Electrical Activity During the Estrous Cycle of the Rat: Cyclic Changes in Limbic Structures

Abstract

Changes in electrical activity in the hippocampus and amygdala during the estrous cycle were investigated in the rat to examine the relationship between the limbic system and gonadal function. It has been shown that localized seizure threshold in the dorsal hippocampus was significantly decreased during the interval between the morning of proestrus and morning of estrus. The lateral part of the amygdala behaved in approximately the opposite direction, with an increased threshold during the same period. The thresholds for the medial part of the amygdala had decreased on the night of the second day of diestrus to the morning of proestrus, but had increased above the diestrous values by the night of proestrus. These observations were discussed with reference to plasma gonadal steroid levels and possible regulatory role of limbic areas on the release of gonadotropin. Whereas ovariectomy eliminated the cyclic aspects of activity in the limbic system, a dampened cyclicity was restored by a single injection of 1...