Stereotyped responses of rats to two 2-halogenoergolines: 2-bromo-alpha-ergocryptine and lergotrile

Stereotyped responses to apomorphine, 2-bromo-alpha-ergocryptine (BEC) and lergotrile were compared in naive animals and after various pretreatments. Lergotrile was about half as effective as apomorphine in naive rats, while BEC produced intense stereotyped reactions only after pretreatment with p-chlorophenylalanine. Inhibitors of catecholamine biosynthesis (alpha-methyltyrosine and alpha-methyldopa) only impaired the response to BEC. Haloperidol, a dopamine antagonist, blocked the lergotrile-induced stereotypy within a few minutes, but had a rather slow effect on the response to BEC. It is concluded that lergotrile mainly activates dopamine receptors directly, similar to apomorphine. BEC, however, has a predominantly indirect effect, stimulating the formation and subsequent release of both dopamine and 5-hydroxytryptamine. The relationship of this difference in mechanism to the differences in structure is discussed.