CYCLIC CHANGES IN ELECTRICAL ACTIVITY OF RAT MIDBRAIN RETICULAR FORMATION DURING ESTROUS CYCLE

The influence of midbrain reticular formation activity on the arcuate nucleus in the hypothalamus and the frontal cortex during the estrous cycle was examined by measuring the average evoked potential and the arousal threshold in the female rat, chronically implanted with electrodes. The major changes in the evoked potential of the arcuate nucleus occur during the morning of proestrus, and in the cortical potential, during the night of proestrus. Arousal thresholds also show changes related to the estrous cycle. The effect of hormones on the arousal threshold of ovariectomized rats indicates that the activity of the midbrain reticular formation is related to estrogen-progesterone levels during the estrous cycle. The findings suggest direct and indirect facilitation in fiber connections between the midbrain tegmental area and the basal hypothalamic area, and/or between the tegmental area and the frontal cortex during the period from proestrous to estrous vaginal smears. © 1969.