SEX-SPECIFIC IMPAIRMENT IN SEXUAL AND INGESTIVE BEHAVIORS OF MONOSODIUM GLUTAMATE-TREATED RATS

L-monosodium glutamate (MSG) (4 mg/g b.wt.) was injected subscutaneously to pups on days 1 and 3. At age 3.5 months, sexual and ingestive behaviors were observed. Neonatal MSG treatment resulted in severe and widespread neuron destruction in the basomedial hypothalamus of both sexes, but only superchiasmatic nucleus in male rats. A decline in sexual behavior was also observed. Serum levels of testosterone and dihydrotestosterone in male rats as well as serum level of progesterone in female rats were decreased. Ovariectomized MSG-treated female rats injected with estradiol benzoate follwed by progesterone showed a dramatic improvement in sexual behavior, whereas castrated MSG-treated male rats injected with testosterone propionate did not meliorate the decline of sexual behavior. Neonatal MSG treatment also induced reductions of body weight in male rats, higher diurnal percentages of food and water intake in male rats than in female rats, and a decline of water-to-food ratio. These observations suggest that neonatal male rats show higher susceptibility to glutamate-induced dysfunction of sexual and ingestive behaviors than females. Our findings also suggest a sex difference in the mechanism of dysfunction of sexual behavior, i.e., decreased copulatory activity in male rats is mainly due to CNS damage, in contrast to decreased blood progesterone level in female rats.