[Regulation of pituitary gonadotropin release of the frontal lobe neocortex (1)]

It has been said that the frontal lobe neocortex regulates the secretion of pituitary hormones. In the present study, the nerve circuit including the frontal lobe neocortex which is concerned in regulating the secretion of pituitary gonadotropin was studied in the 4-day vaginal cycle of female Wistar rats. Electric stimulation (monophasic pulse wave, 1Hz, 6 approximately 9V) of the dorsal part of the anterior frontal lobe neocortex induced evoked potential in the thalamic dorsomedial nucleus (DM), the basolateral amygdaloid nucleus (basolateral-AMYG), the medial septal nucleus (m-SEPT) and the anterior border of the diagonal band of Broca (DBB). Multiple unit activity (MUA) recorded in the DM, basolateral-AMYG and m-SEPT showed a fluctuation with the estrous cycle in which the minimum level was observed on the day of proestrus and the maximum level was observed on the day of estrus. But MUA did not show a distinct fluctuation with the estrous cycle in the frontal lobe neocortex. A horizontal circular cut of the median region in the forebrain-limbic area including the m-SEPT and the anterior border of the DBB on the day of diestrus II induced vaginal cornification on the following day. Excision of the dorsal region of the anterior frontal lobe neocortex on the day of diestrus II increased the serum concentrations of luteinizing hormone (LH) in the afternoon of that day and induced vaginal cornification on the following day. Electrochemical stimulation (DC 120 microA, 30 sec) of the anterior frontal lobe neocortex just before the critical period of ovulation on the day of proestrus blocked the preovulatory surge of LH. Electrochemical stimulation of the anterior frontal lobe neocortex just after excision of the lateral amygdaloid nucleus (lateral-AMYG) including the basolateral-AMYG did not block the preovulatory surge of LH and ovulation. Electrochemical stimulation of the frontal neocortex after excision of the DM did not block the preovulatory LH surge. Excision of the m-SEPT showed a similar effect, but it had little effect on the blockade of the inhibition of LH secretion induced by electrochemical stimulation of the anterior frontal lobe neocortex. It became clear that the dorsal region of the anterior frontal lobe neocortex has an inhibitory function on the secretion of LH and ovulation through the nerve circuit including the DM, the basolateral-AMYG and the median region of the septal area. Then the anterior frontal lobe neocortex probably participates in the periodical rhythm of LH secretion with the estrous cycle.