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The neurointermediate lobe of the hypophysis in the Chameleon (Chamaeleo dilepis) was examined with light and electron microscopic methods, with special reference to the cytology of the pars intermedia (PI). The PI is the largest lobe of the hypophysis consisting of (1) dark cells with secretory granules ranging from 200-600 nm; (2) light cells, far fewer in number, containing granules 150-300 nm in diameter; (3) stellate, non-secretory cells. The secretory cells abut onto the perivascular basal lamina of the capillary sinusoids while their apical part borders an intercellular space. This surface of the cells often bears a cilium. The granules arise from the Golgi cisternae while small detached vesicles are found between circumscribed sites of the cell membrane and the Golgi apparatus. No nervous elements were found in the pars intermedia and it is assumed that the regulation of this lobe is purely humoral. This is supported by the presence of three types of nerve terminals in the pars nervosa: (a) terminals with large secretory granules and small vesicles; (b) terminals with dense-core vesicles and small vesicles; (c) terminals with small vesicles only. All of these are secretory as indicated by the presence of the synaptic semidesmosomes formed with the perivascular basal lamina.

Serotonin-immunoreactive (5-HT-IR) nerve fibers observed in the pars intermedia and pars nervosa of the rat pituitary gland were examined after treatment of animals with antiserotonergic or anti-catecholaminergic drugs. p-Chlorophenylalanine, (PCPA), an inhibitor of 5-HT synthesis, eliminated staining in both areas of pituitary gland. p-Chloroamphetamine (PCA), a serotonin neurotoxin, did not produce a significant change in 5-HT-IR from control tissue. Unexpectedly, 6-hydroxydopamine (6-OHDA), a catecholamine neurotoxin, eliminated 5-HT staining in the pars intermedia, but not in the pars nervosa. These observations suggest that 5-HT present in fibers innervating the intermediate and neural lobes is synthesized in axons locally, or is taken up into fibers from extrinsic sources. In addition, catecholamines and 5-HT may co-exist in nerve terminals of both lobes of the pituitary gland.

The effects of intraventricular injections of the highly specific gamma-amino-butyric acid (GABA) agonist muscimol (5 nmol/animal) on blood LH and prolactin levels were measured in ovariectomized (ovx) and in ovx estrogen-progesterone (OEP) primed rats. While the drug stimulated pituitary prolactin release in both experimental groups, pituitary LH release was significantly inhibited in the ovx animals. Muscimol was without any effect on LH levels in ovx-OEP primed rats. Bilateral implantation of tubes containing a muscimol-mannitol mixture into the medial preoptic/anterior hypothalamic (MPO/AH) area abolished pulsatile LH release whereas blood prolactin values were elevated. The intraventricular injection of GABA (8 mumol) also reduced LH and increased prolactin levels in the blood. Measurements of catecholamine turnover rates in the MPO/AH and in the mediobasal hypothalamus (MBH) yielded reduced preoptic but unchanged hypothalamic norepinephrine (NE) and stimulated hypothalamic dopamine (DA) turnover. In view of the well known stimulatory involvement of the NE system in the mechanism of pulsatile LH release and the inhibitory effect of GABA and its agonist muscimol on pulsatile LH release, it is suggested that GABA inhibits NE release in the MPO/AH by the mechanism of presynaptic inhibition. The observation that muscimol is unable to suppress LH release in vox OEP-primed rats may indicate that those estrogen receptive neurons in the MPO/AH which mediate the negative feedback action of the steroid may use GABA as neurotransmitter and that they are the neurons which inhibit NE release. The inhibitory effect of locally implanted muscimol into the MPO/AH also supports this hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)

In the pars distalis of the hypophysis of adult Rana temporaria, three types of nerve-fiber profiles were found at two distinct sites, in both lateral parts of the bordering regions of the anterior lobe with the intermediate lobe of the hypophysis. The first type of nerve-fiber profile consists of bundles of very fine axonal elements (diameter: less than 0.7 micron). The second type is formed by larger nerve fibers (diameter up to 4 microns) containing a few neurosecretory granules of approximately 100 nm. The third type of nerve-fiber profile resembles the second type but these nerve fibers make synaptoid contacts on at least two different types of glandular cells. The possible functional significance of these nerve fibers in the pars distalis is discussed. No nerve fibers were found in the central part of the bordering region of the pars distalis with the intermediate lobe, at the bordering region with the median eminence and with the neurohypophysial stalk, and in all other parts of the pars distalis.

Activity of glutamic acid decarboxylase GluDCase, the biosynthetic enzyme of gamma-aminobutyric acid (GABA) was measured in low-speed homogenate supernatant of the neural and intermediate (neurointermediate) lobe (28--30 pmol of CO2 per microgram of protein per hr) and of the anterior lobe (2--4 pmol of CO2 per microgram of protein per hr). In the neurointermediate lobe, stalk transection reduced the GluDCase activity by more than 95%. By using an antiserum to rat brain GluDCase and the unlabeled antibody--peroxidase method of Sternberger, GluDCase immunoreactivity was localized in many terminals within the neurointermediate lobe of the hypophysis. In pars intermedia, immunoreactive terminals occurred in apposition to secretory cells and to glial cells and were near nonimmunoreactive axonal profiles; in pars neuralis they were apposed to pituicytes and to unlabeled axons including the neurosecretory terminals and were along fenestrated portal capillaries. GluDCase immunoreactive axons terminals exhibited diverse morphological features and would not have been identified as a distinct population without the GluDCase antiserum. No GluDCase-immunoreactivity was found in the anterior pituitary lobe. Stalk transection abolished GluDCase immunoreactivity in the neurointermediate lobe. These data provide biochemical and morphological evidence for a central GABAergic innervation of neural and intermediate lobes of the hypophysis.

Short-term in vitro incubation of hypothalamo-hypophyseal tissue from young rats was undertaken to discern more clearly the functional relationship between putative dopaminergic neural projections in the pars intermedia and the secretory activity of melanophore stimulating hormone (MSH). This explant consisted of a portion of the mediobasal hypothalamus containing the dopamine neurone cell bodies of interest, with the attached pituitary neuro-intermediate lobe (n.i.l.). The n.i.l. was inserted into the end of a 1 mm diameter tube attached to a perfusion pump which allowed uninterrupted sampling of medium neighbouring the n.i.l. A 'real-time' analysis of hormone secretion was obtained by immediately and continuously bioassaying for MSH. A bipolar stimulating electrode was placed on the ventral floor of the mediobasal hypothalamus either directly on the arcuate nucleus, median eminence or infundibular stalk. Electrical stimulation for 5 min (0.1-20.0 Hz) caused a transient inhibition of basal MSH secretion, while continuous stimulation (0.1-5.0 Hz) led to a much greater, long-term, reversible inhibition. In the latter, the degree of inhibition was generally dependent on stimulation rate up to a maximum at 5 Hz. Application of the dopamine D2 receptor antagonist, 1-sulpiride (0.001-0.1 microM) to the perfusion medium not only completely and reversibly blocked the stimulus-induced inhibition of MSH release but by itself, significantly increased the basal secretion rate. Applied to the isolated n.i.l., 1-sulpiride did not alter release but did prevent the inhibitory response caused by exogenously applied dopamine (0.1 microM). The gamma-aminobutyric acid receptor antagonist, bicuculline (0.01-1.0 microM), had no effect on any of the parameters studied. In explants, cutting the infundibular stalk linking the mediobasal hypothalamus with the n.i.l., mimicked the effects of 1-sulpiride by interrupting impulse flow to the gland. Thus, electrical stimulation of hypothalamic neurones in these explants apparently causes a release of dopamine from nerve terminals in the pars intermedia to inhibit MSH secretion and perhaps other pro-opiomelanocortin-derived peptides as well.

In this study we have investigated the presence of nerve fibers containing dopamine, thyrotropin-releasing hormone (TRH) and neuropeptide Y (NPY) in the pars intermedia of the crested newt and we have examined the possible effect of these neurohormones on the release of alpha-melanotropin (alpha-MSH) by neurointermediate lobes in vitro. By means of immunohistochemistry, we observed the presence of tyrosine hydroxylase (TH)-immunoreactive fibers in the pars intermedia of the crested newt. Using a specific antiserum to dopamine, these fibers appeared to be mainly dopaminergic in nature. Unlike anurans, urodele amphibians do not exhibit TRH or NPY-like immunoreactivity in the pars intermedia. A perifusion system technique for newt pituitaries was developed to investigate the effect of dopamine, TRH and NPY on alpha-MSH secretion. Administration of increasing concentrations of dopamine (from 10(-9) to 10(-5)M) induced a dose-related inhibition of alpha-MSH release. This inhibitory effect was mimicked by the dopamine agonist apomorphine (10(-6)M). In contrast, the secretory activity of the newt pars intermedia was not affected by administration of synthetic TRH or NPY (up to 10(-7) and 10(-6)M, respectively). These results indicate that the neurotransmitter dopamine likely plays a pivotal role in the regulation of melanotropin secretion in urodele amphibians.

The pars intermedia of the pituitary in the rabbit and hare is abundantly innervated by axons reacting selectively with antibodies against oxytocin. These axons contain dense secretory vesicles about 140 nm in diameter, i.e., smaller than those in the neurosecretory axons of the neural lobe. No fiber elements staining for other peptides (vasopressin, somatostatin, substance P) were observed in the pars intermedia, except rare leu-enkephalin axons restricted to the rostral zone of the gland. Dopaminergic innervation appears to be completely absent from the intermediate lobe. This was shown by the lack of reaction with an antibody against tyrosine-hydroxylase, which did reveal a well-developed tubero-infundibular system of nerve fibers. Axons reacting with an antibody against serotonin were irregularly distributed in the pars intermedia. In the absence of dopaminergic axons, the extensive oxytocin-like innervation may play a major role in regulating the melanotrophic cell activity in the Leporidae.

The horseradish-peroxidase (HRP) technique was used to visualize the cell bodies of axons projecting to the goldfish pituitary. Following intravenous injections of HRP, HRP reaction products were observed in axons of the rostral pars distalis, proximal pars distalis, neurointermediate lobe, pituitary stalk and in axons coursing from the pituitary into the hypothalamus. HRP-labelled cells in the brain were localized in two regions only - the nucleus preopticus (NPO) pars magnocellularis and pars parvocellularis, and the nucleus lateralis tuberis (NLT) of the hypothalamus. These observations suggest that the NPO and NLT are the source of the neurosecretory innervation of the goldfish pituitary.

With the aid of lesion experiments and the Falck-Hillarp fluorescence technique, it is shown that the aminergic nerves of the hypophysis, including pars distalis, originate in the caudal hypothalamus and reach the gland via a fibre tract in the floor of tuber cinereum. However, some contribution to the eminentia mediana from the preoptic area could not be excluded. A vasomotor function of the pars distalis nerves is unlikely. Based on a comparative survey the hypothesis is put forward, that the pars distalis nerves, which disappear during the metamorphic climax, are remnants of an aminergic innervation existing together with a hypophyseal portal system as a functional link between brain and pituitary in the fish-like ancestor of amphibians. Aspects are given on the problem of why a direct pars distalis innervation has neither been retained nor evolved during evolution of tetrapods.

The distribution of immunoreactive substance P (IR-SP) neurons was examined in the hypothalamus and pituitary gland of the rhesus monkey by using the peroxidase-antiperoxidase immunocytochemical technique. Immunoreactive SP cell bodies were observed in the arcuate nucleus, in the region lateral to the arcuate nucleus, and in the median eminence (ME). Immunoreactive SP cells were also seen in the periventricular area of the dorsal tuberal region. A rich network of SP fibers was concentrated in the arcuate region, and the fiber stain was particularly dense in the external zone of the median eminence and in the external layer of the infundibular stalk. Also, substance P fibers were seen in the internal layer of the pituitary stalk and in the neural lobe of the pituitary gland. Outside the hypothalamus a dense network of IR-SP fibers was observed in the globus pallidus.

The GABAergic innervation of the goldfish pituitary was studied at the light and electron microscope levels by means of radioautography after in vitro incubation in tritiated gamma-aminobutyric acid (GABA) and immunocytochemistry using antibodies against GABA. Following incubation of pituitary fragments in a medium containing tritiated GABA, a selective uptake of the tracer was observed within the digitations of the neurohypophysis. Silver grain clusters were also observed in the adenohypophyseal tissue. At the electron microscope level, this uptake was found to correspond to nerve endings containing small clear and dense-core vesicles. These labeled profiles were located mainly in neurohypophyseal digitations in close apposition with the basement membrane separating the neurohypophysis from the adenohypophysis. However, they were also encountered in direct contact with most adenohypophyseal cell types in the different lobes. These results were confirmed by immunocytochemical data demonstrating the presence of numerous GABA immunoreactive fibers in both anterior and neurointermediate lobes. They were found either in the digitations of the neurohypophysis or in the adenohypophysis in direct contact with the glandular cells with a distribution and an ultrastructural aspect similar to those observed by radioautography. These data demonstrate that the pituitary of teleosts receives a massive GABAergic innervation. Although physiological data providing a functional significance for such an innervation are lacking, the present study suggests that, as already documented in mammals, GABA may be involved in the neuroendocrine regulation of pituitary functions in teleosts.

Catecholamines were measured in the separated intermediate and posterior lobes of the rat after stalk section and bilateral superior cervical ganglionectomy. In the intermediate lobe, after stalk section, dopamine decreases 96%, norepinephrine decreases 80%, and epinephrine is undetectable. In the posterior lobe, dopamine and epinephrine are absent, and norepinephrine decreases by 70% after the operation. In contrast, bilateral superior cervical ganglionectomy produces only a 40% decrease in norepinephrine in the posterior lobe, and no changes in catecholamines in the intermediate lobe. Our results demonstrate that most of the intermediate and posterior pituitary catecholamines are present in nerve fibers of brain origin, and that the posterior lobe has a dual norepinephrine innervation, partly originating in the superior cervical ganglia.

Color change of the plaice and frog, and development of the testes in duck are induced by light stimuli via the eye. Eliminating experiences on the frog (Hollwich) and on the duck (Benoit) showed that these stimuli-beside vision-use a separate way, the so-called 'energetic portion' of the visual pathway (Hollwich). In compared studies on blind and on temporarily blind patients involved by cataract in both eyes, we found significant low levels of ACTH and cortisol. The levels normalized after cataract extraction. -Furthermore, we studied the influence of strong artificial illumination (3,500 and 3,200 lx) on healthy persons with considerable and, on the other hand, with minimal difference of their spectral composition to daylight. We found stress-like levels of ACTH and cortisol in the first group. These findings explain the agitated mental and physical behavior of children staying the whole day in school under artificial illumination with strong spectral deviation from daylight. Therefore, to avoid mental and physical alterations, the spectrum of artificial illumination should be largely similar to that of natural light.

17 beta-Estradiol (E2) affects the sensitivity of pituitary cells to several neurohormones as LHRH, TRH, or dopamine, presumably by modulating receptor coupling mechanisms. We attempted to pinpoint the membrane processes underlying this modulation and studied the effect of E2 on pituitary membrane phospholipid methylation. Anterior pituitary membranes prepared from ovariectomized (ovx) or ovx plus E2-treated rats were assayed for phospholipid methylation. Methylated phospholipids were separated by TLC. Incorporation of [3H]methyl groups into phospholipids increased with membrane concentration and incubation time with S-adenosyl-L-methyl [3H]methionine; it was not Mg2+ dependent and was inhibited in a dose-dependent manner by S-adenosyl-L-homocysteine, methyltransferase inhibitor. pH was found to be critical. Formation of phosphatidyl-monoethanolamine, phosphatidyl-dimethylethanolamine, and phosphatidylcholine was markedly stimulated by treatment with E2. The effect increased progressively when animals were killed 15 h to 5 days after E2 implantation. The response involved a shift in the maximum velocity (Vmax) although there was no change in the available substrate for the methylating enzyme. This change in Vmax probably reflects changes in the amount of the methylating enzyme itself. Administration of 17 alpha-estradiol, an inactive stereoisomer of E2 was ineffective, pointing to a stereospecific interaction. After differential centrifugation of pituitary membranes, the highest specific methyltransferase activity was found in light mitochondrial (L) and microsomal (P) fractions and the lowest in nuclei (N) and the heavy mitochondrial (M) fractions. After sucrose density gradient centrifugation, methylated phospholipids were preferentially recovered from fractions corresponding to the endoplasmic reticulum and/or secretory granules. E2 treatment for 5 days did not modify the subcellular distribution of methyltransferase activity but stimulated it in all fractions; in contrast, it did not modify the activity of the other enzymes measured as fraction markers. Under the same experimental conditions, phospholipid methylation in membranes prepared from cortex, and anterior and mediobasal hypothalamic structures was not affected by the steroid, with the exception of a slight increment of [3H]methyl incorporation into mediobasal hypothalamic membrane phospholipids after 5 days of E2 treatment. These results indicate that E2-induced changes in pituitary responsiveness might be concomitant with selective effects of the steroid on specific membrane enzymatic activities involved in coupling mechanisms.

Control of the secretion of ACTH appears to involve several mechanisms. It is dependent upon the release, from neurones in the hypothalamus, of corticotrophin releasing factor, which is probably a complex including CRF-41 and vasopressin. The secretion of the complex is influenced by various central inhibitory and excitatory nervous pathways. The releasing factor is conveyed by the hypophyseal portal vessels to the adenohypophysis where it stimulates the secretion of ACTH. The corticosteroids exert a profound control over the basal secretion of ACTH, but only modulate the pituitary adrenocorticotrophic response to stress. The mechanisms which may be involved are summarized in figure 8.

Eels were adapted to black- or white-coloured backgrounds and the pituitary glands were prepared for light and electron microscopy. Immunocytochemical staining was used to study the distribution of the neurohypophysial melanin-concentrating hormone in the neurointermediate lobe. The hormone was located in small, elliptical, electron-opaque neurosecretory granules, measuring approximately 120 x 90 nm. The neurones terminated on blood vessels in the centre of the neurohypophysis and on the basement membrane separating neural and intermediate lobe tissues. The results of both light and electron immunocytochemistry and of radioimmunoassay are consistent with a higher rate of hormone release from eels adapted to white backgrounds than from those adapted to black backgrounds. In addition to this, when fish that had been adapted to white tanks were transferred to black tanks, there was an accumulation of irMCH in the gland and an increased numerical density of secretory granules at nerve terminals. These results reinforce the proposal that MCH is released during adaptation to a white background, to cause melanin concentration and to inhibit MSH release, and that its release is halted in black-adapted fish.

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.

The striatum receives massive dopaminergic projections from neurons in the ventral tegmental area, the substantia nigra and the retro-rubral cell group. Dopaminergic neurons in the arcuate nucleus and periventricular hypothalamic nuclei project to the median eminence and the neuro-intermediate lobe of the pituitary gland. The anterior lobe of the pituitary gland is not innervated by dopaminergic neurons, but receives dopamine via a vascular route from the median eminence. Two categories of dopamine receptors (D-1 and D-2) can be identified on the basis of the ability of various drugs to discriminate between these two entities. Dopamine stimulates both D-1 and D-2 receptors. The affinity of dopamine for the D-2 receptor is approximately 1000 times higher than for the D-1 receptor. Dopamine is involved in synaptic as well as non-synaptic communication. Examples of non-synaptic communication via D-2 receptors are the dopamine induced inhibition of prolactin release from the anterior pituitary gland and most likely the D-2 receptor mediated inhibition of the release of acetylcholine in the striatum. Examples of synaptic communication have been found in the striatum where (with ultrastructural techniques) synaptic contacts between dopaminergic nerve terminals and elements from cells containing GABA, substance P or enkephalin have been demonstrated. It is tempting to speculate that synaptic and non-synaptic communication occurs via D-1 and D-2 receptors respectively.

The distribution of labeled neurons in the paraventricular nucleus of the hypothalamus (PVN) was studied following injections of horseradish peroxidase (HRP) into the spinal cord (C8 to T1) or the hypophysis in the rat. Injections were also made in the spinal cord in another group of animals, which were subjected to water deprivation for a period of 3 days, and the PVN of these animals was examined with the electron microscope. Spinal projection neurons (paraventriculospinal tract, PVST, neurons) formed two groups; the dorsal and the ventral groups. They were located within the parvocellular part of the PVN and fused into one at the caudal level. The neurons of the dorsal group were well assembled whereas those of the ventral group were intermingled with paraventriculohypophyseal tract (PVHT) neurons, which were concentrated in the magnocellular part. Electron microscopic observations revealed that HRP-labeled neurons after spinal injections did not contain neurosecretory granules and that they were not affected by water deprivation. On the other hand, neurons containing a number of neurosecretory granules displayed a significant degree of dilatation of the endoplasmic reticulum as the result of water deprivation. These neurons contained no HRP granules. The present findings suggest that the PVST neurons are distinct from the PVHT neurons and that the neuronal groups of both systems form different cell columns within the nucleus.

To determine the sites of action whereby estradiol (E2) induces the preovulatory luteinizing hormone (LH) surge in pigs, hypophysial-stalk-transected (HST) ovariectomized (OVX) gilts (mean +/- SE: 118 +/- 12 kg) received intramuscular injections of E2 benzoate (10 micrograms E2B/kg body weight) on day 0, plus intravenous pulses of 1 microgram gonadotropin-releasing hormone (GnRH) every 45 min either from days -5 to 4, days -5 to 0 or days -5 to 0 then days 2 to 4. A fourth and fifth group received steroid vehicle on day 0 and pulses of GnRH on either days -5 to 4 or days -5 to 0 then days 2 to 4. In stalk-intact OVX gilts, E2B inhibited LH release for 48 h, then induced an LH surge that peaked 60-84 h after steroid treatment. In HST OVX gilts, serum LH increased from undetectable concentrations (less than 0.17 ng/ml) to 0.42 +/- 0.03 ng/ml after 5 days of pulsatile GnRH replacement. In the presence of pulsatile GnRH stimulation, serum LH concentrations were inhibited for 12 h after E2B but then returned to values that were similar to those for HST gilts given GnRH in the absence of steroid treatment. Discontinuing GnRH pulses at the time of E2B injection caused serum LH concentrations to drop to 0.18 ng/ml or less for the remaining 96 h. When GnRH pulses were interrupted for 48 h, beginning immediately after injecting E2B or vehicle to mimic the secretory hiatus of LH and presumably GnRH observed in stalk-intact pigs prior to the surge, resumption of GnRH pulses caused serum LH concentrations to increase progressively over 3 h in E2B-treated gilts but to peak abruptly in controls given vehicle.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonin [5-hydroxytryptamine (5-HT)] is a constituent of the mammalian pituitary gland. We have used light and electron microscopic immunocytochemistry to locate immunoreactivity in the pituitary glands of mice and bats. In addition, we have compared the distribution of endogenous 5-HT immunoreactivity with that of exogenous [3H]5-HT taken up by elements of the pituitaries and detected by radioautography. 5-HT immunoreactivity was found in neurites in the posterior and intermediate lobes of the glands. These neurites also took up [3H]5-HT. The neural elements reactive with antisera to 5-HT or which labeled with [3H]5-HT differed in their distribution from neurites that labeled with [3H]dopamine or [3H]norepinephrine; moreover, lesioning of catecholaminergic neurites with 6-hydroxydopamine had no effect on the serotonergic structures. 5-HT immunoreactivity was also found in endocrine cells of the anterior lobes of the pituitaries of both species. No 5-HT was detected in neural elements of the anterior lobe, and in fact, no staining with nerve-specific antibodies to neurofilament proteins was found in the anterior pituitary. The ultrastructure of the granules of the 5-HT-immunoreactive endocrine cells suggested that they might be a subset of gonadotrophs, the cell type previously shown to take up exogenous [3H] 5-HT. 5-HT immunoreactivity was found within the granules of these cells. In bats, 5-HT immunoreactivity was present in the anterior pituitaries of active animals when 5-HT levels were high, but was greatly diminished in glands of hibernating animals when the 5-HT content was low. It is concluded that some cells that may be gonadotrophs contain endogenous 5-HT and also have an uptake mechanism for the amine. The function of 5-HT in the anterior pituitary remains to be determined, but 5-HT has previously been shown to inhibit the secretagogue action of LHRH on gonadotrophs.

The immunocytological reactions with anti-met-enkephalin and anti-alpha-endorphin reveal two types of fibres in the intermediate lobe of the Carp. Their pathways through the adenohypophysis and the localization of their terminals are different. The anti-met-enkephalin positive fibres terminate mainly in a zone close to the proximal pars distalis; however some fibres terminate deeper in the intermediate lobe. The anti-alpha-endorphin positive fibres penetrate mainly in the central and ventral part where thye are more numerous than the former. It seems that the anti-met-enkephalin positive fibres belong to the gomori positive preoptico-hypophyseal tract, whereas the anti-alpha-endorphin positive fibres are gomori negative.

Experiments using two retrogradely transported fluorescent dyes (bisbenzimide-true blue, and Evans blue-granular blue) were performed in order to determine whether the same or different populations of neurons of the paraventricular nucleus of the hypothalamus (PVH) project to the pituitary gland, dorsal vagal complex, and spinal cord in the rat. The results suggest that cells projecting to the pituitary gland are concentrated in the magnocellular core of the nucleus, while the descending connections arise primarily from the surrounding parvocellular division. The occurrence of neurons double-labeled with both dyes further indicate that at lease 10-15% of the labeled cells in the parvocellular division send divergent axon collaterals to the dorsal vagal complex and to the spinal cord. Cell counts suggest that at least 1,500 cells in the PVH project to the medulla and/or spinal cord. These results, combined with a cytoarchitectonic analysis, show that the PVH consists of eight distinct subdivisions, three magnocellular and five parvocellular. The lateral hypothalamic area and zona incerta also contain a large number of cells projecting to the dorsomedial medulla and spinal cord; approximately 15% of such cells are the double-labeled following injections of separate tracers into these two regions of the same animal.

5-Hydroxytryptamine (5-HT)-containing axons and terminals have been visualized in the neural and intermediate lobes of the rat pituitary gland, but the origin of these fibers remains in question. This study was designed to determine if 5-HT cell bodies in the brainstem or in the dorsomedial nucleus of the hypothalamus project to either of these pituitary lobes. Since lesions and electrical stimulation of 5-HT cell bodies decrease and increase, respectively, the rate of 5-HT synthesis in regions innervated by these cells, these techniques were employed. The in vivo rate of 5-HT synthesis was determined by quantifying the rate of accumulation of the 5-HT precursor, 5-hydroxytryptophan (5-HTP), in the neural and intermediate lobes of the pituitary gland 30 min after the administration of a decarboxylase inhibitor (NSD 1015, 100 mg/kg, i.p.). The application of 30 min of stimulating current (monophasic cathodal pulses of 1 ms duration and 0.3 mA current delivered at a frequency of 10 Hz) to electrodes implanted in the dorsal and median raphe nuclei increased the rate of 5-HT synthesis in both the neural and intermediate lobes of the pituitary gland. 5,7-Dihydroxytryptamine lesions of these nuclei altered neither 5-HTP accumulation nor 5-HT concentrations in the neural and intermediate lobes, but similar lesions of the nuclei raphe pontis and raphe magnus decreased both the concentration of 5-HT and the accumulation of 5-HTP in these pituitary regions.(ABSTRACT TRUNCATED AT 250 WORDS)