The distribution of neurophysin-secreting pathways in the mammalian brain: light microscopic studies using the immunoperoxidase technique

Role of Isotocin in the Regulation of the Hypophysiotropic Dopamine Neurones in the Preoptic Area of the Catfish, Clarias batrachus

Dopamine (DA) has emerged as a potent inhibitory neuromodulator of luteinsing hormone (LH) secretion and reproduction in teleosts. The DA neurones located in the anterior subdivision of nucleus preopticus periventricularis (NPPa) in the preoptic area (POA) innervate the pituitary gland and regulate LH cells. Although a reduction in the inhibitory DAergic tone is crucial for stimulatory action of gonadotrophin-releasing hormone (GnRH) on LH cells, the role of other hypothalamic factors is suggested but not fully understood. Nonapeptide, isotocin (IST) has emerged as a likely candidate that may also influence the LH cell function. IST neurones reside in the nucleus preopticus and innervate LH cells. While IST treatment dramatically elevated LH secretion, the IST levels in brain peaked during spawning. In a pilot study on the catfish, Clarias batrachus, we observed a dense network of IST-immunoreactive (IST-IR) fibres in the NPPa, the region known to harbour hypophysiotropic DA neurones. Application of the double immunofluorescence method showed a dense IST-IR fibre network around the tyrosine hydroxylase-immunoreactive (TH-IR) neurones in the NPPa region. A great majority of the TH-IR neurones in the NPPa were contacted by IST-IR fibres during the spawning phase. The NPPa therefore appears to be a site for the intense interaction of DA and IST. IST-IR fibre innervation in NPPa showed reproduction phase-dependent changes. The percent fluorescent area of IST-IR fibres showed a gradual increase from the resting through prespawning phases (resting: 7.5 ± 1.04; preparatory: 8.6 ± 0.8; prespawning: 15.5 ± 1.4), reaching a peak in the spawning phase (28 ± 2.3; P < 0.001). Compared to the spawning phase, a drastic reduction in IST-IR fibres in the NPPa was observed during the postspawning phase (8.4 ± 0.9; P < 0.001). Superfused slices of the POA of C. batrachus treated with IST peptide resulted in a significant reduction in TH immunoreactivity in the NPPa (Control: 45.3 ± 4.2; IST peptide, 5 μm: 29.4 ± 4.7; P < 0.05). We suggest that the intense interaction between IST and DA in the NPPa, most probably of an inhibitory nature, may be critical for the regulation of LH cells and reproduction in teleosts.

Immunocytochemical localization of oxytocin and neurophysin in human corpora lutea

Corpora lutea, corpora albicantia, and ovarian stroma from normal human premenopausal ovaries were examined for the presence of oxytocin and neurophysin by using highly specific antisera and peroxidase-antiperoxidase light-microscopic immunohistochemistry. Oxytocin and neurophysin immunoreactivity was found in some but not all cells of the corpora lutea obtained on days 19 to 24 of the menstrual cycle. Stromal tissue and corpora albicantia did not give a positive reaction for either of these peptides, and negative results were also obtained with corpora lutea of mid- and term-pregnancy and preovulatory follicles. Specificity of the immunohistochemical reaction was confirmed by immunoabsorption tests. The specific localization of immunoreactive oxytocin and neurophysin in corpora lutea of the human menstrual cycle directly demonstrates the presence of oxytocin- and neurophysin-positive cells within the human corpus luteum.

Suppression by glucocorticoid of the immunoreactivity of corticotropin-releasing factor and vasopressin in the paraventricular nucleus of rat hypothalamus

The effect of glucocorticoid on the production of corticotropin-releasing factor (CRF) and vasopressin in the paraventricular nucleus of the hypothalamus (PVH) was examined immunocytochemically. Intraperitoneal administration of dexamethasone sulfate in a dose of 0.1 mg/day suppressed the immunoreactivity of CRF and vasopressin in the medial parvocellular divisions of the PVH of the rat subsequent to bilateral adrenalectomy. In the magnocellular divisions, suppression of vasopressin-immunoreactivity was not observed. These results suggest that the vasopressin in the medial parvocellular divisions plays a distinct role from that in the magnocellular divisions, the former having functional significance in the hypothalamo-hypophysio-adrenal axis.

Intraventricular administration of arginine vasopressin suppresses prolactin release via a dopaminergic mechanism

The present study was conducted to determine the effects of intracerebroventricular administration of arginine vasopressin (AVP) on the preovulatory prolactin (PRL) surge. Hourly injections of 1 or 5 micrograms AVP from 1200 to 1700 hr on proestrus prevented increases in plasma PRL levels that afternoon. However, following cessation of AVP treatment, a marked increase in PRL levels occurred between 1830 and 2030 hr. This "rebound" secretion of PRL was greater in rats given 5 micrograms AVP than in rats given the lower dose. The suppression of PRL release by AVP appears to be mediated by dopamine since 5 micrograms AVP failed to inhibit PRL release in animals pretreated with the dopamine antagonist domperidone. Interestingly, under these conditions, AVP increased PRL release compared to levels observed in saline-treated rats. In addition to suppressing PRL release, AVP exerted a dose-dependent inhibition of preovulatory LH release. The results suggest a possible interaction between AVP and dopamine in controlling PRL release which likely takes place within the median eminence.

Isolation and localization of neurophysin-like proteins in rat uterus

Neurophysins are part of the prohormones for vasopressin and oxytocin, and are localized with these hormones in the magnocellular cells of the neurohypophysis. New techniques have identified neurophysins in other areas within and outside the central nervous system, and we report here the isolation of neurophysins from the uterus of the rat. Using immunohistology the neurophysin immunoreactivity was localized to the epithelial lining cells of the uterus, and using radioimmunoassay was also present in uterine fluid suggesting secretion into the uterine cavity. The amount of uterine neurophysin increased in response to administered estrogen and was especially elevated in the pregnant uterus. The neurophysin-like material isolated from the uterus was similar to neurophysins from the neurohypophysis by radioimmunoassay, molecular sieve chromatography, isoelectric focusing and SDS gel electrophoresis. Both neurohypophyseal hormones, vasopressin and oxytocin, were also extracted from uterine endothelium and identified by radioimmunoassay and high pressure liquid chromatography.

Neuropeptides in aging and dementia

Although senile dementia of the Alzheimer's type (SDAT) is a common disease associated with advancing age, recent studies have suggested that SDAT should not be considered synonymous with old age but a disease process separate from normal aging. This study examined the morphology of two neurochemically-defined neuronal populations (i.e., neurophysin, somatostatin) in the cortex and hypothalamus to determine if structural changes in these neuropeptide systems associated with advancing age are similar to those seen with SDAT. Our findings suggest that morphological changes consistent with neuronal degeneration occur in somatostatin but not neurophysin-containing neurons in cases diagnosed to have SDAT, and these structural changes are different from those seen in aged brain without central nervous system disease. These data support the concept that senile dementia of the Alzheimer's type is not a single neurochemical related disease, but may be associated with anatomical lesions and biochemical imbalances among a number of neuropeptide and neurotransmitter systems.

Prosomatostatin-specific antigen in rat brain: localization by immunocytochemical staining with an antiserum to a synthetic sequence of preprosomatostatin

Using an antiserum to a 15-amino acid synthetic peptide corresponding to amino acids 63-77 of rat preprosomatostatin (rat somatostatin cryptic peptide, RSCP), we have compared the distribution of immunoreactive RSCP (IR-RSCP) with that of immunoreactive somatostatin-14 in the rat brain. IR-RSCP was present in neuronal cell bodies, processes, and axon terminals in the hypothalamic tuberoinfundibular system as well as in diverse regions of the central nervous system in an identical distribution to immunoreactive somatostatin. These observations indicate that in neurons the somatostatin prohormone or the NH2-terminal extension peptide of somatostatin-28 (or both) is stored and transported intracellularly along with somatostatin 14. In addition, the presence of IR-RSCP in nerve terminals suggests that this material may be secreted as a hormone or neuromodulator and may serve as a biologic marker of somatostatin secretion.

Distribution pattern in the human pituitary and hypothalamus of a new neuropeptide: the C-terminal glycoprotein-fragment of human pro-pressophysin (CPP)

The distribution pattern of CPP-containing neurons and fibers in the human pituitary and hypothalamus was studied with a specific antiserum to human CPP and the unlabeled antibody technique. Immunoreactive CPP was found in the magnocellular neurons of the supraoptic nucleus (SON), the paraventricular nucleus (PVN) and in neurons scattered in the supraoptic hypophyseal tract. CPP-containing parvocellular neurons were found in the suprachiasmatic nucleus (SCN). The CPP-containing fibers from the magnocellular neurons formed a tract coursing through the median eminence and the pituitary stalk to the posterior lobe of the hypophysis. In contrast, no such fibers from the SCN projected to SON, PVN and the median eminence. This pattern is identical to that of vasopressin and its associated neurophysin-containing neurons and fibers and strongly supports the concept that CPP is a part of the common precursor for vasopressin and neurophysin II. The biological importance of human CPP other than being a precursor fragment remains to be elucidated.

The carboxy terminus of the precursor to vasopressin and neurophysin: immunocytochemistry in rat brain

A pituitary glycopeptide whose amino acid sequence was previously identified has now been recognized as the final portion of the precursor to arginine vasopressin and its associated neurophysin. Immunocytochemical techniques with antiserums against this 39 amino acid peptide and vasopressin were used to study their distribution in the rat central nervous system. The peptide is located in vasopressin-synthesizing cells in the neurosecretory magnocellular nuclei. Positively stained fibers project from the magnocellular nuclei through the median eminence to the posterior pituitary. Studies of the homozygous Brattleboro rat, which is known to be deficient in the production of vasopressin and its related neurophysin, also show the absence of immunoreactivity to this peptide. These immunocytochemical data strongly indicate that the peptide is synthesized with vasopressin.

The tuberoinfundibular system of the rat as demonstrated by immunohistochemical localization of retrogradely transported wheat germ agglutinin (WGA) from the median eminence

The origin of neuronal perikarya which project to the external zone of the median eminence (the tuberoinfundibular neuronal system) was determined in the rat after injection or diffusion of wheat germ agglutinin (WGA) into the median eminence. The retrogradely transported lectin was detected in neurons using an immunohistochemical method based on the peroxidase-antiperoxidase technique. Immunoreactive cell bodies were found both in hypothalamic and extrahypothalamic regions. Within the hypothalamus, the majority of peroxidase-positive cells were present in the dorsomedial and basolateral portions of the arcuate nucleus, regions of the periventricular nucleus, and the preoptic region, particularly at the level of the organum vasculosum of the lamina terminalis (OVLT). Within the extrahypothalamic regions, WGA-positive perikarya were found in the diagonal band of Broca, the region of the medical septum and the brainstem. Only rare cells were labeled in the ventromedial nucleus of the hypothalamus and no cells were labeled in any region of the amygdala. These data demonstrate that neurons with afferent projections to the median eminence are more widely distributed in the rat brain than previously recognized and therefore, that the concept of the tuberoinfundibular neuronal system must be expanded.

Dynorphin and vasopressin: common localization in magnocellular neurons

The opioid peptide dynorphin is widely distributed in neuronal tissue of rats. By immunocytochemical methods, it was shown previously that dynorphin-like immunoreactivity is present in the posterior pituitary and the cells of the hypothalamic neurosecretory magnocellular nuclei which also are responsible for the synthesis of oxytocin, vasopressin, and their neurophysins. By using an affinity-purified antiserum to the non-enkephalin part of the dynorphin molecule it has now been demonstrated that dynorphin and vasopressin occur in the same hypothalamic cells of rats, whereas dynorphin and oxytocin occur in separate cells. Homozygous Brattleboro rats (deficient in vasopressin) have magnocellular neurons that contain dynorphin separate from oxytocin. Thus dynorphin and vasopressin, although they occur in the same cells, appear to be under separate genetic control and presumably arise from different precursors.

Dendritic trees of neurones in the rat supraoptic nucleus

The cytoarchitecture of the rat supraoptic nucleus was studied using the Golgi-Cox method with a neutral red or Cresyl violet counterstain to allow the limits of the nucleus to be determined accurately. A small number of stained neurones were seen in each of the brains sectioned but they were unevenly distributed in the supraoptic nucleus. There were more cells posteriorly and close to the optic tract. A minority of cells studied (a total of 4) were round (diameter approximately 20 micrograms) and multipolar and were interpreted as interneurones. The majority of stained cells studied (60) had oval cell bodies (mean long diameter 22.7 micrograms in coronal sections) with a single fine axon directed dorsally and medially and 1-3 heavier dendrites passing ventrally. Both cell bodies and dendrites of the major cell type showed spines and both dendrites and axons had some varicosities. The anatomy of the larger cell group (the presumed neurosecretory cells) is thus consistent with their having a substantial synaptic input and the presence of long dendrites (up to 205 micrograms) implies that caution is necessary in the interpretation of experiments where cell activity is monitored while active materials are placed near the cell bodies.

A comparison of neuropeptide immunocytochemistry in fluid-fixed and freeze-dried brains

Immunocytochemical staining of luteinizing hormone-releasing hormone (LHRH), somatostatin, and neurophysin was compared in rat brains fixed with 1) formalin, 2) Bouin's solution, 3) freeze-dried (FD), or 4) freeze-dried + paraformaldehyde vapor perfused (FDV). The distribution of LHRH fibers was similar in all preparations; however, beads of granular reaction product often appeared finer and more numerous in the median eminence of FD- and FDV brains. Positively stained LHRH perikarya were not observed in any of the preparations. In contrast, somatostatin-immunoreactive perikarya were present in the fluid-fixed and FD brains, although few were observed in FDV brains. Somatostatin-immunoreactive fibers were present in all preparations, but appeared most numerous in the median eminence of FD brains. Staining of neurophysin-containing perikarya and fibers was similar in all preparations. These observations suggest that the FD brain can provide a suitable tissue substrate for immunocytochemistry, demonstrating staining comparable to or surpassing that of more conventional preparations. However, staining of antigens in FD brain was not uniformly successful and may depend on stereochemical characteristics of each antigen as well as properties of the primary antisera used in the staining procedure.

Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry: II. Correlative distribution of catecholamine varicosities and magnocellular neurosecretory neurons in the rat supraoptic and paraventricular nuclei

The comparative morphology of catecholamine (CA) varicosities and neurophysin (NP)-containing perikarya of the supraoptic (SON) and paraventricular nuclei (PVN) was examined. The major CA innervation to the SON and PVN did not coexist with the major distribution of magnocellular perikarya, but was located peripheral to the nuclei. A dense distribution of CA varicosities was found ventral to the neurosecretory perikarya of the SON and overlapped numerous immunoreactive oxytocin- and vasopressin-containing neuritic profiles. Examination of Golgi-stained sections revealed that dendrites from SON perikarya projected to the CA zone and were likely candidates for the processes identified immunocytochemically. In addition, a heterogenous distribution of axosomatic contacts was found within the SON which suggested a preferential innervation of VP-containing neurons. The densest concentration of CA varicosities in the PVN occurred in the periventricular region adjacent to the third ventricle and in the contiguous parvocellular portion of the PVN. These CA varicosities overlapped scattered oxytocinerigic perikarya in both areas. In addition the ventromedial as well as the dorsolateral subnuclei of the PVN were contacted by CA varicosities; this heterogeneous distribution suggests that the each subnucleus of the PVN with its individual hypothalamic, neurohypophyseal, brainstem, or cortical projections may possibly receive a catecholaminergic innervation by a select group of CA cells or nuclear groups from the brain stem.

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.

Simultaneous monoamine histofluorescence and neuropeptide immunocytochemistry. IV. Verification of catecholamine-neurophysin interactions through single-section analysis

A method was developed that allows the analysis of neuropeptides and monoamines in a single tissue section by the application of the unlabeled antibody method for peptide staining to tissue sections freeze-dried for formaldehyde-induced monoamine histofluorescence. The hypothalamic magnocellular system of male albino rats served as a model for this study; neurons were stained with anti-neurophysin sera, which mark the vasopressin- and oxytocin-associated proteins. Neurophysin-containing perikarya appeared to be surrounded by catecholamine-containing varicosities. This phenomenon was seen to varying degrees within the supraoptic and paraventricular nuclei. The juxtaposition of varicosities and peptidergic neurons suggests an afferent fiber-target neuron relationship that might favor a functional interaction between monoamines and neuropeptides.

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.

Integrated morphology of neuronal catecholamines and neurophysin in the aged macaque

A new method for the simultaneous visualization of brain peptides and monoamine neurotransmitters was employed to analyze the integrated morphology of hypothalamic catecholamines and neurophysins in young and old monkeys. Immunocytochemical analysis using bovine neurophysin revealed a dual papulation of light and dark stained cells in the paraventricular nucleus in young and old macaques. In general, both populations of neurons stained with less density in old macaques indicating the possibility of a reduced content of neurophysin. Further analysis using specific neurophysin antisera for vasopressin or oxytocin revealed an appreciable decrease in the number of vassopressin-containing perikarya in the 20 year monkey whereas oxytocin-synthesizing neurons did not show a similar change in numbers with age. Qualitatively, terminal innervation patterns of hypothalamic catecholamines remained strikingly constant in spite of marked reductions in dark-stained neurophysin perikarya of the paraventricular nucleus.

Assays and dynamics of corticotropin-releasing factor activity in rat hypothalamus

Features of several assays for corticotropin-releasing factor (CRF) were compared, with reference to sensitivity, precision, specificity and convenience. In general, in vivo assays are less specific, whereas in vitro assays with isolated pituitary cells appear to suffer from vulnerability. Promising approaches for overcoming this difficulty are appearing: one is the cell culture technique and the other is the perfusion of pituitary cell column. However, the findings with vasopressin are again discordant. So far, the in vivo-in vitro assay system appears to be the most satisfactory. In this connection, special emphasis was laid on the CRF assay by out intrapituitary injection technique through the parapharyngeal approach, which has features of both in vivo and in vitro systems. The drawbacks with this assay are its complexity and relatively lower precision. Problems of the use of dexamethasone are discussed from a viewpoint of possible multistage feedback inhibition, as postulated by Yates et al. Several findings on the CRF dynamics were mentioned, in order to exemplify the findings obtained with our assay: it was shown that the two-peaked changes of CRF after ether-laparotomy stress in adult rats were composed of heterogeneous components, as revealed by differential effect of cycloheximide. Pretreatment with cycloheximide similarly abolished the delayed CRF peak that was observed in 2-day-old neonatal rats under stress. These findings suggest an operation of a biochemical denominator in common with both cases.

Immunocytochemical localization of the vasopressinergic and the oxytocinergic neurons in the human hypothalamus

The human hypothalamic-neurohypophysial hormone-producing nuclei were investigated with the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique at the light microscopic level. The size, shape and location of the supraoptic, paraventricular, accessory supraoptic and suprachiasmatic nuclei were determined. It was demonstrated in the human hypothalamus, as well as in the hypothalamus of other mammals, that vasopressin and oxytocin are synthesized in separate neurons. In each of the nuclei of the magnocellular neurosecretory system, the distribution, ratios and structural features of the vasopressinergic and oxytocinergic neurons were determined. It was shown that the human suprachiasmatic nuclei contain numerous neurophysin-vasopressin-producing neurons.

Two satiety systems revealed by hypothalamic knife cuts in hypophysectomized rats

When pituitaries are intact, hypothalamic knife cuts produce obesity in adult rats but not in weanlings. Knife cut weaning females do not usually begin to become obese until after they are 7 weeks old. When pituitaries are removed, symmetrical or asymmetrical knife cuts produce obesity promptly in both adults and weanlings. Obesity indices that correct for stunted linear growth reveal that in adults the degree of obesity is independent of the presence or absence of the pituitary. Based on these findings we speculate that there may be two appetite regulating systems, a juvenile one involving the pituitary, and an adult one involving the hypothalamus.

Ontogeny of neurophysin in the rat pituitary gland. An electron microscope immunohistochemical study

The ontogenic development of neurophysin has not been investigated so far. To study this problem, electron microscopic immunohistochemistry was performed on ultrathin sections of the posterior pituitary of foetal and newborn rats. A concomitant appearance of secretory granules and neurophysin was first noted in the posterior pituitary of 18-day foetus. Neurophysin was detected only in the secretory granules, all of which were labelled. The number of granules (75-110 nm in diameter) as well as the intensity of the reaction for neurophysin increased as the foetus became older. In the newborn rat, the secretory granules were more numerous and showed a strong neurophysin positive reaction. The results support the hypothesis that neurophysin is an essential component for the formation of the secretory granules in the hypothalamo-neurophypophysial system.

Electron microscope immunohistochemical localization of neurophysin in the rat with hereditary diabetes insipidus

In order to study the subcellular distribution of neurophysin in the rat with hypothalamic hereditary diabetes insipidus (DI), an immunoelectron microscopic localization of neurophysin was performed in the hypothalamo-neurohypophysial system of both homozygous and heterozygous DI rats. Whereas in control rats neurophysin was localized in the granules present in the secretory neurons, in the homozygous DI rats neurophysin was found in the granules and outside the granules in the perikarya and axons of neurons of both supraoptic and paraventricular nuclei. In the heterozygous DI rats findings similar to those observed in homozygous DI rats were observed, although in the posterior pituitary, the exgranular material appeared to be less abundant than in homozygous DI rats. These results clearly demonstrated that in hyperstimulated neurons neurophysin was distributed in both granular and extragranular compartments.

The role of suprachiasmatic nuclei of the hypothalamus in the production of circadian rhythm

(1) Action potentials were recorded from single neurons in suprachiasmatic nuclei of hypothalamus in urethane anesthetized male rat. The rate of firing ranged from less than 1 to over 10/sec but was generally 4-8/sec, and it varied from one cell to another in the same animal. (2) Repetitive stimulation of optic nerve or light acting on the eye augmented the activity of approximately half of the the suprachiasmatic neurons examined (67 out of 159 cells) while 37 neurons (23%) showed clear inhibition by the same stimuli. (3) Stimulation of the suprachiasmatic nuclei strongly inhibited the electrical activity of cervical sympathetic nerves. Light or optic nerve stimulation also inhibited activity of cervical sympathetic nerves. (4) The rate of discharge of suprachiasmatic nuclei showed, at times, some short duration oscillations occurring every 3-5 min, but at other times the same neuron showed a steady low frequency of firing. (5) Projection of optic nerves to the suprachiasmatic nuclei was demonstrated by anterograde migration of horseradish peroxidase placed in the vitreous body. (6) It was suggested that light excites certain groups of neurons in the suprachiasmatic nuclei which exert inhibitory action on cervical sympathetic nerve. This, in turn, caused a reduction in norepinephrine release by nerve fibers innervating the pineal and a reduction in pineal enzyme production. Thus, neurons in these nuclei contribute to the suppression of pineal enzyme production produced by light.

Neurophysin in the brain and pituitary gland of normal and scrapie-affected sheep—I

By use of an immunofluorescence histochemical technique with a cross-species reactive antiserum to porcine neurophysin-II the precise localization of neurophysin in the pituitary gland and the hypothalamic area of the brain of the sheep has been determined. Neurophysin was confined to neurosecretory pathways originating from the supraoptic and paraventricular hypothalamic nuclei. The major pathway terminates in the neurohypophysis but in addition a second neurophysin-containing pathway proceeds in the external infundibular zone of the median eminence-pituitary stalk and is associated with the presence of vasopressin. In sheep affected with the hereditary degenerative disease known as natural scrapie, this supraoptico-paraventriculo-infundibular pathway is preserved and hypertrophied, while the major pathway to the posterior lobe of the pituitary degenerates. The supraoptic and paraventricular nuclei in the sheep comprise at least two distinct but morphologically similar neuronal populations affected differently by the natural scrapie genome, one undergoing dissolution by middle-age and one surviving and becoming hyperactive. This premature ageing is probably associated with a primary biochemical lesion affecting the rate of the axonal flow of neurosecretory vesicles and of their discharge at synaptic terminals. Possible metabolic and circulatory bases for such an anomaly are considered. The presence of neurophysin in the rostral and caudal adenohypophysis supports the view that vasopressin is acting directly as a trophic-hormone releasing factor, possibly for the quick release of adrenocorticotropic hormone and of growth hormone. The relation of neurophysin-rich aggregations in the neurohypophysis to Herring bodies and the turnover of neurosecretory material are discussed.

Identification, in the external region of the rat median eminence, of separate neurophysin-vasopressin and neurophysin-oxytocin containing nerve fibres

Immuno-enzyme cytochemical investigations, using single and double staining techniques, showed that the external region of the rat median eminence contains separate neurophysin-vasopressin fibres and neurophysin-oxytocin fibres. These neurophysin-hormone containing nerve fibres are influenced by bilateral adrenalectomy and by colchicine treatment. The external region of the median eminence of the homozygous Brattleboro rat contains neurophysin-oxytocin fibres. It does not contain immuno-reactive neurophysin-vasopressin fibres. Bilateral adrenalectomy also influences the neurophysin-vasopressin containing neurons of the suprachiasmatic nuclei. In the neurons of the parvicellular part of the rat hypothalamic paraventricular nuclei, staining for vasopressin and for oxytocin is completely absent.

Immuno-cytochemical demonstration of the inability of the homozygous Brattleboro rat to synthesize vasopressin and vasopressin-associated neurophysin

Immuno-enzyme cytochemical investigations have shown that, (1) the hypothalamic supraoptic and paraventricular nuclei of the Brattleboro rat, as in the normal rat, contain separate neurons which produce oxytocin + neurophysin; (2) the hereditary inability of the Brattleboro rat to synthesize vasopressin and its associated neurophysin is due to a biochemical defect of separate "neurophysin-vasopressin" neurons in the supraoptic and the paraventricular nuclei. These observations strongly support the hypotheses that (1) vasopressin and its associated neurophysin are formed via a common precursor, and (2) the initial point of intracellular appearance of the hereditary defect in the Brattleboro rat lies in the synthesis of this precursor, which occurs on ribosomes. Moreover, observations have demonstrated that, in the Brattleboro rat, in addition to the hereditary inability of the hypothalamic magnocellular neurosecretory system to synthesize vasopressin, there also exists a similar hereditary defect in the hypothetical parvicellular suprachiasmatic-median eminence neurosecretory system.