Yasuhiko Kondo

Functional Association Between the Medial Amygdala and the Medial Preoptic Area in Regulation of Mating Behavior in the Male Rat

We examined the effects of combined lesions of the medial preoptic area and the medial amygdala on male copulatory behavior to understand a functional relation between these two structures in regulation of the behavior in the rat. Young adult male rats were castrated and received Silastic implants containing testosterone. After baseline copulatory tests, a unilateral medial preoptic lesion (uPOL) was made. Males with uPOL showed less intromission behavior than sham-operated males did, but none of them showed elimination of the behavior. Following the observations after the uPOL, these males were subjected to a unilateral medial amygdala lesion (uMAL) ipsilateral or contralateral to the previous uPOL. The ipsilateral uMAL did not affect copulatory behavior compared to that of sham-operated uPOL males. However, the copulatory behavior in the animals with uPOL was severely disrupted by the contralateral uMAL. These results suggest that the medial preoptic area is closely related to the medial amygdala in regulation of male rat copulatory behavior, and these areas may play a critical role in the behavior as an unitary system.

The possible involvement of the nonstrial pathway of the amygdala in neural control of sexual behavior in male rats

The effect of medial amygdala lesions on male sexual behavior in male rats with stria terminalis cut was examined. First, castrated male rats received bilateral transections of the stria terminals (STC) or sham cut (SC). Most STC males showed no ejaculation, but displayed mount and intromission, although the frequencies were not high compared to those of males with SC. Next, bilateral lesions of the medial amygdala (MAL) or sham lesion (SL) were performed in males with STC or SC. The MAL caused severe loss of all aspects of copulatory behavior in males with STC as well as in males with SC. The suppressive effect of the MAL on copulatory activity was stronger than that of the STC. These results indicate that a neural pathway other than the stria terminalis is involved in the regulation of male sexual behavior by the amydgala in male rats.

Facilitation of copulatory behavior by pCPA treatments following stria terminalis transection but not medial amygdala lesion in the male rat

In this study, we examined the effect of p-chlorophenylalanine (pCPA), a serotonin synthesis inhibitor, on masculine sexual behavior in male rats following bilateral medial amygdala lesions (MAL) or bilateral stria terminals cuts (STC). Males with MAL and STC both showed a suppression of sexual behavior, compared to that of sham-operated males, when injected with saline. On the other hand, intraperitoneal injections of pCPA increased mount and intromission frequencies in males with STC. Although pCPA injections also slightly increased mount frequency in males with MAL, the injections failed to affect intromission behavior in MAL males. These suggest that the stria terminalis is insufficient as pathway of a whole output of the medial amygdala in regulating copulatory behavior. The medial amygdala may be involved in some other function, such as erection, than that of the stria terminalis.

Functional relationships between mesencephalic central gray and septum in regulating lordosis in female rats: Effect of dual lesions

In order to clarify the functional relationships between the lateral septum (LS) and the mesencephalic central gray (MCG) in regulating lordosis behavior, ovariectomized female rats received dual lesions in these two areas. In the first experiment, females with unilateral (right or left, R-MCGL or L-MCGL) or bilateral MCG (B-MCG) lesions were subjected to behavioral tests after the implantation of a Silastic tube containing estradiol. Lordosis was observed in only one B-MCGL female. In the R-MCGL and L-MCGL groups, most females displayed lordosis, but lordosis quotients (LQ) were significantly lower than that of the control group. These results suggest the importance of the MCG in lordosis regulation, and that there is no functional laterality in the MCG. In the second experiment, B-MCGL or R-MCGL females received bilateral LS lesions (LSL). The lordotic activity in the LSL + B-MCGL group was extremely low, being comparable to that of B-MCGL alone. On the other hand, in the LSL + R-MCGL females, the LQ was significantly higher than that of females with R-MCGL alone and was comparable to that of controls. Thus, the lateral septum plays an inhibitory role in regulating lordosis, but the influence of the lateral septum is not stronger than the facilitatory influence of the mesencephalic central gray, because the LSL could not recover the suppressive effect of the MCGL.