EXPERIENCE-DEPENDENT PLASTICITY OF ADULT-RAT S1 CORTEX REQUIRES LOCALNMDA RECEPTOR ACTIVATION

The effect of blocking NMDA glutamate receptors in adult rat cortex on experience-dependent synaptic plasticity of barrel cortex neurons was studied by infusing D-AP5 with an osmotic minipump over barrel cortex for 5 d of novel sensory experience. In acute pilot studies, 500 mu M D-AP5 was shown to specifically suppress NMDA receptor (NMDAR)-depend ent responses of single cells in cortical layers I-IV. To induce plast icity, all whiskers except D2 and D1 were cut close to the face 1 d af ter pump insertion. The animals were housed with 2 cage mates before r ecording 4 d later. This pairing of two whiskers for several days in a wake animals generates highly significant biases in responses from D2 layer IV (barrel) cells to the intact D1 whisker as opposed to the cut D3 whisker. D-AP5 completely prevented the D1/D3 surround whisker bia s from occurring in the D2 barrel cells (p > 0.6 for D1 > D3, Wilcoxon ). Fast-spike and slow-spike barrel cells were affected equally, sugge sting parity for inhibitory and excitatory cell plasticity. D-AP5 only partially suppressed the D1/D3 bias in supragranular layers (layers I I-III) in the same penetrations (p < 0.042 for D1 > D3). In control an imals, the inactive L-APS isomer allowed the bias to develop normally toward the intact surround whisker (p < 0.001 for D1 > D3) for cells i n all layers. We conclude that experience-dependent synaptic plasticit y of mature barrel cortex is cortically dependent and that modificatio n of local cortical NMDARs is necessary for its expression.