The hypothalamic magnocellular neurosecretory system of the guinea pig. I. Immunohistochemical localization of neurophysin in the adult

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.

Presence of estrogen receptor immunoreactivity in the oxytocin-containing magnocellular neurons projecting to the neurohypophysis in the guinea-pig

The immunoperoxidase technique was used on adjacent sections of guinea-pig brain to compare precisely the distribution of estrogen receptor-immunoreactive cells and progesterone receptor-immunoreactive cells in the supraoptic nucleus and the paraventricular nucleus. Only estrogen receptor-immunoreactive neurons were found in the supraoptic nucleus. A large number of estrogen receptor-positive cells were observed in the periventricular magnocellular groups throughout the rostrocaudal extent of the paraventricular nucleus, whereas only a few progesterone receptor-immunoreactive cells were scattered in the anterior portion of this region. We used a combination of axonal tracing with double immunocytochemical detection to determine whether estradiol acts directly on the oxytocin-immunoreactive neurons which project to the neurohypophysis. Oxytocin-immunoreactive cells were found in the supraoptic nucleus, ventrally to the optic pathways, in subchiasmatic and retrochiasmatic areas, and in the anterior hypothalamic area. These cells were also retrogradely labeled by Granular Blue when this tracer was injected intravenously. In the paraventricular nucleus, the Granular Blue/oxytocin-positive cells were observed in the periventricular magnocellular groups whereas Granular Blue labeled neurons were found in both parvocellular and magnocellular components. We found that almost all the oxytocin-immunoreactive cells revealed estrogen receptor immunoreactivity. In conclusion, the comparative study of distribution of estrogen receptors and progesterone receptors in the guinea-pig supraoptic and paraventricular nuclei indicates that, in the supraoptic nucleus, only estrogen receptors are present and that, in the paraventricular nucleus, they are far more numerous than progesterone receptors. The present findings demonstrate that the magnocellular cells which contain estrogen receptors are oxytocinergic. In addition, these cells are retrogradely labeled pointing to a neurohypophysial projection. It is likely that estradiol controls the hypothalamo-neurohypophysial oxytocin system by direct action on the magnocellular neurons.

Distribution and morphometric characteristics of oxytocin- and vasopressin-immunoreactive neurons in the rabbit hypothalamus

The distribution, morphological features, and morphometric characteristics of cell bodies producing oxytocin (OT) and vasopressin (AVP) were studied in the rabbit hypothalamus by means of a conventional immunoperoxidase method. The aim of the present study was to determine the existence or not of a species-specific OT-cell group that might be involved in the dense OT innervation of the intermediate lobe in the leporidae. No OT-cell group clearly distinct from the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei was found, even in colchicine-treated animals. Most immunoreactive perikarya were found within these nuclei. In addition, small AVP neurons occurred in the suprachiasmatic nucleus. In the SON, the predominant, tightly packed AVP cells occupied the ventral part of the nucleus, whereas OT neurons were dorsolaterally located. The PVN presented a loose organization without any obvious subdivision. OT cells, which predominated, occupied the medial part of the nucleus. The PVN had a prominent rostral anterobasal extension composed mainly of OT cells. Laterally to the nucleus, numerous large AVP neurons, with few and smaller OT cells, dispersed along the neurosecretory tract without forming definite cell clusters. AVP cell bodies had a rough granular aspect contrasting with the smooth and fine one of OT cells. Spinelike processes were rarely observed on the perikarya, except on large scattered AVP neurons, but frequently covered the proximal dendrites of both types of neurons. Throughout the hypothalamus, OT neurons had definitely smaller mean somal areas and were more homogeneous in size than AVP cells.

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.

Efferent projections from the lateral hypothalamus in the guinea pig: an autoradiographic study

Autoradiography was employed to investigate the efferent projections from the lateral hypothalamus in the guinea pig. Lateral hypothalamic axons were traced along the medial forebrain bundle in both ascending and descending directions. Anteriorly, the label was traced along the medial forebrain bundle in both ascending and descending directions. Anteriorly, the label was traced to the lateral preoptic area, diagonal band of Broca, and septal nuclei. Posterior projections included the ventral tegmental area of Tsai, central gray matter and the reticular formation throughout the brain stem. Laterally, the lateral hypothalamic efferents were found in the stria terminalis, amygdala and globus pallidus. Dorsally, the lateral hypothalamic axons projected to the midline nuclei of the thalamus and bilaterally to the lateral habenular nuclei. Projections to the medial hypothalamus included a labeled fiber bundle to the internal layer of the median eminence and to the posterior lobe of the pituitary gland. Labeled fibers and diffuse label were also found in some areas contralateral to the injection site.

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.

Oxytocin, vasopressin, and estrogen-stimulated neurophysin: daily patterns of concentration in cerebrospinal fluid

The concentrations of oxytocin, arginine vasopressin, and estrogen stimulated neurophysin in cerebrospinal fluid of monkeys showed a daily fluctuation with high concentrations occurring during the light period. The patterns of oxytocin and estrogen-stimulated neurophysin in the cerebrospinal fluid were not observed in the plasma nor were they altered after the administration of a dose of estradiol that increased concentrations of estrogen-stimulated neurophysin in plasma. The disassociation between these cerebrospinal fluid and plasma patterns and values suggests that the secretory activity of neurons that release estrogen-stimulated neurophysin and oxytocin into the cerebrospinal fluid is controlled by mechanisms different from those that control their release into the plasma.

Additional forebrain regions projecting to the posterior pituitary: preoptic region, bed nucleus of the stria terminalis, and zona incerta

Following the injections of horseradish peroxidase (HRP) into the posterior lobe of the pituitary gland of adult albino rats, scattered retrogradely labeled neurons were observed in the caudal part of the bed nucleus of the stria terminalis (ventrally and laterally), in the median and periventricular preoptic nuclei, in the medial and lateral preoptic areas, in the zona incerta, and in the substantia innominata. Immunohistochemical studies indicate that oxytocin-containing, or a mixture of vasopressin- and oxytocin-containing neurons are present in each of these areas. These findings suggest that the cells of the magnocellular neurosecretory system are more widely distributed than has previously been reported.

The nervus terminalis of the guinea pig: a new luteinizing hormone-releasing hormone (LHRH) neuronal system

Immunoreactive LHRH-like material has been found in the cells and fibers of the nervus terminalis in fetal and adult guinea pig brains. LHRH-containing neurons and axons are seen in the nasal mucosa intermingled with fibers of the olfactory nerves, in ganglia along the ventromedial surfaces of the olfactory bulbs and forebrain, and in clusters surrounding perforating branches of the anterior cerebral artery in the regions of the septal nuclei and olfactory tubercle. Nonreactive neurons are found adjacent to the LHRH-positive cells in all of the ganglia. LHRH-immunoreactive cells and axons of the nervus terminalis are in intimate contact with cerebral blood vessels and the cerebrospinal fluid along the intracranial course of this nerve, deep to the meninges. The possible involvement of these structures in the neural mechanisms of sexual behavior and the neurohormonal regulation of reproductive function are discussed.

Efferents of the medial preoptic area in the guinea pig: an autoradiographic study

Medial preoptic axons were traced into the diagonal band of Broca and septum, particularly lateral septum. Other labeled fibers could be followed dorsally from medial preoptic area injections adjacent to the stria medullaris, and in the periventricular fiber system and the stria terminalis and its bed nucleus. The anterior and medial amygdaloid nuclei were labeled by fibers via the stria terminalis and other arching over the optic tract and through the substantia innominata. The lateral habenula was labeled. Labeled periventricular fibers reached the periventricular nucleus of the thalamus. Descending efferents were traced principally below the fornix and in the adjacent lateral hypothalamus to label the anterior hypothalamus, the tuberal nuclei, and median eminence. Axons of the medial preoptic area joined the medial part of the medial forebrain bundle and distributed to the reticular formation and the central gray of the midbrain and pons. A small amount of contralateral connections were described.

Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry: III. Ontogeny of catecholamine varicosities and neurophysin neurons in the rat supraoptic and paraventricular nuclei

The ontogeny of the rat supraoptic (SON) and paraventricular (PVN) nuclei was studied using a combined fluorescence-immunocytochemical technique for the simultaneous localization of catecholamines (CA) and neurophysin (NP). NP neurons and CA varicosities were first detected in the SON and PVN at 1 days postcoitus. The development of NP neurons which included increases in immunoreactivity in both nuclei proceeded through fetal and neonatal stages, approaching maturity by 21-28 days postnatal; the maturation of the PVN lagged behind that of the SON. CA varicosities appear to make contact with NP neurons beginning at 21-22 days postnatal adult-like patterns were established. The prenatal dominance of NP stain relative to CA fluorescence may suggest a possible neurotrophic role for magnocellular neurons and/or their products upon ingrowing noradrenergic axons.

The luteinizing hormone-releasing hormone (LH-RH) neuronal networks of the guinea pig brain. I. Intra- and extra-hypothalamic projections

In the guinea pig brain, LH-RH-containing cell bodies are located not only within the classical hypophysiotrophic area but also in the medial preoptic area, septum and olfactory tubercle. LH-RH fiber tracts project not only to the primary portal plexus in the median eminence but also throughout the limbic forebrain and limbic midbrain regions. Using radiofrequency lesions in different brain regions, the projections of LH-RH cell bodies were determined. Cells in the medial preoptic area project ot the organum vasculosum of the lamina terminalis (OVLT), the suprachiasmatic nucleus, the mammillary body complex and the ventral tegmental area. LH-RH neurons in both the medial septal nucleus and medial preoptic area project via the stria medullaris to the medial habenular nucleus and from there via the fasciculus retroflexus to the interpeduncular nucleus of the midbrain. Other LH-RH neurons in the medial septal nucleus, nucleus of the diagonal band of Broca and olfactory tubercle are congregated in small clusters around large blood vessels which penetrate into this area, and they do not appear to send axons outside their immediate vicinity. The types of LH-RH axonal terminations and the roles of these peptide-containing neurons are discussed.

The hypothalamic magnocellular neurosecretory system of the guinea pig. III. Ultrastructure of the fetal neural lobe

The ultrastructure of the fetal guinea pig neural lobe was studied from day 40 to day 60 of gestation. Pituitaries were taken every five days and at least four glands from each gestational period were examined. Bundles of nerve fibers had invaded the periphery of the gland on day 40. By day 50 axon profiles were distributed throughout the entire posterior pituitary though pituicyte processes continued to act as a barrier between axons and the perivascular space of capillaries. Neural processes established contact with the capillaries between days 55 and 60. Neurosecretory granules (NSG) were present within a few axons on day 40. The number of axons with NSG and the total quantity of granules increased gradually throughout fetal development. Electron-lucent granules (microvesicles) were observed infrequently until the day of birth. A population of dense-cored vesicles, 70-80 mmu in diameter, was present from day 50 onward; a second population with larger diameters was also present throughout the developmental sequence and these increased from 90-130 mmu in diameter to 170-220 mmu in diameter between days 40 to 60. The presence of neurosecretory granules is discussed in relation to the onset of synthesis and storage of neurohypophysial hormones.

The hypothalamic magnocellular neurosecretory system of the guinea pig. II. Immunohistochemical localization of neurophysin and vasopressin in the fetus

The development of the hypothalamic magnocellular neurosecretory system of the fetal guinea pig was examined by immunohistochemistry. Neurophysin was first observed in the supraoptic nucleus (SON), median eminence (ME) and posterior pituitary (PP) on day 40 of gestation. It was not regularly present in the paraventricular nucleus (PVN) until day 47. Vasopressin was first observed in the SON, ME and PP on day 45. In the median eminence immunoreactive deposits indicative of both peptides were observed in both the fibers of the hypothalamo-hypophysial tract (H-HT) in the presumptive zona interna as well as in axons projecting to the developing primary portal plexus.