Strychnine-induced changes of the membrane and postsynaptic potentials in neocortical neurons]

Intracellular responses of neurons of the suprasylvian gyrus to the intracortical stimulation (ICS) before and after superficial application of strychnine were investigated in experiments on immobilized and unanaesthetized cats. The normal cortex neurons reacted to ICS by monosynaptic EPSPs followed by IPSPs. Strychnine application triggered the epileptiform activity and appearance in neurons of paroxysmal depolarization shifts of the membrane potential (MP) which were replaced by hyperpolarization potentials. An increase and summation of the latter elicited the MP enlargement and either reduction or suppression of background spike activity. Intracellular injections of EGTA blocking the membrane calcium-dependent potassium conductivity (gK(Ca)) have eliminated the hyperpolarization potentials. Development of epileptiform activity was accompanied by depression of IPSPs and increase of the monosynaptic EPSPs. The contribution of gK(Ca) and of postsynaptic inhibition to the epileptogenesis is discussed.