Intranuclear coupling of hypothalamic magnocellular nuclei by glutamate synaptic circuits

Magnocellular neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) display bursting activity that is synchronized under certain conditions. They receive excitatory synaptic inputs from intrahypothalamic glutamate circuits, some of which are activated by norepinephrine. Ascending noradrenergic afferents and intrahypothalamic glutamate circuits may be responsible for the generation of synchronous bursting among oxytocin neurons and/or asynchronous bursting among vasopressin neurons located in the bilateral supraoptic and paraventricular nuclei. Here, we tested whether magnocellular neurons of the PVN receive excitatory synaptic input from the contralateral PVN and the region of the retrochiasmatic SON (SONrx) via norepinephrine-sensitive internuclear glutamate circuits. Whole cell patch-clamp recordings were performed in PVN magnocellular neurons in coronal hypothalamic slices from male rats, and the ipsilateral SONrx region and contralateral PVN were stimulated using electrical and chemical stimulation. Electrical and glutamate microdrop stimulation of the ipsilateral SONrx region or contralateral PVN elicited excitatory postsynaptic potentials/currents (EPSP/Cs) in PVN magnocellular neurons mediated by glutamate release, revealing internuclear glutamatergic circuits. Microdrop application of norepinephrine also elicited EPSP/Cs, suggesting that these circuits could be activated by activation of noradrenergic receptors. Repetitive electrical stimulation and drop application of norepinephrine, in some cases, elicited bursts of action potentials. Our data reveal glutamatergic synaptic circuits that interconnect the magnocellular nuclei and that can be activated by norepinephrine. These internuclear glutamatergic circuits may provide the functional architecture to support burst generation and/or burst synchronization in hypothalamic magnocellular neurons under conditions of activation.     

Absence of a prostaglandinic mediator in the lateral hypothalamic cardio-vascular inhibition.

The cardio-vascular inhibition elicited by electrical stimulation of the paraventricular nucleus in the lateral hypothalamus of anaesthesized and desafferentiated dogs is not linked with a mediator release like PGE. The effect of this biological agent is not registered in the isolated femoral artery of a receiver, after deviation by a cruised circulation of the arterial blood of a hypothalamic stimulated donor dog. Antipyretics, which are also prostaglandin-synthetase inhibitors, enhance the lateral hypothalamic reactions. As the thermoregulation centre is localized in the same region as the cardio-vascular inhibition centre and because lowering of temperature depends upon vasodilation and decrease in the general cellular metabolism, both functions of the paraventricular nucleus activity, a hypothesis is proposed that thermoregulation and cardio-vascular inhibition centres are a functional and anatomical unity.     

刺激大鼠穹窿下器官诱发饮水和脑内c—fos表达的胆碱能机制

实验以饮水行为脑内c-fos表达为指标,,观察刺激大鼠穹窿下器官（SFO）的效应,结果显示,刺激SFO能诱发明显的饮水行为,与此同时,前脑8个部位（终板血管器官,正中视前核,室旁核,视上核,下丘脑外侧区,穹窿周核背侧区,丘脑联合核和无名质）和后脑3个部位（最后区,孤束核和壁旁外侧核）的Fos蛋白表达明显增强,免疫组化双重染色结果显示,刺激SFO能诱导视上核和室旁核中部分神经元呈Fos蛋白和加压素共同表达。脑室注射阿托品能部分阻断刺激SFO诱发的饮水行为,脑内上述各部位所诱导的Fos蛋白表达也明显减弱,以上结果提示,M胆碱能机制参与 刺激SFO诱发的饮水行为和脑内Fos蛋白的表达。     

Calcitonin gene-related peptide in the human hypothalamus

Calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) in the human hypothalamus was investigated by radioimmunoassay and by immunocytochemistry. CGRP-LI was detected from two hypothalami obtained at autopsy (2.1 and 7.0 ng/g wet tissue) by radioimmunoassay. Reverse phase high performance liquid chromatography revealed that most of the CGRP-LI in the human hypothalamus was eluted in an identical position with synthetic human CGRP. For immunocytochemistry, human hypothalami obtained at autopsy were fixed and cryostat-sectioned at 40 microns. Free floating sections were immunostained with antibody to CGRP. CGRP-immunoreactive cell bodies were found in the supraoptic nucleus, paraventricular nucleus and infundibular nucleus. These findings indicate that CGRP exists in the cell bodies of the supraoptic nucleus, paraventricular nucleus and infundibular nucleus in the human hypothalamus and CGRP may play some roles in the endocrine and other functions of the human hypothalamus.     

电刺激兔肾脏传入神经对血压,心率及加压素释放的影响

本工作以兔为实验对象,观察电刺激肾脏传入神经（ＡＲＮ）对血压、心率、颈交感神经放电、以及加压素（ＡＶＰ）合成和释放的影响,并对ＡＲＮ进入中枢的通路作了观察。结果显示,电刺激ＡＲＮ可以引起血压下降、心率减慢、颈交感神经放电抑制等反应,ＡＲＮ的兴奋还可使下丘脑的视上核、室旁核中的ＡＶＰ含量增加,垂体中ＡＶＰ含量下降,血浆ＡＶＰ水平升高。硝普钠的降压实验和静脉注射ＡＶＰ受体阻断剂ＡＶＰａ的实验均证实了Ａ     

Central TRH receptor 1 antisense blocks cold-induced gastric emptying but not brain c-Fos induction

We studied whether TRH receptor 1 (TRH-R1) antisense oligodeoxynucleotides injected intracisternally, impaired acute cold-induced c-Fos expression in the brain and vagally mediated stimulation of gastric emptying in conscious rats. Cold exposure (4-6 degrees C, 90 min) increased gastric emptying and the number of c-Fos positive cells in the paraventricular nucleus of the hypothalamus, supraoptic nucleus, raphe pallidus, dorsal motor nucleus of the vagus, nucleus of the solitary tract and area postrema compared with rats at room temperature. TRH-R1 antisense abolished cold-induced stimulation of gastric transit but not c-Fos expression in the brain. TRH-R1 mismatch did not alter the gastric response to cold. These data indicate that central activation of TRH-R1 mediates cold-induced stimulation of gastric emptying but does not influence the induction of c-Fos expression in the brain.     

Quantitative histoenzymatic analysis of the hypothalamic neurosecretory system in rat ontogeny

In experiments on 6 and 16 days old rats cytophotometric studies have been made of histochemical reactions for succinate, lactate and glutamate dehydrogenases, alpha-glycerophosphate dehydrogenase and glucose-6-phosphate dehydrogenase in the supraoptic nucleus, paraventricular hypothalamic nucleus and the posterior hypophysis. It was found that heterochronous development of the neurones in the supraoptic and paraventricular nuclei, as well as the development of their axons in the posterior hypothalamus depend on the rate of maturation of the enzymic systems in postnatal life. In consolidation of the unique structure of the hypothalamic neurosecretory system, the key role is played by afferent influences, succinic dehydrogenase being involved into their realization. The data obtained indicate the importance of heterochronous development of the enzymic activities in the formation of bifunctional properties of neurosecretory hypothalamic neurones and reveal the primary development of neurotransmittery function as compared to the excretory one.     

Demonstration of a different localization of perikarya immunoreactive to oxytocin and vasopressin in the cat hypothalamus

Using immunohistochemical techniques, we demonstrated oxytocin (OT) and vasopressin (AVP) neurons in the cat hypothalamus. The OT immunoreactive neurons were found mainly in the paraventricular nucleus, supraoptic nucleus and dorsal accessory group located lateral to the fornix. In addition to these hypothalamic structures, the AVP immunoreactive neurons were observed in the suprachiasmatic nucleus, ventral accessory group located in the retrochiasmatic area and lateral accessory group, dorsal to the supraoptic nucleus caudally, and ventral to the medial part of the internal capsule rostrally. We further demonstrated a different localization of the OT and AVP immunoreactive neurons in the paraventricular and supraoptic nuclei.     

Functional identification of central pressor pathways originating in the subfornical organ

The functional projections from pressor sites in the subfornical organ (SFO) were identified using the 2-deoxyglucose (2-DG) autoradiographic method in urethane-anesthetized, sinoaortic-denervated rats. Autoradiographs of brain and spinal cord sections taken from rats whose SFO was continuously stimulated electrically for 45 min with stereotaxically placed monopolar electrodes (150 microA, 1.5-ms pulse duration, 15 Hz) following injection of tritiated 2-DG were compared with control rats that received intravenous infusions of pressor doses of phenylephrine to mimic the increase in arterial pressure observed during SFO stimulation. Comparisons were also made to autoradiographs from rats in which the ventral fornical commissure (CFV), just dorsal to the SFO, was electrically stimulated. The pressor responses during either electrical stimulation of the SFO or intravenous infusion of phenylephrine were similar in magnitude. On the other hand, stimulation of the CFV did not elicit a significant pressor response. Electrical stimulation of the SFO increased 2-DG uptake, in comparison to the phenylephrine-infused rats, in the nucleus triangularis, septofimbrial nucleus, lateral septal nucleus, nucleus accumbens, bed nucleus of the stria terminalis, dorsal and ventral nucleus medianus (median preoptic nucleus), paraventricular nucleus of the thalamus, hippocampus, supraoptic nucleus, suprachiasmatic nucleus, paraventricular nucleus of the hypothalamus, and the intermediolateral nucleus of and central autonomic area of the thoracic spinal cord. In contrast, in rats whose CFV was stimulated, these nuclei did not demonstrate changes in 2-DG uptake compared with control animals that received pressor doses of phenylephrine. These data have demonstrated some of the components of the neural circuitry likely involved in mediating the pressor responses to stimulation of the SFO and the corrective responses to activation of the SFO by disturbances to circulatory and fluid balance homeostasis.     

寒冷对大鼠下丘脑核团癌基因c-fos及垂体ACTH细胞表达的变化

本实验用寒冷刺激大鼠,观察垂体ＡＣＴＨ细胞及下丘脑核团ｃ－ｆｏｓ癌基因表达蛋白出现的变化。发现寒冷能促使垂体前叶ＡＣＴＨ细胞数目增多,体积胀大,且具有粗大突起伸到扩张的血窦旁。在视交叉腹外侧的视上核（ＳＯ）神经元及视交叉上核（Ｓｃｈ）周围部神经元皆出现ｃ－ｆｏｓ强阳性反应。第三脑室侧壁室管膜上皮及少数室周核（ｐｅ）神经元为ｃ－ｆｏｓ阳性。视前内侧区（ＭＰＡ）可见分散的阳性神经元。位于室旁核内的外侧,出现ｃ－ｆｏｓ反应较浅的小神经元。本文最后探讨有关ＡＣＴＨ释放的调节。     

Osmotic regulation of substance P and neurokinin A peptide content and substance P binding sites in distinct hypothalamic nuclei of the rat.

Quantitative receptor autoradiography using Bolton-Hunter iodinated substance P (SP) was used to localize specific sites in the rat hypothalamus. The amount of SP and neurokinin A (NkA) in extracts from discrete areas of the hypothalamus was measured using specific radioimmunoassays. A high density of SP binding sites was observed in the perimeter of the magnocellular paraventricular and supraoptic nuclei, while the magnocellular nuclei themselves possessed a low receptor density. In control animals, the number of SP binding sites was also low in the arcuate nucleus and the median eminence. Substance P and NkA peptide concentrations were highest in the paraventricular nucleus (PVN), decreasing in the following order: arcuate nucleus (Arc) greater than median eminence (ME) greater than supraoptic nucleus (SON) greater than subfornical organ (SFO). In animals given 340 mmol/l NaCl instead of tap water to drink for 12 days, significant increases in the number of SP binding sites occurred in the medial parvocellular subdivision of the PVN, periamygdaloid cortex, medial preoptic nucleus, Arc, and ME, but other hypothalamic areas were unaffected. In saline-treated animals, significant increases in SP and NkA peptide concentrations were observed in the ME, while in the SFO only the concentration of NkA increased significantly. In the SON, substance P and neurokinin A levels were doubled, whereas in the PVN and Arc no changes in peptide levels were observed. Chronic osmotic stimulation is associated with lowered circulating levels of adrenocorticotropin releasing hormone (ACTH), and the present data further substantiate the hypothesis that hypothalamic tachykinin-containing neuronal terminals are centrally involved in the inhibition of anterior pituitary ACTH release observed during chronic osmotic stimulation.     

Influence of actinomycin-D on the diurnal rhythm of cytoplasmic RNA in the neurocytes of selected nuclei of mouse hypothalamus

The influence of a single dose of actinomycin-D (1 mg/kg body weight) on the diurnal rhythm of cytoplasmic RNA was studied in neurocytes of the supraoptic nucleus (SON), paraventricular nucleus (PVN), and arcuate nucleus (AN) by microspectrophotometer. Cosinor analysis of the obtained results revealed a disturbed diurnal rhythm of cytoplasmic RNA in the animals treated with actinomycin-D. The mean diurnal RNA content in the SON, PVN, and AN neurocytes decreased, the amplitude of diurnal fluctuation was reduced and the acrophase was shifted to earlier hours.     

Central control of mating call production and spawning in the tree frog Hyla arborea savignyi (Audouin): Results of electrical stimulation of the brain

Electrical stimulation of the anterior preoptic nucleus elicited the production of mating calls by male Hyla arborea savignyi. Such calls are composed of pulses resembling those of natural mating calls both in their duration and in their sequential arrangement. As a rule, the amplitude of successive pulses within a group increases more rapidly in the electrically evoked calls than in natural calls. The frogs could be brought into a state of readiness to call, which did not lead to actual calling activity, by stimulation in the anterior preoptic, posterior preoptic, and magnocellular nuclei as well as in the hypothalamus. Stimulation of the anterior preoptic nucleus of one female elicited repeated vocalizations, which may be interpretable as mating calls. The posture adopted by the female for spawning can be elicited in males as well as in females by electrical stimulation of the anterior preoptic nucleus.     

Hypothalamic activity during altered salt and water balance in the snake <Emphasis Type="Italic">Bothrops jararaca</Emphasis>

The effects of water and salt overload on the activities of the supraoptic and paraventricular nuclei and the adjacent periventricular zone of the hypothalamus of the snake Bothrops jararaca were investigated by measurements of Fos-like immunoreactivity (Fos-ir). Both water and salt overload resulted in changes in body mass, plasma osmolality, and plasma concentrations of sodium, potassium, and chloride. Hyper-osmolality increased Fos immunoreactivity in the rostral supraoptic nucleus (SON), the paraventricular nucleus (PVN), and adjacent periventricular areas. Both hyper- and hypo-osmolality increased Fos immunoreactivity in the intermediate SON, but not in other areas of the hypothalamus. Immunostaining was abundant in cerebrospinal fluid (CSF)-contacting tanycyte-like cells in the ependymal layer of the third ventricle. These data highlight some features of regional distribution of Fos immunoreactivity that are consistent with vasotocin functioning as a hormone, and support the role of hypothalamic structures in the response to disruption of salt and water balance in this snake.     

Heterogeneity in calbindin-D28k expression in oxytocin-containing magnocellular neurons of the rat hypothalamus

We have used a double-labeling immunofluorescence method to examine whether oxytocin-containing magnocellular neurons possess a calcium-binding protein, calbindin-D28k, in the hypothalamus of the rat. In the supraoptic nucleus, most oxytocin-immunoreactive cells were also stained for calbindin-D28k. However, in the magnocellular part of the paraventricular nucleus nearly all oxytocin-labeled cells were devoid of calbindin-D28k. In the anterior commissural nucleus, approximately one-third of oxytocin-stained cells were also calbindin-D28k-immunoreactive, but the other cells were negative for calbindin-D28k. This study indicates that there may be distinct chemical features between oxytocin-containing magnocellular neurons of the supraoptic nucleus compared to those of the paraventricular nucleus.     

Role of the hypothalamus in regulating liver circulation

In acute experiments on nembutal anesthetized dogs stimulation of anterior hypothalamus elicited changes in the hepatic artery blood flow, which followed those of arterial pressure; the vascular resistance remaining unchanged. The stimulation of medial and posterior hypothalamus led to decrease in flow and increase in the resistance of the hepatic artery. In most cases of hypothalamic stimulation the portal blood flow diminished, portal pressure and vascular resistance increased. The opposite reactions were observed during stimulation of sympathoinhibitory area, paraventricular and lateral hypothalamic nuclei. The conclusion is made that the hypothalamus participates in integrative and differential control of the hepatic circulation.     

Histochemical demonstration of acetylcholinesterase in the hypothalamus of the female guinea-pig

Summary The distribution of acetylcholinesterase (AChE) in the hypothalamus of the female guinea pig has been examined histochemically.Activity was found in neurones of the supraoptic, paraventricular and infundibular nuclei; in the lateral hypothalamic area, in cells dorsomedial to the fornix at the level of the paraventricular nucleus and in a large group of cells surrounding the fornix at the level of the in-fundibular nucleus. A small well-stained group of cells, not identified in histological preparations, was present ventral to the paraventricular nucleus. The neuropil stained at the lateral border of the paraventricular nucleus and in the medial mammillary, suprachiasmatic and dorsomedial nuclei. The walls of some blood vessels stained; activity was particularly strong in vessels in the preoptic area and at the base of the median eminence. Nerve fibres on blood vessels ventral to the hypothalamus also stained.The degree of enzyme activity in the cell groups was compared in immature, pregnant, lactating, ovariectomized and hysterectomized animals. The greatest variation occurred in the infundibular nucleus. Hypophysectomy markedly reduced staining in the supraoptic nucleus. The possibility that AChE may be involved in the elaboration or transport of releasing factors is discussed.The authors are indebted to Dr. J. S. Perry for doing the surgery involved in this work. They are also grateful to him and to Dr. R. B. Heap for helpful discussions and to Miss M. Hamon for excellent technical assistance.     

Lateral septal projections onto tubero-infundibular neurons in the hypothalamus of the guinea pig

Efferent projections of the lateral septal nucleus (LS) to the preoptic area and the hypothalamus were identified in 20 female guinea pigs after iontophoretic injection of the anterograde axonal tracer Fluoro-Ruby. Tubero-infundibular (TI) neurons of the preoptic area and the hypothalamus were retrogradely labeled after intracardiac injection of Granular Blue or Fluoro-Gold. Magnocellular neurons of the supraoptic and paraventricular nuclei were also labeled. The double labeling procedure allowed an estimation of the extent of the direct relationship between LS efferents and TI neurons. Contacts between lateral septal fibers and TI cell bodies were mainly observed at the light-microscopical level in the preoptic area. A group of labeled fibers coursing along the third ventricle established sparse connections with hypothalamic periventricular TI neurons. A few appositions was observed in the infundibular (arcuate) nucleus, suggestive of a monosynaptic regulation of TI neurons by a septo-arcuate tract. Close association with labeled magnocellular neurons was also noted at the edge of the supraoptic and paraventricular nuclei. The sparse but direct connections between LS and TI neurons may be involved in the neuroendocrine functions of the LS.     

Effect on vasopressin release of microinjection of cholinergic agonists into the rat supraoptic nucleus.

It is likely that central cholinergic pathways to the paraventricular and supraoptic nuclei participate in the control of vasopressin release. We have shown previously that this is due, in part, to activation of muscarinic, but not nicotinic, receptors in the paraventricular nucleus. There is, however, reason to believe that this cholinergic effect in the supraoptic nucleus may be the result of activation of nicotinic receptors. To test this possibility, we have studied in conscious unrestrained rats the effect of microinjection of muscarinic and nicotinic agonists into the supraoptic nucleus on vasopressin release, mean arterial blood pressure, and heart rate. Under ether anesthesia, a stainless steel guide cannula was placed in the supraoptic nucleus 5-7 days before the experiment, and femoral, arterial, and venous catheters were implanted 1 day before the experiment. Microinjection of nicotine into the supraoptic nucleus at doses of 1 and 10 micrograms resulted in transient increases in the plasma vasopressin concentration that were 7-fold and 11-fold greater, respectively, than control values at 3 min. There were also small transient increases in mean arterial blood pressure, but heart rate was unchanged. The microinjection of 2 and 20 ng of oxotremorine, a muscarinic agonist, into the supraoptic nucleus had no effect on the plasma vasopressin concentration, mean arterial blood pressure, or heart rate. These doses of oxotremorine were previously shown to have potent stimulatory effects on vasopressin release when microinjected into the paraventricular nucleus. These findings suggest that the central cholinergic stimulation of vasopressin release is due, in part, to activation of muscarinic receptors in the paraventricular nucleus and nicotinic receptors in the supraoptic nucleus.