THE EFFECTS OF L-AP4 AND L-SERINE-O-PHOSPHATE ON INHIBITION IN PRIMARY SOMATOSENSORY CORTEX OF THE ADULT-RAT IN-VIVO

The effects of two iontophoretically applied Group III mGluR agonists were studied on the inhibition in neocortex produced by natural stimul ation of vibrissae. The agonists L-AP4 and L-serine-O-phosphate (L-SOP ) were shown to produce qualitatively similar effects on the inhibitio n. Forty-four percent of neurones (total n = 57) displayed disinhibiti on during application of the agonists. The disinhibitory effects often outlasted the offset of the agonist application by at least 10 min. C oncurrent application of the mGluR antagonist(+)-alpha-methyl-4-carbox yphenylglycine ((+)-MCPG) appeared to reverse the disinhibitory effect s of L-AP4 and L-SOP in 3 out of 5 neurones tested. However (+)-MCPG i tself was found to have disinhibitory effects in some neurones. Some n eurones (n = 7) showed increases in inhibition during either L-AP4 or L-SOP application. These appeared most pronounced in those neurones wh ere the initial (pre-drug) inhibition was minimal, perhaps suggesting that the agonists were disinhibiting a local disinhibition. The data o btained in the experiments suggest that the disinhibitory effects are mediated by a heteroreceptor on inhibitory terminals, action at which depresses the release of inhibitory transmitter. The possible role of the modulation of inhibition by presynaptic mGluRs is discussed.