82 Charles H. Sawyer and M. Kawakami 



with reproductive behavior and neuroendocrine function persists. Koikegami 

 et al. (23) were the first to report that stimulation of medial amygdaloid 

 nuclei induces ovulation, and olfactory activity has been implicated in 

 pharmacological induction of ovulation in the rabbit (24). Lesions in the 

 amygdala and underlying pyriform cortex lead to hypersexualism in males of 

 various species (25, 26). The lesions in the female rabbit rhinencephalon 

 depicted in Fig. 2 did not inhibit reproductive behavior or block copulation- 

 induced ovulation (19). However, there were some indications that removal 

 of the olfactory bulbs and section of the fornix (combined lesions A and B) 

 lead to a condition of behavioral hypersexualism in these females. The 

 mammillary body, which receives projections from these areas and in which 

 lesions lead to anestrus, will assume a position of considerable importance 

 in the estrous behavior of the female rabbit if later experiments confirm 

 these preliminary findings. 



The brainstem reticular activating system (27) is also morphologically and 

 functionally closely related to the hypothalamus and its activity. This 

 system is especially sensitive to several of the drugs found to block ovulation 

 in the rabbit and rat (28, 29). However, these drugs have been shown to be 

 capable of blocking ovulation at the hypothalamic level (16), and Critchlow's 

 (30) midbrain lesions which blocked ovulation in the rat did not necessarily 

 destroy the reticular activating system. 



AFTERREACTION TO COITUS; FEED-BACK HYPOTHESIS 



In an effort to obtain neural correlates of pituitary activation by recording 

 EEG activity simultaneously from several regions of the brain under 

 conditions stimulatory to the adenohypophysis, chronic depth electrodes 

 were implanted in the brains of many female rabbits. While continuous EEG 

 records were being made these rabbits were free to move about, eat, drink 

 and even to copulate with or fight other rabbits. Copulation in the estrous 

 rabbit or vaginal stimulation in the estrous, estrogen-treated rabbit (31) was 

 used to trigger the release of pituitary ovulating hormone. An example of 

 the type of EEG change seen under these conditions (32) is contained in 

 Fig. 3. During the stimulation period the changes were almost entirely 

 artifacts attributable to movement. Within several minutes, however, the 

 record characteristically assumed a "sleepy" appearance with spindle bursts 

 in the frontal cortex and related areas (Fig. 3, B). The "sleepy" record 

 continued from several minutes to half an hour or more and was replaced 

 by a most unusual EEG pattern (Fig. 3, C-E). What appeared to be a 

 hyperaroused record, with 8-sec sinusoidal waves predominant in several 

 rhinencephalic areas related to the hippocampus, was associated with 

 behavioral depression. The rabbit lay prone with her head on the floor (Fig. 

 4, c-e), her ears bent back, eyes partially closed, pupils constricted, brady- 

 cardia and depressed respiration. On recovery her EEG record reverted to 



