Muscimol (25 ng), but not saline, infused into the region of the zona incerta and lateral hypothalamus induced significant
catalepsy in female rats. Daily administration of
muscimol for 5 days resulted in a sensitization of the cataleptic response such that there was a significantly greater response to the same dose of
muscimol beginning on Day 3 and continuing to increase up to Day 5. It was determined that the increase in
catalepsy across days was not the result of conditioning after an initial exposure to
muscimol. The endocrine condition of the female affected the degree of
catalepsy induced by the first exposure to intrahypothalamic
muscimol. Ovariectomized rats pretreated with
estradiol benzoate (EB) exhibited significantly greater
catalepsy than did females untreated or treated with
progesterone or combined EB and
progesterone. Weekly administration of
muscimol also produced significant sensitization of the behavioral response, and the degree of sensitization was again affected by endocrine condition. Specifically, although females treated with EB for 2 days before
muscimol infusion showed a significantly greater
catalepsy after the first infusion than did ovariectomized females, they failed to show any increase in
catalepsy scores across the 4 weeks of treatment. The greater
catalepsy induced by
muscimol infusion in EB-treated females may be related to changes in dopaminergic transmission. In contrast, females pretreated with
progesterone 4 hr before
muscimol infusion (with or without prior EB) exhibited highly significant increases in cataleptic response across the 4 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)