, vasopressin has been demonstrated for the first time in the suprachiasmatic nucleus of the pig. The discussion focusses on how our findings in the pig differ from vasopressin and oxytocin systems identified in other mammalian species.

Expression of provasopressin gene during ontogeny in the hypothalamus of developing mice.

We investigated the ontogeny of provasopressin gene expression in neurosecretory neurons of the supraoptic and paraventricular nuclei of developing mice by semi-quantitative in situ hybridization and immunohistochemical techniques in combination with stereometry of vasopressin-immunoreactive neurons. Provasopressin mRNA was detected in paraffin sections using a mixture of radiolabeled synthetic oligonucleotide probes complementary to the mRNA loci encoding vasopressin (2-9) and vasopressin neurophysin (1-8). Vasopressin immunoreactivity was located with a polyclonal anti-vasopressin antiserum and a monoclonal anti-vasopressin-neurophysin antibody either with or without enhancing technique for the diaminobenzidine reaction. Autoradiographic hybridization signals that indicate the localization of provasopressin mRNA were first detected on embryonic day 15 in the supraoptic nucleus and embryonic day 18 in the paraventricular nucleus. Vasopressin immunoreactivity was first found in the median eminence on embryonic day 14, and then in the supraoptic and paraventricular nuclei on embryonic days 15 and 16, respectively. The provasopressin mRNA levels were markedly increased in both the supraoptic and the paraventricular nuclei just after birth. The immunoreactivity of vasopressin neurons was drastically decreased in both nuclei on postnatal days 1 and 2, suggesting marked vasopressin release in the neonates. Cross-sectional areas of vasopressin-immunoreactive somata and their cell nuclei gradually increased in both the supraoptic and the paraventricular nuclei during the perinatal period by day 5, and then attained adult size between days 10 and 20. During this phase, the level of provasopressin mRNA remained low compared with that in the adult magnocellular neurosecretory cells. These results indicate that the expression of provasopressin gene is markedly increased in both the supraoptic and the paraventricular nuclei soon after birth. Secretory activity of vasopressin neurons is elevated in neonatal mice. Vasopressin may have an important osmoregulatory role in neonatal mice undergoing drastic changes in water metabolism following birth.

Chronic ethanol ingestion decreases vasopressin mRNA in hypothalamic and extrahypothalamic nuclei of mouse brain.

Endogenous arginine vasopressin was previously shown to modulate the rate of loss of functional (CNS) tolerance to ethanol, suggesting that chronic ethanol ingestion might alter vasopressin synthesis and/or release. Since extrahypothalamic vasopressin is believed to be involved in the CNS effects of the peptide, we determined the effect of ethanol on vasopressin mRNA in the bed nucleus of the stria terminalis (BST), as well as in several hypothalamic nuclei. Chronic ethanol ingestion, that produced functional tolerance and physical dependence in mice, resulted in decreased vasopressin mRNA levels in all areas examined. In contrast, as expected, dehydration resulted in increases in vasopressin mRNA in the BST and in all hypothalamic nuclei except the suprachiasmatic nucleus. In the BST, both ethanol ingestion and dehydration affected cells in the central region of the nucleus, while cells in the caudal portion were only affected by ethanol treatment. The results indicate that chronic ethanol ingestion generally reduces the synthesis of vasopressin, and that increased vasopressin synthesis is not necessary in order for the peptide to affect ethanol tolerance.

A comparative analysis of the vasotocin and vasopressin systems in the chicken and rat hypothalamus. An immunocytochemical study.

By means of the peroxidase-antiperoxidase technique a comparative immunocytochemical study of the distribution of the vasotocin- and vasopressin-reacting system in the chicken and rat hypothalamus was carried out. In both species it is possible to distinguish, on the basis of their topographical location, three different comparable populations: The first one is situated very close to the pial surface and the optic chiasma (L1 and L2 groups in the chicken and the supraoptic nucleus in the rat). The second one is located near to the third ventricle and corresponds to the suprachiasmatic nucleus of both species and the periventricular groups of the chicken (P1, P2, and P3 groups) and the periventricular subdivision of the paraventricular nucleus of the rat. The third one is situated between the two previous populations and consists of small clusters of reacting neurons (L3 and L5 groups in the chicken and the nucleus circularis and fornicalis in the rat) and to a large cluster of reacting neurons (L4 group in the chicken and the magnocellular part of the paraventricular nucleus in rat). In the median eminence of the chicken the immunoreactive axons were located in the internal zone and the anterior part of the external zone. However in the rat, the reaction was exclusively located in the internal zone.

Suprachiasmatic nucleus and retinohypothalamic projections in moles.

The suprachiasmatic nucleus of the hypothalamus (SCN) and the retinohypothalamic projections were identified in one species of old-world moles, all of whom are blind as a result of natural loss of vision. A cyto-architectonic study revealed that the SCN is well developed, even though other visual nuclei in the dorsal thalamus and the midbrain are not. An immunohistochemical study showed that vasoactive intestinal polypeptide (VIP)-like immunoreactive cell bodies and fibers were distributed in the SCN, as has been reported in other mammals. Following intraocular injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA-HRP), the central retinal projections were examined. The results indicated that the SCN receives a direct projection from the retina, as seen in many other mammals. In addition to the projection to the SCN, retinal fibers were seen to terminate in the anterior hypothalamic region and the retrochiasmatic area, as observed in some other mammals. In moles, retinohypothalamic projections are bilateral, with an ipsilateral predominance. Considering that the retinogeniculate and retinotectal projections are vestigial, it is highly probable that the optic pathway in moles primarily consists of retinohypothalamic projections, which are devoted to the entrainment of circadian and circannual rhythms.

Comparative analysis of vasotocin-like immunoreactivity in the brain of the turtle Pseudemys scripta elegans and the snake Python regius.

The distribution of vasotocin in the brains of the turtle Pseudemys scripta elegans and the snake Python regius was studied with immunohistochemical methods. In both species, vasotocin-immunoreactive (VTi) cells were found in the supraoptic nucleus, the paraventricular nucleus and the bed nucleus of the stria terminalis. No VTi cell bodies were seen in the brainstem. Vasotocinergic fibers were found in all major brain divisions. Intrahypothalamic VTi fibers were observed between the supraoptic and the paraventricular nuclei and in the median eminence. An extensive network of extrahypothalamic VTi fibers extends from the olfactory bulb to the spinal cord. Limbic structures, such as the nucleus accumbens, the septal area and the ventral amygdaloid nucleus, contain a moderate to dense VTi plexus. Other areas with a substantial number of VTi fibers are the lateral habenular nucleus, the ventral tegmental area, the substantia nigra, the locus coeruleus and the nucleus of the solitary tract. Sex-related differences in the density of the VTi fibers were observed in the lateral septal nucleus, the mid-brain periaqueductal gray and, to a lesser extent, in the ventral amygdaloid nucleus, the lateral habenular nucleus, the ventral tegmental area and the substantia nigra. In these areas, the density of VTi fibers is higher in males than in females. The distribution of vasotocin-like immunoreactivity in the brains of Pseudemys and Python resembles the pattern previously observed in the lizard Gekko gecko. However, among the three species several differences exist, the most remarkable one being the variation in number of liquor-contacting VTi cells in the paraventricular nucleus.

Projections from the hypothalamus and its adjacent areas to the posterior pituitary in the rat.

Cholera toxin conjugated horseradish peroxidase was injected into the posterior pituitary and its afferents traced in 21 albino rats. The neuronal processes as well as the perikarya were elaborately displayed. The principal and retrochiasmatic supraoptic nuclei and the magnocellular paraventricular subnuclei were densely labelled. The accessory cell groups or nuclei labelled included: the medial preoptic and anterior hypothalamic areas, the anterior and posterior fornical nuclei, the lateral hypothalamic area, the nucleus circularis and nucleus of the forebrain bundle and hitherto unknown or not fully appreciated retrochiasmatic area, the dorsal accessory groups in an area between the stria medullaris and fornix, on the one hand, and the stria terminalis and internal capsule, on the other, and a well developed subependymalperiventricular zone. The medial preoptic nucleus, subfornical organ and organ vasculosum laminae terminalis were also weakly stained. Dendrites of the magnocellular paraventricular nucleus have been said by some to be largely confined to the subnuclei in which they lie. Immunohistochemical studies have proved that they extended beyond their nuclear confinement. The present study has found much wider extension of their dendritic fields. In fact, dendrites of the magnocellular neurosecretory cells in general were long and had a certain degree of directional bias. Several sites projecting to the posterior pituitary were closely related to the cerebrospinal fluid. Namely, the subependymal neuronal plexuses along the third ventricle and beneath the interventricular foramen, and the subpial dendritic plexuses of the supraoptic and retrochiasmatic supraoptic nuclei. Neurons were seen to squeeze in-between the ependymal cells, bringing themselves very close to the cerebrospinal fluid. No direct cerebrospinal fluid-contacting elements, either cell bodies or processes, however, could be ascertained. It is proposed that these plexuses may monitor changes in the cerebrospinal fluid. Besides the principal neurohypophysial tract the posterior pituitary was found in the present study to receive its afferents via two accessory fasciculi, one coursing in the medial forebrain bundle and the other running along the lateral wall of the infundibular recess subependymally.

Structure and ultrastructure of the external glial layer in the hypothalamus of the hamster.

The hypothalamic subpial limitans has been studied by light and electron microscopy. It consists of a palisade of astrocytic cell bodies or their processes. Beneath the optic chiasma (white matter) the glial layer consists of flattened astrocytic cell bodies arranged in parallel to the myelinated fibres or located between the fibres, but sending their processes towards the basement membrane. Beneath the ventral hypothalamus nuclei, the astrocytic cell bodies can appear in two places: a) in contact with the basement membrane with their processes arranged in parallel to it, or b) located a certain distance from the basement membrane, sending long processes that, near the limitant zone, enlarge to form end-feet (supraoptic nuclei) or sending processes located in parallel to the basement membrane (mamillary nuclei). The astrocytic processes forming the glia limitans show gap junctions, and desmosomes. The different arrangement of the astrocytic processes and the different types of junctions suggest that the marginal glia might represent a regulatory mechanism for the diffusion between the different compartments of the brain.

Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry: VI. Catecholamine innervation of vasopressin and oxytocin neurons in the rhesus monkey hypothalamus.

The co-localization patterns of catecholamine varicosities and peptide-specific neuronal perikarya were assessed within the supraoptic and paraventricular nuclei in the rhesus monkey, Macaca mulatta. Formaldehyde-induced histofluorescence was coupled with the unlabelled antibody technique for the demonstration of neuropeptides. Hormone-specific neurophysin staining served to identify vasopressin and oxytocin-containing neurons in these hypothalamic nuclei. Catecholamine varicosities were seen in juxtaposition to vasopressin- and oxytocin-containing perikarya and proximal dendrites. The densest catecholamine innervation patterns were seen in the ventrolateral portion of the supraoptic nucleus; the dorsomedial portion of this nucleus received a considerably less dense innervation pattern. Oxytocin neurons were clustered in this relatively catecholamine poor region, whereas the vasopressin-containing neurons were more abundantly found in the catecholamine rich region. The paraventricular nucleus presented a considerably more complex pattern, perhaps reflecting the more diverse organization of this nucleus. Nevertheless, some separation of the oxytocin neurons, in a region less densely innervated by catecholamine varicosities, was noted. These observations confirm our earlier reports, in rat hypothalamus, that the norepinephrine innervation of the hypothalamic magnocellular neurons as seen with catecholamine histofluorescence favors the vasopressin-containing neurons over those located within the same nuclei which synthesize another neurohyphysial principal, oxytocin.

Relationship of the central ACTH-immunoreactive opiocortin system to the supraoptic and paraventricular nuclei of the hypothalamus of the rat.

ACTH-immunoreactive (ir) fibers of the central opiocortin system are present in high density in the mid-portion of the paraventricular nucleus (PVN). ACTH-ir fibers, however, do not appear to directly contact oxytocin-ir vasopressin-ir, containing perikarya or axons of vasopressinergic neurons. Magnocellular neurons located more anteriorly and posteriorly in the PVN as well as those located laterally have few ACTH-ir fibers associated with them. No ACTH-ir fibers are present in the supraoptic nucleus.

The magnocellular and parvocellular paraventricular nucleus of rat: intrinsic organization.

The magnocellular and paravocellular regions of the rat hypothalamic paraventricular nucleus (PVN) were examined in several hundred brains. Converging qualitative and quantitative anatomical methods, including Golgi impregnations, Nissl stains, silver stains, and immunocytochemistry were used to study the intrinsic organization of the PVN with light, scanning, and transmission electron microscopy. A computer-assisted quantitative analysis of dendritic branching patterns was used to examine total dendritic length, center of mass, orientation of dendritic tree, and several other parameters of dendritic organization and revealed statistically significant differences between cells in the lateral and posterolateral magnocellular and medial parvocellular areas of PVN. Electron microscopy, Golgi impregnation, and neurophysin immunohistochemistry showed that dendrites of posterolateral cells were generally oriented perpendicular to the third ventricle; dendrites of cells in the lateral PVN usually projected medially from the perikaryon. Cells in the medial zone of PVN had dendritic trees which often paralleled the third ventricle. Large numbers of axons entered and left PVN ventrally near the midline and laterally in the area of the posterolateral PVN; axons generally were oriented parallel to the mean major axis of dendritic trees in these areas. Ultrastructural examination of serial thin sections showed a peculiar astroglia multiple lamellar isolation of axodendritic synaptic contacts. Intrinsic axons commonly arose from parvocellular but not from magnocellular neurons and contacted dendrites of both medial parvocellular and more lateral magnocellular neurons. Synapses were found on shafts and spines of dendrites, on perikarya and somatic appendages, and invaginated into the soma. Both dendrites axons with large neurosecretory vesicles and immunostained with neurophysin antiserum were found postsynaptic to other axons. Presynaptic neurosecretory axons were not found within the PVN. A semiquantitative analysis of catecholamine axons identified with the glyoxylic acid method and fibers immunoreactive with ACTH and Substance P antisera indicated that the parvocellular region of PVN received ggreater innervation than the lateral magnocellular area; similarly, a reater density of stained fibers was found in the medial parvocellular PVN region with Golgi impregnations and silver stains. With a stereological analysis of 1-micrometer plastic sections, the parvocellular area had a significantly greater neuropil to cell volume ration, with cells accounting for 48 +/- 9% in the lateral magnocellular zone, but only for 26 +/- 7% in the parvocellular area. A quantitative analysis of vasculature from thin sections showed that the PVN had 3.3 times more blood vessels, and 3.6 times more lumen perimeter than a control area ventrolateral to PVN; an interesting finding here was that the medial parvocellular PVN had a high degree of vascularity, not significantly different from the lateral magnocellular zone...

Immunocytochemical, Golgi and electron microscopic characterization of putative dendrites in the ventral glial lamina of the rat supraoptic nucleus.

Processes of magnocellular neurosecretory cells in the rat supraoptic nucleus which project along the pial surface in the ventral glial lamina were investigated using immunocytochemistry, Golgi stains and electron microscopy. Immunocytochemical studies revealed that although both oxytocin- and vasopressin-containing processes were evident in the ventral glial lamina, vasopressin-containing processes predominated. Ventral processes were thicker and of a different morphology than dorsal axon-like processes which joined the hypothalamo-neurohypophysial tract and exhibited large varicosities along their length or at their apparent termination. Golgi stains revealed that classically defined dendrites of supraoptic neurons projected primarily ventrally and often invaded the ventral glial lamina. No axons were traced to the lamina. Ultrastructurally, processes within the ventral glial lamina characterized as dendrites could be stained immunocytochemically for neurophysin and were post-synaptic to a variety of presynaptic elements. The results suggest that many dendrites from magnocellular neurosecretory cells in the supraoptic nucleus project to the ventral glial lamina and form a restricted, receptive plexus. The previously demonstrated coexistence of catecholamine-containing varicosities and other axon types with these processes in the lamina indicates an important role for supraoptic dendrites in integrating a wide variety of information relevant to neurohypophysial hormone release.