Showing papers in "Neuroendocrinology in 1976"
TL;DR: The results indicate that daily MEL injections are capable of suppressing reproductive physiology in male hamsters, but only when the indole is injected late in the light period, in this case, 13 h after light on.
Abstract: The daily s.c. injection of 25 µg melatonin (MEL) in oil into adult male hamsters at 7 p.m. (lights on 6 a.m. to 8 p.m.) for 50 days caused involution of the testes, coagulation of
168 citations
TL;DR: The results suggest that the PRL-induced increase in activity of dopaminergic neurons in the median eminence or anterior hypothalamus may be responsible for the reduction of the post-castration rise in serum concentrations of LH and FSH.
Abstract: The effects of prolactin (PRL) administration on catecholamine turnover in various brain regions of ovariectomized rats were determined by observing the decline of dopamine and norepinephrine concentrations after α-methyltyrosine (αMT) administration PRL had no effect on the steady state concentration of dopamine in the median eminence, anterior hypothalamus and corpus striatum or on the norepinephrine concentration in the anterior hypothalamus However, PRL selectively enhanced dopamine turnover in the median eminence and anterior hypothalamus after a latent period of 10–26 h In addition, PRL administration significantly decreased serum concentrations of LH and FSH These results suggest that the PRL-induced increase in activity of dopaminergic neurons in the median eminence or anterior hypothalamus may be responsible for the reduction of the post-castration rise in serum concentrations of LH and FSH
158 citations
TL;DR: Blood samples were removed via chronic intra-atrial cannulae every 15 min in female rats during the estrous cycle, the last week of pregnancy, parturition and suckling to provide a basis for further studies on the dynamics of GH and PRL secretion in the female rat.
Abstract: Blood samples were removed via chronic intra-atrial cannulae every 15 min in female rats during the estrous cycle, the last week of pregnancy, parturition and suckling. Growth hormone (GH) secretion d
141 citations
TL;DR: The results concur with findings utilizing systemic LRH injections and support the notion that LRH may act directly on neural tissue to potentiate lordosis behavior in the female rat.
Abstract: Saline and luteinizing hormone-releasing hormone (LRH) were infused into the medial preoptic area (MPOA), arcuate nucleus (ARC), lateral hypothalamic area (LHA) and the cerebral cortex (CC), and the effects on sexual behavior were studied in estrone- (E-) primed ovariectomized (OVX) female rats. Each cannulated, OVX female known to be sexually active was primed with E in doses too low to initiate consistent mating behavior. LRH infusion in either the MPOA or ARC facilitated sexual behavior as measured by the lordosis-to-mount (L/M) ratio; LRH infusion in the LHA or CC, as well as saline infusion in all neural sites, was ineffective in initiating comparable behavior patterns. The results concur with findings utilizing systemic LRH injections and support the notion that LRH may act directly on neural tissue to potentiate lordosis behavior in the female rat.
126 citations
TL;DR: The neuroanatomical pattern of estrogen-concentrating cells in the hamster supports the concept of a generalized vertebrate pattern and a comparison of hamster and rat patterns of cellular 3H-estradiol (3H-E2) concentration appears to suggest that species differences in their responsiveness to estrogen may be paralleled by differences in estrogen binding.
Abstract: Autoradiographic methods were used to study the location of estrogen-concentrating cells in the brain of the female hamster. In the hypothalamus, well-labelled cells were reliably found in the posterior medial preoptic area (MPOA), the anterior hypothalamus (AHA), and the ventromedial (VM), arcuate (ARC) and ventral premammillary nuclei (VPM). In the limbic system, well-labelled cells were found in the ventro-lateral septum, bed nucleus of the stria terminalis, and the medial and cortical nuclei of the amygdala. Labelled cells, in small numbers, were also detected in the mesencephalic central gray (CG), lateral hypothalamus, subiculum and entorhinal cortex. The neuro-anatomical pattern of estrogen-concentrating cells in the hamster supports the concept of a generalized vertebrate pattern. Furthermore, a comparison of hamster and rat patterns of cellular 3H-estradiol (3H-E2) concentration appears to suggest that species differences in their responsiveness to estrogen may be paralleled by differences in estrogen binding.
119 citations
TL;DR: Female rats were subjected to 8 h of daily immobilization for 1, 3, 6, 10 or 15 days to induce adrenal enlargement as well as thymus involution in response to stress.
Abstract: Female rats were subjected to 8 h of daily immobilization for 1, 3, 6, 10 or 15 days. Exposure for 3 days inhibited b.w. and induced adrenal enlargement as well as thymus involution; 6 days of stress
115 citations
TL;DR: The overall results of this study indicate that DA agonists inhibit PRL and TSH, stimulate GH but do not stimulate LH release in male rats.
Abstract: The dose-response effects of apomorphine and ET-495 (piribedil), 2 specific dopamine (DA) receptor stimulators, and haloperidol, a DA receptor blocker, were tested on the secretion of prolactin (PRL), thyroid stimulating hormone (TSH), growth hormone (GH) and luteinizing hormone (LH) in male rats. Both apomorphine and piribedil reduced serum PRL and TSH levels, stimulated GH release at low but not at high doses and either had no effect or tended to reduce serum LH levels. The minimal effective dose of apomorphine for reducing PRL by 30 min was 0.01 mg/kg; TSH inhibition was observed with a dose of 0.1-0.3 mg/kg. The inhibitory effects of apomorphine (1.0 mg/kg) on PRL and TSH levels were maximal by 15 min and diminished by 120 min; plasma GH was highest 120 min after injection. Thyroidectomy (10 days) markedLH elevated serum TSH, had no effect on serum PRL and inhibited the ability of apomorphine (0.1 or 0.3 mg/kg) to reduce TSH but not PRL levels. These observations may indicate that separate dopaminergic control mechanisms exist for TSH and PRL secretion. Administration of haloperidol elevated serum PRL, tended to lower TSH, dramatically reduced GH and had no effect on LH levels. Haloperidol pre-treatment blocked the effects of apomorphine on PRL, TSH, and GH secretion. The overall results of this study indicate that DA agonists inhibit PRL and TSH, stimulate GH but do not stimulate LH release in male rats.
113 citations
TL;DR: It is suggested that histamine may be involved in the hypothalamic control of prolactin release and possibly of gonadotropin release in ovariectomized rats.
Abstract: To evaluate a possible role of histamine in the CNS control of prolactin and gonadotropin release, adult ovariectomized rats, with stainless steel cannulae implanted in the 3rd ventricle, were given s.c. injections of 10 µg of estradiol benzoate. 48 h later, 2 µl of 0.9% NaCl alone or of saline containing 1, 5, 25 or 125 µg of histamine dihydrochloride was microinjected into the ventricle. Immediately before and then 15, 30 and 60 min after, blood samples were withdrawn from etherized rats for radioimmunoassay (RIA) of serum prolactin, LH and FSH. In the histamine-injected rats, an increase in prolactin titers was observed and was highly significant in groups receiving the higher doses. A small yet significant release of LH, but not of FSH, was also observed. When 25 µg of histamine was injected directly into the pituitary or into the jugular vein, no elevations were observed, indicating a site of action in the brain. Restraint stress elevated serum prolactin and lowered serum LH and FSH in ovariectomized rats. These responses were blocked by the intrajugular injection of diphenhydramine (5 mg/kg). It is suggested that histamine may be involved in the hypothalamic control of prolactin release and possibly of gonadotropin release.
108 citations
TL;DR: Lesions in the VMN and DMN, both of which have previously been shown to disrupt normal diurnal feeding rhythms, were also observed to disruptnormal plasma corticosterone rhythms in the present study.
Abstract: Weanling rats received bilateral electrolytic lesions in the dorsomedial (DMH) or ventromedial (VMH) hypothalamic areas destroying primarily the dorsomedial (DMN) or ventromedial (VMN) hypothalamic nuclei. Sham-operated rats served as controls. Lesions in the VMN and DMN, both of which have previously been shown to disrupt normal diurnal feeding rhythms, were also observed to disrupt normal plasma corticosterone rhythms in the present study. The a.m. values of plasma corticosterone in the DMN-lesioned rats were higher than the sham-operated controls. In the p.m., the values of both VMN- and DMN-lesioned rats were lower than those of the controls but unchanged in comparison to their own a.m. concentrations. This disruption of the normal diurnal plasma corticosterone rhythm persisted for at least 9 post-operative weeks.
85 citations
TL;DR: Results are consistent with the hypothesis that the pulsatile release of LH in the long-term ovariectomized rat is caused by the stimulating activity of adrenergic and cholinergic, probably nicotinic, systems and the inhibitory activity of a dopaminergic system.
Abstract: In the long-term ovariectomized rat the secretion of LH has a pulsatile character. In such rats no difference was observed between morning and afternoon LH secretion. The administration of phenoxybenz
84 citations
TL;DR: Evidence is provided for a possible role for certain neurally excitant amino acids in the neuronal control of LH secretion and a significant increase in LH levels following injection into the pituitary of anesthetized male rats.
Abstract: Several neurally excitant amino acids were injected into the third ventricle of anesthetized male rats, and plasma levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured. LH levels increased following injections of 2.0 mum glutamate, lysine, or beta-alanine. Glycine (2.0 mum), alpha-alanine (2.0 mum), and 0.9% saline were ineffective in altering LH levels. None of the amino acids tested significantly altered FSH levels. Of the 3 amino acids which raised blood LH levels following an intraventricular injection, i.e., glutamate, beta-alanine, and lysine, only lysine caused a significant increase in LH levels following injection into the pituitary. The present study provides evidence for a possible role for certain neurally excitant amino acids in the neuronal control of LH secretion.
TL;DR: The existence of two types of hypothalamic neurons sensitive to estrogen is suggested, one of which could not be antidromically invaded using the authors' techniques and the other which was observed to besensitive to estrogen.
Abstract: Experiments performed on unanesthetized ovariectomized female rabbits demonstrated the effects of estradiol benzoate (EB; 20 µ g i.v.) on the electrical activity of hypothalamic unit
TL;DR: The influence of the hippocampus upon pituitary release of adrenocorticotropic hormone (ACTH) was studied in male Sprague-Dawley rats which had concentric bipolar stainless stell electrodes chemically implanted in the dorsal and ventral hippocampus.
Abstract: The influence of the hippocampus upon pituitary release of adrenocorticotropic hormone (ACTH) was studied in male Sprague-Dawley rats which had concentric bipolar stainless steel electrodes chronicall
TL;DR: Variation in basal hormone levels due to sex, circadian rhythmicity, or estrous cyclicity did not alter the pattern of the response of individual hormones to the stress but did markedly influence the magnitude of theresponse.
Abstract: To further evaluate the influence that sex, time of day and/or stage of the estrous cycle have on stress-induced changes in gonadotropin secretory patterns, rats were subjected to acute ether stress and subsequently sacrificed at 1.5, 3, 5, 10 and 15-min intervals. A significant change in FSH levels was not detectable, however serum LH levels consistently showed a transient elevation, and prolactin release occurred rapidly and in large increments in every case. Variation in basal hormone levels due to sex, circadian rhythmicity, or estrous cyclicity did not alter the pattern of the response of individual hormones to the stress but did markedly influence the magnitude of the response.
TL;DR: A rapid release of 5-HT both from the cells and the axon terminals in the central nervous system is suggested, and failure, even with repeated stresses, to elicit induction of increased levels of the biosynthetic enzyme regulating the synthesis of the neurotransmitter is suggested.
Abstract: The effects of a single stressful stimulus on serotonin (5-HT) concentration and of repeated stressful stimuli on tryptophan hydroxylase (THy) activity were measured in individual hypothalamic nuclei
TL;DR: Progesterone and ACTH were the most effective agents used for re-establishing estrous cycles in old non-cyclic, constant estrous rats by daily injections of progesterone, ACTH or L-dopa or by subjection to ether stress.
Abstract: Cycling was induced in old non-cyclic, constant estrous rats by daily injections of progesterone, ACTH or L-dopa or by subjection to ether stress. Progesterone and ACTH were the most effective agents
TL;DR: The hypothesis that DA has a dominant role as an inhibitor of Prl secretion by acting itself as the Prl inhibiting factor (PIF) on dopaminergic receptors located within the pituitary is supported.
Abstract: Inhibitors of dopaminergic neurotransmission, such as reserpine (RES), given alone or combined with alpha-methyl-p-tyrosine (alpha-MpT)or Ro 4-4602, as well as haloperidol (HAL) and sulpiride (SUL), induced highly elevated serum prolactin (Prl) concentrations in intact rats. In contrast, the dopaminergic agonists apomorphine (APO), lisuride hydrogen meleate (LHM), D-amphetamine (AMPH), piribedil and L-dopa greatly lowered the high serum Prl concentrations in female rats induced by i.p. pretreatment with 2 mg/kg RES. Additional inhibition of catecholamine synthesis in RES-treated animals by alpha-MpT abolished the effect of AMPH, which indicates that the effect of this compound is mediated through newly synthesized dopamine (DA), while the effect of APO and LHM remained unchanged. Inhibition of dopa decarboxylation by Ro 4-4602 within the whole body abolished the effect of L-dopa, while lower dosages of Ro 4-4602, which do not penetrate the blood-brain barrier, had less effect. The noradrenergic receptor-stimulating agent clonidine (CLON) had no Prl-lowering effect in RES-treated female rats. In hypophysectomized rats bearing 4 pituitaries transplanted under the kidney capsule, APO and LSM still lowered serum Prl concentrations, while AMPH had no effect; SUL produced a strong increase. These results support the hypothesis that DA has a dominant role as an inhibitor of Prl secretion by acting itself as the Prl inhibiting factor (PIF) on dopaminergic receptors located within the pituitary.
TL;DR: It would appear that LHRH's resynthesis does not keep pace with its release in ovariectomized rats, resulting in a decline in hypothalamic stores, and the values were significantly lower 4 weeks following ovariectomy.
Abstract: Plasma and hypothalamic LHRH was measured by specific radioimmunoassay in intact and ovariectomized rats, and the values were correlated with peripheral plasma (PP) FSH and LH titers. At most stages of the estrous cycle, plasma LHRH was either undetectabie or present at very minimal values. An increase in PP LHRH concentration was observed in some animals between 13.00 and 20.00 h on proestrus. The mean elevation in LHRH was greatest in rats when blood samples were taken by decapitation; elevation was somewhat less when samples were taken from etherized rats and minimal when taken from rats bearing indwelling jugular cannulae. LHRH was elevated in approximately half the ovariectomized animals; repeated samples were drawn at 15-min intervals from intrajugular cannulae. In animals with LHRH elevations, LHRH was highly variable, which indicates that it is released in pulsatile fashion. Plasma LHRH and LH titers were correlated in ovariectomized animals. The relatively low correlation between LHRH and LH may be explained by the fact that a pulse of LHRH can elicit LH release over a considerable time span; also, LHRH is cleared much more rapidly from the circulation than is LH, as revealed by the time course of disappearance of exogenous LHRH given by bolus injection. In intact rats, hypothalamic LHRH content was slightly lower at 10.00 h on diestrus day 1 than at other sample times. LHRH was significantly lower 4 weeks following ovariectomy compared to levels in intact rats at any sample time. It would appear that LHRH’s resynthesis does not keep pace with its release in ovariectomized rats, resulting in a decline in hypothalamic stores.
TL;DR: It is indicated that cellular activity in the adenohypophysis correlates well with the circulating levels of corticosterone, and the luteotrope seems to be an exception in that its level of activity increased throughout the duration of the stress procedure.
Abstract: A morphological and ultrastructural study is described which indicates that cellular activity in the adenohypophysis correlates well with the circulating levels of corticosterone. Intense secretory activity is observed in all tropic cells of the adenohypophysis over 10 days; thereafter the cellular morphology shows a return to the control condition. There are, however, differences in the degree of adaptation between the different tropic cells. After its initial hyperactivity, corticotrope activity returned to a control level by 20 days. Thyrotrope activity was also found to adapt to control activity, but only after 40 days. Similar patterns were observed in the stomatotrope and gonadotrope, where the initial hypertrophy returned to control levels by 20 days; thereafter, however, an inhibition was observed. The luteotrope however, seems to be an exception in that its level of activity increased throughout the duration of the stress procedure.
TL;DR: The results indicate that, especially in immature animals, there is a circulating substance which cross-reacts with antibodies to estradiol but which does not appear to be a biologically-active estrogen.
Abstract: Plasma LH and ‘estradiol’ were measured by radioimmunoassay in female rats 5, 10, 15, 20, 25, 30, 40 and 80 days of age, and the changes in these hormone levels 24 h after ovariectomy, ovariectomy plu
TL;DR: Pituitary LH responsiveness to small dosages of synthetic gonadotropin-releasing hormone (GnRH) was tested repeatedly at 2-h intervals during the time periods when plasma LH was inhibited and when it was facilitated and E2beta probably increased endogenous LRF during the period of facilitated LH release.
Abstract: Single injections of 50 µ g estradiol-17 β (E2 β ) into ovariectomized sheep caused biphasic changes in plasma luteinizing hormone (LH).
TL;DR: It is indicated that circulating testosterone in physiological concentrations can maintain a normal hypothalamic LH-RH content and demonstrate an action of testosterone, in physiological concentration, in the feedback regulation of LH- RH secretion.
Abstract: Hypothalamic LH-RH content in male rats is lowered after castration. The s.c. implantation of testosterone or testosterone propionate-packed Silastic tubing (from 0.5 to 6 cm in length) in a range which encompassed the normal circulating plasma testosterone concentration, prevented this lowered LH-RH content 21 days following castration and simultaneous implantation. The temporal response to implanted testosterone was then studied: rats were killed 1,2,4,8,14 and 21 days after castration and simultaneous implantation of 3 cm testosterone-packed Silastic tubing. The hypothalamic LH-RH content began to decrease in the castrated group after 4 days and fell progressively thereafter. However, the hypothalamic LH-RH content of the castrated group maintained with constant levels of testosterone showed no such reduction at any time following castration. These experiments indicate that circulating testosterone in physiological concentrations can maintain a normal hypothalamic LH-RH content and demonstrate an action of testosterone, in physiological concentrations, in the feedback regulation of LH-RH secretion.
TL;DR: Serotonin (5-HT) concentrations showed characteristic changing patterns in many hypothalamic, limbic and midbrain structures with a decrease during proestrus and an increase during estrus being observed, further indication of its inhibitory effect on gonadotropin release mechanisms before the 'critical period'.
Abstract: Normal 4-day cyclic rats were sacrificed at 10 a.m. and 3 p.m. on proestrus or estrus and at 10 a.m. on metestrus. Noradrenaline (NA), dopamine (DA) and tryptophan (T) concentrations varied only slightly. Serotonin (5-HT) concentrations showed characteristic changing patterns in many hypothalamic, limbic and midbrain structures with a decrease during proestrus and an increase during estrus being observed. Monoamine oxidase (MAO) activity changes were often parallel to the 5-HT changes, but were not as great. The marked changes in 5-HT early in proestrus are a further indication of its inhibitory effect on gonadotropin release mechanisms before the ‘critical period’.
TL;DR: The metabolism of striatum dopamine was studied in mice during proestrus, estrus and diestrus and the possible role of dopaminergic mechanisms in the control of gonadotropin secretion was discussed.
Abstract: The metabolism of striatum dopamine (DA) was studied in mice during proestrus, estrus and diestrus. The following results have been obtained: (1) the concentration of DA is higher in diestrus than in
TL;DR: The total amount of LH secreted appeared more or less determined by the LH-RH dose, indicating that the size of the releasable LH pool is not fixed.
Abstract: Preovulatory LH surges were measured in cannulated proestrous rats. Such LH peaks were also obtained by infusing pentobarbital-blocked animals with LH-RH for periods of up to 20 h; this suggested that the pituitary LH stores were exhausted. However, the total amount of LH secreted appeared more or less determined by the LH-RH dose, indicating that the size of the releasable LH pool is not fixed.
TL;DR: It is concluded that the release of ACTH from the PI may be controlled by direct serotonergic innervation, and 5-hydroxytryptamine stimulated ACTH release in a dose-related manner, from 10(-6) to 10(-3)M, while having no effect onACTH release from the pars distalis (PD).
Abstract: Studies were carried out to test the responsiveness of dispersed pars intermedia (PI) cells to a number of neurotransmitter substances known to be present in the PI. These substances were tested over an extended dose range. The catecholamines, adrenaline, noradrenaline, and dopamine inactivated PI ACTH at high concentrations; at lower concentrations, they were without effect. Histamine and carbachol had no effect on ACTH release. 5-hydroxytryptamine stimulated ACTH release in a dose-related manner, from 10–6 to 10–3M, while having no effect on ACTH release from the pars distalis (PD). We conclude that the release of ACTH from the PI may be controlled by direct serotonergic innervation.
TL;DR: The data suggested that the adrenergic and serotonergic systems have a positive input in the occurrence and magnitude of the surge and that the cholinergic system does not appear to have a physiologic role in tonically inhibiting Prl release, but may function under certain special conditions.
Abstract: The involvement of adrenergic, serotonergic and cholinergic mechanisms in the diurnal surge of plasma prolactin (Prl) secretion has been examined using ovariectomized, polyestradiol phosphate-treated (PEP) rats bearing aortic catheters. An afternoon surge in plasma Prl was observed to peak at 15.00 h and 17.00 h followed by declining levels at 19.00 and 21.00 h. This pattern was observed between 5 and 21 days after PEP administration. The alpha-adrenergic blocker, phenoxybenzamine (Phenox), completely prevented the Prl surge. The beta-blocker, propranolol (Propra), appeared to delay the onset and intensity of the diurnal Prl surge so that maximum levels were observed at 19.00 and 21.00 h. The serotonergic blocker, methysergide (MES), delayed the maximum diurnal Prl level until 21.00 h, while cyproheptadine (Cypro), another serotonergic blocker, significantly inhibited the surge. The muscarinic cholinergic agonist, arecoline (Arec), when administered at 12.00 h, delayed the surge, while the repeated administration of Arec completely blocked the surge. Atropine (Atro) (10 m/kg at 12.00 h and 5 mg/kg every 2 h thereafter) did not have any effect on the Prl surge, but when administered simultaneously with Arec, prevented the inhibitory effect of Arec on Prl release. The data suggested that the adrenergic and serotonergic systems have a positive input in the occurrence and magnitude of the surge and that the cholinergic system does not appear to have a physiologic role in tonically inhibiting Prl release, but may function under certain special conditions.
TL;DR: It seems that the throidal endocytotic response to exposure to cold as a reflection of TSH secretion was directly influenced by alterations of brain biogenic amine concentrations or turnover rates.
Abstract: L-Dihydroxyphenylalanine (L-DOPA)significantly inhibited intrathyroidal colloid droplet formation induced by exposure to cold in the rat. Diethyldithiocarbamate (DDC) also inhibited colloid droplet formation in response to cold. The combined administration of L-DOPA and DDC produced an additive inhibition of the thyroidal endocytotic response to exposure to cold. Pretreatment with chlorpromazine (CPZ) ameliorated the inhibitory effect of (L-DOPA)DL-alpha-methyl-p-tyrosine (α-MT) also significantly depressed the thyroidal response. Inhibition of colloid droplet formation induced by α-MT was not altered by the administration of DL-dihydroxyphenylserine (DL-DOPS). On the other hand, treatment of the α-MT-treated rats with L-DOPA to normalize dopamine synthesis resulted in a dramatic recovery from the inhibition. Blockade of serotonin biosynthesis with p-chlorophenylalanine (p-CPA) failed to produce a significant inhibition of colloid droplet formation. However, 5-hydroxytryptophan (5-HTP) markedly inhibited the thyroidal response to cold. Brocresine phosphate (BP) was another inhibitor of the thyroidal endocytotic response to exposure to cold. Oxotremorine also markedly depressed the thyroidal response to cold. Since these drugs did not interfere with pituitary-thyroid responsiveness to exogenous thyrotropin-releasing hormone (TRH), it seems that the thyroidal endocytotic response to exposure to cold as a reflection of TSH secretion was directly influenced by alterations of brain biogenic amine concentrations or turnover rates.
TL;DR: The effect of unilateral ovariectomy on the protein-synthesizing activity of the hypothalamic arcuate and dorsomedial nucleus on both sides was studied in vivo as well as in vitro and the existence of a neural pathway between the ovary and the hypothalamus nucleus is assumed.
Abstract: The effect of unilateral ovariectomy on the protein-synthesizing activity of the hypothalamic arcuate and dorsomedial nucleus on both sides was studied in vivo as well as in vitro. Four weeks after the removal of 1 ovary, there was a significant increase in labelled amino acid incorporated into the arcuate neurons contralateral to the removed ovary as compared to those incorporated into the nerve cells of the nucleus on the ipsilateral side. In the dorsomedial nucleus, there was no difference between the 2 sides. On the basis of the present findings, the existence of a neural pathway between the ovary and the hypothalamic arcuate nucleus is assumed.