Modulation of sensory inhibition in the ventrobasal thalamus via activation of group II metabotropic glutamate receptors by 2R,4R-aminopyrrolidine-2,4-dicarboxylate.

Recordings were made from single neurones responsive to somatosensory input in the ventrobasal thalamus of the anaesthetised rat. GABAergic afferent inhibition arising from the thalamic reticular nucleus was evoked using a condition-test vibrissal stimulation paradigm. Local iontophoretic application of the group II metabotropic glutamate receptor (mGluR) agonist 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC) in the vicinity of the recorded neurones produced a reduction of the afferent inhibition (from 78+/-3.0% to 25+/-5.3%), presumably via a presynaptic mechanism. This effect could be antagonised by LY307452, a known group II mGluR antagonist. In contrast, two selective group I mGluR agonists, (S)-3,5-dihydroxyphenylglycine (DHPG) and trans-azetidine-2,4-dicarboxylate (tADA), were without effect on the GABAergic inhibition. These data show that group II but not group I mGluRs can have a significant role in the modulation of GABAergic afferent inhibition in the ventrobasal thalamus. This could be of importance in the control of sensory discriminative processes and functions of sleep, arousal and seizure generation.