Effects of ketamine on synaptic transmission and long-term potentiation in layer II/III of rat visual cortex in vitro

The effects of ketamine, which has NMDA receptor antagonist properties, on synaptic transmission and long-term potentiation in layer II/III of adult rat visual cortex were examined in vitro. Field potentials were recorded in layer II/III following layer IV stimulation. Primed-burst stimulation was used for induction of long-term potentiation. Stimulation of layer IV resulted in a two-component response in layer II/III, a population excitatory postsynaptic potential1 (EPSP1) and a population excitatory postsynaptic potential2 (EPSP2). DL-2-Amino-5-phosphono-valeric acid (AP5), a competitive NMDA receptor antagonist, reduced the amplitude of the population EPSP1 while ketamine increased the amplitude of the population EPSP2. The results showed that primed-burst stimulation induced long-term potentiation in layer II/III of the visual cortex in vitro. Preincubation for 30 min with AP5 (25-100 microM) reduced the extent of long-term potentiation of the population EPSP2 and blocked the induction of long-term potentiation of the population EPSP1. When ketamine (100-200 microM) was present for 30 min prior to tetanic stimulation, it blocked the induction of long-term potentiation of the population EPSP1 and reduced the extent of long-term potentiation of the population EPSP2. We conclude that ketamine can interfere with synaptic transmission in the visual cortex. Primed-burst stimulation is an effective protocol for neocortical potentiation. NMDA receptors are involved in the induction of long-term potentiation by primed-burst stimulation of the population EPSP1 and population EPSP2 in adult rat visual cortex in vitro.