Tetraethylammonium-induced long-term potentiation in layer V horizontal connections of rat motor cortex

The possibility for the induction of long-lasting synaptic plasticity by the potassium channel blocker tetraethylammonium (TEA) was investigated in adult rat motor cortex in vitro. Brief application of TEA (25 mM) resulted in a long-term potentiation (LTP(K)) of field potentials evoked in layer V intralaminar connections by 59+/-17%. This effect could be prevented by preincubation with nifedipine, a voltage-dependent calcium channel blocker (20 microM), but not by N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (APV, 100 microM). LTP(K) induction resulted in a smaller relative potentiation of a response to the second pulse of a pair (60 ms interpulse interval). These results indicate a potential of layer V horizontal connections for a NMDA receptor-independent form of persistent synaptic enhancement.