Absence of Alteration in Puberal Onset in Male Rats Following Amygdaloid Lesioning

In a previous experiment, bilateral amygdaloid lesions in 4-day-old rats of both sexes unexpectedly produced delayed puberty (judged by vaginal opening) in the females. The onset of puberty (judged by testicular descent) in the males (not studied), however, did not appear to be affected. To investigate the possibility that amygdaloid lesions produce different effects in the sexes, alternate litter mates underwent either bilateral amygdaloid lesioning or a sham operation on the sixth day of life. All rats were reared in diurnal lighting. All males were sacrificed on the day of testicular descent and random females on the day of vaginal opening. Multivariate analysis of covariance revealed no difference between the 2 male groups as regards the day of maturation, body weight, tail length, or testicular, ventral prostate or seminal vesicle weights (p>0.1). However, a multivariate analysis of the female groups, as regards the same first 3 variables, plus ovarian and uterine weights, revealed a significant difference (p<0.005), with a delay in puberty in the lesioned groups confirming previous work. Thus, male and female rat pups do not respond similarly to amygdaloid lesioning. It is possible that differences between the sexes in the degree of maturation of the connections between the stria terminalis afferents and the medial hypothalamic area, as well as those of this circuit with the suprachiasmatic-preoptic area, may account for the divergent effects of amygdaloid lesioning on sexual maturation. {Endocrinology 88: 1272, 1971) I A RECENT study of factors affecting puberaJ onset, this author noted that bilateral amygdaloid lesions in 4-day-old rats of both sexes unexpectedly produced delayed puberty (judged by vaginal opening) in the females (1). This finding was in contrast to the acceleration of puberty reported when bilateral amygdaloid lesions were produced in 18to 20-day-old female rats (2). Furthermore, in the former experiment the onset of puberty (judged by testicular descent) in the male rats (not studied) did not appear to be affected. To investigate the possibility that amygdaloid lesions produce different effects in the sexes the following experiment was performed. Materials and Methods Inbred rats of the Wistar strain were used. Eighty-two pups were randomly chosen from litters of varying size. These animals, comprised of even-numbered groups of litter mates, were exposed daily to an environment of 16 hr of darkness and 8 hr of overhead lighting, yielding 100-150 ft-c at the cage surface. On the sixth day of life alternate members underwent either bilateral amygdaloid lesioning according to the method described elsewhere (1), or a sham operation. This day was chosen to perform the lesioning because physiologic "masculinization" of the rat brain is completed by day 6 of life (3). Coding for designation was achieved by injecting India ink under the skin of the lateral aspect of one or more legs. Received October 20, 1970. Throughout the experiment water was available ad lib. and a standard comprehensive diet (Purina laboratory chow) was used. The temperature in the room was controlled and kept at approximately 23 C (range 21-25 C). Litters were weaned at age 23 days and, commencing at this age, male young were observed daily for testicular descent without being handled (to obviate testicular retraction). Until a litter was depleted of males, females were left in the cage. To obviate any question about the validity of comparing lesioning performed on the 4th day in the previous experiment (1) with sixth-day lesioning herein described, day of vaginal opening was recorded in 6 lesioned and 7 sham-operated females taken at random from some of the same litters as were used in this experiment. Testicular descent was chosen as a maturational parameter comparable to that of vaginal opening because prior investigation (1, 4, 5) has shown that both events can be similarly affected by a procedure (i.e., pinealectomy) which accelerates the time of puberal onset. All males, and the randomly selected females, reaching puberty were sacrificed with ether the day testicular descent or vaginal opening was discovered, their body weights recorded, and tail length measured. Testes, ventral prostate, seminal vesicles (with coagulating glands), ovaries and uteri were dissected and weighed fresh. Testes and ovaries were fixed in 10% formalin, embedded in paraffin, and 10 n sections stained with hematoxylineosin. The brains were removed in toto and fixed in 10% formalin, embedded in paraffin, cut in 10 M sections, and every fifteenth section mounted and stained with hematoxylin-eosin.