The effects of stimulation and lesion of raphe nuclei on luteinizing hormone release in estrogen-progesterone-treated ovariectomized rats

Inhibition of Proestrous LH Surge and Ovulation in Rats Evoked by Stimulation of the Medial Raphe Nucleus Involves a GABA-Mediated Mechanism

“…The ability of electrochemical stimulation of the MRn to in hibit the preovulatory surge of LH and ovulation observed in the present work is in agreement with previously reported re sults [5,8,33,52], These findings suggest that activation of MRn neurons inhibits the release of LH on the day of proest rus. That this effect is due to the activation of a serotonergic pathway is supported by several facts, namely: (a) the MRn is rich in neurons that contain and synthezise 5-HT (12,53] and send ascending axons to the preoptic area-medial basal hypo thalamus [2,3,11,32,38,43,54]; (b) local injections of the 5-HT synthesis inhibitor, /;-chlorophenylalanine (PCPA), pre vented the inhibitory effect of MRn stimulation on LH release [33]; (c) systemic injection of the 5-HT antagonist, methyser gide, in the present work also prevented the inhibition of LH release evoked by MRn stimulation; and (d) lesions in the MRn produced a significant decrease of 5-HT content [21,27] and tryptophan hydroxylase activity [18,23] in the hypothalamus, and electrochemical stimulation of this nucleus has been shown to produce an increase in multiunit spike activity in the medial preoptic area [7].…”

Neural Regulation of Luteinizing Hormone Secretion in the Rat*

“…Manipulation of brain 5-HT levels by pharmacologic means by either raising or decreasing the levels in untimely fashion (381)(382)(383)(384) in order to disrupt the daily rhythm of 5-HT metabolism blocked ovulation (382,383) and the LH surge induced by estrogen in ovariectomized rats (384,385). Similarly, stimulation of the dorsal raphe nucleus inhibited ovulation (386) and ovarian steroid-induced LH secretion (387). On the other hand, drastic reduction of hypothalamic 5-HT levels on a chronic basis attenuated the estrogen-induced LH surge (388), but appropriate supplementation with P overcame the 5-HT deficiency and elicited a normal LH surge (387,389).…”

“…Similarly, stimulation of the dorsal raphe nucleus inhibited ovulation (386) and ovarian steroid-induced LH secretion (387). On the other hand, drastic reduction of hypothalamic 5-HT levels on a chronic basis attenuated the estrogen-induced LH surge (388), but appropriate supplementation with P overcame the 5-HT deficiency and elicited a normal LH surge (387,389). In general, although there is considerable evidence in support of a facilitory role of 5-HT, the nature of 5-HT participation in preovulatory LH release remains to be determined especially in view of the fact that pharmacological agents which modify 5-HT levels also concurrently affect hypothalamic E concentrations (390).…”

Serotonergic Innervation of the Forebrain in the North American Opossum; pp. 213–228

“…In the hypothalamus serotonergic innervation is dense within the ventrome dial and supraoptic nuclei, consistent with its known role in neuroendocrine and re productive funtions [Arendash and Gallo, 1978;Caggiula et al, 1976;Crowley and Zemlan, 1981;Hery et al, 1978;L u m e t t al., 1984;Walloch et al, 1981], In the thala mus serotonergic innervation is particu larly rich within the midline nuclei. Such nuclei receive multiple inputs and are known to innervate the amygdala and hip pocampus [Amaral and Cowan, 1980;Mehler, 1980;Oilerson and Ben-Ari, 1979;Riley and Moore, 1981;Russclien, 1982;Veening, 1978;fLyss et al, 1979].…”