N-METHYL-D-ASPARTATE ENHANCEMENT OF PHASIC RESPONSES IN PRIMATE NEOCORTEX

In area 17 of the awake macaque, disinhibition by blockade of GABA(A) receptors results in a marked elevation in neuronal excitability, with a particular focus in the supragranular laminae. We examined the poss ibility that the excitatory supragranular response is N-methyl-D-aspar tate (NMDA)-mediated. Laminar activity profiles consisting of flash-ev oked field potential, current source density (CSD) and multiunit activ ity (MUA) measures were obtained during striate cortex penetrations us ing multicontact electrodes that incorporated single or double microin jection cannulae. Profiles were recorded before and at successive time points after bicuculline induction of disinhibition. Both the noncomp etitive NMDA antagonist MK-801 and the competitive antagonist APV reve rsed bicuculline effects, producing a normal laminar activity profile. NMDA-mediated enhancement of excitatory responses in the supragranula r laminae of neocortex is believed to play a role in normal signal pro cessing, as well as in epileptic manifestations.