The behavior of presumed glial cells during seizure discharge in cat cerebral cortex

Presumed glial cells (PG cells) and neurons were examined during seizure activity and their intracellular potentials were compared to the steady potential (SP) shifts which occurred at the cortical surface. The seizures studied in these experiments developed after irrigation of the cortical surface with low Cl^- concentration solutions and may have been due to the conversion, within the upper cortical layers, of inhibitory synaptic potentials into depolarizing potentials.

PG cells impaled in seizure foci appeared to have unusually large resting membrane potentials (RMPs; average = -105 mV). Slow depolarizations (SDs) elicited during interictal periods by low frequency direct cortical stimulation were also very large (average = 29 mV). Following paroxysms, PG cells frequently demonstrated hyperpolarizing potentials resembling those seen in normal cortex after repetitive direct cortical stimulation⁴¹.

With tonic paroxysms PG cells underwent long duration depolarizing shifts whose shape and time course were perfectly mirrored by negative SP shifts. tI was demonstrated that the PG cell depolarizations associated with negative SP shifts were of sufficient amplitude to have produced the surface shifts. In contrast to PG cells the neurons studied during seizures showed potential fluctuations which were not well correlated with SP shifts. It was estimated from the magnitude of PG cell depolarizations, that during tonic paroxysms the (K)₀ increased to an average value of 13 mM. © 1974.