CHARLES H. SAWYER 



171 



Multiple recordings (31) have been made of the electrical activity of 

 various regions of the stereotaxically approached brains in several such 

 rabbits. An example of the changes evoked by vaginal stimulation is seen in 

 figure 5. Usually between a half minute and a minute after stimulation high 

 amplitude slow waves appeared in the limbic cortex and lateral preoptic region, 

 spindles in the frontal cortex and some spikes in the ventromedial region. The 

 changes could not be correlated with a behavioral after-reaction, which is lack- 

 ing in the rabbit, but they lasted from 5-7 minutes and then disappeared 

 abruptly. No such changes in the electrical record were observed on similar 

 stimulation of the anestrous rabbit. 



Various nerve-blocking agents, including atropine sulfate, have blocked the 

 release of pituitary gonadotrophin not only following artificial stimulation of 

 the vagina but also after the natural copulation-ovulation reflex, if injected 

 within a half minute post-coitum (37). In pituitary-blocking dosages atropine 

 sulfate induces high amplitude slow waves in the rabbit electroencephalogram 



Fig. 6. Efifects of a pituitary- 

 blocking dose of intravenous 

 atropine on rabbit EEG. High 

 amplitude slow waves were evident 

 in B in less than a minute after 

 atropine sulfate (15 mgAg) had 

 been injected intravenously, and 

 the threshold of arousal (not illus- 

 trated) was simultaneously ele- 

 vated. For abbreviations, see 

 figure 3. 





PO 



LHA 



. — ,5^ 



(EEG) within seconds after intravenous injection (fig. 6). It also raises the 

 threshold of EEG arousal on afferent or direct stimulation of the midbrain 

 reticular formation. Similar results with atropine by Rinaldi and Himwich 

 (26) have led them to propose the existence of a cholinergic mechanism within 

 the reticular activating center. Irrespective of this interpretation, the present 

 results suggest that afferent impulses concerned with pituitary activation may 

 have to traverse the multisynaptic extralemniscal reticular formation en route 

 to higher centers, or that a certain degree of arousal of the reticular formation 

 is required to permit or facilitate activation of higher centers. It is perhaps 

 significant that atropine blocks copulation-induced ovulation if an effective 

 dose reaches the brain prior to the onset of the aforementioned post-coital 

 EEG changes, roughly half a minute after stimulation. 



In pituitary-ovarian control mechanisms, the rat differs from the cat and 

 rabbit and more closely resembles the human in that it ovulates in a so-called 

 "spontaneous' manner. Working on the rat cycle with Everett and Markee 

 (9-1 1), we were able to show, with the use of such nerve-blocking agents as 



