POSTNATAL-DEVELOPMENT OF NMDA RECEPTOR-MEDIATED SYNAPTIC TRANSMISSION IN CAT VISUAL-CORTEX

Postnatal development of N-methyl-D-aspartate (NMDA) receptors in cat visual cortex (area 17) was studied by intracellular recording from cortical cells in slice preparations obtained from kittens aged 0-20 weeks after birth and adult cats. Cells were sampled from layer IV and the lower half of layer II-III, where it is known that most cells receive direct inputs from lateral geniculate nucleus. Excitatory postsynaptic potentials (EPSPs) evoked in cortical cells by white matter stimulation were mediated by both non-NMDA and NMDA receptors, because bath application of a non-NMDA receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX), left slow depolarizing responses which were abolished by an NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid. The contribution of NMDA receptors to the synaptic transmission was assessed by the ratio of the initial rising slope of EPSPs in the presence of DNQX to that in control solution. The NMDA receptor-mediated component of monosynaptic EPSPs was small at 0-2 weeks after birth, steeply increased to the peak value at 5-6 weeks and then declined gradually to the almost initial value by 20 weeks. This time-course agrees with the developmental changes in susceptibility of ocular dominance preference of visual cortical cells to monocular deprivation, suggesting that NMDA receptors play a role in plastic changes in geniculocortical synapses.