Effects of intranigral injections of dopamine agonists and antagonists, glycine, muscimol and N-methyl-D,L-aspartate on locomotor activity.

Previously it has been shown that bilateral intranigral injections of dopamine into rats pretreated with a monoamine oxidase inhibitor induced prolonged stimulation of locomotor activity, while bilateral intranigral injections of haloperidol reduced the locomotor stimulation evoked by systemic amphetamine. In the present studies, the role of the substantia nigra in locomotor activity was further investigated using a variety of dopaminergic and other agonists and neuroleptics. Ergometrine, epinine, (+/-)-2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronapthalene hydrobromide (ADTN), 1,2,3,4-tetrahydro-6,7,-dihydroxyisoquinoline hydrochloride (THIQ), muscimol and glycine elicited locomotor activity when injected into the substantia nigra pars reticulata bilaterally. Additionally the non-dopaminergic agonists also elicited a degree of stereotyped behavior. Locomotor activity induced by intranigral ergometrine was blocked by systemic haloperidol but was not affected by intranigral haloperidol. Locomotor activity elicited by systemic amphetamine was blocked by bilateral intranigral alpha-flupenthixol, but that elicited by bilateral intra-accumbens ergometrine was not affected by alpha-flupenthixol or haloperidol injected into the substantia nigra pars reticulata bilaterally. The results provide further evidence that alterations of neurotransmission in the substantia nigra exert effects on locomotor activity.