| Abstract: | Bilateral microinjections of an excitatory amino acid, α-kainate (KA), 5–50 ng, into the substantia nigra pars reticulata (SNR) result in an increase in the muscle tone and catalepsy in rats. The preferential KA/quisqualate antagonist, γ-d-glutamylaminomethylsulphonate (γ-D-GAMS), 10 μg, blocks the actions of KA, 25 ng, when coadministered into the SNR. The chemical lesion of the caudate-putamen with 6-hydroxydopamine (6-OHDA) does not affect either increases in the muscle tone or catalepsy produced by KA, 25 ng, from the SNR. The lesion of the caudate-putamen with ibotenate moderately enhances the effect of KA, 25 ng, on the muscle tone. Microinjections of KA, 25 ng, into the substantia nigra pars compacta (SNC) do not increase the muscle tone and lead to significantly less pronounced catalepsy relative to the observed following the injections of KA into the SNR. Unilateral microinjections of KA, 10–50 ng, into the SNR elicit ipsilateral turning in rats in a dose- and time-dependent manner. Unilateral application of γ-d-GAMS, 1–10 μg, into the SNR produces contralateral turning. The turning evoked by KA, 25 ng, or γ-D-GAMS, 10 μg, is affected neither by 6-OHDA nor by ibotenate lesion of the caudate-putamen. These results demonstrate that excitatory neurotransmission in the substantia nigra participates in the regulation of the muscle tone and posture in rats. |
