Intranigral infusion of enkephalins elicits dyskinetic biting in rats.

Leu- and Metenkephalin (Lenk and Menk) and their more stable analogues D-Ala-Leu- and D-Ala-Metenkephalin (DALenk and DAMenk) as well as D-Ala-D-Leu- and D-Ala-D-Metenkephalin (DADLenk and DADMenk) were infused bilaterally into substantia nigra in awake rats and oral movements were recorded for 90 min. DADLenk and DADMenk elicited dose-dependent biting dyskinesias with a chewing rate of about 90 jaw movements/min. DALenk produced a similar but weaker effect, whereas DAMenk, Lenk and Menk were ineffective in the doses given. These findings suggest a possible enkephalinergic mechanism underlying neuroleptic-induced tardive dyskinesias.