Comparative immunohistochemical study of the distribution of neuropeptide Y, growth hormone-releasing factor and the carboxyterminus of precursor protein GHRF in the human hypothalamic infundibular area

It is now well documented that various polyclonal antisera to the human growth hormone-releasing factor (hGHRF, somatocrinin) visualize in the brain by immunohistochemistry the classical hypothalamic hypophysiotropic neurons and also antigens present in otherwise characterized peptidergic neuronal systems. The nature of these antigens is still an open question. One of these hGHRF antisera, raised against an immunogen of hGHRF1-44NH2, labels in the arcuate nucleus of the human mediobasal hypothalamus the neuropeptide Y (NPY) containing neurons which for the most part constitute a tuberoextrainfundibular system. The identity of the hGHRF-like substance present in these neurons with true somatocrinin has been assessed by performing a comparative immunohistochemical study including sequential double and triple labeling using the antiserum to hGHRF1-44NH2 in conjunction with antisera to the carboxyterminus of preprosomatocrinin (CTPG) and to NPY. This made it feasible to dissociate the hGHRF1-44NH2-immunoreactive neurons into two major subpopulations costaining either for CTPG of NPY, and a minor neuronal group displaying simultaneously the three labelings. A subset of arcuate neurons also showed NPY staining only. These results suggest that (1) the hGHRF-like antigen present in the majority of the NPY neurons is not true somatocrinin, or alternatively that preprosomatocrinin undergoes a unique maturational processing in these neurons, and (2) a subset of tuberoinfundibular somatocrininergic neurons produces and releases NPY which may be involved in the multifactorial control of the pituitary function.

Ultrastructural characterization of prolactin-like immunoreactivity in rat medial basal hypothalamus

Prolactin-like immunoreactivity has been reported in the medial basal hypothalamus at the light microscopic level, in hypophysectomized rats. Here, with preembedding immunocytochemistry at the electron microscopic level, we have observed prolactin-immunoreactive neurons and synapses in the hypothalamus. Reaction product was discovered in medial basal hypothalamic neurons, which had typical large nucleoli and received axosomatic synapses. In the cytoplasm, reaction product was distinctly granular. Immunoreactive neurons were usually surrounded by nonreactive cells. Reaction product was also seen in dendrites, some of which had spines. Some axons in the hypothalamus contained reaction product, usually surrounded by nonreactive axons, and immunopositive synapses were detected both in the hypothalamus and in the midbrain. In a small number of cases immunoreactive axons could be seen synapsing on immunoreactive dendrites.

[Serotonin contents in the hypothalamus of adult males, females and males castrated during the neonatal period]

The aim of the present work was to study the character of the change in serotonin level in the anterior and medial basal hypothalamus of adult rats after the effect of testicular hormones had been switched off on the first day of postnatal life. It was shown in our work that in males serotonin level was significantly lower than that in females by 67 and 46% in the anterior and medial basal hypothalamus, respectively. Castration of newborn males resulted in a significant increase in serotonin level in both anterior and medial basal hypothalamus-up to the level observed in females. It is supposed that the male sex hormones affect differentiation of serotoninergic system of the brain.

Localization of luteinizing hormone-releasing hormone in the forebrain of the pig

The distribution of luteinizing hormone-releasing hormone (LHRH)-immunostained perikarya and processes was examined in the forebrains of six sexually mature female pigs by use of indirect biotin-avidin horseradish peroxidase immunocytochemistry. Two primary antisera (Drs. Y.F. Chen and V.D. Ramirez CRR11B73 and Miles-Yeda UZ-4) yielded positive staining. Adjacent sections treated either primary antiserum preabsorbed with LHRH or with normal rabbit serum substituted for primary antiserum lacked positive staining. The greatest proportion of LHRH-immunostained perikarya were found in the medial preoptic area adjacent to the organum vasculosum of the lamina terminalis. The LHRH-immunostained perikarya were also scattered rostrally in the diagonal band of Broca, and within the lateral hypothalamic area, paraventricular nucleus, periventricular zone, suprachiasmatic nucleus, and medial basal hypothalamus. LHRH-immunostained processes, which extended from the medial preoptic area, coursed either along the ventral surface to the median eminence or medially and ventrally along the third ventricular wall ventrally to the median eminence and caudally to the level of the mammillary bodies. Extrahypothalamic processes were located adjacent to the lateral ventricular floor and the third ventricle from the lateral septal area (stria terminalis) to the level of the habenular nucleus. LHRH-immunostained neurons were unipolar, bipolar, and multipolar. Close associations between individual LHRH-immunostained neurons were observed.

[Sexual dimorphism in the content of luliberin following deafferentation of the mediobasal hypothalamus]

Luliberin (LH-RH) was assayed radioimmmunologically in the hypothalamic fragments taken from male and female rats, intact or with isolated mediobasal hypothalamus. An increased amount of LH-RH was found in the fragments containing organum vasculosum of the lamina terminals (OVLT) and taken from intact males. LH-RH amount was negligible in isolated parts of hypothalamic fragments containing arquate nucleus of median eminence. OVLT of females was mu;ch richer with LH-RH than that of the males. The females though were characterized by a lower blood lutropin. The inhibitory influences on the secretion of LH-RH seem to be more obvious in intact males than in females.

Luteinizing hormone-releasing hormone (LHRH) neurons in the male and female rats at peripubertal period

Luteinizing hormone-releasing hormone (LHRH) neurons were immunohistochemically studied in rats of both sexes at peripubertal ages. The number of immunoreactive LHRH neurons (irLHRH neurons) was counted in the brain region from the level of the septum-preoptic area to the level of the rostral part of the infundibulum in colchicine-treated male and female rats at 30 and 60 days of age. At 30 days, irLHRH neurons were more numerous in male rats than females. At 60 days, the number of irLHRH neurons in female rats increased to the level of male rats of the same age. In non-colchicine-treated rats, the count of irLHRH neuron was quite low. The difference in the number of irLHRH neurons between colchicine-treated and non-treated rats may be regarded as the activity of LHRH system. The difference in the number of irLHRH neurons was larger in male rats than in female rats at 30 days of age. On the contrary, at 60 days of age, the difference was larger in females than in males. LHRH contents were measured in the preoptic-anterior hypothalamic area (POA-AH), where LHRH neuronal perikarya are mainly located, and in the mid-hypothalamic area. LHRH content of the POA-AH in male rats at 60 days of age was not significantly different from that at 30 days of age. While, LHRH content in the POA-AH was greater in 60-day-old female rats at proestrous morning than that in 30-day-old females. At 30 days of age, male rats tended to contain more LHRH in the POA-AH than female rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired growth hormone secretion in neonatal hypothyroid rats: hypothalamic versus pituitary component

In 10-day-old rats made hypothyroid by giving dams propylthiouracil (PTU) in the drinking water since the day of parturition, simultaneous radioimmunoassay (RIA) determinations of basal and stimulated growth hormone (GH) secretion, hypothalamic GH-releasing hormone (GHRH)-like immunoreactivity (LI) content, immunocytochemical localization of somatotrophs, and hypothalamic GHRH-LI-positive structures were performed. The frequency of somatotrophs was also determined. One-day-old hypothyroid rats, whose mothers had been given PTU since the 14th day of pregnancy, were also used for comparison. In 10-day-old hypothyroid rats, pituitary and plasma GH levels and the number of somatotrophs were considerably lower and plasma TSH levels were significantly higher than those in age-matched control rats; however, GHRH-LI titers in the mediobasal hypothalamus and the morphology of GHRH-LI-positive structures were unaltered. In 1-day-old rats the only alteration present, in addition to elevated plasma TSH levels, was a clear-cut decrease in plasma GH levels. An acute challenge with GHRH (20 ng/100 g body wt, sc) or clonidine (15 micrograms/100 g body wt, sc) induced a clear-cut rise in plasma GH levels 15 min postinjection in 10-day-old control rats but failed to do so in age-matched hypothyroid rats. Both compounds failed to rise plasma GH in both hypothyroid and control 1-day-old rats. Taken together these data indicate that in neonatal and infant rats deprivation of thyroid hormones acts primarily to depress pituitary somatotroph function and that possible changes in GHRH-secreting structures represent a later postnatal event.

Pituitary receptors for GnRH and estradiol, and pituitary content of gonadotropins in beef cows. II. Changes during the postpartum period

Pregnant beef heifers (n = 24) were assigned randomly to four groups and slaughtered at day 1, 15, 30 or 45 postpartum. The day prior to slaughter blood samples were taken from each cow every 15 min for 8 hr. The anterior pituitary gland, preoptic area (POA) and medial basal hypothalamus (HYP) were collected from each cow. Contents of gonadotropin-releasing hormone (GnRH) in extracts of POA and HYP, and luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in extracts of anterior pituitary were quantified by radioimmunoassay. In the anterior pituitary gland, membrane receptors for GnRH were quantified by a standard curve technique and cytosolic receptors for estradiol were quantified by saturation analysis. Concentrations of LH, FSH and prolactin in serum were quantified by radioimmunoassay. Only one cow of eight had a pulse of LH during the 8 hr bleeding period on day 1 postpartum. This increased to 8 pulses in 6 cows on day 30 postpartum. Contents of GnRH in POA (15.0 +/- 3.2 ng) and HYP (14.0 +/- 2.0 ng) did not change significantly during the postpartum period. Pituitary content of LH was low following parturition (.2 +/- .1 mg/pituitary) and increased significantly through day 30 postpartum (1.2 +/- .1 mg/pituitary). Pituitary content of FSH did not change over the postpartum period. Receptors for both GnRH (.9 +/- .2 pmoles/pituitary) and estradiol (5.0 +/- .9/moles/pituitary) were elevated on day 15 postpartum, possibly increasing the sensitivity of the anterior pituitary gland to these hormones and leading to an increased rate of synthesis of LH that restored pituitary content to normal by day 30 postpartum.

The effect of hypothalamic deafferentation on rat growth hormone-releasing factor (rGRF)-like immunoreactivity content in the medial basal hypothalamus of rats

Rat growth hormone releasing factor (rGRF)- and somatostatin (SRIF)-like immunoreactivities (LI) were determined by radioimmunoassay in the medial basal hypothalamus (MBH) of the rat with either complete deafferentation (CD) or a sham operation. Two weeks after the surgery the mean amount of SRIF-LI in the isolated MBH was about 70% less than that in the sham-operated animals. On the other hand, the mean rGRF-LI in the MBH decreased only approximately 30% as compared to the levels in the sham-operated animals, the difference being statistically insignificant. These findings are consistent with anatomical evidence that the majority of the GRF perikarya are located in the arcuate nucleus, but a few are found outside the MBH, whereas the majority of the SRIF perikarya are located outside the MBH.

A model for combined morphological and functional investigations on the isolated mediobasal rat hypothalamus

We have developed a model for combined morphological and functional in vitro studies of the isolated mediobasal hypothalamus (MBH) by considering two prerequisites: (1) the tissue must be well preserved, free of morphological artefacts and functionally unimpaired until the end of the in vitro incubation, and (2) the tissue must be processed for morphology in optimal conditions. To test our model we have studied some aspects of the luteinizing hormone-releasing hormone (LHRH) system in 4-month-old male Sprague-Dawley rats. After decapitation the MBH was isolated and put in a flask containing 0.5 ml Hepes-buffered Locke's medium gassed by 5 ml/min of O2/CO2 (95%/5%) and shaken in a water bath at 37 degrees C. After a 10-min washing, the medium was changed twice at an interval of 20 min. After the in vitro incubation the tissue was satisfactorily preserved as judged by light- and electron-microscopic analysis. LHRH, somatostatin and thyrotropin-releasing hormone could be demonstrated by alkaline phosphatase or peroxidase-antiperoxidase immunohistochemistry on semithin sections and by immunogold technique on thin sections. The LHRH secretion was close to basal values after 30 min of incubation (22.1 +/- 4.8 pg/MBH) and then remained constant for another period of 20 min (17.6 +/- 2.6 pg/MBH). During the second 20 min of incubation LHRH secretion increased in presence of 61.6 mM K+ (110.7 +/- 8.7 pg/MBH). Thus the isolated hypothalamus was excitable until the end of the in vitro incubation. We conclude that this model can be successfully used for combined morphological and functional studies.

Morphological evidence that luteinizing hormone-releasing hormone neurons participate in the suppression by estradiol of pituitary luteinizing hormone secretion in ovariectomized rats

Morphological characteristics of LHRH neurons identified by immunocytochemistry were studied using light and electron microscopy in female rats in which estradiol was replaced at the time of ovariectomy ('pseudo-intact' rats) or 3 weeks after ovariectomy (long-term ovariectomized, estradiol-treated). While estradiol levels were equivalent in these two groups, the rise in LH after ovariectomy was prevented by the immediate administration in the pseudo-intact rats, while the augmented plasma LH levels present three weeks following ovariectomy were only reduced by 50% as a result of delayed estradiol treatment. The LHRH content of the medial basal hypothalamus (MBH) including the median eminence (ME) was greater in pseudo-intact females than in untreated long-term ovariectomized control females or long-term ovariectomized, estradiol-treated females, both 1 and 14 days after estradiol exposure. Immunocytochemistry revealed fewer LHRH-immunopositive neuronal processes coursing throughout the MBH and terminating in the ME of long-term ovariectomized, estradiol-treated rats compared to those in pseudo-intact rats. However, within individual neurovascular terminals in the ME, image analysis revealed that the area of reaction product was greater in long-term ovariectomized, estradiol-treated animals. Equivalent amounts of LHRH were assayed in the MBH within each group of animals by several LHRH antisera regardless of their different binding requirements (R42, IJ29 and A-R743), suggesting that the predominant moiety present in neuronal terminals is the fully mature decapeptide. In contrast, in the preoptic area-anterior hypothalamus (POA-AH) these antisera assayed amounts of LHRH that varied as a function of binding characteristics, although the quantities did not vary with the estradiol treatment schedule. Immunocytochemical results paralleled these assay data; antisera requiring an interior sequence of amino acids (A-R743 and A-R419) detected approximately 3 times as many immunoreactive perikarya in the POA-AH as did an antiserum requiring the free amidated C terminal (IJ29). The estradiol treatment schedules had no effect on the total number of LHRH-immunopositive neurons detected by each antiserum or the distribution of LHRH-immunopositive neuronal perikarya. These data support the hypothesis that the predominant moieties present in neuronal cell bodies are precursor forms. The fine-structural characteristics of LHRH-immunopositive neuronal cell bodies are consistent with greater secretory and biosynthetic activity in LHRH neurons of long-term ovariectomized, estradiol-treated rats.(ABSTRACT TRUNCATED AT 400 WORDS)

The influence of suckling on the hypothalamic and pituitary secretion of immunoreactive alpha-melanocyte stimulating hormone

The effect of suckling on the secretion of alpha-melanocyte stimulating hormone (alpha-MSH) from the hypothalamus and pituitary was determined by a specific radioimmunoassay. There was an increase in the neurointermediate lobe (NIL) content of alpha-MSH 1 h after the onset of suckling. The values were restored to control levels within 3 h. The anterior lobe content of alpha-MSH was not affected by suckling. Plasma alpha-MSH levels were also unaffected by suckling, indicating that suckling probably affects the synthesis of NIL alpha-MSH, and not its release. Suckling lowered the alpha-MSH content in the mediobasal hypothalamus of lactating rats, and had no effect on the median eminence content of this peptide. In vitro, hypothalami from lactating rats released more alpha-MSH than hypothalami of random cycling females under basal, and stimulated (56 mM potassium) conditions. These results suggest that hypothalamic alpha-MSH may play a role in mediating some of the hormonal changes occurring during lactation.

Cholinergic agonist and antagonist drugs modulate the growth hormone response to growth hormone-releasing hormone in the rat: evidence for mediation by somatostatin

Recently, data have been presented showing that muscarinic cholinergic agonists or antagonists can modulate, in opposite ways, GH-releasing hormone GHRH)-induced GH release in man. The aim of the present study was, first, to confirm these findings in the rat and, secondly, if confirmed, to investigate the mechanism(s) subserving the effect of cholinergic drugs. In adult male rats bearing chronic indwelling atrial cannulae, pretreatment with the cholinergic antagonists pirenzepine (0.5 mg/kg, i.v.) or atropine (0.5 mg/kg, i.v.) significantly reduced the rise in plasma GH induced by GHRH (2 micrograms/kg, i.v.), while pretreatment with the cholinergic agonist pilocarpine (3 mg/kg, i.v.) potentiated it. In rats with hypothalamic somatostatin (SRIF) depletion, i.e. rats with anterolateral deafferentation of the mediobasal hypothalamus or rats treated with cysteamine, the modulatory action of cholinergic drugs on the neuroendocrine effect of GHRH was completely lacking. In these two experimental models, an antiserum raised against SRIF failed to elicit a rise in plasma GH and measurement of hypothalamic SRIF content revealed a clear-cut reduction of the neuropeptide. Atropine (1 mumol/l) and pilocarpine (1 mumol/l), added to pituitary cells in vitro, failed to alter GHRH-induced GH release. The present results indicate that muscarinic cholinergic agonists and antagonists modulate GHRH-induced GH release in the rat and suggest that the effect of cholinergic modulation takes place through SRIF.

Abbreviation of the period of sexual behavior in female guinea pigs by the progesterone antagonist RU 486

In previous studies we have tested the hypothesis that the termination of the period of sexual behavior in female guinea pigs results from the loss of progestin receptors from hypothalamic cell nuclei. We have shown that hormonal manipulations that delay heat termination also delay loss of hypothalamic nuclear progestin receptors. In order to determine if accelerated nuclear receptor loss results in abbreviation of the period of sexual behavior, we tested the effect of 17 beta-hydroxy-11 beta-(4-dimethylaminophenyl)-17 alpha-(1-propyl)-estra-4,9-diene-3-one (RU 486), a progesterone antagonist, on heat termination. Ovariectomized guinea pigs were treated with estradiol benzoate. Forty hours later, they received progesterone followed 4 h later by injection of RU 486 or vehicle. RU 486 injected 4 h after progesterone caused heat abbreviation. We have found that RU 486 administration to estradiol-treated guinea pigs causes accumulation of progestin receptors in cell nuclear extract. Because this accumulation can be detected only when assay conditions are used that promote exchange of RU 486 progestin receptor complexes (15 degrees C incubation rather than 0 degree C); our routine assay conditions (at 0 degree C) can be used to measure primarily receptors that are occupied by progesterone. In order to confirm that RU 486 decreased progesterone-occupied nuclear progestin receptor levels when injected 4 h after progesterone, animals treated as in the behavioral experiment were killed 6 or 10 h after progesterone injection (2 or 6 h after RU 486), and nuclear progestin receptor levels were measured. RU 486 treatment resulted in lowered nuclear concentrations of hypothalamic progestin receptors at both times. These results support our hypothesis that the termination of the period of sexual receptivity in female guinea pigs is the result of loss of progestin receptors from hypothalamic cell nuclei.

Hypothalamic localization of multiunit electrical activity associated with pulsatile LH release in the rhesus monkey

Abrupt increases in electrical activity can be recorded from the medial basal hypothalamus of the rhesus monkey and these bursts are correlated with a pulse of LH release from the anterior pituitary. In this study we have localized the tips of the electrodes from which such electrical activity can be recorded and have attempted to correlate the placement with the presence of immunoreactive LHRH neurons and axons. Electrodes associated with bursting activity were found as far rostral as the suprachiasmatic nucleus and as far caudal as the premammillary nuclei. The majority were found in the medial basal hypothalamus including the region of the arcuate nucleus, the retrochiasmatic zone and the dorsal aspect of the median eminence. The tips of the electrodes were associated with either LHRH neurons or axon bundles. Negative electrodes (those not associated with bursting electrical activity) which did not exit through the ventral surface of the brain nor enter the ventricle were found in the same regions of the hypothalamus as positive electrodes. Although it is tempting to associate the bursting electrical activity with the LHRH neurosecretory system, such a correlation cannot yet be made.

Hypothalamic LHRH in aging rats: effects of ovariectomy and steroid replacement

Hypothalamic LHRH was measured by RIA in young and middle-aged (MA) female rats in several endocrine conditions. Temporal alterations in LHRH content associated with the steroid induced gonadotropin surge were compared in medial basal hypothalamic and anterior hypothalamic-preoptic area fragments of ovariectomized young and MA subjects. LHRH content was also compared in ovariectomized, untreated subjects from the two age groups. Finally, LHRH content in MA constant estrous females was compared with content in young females on the morning of proestrus. In all conditions, LHRH levels in both brain regions of MA females were similar to, or significantly elevated above levels measured in young females, yet both the steroid induced surge and the castration induced hypersecretion of gonadotropins were markedly attenuated in aging females. Because studies have verified the responsiveness of the pituitary of MA rats to LHRH, the data suggest that adequate amounts of hypothalamic LHRH do not reach the pituitary. Rather, high levels of hypothalamic LHRH measured in MA subjects may represent accumulation of the peptide in LHRH neurons due to an age-related impairment in release.

Reduction of central epinephrine concentrations is consistent with the continued occurrence of ovulation in rats treated with an inhibitor (LY 134046) of phenylethanolamine N-methyltransferase

Groups of 4-day cyclic rats were injected (i.p.) with LY 134046 (50 mg/kg), a central inhibitor of phenylethanolamine N-methyltransferase, or saline at 09.00, 13.00 and 19.00 h on the day of proestrus. The incidence of ovulation was examined the following estrous morning. There was no difference in the number of ova in drug-treated animals compared to saline-treated controls. In other groups of 4-day cyclic rats, LY 134046 or saline was injected daily at 10.00 h for 5 consecutive days from proestrus to proestrus inclusive. The animals were decapitated the following day and ova were counted. Epinephrine concentrations were determined by radioenzymatic assay in the mediobasal hypothalamus (MBH) and the medial preoptic area (MPOA). All saline-treated controls and 10/14 of the drug-treated animals had ovulated, while epinephrine concentrations in the MBH and MPOA had been reduced by 95.8 and 94.7%, respectively, compared to saline-treated controls. These experiments suggest that a significant surge of luteinizing hormone occurs to initiate ovulation even after a severe reduction in central epinephrine concentration has taken place.

Changes in anterior pituitary hormone secretion and hypothalamic catecholamine metabolism during morphine withdrawal in the female rat

Studies were undertaken to evaluate the acute responses of hypothalamic noradrenergic and dopaminergic neurons and anterior pituitary hormones to naloxone (NAL)-precipitated morphine (MOR) withdrawal in the rat. Ovariectomized female rats were rendered MOR-dependent and injected with NAL (1 mg/kg b.w., s.c.). During precipitated MOR withdrawal, a decline in norepinephrine (NE) concentrations was preceded by an increase in the level of its metabolite normetanephrine (NME) in the medial basal hypothalamus (MBH) as well as the preoptic area-anterior hypothalamus (POA-AH). Both dopamine (DA) and its major acid metabolite, dihydroxyphenylacetic acid (DOPAC), showed increased concentrations in these two hypothalamic regions within 30 min of NAL administration. Elevated luteinizing hormone (LH) and beta-endorphin secretion was evident within 5 min of NAL injection to MOR-dependent rats, while serum prolactin (PRL) increased 15 min into MOR withdrawal. Both growth hormone (GH) and thyroid-stimulating hormone (TSH) were depressed over the course of MOR withdrawal. Although a cause and effect relationship cannot be established, during NAL-precipitated MOR withdrawal, a heightened hypothalamic monoaminergic neuronal activity is accompanied by a differential response of anterior pituitary hormones. The observed responses, which are similar to those seen during acute stress, indicate that MOR withdrawal may activate the same mechanisms which mediate the neuroendocrine response to stress.

Characterization of proenkephalin B-derived opioid peptides in the human hypothalamo-neurohypophyseal axis

Proenkephalin B-derived opioid peptides, such as dynorphin1-17, dynorphin1-8, dynorphin B, alpha-neo-endorphin and beta-neo-endorphin in the human hypothalamo-neurohypophyseal tract were quantitated and characterized by the combined use of various radioimmunoassays, gel filtration, high performance liquid chromatography and enzymatic cleavage. Chromatographic analysis of immuno-reactive peptide levels determined that, in each case, these were comprised almost exclusively of the authentic peptides both in the neurohypophysis and hypothalamus. Concentrations of authentic proenkephalin B-peptides were 100-5000-fold lower in the human as compared to the rat neurohypophysis. However, in the paraventricular nucleus (PVN), supraoptic nucleus (SON) and certain other nuclei of the human hypothalamus concentrations of authentic peptides were found to be in the same range as those in the rat hypothalamus. The ratio of proenkephalin B-peptides in PVN and SON to those of the neurohypophysis in the rat was ca. 1:50. Conversely, in man these ratios were shown to be 80:1 for dynorphin B, 6:1 for alpha-neo-endorphin and 1:1 for all other peptides evaluated. Examination of postmortem degradation of peptides indicated that these lower levels in the neurohypophysis are not due to a higher rate of postmortem breakdown. Since levels of both vasopressin and beta-endorphin were very high, these deficits in proenkephalin B-peptides were selective and do not represent a generalized property of the human pituitary. Experiments involving enzymatic cleavage demonstrated the occurrence of higher molecular weight forms containing the Leu-enkephalin sequence which were not recognized by the antisera employed.(ABSTRACT TRUNCATED AT 250 WORDS)

Norepinephrine turnover in the hypothalamus of adult male rats: alteration of circadian patterns by semistarvation

Norepinephrine (NE) turnover, as estimated by 3-methoxy-4-hydroxyphenylethyleneglycol concentration, was studied in the mediobasal hypothalamus of control and semistarved adult male rats at eight time points of a 24-h period. The marked circadian periodicity of NE turnover with a peak in the dark phase in control rats is completely suppressed in semistarved rats. The average 24-h concentration of the NE precursor tyrosine in brain and of tyrosine flow into brain (calculated from plasma amino acid concentrations) is reduced in semistarved rats, but both brain tyrosine and tyrosine flow show continuing circadian fluctuations.

A possible physiological basis for the dud-stud phenomenon

Intact male rats were tested on two successive weekly tests with females to determine their level of sexual activity. Nuclear estrogen receptor content was measured in specific brain regions of individual sexually responsive and sexually nonresponsive males. Sexually nonresponsive male rats had significantly reduced nuclear estrogen receptor levels in the preoptic area compared to sexually responsive males. Sexually active males did not differ from inactive males in nuclear estrogen receptors in the medialbasal hypothalamus.

Effects of progesterone on hypothalamic and plasma LHRH

The hypothalamic action of progesterone on the regulation of LH secretion was investigated in a rat model ideally suited for the study of progesterone effects under conditions in which the animal is sensitive to progesterone but does not have an estrogen-induced gonadotropin surge. Immature female rats were ovariectomized at 26 days of age and treated for 4 days with a subphysiological dose of 0.1 microgram/kg/day estradiol followed by the injection of either 0.8 or 3.2 mg/kg progesterone at 9.30 a.m. on day 5. Serum LH levels were significantly depressed below control and pretreatment values 30 min after either dose of progesterone. At this time, 0.8 mg/kg progesterone administration resulted in a significant increase in MBH-LHRH and plasma LHRH levels. In contrast, the administration of the 3.2 mg/kg dose of progesterone did not result in an increase in MBH-LHRH levels. By 2 p.m., rats receiving 0.8 mg/kg progesterone, but not those receiving 3.2 mg/kg progesterone, showed a significant increase in serum LH concentration and this elevation was maintained at 4 p.m. The increase in serum LH levels was preceded by a rise in MBH-LHRH levels by 1 p.m., followed by a fall at 2 p.m. The LH rise was maintained during the rise and replenishment of the MBH-LHRH by 3 p.m. Between 2 and 3 p.m. the replenishment of MBH-LHRH levels was accompanied by a fall in POA-LHRH levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The masking of amine accumulation by catecholamine depletion

6-Hydroxydopamine (2 microliter of 8 micrograms/microliter) was injected bilaterally into the lateral hypothalamus of male Sprague-Dawley rats to produce depletion of forebrain terminal fields and an accumulation of amines proximal to the site of injection. Two additional groups of animals were injected with either vehicle or were food and water intake-matched to those receiving 6-hydroxydopamine. Motor performance, food and water intake and body weight were measured in all animals for 2 days before and 6 days after injection. Animals were then sacrificed and brain tissue was prepared for biochemical assay or fluorescence histochemistry. The area of hypothalamic tissue proximal to 6-hydroxydopamine injection, that which contains the amine accumulation, was sectioned from the surrounding tissue with a biopsy punch and assayed for noradrenaline and dopamine content. The nucleus caudatus-putamen, basomedial hypothalamus, and tissue containing the olfactory tubercle and accumbens nucleus were also assayed. Fluorescent histochemical examination of tissue showed that in addition to the depletion of catecholamines in various terminal fields there was also an increase in the fluorescent amine accumulation proximal to the injection site in the impaired animals. This accumulation was not detected with the biochemical assay and is probably due to the occurrence of a masking effect by adjacent depletions. A significant rise in noradrenaline levels was seen in the basomedial hypothalamus of intake-matched controls. However, this too was not detected in 6-OHDA-treated animals and was probably due to masking by adjacent depletions in these areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous opioid peptides and the control of the menstrual cycle

This paper reviews recent experimental evidence which supports a role for endogenous opioid peptides in the control of gonadotropin function. In primates, cell bodies containing endogenous opioid peptides have been located within the hypothalamus in areas rich in gonadotropin-releasing hormone (GnRH) and dopamine. The release of beta-endorphin from these hypothalamic neurons is influenced by gonadal steroids, maximal release being observed when both estradiol and progesterone are present. beta-Endorphin has been shown to decrease LH secretion, and naloxone, an opiate antagonist, reverses this action. The LH-releasing activity of naloxone parallels variations in hypothalamic beta-endorphin secretory activity, so that maximal effects are seen during the luteal phase of the cycle. Present evidence indicates that opiates exert their effect on LH via a hypothalamic site. It is concluded that increased opioid inhibition of the GnRH-LH axis is responsible for the decline in LH pulse frequency during the luteal phase. The studies provide evidence for a chemical basis rationalizing relationships between reproductive function and stress, and have further implication on other forms of amenorrhea.

Simultaneous determination of norepinephrine, dopamine, 5-hydroxytryptamine and their main metabolites in rat brain using high-performance liquid chromatography with electrochemical detection. Enzymatic hydrolysis of metabolites prior to chromatography

In order to measure turnover rates of the noradrenergic, dopaminergic, and serotonergic transmitter systems in rat brain, a method was developed by which norepinephrine, dopamine, and 5-hydroxytryptamine, and their main metabolites 3-methoxy-4-hydroxyphenylglycol, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylacetic acid, and 5-hydroxyindole-3-acetic acid, could be measured simultaneously. High-performance liquid chromatography in the reversed-phase mode, including ion pairing, separated the transmitters and their metabolites well. By means of enzymatic hydrolysis of the sample prior to chromatography, it was also possible to measure the conjugated forms of the metabolites. Since there was no prepurification step, the hydrolysed supernatants of tissue homogenates were injected directly into the chromatographic system; additional selectivity tests were necessary. Peak identification was confirmed by comparison of hydrodynamic voltagrams and capacity factors at different pH values of the mobile phase of the components in the sample and the standard solution. The method is demonstrated by analysing mediobasal hypothalamic tissues of probenecid-treated rats.

Differential sensitivity of estrogen target tissues: implications for estrogen regulation of serum luteinizing hormone

In the rat, it is generally accepted that the primary site of estrogen's stimulatory (positive) effects on serum LH is the preoptic area-anterior hypothalamus (POA/AH). In contrast, the primary site of estrogen's inhibitory (negative) effects on serum LH levels has not been conclusively identified. There is evidence to suggest both a medial basal hypothalamic (MBH) and an anterior pituitary site of action. The present studies utilized a unique characteristic of these estrogen effects to investigate their putative loci. Extensive dose-response curves of estrogen's induction of positive and negative feedback indicated that the negative feedback response was activated at a lower concentration of serum estradiol than the positive feedback response. The differential sensitivities of these two responses suggested that the tissues mediating them might also be differentially sensitive to estradiol. In a previous paper, we showed that receptor translocation is an index of estrogen sensitivity. We measured receptor translocation in response to a series of estradiol doses in the POA/AH, the MBH, and the pituitary. Dose-response curves for estrogen's effect on receptor translocation showed that the pituitary receptor translocation mechanism is activated at significantly lower levels of serum estradiol than that of either the POA/AH or the MBH. These results are consistent with the POA/AH as a site of estrogen's positive feedback effects. In addition, they suggest that negative feedback in the rat may be mediated via estrogen's action at the anterior pituitary. Estrogen's negative feedback effect on serum LH occurs at a serum level of estrogen at which no receptor is translocated in the MBH. Therefore, the pituitary, which does possess nuclear receptors at these estradiol dose levels, is more likely to be the primary mediator of estrogen's negative feedback effects. In another experiment, pituitary, but not hypothalamic, receptor was translocated to the nuclear fraction with an injection of 100 micrograms clomiphere (Clomid). Under these conditions serum LH is depressed, thus strengthening the hypothesis that, in the rat, estrogen action on the pituitary can cause suppression of serum LH independently of the hormone's action in the hypothalamus.

[Functional state of the frontal cortex and ventromedial hypothalamus during physical overexertion and experimental neurosis in the rabbit]

A change of excitability, pO2 and local cortical blood flow under a long-term maximum physical load and in conditions of experimental neurosis, was investigated in rabbits with electrodes implanted in the frontal cortex and ventromedial hypothalamus. It was found that functional activity of these structures under physical orverstrain rises as the blood flow and pO2 increase, and the excitability also increases. In experimental neurosis, a discoordination in functioning of the cortex and hypothalamus is observed. Relative stabilization of the functional state of tested structures, observed during physical overstrain, is absent in conditions of experimental neurosis.

Topographical and ontogenetic study of the neurons producing growth hormone-releasing factor in human hypothalamus

Neurons producing growth hormone-releasing factor have been characterized and analyzed by immunohistochemistry in the hypothalami of human fetuses, neonates, infants and adults, using two antibodies against human pancreatic GRF (hpGRF). One of the antibodies recognized both the hpGRF(1-40)OH and hpGRF(1-44)NH2 in the mid portion (between the 28th and 39th amino acid), the other one specifically recognized the C-terminal end of hpGRF(1-44)NH2. These two antibodies stain a single neuronal system with cell bodies mainly located in the infundibular (arcuate) nucleus, and in the ventromedial and lateralis tuber nuclei. These neurons project to the median eminence where they give numerous endings in contact with portal vessels. These neurons are distinct from those containing LH-RH, somatostatin, CRF or pro-opiocortin. In fetuses, neurons immunoreactive with hpGRF antibodies are first detected at the 29th week. They display a neuroblastic aspect which persists after birth. Immunoreactive fibers are detectable in the median eminence after the 31st week. These results demonstrate that the infundibular nucleus plays a major role in control of GH secretion in man and that secretion of GRF appears late during fetal life; this suggests that the first stages of differentiation and development of GH producing cells in the human fetus do not depend on hypothalamic GRF secretion.

Immunoreactive corticotropin-releasing hormone in the hypothalamoinfundibular tract

Ovine corticotropin-releasing hormone (CRF)-like immunoreactivity has been examined in the rat hypothalamus by light microscopy. Immunoreactivity was found in nerve fibers of the median eminence, mainly in the external zone around the portal vessels. In rats pretreated with colchicine or with hypothalamic knife cuts, small to moderate sized cells with two (bipolar) or rarely more (multipolar) dendrites, showing CRF-like immunoreactivity were present in the anterior and medial parvocellular subdivisions of the paraventricular nucleus. Scattered CRF-like immunopositive cells were found in the periventricular and medial preoptic nuclei. CRF-like immunoreactivity was clearly enhanced in the median eminence and paraventricular nucleus 8-10 days after bilateral adrenalectomy. A variety of hypothalamic transections had to be performed to determine reliably the topography of CRF-like nerve fibers projecting to the stalk-median eminence. Axons left the paraventricular nucleus in a lateral direction, turned ventrally in the lateral hypothalamus then medially as they approached the base of the hypothalamus above and behind the optic chiasm (lateral retrochiasmatic area). Fibers reached the median eminence by traveling caudally and medially from the rostral half of the lateral retrochiasmatic area. Scattered fibers were present in the retroinfundibular (posterior) portion of the median eminence. No immunoreactive fibers remained in the stalk-median eminence 1 or 4 weeks after transection of that loop-like pathway of CRF-containing fibers in the lateral retrochiasmatic area.

Effects of ovariectomy and steroid replacement on hypothalamic LHRH content in aging female rats

To examine the role of age on the hypothalamic LHRH response to ovariectomy (ovx) and steroid replacement, young cycling (3-4 months) and old constant estrous (18-20 months) rats were ovariectomized. Two weeks later, rats were treated for 5 days with estradiol benzoate (E, 5 micrograms/kg), progesterone (P, 10 mg/kg), E + P (5 micrograms E + 10 mg/kg) or corn oil, after which time they were killed for determination of hypothalamic LHRH content. The young and old ovx rats had similar levels of LHRH in the medial basal (MBH) and anterior (AH) hypothalamus, but E treatment was only effective in increasing MBH-LHRH content in the young animals. There was no significant effect of P alone or in combination with E. In the second experiment, similar results were seen using a single dose of E (1 microgram/rat) in young and old ovx rats. In addition, the radioimmunoassay of LHRH using two different antibodies binding to different portions of LHRH gave similar results in young and old rats, suggesting that the LHRH peptide was being processed similarly in the two age groups. In conclusion, it appears that hypothalamic LHRH content of young and old ovx rats does not differ with age despite a marked attenuation of serum LH levels with age. The hypothalamus from old rats, however, is less responsive to steroid stimulation of LHRH content.

Improved method for determination of catecholamines in rat brain by isolation on boric acid gel and high-performance liquid chromatography with electrochemical detection

An improved sensitive, simple and time-saving method for determining catecholamine (CA) in rat brain is described. The method involves isolation on boric acid gel and high-performance liquid chromatography with electrochemical detection. Boric acid gel effectively adsorbs CA at weakly alkaline pH and the over-all recoveries of 5 ng and 10 ng samples of authentic norepinephrine (NE) and dopamine (DA) added to a homogenate of rat brain were 98.9 +/- 9.2% and 103.4 %/- 9.3% for NE and 96.2 +/- 4.6% and 99.4 +/- 4.8% for DA, respectively. Intra-assay variation was 5.3% (5 ng) and 3.0% (10 ng) for NE and 4.4% (5 ng) and 3.8% (10 ng) for DA. Inter-assay variation was 7.7% (1 ng) for NE and 5.0% (1 ng) for DA. With this analytical system, the lowest amount of NE or DA detectable was 40 pg. Application of this method to determination of the DA and NE contents of rat hypothalamus during estrous cycle revealed significant increases in the turnovers of both in the proestrus stage. This method should be useful for routine determination of plasma NE and DA because it is sensitive and inexpensive.

Subcellular distribution of corticotropin-releasing factor in the medio-basal hypothalamus of the rat

Subcellular fractionation of the mediobasal hypothalamus (MBH) and frontal cerebral cortex was performed by differential and discontinuous sucrose gradient centrifugation. Corticotropin-releasing factor (CRF) activity of the different fractions was evaluated by bioassay. Significant CRF activity was found in acidic extracts of the MBH but not of the cerebral cortex. About 80% of the MBH effect on adrenocorticotropic hormone release was recovered in the crude mitochondrial pellet (P2) which contains synaptosomes. After further fractionation, distribution of CRF activity paralleled that of lactate dehydrogenase activity, a marker of the soluble cytoplasm. It is concluded that most CRF in the MBH is located in nerve endings as already shown for several other neurohormones.

[Gonadotropin releasing activity of different regions of rat brain and the probability of presence of a factor which inhibits it in the suprachiasmatic region]

The amount of gonadotropin-releasing hormone (Gn--RH) was measured in the preoptic area and in some parts of hypothalamus by radioimmunoassay. Maximal level was found in the median eminence next followed by that in the portions containing n. arquatus or retrochiasmatic area. The preoptic area contained less Gn--RH. The quantity of Gn--RH was negligible in the suprachiasmatic area. If tested in both supra- and retrochiasmatic areas simultaneously the amount of Gn--RH was much lower than in the retrochiasmatic area alone. Existence of inhibiting or inactivating factor in the suprachiasmatic fragment is suggested. The amount of Gn--RH was small in hypothalamic areas including n. paraventricularis, n. supraopticus, mamillary bodies. From among all the fragments tested the pineal body showed the lowest Gn--RH. There was no correlation between the serum LH concentration and the amount of Gn--RH in any investigated area except the preoptic one.

A diurnal rhythm of immunoreactive alpha-melanocyte-stimulating hormone in discrete regions of the rat brain

A significant diurnal variation in alpha-melanocyte stimulating hormone (alpha-MSH) concentrations was observed in discrete regions of the rat brain. During the 12 h light: 12 h dark cycle, alpha-MSH concentrations in each case were highest during the light period and lowest during the dark period. At 09.00 h, 3 h after lights were turned on, the peak alpha-MSH concentration occurred in the median eminence, the arcuate and dorsomedial hypothalamic nuclei and the periventricular thalamic nucleus. The paraventricular and anterior hypothalamic nuclei had highest alpha-MSH concentrations at 13.00 h. In the medial preoptic nucleus, the peak alpha-MSH concentrations appeared at 17.00 h. These changes in alpha-MSH content may reflect an alpha-MSH role in circadian variations in behavioral and neuroendocrine processes.

Models of neuroendocrine regulation: use of monosodium glutamate as an investigational tool

The administration of monosodium-L-glutamate (MSG) during the neonatal period is known to result in central nervous system lesions in the arcuate nucleus of the hypothalamus and the retina. Rodents so treated exhibit behavioral deficts and endocrinopathies including obesity, hypogonadism, hypothyroidism, pituitary atrophy, tail automutilation and diminished locomotor activity. Assessment of endocrine status revealed normal serum levels of glucagon, thyroid-stimulating hormone and luteinizing hormone, and diminished levels of thyroid hormones and growth hormone in MSG-treated rats. Prolactin levels were elevated in the glutamate-treated male rats. Within the brain hypothalamic levels of thyrotropin-releasing hormone, luteinizing hormone-releasing hormone, and somatostatin were unchanged. Measurement of neurotransmitters and neurotransmitter-related enzymes in individual hypothalamic nuclei derived from MSG-treated rats revealed normal levels of norepinephrine, serotonin and glutamic acid decarboxylase, but reduced levels of choline acetyltransferase and dopamine in the arcuate nucleus and median eminence. Histochemical methods for visualization of dopamine and acetylcholinesterase in the mediobasal hypothalamus confirmed these findings. The MSG-treated animals exhibited a normal diurnal rhythm of pineal serotonin N-acetyltransferase activity. These data indicate that the MSG-induced endocrine deficiency syndrome results at least partly from destruction of cholinergic and dopamingeric tuberoinfundibular systems in the hypothalamus.