Abstract
The effect of electrical stimulation of the medial preoptic area (MPO) on integrated multiple unit activity (MUA) in the arcuate nucleus (ARC) during the estrous cycle of the Wistar rat was examined with reference to the release of “the ovulating hormone” from the anterior pituitary gland. The electrical stimulation (0.5ms, 200Hz, SW, 100-500μA) was applied for 30min between 14:00 and 16:00 under pentobarbital anesthesia. 1) When the stimulus induced ovulation on the following day, MUA changes in the ARC were observed during the electrical stimulation on the day of proestrus, in contrast to their appearance after the electrical stimulation on the day of diestrus II. 2) The electrical stimulation facilitated the release of “the ovulating hormone” on the day of proestrus, while on the day of diestrus II it increased pituitary potency to induce ovulation as well, tested by an injection of a crude extract from the anterior pituitary of the experimental animals into recipients of diestrus II. 3) The circulatory level of the luteinizing hormone (LH) elevated immediately after the electrical stimulation, reached the maximum level 30 min later and returned to the control level after 60min on the day of proestrus. However, on the remaining days of the cycle it elevated immediately, reached the maximum level at 60min, but did not return to the control level even 120min after the electrical stimulation.
Therefore, that the electrical stimulation of the MPO induces neural excitation of the ARC and increase of LH content in the circulation with a discrepancy in the timing throughout the cycle, indicates that the stimulation induces both synthesis and release of LH in the pituitary gland.
