1 78 Discussions 



of a persistent corpus in these animals was ruled out by examining the ovaries at 

 laparotomy and later, at autopsy. Accordingly, in eight ewes the behavioral manifesta- 

 tions of heat were abolished by hspothalamic lesions, presumably without affecting 

 pituitary gonadotropin secretion. The area destroyed by the lesions in se%en of these 

 animals is shown in Fig. 1. Part of the brain of the other sheep was inadsertently 

 destroyed, so detailed localization was not possible. The se\en lesions were in the 

 basal ponion of the h>pothalamus, sharing in common an area of destruction just 

 in front of the infundibulum and above the median eminence. 



Lesions in other pans of the h>pothalamus in 17 animals had no effect on either 

 ovarian cycling or heat. The areas of destruction in these sheep are showTi in Fig. 2. 

 It is apparent that extensive lesions in the diencephalon did not affect sexual behavior. 



SITES OF HYPOTHALAMIC LESWNS K 17 EWES WITH HCfiVAL 

 HEAT PERIODS AND CYCUC OVARIES 



:£5'=7r£D BYLE30NS 



Fig. 2. 



Indeed, in a number of instances, ewes with control lesions accepted the male less 

 than 24 hr postoperatively, while still staggering from the effects of the pentobarbital 

 anesthesia. Therefore, the data indicate that the effect of lesions on sexual behavior is 

 specific, and depends on a reasonably discrete area in the anterior h>pothalamus. 



The idea of a diencephalic centre concerned with sexual behavior is, of course, not 

 new. Dempsey and Rioch (/. Neurophysiol. 2, 9, 1939j and Bard (Res. Publ. Assn. 

 Nerv. Ment. Dis. 20, 551, 1940) originally presented evidence for such a centre by 

 comparing the sexual responses of decorticate and decerebrate guinea-pigs and cats. 

 Subsequently, Brookhart and his associates (Endocrinology 28, 561, 1941) obser\ed 

 absence of mating behavior in female guinea-pigs with anterior hvpoihalamic lesions, 

 in some cases without ovarian atrophy. Sawyer and Robison (/. Clin. Endocrinol. 

 and Metab. 16, 914, 1956) reported similar results following lesions of the anterior 

 hypothalamus in cats, as Dr. Sawyer mentioned this morning. The exact role played 

 by this "centre" in heat is not clear. Harris, Michael and Scott (Ciba Symposium on 

 Neurological Basis of Behavior, p. 236, London, 1958) were able to produce heat in 

 ovariectomized cats by the implantation of minute amounts of estrogen in the posterior 

 hypothalamus, while implantations in the anterior hvpothalamus, other parts of the 

 brain, and the periphery were ineffeai\e. An interesting feature of these experiments 

 was the seemingly fixed latent period of three days between hormone implantation 

 and the onset of heat. Somewhat similar results but with a shorter latent period have 

 been obtained in rats by Fisher (Reticular Formation of the Brain, p. 251, Boston, 1958). 

 Delgado (Abstr. list Inter. Congr. Physiol., p. 29, 1959) has reported "increased sexual 

 aaivity" in monkeys following remote control stimulation of the h>pothalamus, but 

 except for this observation, there is little data on whether or not sexual receptivity can 

 be induced by electrical stimulation of appropriate diencephalic centres. An indirect 

 connection between the hypothalamic centre and the behavioral events has also not 

 been ruled out. As Mr. Hammond said, his original suggestion that tonic contractions 

 of the uterus play a role in heat (Hammond, Jun., /. Endocrinol. 4, 1 69, 1 945) is probably 

 not true for sheep, since Robinson (Endocrinology 55, 403, 1955) was able to produce 

 heat in hysterectomized ewes. However, the cow is apparently different. The cow 



