Abstract
Various peptides found in the brain have been considered to have a regulatory role in neural transmission and some of them are suggested to have neuroleptic activity. In the present study, the effects of five endorphins, haloperidol, and DN-1417, a derivative of thyrotropin-releasing hormone (TRH), were examined on two grip tests in rats, which are sensitive methods for screening neuroleptic drugs. Intraperitoneal injections were made with 50μg of α-endorphin, β-endorphin, γ-endorphin and δ-endorphin, 10 μg and 50 μg of [Des -Tyr1] γ-endorphin (DTγE), 10 μg of haloperidol, and 10 μg and 50 μg of DN-1417. The two grip tests, the pencil test and the horizontal bar test, were repeated before, 1 hour and 2 hours after the respective injections. γ-Endorphin, δ-endorphin, both doses of DTγE, haloperidol and both doses of DN-1417 were positive in both grip tests, however, both α-endorphin and β-endorphin were negative in both of the grip tests. These results raise the possibility that small doses of DN -1417 might be effective as neuroleptic agents as well as DTγE.
