Localized Changes in Electrical Activity of the Hypothalamus in Estrous Cats Following Vaginal Stimulation

¹ From the Department of Anatomy, University of California Medical Center, Los Angeles and Medical Research Programs, Veterans Administration Hospital, Long Beach, California

In experiments designed to record central nervous electrical activity related to neurogenic stimulation of the adenohypophysis, hypothalamic EEG records were made of the effects of vaginal stimulation in the estrous cat. Mechanical stimulation, known to be capable of activating release of pituitary ovulating hormone in the estrous animal, evoked a reproducible EEG pattern in the anterior and lateral hypothalamus, in and around the medial forebrain bundle. This alteration of the spontaneous resting EEG was characterized by bursts of increased frequency and amplitude lasting several seconds or by trains of high amplitude slow waves. These changes recurred spasmodically for 3–7 minutes and may be temporally related to the behavioral after-reaction in the unrestrained unanesthetized cat. Although present in 10 out of 13 estrous cats no such EEG changes could be recorded in any of 9 anestrous animals. The likelihood that these alterations in nervous activity represent some of the electrical concomitants of neurogenic stimulation of the release of pituitary ovulatory hormone is discussed.