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Immunostaining of brain and pituitary sections of teleost fishes (eels, salmonidae, cyprinidae, gourami, sculpin, mullet) with anti porcine galanin (GAL) revealed the presence of immunoreactive (ir) perikarya and a rich network of fibers. Ir-perikarya were located rostrodorsally to the recessus preopticus, and in the posterior tuberal hypothalamus. Ir-fibers were abundant in basal telencephalon and around diencephalic ventricular recesses but never contacted their lumen. Furthermore, they were observed in basal hypothalamus, brainstem and ventral medulla. Ir-fibers passed along corticotropic (ACTH), gonadotropic cells and somatotropes (GH cells) in eel and trout pars distalis, but rarely ended in caudal neurohypophysis. In goldfish pituitary ir-fibers occurred in neural digitations and among different cell types which however did not contain a GAL-like peptide. The relation GAL fibers/GH cells appeared more evident in species with a high growth rate. The other species showed a similar distribution of brain GAL. In eels and trout, ir-perikarya were not observed in areas containing somatostatin, GH- and ACTH-releasing factor, and ACTH-like perikarya, suggesting that GAL did not coexist with these peptides. The widespread distribution of a GAL-like peptide in teleost brain suggests that it could play a role of neurotransmitter and/or neuromodulator and regulate the secretion of adenohypophysial hormone(s).

During ontogenesis, proopiomelanocortin (POMC) mRNA appears in the pituitary intermediate lobe (IL) at embryonic day 16 (E16), rather later than in the hypothalamic arcuate nucleus (E13) or the pituitary anterior lobe (E15). POMC mRNA onset in the IL correlates with the appearance of POMC-derived peptides detected by immunocytochemistry (ICC), indicating that there is probably no time lag between POMC mRNA translation. Subsequently, while the IL lobular organization developed progressively, the number of in situ hybridization- (ISH) and ICC-positive cells increased until after birth. During postnatal development, coinciding with innervation of the IL, the POMC mRNA level in the lobe, measured by quantitative ISH, increased about 4-fold to reach the adult value at weaning. The effects of acute or chronic postnatal treatment with a dopamine antagonist (haloperidol) or a dopamine agonist (bromocriptine) show that the physiological dopaminergic inhibitory control of POMC gene expression operates as early as postnatal day 5. The subsequent increase in mRNA levels despite the inhibitory innervation raises the question of the existence of some unknown positive regulation active during postnatal development.

The pituitary intermediate lobe, a source of pro-opiomelanocortin (POMC) peptides, was examined with light and electron microscopic techniques in Sprague-Dawley rats aged 5-18 months and Zucker rats aged 18 months. Cysts were common in the intermediate lobe in the Zucker animals, a finding also noted in human pituitary glands by other investigations. The nuclear envelopes were often indented in cells of aging rats, while those of young animals were generally smooth. Lipid droplets and lysosomes, rarely seen in tissue from young animals, were frequently observed in endocrine cells of older rats. Most cells had an abundance of secretory granules, suggestive of enhanced storage of peptides in the cytoplasm. Nerve terminals which were present among endocrine cells contained myelin figures in some of the old rats, and may indicate degenerative changes, while other terminals appeared normal. These morphologic findings suggest that the aging phenomena in intermediate lobe tissue have characteristics in common with nervous tissue, and may also reflect a diminished inhibitory neuroregulation.

The effects of elevated circulating concentrations of prolactin were examined on neurochemical estimates of activity of dopaminergic neurons in the infundibulum/pituitary stalk of Holstein bull calves (8-10 weeks of age). Activity of these neurons was estimated by measuring the accumulation of dihydroxyphenylalanine, the immediate precursor of dopamine, 15 min after an intravenous injection of the aromatic L-amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine. Subcutaneous injections of the dopamine antagonist haloperidol every 6 hr for 1 day increased serum concentrations of prolactin and accumulation of dihydroxyphenylalanine in the infundibulum/stalk. Intravenous infusions of prolactin for 1 or 9 days increased accumulation of dihydroxyphenylalanine in the infundibulum/stalk, indicating that these neurons remain responsive to elevated prolactin for at least 9 days. It is concluded that elevated concentrations of prolactin in blood stimulate dopaminergic neurons in the infundibulum/pituitary stalk of bull calves. We speculate that these neurons may be analogous to the tuberoinfundibular dopaminergic neurons that regulate prolactin in rats.

The purpose of this study was to ascertain whether the pars intermedia of the rat adenohypophysis, isolated from direct innervation via the infundibular stem, could maintain adrenal cortical weight and plasma corticosterone levels. We compared the adrenal cortical response of rats 40 days after either complete hypophysectomy, hypophysectomy with reinsertion of only the pars distalis, or hypophysectomy with reinsertion of only the nervosa-intermedia. Adrenal weight and plasma corticosterone levels were partially maintained in the group with reinserted pars distalis. These parameters were not different from the complete hypophysectomy group in the animals with reinserted nervosa-intermedia. Thus, the pars intermedia, with its nerve supply disrupted, cannot maintain adrenal cortical function.

The extracellular spaces of the rat pars intermedia were examined after perfusion with fixation containing lanthanum. The tracer reveals complex and extensive interdigitations among secretory cells. Spaces appear continuous with extracellular "channels" between the epithelial cells lining the hypophyseal cleft. Some suggestions for close contiguity between endocrine cells was present as "narrowing" or discontinuous areas within lanthanum-filled spaces. Extracellular regions surrounding nerve fibers and terminals appear continuous with the spaces between secretory cells. Areas between cells are thought to provide access to vascular and local neurotransmitter input, as well as to provide an extensive area for extrusion of peptide hormones and endogeneous opiates.

The possible role of microvesicles and vacuoles in the recapture of membrane after pituitary hormone release by exocytosis has been studied in homozygous Brattleboro rats. These mutant animals are unable to synthesize vasopressin and exhibit a steady state hypersecretion of oxytocin from the neural lobe as a result of the osmotic imbalance caused by their diabetes insipidus. This can be converted to a second steady state which approximates to the rate of secretion found in normal Long Evans rats by the administration of exogenous vasopressin daily for 30 days. In the Brattleboro rat, presumptive oxytocinergic nerve endings contain typical 160-170 nm diameter neurosecretory granules; other magnocellular nerve endings contain a population of smaller (approximately 100 nm diameter) dense-cored granules. The number of dense-cored granules was reduced in both types of nerve ending in the hypersecreting Brattleboro rats, but increased as a result of vasopressin treatment to levels which, for the classical neurosecretory granules, approximated that found in Long Evans rats. The microvesicle population of the nerve endings was essentially similar in quantitative terms in all the three groups (i.e. hypersecreting Brattleboro rats; vasopressin-treated Brattleboro rats and Long Evans controls). The number of vacuoles, on the other hand, was increased in nerve endings in the hypersecreting animals but reduced to levels found in Long Evans rats in the Brattleboro animals treated with vasopressin. Furthermore, the size of the vacuoles was comparable to the size of the dense-cored granules contained in the nerve endings. These changes in the vacuole population are exactly those that would be predicted for an organelle responsible for recapture of the granule membrane. We therefore conclude that membrane retrieval after exocytosis of neurosecretory granules in the neural lobe is achieved by vacuoles and that these organelles probably retrieve the membrane of the granule intact.

The peptidergic nature of most of the fibres of the neurosecretory system of Scyliorhinus caniculus has been demonstrated with the oxidation method of Naumann and Sterba (1976). Some of the fibres of this peptidergic system terminate on capillaries in the hypothalamic floor, some on neurointermediate cells. The evolutionary aspects of these observations are discussed.

The existence of monosynaptic connections between neurons in the paraventricular nucleus (PVN) of the hypothalamus and the intermediolateral cell column (ILC) of the spinal cord was studied by electrophysiological techniques in chloralose-anesthetized cats. Sympathetic preganglionic discharges (recorded from the 2nd or 3rd thoracic white ramus) were evoked by microstimulation of certain regions in or near the PVN with short train of pulses and below 50 microA current. By recording responses of 'identified' and 'non-identified' neurosecretory cells in the PVN and supraoptic nucleus (SON) to stimulation of the ILC of the thoracic cord, it was possible to identify antidromically evoked action potentials in 9 out of 297 neurons tested. Among them, 2 neurons were also antidromically excited by the pituitary stalk stimulation, 5 were orthodromically excited by the same stimulus and the remaining 2 were not excited by the stalk stimulation. Our results indicate that some PVN neurons, though small in number, send axons directly to the ILC of the cord, and that a very few neurons among these also send their axons to the pituitary gland.

Serotonin (5-HT)-containing nerve fibers and terminals, but not cell bodies, have been demonstrated by light and electron microscopic immunocytochemistry in the intermediate lobe of the rat pituitary. Seven days after pituitary stalk transection, 5-HT immunoreactive fibers disappeared almost entirely from the intermediate lobe. Intermediate lobe 5-HT and 5-hydroxyindoleacetic acid concentrations, measured by high pressure liquid chromatography coupled to electrochemical detection, fell to 56% and 62% of control, respectively. There were no changes in 5-HT concentrations in anterior or posterior lobes of the pituitary or in the median eminence. These findings, and the failure of sympathectomy to cause a drop in pars intermedia 5-HT, indicate that in the intermediate lobe of the pituitary neuronal 5-HT originates in cells situated in the central nervous system.

The combined neural and intermediate lobes (N.I.L.) of the pituitary glands of Brattleboro rats contained significantly more noradrenaline (NA) than those of normal controls of the same age. In addition, in 4 and 6 months old rats the N.I.L. of the homozygotes (Di-rats) contained about twice as much NA as those of the heterozygotes (non-Di-rats). In the enlarged and hyperaemic neural lobes of the Di-rats enlarged blood vessels could be seen. They were surrounded by a rich network of nerve fibres which displayed catecholamine fluorescence. The NA concentrations in the medial basal hypothalamus (M.B.H.) of 4, 6, and 9 months old Di-rats were significantly higher than those of the non-Di-rats and of controls of the same age. This may contribute to the diminished ACTH secretion in Brattleboro rats. The total amount of DA contained in the N.I.L. of 9 months old Di-rats was 20% lower than in the non-Di-rats of the same age. The concentrations of homovanillic acid (HVA) in the corpora striata of 4 months old Di- and non-Di-rats was significantly higher than in older Brattleboro rats and in control rats of various strains and ages. At 9 months it was nearly twice as high in the Di-rats as in the non-Di-rats. The concentrations of dihydroxyphenylacetic acid in the striata of 4--6 months old Di- and non-Di-rats were higher than those of Long Evans rats of the same age.

Somatostatin 14 and 28 (SS-14 and SS-28) have been measured in hypophysial portal blood of male Wistar rats. The concentration and total amount of SS released into portal blood were increased 6- to 7-fold by electrical stimulation of the median eminence. On HPLC, only two peaks of immunoreactivity were detected in extracts of portal plasma and these peaks corresponded with SS-14 and SS-28, respectively. The amount of SS-28 in portal plasma was, on a molar basis, similar or greater than that of SS-14 and this together with other evidence suggests that SS-28 is an hormonally active peptide.

The bovine pituitary intermediate lobe was studied by light microscopy after staining with a modified Bodian procedure. The study revealed a number of dissimilar intermediate lobe elements characteristic of mature and immature cells found in the adult and embryonic central nervous system and ganglia. In this study the elements are referred to as non-secretory neuronal elements. The elements, forming part of the parenchyma, have multiple processes which distribute themselves throughout the lobe. The typical secretory intermediate lobe cells have only a slight affinity for the Bodian stain. The intermediate lobe basophilic staining secretory cells and the neuronal elements maintain their general differences in appearance and possibly their function. Since the intermediate lobe in bovine is rather avascular and neuronal elements are usually associated with blood vessels, these elements may be involved in certain mechanisms yet unknown. It is possible that the elements provide common precursor proteins that reach the secretory intermediate lobe cells through their dendritic branches. In addition, the non-secretory neuronal elements may be directly involved in the spike potentials recorded from the lobe as well as in stimulus-secretion coupling. This study does not treat the function of the neural elements at this time, but directs attention strictly to their presence in the intermediate lobe of the bovine pituitary gland.

A short review of the present knowledge on the innervation of the pituitary gland by 5-hydroxytryptamine (5-HT) containing nerves is given. This is followed by results of recent experiments in which the concentrations of 5-HT in different lobes of the rat hypophysis were measured under conditions in which pituitary hormone secretion was increased. A prolonged increase in hormone secretion induced by dehydration and increased sodium chloride intake resulted in a decrease in the 5-HT concentrations in the anterior lobe (AL). The 5-HT content of the neural (NL) and the intermediate lobe (IL) of these rats was hardly changed whereas that of DA was about doubled. Acute stimulation of pituitary hormone secretion by exsanguination under ether anaesthesia also caused a fall in the 5-HT content of the AL. In contrast, in the NL and in the IL of these rats, the 5-HT concentrations were significantly increased. This indicates that the 5-HT system in the AL reacts differently from those in the NL and IL. Pituitary dopamine (DA) contents were not affected by ether and exsanguination. Thus, the pituitary DA and the pituitary 5-HT neuronal systems are activated independently in different endocrine states. The concentrations of 5-HT were also measured in 10 groups of normal male or female rats in the course of 2 years and compared with those of DA. The concentrations of 5-HT were lowest in the AL with little variation between the different groups. In the rest of the tubero-hypophyseal system the concentrations of 5-HT were at least 3, and up to 10 times, higher than in the AL, with larger inter group variations. The DA concentrations in the AL were only 10-20% of those of 5-HT; in the other regions they were equal to or higher than those of 5-HT.

Adult male Sprague-Dawley rats were examined for possible co-localization of tyrosine hydroxylase (TH) and serotonin (5-HT) within innervation of the pituitary neurointermediate lobe. Use of sheep antiserum to TH and a secondary antibody coupled to fluorescein isothiocyanate (FITC), followed by rabbit anti-5-HT, then rhodamine-coupled second antibody, produced co-existent staining in some, but not all fibers of both the neural and intermediate lobes, using paraffin embedded tissues. Application of a combination of the two primary antibodies followed by sequential application of secondary antibody also resulted in co-localized antigens in selected fibers. Multiple 'classic' neurotransmitters within the same nerve terminals may modulate selected areas of endocrine tissue to control hormone release.

Recent immunohistochemical evidence from the rat, indicating that gamma-aminobutyric acid (GABA)-containing fibres of central nervous origin project to the pars intermedia of the pituitary1,2, prompts inquiry into the function of this innervation. There is electrophysiological evidence that GABA acts directly on melanotrophs isolated from rat, through bicuculline-blockable receptors, to increase Cl- conductance and thereby drive the membrane potential towards the Cl- equilibrium potential in these cells, resulting in depolarization at rest or reduction of the depolarization caused by excess K+ (ref. 3). As voltage-dependent Ca channels can participate in the regulation of secretion in these cells4, we have now examined the effect of GABA on hormone output and find that it first stimulates and then inhibits spontaneous secretion of melanocyte-stimulating hormone (MSH) and inhibits K+-evoked secretion. Moreover, our pharmacological evidence suggests that similar receptors are involved in the secretory and the electrophysiological responses. A function of the GABAergic innervation may therefore be to regulate hormone output by acting directly on the melanotrophs, and this regulation may be affected by the changes in electrical properties induced by GABA.

Retrograde transport of horseradish peroxidase (HRP) was used to identify supraependymal neurons projecting to the pituitary gland in the hamster. Supraependymal neurons overlying the median eminence were labeled by HRP injections into the neural and intermediate lobes of the pituitary gland; no neurons were labeled following HRP injections confined to the anterior lobe. Supraependymal neurons innervating the pituitary gland may provide a means whereby cerebrospinal fluid-borne substances modulate neuro-intermediate lobe function.

Vasoactive intestinal polypeptide (VIP) is a widely distributed neuropeptide which has recently been found in the hypothalamus and in hypothalamo-hypophyseal portal blood. We have examined the pituitary of several mammalian species for the presence of VIP by immunocytochemistry and radioimmunoassay and report here that the pars nervosa contains a considerable quantity of VIP (100-250 fmol/mg) which, in the dog, can be shown to be present in nerve fibres. It is possible that neurohypophyseal VIP may be a local releasing agent for vasopressin.

Monosodium L-glutamate was injected intraperitoneally into goldfish at a dosage of 2.5 mg/g body wt. The first noticeable effect in the pituitary, 30 min postinjection, was marked swelling of pituicytes in the neurohypophysis (NH). Eighteen hours postinjection a large number of degenerating type B fibers were found in the NH of the proximal pars distalis (PPD), while all type A fibers, and type B fibers in other parts of the pituitary, remained unaffected. Because glutamate causes a lesion in the nucleus lateral tuberis (NLT), from the anterior margin of the pituitary stalk through to the posterior end of the nucleus, and a minor lesion in the nucleus preopticus periventricularis, it is likely that the NLT is the origin of the degenerative type B fibers in the proximal NH. The significance of these results is discussed in relation to the neuroendocrine regulation of the pituitary functions in goldfish.

The purpose of this study was to determine whether changes in the levels of neural progestin receptors are associated with mating-induced heat abbreviation in the rat. Mating caused a decrease, 8-10 hr after stimulation, in the duration of sexual receptivity. No difference in the concentration of cytosol progestin receptors was found between mated and nonmated animals 8-10 hr after treatment. Mating caused a statistically significant decrease in the concentration of nuclear progestin receptors at that time. However, this difference was probably not related to heat abbreviation, because no difference in nuclear progestin receptor levels was found between animals mated with vaginal masks and animals mated without masks, while mated-masked animals were found to exhibit significantly higher levels of sexual receptivity than mated-nonmasked animals after treatment. In addition, mating either with or without masks caused a statistically significant increase in serum progesterone levels relative to that measured in nonmated animals. Therefore, it is suggested that mating, even in the absence of cervical-vaginal stimulation, may cause the release of adrenal progestins which, in turn, may influence the rate at which neural progestin receptors accumulate and are processed within cell nuclei. The results of the present study suggest that mating-induced heat abbreviation in the rat is not associated with decreased levels of neural cytosol or nuclear progestin receptors.

The diencephalon of nonmammalian vertebrates contains aminergic perikarya situated beneath the ependyma lining the third ventricle, known as the paraventricular organ (PVO). Catecholamines were visualized in the goldfish forebrain by formaldehyde-glutaraldehyde-induced fluorescence. Neuronal somata containing catecholamines were found in three paraventricular nuclei--the nucleus recessus posterioris (NRP), the nucleus recessus lateralis (NRL), and the nucleus posterioris paraventricularis (NPPv)--which may be considered to constitute the PVO of the goldfish. Lesion-degeneration investigations were conducted to determine whether the PVO contributes to the innervation of the goldfish pituitary. Following electrothermic lesions of the NRP, degenerating axons and nerve terminals were observed in the rostral pars distalis and in the proximal pars distalis, but not in the neuro-intermediate lobe of the pituitary. Following lesions of the NRL or of the NPPv, degenerating axons and nerve terminals were observed in the rostral pars distalis, the proximal pars distalis, and in the neurointermediate lobe. These observations demonstrate that the PVO is a source of pituitary afferents in the goldfish and suggest that the PVO is a source of the catecholaminergic innervation of the teleost pituitary.

Iontophoretic deposit of horseradish peroxidase (HRP) in the hypophysial neural lobe (NL) of the toad labeled neurons in the classical neurosecretory preoptic magnocellular nucleus. Further, a number of labeled neurons appeared in the whole extension of the periventricular and medial preoptic nuclei. The latter were continuous dorsally with two other labeled areas known as the bed nucleus of the hippocampal commissure (which appears to be homologous to the subfornical organ in mammals) and the ventromedial thalamic area of Frontera. The possible functional role of many of these afferents to the neural lobe is unknown because all types of neurons were labeled in the projecting zones and, in addition, many are outside of the generally recognized neurosecretory groups.

Regulation of the synthesis and release of peptides by the melanotropic cells of the intermediate lobe of the murine hypophysis is mainly brought about by innervation of the lobe by dopaminergic and GABAergic fibres. The present work reports on a study of the distribution of nerve fibres inside the gland by immunocytochemical identification of the GABA contained in the axons.

Immunoperoxidase histochemical investigations on pig hypophysis show that CRF immunoreactive nerve terminals are distributed around the blood vessels in the posterior lobe, particularly in its proximal part adjacent to the intermediate lobe. CRF immunoreactive nerve fibers are also seen in the intermediate lobe. The distribution of the CRF-containing nerve in the posterior lobe was found to be similar to that of the vasopressin-containing nerve terminals. The functional significance of the presence of CRF-containing nerve fibers representing a new component of the hypothalamo-hypophyseal neurosecretory system is discussed.

Adult Rana pipiens (common frog) were treated with the long-acting opiate antagonist drug naltrexone hydrochloride to study potential effects of an opiate-receptor block on release of pro-opiomelanocortin (POMC) peptides from the pituitary intermediate lobe. The melanophore response of the animals was used to assess relative release of melanocyte-stimulating hormone (MSH). Animals were adapted to a light background, then injected with 20 or 50 mg/kg naltrexone for up to 3.5 days. All drug-treated animals showed increased release of MSH while on the light background while controls remained light-adapted. Ultrastructure of the pars intermedia of naltrexone-treated frogs revealed nerve fibers containing myelin figures, swelling of neurovesicles, and abnormal membrane components indicative of degenerative changes. The observations suggest that naltrexone has a damaging effect on pituitary innervation, and that MSH release may be the result of loss of neuroregulation from the normally inhibitory innervation. The findings are in agreement with our earlier studies in rats, which also demonstrated degenerative changes induced by naltrexone in intermediate lobe innervation. The long-acting antagonist may therefore have a "neurotoxic" effect after multiple injections or chronic use.

Fluorescent (aminergic) fibers were demonstrated by the Falck-Hillarp technique in all parts of the neurohypophysis (NH) in the roach (Leuciscus rutilus). The fibers are very thin and few in number in the rostral (RNH) and proximal neurohypophysis (PNH) but slightly more numerous in the NH adjacent to the pars intermedia (PI). The fibers occur in normal fish as well as in specimens pre-treated with gamma-methyl-noradrenaline. It is proposed that all parts of the adenohypophysis have a very sparse aminergic innervation. There is no correlation between the number of type "B' fibers and fluorescent fibers in the roach NH. The technical difficulties in obtaining good and reliable results in teleost material are discussed.

The dopaminergic innervation of the goldfish pituitary gland was studied by immunocytochemistry at the electron-microscope level using highly specific antibodies against dopamine coupled to bovine serum albumin with glutaraldehyde. A satisfactory preservation of the tissue was achieved after immersion in 5% glutaraldehyde in phosphate buffer containing sodium metabisulfite to prevent oxidation of the endogenous dopamine. The immunocytochemical procedure was performed on Vibratome sections using the preembedding method. Immunoreactivity was restricted to part of the neurosecretory type-B fibers (diameter of the secretory vesicles lower than 100 nm) in which it was found to occupy the whole cytoplasm. Labeled fibers were observed within the neurohypophysis in the different parts of the gland and in the adenohypophyseal tissue where immunoreactive profiles were detected in close apposition to the different cell types. These data are in agreement with previous results obtained by means of radioautography and further support a role for dopamine in the neuroendocrine regulation of pituitary functions in teleosts.

Using immunocytochemical methods at the electron microscope level, immunoreactivity for both melanin-concentrating hormone (MCH) and alpha-melanocyte-stimulating hormone (alpha-MSH) has been demonstrated in the carp neurohypophysis. A double-labelling technique, using colloidal gold probes of different sizes showed that immunoreactivity to both molecules coexists within the same neurosecretory granules in some neurones, while in other neurones the granules exhibit only MCH-like immunoreactivity. These observations suggest that the two immunoreactivities are attributable to separate molecules; if they are derived from the same precursor molecule, then this must be cleaved differently in the two sets of neurones. The absence of adrenocorticotropic hormone (ACTH)-like immunostaining in any neurosecretory granule might suggest the alpha-MSH-like molecule is not derived from the conventional pro-opiomelanocortin precursor.

Distribution of the gamma-aminobutyric acid (GABA)ergic and dopaminergic innervations was studied in the rat neurointermediate lobe using antibodies against GABA and tyrosine hydroxylase. In light microscopy, immunoperoxidase staining revealed similar distribution patterns of the axons reacting with both antibodies. Diffusely scattered in both lobes, they were more concentrated along the marginal zone of the neural lobe. Application of a double, recto-verso, immunogold labelling method in electron microscopy revealed systematic colocalization of GABA and tyrosine hydroxylase (TH) immunoreactivities in the axons innervating the intermediate lobe; in the neural lobe, almost all GABA-immunoreactive axons were also labelled for TH. Thus, GABA and dopamine, hitherto reported to occur in distinct axons, in fact colocalize in the axonal systems which innervate the pituitary neurointermediate lobe. These observations suggest possible interactions (pre- or postsynaptic) of both transmitters in the functional regulation of the intermediate and neural lobes.

Double labeling experiments with the retrogradely transported fluorescent tracers bisbenzimide and True blue indicate that separate populations of cells in the paraventricular nucleus of the hypothalamus project to the median eminence and to the dorsomedial medulla or spinal cord in the rat. The cell populations giving rise to each projection are, however, at least partially intermixed in different parts of the nucleus.