Electrophysiological thalamic responses evoked by dopamine-receptor stimulation into the striatum

Electrophysiological experiments were performed in rats anesthetized with halothane to examine the effects of acutely administering drugs into the striatum on the responses of cells from the ventromedial nucleus of the thalamus (VMT). VMT cells increased their discharge to striatal administration of apomorphine only if the injection was performed in the ventral portion of the nucleus. However, an increase in VMT firing rate was observed after administration of either glutamate or picrotoxin into the dorsomedial area of the striatum. Each of the nuclei which could have relayed the information from the striatum to VMT were lesioned with kainic acid in preliminary operations prior the acute recording experiment. Lesions of the globus pallidus or the entopeduncular nucleus did not alter VMT response to striatal apomorphine administration, only lesions of substantia nigra abolished the observed increase in VMT cell discharge. It was concluded: that within the striatum there are highly significant topographical differences determined by the electrophysiological response induced in VMT after striatal-dopamine receptor stimulation; and that the increase in firing rate seen in VMT after the administration of apomorphine in the striatum is mediated by a relay in the substantia nigra.