TRANSIENT EXPRESSION OF POLYSYNAPTIC NMDA RECEPTOR-MEDIATED ACTIVITY DURING NEOCORTICAL DEVELOPMENT

During a restricted period of early postnatal development, rat neocortical neurons receive a powerful N-methyl-d-aspartate (NMDA) receptor-mediated synaptic input of variable onset latency and duration. These large-amplitude excitatory postsynaptic potentials are especially pronounced in supragranular layers and are generated by activities in polysynaptic circuits. Their occurrence in cortical slices from juvenile (postnatal (P) days 11-20), but not neonatal (P5-10) or adult (≧P28) animals, appears to be in part a consequence of the relative immaturity of γ-aminobutyric acid (GABA)-mediated inhibition, at a time when the requisite functional excitatory circuitry has been established. The transient manifestation of strong NMDA receptor-mediated potentials coincides temporally with a 'developmental window' within which there is enhanced sensitivity for epileptogenesis and for induction of long-term synaptic modifications in rat cortex. © 1990.