Role of angiotensin II in elaborating the escape reaction during electric stimulation of the ventromedial hypothalamus in rabbits

The action of angiotensin-II, saralazin, captopril and antiserum to angiotensin-II, injected into the brain ventricles, on avoidance reaction to electrical stimulation of ventromedial hypothalamus was studied in experiments on rabbits. It has been found that angiotensin-II had a pronounced inhibitory effect, while saralazin, captopril and antiserum to angiotensin-II had a facilitating effect on the reaction.     

Analysis of the effect of increasing electrodermal stimulation on the somatovegetative reactions evoked by stimulation of the ventromedial hypothalamus

The influence of increasing electrodermal stimulation (EDS) on the dynamics of the somatovegetative reactions evoked by electrical stimulation of negative emotiogenic regions of the hypothalamus was studied. EDS produced a blocking effect on the somatovegetative reactions evoked by stimulation of the ventromedial hypothalamus (VMH). Pretreatment with naloxone prevented the effects of EDS. Injection of beta-endorphine in a dose of 10 micrograms to the lateral ventricules of the animal brain also blocked the somatovegetative reactions during VMH stimulation. Injection of beta-endorphine in doses of 50-100 micrograms enhanced and prolonged the somatovegetative reactions evoked by VMH stimulation. Elevated arterial blood pressure, pronounced bradycardia, extrasystoles, muscle tremor, and pathologic respiration were recorded. These disorders were completely reversed by EDS. It is assumed that both opiate peptides and their receptors are involved in the mechanism of the somatovegetative reactions evoked by VMH stimulation, experiencing the influence of EDS.     

Ibotenate lesion of the ventromedial hypothalamus lowers hyperthermic effects of prostaglandin E1

This experiment tested the effects of an intracerebroventricular injection of prostaglandin E1 on the sympathetic activation and the thermogenic changes in rats with ibotenate lesions of the ventromedial hypothalamus. Under pentobarbital anesthesia, twelve Sprague-Dawley male rats were lesioned bilaterally in the ventromedial hypothalamus with an injection of ibotenic acid (30 nmol into each side). Sham lesions were carried out in other twelve control rats. After 48 h, all animals were anesthetized with ethyl-urethane. The firing rate of the sympathetic nerves innervating the interscapular brown adipose tissue and the colonic and interscapular brown adipose tissue temperatures were monitored before and after an intracerebroventricular injection of prostaglandin E1 (500 ng) or saline. Prostaglandin E1 induced an increase in the firing rate of sympathetic nerves and the colonic and interscapular brown adipose tissue temperatures. These effects were reduced by the ventromedial hypothalamic lesion. Since ibotenic acid destroys cell bodies, the findings indicate that neurons of the ventromedial hypothalamus play a considerable role in the control of sympathetic activation and the thermogenic changes during prostaglandin E1 hyperthermia.     

Differentiated pressor and sympathetic responses to dual brain stimulation: ventromedial hypothalamus versus locus coeruleus

Sensitivity of the ventromedial hypothalamus (VMH) to electrical stimulation was compared with that of the locus coeruleus (LC) in urethane-anesthetized rats. Based not only on current strengths required to elicit threshold effects, but also on magnitude of pressor responses to suprathreshold stimulation, the LC was consistently more sensitive than the VMH. Despite this greater pressor sensitivity, splanchnic nerve firing increased almost equally upon stimulation of either brain area. Similar comparisons made in other rats following bilateral adrenalectomy or pretreatment with a vasopressin antagonist showed no significant alteration of pressor and sympathetic responsiveness to stimulation of either the LC or the VMH. When frequency of neural firing was recorded from a lumbar sympathetic trunk instead of the splanchnic nerve, increases in sympathetic nerve activity produced by LC stimulation were significantly larger than those produced from the VMH. The results suggest that greater pressor sensitivity of the LC is due, at least in part, to stronger constriction in vascular beds innervated by the lumbar sympathetic chains.     

Vaginocervical stimulation induces Fos in glutamate neurons in the ventromedial hypothalamus: Attenuation by estrogen and progesterone

Vaginocervical stimulation (VCS) induces the immediate-early gene product Fos in the ventromedial hypothalamus (VMH) of female rats. However, this induction is lower in ovariectomized rats that receive estradiol benzoate (EB) and progesterone (P) relative to an oil vehicle. We have observed that a substantial proportion of cells activated in the VMH by VCS stain for glutamate, and infusions of glutamate or its selective receptor agonists to the VMH inhibit both appetitive and consummatory sexual behaviors in females. This raises the possibility that VCS activates an inhibitory glutamate system in the VMH, and that ovarian steroids blunt the activation, although it is not known whether EB or P, alone or in combination, lead to this effect. The present experiment examined the ability of VCS to induce Fos in glutamate neurons in the VMH of ovariectomized rats under 4 hormonal regimens: oil, EB alone, P alone, or EB + P, following 1 or 50 distributed VCSs administered with a lubricated glass rod over the course of 1 h. Treatment with EB or P alone significantly reduced the number of glutamate neurons activated by 1 VCS, with P being more effective than EB. Treatment with EB + P also produced a significant reduction, but not to the extent of EB or P alone. Although EB and P work in synergy to activate sexual behavior in female rats, actions of EB or P alone are sufficient to blunt the ability of VCS to activate glutamate neurons in the VMH. It thus appears that ovarian steroids may “disinhibit” sexual responding, in part, by dampening the ability of VCS to activate glutamate neurons in the VMH. In turn, this may allow females to receive a sufficient number of intromissions for the activation of sexual reward and the facilitation of pregnancy.     

GABA influences the development of the ventromedial nucleus of the hypothalamus

The region that becomes the ventromedial nucleus of the hypothalamus (VMH) is surrounded by cells and fibers containing immunoreactive gamma‐aminobutyric acid (GABA) by embryonic day 13 (E13), several days before the nucleus emerges in Nissl stains. As GABA plays many roles during neural development, we hypothesized that it influences VMH development, perhaps by providing boundary information for migrating neurons. To test this hypothesis we examined the VMH in embryonic mice in which the β3 subunit of the GABA_A‐receptor, a receptor subunit that is normally highly expressed in this nucleus, was disrupted by gene targeting. In β3 ?/? embryos the VMH was significantly larger, and the distribution of cells containing immunoreactive estrogen receptor‐α was expanded compared to controls. Using in vitro brain slices from wild‐type C57BL/6J mice killed at E15 we found that treatment with the GABA_A antagonist bicuculline increased the number of cells migrating per video field analyzed in the VMH. In addition, treatment with either bicuculline or the GABA_A agonist muscimol altered the orientation of cell migration in particular regions of this nucleus. These data suggest that GABA is important for the organization of cells during VMH formation. © 2001 John Wiley & Sons, Inc. J Neurobiol 49: 264–276, 2001     

Electrophoretic characteristics of nuclear proteins in the rat liver after electric stimulation of the hypothalamus

The liver nuclear proteins of 3- and 6-month old rats were studied by the gel-electrophoresis technique after electrostimulation of hypothalamus. In this case new nuclear proteins with low molecular weight were found. The electrophoretic rate of these proteins is higher than that of histone H4. A decrease in the content of histone H2B in the nuclear liver of 6-month old rats was also found after electrostimulation of hypothalamus. The mechanism of this phenomenon is discussed.     

Neurochemical characteristics of the ventromedial hypothalamus and anti-aversive effects of anxiolytic agents in various anxiety models]

Neurochemical analysis using anxiosedative and anxioselective agents injected into the hypothalamus revealed that antiaversive action of camprione is only realised under conditions of domineering fear motivation whereas that of chlordiazepoxide, phenibut, indoter may also be realised under conditions of negative stressful zoo-social impacts mediated by serotonin.     

Neuropeptides in the mechanisms of the activation of escape reactions induced by stimulation of the ventromedial hypothalamus during food motivation satiation

Influence of food intake on hypothalamically induced avoidance reactions have been studied in rabbits. It was shown that first contact with food and beginning of food intake accompany with activation of avoidance reactions. Central action of cholecystokinin-octapeptide, pentagastrin, beta-endorphin and naloxone on avoidance reactions of fed and fasted rabbits before and during food intake was investigated. It was found that injection of cholecystokinin and naloxone, which had a satiated effect, act on avoidance reactions similarly in fed and fasted rabbits. Beta-endorphin inhibits avoidance behavior, and only pentagastrin activates avoidance reactions of fasted but not fed rabbits. It is concerned that influence of feeding motivation may modulate avoidance behavior by participation of endogenous gastrin-like peptide release into the perineuronal area during contact of rabbits with food and beginning of its intake.     

GABA influences the development of the ventromedial nucleus of the hypothalamus.

The region that becomes the ventromedial nucleus of the hypothalamus (VMH) is surrounded by cells and fibers containing immunoreactive gamma-aminobutyric acid (GABA) by embryonic day 13 (E13), several days before the nucleus emerges in Nissl stains. As GABA plays many roles during neural development, we hypothesized that it influences VMH development, perhaps by providing boundary information for migrating neurons. To test this hypothesis we examined the VMH in embryonic mice in which the beta3 subunit of the GABA(A)-receptor, a receptor subunit that is normally highly expressed in this nucleus, was disrupted by gene targeting. In beta3 -/- embryos the VMH was significantly larger, and the distribution of cells containing immunoreactive estrogen receptor-alpha was expanded compared to controls. Using in vitro brain slices from wild-type C57BL/6J mice killed at E15 we found that treatment with the GABA(A) antagonist bicuculline increased the number of cells migrating per video field analyzed in the VMH. In addition, treatment with either bicuculline or the GABA(A) agonist muscimol altered the orientation of cell migration in particular regions of this nucleus. These data suggest that GABA is important for the organization of cells during VMH formation.     

Estrogen regulation of proteins in the rat ventromedial nucleus of the hypothalamus

The effects of estradiol (E2) on the expression of proteins in the pars lateralis of the ventromedial nucleus of the hypothalamus (VMNpl) in ovariectomized rats was studied using 2-dimensional gel electrophoresis followed by RPLC-nanoESI-MS/MS. E2 treatment resulted in the up-regulation of 29 identified proteins. Many of these proteins are implicated in the promotion of neuronal plasticity and signaling.     

Effect of centrally administered cholecystokinin on feeding behavior induced by electric stimulation of the lateral hypothalamus in the rabbit

In experiments on 15 freely moving rabbits cholecystokinin octapeptide sulfate (CCK-8-S) in a dose of 10 ng considerably suppressed alimentary behaviour of the animals elicited by electrical stimulation of the lateral hypothalamus. Increasing of the peptide doses to 100 and 200 ng elicited an analogous effect. CCK-8-NS in 10 ng dose produced a lesser effect on feeding of the animal, but increasing of the dose of nonsulphated CCK to 100 ng led to a considerable prolongation of feeding. CCK-8-S and CCK-8-NS in doses used did not affect the reaction of avoidance in rabbits caused by electrical stimulation of the ventromedial nucleus of the hypothalamus.