Suppression of paraquat-induced wet dog shakes by nitric oxide synthase inhibitors in rats

We have found that paraquat (PQ), a widely used herbicide, causes wet dog s hakes (WDS), which involve the central opioid system, in rats. A non-select ive nitric oxide (NO) synthase (NOS) inhibitor, N-omega-nitro-L-arginine (L -NA), but not its less active enantiomer, N-omega-nitro-D-arginine, decreas ed the PQ-induced WDS in a dose-related manner. A selective neuronal NOS in hibitor in vivo, 7-nitroindazole, also decreased the PQ-induced WDS. Althou gh an opioid receptor antagonist, naloxone, reversed the suppressive effect of these NOS inhibitors on the PQ-induced WI L-arginine, an NO precursor, had no effect on it. These findings suggest that the suppression of the PQ- induced WDS by NOS inhibition is associated with the central opioid system and is insusceptible to exogenous L-arginine. (C) 2000 Elsevier Science Inc .