REPRODUCTIVE BEHAVIOR 



1229 



centers' within the brain and spinal cord. A 'center,' 

 as the term will be employed here, is a locus of inte- 

 gration of the component activities of a total pattern. 

 Destruction of the center may leave individual com- 

 ponents or lesser complexes of the pattern intact. The 

 center may be influenced by afferent or humoral 

 mechanisms or both from the periphery or by projec- 

 tions from higher levels but is capable of basic 

 independent activity after extirpation of higher con- 

 trols. The principal "sex center' would be the critical 

 area influenced by sex hormones to evoke patterns 

 of reproductive behavior, the destruction of which 

 would eliminate such bcha\ior patterns. 



Peripheral and Spinal Meehanisms 



It is remarkal)le how relatively unimportant the 

 afferent impulses from genitalia are in maintaining 

 sex behavior in lower mammals. Anesthetizing (29a) 

 or deafferenting the vagina (18) or surgically remov- 

 ing the vagina and uterus (3) have not prevented 

 mating in rabbits and rats. Female cats retain 

 estrous behavior after removal of the sacral region of 

 the spinal cord or the abdominal sympathetics (5). 



Similarly in the male cat Root and Bard (6) have 

 found that anesthesia of the penis and perineum 

 through surgical removal of the lower end of the 

 spinal cord does not diminish sexual aggressi\eness. 

 In the presence of an estrous female, such a cat de- 

 velops an erect penis and attempts copulatory mo\e- 

 ments. The addition of sympathectomy to the cord 

 injury removes the power of erection but not the at- 

 tempts to copulate. Beach and his colleagues (12) 

 have shown that elimination of the penile ijone in the 

 rat, either surgically or through castration on the day 

 of birth, interfered with the achievement of copula- 

 tion but not with attempts to copulate. Their results 

 reveal that regardless of the influence of hormones 

 on genitalia a neural site of hormone target action 

 central to the peripheral sense organs is capable of 

 maintaining sex drive. Genital sensation may, how- 

 ever, strengthen the force of the drive. 



Spinal male animals of .several species including 

 the dog and man maintain the capacity of penile erec- 

 tion and ejaculation on manipulation of the genitalia 

 (32, 86). In male cats after spinal transection a type 

 of flexor rigidity reminiscent of mating posture was 

 described by Dusser de Barenne & Koskoff (26, 27). 

 Accompanied by erection this reaction was suggestive 

 of a spinal copulation reflex, but it could hardly qual- 

 ify as real mating behavior. 



Spinal female animals can be impregnated, can 



maintain pregnancy and can deliver normal litters, 

 as first described in the dog by Goltz (36). These ob- 

 servations, however, are less concerned with be- 

 havior than with other reproductive phenomena. No 

 change in spinal reflexes in the female guinea pig 

 which could be attributed to the injection of estrogen 

 and progesterone was observed by Dempsey & 

 Rioch (22). A similar failure to observe reflexes 

 which could be altered by estrogen was reported by 

 Bromily and Bard (6) in the spinal cat. These authors 

 found that reflexes, such as tail deviation on prodding 

 the perineum, which had been reported in the de- 

 capitate cat as dependent on estrogen (61), could 

 also be elicited in the anestrous female and even 

 in the male cat. It appears that the partial behavioral 

 pattern is present in the spinal cord of either sex, but 

 its differential hormonal activation requires integra- 

 tion from higher centers. 



Lower Brain-Stem Mechanisms 



Sectioning the brain stem in such a way as to leave 

 the cord, medulla, pons and lower mesencephalon 

 intact results in 'decerebration.' Among the differ- 

 ences between the spinal animal and the decerebrate 

 preparation is the development of rigidity in the 

 latter, and this rigidity might interfere nonspecifically 

 in reproductive behavior patterns. Dempsey & Rioch 

 (22) could find no evidence of estrous behavior in 

 decerebrate female guinea pigs; Maes (61) attributed 

 their failure to observe sexual reflexes, such as tread- 

 ing and elevating the pelvis, to the decerebrate 

 extensor rigidity which they all displayed. However, 

 in decerebrate female cats Bromily and Bard (6) 

 were able to reverse the rigidity and induce a crouch- 

 ing posture by stimulating the vagina with a gla.ss 

 rod. This component of the female cat pattern could 

 not be duplicated in decerebrate bitches, which do 

 not crouch at mating, nor in male cats; but it was 

 elicited in anestrous as readily as in estrous cats. The 

 conditioning influence of estrogen (and progesterone 

 in the guinea pig) would appear to be exerted at 

 some level higher than the plane of decerebration. 



Neocortical and Rhineneephalic Mechanisms 



The cerebral cortex is relatively unimportant in 

 the maintenance of mating behavior in most female 

 mammals. Rioch and Bard (5) removed increasingly 

 larger portions of the cortex in the cat until all of the 

 neocortex, most of the rhinencephalon, and a large 

 part of the striatum and thalamus had been de- 



