PARENTAL BEHAVIOR 



1349 



an action on the liyi)otlialamiis. The in- 

 volvement of the hypothalamus (or at least 

 of extra-ovarian factors) is suggested by 

 the fact that the ovaries appeared his- 

 tologically normal until puberty, when the 

 abnormal estrous cycles began (Turner, 

 1939; Tedford and Young, 1960). At this 

 point it may be remarked that the dif- 

 ferences in secretory activity and in re- 

 sponsiveness to gonadal hormones between 

 male and female pituitary glands (Pfeiffer, 

 1936, 1937) are apparently due, not to 

 sexual differentiation of the hypophysis 

 during development, but to differentiation 

 of the hypothalamus (Harris and Jacob- 

 sohn, 1952; Martinez and Bittner, 1956). 

 There is evidence, summarized by Harris 

 (1955), that the hypothalamus is differen- 

 tiated into male and female types of activity 

 (with respect to its relationship with the 

 pituitary gland), very early in life. 



Stimulation and regulation of behavior 

 by central effects. In addition to these ef- 

 fects upon the ontogeny of central mecha- 

 nisms, evidence has recently accumulated 

 that some of the effects of hormones in 

 arousing and regulating behavior in adult 

 animals are exerted through direct effects 

 on central nervous structures. 



Fisher (1956) injected sodium testoster- 

 one sulfate into various hypothalamic loci 

 by a cannula introduced through an im- 

 planted electrode. In a number of male rats 

 tested by this method, he found various 

 combinations of "maternal" and "sexual" 

 behavior, sometimes occurring simultane- 

 ously. Among the responding animals, 

 Fisher noted that the overt responses were 

 characterized by exaggerated speed, com- 

 pulsiveness, and frequency, as compared 

 with the normal sexual and maternal be- 

 havior of untreated animals. In some ani- 

 mals, the behavior continued without dec- 

 rement for 90 minutes after the chemical 

 stimulus was supplied. 



Harris, Michael and Scott (1958) im- 

 ]ilanted into the brains of ovariectomized 

 female cats a fine platinum wire which had 

 been dipped into a molten fatty acid ester 

 of stilbesterol, so that the tip of the needle 

 was coated with a thin film of the estro- 

 genic substance. Of 17 animals so treated, 

 in which the tip of the implanted wire was 



in the posterior hypothalamus, 13 developed 

 estrous behavior, including complete mating 

 responses to male cats. In a control group 

 in which the same implant was made into 

 regions of the brain other than the hypo- 

 thalamus, only one of the 19 animals showed 

 any estrous response. Although on sys- 

 temic administration of estrogens, mating 

 behavior is stimulated only after a fully 

 cornified vaginal smear has developed 

 (Harris, 1959), 9 of the 13 animals which 

 showed mating behavior in response to the 

 hypothalamic implant had reproductive 

 tracts completely indistinguishable from 

 those of untreated control animals, as shown 

 by vaginal smears, weight of the genital 

 tract, and endometrial development. This 

 experiment makes it seem likely that, al- 

 though estrous behavior normally occurs at 

 a time when the reproductive tract is in 

 an estrous condition, the behavior itself 

 is aroused not by afferent effects of the 

 condition of the reproductive tract, but by 

 the direct effects of gonadal hormones on 

 the brain. 



A number of other experiments show 

 that humoral conditions which are known to 

 affect behavior have direct and, to some 

 extent, local effects on central nervous struc- 

 tures. Flerko and Szentagothai (1957) im- 

 planted small fragments of ovarian tissue 

 into various regions of the hypothalamus 

 and hypophysis of female rats. Estrogenic 

 hormone produced by the ovary is capable 

 of inhibiting the secretion of FSH by the 

 pituitary gland (see chapter by Greep). 

 Flerko and Szentagothai found that ovarian 

 fragments implanted into the anterior lobe 

 of the hypophysis had no effect on FSH 

 secretion. Implants in the mammillary re- 

 gion of the hypothalamus failed to induce 

 a significant change in FSH secretion (as 

 indicated by uterine weights), whereas 

 imi)Iants into the neighborhood of the para- 

 ventricular nuclei caused a significant de- 

 crease in uterine weights. From this ex- 

 periment, it seems probable that the effect 

 of the ovarian hormone on pituitary secre- 

 tion is mediated by its effect on hypo- 

 thalamic activity. 



Andersson (1953) found that the injec- 

 tion of very small amounts of hypertonic 

 saline solution into the third ventricle of 



