The neostriatal inhibition of catalepsy, but not of muscle rigidity, evoked from the substantia nigra pars reticulata.

The effects of a bilateral blockade of neo- and palleostriatal GABAergic mechanisms on catalepsy and muscle rigidity resulting from picrotoxin injection into the substantia nigra pars reticulata (SNR) were studied. The catalepsy and rigidity were induced by a unilateral injection of 100 ng/0.5 microliter of picrotoxin. Bilateral injections of 250 ng/l microliter of picrotoxin into the intermediate-ventral parts of the caudato-putamen (CP) abolished the catalepsy but had no effect on the muscle rigidity induced by an intranigral injection of the drug. Bilateral injections of 250 ng/l microliter of picrotoxin into the globus pallidus (GP) did not influence the catalepsy and rigidity induced by the intranigral injection of the drug. The results indicate that the impulses, connected with the catalepsy evoked from the SNR seem to be transmitted back to the CP and blocked therein by inhibition of GABAergic synapses in its intermediate-ventral part. The impulses, connected with the muscle rigidity evoked from the SNR, presumably do not return to the striatum.