HORMONES AND MATING BEHAVIOR 



1203 



Valonstcin, Sinks and Young, 1955; Gerall, 

 1958). Experimental males were castrated 

 within 2 days after birth and injected daily 

 witii up to 500 ixg. testosterone propionate 

 per 100 gm. body weight. In neither experi- 

 ment, and contrary to what was found in 

 the rat, was the time of the first ejaculation 

 or the ultimate level of sexual behavior 

 affected; mounting may have been preco- 

 cious. 



Examination of data ol)tained from young 

 female chickens and jjrepubertal female rats 

 and guinea i)igs injected with gonadotrophic 

 hormone, with estradiol benzoate alone, or 

 with estradiol benzoate in combination with 

 l)rogesterone reveals results that are not 

 clear. Masculine head furnishings and an 

 "astonishing hypertrophy" of the oviducts 

 were seen in brown Leghorn females receiv- 

 ing daily injections of pituitary gonado- 

 troiihin for 14 to 36 days beginning at 21 

 to 47 days of age, but behavior was "ap- 

 l)arently unaffected" (Domm and Van 

 Dyke, 1932b). Female white Leghorn chicks 

 injected with 0.17 mg. estradiol benzoate 

 daily beginning the 15tli day of age squatted 

 for treading males after 18 to 26 treat- 

 ments, but chicks in which injections were 

 started the 2nd day and continued for 34 

 days were never seen to scjuat for a tread- 

 ing male (Noble and Zitrin, 19421. 



Estrous reactions were induced in 4 of 

 18 spayed female rats given estradiol ben- 

 zoate and progesterone beginning the 20th 

 day, and in 6 of 20 ovariectomized guinea 

 pigs injected beginning the 15th day. By 

 the 30th day all of 6 injected rats and 14 

 injected guinea pigs responded, from which 

 it was concluded (1) that mating behavior 

 can be induced precociously, and (2) that 

 the sensitivity to estrogen which is charac- 

 teristic of the adult does not develop until 

 after the 20th day (Wilson and Young, 

 1941). The possibility of inducing preco- 

 cious estrous behavior in the female rat was 

 demonstrated shortly thereafter by Beach 

 1 1942c I. 



The information yielded by these experi- 

 ments on young male and female animals 

 is not sufficient to justify more than the 

 cautious generalization that early in the 

 l)repubertal period the tissues mediating 

 mating behavior acquire the responsiveness 



to androgenic or estrogenic stimulation 

 which characterizes them as adults. In 

 neither the rat nor the guinea pig does the 

 presence of the gonads seem necessary for 

 the acquisition of this responsiveness. 



Scattered data contribute information 

 with respect to changes in sexual behavior 

 associated with advancing adulthood and 

 old age but the lacunae are large. In old 

 rats running activity in the male (Hitch- 

 cock, 1925) and female (Slonaker, 1924) is 

 less than in young rats. A number of ob- 

 servations on the male rabbit (Stone, 

 1932a I, rat (Stone, 1939a; Beach and Holz, 

 1946), and guinea pig (Grunt and Y^oung, 

 1952a) indicate that copulation frequency 

 is lower in old animals. Some of the most 

 careful observations have been reported by 

 Larsson (1956, 1958a). Ejaculations per 

 hour by male rats increase up to 1 year of 

 age and decrease after 20 months. Intro- 

 missions per hour are greatest at puberty 

 and decline slowly but steadily thereafter. 

 The duration of each series of copulations is 

 prolonged as animals age,- likewise the 

 length of the refractory periods. Light had 

 a greater inhibitory effect on the number of 

 ejaculations per hour in the older animals 

 than in the younger ones (Larsson, 1958c). 

 The difference was attributed to an en- 

 hancement of the inhibitory influence of un- 

 conditioned and conditioned stimuli with in- 

 creasing age. 



The relationship between age and the 

 character of copulatory behavior in female 

 laboratory mammals does not seem to have 

 been investigated. The only information we 

 have found was obtained during a rela- 

 tively short period when the hormonal regu- 

 lation of estrous behavior in the female 

 guinea pig was first being studied (Y'oung, 

 Dempsey, Hagquist and Boling, 1939). Ta- 

 ble 2 in that article contains a record of the 

 length of consecutive heat periods in 30 fe- 

 males during the academic years 1935-36 

 and 1936-37. The mean length of the first 

 4 heat periods in 1935-36 was 7.3 hours; the 

 mean length of 4 heat periods 6 to 9 months 

 later was 8.1 hours. It is clear that the de- 

 tection of any changes as the female guinea 

 pig ages will depend on observations of 

 animals older than 12 to 18 months. 



If the figures presented by Hitchcock 



