NMDA RECEPTORS IN LAYER-II AND LAYER-III OF RAT CEREBRAL-CORTEX

Glutamate receptors are found in all layers of the cerebral cortex, bu t NMDA receptors are concentrated in layers II and III in the adult. W e investigated the location of these receptors, and their contribution to the responses of cells in layers V and VI, by iontophoresing NMDA at various distances from the cell body along the apical dendrite of t he cells, first in artificial CSF, then in TTX to abolish action poten tials. Comparison of responses at various distances along the apical d endrite showed that the response generally increases as distance from the cell body decreases. Comparison of responses in layers II and III, before and after TTX, showed that TTX reduced the response considerab ly. We conclude first that NMDA receptors in layers II and III are loc ated primarily on cells in layers II and III, rather than on the apica l dendrites of cells in layers V and VI, and second that the contribut ion of NMDA receptors to the response of cells in layers V and VI come s primarily from receptors close to the cell body.