Discussions 



181 



(ICSH) in the male dog, the castrate dog with a hypothalamic lesion shows approxi- 

 ately the same low level of gonadotropin as the non-castrate lesion dog. This is shown 

 in Fig. 4, which summarizes data obtained using Dr. Simpson's assay method for the 



50 



Normal rats 



No. of animals (29) 



Lesions of 

 hippocampus, 

 thalamus, 

 cortex 



(20) 



Lesions of Lesions of 



anterior tuberal 



hypothalamus region 



(8) 



(8) 



\^ j = Day of vaginal opening 



= Day of first estrus 



I =Standard error 

 Fig. 5. EfTect of brain lesions on the onset of puberty. 



gonadotropins (Davidson, Contopoulos and Ganong, Endocrinology, in press, 1960). 

 This suggests that the feedback mechanism regulating gonadotropin secretion in the 

 male dog is primarily at the hypothalamic rather than the pituitary level. In the case 



