THALAMOCORTICAL AND CORTICOCORTICAL EXCITATORY POSTSYNAPTIC POTENTIALS MEDIATED BY EXCITATORY AMINO-ACID RECEPTORS IN THE CAT MOTOR CORTEX IN-VIVO

Intracellular recordings were made from neurons in the motor cortex of an anaesthetized cat, together with iontophoretic application of exci tatory amino acid receptor agonists and antagonists, in order to evalu ate the role of such receptors in excitatory postsynaptic potentials e voked from stimulation of afferent and recurrent pathways in vivo. Exc itatory postsynaptic potentials which were evoked by stimulation of th e ventrolateral thalamus were found to be largely insensitive to antag onism by N-methyl-D-aspartate receptor antagonists, although they were susceptible to blockade by the non-N-methyl-D-aspartate receptor anta gonist, 6-cyano-7-nitroquinoxaline-2,3-dione. Increasing the ventrolat eral thalamus stimulation frequency from 0.5 or 1 to 5 Hz caused an in crease of evoked excitatory postsynaptic potential amplitudes and numb er of action potentials. These augmented excitatory postsynaptic poten tials remained insensitive to application of N-methyl-D-aspartate anta gonists. In contrast, recurrent excitatory postsynaptic potentials evo ked by stimulation of the pyramidal tract were found to be sensitive t o N-methyl-D-aspartate receptor antagonists and/or non-N-methyl-D-aspa rtate receptor antagonists in some neurons. These results demonstrate the involvement of both N-methyl-D-aspartate- and non-N-methyl-D-aspar tate receptors in synaptic responses of cat motor cortex neurons in vi vo, and that the synaptic pharmacology of the thalamic input may diffe r from that of the local recurrent pathways.