Role of transmitters in mediating hypothalamic control of electrolyte excretion.

Changes in urinary volume and electrolyte excretion were monitored after the injection of cholinergic and monoaminergic drugs into the third cerebral ventricle of conscious male rats made diuretic by an intravenous infusion of 5% dextrose. A natriuretic and kaliuretic response was induced by the intraventricular injection of norephrine (NE) or carbachol, whereas dopamine (DA) had no effect. The beta-receptor stimulator isoproterenol (ISO) induced an antinatriuretic and antikaliuretic effect. Intraventricular injection of the alpha-adrenergic blocker phentolamine abolished the natriuretic response to NE and carbachol and to intraventricular hypertonic saline (HS). By contrast, the beta-adrenergic blocker propranolol induced a natriuresis and kaliuresis when injected alone and an additive effect when its injection was followed by NE or HS. Propranolol potentiated the natriuretic response to carbachol. Cholinergic blockade with atropine diminished the response to NE and blocked the natriuretic response to HS. It is suggested that sodium receptors in the ventricular wall can modify renal sodium excretion via a stimulatory pathway involving cholinergic and alpha-adrenergic receptors and can inhibit sodium excretion via a tonically active beta-receptor pathway.     

On the brain involvement in saline loading natriuresis--an indirect evidence for the cerebral participation in the functional expression of the atrial natriuretic system

The ablation of the anterior third cerebral ventricle region totally prevented the homeostatically effective natriuresis which should have followed hypertonic saline loading in conscious sheep. The increased cerebrospinal fluid (CSF) sodium concentration potentiated, and the decreased CSF[Na] prevented, natriuresis during isotonic saline loading. It is thus probable that a cerebral natriuretic system is involved in the functional expression of any other peripheral natriuretic system, e.g. the heart atrial natriuretic system which has been found to play a role in both hypertonic and isotonic saline loading natriuresis.     

Hypothalamic and hormonal control of the photoperiodically induced vernal functions in the White-crowned Sparrow,Zonotrichia leucophrys gambelii

To assess the role of the hypothalamo-hypophysial complex in the control of photoperiodically induced vernal premigratory responses in the White-crowned Sparrow, the effects of hypothalamic lesions and systemic administration of several hormones on these responses were investigated. Lesions that destroyed the posterior median eminence (PME) or the entire median eminence (ME) inhibited photoperiodically induced testicular growth, premigratory fattening and Zugunruhe. Lesions in the basal infundibular nucleus (IN) that resulted in complete inhibition of testicular growth abolished Zugunruhe, but allowed varying degrees of fattening. The systemic administration of prolactin, testosterone propionate (TP) or the combination thereof in the PME-lesioned birds induced fattening similar to that observed in photostimulated controls but did not induce Zugunruhe. It is concluded that testosterone and prolactin are the most important hormones involved in the control of vernal premigratory fattening. The role of these hormones in the induction of vernal Zugunruhe is not positively proven.     

大鼠脑室内注射氨甲酰胆碱对肾钠,钾,水排出的影响

在麻醉大鼠侧脑室注射胆碱能激动剂氨甲酰胆碱（ＣＢＣ）引起显著的促钠排泄、促钾排泄和利尿反应（Ｐ＜０．０５）,其中促钠排泄反应与剂量之间呈量效关系（ｒ＝０．９９９７,Ｐ＜０．０５）。由脑室注射ＣＢＣ（２．７４×１０－３μｍｏｌ）引起的上述反应可以被胆碱能Ｍ受体阻断剂阿托品或Ｎ受体阻断剂六甲双胺预处理完全阻断（Ｐ＜０．０５）。同样,ＣＢＣ的肾脏效应也可被肾上腺素能α受体阻断剂酚妥拉明预处理所部分阻断（Ｐ＜０．０５）。上述结果表明脑室注射ＣＢＣ引起的促钠排泄、促钾排泄和利尿反应是刺激了脑胆碱能Ｍ或Ｎ受体,有部分效应可能继发刺激去甲肾上腺素能α受体。     

Arginine vasotocin and renal function in the conscious dog

The effects of arginine vasotocin (AVT), 4–6 ng/kg, on renal function and plasma prolactin (PRL) were determined in conscious American foxhounds undergoing a water diuresis. Intravenous AVT produced an antidiuresis, kaliuresis and inconsistent natriuresis, independently of changes in GFR, blood pressure, heart rate and plasma PRL.     

A Cyclic AMP Mechanism Mediates the Serotonin-Induced Increase in Glutamic Acid Decarboxylase Activity in the Preoptic Area and Hypothalamus

Previous studies have shown that the injection of 5-hydroxytryptamine (5-HT) into the third ventricle of rats on the afternoon of proestrus increases glutamic acid decarboxylase (GAD) activity in the preoptic area and the hypothalamus. In the present report we examine the adenylate cyclase-cyclic AMP (cAMP) system as mediator of that effect. The increase in GAD activity induced by intraventricular injection of 5-HT was completely blocked by injecting an antiserum against cAMP into the third ventricle 30 min earlier, whereas an injection of serum from normal rabbits was ineffective. On the contrary, activation of adenylate cyclase activity by intraventricular injection of forskolin increased GAD activity, an effect that was also blocked by anti-cAMP serum. Anti-cAMP serum also lowered GAD activity in the preoptic area and hypothalamus when injected on the morning of proestrus but not when injected in the afternoon, when the values of GAD activity were already low. The results suggest that a cAMP mechanism may be involved in the changes in preoptic-area and hypothalamic GAD activity such as the rise in enzyme activity induced by intraventricular injection of 5-HT.     

Neuropeptide Y enhances potassium excretion by mechanisms distinct from those controlling sodium excretion

Neuropeptide Y (NPY) is an established modulator of renal function. Although NPY reduces renal blood flow and does not alter glomerular filtration rate, it enhances diuresis and natriuresis. Although initial studies on natriuresis did not detect kaliuresis, we now report that a retrospective analysis of previous studies regarding natriuresis demonstrates NPY-induced kaliuresis under several experimental conditions. Kaliuresis was observed despite a marked reduction in urinary potassium concentrations, which may explain why it has not been noted in some initial studies. In a direct comparison of NPY-induced kaliuresis and natriuresis, both effects were slow in onset (requiring >45 min to develop fully) and blocked by the cyclooxygenase inhibitor indomethacin. While natriuresis occurred solely via a Y5 receptor, kaliuresis involved a Y1 receptor and an additional receptor subtype, possibly Y2. The L-type Ca2+ entry blocker nifedipine abolished natriuresis but did not inhibit kaliuresis. A combination of experiments with the bradykinin B2 receptor antagonist icatibant, the angiotensin II receptor antagonist losartan, and the converting enzyme inhibitor ramiprilat revealed that NPY-induced natriuresis involves bradykinin while kaliuresis involves angiotensin II. We conclude that NPY-induced kaliuresis is much less pronounced than natriuresis and is mediated by distinct mechanisms.     

Changes in urine volume and urinary electrolyte excretion after intracerebroventricular injection of arecoline and hemicholinium-3

Activation of cholinergic neurons in specific brain regions evokes a hypernatriuretic response, which appears to be atropine-sensitive and, perhaps, independent from the renal innervation. However the role of cholinergic neurons in central control of renal function is not well understood. The purpose of this study was to further investigate whether brain acetylcholine stores are able to influence kaliuresis and natriuresis in conscious rats. Therefore, the renal response to cholinergic drugs was examined in Wistar rats which underwent to a 0.15 M NaCl solution (saline) load administered by gavage. Central injection of arecoline, a muscarinic agonist, produced a dose-dependent reduction in water diuresis and a highly significant increase in sodium excretion within two hours from the oral saline load. An intracerebroventricular (ICV) injection of methylatropine completely blocked both the antidiuretic and the natriuretic response induced by arecoline. Hemicholinium-3 (HC), centrally administered at a dose (34.8 nmol) known to be capable of inducing a maximal depletion of brain acetylcholine, elicited a time-dependent antidiuretic effect accompanied by a highly significant reduction in potassium and sodium urinary excretion. Therefore, we suggest that brain cholinergic neurons are involved in the regulation of the electrolyte balance.     

Effects on gonadal function by lesioning tanycytes in the median eminence of the rat and Japanese quail

Summary The ependymal linings of the median eminence were destroyed by electric cautery or intraventricular injection of picric acid in the rat and Japanese quail. In these animals the ventricular lumen near the median eminence disappeared due to adhesion of lesioned walls on both sides of the third ventricle. Electric lesions of the ependymal layer containing tanycytes did not induce appreciable disturbance in the estrous cycles. Rats in which tanycytes were lesioned by picric acid displayed 4-day estrous cycles after prolonged diestrus (10–22 days). After destruction of tanycytes in the quail, a photostimulated gonadal growth was observed. It is concluded that the tanycyte transport of the ventricular fluid to capillaries of the portal vessels appears unnecessary for maintenance of adenohypophysial gonadotrophic activities.Supported by a grant from the Ministry of Education of Japan and by a grant from the Ford Foundation. The authors wish to express their gratitude to Dr. B.K. Follett for providing chicken LH (IRC2) and to the late Mr. T. Asai for assay of serum LH     

Heart atrial auriectomy reduces the diuretic and natriuretic responses to a hypertonic saline load

Acute bilateral atrial auriectomy in anesthetized dogs reduced diuresis and natriuresis induced by both extracellular fluid volume expansion with isotonic saline and a hypertonic saline load. Since a hypertonic saline load, in contrast to isotonic saline infusion, was not accompanied by a significant increase in central venous pressure it is proposed that either increased plasma osmolality or plasma sodium concentration (or both) participate in the modulation of the atrial natriuretic mechanism.     

The tubero-infundibular neuron system: a component of the photoperiodic control mechanism of the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary To assess the roles of the hypothalamic neurosecretory and tubero-infundibular neuron systems in the mechanism of photoperiodic control of testicular growth in Zonotrichia leucophrys gambelii, midline electrolytic lesions were created in the median eminence, in its individual divisions, and in the region of the infundibular nucleus. Radiography was employed to facilitate the stereotaxic placement of lesions. Extensive damage to the neurosecretion-rich anterior division of the median eminence neither prevented the initiation of testicular growth in photosensitive, photostimulated birds nor induced gonadal regression in birds in which gonadal growth had previously been initiated by natural photoperiodic stimulation. Likewise, there was no impairment of the gonadotropin release mechanism when damage was restricted primarily to the neurosecretion-deficient posterior division of the median eminence. However, in birds in which the zone of damage included both divisions of the median eminence, the photoperiodic testicular response was abolished or markedly suppressed; if testicular growth had been initiated prior to electrocoagulation of the median eminence, testicular regression was induced. Gonadotropic insufficiency comparable to that induced by lesions in the median eminence was caused also by large lesions in the region of the infundibular nucleus or by smaller ones restricted primarily to its median, basal portion. Zones of damage that impair gonadotropic function thus correspond to (a) the chief nucleus of origin of the tubero-infundibular tract, (b) the principal route of entry of tubero-infundibular fibers into the anterior and posterior divisions of the median eminence, and (c) the terminal distribution of tubero-infundibular fibers in the eminential zones of neurovascular contact. These observations suggest that the tubero-infundibular neuron system is an essential component of the photoperiodic control mechanism of Z. leucophrys gambelii and are consistent with an hypothesis that assigns to this parvicellular neuron system the production of a neurohormone that regulates the release of a growth-stimulating gonadotropin from the pars distalis. The failure of anterior median eminence lesions to eliminate gonadotropin release is inconsistent with the hypothesis that the eminential component of the hypothalamic neurosecretory system is an essential element of the mechanism that controls photoperiodic testicular growth.This investigation was supported by a research grant (NB 01353) to Professor Donald S. Farner from the National Institutes of Health. A portion of the research was conducted while the author held the William T. Porter Fellowship of The American Physiological Society. I am grateful to Professor Farner for his suggestions and criticisms.This paper is based on a thesis submitted in partial fulfillment of the requirements for the Ph. D. in Zoophysiology at Washington State University. Portions of this study have been published previously in abstract form (F. E. Wilson and Farner, 1965).     

Potentiation of vasopressin analgesia in rats treated neonatally with monosodium glutamate

The analgesic response elicited by central administration of arginine vasopressin (AVP) appears to be dependent upon the integrity of the hypothalamic paraventricular nucleus (PVN), since lesions placed in the PVN eliminate AVP analgesia. A projection to the zona externa of the median eminence constitutes one of the VP-containing efferents of the PVN. Neonatal treatment with monosodium glutamate (MSG) destroys perikarya of the arcuate nucleus and median eminence. The present study examined whether AVP analgesia was affected in the MSG-treated rat and whether these alterations were accompanied by specific changes in VP immunoreactivity in the zona externa of the median eminence. Female rats, neonatally treated with either MSG or a saline control, were tested as adults on the tail-flick test following intracerebroventricular injections of 0, 75, 150 and 500 ng doses of AVP. After testing, selected animals were prepared for AVP and oxytocin immunocytochemistry of the median eminence. Significant potentiations in the magnitude of AVP analgesia were observed in MSG-treated rats. AVP and oxytocin immunoreactivity in the zona interna and oxytocin immunoreactivity in the zona externa of the median eminence were similar in MSG-treated and control rats. In contrast, AVP immunoreactivity in the zona externa of the median eminence was markedly reduced in the MSG-treated rat. These data suggest that VP analgesia may normally be inhibited by those medial-basal hypothalamic neurons affected by neonatal MSG treatment.     

Tanycyte absorption affected by the hypothalamic deafferentation in Japanese quail,Coturnix coturnix japonica

In Japanese quail, Coturnix coturnix japonica the tanycytes of the median eminence absorbed peroxidase injected into the third ventricle. The number of tanycytes showing peroxidase reaction was greater in the posterior median eminence than in the anterior median eminence. Following hypothalamic deafferentation, the tanycyte absorption was augmented both in the posterior and anterior median eminence. These findings suggest that axons of some neurons, which have inhibitory action on the tanycyte absorption, were transected by deafferentation resulting in augmentation of tanycyte absorption. A considerable number of ependymal cells lining the upper portion of the third ventricle and those of the pars nervosa also absorbed peroxidase. In birds with a deafferented hypothalamus, photostimulated ovarian growth was completely inhibited.     

Ascending projections to the hypothalamus and limbic nuclei from the dorsolateral pontine tegmentum: a biochemical and electron microscopic study.

Axons arising from the dorsolateral pontine tegmentum of the rat were traced in various hypothalamic and limbic nuclei by the electron microscopic degeneration method (0.5-8 day survival times) and by measuring regional norepinephrine (NE) concentrations after 12 days of survival using a radioenzymatic method. Significant reductions (41-85%) in NE contents were observed in the supraoptic, arcuate, basal and lateral amygdaloid nuclei and in the hippocampus 12 days after the bilateral electrolytic lesions of the locus coeruleus. No changes in NE concentrations were observed in the ventromedial, septal, central amygdaloid nuclei, in the median eminence and olfactory tubercle. Parabrachial lesions resulted in a decrease of NE content only in the olfactory tubercle. By means of electron microscopy terminal degeneration was found in the hypothalamic paraventricular, dorsomedial nuclei, in the median eminence, in the bed nucleus of the stria terminalis, in the central, lateral and basal amygdaloid nuclei, in the hippocampus and in the anterior ventral thalamic nucleus.     

Calcitonin inhibition of physiological and stimulated prolactin secretion in rats

The administration of salmon Calcitonin (sCT) intravenously (2.5 or 10 μg/kg) or into the lateral cerebral ventricles (2.5 or 25 ng/rat, i.c.v.) of unanaestized male rats induced clearcut decreases in plasma prolactin(PRL) levels. The i.c.v. injection of one of these doses of sCT (25 ng/rat) into rats with median eminence lesions was completely ineffective, while it induced a dramatic decrease in plasma PRL levels of sham-operated rats. Morphine- and heat stress-stimulated PRL levels were also abolished by sCT injection (250 ng/rat i.c.v.). The sCT-induced decrease in PRL levels was completely overcome by haloperidol, a dopamine-receptor blocker. We conclude that sCT may affect PRL secretion via an hypothalamic system, probably involving dopaminergic neurons. The present results indicate that CT, like many others peptides, may affect PRL secretion, directly or indirectly, even though further research is necessary to determine whether this effect has pharmacological or physiological importance.     

Gastrointestinal osmoreceptors and renal sodium excretion in humans

The hypothesis that natriuresis can be induced by stimulation of gastrointestinal osmoreceptors was tested in eight supine subjects on constant sodium intake (150 mmol NaCl/day). A sodium load equivalent to the amount contained in 10% of measured extracellular volume was administered by a nasogastric tube as isotonic or hypertonic saline (850 mM). In additional experiments, salt loading was replaced by oral water loading (3.5% of total body water). Plasma sodium concentration increased after hypertonic saline (+3.1 +/- 0.7 mM), decreased after water loading (-3.8 +/- 0.8 mM), and remained unchanged after isotonic saline. Oncotic pressure decreased by 9.4 +/- 1.2, 3.7 +/- 1.2, and 10.7 +/- 1.3%, respectively. Isotonic saline induced an increase in renal sodium excretion (104 +/- 15 to 406 +/- 39 micromol/min) that was larger than seen with hypertonic saline (85 +/- 15 to 325 +/- 39 micromol/min) and water loading (88 +/- 11 to 304 +/- 28 micromol/min). Plasma ANG II decreased to 22 +/- 6, 35 +/- 6, and 47 +/- 5% of baseline after isotonic saline, hypertonic saline, and water loading, respectively. Plasma atrial natriuretic peptide (ANP) concentrations and urinary excretion rates of endothelin-1 were unchanged. In conclusion, stimulation of osmoreceptors by intragastric infusion of hypertonic saline is not an important natriuretic stimulus in sodium-replete subjects. The natriuresis after intragastric salt loading was independent of ANP but can be explained by inhibition of the renin-angiotensin system.     

Participation of the lower brain stem in induction of preovulatory gonadotropin surges in female rats

The role of the lower brain stem in controlling preovulatory gonadotropin surges was investigated in female rats under acute experimental conditions. Electrolytic lesions or diethyldithiocarbamate implantations in the ventrolateral part of the medulla oblongata (VLMO), which were carried out at 1100-1330 h on the day of proestrus, resulted in a blockade of the preovulatory surges of LH, FSH and PRL as well as subsequent ovulation. Such treatments in the dorsomedial part of the medulla oblongata did not affect gonadotropin surges or ovulation. By means of electrolytic lesions in the VLMO, norepinephrine concentrations were significantly reduced in the preoptic-anterior hypothalamic area at 1700-1800 h on proestrus, though they did not change in the mid-posterior hypothalamus. Electrochemical stimulations of the suprachiasmatic part of the preoptic area or norepinephrine injections into the third ventricle at 1400-1500 h on proestrus in animals with VLMO lesions succeeded in induce gonadotropin surges and ovulation. These results suggest that the lower brain stem is involved in the induction of preovulatory gonadotropin surges and that the process may be mediated by the ascending noradrenergic system which originates in the VLMO.     

Effects of p-chloroamphetamine, a serotonin-depleting drug, on the median eminence and pituitary pars intermedia

p-Chloroamphetamine (PCA), an agent known to cause depletion of levels of brain serotonin in rodents, was administered to rats in three sequential injections (10mg/kg) to study effects on the hypothalamic median eminence and pituitary gland. One week following the initial sequence of injections of PCA, light and electron micrographs revealed degenerate fibers in the outer zone of the median eminence. Lower drug doses or single 10-mg/kg doses did not lead to morphologic changes. Neuronal processes located in the pituitary intermediate lobe appeared normal although there was a significant increase in the numbers of secretory granules contained within intermediate lobe cells drug-treated rats, as compared to controls. Fluorometric analysis of levels of catecholamine and indoleamine showed a decrease in serotonin in median eminence and pons-medulla, but no change in that of the pituitary. Levels of dopamine and norepinephrine remained unchanged after PCA treatment. The data suggest that fibers affected in the median eminence contain serotonin. Processes in the intermediate lobe may be resistant to the serotonin-lowering effects of PCA observed in brain tissue. In addition, PCA may directly affect granule release from pituitary cells, or may alternatively act on hypothalamic regions which affect the release of intermediate lobe cell hormones.     

Effects of Neuropeptide Y (NPY) on the release of anterior pituitary hormones in the rat

Neuropeptide Y (NPY) has been recently localized in several hypothalamic nuclei in the mammalian brain. In order to investigate the possible role of NPY on neuroendocrine function, we have investigated the effects of the peptide on the release of anterior pituitary hormones in the rat. Both intravenous (300 μg) or intraventricular (2 to 15 μg) injection of NPY produced in gonadectomized male rats a significant and long-lasting decrease of plasma LH levels. A short duration stimulating effect on prolactin plasma levels was also observed after the intravenous but not after the intraventricular injection of NPY. Plasma levels of the other pituitary hormones were not significantly modified after NPY injection. When incubated in vitro with anterior pituitary cells in monolayer culture, NPY produced no significant change in release of pituitary hormones. Thus NPY seems to exert a selective effect on LH release. Since this effect can be observed after both intravenous and intraventricular injection, it might be hypothesized that NPY could affect LHRH release in two areas which lack blood-brain barrier: the organum vasculosum of the lamina terminalis (OVLT) which contains LHRH cell bodies and NPY fibers and the median eminence which contains both LHRH and NPY fibers. The effect on prolactin release needs to be carefully evaluated in different experimental conditions.     

Possible negative ultra-short loop feedback of luteinizing hormone releasing hormone (LHRH) in the ovariectomized rat

To determine if LHRH might act within the brain to modify its own release, repeated blood samples were removed from conscious ovariectomized rats and minute doses of LHRH were injected into the third ventricle (3V). The effect of these injections on plasma LH and FSH was measured by radioimmunoassay (RIA). The higher dose of intraventricular LHRH (10 ng in 2 microliter) induced an increase in plasma LH within 10 min after its injection. Plasma LH decreased for the next 60 min. This was followed by restoration of LH pulses characteristic of the ovariectomized rat. This dose of LHRH slightly elevated plasma FSH concentrations. In stark contrast, a 10 fold lower dose of 1 ng of LHRH injected into the ventricle resulted in a highly significant decrease of plasma LH at 10 min following injection, followed by return of LH pulsations. There was no effect on the pulsatile release of FSH. The results are interpreted to mean that at the higher dose, sufficient LHRH reached the site of origin of the hypophyseal portal vessels in the median eminence so that it diffused into portal vessels and was delivered to the gonadotrophs to induce LH release. In contrast, the lower dose provided sufficient hypothalamic concentrations of the peptide to suppress the discharge of the LHRH neurons, thereby leading to a decline in plasma LH, indicative of an ultrashort-loop negative feedback of LHRH to suppress its own release.