Showing papers on "Hypothalamus published in 1987"

Interleukin-1 stimulates the secretion of hypothalamic corticotropin-releasing factor.

Abstract: There is now evidence that the immune system, during times of infectious challenge, can stimulate the secretion of glucocorticoids, the adrenal steroids that mediate important aspects of the response to stress. Specifically, secretion of interleukin-1 (IL-1), a monocyte lymphokine secreted after infection, appears at least in part responsible for this effect. Glucocorticoids are secreted in response to a neuroendocrine cascade involving, first, the brain, then the pituitary, and finally the adrenal gland. In this report, human IL-1 is shown to activate the adrenocortical axis at the level of the brain, stimulating the release of the controlling hormone corticotropin-releasing factor (CRF) from the hypothalamus. Infusion of IL-1 induced a significant secretion of CRF into the circulation exiting the hypothalamus, whereas immunoneutralization of CRF blocked the stimulatory effect of IL-1 on glucocorticoid secretion. IL-1 appeared to have no acute direct stimulatory effects on the pituitary or adrenal components of this system. Furthermore, IL-1 did not cause a nonspecific release of other hypothalamic hormones. Thus, the lymphokine acts in a specific manner to activate the adrenocortical axis at the level of the brain; this effect appears to be unrelated to the known pyrogenic effects of IL-1 within the hypothalamus.

Efferent projections of the suprachiasmatic nucleus: I. Studies using anterograde transport of Phaseolus vulgaris leucoagglutinin in the rat

Abstract: The efferent projections of the suprachiasmatic nucleus (SCh) in the rat hypothalamus have been reexamined with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L), which displays labeled axons with the clarity of a Golgi impregnation. Fibers from the SCh can be divided into six pathways for descriptive purposes. By far the densest terminal field arising from cells in the SCh ends in a roughly comma-shaped zone between the SCh and paraventricular nucleus on the one hand and the periventricular nucleus and anterior hypothalamic area on the other. A few axons continue dorsally from this "subparaventricular zone" to pass through parvicellular parts of the paraventricular nucleus and the overlying midline thalamic nuclei to end in midrostrocaudal parts of the paraventricular nucleus of the thalamus, and a larger number continue caudally to end in the dorsomedial nucleus, dorsal parts of the cell-sparse zone surrounding the ventromedial nucleus, and the posterior hypothalamic area. The other five pathways all consist of relatively small numbers of fibers and give rise to relatively sparse terminal fields. The second pathway consists of rostrally directed fibers that end in ventral parts of the medial preoptic area and anteroventral periventricular nucleus. The third consists of anterodorsally oriented fibers that pass through the medial preoptic nucleus and adjacent regions to end ventrally in the intermediate lateral septal nucleus. The fourth consists of fibers just caudal to the third group that end in the preoptic continuation of the bed nucleus of the stria terminalis, as well as in the parataenial nucleus and rostral part of the paraventricular nucleus of the thalamus. The fifth consists of laterally directed fibers that course over the optic tract to end in the ventral lateral geniculate nucleus. And the sixth consists of fibers that course posteriorally through the anterior hypothalamic and retrochiasmatic areas to end in the cell-sparse zone between the arcuate nucleus and ventral parts of the ventromedial nucleus, as well as in adjacent parts of the lateral hypothalamic area. The distribution of projections labeled following PHA-L injections centered in the subparaventricular zone was also examined and was confirmed with retrograde tracer experiments (Watts and Swanson: J. Comp. Neurol. 258:230-252, '87). The results indicate that the subparaventricular zone projects to essentially the same regions as the SCh, only much more densely, and also sends fibers back to the SCh.(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent projections of the suprachiasmatic nucleus: II. Studies using retrograde transport of fluorescent dyes and simultaneous peptide immunohistochemistry in the rat

Abstract: In a previous study (Watts et al., '87) we reexamined the projections of the suprachiasmatic nucleus (SCh) with the PHA-L method and found that they could be divided conveniently into six groups of fibers. By far the densest projection ends just dorsal to the SCh in a comma-shaped region designated the "subparaventricular zone," although some fibers continue on through the paraventricular nucleus of the hypothalamus to end in the overlying midline thalamus, and others continue on to end in the dorsomedial nucleus, the region around the ventromedial nucleus, and the posterior hypothalamic area. Other relatively sparse projections from the SCh were also described to the preoptic region, lateral septal nucleus, parataenial and paraventricular nuclei of the thalamus, and ventral lateral geniculate nucleus. In addition, the same method was used to show that the subparaventricular zone projects in turn massively to these same regions, as well as back to the SCh itself and to the periaqueductal gray. The present series of experiments was designed to confirm these observations with retrograde tracer injections and to investigate the cellular and possible neurotransmitter organization of the major projections from the SCh and subparaventricular zone with a combined retrograde tracer-immunohistochemical method. For this, the distribution of neuronal cell bodies within the SCh that stain with antisera to vasopressin, vasoactive intestinal polypeptide (VIP), corticotropin-releasing factor, bombesin, substance P, neurotensin, somatostatin, thyrotropin-releasing hormone, and angiotensin II was described in detail first. Then the distribution of retrogradely labeled neurons that were also stained for one or another of these peptides was described after injections of true blue, or in some cases SITS, into the regions of the subparaventricular zone, the paraventricular and parataenial nuclei of the thalamus, the ventromedial nucleus, the dorsomedial nucleus, and the periaqueductal gray. The results confirm previous immunohistochemical and anterograde tracing studies and in addition indicate that cells in dorsal as well as ventral parts of the SCh project to each of the terminal fields examined, as do many cells in surrounding areas, including the subparaventricular zone. Our results also suggest that, at the very least, vasopressin-, VIP-, and neurotensin-stained cells in the SCh project to the subparaventricular zone, midline thalamus, and dorsomedial nucleus, and that the vasopressin and VIP-stained fiber systems are partially segregated at the level of the subparaventricular zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization and Characterization of Insulin Receptors in Rat Brain and Pituitary Gland Using in Vitro Autoradiography and Computerized Densitometry

Abstract: In order to identify likely sites of action in insulin in rat brain we have used the technique of in vitro autoradiography and computerized densitometry to map, characterize, and quantify its receptors in coronal and sagittal sections A discrete and characteristic distribution of insulin receptor binding was demonstrated, with specific binding representing 92% of total binding Displacement and specificity competition curves in olfactory bulb are typical for authentic insulin receptors, and computer analysis indicates a single class of binding site with a dissociation constant (Kd) 048 nM for choroid plexus and 044 nM for olfactory bulb external plexiform layer Insulin receptor density is maximum in the choroid plexus, and high in the external plexiform layer of olfactory bulb Structures of the limbic system and hypothalamus reveal moderate to high insulin receptor density, particularly the lateral septum, amygdala, subiculum, hippocampal CA1 region, mammillary body, and arcuate nucleus Moderate ins

Thyroid Hormone Regulates TRH Biosynthesis in the Paraventricular Nucleus of the Rat Hypothalamus

Abstract: Thyroid hormone is important in the regulation of synthesis and secretion of thyroid-stimulating hormone (TSH) in the anterior pituitary, but its role in the control of hypothalamic thyrotropin-releasing hormone (TRH) is controversial. To determine whether thyroid hormone regulates the function of TRH in the hypothalamic tuberoinfundibular system, a study was made of the effect of hypothyroidism on thyrotropin-releasing hormone messenger RNA (proTRH mRNA) and TRH prohormone in the rat paraventricular nucleus. Extracts of rat hypothalamic paraventricular nucleus were examined by quantitative Northern blot analysis, and coronal sections of rat brain were examined by in situ hybridization histochemistry and immunocytochemistry. A nearly twofold increase in proTRH mRNA was observed in hypothyroid animals; this increase could be obliterated by levothyroxine treatment, suggesting an inverse relation between circulating thyroid hormone and proTRH mRNA. In situ hybridization showed that this response occurred exclusively in medial parvocellular neurons of the paraventricular nucleus. A simultaneous increase in proTRH mRNA and immunoreactive TRH prohormone in this region suggests that hypothyroidism induces both transcription and translation of the TRH prohormone in the paraventricular nucleus.

Corticotropin-releasing factor receptors in the rat central nervous system: characterization and regional distribution.

Abstract: A stable, iodine-125-labeled analog of rat/human corticotropin- releasing factor (CRF) was used to define the characteristics of CRF receptors in a crude mitochondrial/synaptosomal membrane preparation of rat olfactory bulb, and to study the distribution of CRF binding sites in discrete regions of the rat CNS. The binding of 125I-Tyro rat/human CRF (125I-rCRF) was time- and temperature-dependent, was sensitive to the pH, ionic strength, and cationic composition of the incubation buffer, and was linear over a broad range of membrane protein concentrations. 125I-rCRF binding to olfactory bulb membrane was saturable, reversible, and, on Scatchard analysis, revealed a high- affinity component with an apparent equilibrium dissociation constant (Kd) of 0.2 nM and a low-affinity binding site with Kd of approximately 20 nM. Data from pharmacological studies indicated that the ability of a variety of CRF fragments and analogs to inhibit 125I-rCRF to olfactory bulb membranes correlates well with their reported relative potencies in stimulating pituitary adrenocorticotropic hormone secretion in vitro. Consistent with a coupling of CRF receptors to adenylate cyclase, the binding of 125I-rCRF was decreased by guanine nucleotides and increased by magnesium ions. A heterogeneous distribution of 125I-rCRF binding sites was found in the rat CNS, with highest densities present in olfactory bulb, cerebellum, cerebral cortex and striatum, and progressively lower but significant levels of binding were detected in cervical spinal cord, hypothalamus, medulla, midbrain, thalamus, pons, and hippocampus. These data, using a rat CRF ligand homologous to the endogenous peptide, are consistent with those from previous studies demonstrating the presence of specific binding sites for ovine CRF in rat brain, and provide further support for the suggestion that endogenous CRF may function as a neurotransmitter in the CNS.

Vasopressin, oxytocin, dynorphin, enkephalin and corticotrophin‐releasing factor mRNA stimulation in the rat.

Abstract: 1. Cryostat sections were cut through the hypothalamus of rats which had been given a 2% (w/v) NaCl solution to drink for up to 12 days. 2. In situ hybridization histochemistry was performed on these sections using synthetic oligonucleotide probes against part of the precursor sequence for vasopressin, oxytocin, dynorphin, enkephalin and corticotrophin-releasing factor (CRF). 3. Drinking 2% NaCl solution resulted in a progressive increase of vasopressin, oxytocin and dynorphin mRNAs hybridized in the magnocellular neurones of the supraoptic (s.o.) and paraventricular (p.v.) nuclei. No enkephalin mRNA was detected in the magnocellular areas of the control animals although small quantities of probe did hybridize after 12 days of salt loading and after the stress of I.P. hypertonic saline. 4. Ten-day-lactating female rats were also studied. They had a very marked increase in oxytocin mRNA with smaller increases of vasopressin and dynorphin mRNAs. No detectable enkephalin mRNA was hybridized in the magnocellular s.o. or p.v. nuclei and CRF mRNA was unchanged in both the s.o. nucleus and the p.v. nucleus.

Effect of neuropeptide Y on ingestive behaviors in the rat

Abstract: Neuropeptide Y (NPY) is a potent stimulator of food and water intake in rats. NPY still increases food intake even after a 2-h delay in access to food after central injection. When two injections of NPY are given 2 h apart, the second injection produced a substantial increase in food intake. This suggests that tolerance to the NPY effect does not develop after a single injection of NPY. NPY increases moving and exploration in the absence of food when rats are in their home environment but not when tested in a novel environment. Following administration of NPY, rats preferred a high-carbohydrate diet over a high-fat or high-protein diet. Microinjections of NPY showed that active sites included the anterior ventromedial nucleus, paraventricular nucleus of the hypothalamus, and the posterior lateral hypothalamus. NPY was neither additive nor synergistic when coadministered with norepinephrine. Whereas norepinephrine-induced feeding was inhibited by adrenalectomy and vagotomy, these maneuvers had no effect on NPY-induced food intake. This provides further evidence that NPY does not exert its effects on food intake through an alpha-adrenergic mechanism. The effects of NPY on food intake were attenuated by peripherally administered bombesin and centrally administered corticotropin-releasing factor and calcitonin. Cholecystokinin failed to inhibit NPY-induced feeding. NPY did not alter circulating glucose levels. These studies provide further insights into the role of NPY as a stimulator of ingestive behaviors.

Corticotropin-Releasing Factor Decreases Plasma Luteinizing Hormone Levels in Female Rats by Inhibiting Gonadotropin-Releasing Hormone Release into Hypophysial-Portal Circulation

Abstract: To evaluate whether the hypothalamus is the site of action of CRF in inhibiting LH levels in female rats, we measured hypophysial-portal blood concentrations of immunoreactive GnRH (irGnRH) after the central injection of CRF. Ovine CRF (0.1, 1.0, 2.0, and 5.0 nmol) was injected intracerebroventricularly to intact rats on the afternoon of proestrus and in long term ovariectomized (OVX) rats in the presence or in absence of estradiol benzoate (OVX + EB). CRF injection decreased the amplitude of the proestrous irGnRH surge without affecting presurge levels. CRF (0.1 nmol) attenuated the afternoon irGnRH surge in OVX + EB rats; higher doses of CRF blocked this surge and decreased nonsurge irGnRH levels. No dose-related alterations of irGnRH levels were observed in OVX rats; only the highest dose of CRF was active. For comparison, plasma LH concentrations were measured after a single dose of CRF (2 nmol) in rats under the same experimental conditions. While CRF decreased LH concentrations in anesthetized proes...

N-methyl-D,L-aspartate elicits hypothalamic gonadotropin-releasing hormone release in prepubertal male rhesus monkeys (Macaca mulatta).

Abstract: In higher primates, the protracted delay from infancy to puberty results from an interruption in hypothalamic GnRH release. To determine whether the quiescent hypothalamic GnRH neurons of the prepubertal macaque are capable of discharging the decapeptide in response to a generalized neural depolarization, an excitatory amino acid analog, N-methyl-D,L-aspartate (NMA), was administered systemically to orchidectomized rhesus monkeys between 13 and 20 months of age. GnRH secretion was estimated indirectly by monitoring changes in circulating LH concentrations after the responsivity of pituitary gonadotropes to GnRH had been greatly facilitated by the chronic intermittent iv infusion of GnRH (0.1 microgram/min for 3 min every hour). The iv bolus administration of increasing doses of NMA (1.5, 4.8, and 15.0 mg/kg BW), 10-14 h after termination of the priming infusion of GnRH, elicited distinct discharges of LH, with magnitudes directly related to the amount of the excitant injected. Administration of a higher dose of NMA (48 mg/kg BW), however, failed to induce further LH release. The finding that pretreatment with a long-acting and potent GnRH receptor antagonist [( AcD2Nal1,4ClPhe2,DTrp3,DArg6,DAla10] GnRH-HOAc) abolished the LH-releasing activity of NMA provides compelling evidence for the view that the action of the neural excitant to induce gonadotropin release was exerted at a suprapituitary level. The additional observation that an N-methyl-D-aspartate receptor antagonist (D,L-2-amino-5-phosphono-valeric acid) blocked the NMA-induced release of GnRH suggests that the amino acid analog interacted with the N-methyl-D-aspartate receptor on neurons that synthesize and/or control the release of the hypothalamic hormone. Most interestingly, three sequential GnRH discharges, with a period and an amplitude apparently similar to those generated by the hypothalamus of the adult, were elicited from the brain of prepubertal monkeys by the sequential administration of three injections of NMA at hourly intervals. Taken together these findings demonstrate that the apparent dormancy of hypothalamic GnRH neurons, which is characteristic of prepubertal development in higher primates and underlies the protracted delay in the onset of puberty in these species, may be readily terminated by application of a generalized neural excitation. Plasma FSH, PRL, GH, and cortisol concentrations were also monitored during the course of some of these experiments, and release of each of these four hormones was observed after the iv injection of NMA (15 mg/kg BW).

Afferent and efferent connections of the A5 noradrenergic cell group in the rat.

Abstract: The supraspinal afferent and efferent connections of the A5 noradrenergic cell group were examined in rats. Very small deposits of HRP-WGA were made in the rostral A5 area. Catecholamine histofluorescence techniques were used to confirm that the deposits overlapped the A5 column. Retrogradely labeled cells were present in the perifornical area and paraventricular nucleus of the hypothalamus, the Kolliker-Fuse nucleus, dorsal parabrachial area, intermediate and caudal portions of the nucleus of the solitary tract, and the ventral medullary reticular formation in the areas of the A1 and B1 cell groups. Anterograde HRP-WGA labeling was found in several areas of the subcortical CNS. The contribution of A5 neurons to this labeling was confirmed with retrogradely transported fluorescent latex microspheres combined with catecholamine histofluorescence techniques. The A5 cell group was found to have significant projections to the central nucleus of the amygdala, perifornical area of the hypothalamus, midbrain periaqueductal gray, parabrachial area, and the nucleus of the solitary tract. Other A5 projections include the paraventricular nucleus of the thalamus, the bed nucleus of the stria terminalis, and possibly the zona incerta and lateral and dorsal hypothalamic areas. In addition, A5 neurons may innervate the ventrolateral reticular formation of the medulla. Virtually all of the areas innervated by A5 noradrenergic neurons are involved in cardiovascular regulation. In addition, the A5 area receives afferent input from major cardiovascular regulatory centers of the supraspinal CNS. Thus the A5 cell group has the potential to exert a significant influence on the cardiovascular regulatory system.

Morphological analysis of the tuberomammillary nucleus in the rat brain: delineation of subgroups with antibody against L-histidine decarboxylase as a marker.

Abstract: With an antibody specific for L-histidine decarboxylase (HD) in combination with immunohistochemical techniques and retrograde fluorescent tracing, the morphology, distribution, and projections of the histamineragic neurons of the posterior hypothalamus were studied in the adult male rat. Magnocellular neurons, situated on both sides of the mammillary recess and close to the ventral surface of the brain rostral and caudal to the mammillary bodies, were found to contain HD-immunoreactivity (HD-i). In addition to these magnocellular neurons, a substantial number of small and medium-sized neurons were immunostained, as were strands of cells of all sizes bridging the HD-i cell groups: A detailed mapping of the HD-i cells in frontal, sagittal, and horizontal sections showed that these neurons make up one continuous cell group, defined as the tuberomammillary nucleus (TM). This nucleus can be divided into several subgroups. Thus, approximately 600 HD-i neurons situated on each side of the mammillary recess compose the medial subgroup of the TM (TMM). The ventral subgroup of the TM (TMV) consists of some 1,500 neurons situated at the ventral surface of the brain, rostral (TMVr) and caudal (TMVC) to the mammillary bodies. The TMM contains a greater proportion of parvicellular neurons compared to the TMV. About 100 HD-i cells are scattered within the lateral hypothalamic area, the posterior hypothalamic region, the perifornical area, the supramammillary nucleus, and the dorsomedial hypothalamic nucleus. These cells are collectively named the diffuse part of the TM (TMdiff). The morphological differences between the TMM and the TMV did not signal differences in the efferent connections of these subgroups. Thus, single injections of the fluorescent tracer Fast Blue into different regions of the brain, including the spinal cord, resulted in retrograde labeling of HD-i neurons, which were distributed throughout the TM with no discernible topographic pattern. More specifically, each subgroup of the TM contributed projections innervating or passing through a large number of brain regions, including the olfactory bulb, hippocampus, caudate nucleus, paraventricular and supraoptic nuclei of the hypothalamus, cerebellum, tectum, medulla, and spinal cord. The widespread projections of the HD-i neurons contrasted to the more specific projections observed from non HD-i neurons in cell groups situated around the TM. Taken together, these findings suggest that the HD-i cells of the posterior hypothalamus constitute one major nucleus, the TM, and that this nucleus may be subdivided into three components, each of which has diffuse projections throughout the neuraxis.

Further evidence for a central stimulatory action of catecholamines on adrenocorticotropin release in the rat.

Abstract: Catecholamines may stimulate ACTH secretion during stress. To investigate the nature and site of such an action, plasma ACTH was measured in four groups of unanesthetized adult female rats with an indwelling carotid cannula. Sequential 300-microliter blood samples were taken 60 min, 30 min, and immediately before an intracerebroventricular (icv) infusion of 2.5 microliter adrenaline or noradrenaline and 5, 15, 45, 60, and 120 min after the infusion. The four groups were: 1) intact rats; 2) rats infused 7 days after undergoing a discrete bilateral lesion of the ventral noradrenergic ascending bundle caused by 6-hydroxydopamine, which depleted their hypothalamic adrenaline and noradrenaline levels by 90% and 80%, respectively; 3) rats infused 30 min after pretreatment via the icv route with either prazosin or propranolol; and 4) rats infused 16 and 2 h after two successive intracarotid injections of an anti-rCRH-41 serum. In another group, the effects of icv catecholamine administration were compared with those of an intracerebral (ic) microinfusion close to a single paraventricular nucleus (PVN). Finally, in two additional groups blood was sampled at the above-mentioned times before and after a 2-min ether inhalation by intact rats or prazosin- and/or propranolol-pretreated rats. In the intact rats (group 1), a stress-like stimulatory dose response was noted after both adrenaline and noradrenaline infusions, with a half-maximal effect at concentrations of about 0.6 nmol and a maximal effect at 2.7 nmol or more. At maximally effective doses, adrenaline was significantly more active than noradrenaline. In the rats with ventral noradrenergic ascending bundle lesions (group 2), 2.7 nM adrenaline or noradrenaline stimulated ACTH release as in the controls without lesions. In group 3, prazosin blocked the ACTH responses to both adrenaline and noradrenaline, whereas propranolol only blocked the response to adrenaline. In group 4, i.e. rats pretreated with an anti-rCRH-41 serum, the amplitude of the ACTH surge after icv adrenaline or noradrenaline infusion was halved. A unilateral ic catecholamine microinfusion next to the PVN (half the icv dose given in group 1) led to a rapid ACTH release that peaked at half the response measured in the icv infused rats. Ether stress-induced ACTH release was decreased by 50-60% after icv pretreatment with 1 or 10 micrograms prazosin, 1 or 6.5 micrograms propranolol, or a combined dose comprising 1 microgram of both. The following conclusions were reached.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenalectomy-induced enhancement of CRF and vasopressin immunoreactivity in parvocellular neurosecretory neurons: anatomic, peptide, and steroid specificity

Abstract: Following adrenalectomy (ADX), corticotropin-releasing factor (CRF) and vasopressin immunoreactivity are jointly expressed by a population of parvocellular neurosecretory neurons in the paraventricular nucleus of the hypothalamus (PVH) Because these cells stain positively for CRF, but not for vasopressin, after pretreatment with colchicine, the results suggest the existence of state-dependent alterations in the expression of peptides by neuroendocrine neurons The present study sought to determine whether other neuropeptides (eg, neurotensin, met- enkephalin) that have been colocalized with CRF in the parvocellular division of the PVH are influenced similarly by ADX; whether the enhancement of CRF and/or vasopressin immunoreactivity after ADX is limited to neurons of the PVH; and what factors might be involved in the regulation of the expression of these peptides in the PVH The results confirmed that CRF and vasopressin immunoreactivity are both enhanced, and may be colocalized in a substantial population of parvocellular neurosecretory neurons after ADX; no comparable enhancement of staining for met-enkephalin or neurotensin was observed The effect of ADX on CRF immunoreactivity was not limited to cells in the PVH, as neurons in the cerebral cortex, amygdala, and the bed nucleus of the stria terminalis also showed heightened CRF immunostaining after ADX; vasopressin immunoreactivity was never colocalized with CRF in these extrahypothalamic sites Hypophysectomy produced an enhancement of CRF and vasopressin staining in the PVH that was comparable to that seen after ADX, implicating adrenal steroids as primary regulators of peptide expression in this system Corticosteroid replacement studies in ADX rats indicated that lower doses of dexamethasone attenuated, and higher doses essentially abolished, the expected enhancement of both CRF and vasopressin immunoreactivity after ADX The relative potency of steroids in mitigating these effects was dexamethasone greater than corticosterone greater than deoxycorticosterone greater than aldosterone Collectively, these results indicate that the ADX-induced enhancement of CRF and vasopressin immunoreactivity in parvocellular neurosecretory neurons is at least somewhat specific to these peptides and to this cell type Both peptides would appear to be regulated similarly by adrenal steroids, with glucocorticoids playing a primary role

Cholecystokinin and gastric distension activate oxytocinergic cells in rat hypothalamus

Abstract: Systemic administration of cholecystokinin octapeptide (CCK-8) prompts an abrupt increase in circulating levels of oxytocin (OXY) but not vasopressin (VP) in rats. The present study determined whether CCK-8 selectively stimulated OXY-secreting neurons in the hypothalamic supraoptic nucleus of pentobarbital-anesthetized male rats. Antidromically identified neurosecretory neurons were categorized into putative OXY- and VP-secreting cells on the basis of their firing patterns and response to peripheral baroreceptor activation. Of 36 OXY-secreting cells studied, 30 demonstrated a 50-200% increase in firing frequency within 2 min of administering CCK-8 by intravenous or intraperitoneal injection, whereas none of the eight VP-secreting neurons studied was activated. In related experiments, 4-10 ml of air were used to inflate an intragastric balloon in rats; 20 of 22 OXY-secreting neurons displayed an abrupt and readily reversible increase in firing frequency, whereas only 2 of 17 VP-secreting cells were activated. Gastric distension similarly elevated plasma OXY levels in unanesthetized rats with indwelling gastric cannulas. Together with previous findings that the effects of CCK-8 on OXY release were attenuated by gastric vagotomy, these observations clearly demonstrate the existence of a sensitive neural link between the stomach and the neurohypophysis in the rat.

Corticotropin-releasing factor administration elicits a stress-like activation of cerebral catecholaminergic systems

Abstract: The cerebral content of the biogenic amines, dopamine (DA), norepinephrine (NE), and serotonin (5-HT) and their catabolites 30 min after CRF or saline injections was determined using HPLC with electrochemical detection. Injection of CRF (1.0 μg) into the lateral ventricles (ICV) of mice produced a behavioral activation in which their motor movements appeared as bursts of activity followed by periods of immobility. CRF administration (ICV or SC) did not alter the concentrations of DA, NE, tryptophan, 5-HT, or 5-hydroxyindoleacetic acid (5-HIAA) in any brain region measured. ICV CRF increased the concentrations of dihydroxyphenylacetic acid (DOPAC), the major catabolite of DA, and of 3-methoxy,4-hydroxyphenylethyleneglycol (MHPG), the major catabolite of NE, in several brain regions. DOPAC:DA ratios were consistently increased in prefrontal cortex, septum, hypothalamus, and brain stem relative to animals injected with saline. MHPG:NE ratios were also increased in the prefrontal cortex and hypothalamus, with a marginal effect (p=0.06) in brain stem. SC CRF significantly increased DOPAC:DA in prefrontal cortex, and MHPG:NE in prefrontal cortex, hypothalamus and brain stem. Pretreatment with naloxone did not prevent any of the neurochemical responses to ICV CRF, but naloxone alone increased DOPAC:DA in medial profrontal cortex, and decreased MHPG:NE in nucleus accumbens in CRF-injected mice. These results suggest that administration of CRF either centrally or peripherally induces an activation of both dopaminergic and noradrenergic systems in several regions of mouse brain. The pattern resembles that we observe in mice following stressful treatments such as footshock or restraint, but the effect of CRF on noradrenergic systems is less pronounced. Also, brain free tryptophan which is consistently increased in all brain regions by footshock or restraint was not altered by CRF. Thus CRF triggers a response in CNS catecholamine systems that resembles, but does not precisely mimic, that observed following commonly used stressors. This activation of CNS catecholamine metabolism may be related to some of the behavioral effects of CRF, but not all of them because naloxone, which prevents the effects of CRF on exploratory behavior, did not alter the catecholamine responses to CRF.

Thyroid hormones regulate levels of thyrotropin-releasing-hormone mRNA in the paraventricular nucleus.

Abstract: Cellular levels of messenger RNA encoding thyrotropin-releasing hormone (TRH) were measured in the paraventricular nucleus of the hypothalamus and the reticular nucleus of the thalamus in male rats after chemical thyroidectomy and thyroid hormone replacement. TRH mRNA levels were measured by quantitative in situ hybridization histochemistry using a 35S-labeled synthetic 48-base oligodeoxynucleotide probe and quantitative autoradiography. Chemical thyroidectomy, produced by the administration of 6-(n-propyl)-2-thiouracil (PrSur), reduced plasma thyroxine below detection limits and significantly increased TRH mRNA in the paraventricular nucleus. Treatment with exogenous L-triiodothyronine (T3) reduced TRH mRNA to the same level in both hypothyroid and euthyroid animals. Neither PrSur treatment nor T3 replacement influenced TRH mRNA levels in the reticular nucleus of the thalamus. Blot hybridization analysis of electrophoretically fractionated total RNA from pituitaries of these animals indicated that thyrotropin-beta mRNA levels were elevated after thyroidectomy and reduced by T3 treatment, showing that the pituitary-thyroid axis was indeed stimulated by PrSur treatment. These results suggest that thyroid hormones are involved, either directly or indirectly, in regulating the biosynthesis of TRH in the thyrotropic center of the hypothalamus.

Organization of galanin-immunoreactive inputs to the paraventricular nucleus with special reference to their relationship to catecholaminergic afferents.

Abstract: Immunohistochemical and axonal transport techniques were used to characterize the origin and distribution of galanin-immunoreactive inputs to the paraventricular (PVH) and supraoptic (SO) nuclei of the hypothalamus in the rat. In the parvicellular division of the PVH, the most prominent inputs were confined to the anterior and periventricular parts of the nucleus rostrally and the dorsal and ventral medial subdivisions caudally; the galaninergic inputs to the magnocellular division of PVH and SO were very sparse and were preferentially distributed to regions containing predominantly oxytocinergic neurons. A combined retrograde transport-immunohistochemical method was employed to identify sources of these projections. Galanin immunoreactivity was found to coexist with dopamine-beta-hydroxylase (DBH) immunoreactivity in subsets of retrogradely labeled neurons of the A1 and A6 (locus coeruleus) catecholamine cell groups; no evidence was adduced for the presence of galanin in adrenergic (i.e., phenylethanolamine-N-methyltransferase-positive) neurons that project to the PVH. Apart from minor contributions from the mesencephalic raphe nuclei, no other brainstem cell groups contributed to the galaninergic innervation of the PVH. In the forebrain, the most prominent grouping of doubly labeled cells was centered in the rostral part of the dorsomedial nucleus of the hypothalamus (DMH), though significant numbers were also found in the lateral hypothalamic area, the arcuate nucleus, and the medial preoptic area. In experiments designed to define the subnuclear specificity of some galanin-containing inputs to the PVH, iontophoretic deposits of the anterogradely transported plant lectin, Phaseolus vulgaris-leucoagglutinin (PHA-L), were placed in the A1 and A6 cell groups and in the DMH. Sections through the PVH were prepared so as to allow colocalization of anterogradely transported PHA-L and galanin immunoreactivity in individual fibers and varicosities. Consistent with the retrograde transport data, the greatest degree of galanin-PHA-L correspondence was seen after lectin deposits in the DMH, and over 80% of the doubly labeled varicosities were confined to the anterior, periventricular, and medial parvicellular subdivisions of the nucleus. The galanin-containing projection from the locus coeruleus was most circumscribed, with the vast majority of doubly labeled varicosities confined to the periventricular and adjoining aspects of the anterior and medial parvicellular subdivisions.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y stimulates the release of luteinizing hormone-releasing hormone from medial basal hypothalamus in vitro: modulation by ovarian hormones.

Abstract: These studies investigated the effects of neuropeptide Y (NPY) on in vitro release of luteinizing hormone-releasing hormone (LHRH) from the medial basal hypothalmus (MBH) and tested whether ovarian st

Changes in hypothalamic preproenkephalin A mRNA following stress and opiate withdrawal.

Abstract: The median eminence of the pituitary is rich in opioid receptors, and exogenous opioids have major effects on the release of adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), prolactin, growth hormone (GH) and thyrotropin. Stress results in similar changes in anterior pituitary hormone secretion. Enkephalin immunoreactivity has been reported in the medial parvocellular neurons of the hypothalamic paraventricular nucleus which project to the median eminence, the site where hypothalamic releasing factors are secreted into the portal blood and thence to the anterior pituitary gland. The endocrine response to stressful stimuli might therefore, at least in part, be mediated through the activation of hypothalamic enkephalinergic neurons. We show that two stressful stimuli, opiate withdrawal and intraperitoneal injection of hypertonic saline, both result in very rapid and marked increases in enkephalin mRNA in the parvocellular paraventricular nucleus. The activation of hypothalamic enkephalin neurons may be important in the neuroendocrine response to stress.

The mammalian GnRH gene and its pivotal role in reproduction.

Abstract: Publisher Summary The key regulatory brain peptide controlling reproduction in mammals and sub-mammalian vertebrate species is the decapeptide luteinizing hormone-releasing hormone (LHRH), also called gonadotropin-releasing hormone (GnRH). This peptide, synthesized in and secreted from hypothalamic neurosecretory cells, stimulates the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from pituitary gonadotrophs. The miniscule amounts of GnRH in hypothalamus as well as its modified N- and C-termini made its isolation and structural determination a monumental task. This chapter explains the structure and restriction map of the human and rat GnRH-GAP gene. The description of the gene structure and the GnRH precursor sequence has aided in the investigation of GnRH gene expression in various parts of the mammalian organism. Using mainly immunological procedures, it has been found that GAP and GnRH are produced in a surprisingly large number of tissues. They occur in varying amounts in placenta, mammary tissue, gonads, kidney, as well as in certain extra-hypothalamic parts of the central nervous system.