Stimulation of N-methyl- D-aspartate receptors in the rat nucleus reticularis thalami suppresses somatosensory evoked potentials

Abstract

The role of excitatory amino acid receptors in the rat nucleus reticularis thalami (NRT) for the modulation of cortical somatosensory evoked potentials (SEPs) was examined. The effects of microapplication of N-methyl- D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), an agonist at the non-NMDA receptors, into the NRT on the amplitude and latency of cortical SEPs were measured. SEPs were recorded from the somatosensory cortex of anaesthetized rats, in response to single shock stimulation of the contralateral forepaw. Injection of NMDA into the NRT resulted in a decrease in amplitude and increase in latency of SEPs. These effects were dose-dependent over the range from 0.05 to 0.5 nmol. Co-administration of (-)-2-amino-7-phosphono-heptanoate, a specific NMDA antagonist, with NMDA into the NRT prevented these changes. The depressant action of NMDA on cortical SEPs was site-specific for the NRT. Application of AMPA into the NRT did not affect cortical SEPs. The present results are in line with the assumption that an excitatory amino acid serves as transmitter to stimulate NRT neurons which in turn leads to suppression of cortical SEPs. NMDA receptors within the NRT appear to be involved in this depressant action.