Quantitative autoradiographic mapping of neurohypophysial hormone binding sites in the rat forebrain and pituitary gland--I. Characterization of different types of binding sites and their distribution in the Long-Evans strain

Oxytocin and vasopressin binding sites were localized and characterized by quantitative autoradiography on consecutive sections of Long-Evans rat forebrains and pituitary glands, incubated in the presence of 5 nM [3H]oxytocin or 5 nM [3H]vasopressin. In the forebrain, two types of neurohypophysial hormone binding sites were thus defined. (1) Oxytocin/vasopressin sites with similar nanomolar-range affinities for [3H]oxytocin and [3H]vasopressin; both tritiated peptides were displaced from these sites in the presence of 10 microM of either oxytocin or vasopressin. The main areas bearing such sites were the ventral subiculum, several nuclei of the amygdala, the ventromedial hypothalamic nucleus, the bed nucleus of the stria terminalis and the olfactory tubercle. (2) Selective vasopressin sites, binding [3H]vasopressin with nanomolar-range affinity and [3H]oxytocin with a much lower affinity; these sites were not labelled in the presence of 5 nM [3H]oxytocin, and 10 microM oxytocin displaced [3H]vasopressin binding by 80%. Such sites occurred in several thalamic nuclei, in the dopaminergic A13 cell group of the zona incerta, the suprachiasmatic nucleus, the fundus striati and the lateral septal nucleus. No selective oxytocin sites were detected. Different oxytocin and vasopressin binding characteristics were found in the hypothalamo-neurohypophysial system. In the paraventricular and supraoptic nuclei and in the pituitary neural lobe the [3H]vasopressin binding density was twice that of [3H]oxytocin; vasopressin was always more potent than oxytocin in displacing both [3H]vasopressin and [3H]oxytocin binding from those sites. Interaction of the tritiated peptides with neurophysins cannot be completely ruled out in these locations. The present data are discussed in correlation with the functional roles of the neurohypophysial peptides in the brain and the pharmacological characteristics of their receptors.     

Ultrastructural localization of GABA in the supraoptic nucleus and neural lobe

Antibodies directed against the neurotransmitter gamma-aminobutyric acid (GABA) enabled the ultrastructural localization of GABA in conventional glutaraldehyde fixed and osmium postfixed material of the rat supraoptic nucleus and neural lobe. GABA was visualized using immunogold postembedding staining in axonal profiles that terminate on dendrites, axons or cell bodies throughout the supraoptic nucleus. The optimum ultrastructural preservation made possible the visualization of GABA terminals, also in the neural lobe. Here GABA axons were found to terminate synaptically on pituicytes and axonal profiles containing large dense core vesicles. These results emphasize, from an anatomical point of view, the potency of GABA to influence, as a transmitter, the release of vasopressin and oxytocin, both at the level of the cell body and of the neural lobe.     

Pathophysiological roles of galanin-like peptide in the hypothalamus and posterior pituitary gland

The hypothalamo–neurohypophyseal system is known to be involved in the regulation of body fluid balance, reproduction and stress response. Galanin-like peptide (GALP) is a 60-amino acid peptide, which has been isolated and cloned from porcine hypothalamus. GALP is abundantly expressed in the arcuate nucleus (Arc) neurons of the hypothalamus and the pituicytes of the posterior pituitary gland (PP). Intracerebroventricular administration of GALP causes significant increases of neurohypophyseal hormones (arginine vasopressin and oxytocin) and ACTH in rat plasma. GALP-containing neurons in the Arc are activated by foot shock stress. The expression of the GALP gene in the Arc is up-regulated by acute inflammatory stress but not chronic stress. On the other hand, the expression of the GALP gene in the pituicytes of the PP is up-regulated by both acute and chronic stress such as nociception, inflammation and osmotic challenge. These results suggest that GALP in the hypothalamus and PP has different pathophysiological roles in the regulation of stress responses involving the hypothalamo–neurohypophyseal system.     

Lack of response in the release of oxytocin and vasopressin from isolated neurohypophyses to dopamine,met-enkephalin and leu-enkephalin

Summary We investigated the effects of dopamine, met-enkephalin and leu-enkephalin on basal and ouabain-stimulated release of oxytocin and vasopressin from isolated neurointermediate lobes. The present study revealed that neurohypophyseal hormone release was not affected by dopamine, neither from lobes of untreated rats nor from those of rats with dopamine-deficiency (pretreated with -methyl-p-tyrosine-methylester). Likewise, metoclopramide, a dopamine antagonist, was unable to alter the neurohypophyseal hormone release. Our results also indicate that the opioid peptides met-enkephalin and leu-enkephalin do not influence spontaneous or ouabain-stimulated oxytocin and vasopressin release, which is in accordance with our findings that naloxone under our experimental conditions is also ineffective.     

Effect of water and salt intake on pituitary catecholamines in the rat and domestic pig

The dopamine content of the combined neural and intermediate lobes of the rat pituitary gland was increased when the secretion of posterior lobe hormones was maximally stimulated by a restricted water intake followed by the administration of NaCl in the drinking water (dehydration). This was accompanied by vasodilatation in the posterior lobe and by an increase in the intensity of catecholamine fluorescence in the perivascular nerve fibres. The quantity of noradrenaline in the neural and intermediate lobes, which amounts to about 10% of that of dopamine, was also increased after dehydration. Bilateral removal of the sympathetic superior cervical ganglia did not prevent the rise in pituitary dopamine levels after dehydration but the perivascular catecholamine-containing nerve fibres were no longer detectable. The operation caused a decrease in the noradrenaline content of the neural and intermediate lobes by about 50% in rats on normal water intake and in dehydrated rats. Thus, one half of the noradrenaline present in the neural and intermediate lobes is not contained in vasomotor fibres or other nerve fibres with cell bodies in the superior cervical ganglion. The increase in pituitary dopamine levels after dehydration was also observed in domestic pigs.It is concluded that the increase in the concentration of dopamine in the combined neural and intermediate lobes that follows dehydration and salt-loading does not occur in the perivascular sympathetic nerve fibres and that it may be related to the fall in the pituitary content of oxytocin and vasopressin.     

A re-examination of the localization of immunoreactive dynorphin(1–8), [Leu]enkephalin and [Met]enkephalin in the rat neurohypophysis

We addressed in this study, with immunocytochemical methods, the following questions:

(1) are immunoreactive enkephalins in the rat neurohypophysis stored in nerves distinct from neurosecretory nerves;

(2) where is [Met]enkephalin immunoreaction localized;

(3) does immunoreactive [Leu]enkephalin coexist with pro-enkephalin or with pro-dynorphin fragments; and

(4) are the interpretations of localization studies influenced by the choice of pre-embedding or post-embedding immunocytochemical techniques? We compared immunoreactions due to antibodies which had been used by others in previous studies, examined both lyophilized and conventionally fixed specimens, and applied pre- and post-embedding protocols. Both pre- and post-embedding stainings confirmed co-storage of immunoreactive dynorphin(1–8)-like materials with vasopressin. Immunoreactive [Met]enkephalin-like material always coexisted with oxytocin. Most of the immunoreactive [Leu]enkephalin-like material appeared to occur in oxytocin nerves; only in larger vasopressin varicosites was there some dot-like [Leu]enkephalin immunoreaction. This indicates that neural lobe [Leu]enkephalin predominantly is cleaved from a precursor which also contains [Met]enkephalin.

When pre-embedding methods were modified in order to block diffusion and to enhance penetration of antibodies, enkephalin immunoreactivity was always found in typical neurosecretory varicosities with large granules. Structures previously interpreted as enkephalinergic nerve terminals contacting pituicytes most likely are neurosecretory varicosities.     

Comparative immunohistochemical study of the presence of glial fibrillary acidic protein in the pituitary of several vertebrates

The presence and distribution of the astrocytic marker protein GFAP (glial fibrillary acidic protein) in the pituitaries of several mammalian as well as of some submammalian vertebrates were examined immunohistochemically. Our study revealed that GFAP-immunoreactive pituicytes, probably reflecting the presence of the filament-rich fibrous type of pituicyte, are a common feature of the mammalian neural lobe. Moreover, interspecific and interindividual differences of the neurohypophyseal immunostaining could be observed. In the distal neurohypophysis of some submammalian vertebrates, processes of ependymal glia showed GFAP-like immunoreactivity. Our results are in agreement with the well established evolutionary stability of GFAP elsewhere in the brain. In contrast to the neurohypophysis, GFAP-positive cells within the intermediate lobe were inconstantly present in only some species. They may be derived from neurohypophyseal glia. Folliculo-stellate cells of the adenohypophyseal pars distalis were not stained.     

Vasopressin and oxytocin in the rat spinal cord: distribution and origins in comparison to [Met]enkephalin, dynorphin and related opioids and their irresponsiveness to stimuli modulating neurohypophyseal secretion

Immunoreactive-vasopressin, -oxytocin, -dynorphin, -dynorphin-(1-8), -alpha-neo-endorphin and -[Met]enkephalin were, in each case, present in greater concentrations in dorsal as compared to ventral, and lumbo-sacral as compared to cervico-thoracic, spinal cord. These differences were significantly more pronounced for vasopressin and oxytocin than for the other peptides. Lesions of the hypothalamic paraventricular nucleus depleted levels of immunoreactive-vasopressin and -oxytocin throughout the cord whereas levels of the opioid peptides therein were unaffected. In contrast, destruction of either the supraoptic or suprachiasmatic nucleus failed to change the content of immunoreactive-vasopressin, -oxytocin or any of the opioid peptides in the cord. Dehydration for 3 days depressed levels of immunoreactive-vasopressin, -oxytocin and -dynorphin in the neurointermediate lobe of the pituitary. In distinction, the levels of these were not modified in the spinal cord. Further, treatment with the synthetic corticosteroid, dexamethasone, elevated levels of immunoreactive-vasopressin, -oxytocin and -dynorphin in the neurointermediate pituitary whereas these were unaffected in the spinal cord. It is concluded that vasopressin and oxytocin in the spinal cord are predominantly derived from the paraventricular nucleus, localized in dorsal lumbo-sacral regions of the cord and insensitive to endocrinological manipulations. These pools may, thus, be modulated differently from their counterparts in the neurohypophysis and have a differing role, possibly in the control of the primary processing, autonomic or motor junctions. Further, there is no evidence from these or our prior studies for a close interrelationship of spinal cord vasopressin with dynorphin-related peptides (or oxytocin with [Met]enkephalin), likewise in contrast to the neurohypophysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrastructural demonstration of oxytocin and vasopressin release sites in the neural lobe and median eminence of the rat by tannic acid and immunogold methods

We have investigated the localization of oxytocin (OXT) and vasopressin (AVP) release sites in the neural lobe and median eminence (ME) of the rat. Ultrastructural and post-embedding immunocytochemical studies with protein A-gold as a marker were used for the identification of OXT and AVP neurosecretory granules (NSG). Release of the contents of these OXT and AVP NSG by exocytosis has been clearly demonstrated with the tannic acid-Ringer incubation method in axon terminals of the neural lobe and in varicose fibres with OXT and AVP NSG in the internal zone of the ME. As these fibers lack synaptic specializations, and are not located in the direct vicinity of capillaries of the primary portal plexus, these observations suggest that OXT and AVP are released in a paracrine way in the ME of the rat.     

Immunocytochemical localization of the brain-specific S-100 protein in the pituitary gland of adult rat

Summary The brain-specific S-100 protein was localized at the electron microscopic level in the anterior and posterior pituitary gland of adult rat by indirect immunoperoxidase histology. The protein was found in the stellate cells of the pars distalis and tuberalis, in the marginal cells that line the hypophyseal cleft and in the glia-like cells, the pituicytes, of the neural lobe. The pituicytes, the stellate cells and the marginal cells have in common at least two properties: they all express a brain-specific marker and they are satellite cells to the secretory axons in the neural lobe and of the secretory cells in the adenohypophysis. These properties suggest that the S-100 cells in the pituitary gland are neuroectodermal in origin, possibly glial in nature.     

The effect of dopamine on neurohypophysial hormone release in vivo and from the rat neural lobe and hypothalamus in vitro.

1. The rat hypothalamus (containing the supra-optic nuclei, paraventricular nuclei, median eminence and proximal pituitary stalk) has been incubated in vitro and shown to be capable of releasing the neurohypophysial hormones, oxytocin and arginine vasopressin, at a steady basal rate about one twentieth that of the rat neural lobe superfused in vitro. 2. The hypothalamus and neural lobe in vitro released both hormones in a similar arginine vasopressin/oxytocin ratio of about 1-2:1. However, when release was expressed relative to tissue hormone content, the hypothalamus was shown to release about three times as much arginine vasopressin and six times as much oxytocin as the neural lobe. 3. Dopamine in a concentration range of 10(-3)-10(-9)M caused graded increases in hormone release from the hypothalamus in vitro to a maximum fivefold increase over preceding basal levels. The demonstration that apomorphine also stimulated hormone release whereas noradrenaline was relatively ineffective suggested that a specific dopamine receptor was involved. A separate cholinergic component in the release process was indicated by the finding that acetylcholine stimulated release to a maximum fivefold increase in concentrations of 10(-3)-10(-9)M. 4. The fact that the isolated hypothalamus can be stimulated by dopamine and acetylcholine to release increased amount of oxytocin and arginine vasopressin raises the question of the origin and fate of the hormones released in this way. The possibility that they could be released into the hypophysial portal circulation from median eminence to affect the anterior lobe of the pituitary is discussed. 5. In similar doses, both dopamine and noradrenaline injected into the lateral cerebral ventricles of the brain of the anaesthetized, hydrated, lactating rat caused the release of arginine vasopressin and oxytocin. Apomorphine release both hormones but at a higher dose level and to less effect than the catecholamines. 6. The hormone release induced in vivo by dopamine could be prevented by the prior administration of haloperidol or phentolamine and these antagonists were equally effective in blocking the hormone release due to noradrenaline. The involvement of a specific dopamine receptor was more clearly implicated by the use of pimozide which completely inhibited the hormone release due to dopamine and apomorphine but not that due to noradrenaline. 7. It is suggested that the release of neurohypophysial hormones can be stimulated via a dopaminergic nervous pathway in addition to a cholinergic one. The possibility that the osmoreceptor mechanism for the release of antidiuretic hormone from the neural lobe of the pituitary may involve such a dopaminergic pathway is discussed.     

Central inhibitory control of sodium appetite in rats: correlation with pituitary oxytocin secretion

In the present experiments we examined neurohypophyseal hormone secretion in various models of sodium appetite in rats. Basal plasma levels of oxytocin were found to be low in sodium-deficient adrenalectomized rats and in intact animals treated daily with desoxycorticosterone acetate, both of which groups drank large amounts of NaCl solution, whereas basal plasma levels of arginine vasopressin were neither stimulated nor suppressed. Conversely, sodium appetite consistently was inhibited by treatments that stimulated pituitary oxytocin secretion. However, sodium appetite was not inhibited by administration of exogenous oxytocin, nor was it stimulated by administration of an oxytocin receptor antagonist. These and other results suggest that sodium appetite may be inhibited by activity in the supraoptic and/or paraventricular nuclei, the location of the neurons responsible for the synthesis of oxytocin, and can be stimulated only when activity in those neurons is reduced. Whatever the final neural pathway, our data support the hypothesis that the control of sodium appetite is governed by inhibitory as well as excitatory central mechanisms.     

The role of steroid hormones in the regulation of vasopressin and oxytocin release and mRNA expression in hypothalamo neurohypophysial explants from the rat

Vasopressin and oxytocin release from the neural lobe, and the vasopressin and oxytocin mRNA contents of the supraoptic and paraventricular nuclei are increased by hypertonicity of the extracellular fluid. The factors regulating these parameters can be conveniently studied in perifused explants of the hypothalamo-neurohypophysial system that include the supraoptic nucleus (but not the paraventricular nucleus) with its axonal projections to the neural lobe. Vasopressin and oxytocin release and the mRNA content of these explants respond appropriately to increases in the osmolality of the perifusate. This requires synaptic input from the region of the organum vasculosum of the lamina terminalis. Glutamate is a likely candidate for transmitting osmotic information from the organum vasculosum of the lamina terminalis to the magnocellular neurones, because agonists for excitatory amino acid receptors stimulate vasopressin and oxytocin release, and because increased vasopressin release and mRNA content induced in hypothalamo-neurohypophysial explants by a ramp increase in osmolality are blocked by antagonists of both NMDA ( N -methyl-D-aspartate) and non-NMDA glutamate receptors. Osmotically stimulated vasopressin release is also blocked by testosterone, dihydrotestosterone, oestradiol and corticosterone. Both oestrogen and dihydrotestosterone block NMDA stimulation of vasopressin release, and in preliminary studies oestradiol blocked AMPA stimulation of vasopressin release. Thus, steroid inhibition of osmotically stimulated vasopressin secretion may reflect inhibition of mechanisms mediated by excitatory amino acids. Recent studies have demonstrated numerous mechanisms by which steroid hormones may impact upon neuronal function. Therefore, additional work is warranted to understand these effects of the steroid hormones on vasopressin and oxytocin secretion and to elucidate the potential contribution of these mechanisms to regulation of hormone release in vivo.     

In vivo biosynthesis and transport of oxytocin, vasopressin and neurophysin from the hypothalamus to the spinal cord

The biosynthesis of oxytocin, vasopressin and their associated neurophysins were studied in the projection from the paraventricular nucleus of the hypothalamus to the spinal cord in individual freely-moving adult male rats. Neuropeptide biosynthesis was studied in vivo by the delivery of [35S]cysteine through stereotaxically implanted indwelling cannulae using an osmotic minipump delivery system. Following the appropriate chase times, the neural lobe and spinal cord segments T1-T4 and T12-L2 were removed from fresh tissue; in addition, the nucleus of the solitary tract was punched from frozen coronal sections. The radiolabeled peptides were purified from the tissue homogenates by sequential linear and exponential gradient elution from reverse-phase high performance liquid chromatography columns. This approach has allowed us to purify radiolabeled oxytocin and vasopressin from both the upper and lower spinal cord. However, the kinetics of oxytocin and vasopressin biosynthesis appeared to be remarkably different, as judged by their differential labeling with different pulse and chase times. Additionally, the use of different chase periods following the pulse of radiolabel has allowed us to determine that oxytocin reaches the spinal cord via the fast component of axonal transport (greater than 8 mm h-1). Using immunoprecipitation and purification by high performance liquid chromatography, we were also able to purify radiolabeled neurophysins from spinal cord tissue homogenates. These results lend further support to a role for oxytocin and vasopressin in the modulation of autonomic nervous system function and to the role of the paraventricular nucleus as an integration center for endocrine and autonomic function.     

Neurohypophysial opioids and oxytocin secretion: source of inhibitory opioids

Summary When electrical stimuli are applied to the neural stalk of the pituitary, oxytocin, vasopressin, and probably several opioid peptides also contained in nerve terminals in the gland are released: one action of the released opioids appears to be to inhibit oxytocin release by an action that has been likened to pre-synaptic inhibition. Thus, when Clarke et al. (1979) stimulated the neural stalk following intravenous injection of the opioid antagonist naloxone, they observed that the evoked oxytocin release was potentiated. In the present study we confirm this result and show that oxytocin release evoked by stimulation of the supraoptic nucleus is similarly potentiated by naloxone. This finding is consistent with the hypothesis that the opioid responsible for inhibition of oxytocin release coexists with either oxytocin or vasopressin. We further report that the specific -receptor antagonist ICI 174864 does not potentiate oxytocin release either in vivo or in vitro. Thus, it seems unlikely that the enkephalins, putative -receptor agonists present in neurohypophysial fibres, are the opioids responsible for the observed inhibition of oxytocin release.     

Intracellular calcium and hormone release from nerve endings of the neurohypophysis in the presence of opioid agonists and antagonists

Summary Rat neural lobes and isolated nerve terminals from the neurohypophysis were stimulated in the presence of different opioid agonists and antagonists. The secretion of arginine vasopressin and oxytocin and rise in cytoplasmic calcium induced by depolarization were analyzed by radioimmunoassay and the fluorescent probe fura-2, respectively. The kappa-agonists dynorphin A_{1 -13} and dynorphin A_{1 -8} did not affect electrically evoked release of vasopressin, although oxytocin release was slightly reduced. U-50 488, a relatively specific kappa-receptor agonist, had no effect on the amount of vasopressin or oxytocin secreted, although it significantly reduced K⁺-evoked changes in [Ca²⁺]_i in isolated nerve endings. Two kappa-receptor antagonists, MR 2266 and diprenorphin, alone had no effect on vasopressin and oxytocin secretion from isolated nerve endings depolarized with potassium. Opioid agonists less selective for the kappa receptors, etorphin and ethylketocyclazocin, were found to inhibit the release of both vasopressin and oxytocin significantly. Naloxone, a nonselective opiate receptor antagonist, alone had no effect on vasopressin release but potentiated the electrically evoked release of oxytocin. Naloxone also could overcome the inhibitory effect of etorphin on oxytocin and vasopressin release observed after electrical stimulation of the neural lobe. A number of inconsistencies therefore exist between the effects of opioid agonists and antagonists on neuropeptide release and on the evoked changes in [Ca²⁺]_i. In view of these inconsistencies and the high concentrations of opioid agonists and antagonists necessary to modify release, we conclude that it is doubtful that opioid molecules have a physiological role in controlling neurohypophysial secretion.     

Co-existence of unrelated peptides in oxytocin and vasopressin terminals of rat neurohypophyses: Immunoreactive methionine5-enkephalin-, leucine5- enkephalin- and cholecystokinin-like substances

In neurohypophyses of normal rats and of vasopressin-deficient Brattleboro rats, applying immunocytochemical methods, we have found (1) in oxytocin terminals co-existing methionine-enkephalin-, cholecystokinin- and possibly leucine-enkephalin-like substances and (2) in vasopressin terminals, co-existing leucine-enkephalin-like material. The correspondence between the enkephalin immunoreactivity patterns and the oxytocin or vasopressin immunoreactivity pattern in serial 0.5 μ thick sections was so close that occurrence of enkephalin in separate nerves appears unlikely. At a subcellular level the enkephalin- and the cholecystokinin-like immunoreactivities were localized mainly in the neurosecretory granules that also contain oxytocin or vasopressin; there was no evidence for separate enkephalingranule populations. The intensity and frequency of leucine-enkephalin immunostaining in vasopressin terminals was much enhanced by treatment of the deplasticized sections with trypsin prior to incubation with antibodies. This suggests incorporation of the leucine-enkephalin sequence into longer peptide chains, presumably dynorphin and/or α-neo-endorphin. In oxytocin endings tryptic cleavage enhanced cholecystokinin-like immunoreactivity, while methionine-enkephalin immunostaining was as intense without enzyme treatment.The opioid peptide forms of vasopressin neurons appear to be elongated chains containing exclusively the leucine-enkephalin sequence, whereas in oxytocin neurons methionine-enkephalin as free pentapeptide seems to prevail. Association of enkephalins with vasopressin and oxytocin was also indicated when methionine- and leucine-enkephalin contents of neurointermediate lobes of homozygous Brattleboro rats were compared with peptide stores in heterozygous controls in a high pressure liquid chromatography system and highly specific leucine- and methionine-enkephalin radioimmunoassays. We assume that the opioid peptides in the oxytocin system and in the vasopressin system are derived from different opioid precursor molecules.     

Regional neurohypophyseal blood flow and its control in adult sheep

Regional neurohypophyseal and cerebral blood flows were measured by the radiolabeled microsphere technique in 30 adult sheep under light barbiturate anesthesia. Regional blood flows were determined under basal conditions. The responses of regional blood flow to alterations in arterial PCO2 and to changes in arterial blood pressure wee also determined. In addition, the relationship between regional neurohypophyseal blood flow and neurosecretory activity as judged by plasma arginine vasopressin levels was assessed. Under basal conditions median eminence blood flow averaged 461 ml.100 g-1.min-1 and did not significantly differ from neural lobe blood flow (436 ml.100 g-1.min-1). Blood flow in the neurohypophysis was about 8 times cortical and 16 times white matter blood flow in these animals. Median eminence and neural lobe blood flow proportionately increased far less than regional cortical or white matter blood flow under conditions of hypercarbia. With alteration of arterial blood pressure, regional neurohypophyseal blood flow remained constant beyond the limits of cerebral autoregulation. The neurohypophysis demonstrates a degree of blood flow homeostasis that exceeds that of any other brain area studied. Although the neurohypophysis is a diverticulum of the brain, its vascular system forms a unique functional as well as a unique anatomic unit.     

Biosynthesis of pro-opiomelanocortin is increased in the rat intermediate pituitary following denervation

In order to study the effect of pituitary intermediate lobe denervation on pro-opiomelanocortin (POMC) biosynthesis and processing, radioactive amino acids were incorporated in vitro into whole neurointermediate lobe (NIL) explants obtained from hypothalamic lesioned rats and control animals. The lesion in the basal hypothalamus removed the neural input to the intermediate pituitary and cut the neurohypophyseal neurons. One week after the lesion, approximately a 3-fold increase in the rate of synthesis of POMC peptides was found in the NIL. The content of POMC peptides was decreased. The results imply that denervation increases the rate of POMC synthesis and release, without altering the pattern of proteolytic processing.