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 ev oked using a condition-test vibrissal stimulation paradigm. Local iont ophoretic application of the group II metabotropic glutamate receptor (mGluR) agonist 2R,3R-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-azet idine-2,4-dicarboxylate (tADA), were without effect on the GABAergic i nhibition. These data show that group II but not group I mGluRs can ha ve a significant role in the modulation of GABAergic afferent inhibiti on in the ventrobasal thalamus. This could be of importance in the con trol of sensory discriminative processes and functions of sleep, arous al and seizure generation.