170 



PHYSIOLOGICAL TRIGGERS 



-7t 



^ -2 



were characterized by the ap- 

 pearance of high amphtude 

 fast (30/sec) activity (fig. 3) 

 centering in the lateral pre- 

 optic region. Both the altered 

 electrical activity and the 

 capacity of the treatment to 

 activate the pituitary were 

 eliminated by transecting the 

 olfactory tracts just behind 

 the olfactory bulbs. The areas 

 from which the 'intrinsic ol- 

 factory activity' was recorded 

 are seen in figure 4. This ac- 

 tivity is most likely transmit- 

 ted to hypothalamic nuclei 

 via the medial forebrain bun- 

 dle. An alternative route is 

 via the amygdala and the 

 stria terminalis. Perhaps both 

 channels transmit the artifi- 

 cially induced rhinencephalic 

 activity to its hypothalamic 

 target. The role of histamine 

 in these experiments cannot 

 be that of a final neurohu- 

 moral mediator to the hypo- 

 physis for, if so, it should have 

 been equally efifective in the 

 absence of the olfactory bulbs. 

 The naturally estrous fe- 

 male rabbit, at least in the 

 New Zealand strain most 

 commonly employed by us, 

 does not ovulate in response 

 to artificial stimulation of 

 the vagina with a glass rod. 

 Primed with extrinsic estro- 

 gen, however, these rabbits 

 will respond positively to 

 this treatment in about 50 

 per cent of the cases (29). 



