Dual effect of electrochemical stimulation of the medial preoptic area on the release of LH: possible neurotransmitter involvement.

Electrochemical and electrical stimulation of the medial preoptic area (MPA) was shown to induce release of LH in rats. Owing to differences in cytoarchitecture and neural afferents between the medial (mMPA) and lateral (lMPA) parts of the MPA, we decided to explore whether this difference in organization would distinctly influence the secretion of gonadotropin. Both parts of the MPA were electrochemically stimulated on the day of proestrus in freely behaving rats bearing chronic implanted electrodes.

Intraventricular injection of agents that enhance cyclic adenosine monophosphate formation leads to inhibition of proestrous luteinizing hormone surge in rats.

The effect of increasing hypothalamic levels of 3',5'-cyclic adenosine monophosphate (cAMP) on the preovulatory surge of luteinizing hormone (LH) and ovulation was studied in cycling rats. Animals hearing chronically implanted guiding cannulae into the third ventricle were injected with agents known to enhance the cellular levels of cAMP. Hourly blood samples from the unanesthetized, unrestrained rats were obtained between 11.

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.

Daily variations in the sensitivity of proestrous LH surge in the inhibitory effect of intraventricular injection of 5-HT or GABA in rats.

Intraventricular injection of 5-hydroxytryptamine (5-HT) into female rats at 11:00 h on the day of proestrus inhibited the preovulatory surge of luteinizing hormone (LH) and ovulation. A similar response was observed after the activation of the serotonergic system by stimulation of the median raphe nucleus. A diurnal rhythm of these responses was observed.

Norepinephrine--stimulated activity of hypothalamic adenylate cyclase varies throughout the estrous cycle of the female rat.

The activity of hypothalamic adenylate cyclase was studied throughout the estrous cycle of the female rat. The activity of the enzyme was determined in particulate fractions obtained from hypothalami of rats killed at 10.00 h and 16.

Glutamic acid decarboxylase activity of the preoptic area and hypothalamus is influenced by the serotonergic system.

The effect of the serotonergic system on glutamic acid decarboxylase (GAD) activity of the preoptic area and the hypothalamus was studied in female rats on the day of proestrus. A circadian rhythm of GAD activity was observed with higher values in rats killed at 1130 h than in rats killed at 1500 h. In rats bearing lesions of the median raphe nucleus (MRn), a nucleus that sends 5-hydroxytryptamine nerve terminals to the areas under study decreased GAD activity.

Further evidence of an opposite effect of dorsal and median raphe nuclei on the proestrous surge of LH.

The effect of stimulation or lesions of either the dorsal or the median raphe nucleus on the proestrous surge of LH and on ovulation was studied in rats kept under constant illumination. Electrochemical stimulation (anodic DC of 100 microA during 30 sec) was applied at noon on the day of proestrus through chronically implanted electrodes. Lesions of the raphe nuclei were made by passing a cathodic current of 1 mA for 20 sec through nichrome electrodes stereotaxically implanted.

Inhibition of proestrous LH surge and ovulation in rats evoked by stimulation of the medial raphe nucleus involves a GABA-mediated mechanism.

The neurotransmitters involved in the inhibition of luteinizing hormone (LH) release induced by electrochemical stimulation (anodic d.c., 100 microA/30 s) of the medial raphe nucleus (MRn) were studied.

The Pineal Gland Mediates the Inhibition of Proestrous Luteinizing Hormone Surge and Ovulation in Rats Resulting from Stimulation of the Medial Raphe Nucleus or Injection of 5-HT into the Third Ventricle.

Abstract In cycling rats, electrochemical stimulation of the medial raphe nucleus or injection of 5-HT into the third ventricle on the day of proestrus blocked the preovulatory surge of luteinizing hormone and inhibited ovulation. The inhibitory effect of these procedures on gonadotropin secretion failed to occur in rats that had been pinealectomized a few weeks earlier. In contrast, sham-pinealectomized rats exhibited a response similar to that of intact rats.

Hypothalamic cyclic AMP after the injection of ovarian steroids into ovariectomized rats.

The effect of ovarian steroids on the concentration of adenosine 3',5'-cyclic monophosphate (cAMP) in the hypothalamus was studied in ovariectomized rats. Ovariectomized rats exhibited a lower cAMP concentration than intact rats. The administration of a single dose of estradiol benzoate (50 micrograms/kg body weight) resulted 3 days later in a rise of cAMP values, but levels did not reach those observed in estrous rats.

The inhibition of proestrous LH surge and ovulation in rats bearing lesions of the dorsal raphe nucleus is mediated by the locus coeruleus.

Lesions of the dorsal raphe nucleus (DRn) were shown to block the proestrous surge of LH and the shed of ova normally found the following morning. The possibility that this effect could be mediated by the locus coeruleus (LC) was studied in the present work in view of the fact that stimulation of the LC produced similar responses on LH release and that systemic injection of the beta-adrenergic blocking agent, propranolol, partially prevented the effect of DRn lesions. The blocking effect of DRn lesions on proestrous LH surge and ovulation was reproduced by the injection of either methysergide (1 microgram on the day of proestrus), a serotonin (5-HT) blocking agent, or p-chlorophenylalanine (0.

Activation of the CNS noradrenergic system may inhibit as well as facilitate pituitary luteinizing hormone release.

Earlier work established that neural secretion of luteinizing hormone-releasing hormone (LH-RH) and the resultant release of pituitary gonadotropins could be facilitated by activating alpha-receptors of a central noradrenergic (NA) system. The present study emphasizes that central NA mechanisms may also inhibit LH release largely through activation of beta-adrenergic receptors.

Changes of the release of luteinizing hormone (LH) on the day of proestrus after lesions or stimulation of the raphe nuclei in rats.

The effect of stimulation or lesion of the raphe nuclei on ovulation and on the release of luteinizing hormone (LH) on the day of proestrus was studied in unanesthetized, unrestrained rats. Electrochemical stimulation (anodic DC or 100 microA during 30 s) was applied at 12.00 h on the day of proestrus through chronically implanted stainless steel electrodes.

Ventral premammillary nuclei mediate pheromonal-induced LH release stimuli in the rat.

The rise in the concentration of LH in the serum that takes place in ovariectomized, estrogen-primed rats exposed to the odors from a cage with bedding soiled by a male rat was completely prevented by bilateral lesions destroying the ventral premammillary (PMv) nuclei. These results suggest that the pheromonal stimuli generate stimuli that course through a pathway which involves the PMv nuclei before they reach the hypothalamus. In addition, the chemosensory information is apparently transmitted centrally by an uncrossed pathway in view of the fact that removal of one vomeronasal organ combined with lesions of the contralateral PMv nucleus, but not of the ipsilateral nucleus, suppressed the release of LH in rats exposed to male odors.

Inhibitory influence of the nuclei of the posterior hypothalamus on the pro-oestrous surge of LH.

The effect of transecting caudal afferents to the medial basal hypothalamus on the pro-oestrous surge of LH was studied in cyclic female rats. Rats with transverse cuts placed just in front of the mammillary bodies and caudal to the ventromedial hypothalamic nucleus showed an earlier time of onset of pro-oestrous surge of LH. Conversely, rats with transverse cuts placed 2 mm more caudally or with cuts along the lateral edges of the hypothalamus showed no altered release of LH.

Blockade of the release of LH induced by pharmacological suppression of adrenergic inflow into the locus coeruleus.

Previous studies have indicated that stimulation of the locus coeruleus (LC) produced inhibition of the release of LH induced by stimulation of the medial preoptic area (mPOA) in ovariectomized, estrogen-primed rats. A similar response following the application of drugs into the LC was taken as an index of activation of the LC neurons. The injection of the phenylethanolamine N-methyltransferase (PNMT) blocking-agent, 2,3- dichloromethylbenzylamine ( DCMB , 0.

Beta-adrenergic receptors in the premammillary nucleus mediate the inhibition of LH release evoked by locus ceruleus stimulation.

The neurotransmitter and andrenoceptors involved in the inhibition of luteinizing hormone (LH) release induced by stimulating the locus ceruleus nucleus (LC) have been characterized in ovariectomized, estrogen-primed rats in which the release of LH was triggered by electrical stimulation of the medial preoptic area. Blockade of norepinephrine synthesis by the injection of the dopamine beta-hydroxylase inhibitors, diethyldithiocarbamate or fusaric acid, prevented the inhibition of LH release, whereas blockade of epinephrine synthesis by injecting the phenylethanolamine N-methyltransferase inhibitor, 2,3-dichloro-methylbenzylamine, had no effect. In addition, the inhibition of LH release was prevented by systemic injection of propranolol but not of phenoxybenzamine.

Hypothalamic cyclic-AMP throughout the 4-day estrous cycle of the female rat.

The concentration of adenosine 3',5'-cyclic monophosphate (cAMP) in the hypothalamus was measured in the morning (10.00 h) and in the afternoon (16.00 h) during the 4-day estrous cycle of the female rat.

Prolactin release induced by stress and the influence of oestrogen and progesterone treatments, sex and daily rhythm.

The effect of sex, ovarian steroids and time of the day on the release of prolactin induced by stress was studied. Albino rats were bled by heart puncture and immediately anaesthetized with ether; 10 min later they were bled again. Ovariectomized, oestrogen-primed rats showed a daily rhythm in the stress (bleeding plus ether) induced prolactin release with maximal concentration of prolactin in the serum at night (01.

Release of LH in the female rat by olfactory stimuli. Effect of the removal of the vomeronasal organs or lesioning of the accessory olfactory bulbs.

The release of LH in ovariectomized, estrogen-primed rats exposed to male or female rats was studied. The concentration of LH in the serum was measured in blood samples obtained by an indwelling jugular cannula. A blood sample was taken at 12.