Triggering of the Pituitary by the Central 

 Nervous Sy stent 



CHARLES H. SAWYER 



University of California, Los Angeles and 

 Veterans Administration Hospital, Long Beach, California 



FOR SEVERAL YEARS it has been realized that the anterior lobe of the pituitary 

 gland, though all but lacking in nerve fibers, is nevertheless partially con- 

 trolled by the nervous system. The secretions of adrenocorticotrophin, thyro- 

 trophin and gonadotrophin from the adenohypophysis are influenced by 

 extrinsic stimuli and psychic factors via nervous pathways. There is strong 

 evidence (i6), generally though not universally (44) accepted, that the final 

 pathway to the hypophysis involves humoral mediation via the hypophyseal 

 portal system (42, 13). Although we have been interested in certain aspects of 

 humoral mediation (22-24, 28, 36-39), the present discussion is concerned, not 

 with this final pathway, but with recent work in our laboratory on more cen- 

 tral mechanisms triggering the release of gonadotrophin. Topographically, the 

 area under consideration is the hypothalamus and its afiferent nervous path- 

 ways. 



In studies on nervous control of the release of gonadotrophin the rabbit 

 and the cat are excellent experimental subjects, since neither ovulates spon- 

 taneously but only after the nervous system triggers the release of pituitary 

 ovulating hormone at copulation. These forms have been used to test the effects 

 of artificial stimulation and nervous lesions and to record changes in the electri- 

 cal activity of the brain accompanying various types of artificial stimulation, 

 with ovulation as the index of effectiveness of stimulation and intactness of 

 nervous pathways. 



The estrous cat appears to have a lower threshold to afferent stimulation of 

 gonadotrophin release than does the rabbit. It was discovered some 20 years 

 ago by Greulich (14) that the estrous cat would ovulate in response to stimulat- 

 ing the vagina with a glass rod about as readily as to natural coitus. With 

 Everett (33), we found that the anestrous cat could be primed with estrogen 

 and equine (PMS) gonadotrophin to a state at which it would likewise ovulate 

 after vaginal stimulation. Behaviorally, such a cat undergoes the typical 'after- 

 reaction' which characteristically follows mating and perhaps signifies orgasm: 



' Several of the investigations herein reviewed were supported in part by a grant B-334, 

 from the National Institutes of Health. 



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