REPRODUCTIVE BEHAVIOR 



1227 



TIME IN WEEKS 



FIG. 2. Effects of castration and therapy with testosterone on sex drive in the male guinea pig. 

 [From Grunt & Young (43).] 



estrus. More recently Gov and Young (98) have de- 

 scribed several measures of receptivity in the guinea 

 pig, including latency of estrus after hormone treat- 

 ment, duration of estrus, duration of maximum 

 lordosis, frequency of male-like mounting and per 

 cent of animals brought into heat by the treatment. 



Similarly in the male guinea pig Grunt & Young 

 (43) have evolved a quantitative measure of sex 

 drive based on counting and weighting arbitrarily the 

 following activities during a lo-minute period in the 

 presence of an estrous female: nibbling, nuzzling, 

 mounting, intromission and ejaculation. An example 

 of the use of this .scoring method appears in figure 2. 

 Similar methods iin\'e been emplo\ed with male rats 



(13)- 



Other assay methods which have been employed 

 in studies on male experimental animals have also 

 been reviewed (13, 35, 85); these include the use of 

 mazes, runways. Skinner boxes and various electrical 

 shocking devices. The readiness with which a male 

 rat will learn to run a T-inaze for an estrous female 

 as the reward may be extrapolated to test motivation. 

 With a receptive female as the object, the rate of bar 

 pressing by a male rat in a Skinner box has been ob- 

 served to correlate with its presumed level of sex 

 drive. The running speeds of male rats, guinea pigs 

 and dogs along alleys or over hurdles and the per- 



sistence of males in crossing an electric grid to reach 

 estrous females ha\e been observed to be positi\ely 

 related to sexual performance. 



ENDOCRINE, GENETIC .'VND SOCI.'VL F.ACTORS 

 IN SEX BEH.AVIOR 



The effects of castration in the male depend on the 

 species, the relative age of the individual at surgerv 

 and his previous sexual performance. In general the 

 changes in behavior are similar to those illustrated 

 for the guinea pig (fig. 2) by Grunt & Young (43). 

 There is a gradual loss in sexual activity, with the 

 processes of ejaculation and intromission disappearing 

 earlier than the less consummative phenomena. 

 Similar effects have been reported in dogs (13, 35) 

 and cats (41). In the adult human (90) castration 

 may be followed by little or no perceptible loss in 

 sexual performance. 



Replacement therapy with testosterone rapidly re- 

 stores sex drive to animals in which castration has 

 reduced it. In the guinea pig (fig. 2) raising the an- 

 drogen dosage above the minimum needed to restore 

 the preoperative behavior level does not result in 

 increased performance. In the rat, however, testos- 

 terone dosages higher than the maintenance level 



