Cellular correlates of neuronal hyperexcitability in the vicinity of photochemically induced cortical infarcts in rats in vitro.

Intrinsic membrane properties and synaptic responses of neocortical neurons located lateral to photochemically induced ischemic lesions were investigated using neocortical slice preparation. In comparison to neurons from control slices, these neurons had a significantly less negative resting membrane potential without any significant change in input resistance. In addition, gamma-aminobutyric acid (GABA) mediated synaptic inhibition was found to be less efficient; the conductances of both the early and late inhibitory postsynaptic potentials (IPSPs) were significantly smaller, and the reversal potential of the early IPSP was shifted to a more positive value. In some of the neurons, 'epileptiform' postsynaptic potentials could be elicited, which were abolished after wash-in of the N-methyl-D-aspartic acid (NMDA)-receptor antagonist D-2-amino-5-phosphonovaleric acid (AP-5). The results provide a possible explanation for the hyperexcitability found in the vicinity of cortical infarcts.