Effects of intrastriatal microinjection of beta-casomorphins and its Des-tyrosine derivatives on rat motor behaviour.

After unilateral striatal application the tyrosine-containing and Des-tyrosine analogues of beta-casomorphin were investigated with regard to the properties inducing rotational behaviour in rats. The tyrosine-containing beta-casomorphins (D-Pro4)-beta-casomorphin1-5, (D-Phe3)-beta-casomorphin1-5 or (D-Pip4)-beta-casomorphin1-5 produced contralateral rotations like apomorphine, whereas the Des-tyrosine-beta-casomorphins brought about an ipsilateral haloperidol-like asymmetry; (Des-Tyr1-D-Pip4)-beta-casomorphin2-5 did not evoke a lateralization of motor behaviour. The contralateral turning following unilateral apomorphine application into striatum was increased by striatal administration of tyrosine-containing beta-casomorphin analogues and antagonistically influenced by (Des-Tyr1-D-Pro4)-beta-casomorphin2-5 or (Des-Tyr1-D-Phe3)-beta-casomorphin2-5; however, (Des-Tyr1-D-Pip4)-beta-casomorphin2-5 has no effect on apomorphine-induced rotation behaviour. The time course of the animals' asymmetric motor behaviour after striatal apomorphine administration was antagonistically influenced by haloperidol, (Des-Tyr1-D-Phe3)-beta-casomorphin2-5 or (Des-Tyr1-D-Pro4)-beta-casomorphin2-5; quantitative differences were observed as far as the strength and the duration of the apomorphine antagonistic effect of Des-Tyr-beta-casomorphins are concerned.