64 G. W. Harris 



the cerebral cortex. He found that none of these structures was essential for 

 post-coital ovulation in the rabbit, and concludes ". . . that ovulation occurs 

 as a result of intense sexual or emotional excitement rather than as a result of 

 a reflex initiated by stimulation of any specific group of sensory endings". 

 It seems likely, then, that under normal conditions of coitus afferent impulses 

 from many dilTerent receptors converge in the diencephalon and in some way 

 excite anterior pituitary activity. 



Electrical Stimulation of Central Nervous System 



The first positive evidence that reflex nerve tracts do activate LH release 

 came from the experiments of Marshall and Verney (69). These workers 

 showed that electrical stimuli applied through the lumbar spinal cord or 

 through the head of rabbits resulted in ovulation and pseudopregnancy in 

 a large proportion of animals. The stimulation used was strong and diffuse, 

 resulting in generalized convulsions, so that no localization was possible. It 

 seemed likely, hovv'ever, that the site of action was some region in the central 

 nervous system. The results of experiments in which localized stimuli were 

 applied to different sites in the diencephalon were soon forthcoming. Harris 

 (43), using a stereotaxic machine, stimulated the hypothalamus or pituitary 

 gland of ether-anesthetized rabbits. It was found that stimulation of the 

 tuber cinereum, posterior hypothalamus or pituitary gland directly might 

 result in ovulation or the formation of cystic or hemorrhagic follicles. 

 Similar results were reported by Haterius and Derbyshire (50) who found 

 that electrical stimuli applied to the preoptic region evoked ovulation. Some 

 ten years after these reports two groups of workers observed that electrical 

 stimuli, too weak to excite LH discharge and ovulation if applied directly to 

 the pituitary gland, might be fully effective if applied to the tuber cinereum. 

 Markee, Sawyer and Hollinshead (65) anesthetized rabbits with ether and 

 stimulated the pituitary at operation by a pharyngeal or temporal route, 

 and the hypothalamus via the superior orbital fissure. It was found that 

 stimulation of the pituitary did not result in ovulation unless there were signs 

 of spread of the stimulus, whereas stimulation of the hypothalamus at a 

 lower voltage resulted in ovulation in three out of four animals. Harris (44) 

 used the remote control method of stimulation which permits the use of 

 unanesthetized animals and the repetition of an experiment in any one 

 animal. The method consisted essentially of implanting a coil of wire (about 

 2000 turns) beneath the scalp. The ends of the coil were connected to 

 electrodes, one of which was inserted through a trephine hole in the skull so 

 that the stimulating tip was placed in some part of the hypothalamus or 

 pituitary gland. After recovery from the operation, electrical stimulation was 

 applied by placing the animal in an electro-magnetic field. Forty-two experi- 

 ments on seventeen rabbits showed that stimuli applied to various regions of 

 the tuber cinereum might elicit a full ovulatory response, even when applied 



