Cytoarchitectonic pattern of the hypothalamus in the turtle,Lissemys punctata granosa

Summary In the hypothalamus of the turtle, Lissemys punctata granosa, two magnocellular and 23 parvocellular neuronal complexes can be distinguished. The magnocellular complexes include the nucleus supraopticus and the nucleus paraventricularis; paraventricular neurons are partly arranged in rows parallel to the third ventricle. Most infundibular parvocellular nuclei display neurons disposed in rows parallel to the ventricular surface. In the preoptic region, the prominent parvocellular neuronal complexes encompass the nucleus periventricularis anterior, lateral preoptic area, the nucleus of the anterior commissure and the nucleus suprachiasmaticus. The prominent nucleus periventricularis posterior extends caudad and shows neurons arranged in vertical rows parallel to the third ventricle. Other parvocellular nuclei of the rostral hypothalamus are composed of clustered subunits. The nucleus arcuatus is a fairly large nuclear entity extending from the level marked dorsally by the nucleus paraventricularis to the area occupied by the nucleus of the paraventricular organ. A well-developed ventromedial nucleus is located ventrolateral to the paraventricular organ. The prominent paraventricular organ consists of tightly arranged neurons, some of which possess apical projections into the third ventricle; it is surrounded by the nucleus of the paraventricular organ. Nucleus hypothalamicus medialis et lateralis, nucleus hypothalamicus posterior and the nuclei recessus infundibuli are further nuclear units of the tuberal region. The caudal end of the hypothalamus is marked by the nucleus mamillaris; its neurons are scattered among the fibers of the retroinfundibular commissure. The median eminence is well developed and shows a large medial and two lateral protrusions into the infundibular recess.     

Lymphoid cells in the Harderian gland of birds

Summary Numerous secretory parvocellular perikarya were found in the preoptic region of the domestic fowl (Gallus gallus). The dense-core secretory vesicles belong to two categories: vesicles with a diameter of (i)80–90 nm and (ii) 110–140nm. Scattered magnocellular elements display larger dense-core granules. The parvocellular neurons form unit-like clusters, showing also zones of direct apposition of neuronal membranes. The surrounding neuropil is rich in synaptic structures, formed by at least three types of axon terminals, distinguishable on the basis of vesicular morphology. These observations confirm the findings in other avian species. The hypothetical function of this system of peptidergic neurons in the rostral hypothalamus of birds is discussed.     

GABA-immunohistological observations, at the electron-microscopical level, of the neurons of isthmic nuclei in chicken, Gallus domesticus

Following a demonstration of Golgi-impregnated neurons and their terminal axon arborization in the optic tectum, the neurons of the nucleus parvocellularis and magnocellularis isthmi were studied by means of postembedded electron-microscopical (EM) γ-aminobutyric acid (GABA)-immunogold staining. In the parvocellular nucleus, none of the neuronal cell bodies or dendrites displayed GABA-like immunoreactivity in EM preparations stained by postembedded GABA-immunogold. However, numerous GABA-like immunoreactive and also unlabeled terminals established synapses with GABA-negative neurons. GABA-like immunoreactive terminals were usually found at the dendritic origin. Around the dendritic profiles, isolated synapses of both GABA-like immunoreactive and immunonegative terminals established glomerulus-like structures enclosed by glial processes. All giant and large neurons of the magnocellular nucleus of the isthmi displayed GABA-like immunoreactivity. Their cell surface was completely covered by GABA-like immunoreactive and unlabeled terminals that established synapses with the neurons. These neurons are thought to send axon collaterals to the parvocellular nucleus; their axons enter the tectum opticum. The morphological characteristics of neurons of both isthmic nuclei are like those of interneurons, because of their numerous axosomatic synapses with both asymmetrical and symmetrical features. These neurons are not located among their target neurons and exert their modulatory effect on optic transmission in the optic tectum at a distance.     

Corticotropin-releasing factor mRNA in the hypothalamus is affected differently by drinking saline and by dehydration

Corticotropin-releasing factor (CRF) stimulates the synthesis and release of adrenocorticotropin in the anterior pituitary and may help maintain fluid and electrolyte balance. 'Salt-loaded' rats had an increase in CRF mRNA in hypothalamic magnocellular neurons of the paraventricular and supraoptic nuclei and a decrease in message in the parvocellular paraventricular neurons. After salt-loaded rats were adrenalectomized, CRF mRNA increased in the parvocellular cells. In contrast to salt loading, water deprivation lead to a decrease in CRF mRNA in magnocellular and parvocellular neurons. These results show that CRF synthesis within separate populations of hypothalamic neurons is regulated differently under various conditions.     

The distribution of corticotropin releasing factor-like immunoreactive neurons in rat brain

Using the indirect immunofluorescent technique, corticotropin releasing factor (CRF)-like immunoreactive nerve fibers and cell bodies were observed to be widely distributed in rat brain. A detailed stereotaxic atlas of CRF-like immunoreactive neurons was prepared. Large numbers of CRF-containing perikarya were observed in the nucleus paraventricularis, with scattered cells in the following nuclei: accumbens, interstitialis stria terminalis, preopticus medialis, supraopticus, periventricularis hypothalami, amygdaloideus centralis, dorsomedialis, substantia grisea centralis, parabrachialis dorsalis and ventralis, tegmenti dorsalis lateralis, vestibularis medialis, tractus solitarius and reticularis lateralis. The most intense staining of CRF-containing fibers was observed in the external lamina of the median eminence. Moderate numbers of CRF-like fibers were observed in the following nuclei: lateralis and medialis septi, tractus diagonalis, interstitialis stria terminalis, preopticus medialis, supraopticus, periventricularis thalami and hypothalami, paraventricularis, anterior ventralis and medialis thalami, rhomboideus, amygdaloideus centralis, habenulae lateralis, dorsomedialis, ventromedialis, substantia grisea centralis, cuneiformis, parabrachialis dorsalis and ventralis, tegmenti dorsalis lateralis, cerebellum, vestibularis medialis, reticularis lateralis, substantia gelatinosa trigemini and lamina I and II of the dorsal horn of the spinal cord. The present findings suggest that a CRF-like peptide may be involved in a neurotransmitter or neuromodulator role, as well as a hypophysiotropic role.     

Age-related changes in central nervous system enkephalins and substance P

Concentrations of substance P and met- and leu-enkephalins were measured by radioimmunoassay in discrete rat brain nuclei of young (4–5 months) and old (24–26 months) rats. The substance P content of n. anterior (hypothalami), n. ventromedialis, n. premamillaris ventralis, n. interstitialis striae terminalis, n. entopeduncularis and n. dorsalis raphes is reduced in old rats. The met-enkephalin content is decreased in n. suprachiasmaticus, n. arcuatus and n. premamillaris ventralis while the leu-enkephalin content of n. preopticus medialis, n. suprachiasmaticus, n. paraventricularis, n. ventromedialis and n. premamillaris ventralis is decreased in old rats.     

Cytoarchitectonic pattern of the hypothalamus in the crocodile,Gavialis gangeticus

Summary The hypothalamus of the crocodile, Gavialis gangeticus, was investigated to reveal the organization of various nuclear complexes and to suggest homologies. The hypothalamic nuclei of G. gangeticus are composed of magnocellular and parvocellular neuronal entities. In the magnocellular system the nucleus supraopticus is well developed, whereas the nucleus paraventricularis and nucleus retrochiasmaticus are represented by scattered somata. Application of cytoarchitectonic criteria permits the delineation of 24 distinct parvocellular nuclear complexes extending rostrocaudally from the anterior commissure to the level indicated by the median eminence and nucleus mamillaris; some are further divisible into subgroups. The nucleus of the preoptic recess appears to be a unique property of the crocodilian hypothalamus. The nucleus suprachiasmaticus possesses a wing-like ventrolateral expansion that protrudes along the lateral aspect of the optic nerve. The tuberal region displays an elaborate pattern of nuclei segregated by regional specializations of the neuropil. The nucleus hypothalamicus posterior occupies the periventricular zone, flanked laterally by the nucleus hypothalamicus dorsomedialis and nucleus arcuatus. Further laterally, extended subdivisions of the nucleus hypothalamicus lateralis contain neurons rich in Nissl substance; the specializations shown by these subdivisions, in comparison to the lateral cell groups in lizards and snakes, are suggestive of enhanced integrative functions. The conspicuous paraventricular organ is encircled by dorsal and ventral divisions of the nucleus of the paraventricular organ. The neurons of the nucleus subfornicalis and nucleus hypothalamicus medialis are few in number, but large in size. The general organization of the hypothalamus of G. gangeticus reveals a mosaic-like pattern with the constituent groups appearing as clusters of small and large neurons, arranged medially and laterally in a definitive manner and accompanied by extensive zones of neuropil in the subependymal and lateral zones of the hypothalamus. The median eminence is divisible into an anterior and a posterior region. The nuclear pattern in the crocodilian hypothalamus reveals a higher state of morphologic organization compared to the situation in lizards or snakes, and thus reflects an evolutionary trend in the avian direction.     

Co-localization of putative vasopressin receptors and vasopressinergic neurons in rat hypothalamus

Summary Vasopressin and oxytocin are synthesized by neurons in the paraventricular and supraoptic nuclei of hypothalamus. Dense concentrations of vasopressin binding sites have also been localized in these nuclei. Using a vasopressin anti-idiotypic antiserum, a dual immunocytochemical labeling procedure has been employed to elucidate the distribution of putative vasopressin receptors in anatomical relation to vasopressin and oxytocin immunoreactive cells in rat brain. Putative vasopressin receptors are observed in relation to magnocellular neurons in hypothalamus that are vasopressin immunoreactive. They do not appear to be associated with parvocellular vasopressinergic cells or oxytocin immunoreactive neurons. The presence of these presumed autoreceptors would support evidence that vasopressin may autoregulate the activity of magnocellular vasopressinergic neurons in hypothalamus.     

Neuronal organization of the avian paraventricular nucleus: intrinsic, afferent, and efferent connections

The heterogeneous paraventricular nucleus (PVN) of birds offers favorable conditions for the analysis of intrinsic, afferent, and efferent connections of neuroendocrine systems. Paraventricular neurons are successfully impregnated with the Golgi-technique. The findings indicate a direct influence of the cerebrospinal fluid (CSF) on the magnocellular neurons that, via their axon terminals in the neural lobe of the pituitary, are also exposed to the hemal milieu. The magnocellular neurons are intermingled with parvocellular elements which may represent local interneurons. A group of parvocellular nerve cells is identified as CSF-contacting neurons. This type of cell forms a basic morphologic component of the avian neuroendocrine apparatus. Immunocytochemical and ultrastructural studies further support the concept of neuronal interactions between parvocellular and magnocellular elements. Moreover, these findings speak in favor of the existence of recurrent collaterals of the magnocellular neurons. Nerve cells giving rise to afferent connections to the PVN are located in the limbic system and autonomic areas of the upper and lower brainstem. Further afferents may originate from the subfornical organ, the organon vasculosum laminae terminalis, the ventral tegmentum, and the area postrema. Via efferent projections, the PVN is connected to the nucleus accumbens, lateral septum, several hypothalamic nuclei, the neural lobe of the pituitary, the organon vasculosum laminae terminalis, the subfornical organ, the pineal organ, the area postrema, the lateral habenular complex, and various autonomic areas of the reticular formation in the upper and lower brainstem and the spinal cord. In conclusion, the PVN may be regarded as an integral component of the neuroendocrine apparatus reciprocally coupled to the limbic system, several circumventricular organs, and various autonomic centers of the brain.     

Histochemical localization of FMRFamide-like immunoreactivity in the rat brain

Molluscan cardioexcitatory neuropeptide or FMRFamide is present in the invertebrate central nervous system (CNS) and FMRFamide like peptide has been demonstrated in the mammalian CNS. In this study, the distribution of FMRFamide immunoreactivity was studied in rat brain using the indirect immunofluorescent method. The highest number of FMRFamide staining cell bodies was found in the nucleus (n) arcuatus. N. paraventricularis, n. hypothalamus, n. ventromedialis, n. dorsomedialis and n. tractus solitarii also contained high numbers. FMRFamide positive nerve fibers and terminals were widely distributed. The septal complex contained high densities, especially in n. interstitialis striae terminalis. N. paraventricularis hypothalami, n. paraventricularis, n. hypothalamicus, n. ventromedialis and n. dorsomedialis showed a high to very high degree of immunoreactivity. In myelencephalon, n. tractus solitarii had the densest innervation. Spinal cord had a dense band of FMRFamide positive fibers in lamina I and II of the dorsal horn. The present findings support a neurotransmitter role for a FMRFamide like peptide in the mammalian brain, possibly related to endocrine and autonomic regulation as well as pain modulation.     

Co-localization of putative vasopressin receptors and vasopressinergic neurons in rat hypothalamus

Vasopressin and oxytocin are synthesized by neurons in the paraventricular and supraoptic nuclei of hypothalamus. Dense concentrations of vasopressin binding sites have also been localized in these nuclei. Using a vasopressin anti-idiotypic antiserum, a dual immunocytochemical labeling procedure has been employed to elucidate the distribution of putative vasopressin receptors in anatomical relation to vasopressin and oxytocin immunoreactive cells in rat brain. Putative vasopressin receptors are observed in relation to magnocellular neurons in hypothalamus that are vasopressin immunoreactive. They do not appear to be associated with parvocellular vasopressinergic cells or oxytocin immunoreactive neurons. The presence of these presumed autoreceptors would support evidence that vasopressin may autoregulate the activity of magnocellular vasopressinergic neurons in hypothalamus.     

Relationship of ACTH1-39-immunostained fibers and magnocellular neurons in the paraventricular nucleus of rat hypothalamus

Dual antigen immunocytochemical staining procedures were used in the same tissue section to determine the distribution of ACTH immunostained fibers and varicosities within the magnocellular and parvocellular divisions in the paraventricular nucleus (PVN) of rat hypothalamus and elucidate its anatomical relationship to vasopressin (VP) and oxytocin (OXY)-containing neurons. Double immunostained preparations using glucose oxidase-antiglucose oxidase complex combined with PAP complex to visualize two antigens with contrasting colors in the same tissue section were employed. ACTH-immunoreactive (ir) fibers were distributed throughout the periventricular stratum and the parvocellular component of the PVN; in the latter area fibers were particularly dense in the ventral medial portion of the medial parvocellular division. Dual immunostained sections revealed a close anatomical association between opiocortin fibers and oxytocin and vasopressin parvocellular neurons. ACTH immunostained fibers were present in the anterior and medial magnocellular component of PVN and in the ventral medial portion of the posterior magnocellular division; these immunoreactive fibers were in intimate proximity to oxytocin-ir perikarya. The very close approximation between the ACTH-ir fibers and oxytocin-containing cell bodies suggests potential cell to cell communication between the two peptidergic systems in PVN. Few ACTH immunostained fibers were seen in the dorsal lateral portion of the posterior magnocellular division in which vasopressinergic neurons predominate. The present anatomical study supports pharmacological and physiological studies which indicate that opioids can influence the activity of magnocellular PV neurons. This study also elucidates an anatomical relationship between opiocortins (ACTH1-39) and parvocellular PV neurons which suggests that the opiocortin system may play a role in the regulation of both the neuroendocrine and autonomic activities of specific PV neurons.     

The kallikrein-kinin system in the rat hypothalamus

Summary High molecular weight kininogen (HKg) and T kininogen (TKg) were detected and localized by immunocytochemistry in adult rat hypothalamus. In addition, kininogens were measured by their direct radioimmunoassay (RIA) or by indirect estimation of kinins released after trypsin hydrolysis and high pressure liquid chromatography (HPLC) separation of bradykinin (BK) and T kinin. A specific HKg immunoreactivity demonstrated with antibodies directed against the light chain (LC) of HKg was colocated with SRIF in neurons of hypothalamic periventricular area (PVA) projecting to external zone (ZE) of median eminence (ME). Heavy chain (HC) immunoreactivity which could be related to HKg or to low molecular weight kininogen (LKg) was detected in some other systems: i) parvocellular neurons of suprachiasmatic (SCN) and arcuate nuclei containing SRIF, ii) magnocellular neurons (mostly oxytocinergic) of paraventricular (PVN) and supraoptic (SON) nuclei, iii) neurons of dorsomedian and lateral hypothalamic areas. TKg immunostaining was restricted to magnocellular neurons of PVN, SON, accessory nuclei (mostly vasopressinergic) and to parvocellular neurons of SCN (vasopressinergic). TKg projections are directed towards the internal zone (ZI) of ME, but very few immunoreactive terminals are detectable in neurohypophysis. TKg staining parallels with vasopressin during water deprivation, and is undetectable in homozygous Brattleboro rats. In some magnocellular neurons, TKg and HC (related to HKg or LKg) are coexpressed. TKg, was also detected in hypothalamus and cerebellum extracts by direct RIA, and BK and T kinin were identified after trypsin hydrolysis. HKg and LKg can act as precursor of BK which can play a physiological role as releasing factor, neuromodulator — neurotransmitter, — or modulator of local microcirculation in hypothalamus. The three kininogens are also potent thiolprotease inhibitors which could modulate both the maturation processes of peptidic hormones and their inactivation and catabolism.     

Distribution of oxytocin and vasopressin neurons in the diencephalon of the Japanese horseshoe bat, Rhinolophus ferrumequinum. An immunohistochemical study.

The distribution of oxytocin (OXT) and vasopressin (VP) neurons in the diencephalon of the hibernating Japanese horseshoe bat, Rhinolophus ferrumequinum, was immunohistochemically investigated by the avidin-biotin complex method. Magnocellular OXT and VP neurons were localized mainly in the paraventricular nucleus and the supraoptic nucleus. In addition to these main nuclei, both kinds of magnocellular neurons were also found in the periventricular nucleus, perifornical area and lateral hypothalamic area. Extensively distributed parvocellular neurons containing only VP were observed in the rostral and middle portions of the suprachiasmatic nucleus. The size of OXT and VP magnocellular neurons was almost equal in the paraventricular and ventromedial supraoptic nuclei, whereas VP neurons were significantly larger than OXT neurons in the dorsolateral supraoptic nucleus. The OXT and VP cells in the ventral supraoptic nucleus showed a distinctive elliptical shape. Both OXT and VP fibers were distributed in the lateral habenular nucleus, stria medullaris thalami, lateral preoptic area, stria terminalis, and medial and supracapsular part of the bed nucleus of the stria terminalis. Moreover, OXT fibers were found in the substantia nigra, and VP fibers were noted in the nucleus reunions and the paraventricular nucleus of the thalamus.     

Vasopressin receptor distribution in adrenalectomized rats using vasopressin anti-idiotype

Following adrenalectomy, it has been demonstrated that parvocellular corticotropin-releasing factor-containing neurons in the paraventricular nucleus (PVN) of rat hypothalamus synthesize vasopressin. The present study examined whether putative vasopressin receptors are expressed in parallel with the appearance of vasopressin immunoreactivity in these parvocellular neurons. A vasopressin anti-idiotypic antibody which immunostains putative vasopressin receptors associated with magnocellular PVN neurons was utilized. Following adrenalectomy, antivasopressin immunostained neurons in parvocellular and magnocellular PVN, whereas the anti-idiotypic antibody immunostained magnocellular neurons only. We therefore conclude that the putative vasopressin receptor recognized by the anti-idiotype is not demonstrated in association with parvocellular vasopressin-producing neurons of the adrenalectomized rat.     

The kallikrein-kinin system in the rat hypothalamus. Immunohistochemical localization of high molecular weight kininogen and T kininogen in different neuronal systems

High molecular weight kininogen (HKg) and T kininogen (TKg) were detected and localized by immunocytochemistry in adult rat hypothalamus. In addition, kininogens were measured by their direct radioimmunoassay (RIA) or by indirect estimation of kinins released after trypsin hydrolysis and high pressure liquid chromatography (HPLC) separation of bradykinin (BK) and T kinin. A specific HKg immunoreactivity demonstrated with antibodies directed against the light chain (LC) of HKg was colocated with SRIF in neurons of hypothalamic periventricular area (PVA) projecting to external zone (ZE) of median eminence (ME). Heavy chain (HC) immunoreactivity which could be related to HKg or to low molecular weight kininogen (LKg) was detected in some other systems: i) parvocellular neurons of suprachiasmatic (SCN) and arcuate nuclei containing SRIF, ii) magnocellular neurons (mostly oxytocinergic) of paraventricular (PVN) and supraoptic (SON) nuclei, iii) neurons of dorsomedian and lateral hypothalamic areas. TKg immunostaining was restricted to magnocellular neurons of PVN, SON, accessory nuclei (mostly vasopressinergic) and to parvocellular neurons of SCN (vasopressinergic). TKg projections are directed towards the internal zone (ZI) of ME, but very few immunoreactive terminals are detectable in neurohypophysis. TKg staining parallels with vasopressin during water deprivation, and is undetectable in homozygous Brattleboro rats. In some magnocellular neurons, TKg and HC (related to HKg or LKg) are coexpressed. TKg, was also detected in hypothalamus and cerebellum extracts by direct RIA, and BK and T kinin were identified after trypsin hydrolysis. HKg and LKg can act as precursor of BK which can play a physiological role as releasing factor, neuromodulator--neurotransmitter,--or modulator of local microcirculation in hypothalamus. The three kininogens are also potent thiolprotease inhibitors which could modulate both the maturation processes of peptidic hormones and their inactivation and catabolism.     

Scanning and transmission electron microscopy of intraventricular dendrite terminals of hypothalamic cerebrospinal fluid contacting neurons in Triturus vulgaris

A scanning (SEM) and transmission electron microscopic (TEM) study of the ventricular wall of the hypothalamus of Triturus vulgaris was performed with special regard to the intraventricular dendrite terminals of the cerebrospinal fluid (CSF) contacting neurons of the preoptic area (magnocellular and parvocellular preoptic nuclei), the infundibular lobe (anterior periventricular nucleus, infundibular nucleus), and the paraventricular organ. In the preoptic area and infundibular lobe, the terminals were knob-like or club-shaped, of various sizes (diameter about 0,5 to 3,0 micrometer) and located immediately above the ependyma. Ultrastructurally, they may contain dense-core vesicles of varying sizes. The CSF contacting dendrite endings of the paraventricular organ built up a supraependymal labyrinthic layer which could be divided into a rostral crest-like part and a caudal flat and broad division. In both parts, three main types of terminals of various size and shape could be distinguished: a) ramifying, b) elongated, and c) bulb-like dendrite endings which also differed by their TEM structure. The bulk-like terminals, first of all the small ones, originated from the distal part of the nucleus of the organ (nucleus organi paraventricularis) while the other two types took their origin from its intra- and subependymal part. In all areas investigated, each intraventricular dendrite ending gave rise to a solitary cilium (type 9 X 2 + 0). It differed from the ependymal kinocilia by both SEM and TEM characteristics. In the paraventricular organ, the neuronal cilia were hidden inside, or below the supraependymal layer of terminals. There were intraventricular axons which formed synapses on CSF contacting dendrite endings of both parts of the paraventricular organ. Free intraventricular neurons, further ependymal areas heavily or scarcely ciliated, were described. The CSF contacting dendrite terminals were predominantly present near ventricular recesses and in regions where the ependyma was scarcely ciliated.     

The distributions of the duplicate oestrogen receptors ER-beta a and ER-beta b in the forebrain of the Atlantic croaker (Micropogonias undulatus): evidence for subfunctionalization after gene duplication

Teleost fishes have three distinct oestrogen receptor (ER) subtypes: ER-alpha, ER-beta a (or ER-gamma) and ER-beta b. ER-beta a and ER-beta b arose from a duplication of an ancestral ER-beta gene early in the teleost lineage. Here, we describe the distribution of the three ER mRNAs in the hypothalamus and cerebellum of the Atlantic croaker to address two issues: the specific functions of multiple ERs in the neuroendocrine system and the evolution and fate of duplicated genes. ER-alpha was detected in nuclei of the preoptic area (POA) and hypothalamus previously shown to possess ER-alphas in teleosts. AcER-beta b, but not ER-beta a, labelling was detected in the magnocellular neurons of the POA, nucleus posterior tuberis, the nucleus recessus posterior and cerebellum. By contrast, acER-beta a, but not ER-beta b, was detected in the dorsal anterior parvocellular POA and suprachiasmatic nucleus. Both ER-betas were found in posterior parvocellular and ventral anterior POA nuclei, the ventral hypothalamus, and periventricular dorsal hypothalamus. The differences we observed in ER subtype mRNA distribution within well-characterized brain nuclei suggest that ER-beta a and ER-beta b have distinct functions in the neuroendocrine control of reproduction and behaviour, and provide evidence that the teleost ER-beta paralogues have partitioned functions of the ancestral ER-beta gene they shared with tetrapods.     

Immunocytochemical localization of somatostatin-containing neurons in the rat hypothalamus

Summary The rat hypothalamus was studied at the light microscopic level with the use of single and double immunocytochemical staining methods. It was shown that the rat supraoptic and paraventricular hypothalamic nuclei, and their accessory neurosecretory nuclei, do not contain magnocellular somatostatin neurons. The distribution of the hypothalamic parvocellular somatostatin cells is described. The parvocellular component of the rat hypothalamic paraventricular nucleus is, at least partly, composed of somatostatin cells: they form a fairly well circumscribed periventricular cell mass. The rat suprachiasmatic nuclei contain separate somatostatin neurons and vasopressin neurons. Scattered somatostatin cells are present in the entire arcuate nucleus. In addition to the periventricular somatostatin cells located in the preopticanterior hypothalamic area and in the arcuate nucleus, the rat hypothalamus also contains numerous scattered somatostatin cells located distant from the third ventricle.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Genomic Effects of Cold and Isolation Stress on Magnocellular Vasopressin mRNA-Containing Cells in the Hypothalamus of the Rat

We assessed the effects of cold and isolation stress on arginine vasopressin (AVP) mRNA in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Vasopressin mRNA levels were determined by in situ hybridization histochemistry at the cellular level. In posterior magnocellular neurons of the PVN isolation stress for 7 or 14 days increased vasopressin mRNA levels 28 and 29%, respectively, compared to group-housed controls. No significant alterations in vasopressin gene expression were observed in the SON after 7 or 14 days of isolation stress. Scattered magnocellular AVP mRNA-expressing cells of the medial parvocellular PVN showed increases of 19 and 34% after 7 and 14 days of isolation, respectively. We also studied the effect of cold or combined cold and isolation stress on vasopressin gene expression in the PVN and SON. Cold stress for 3 h daily for 4 consecutive days increased AVP mRNA levels in the posterior magnocellular PVN by 15%. Cold-isolated animals showed an increase of 21%. No significant effect on AVP mRNA levels in the SON was observed. In contrast to the posterior magnocellular PVN, cold or cold-isolation stress increased AVP mRNA in magnocellular neurons of the medial parvocellular region of the PVN by 25 and 43%, respectively, relative to control rats. These results suggest that psychological and metabolic stress may be added to the list of stressors that activate the hypothalamo-neurohypophysial system.