Role of muscarinic cholinergic mechanisms in the substantia nigra pars reticulata in mediating muscular rigidity in rats

Summary Bethanechol chloride (5–25 g), when injected into the substantia nigra pars reticulata (SNR) of rats, produced muscular rigidity in a dose-dependent way, and in addition, catalepsy and ipsilateral posture. The effects of bethanechol in the dose of 25 g were prevented by coadministration of 10 g scopolamine hydrochloride. Injections of 25 g betanechol or 10 g scopolamine into the reticulata only slightly affected the muscular rigiditiy produced by 15 mg/kg i.p. morphine hydrochloride. The results suggest that muscarinic cholinergic mechanisms in the substantia nigra pars reticulata, although effective by themselves, affect by expression of at least one striatal functional alteration, the muscular rigidity, in a less effective way than GABAergic or endogenous opioid mechanisms do.