Toward a Unified Theory of Focal Penicillin Epileptogenesis: An Intracortical Evoked Potential Investigation

Abstract

Microinjection of picoliter quantities of isotonic sodium penicillin through 1 barrel of a double micropipet into cortical area 17 of cats induced discrete and temporary foci of epileptogenic alteration in evoked potentials. These were elicited by punctate visual stimuli, recorded through the 2nd barrel and from a 2nd micropipet located in surrounding cortex. Penicillin induced an initial graded increase in the primary latency, physiologic response and subsequently a new late response which evolved into an interictal spike potential. The enhanced physiologic response appears to represent a direct effect of penicillin upon neuronal excitability. The epileptic late response possessed distinctive properties that suggest the additional involvement of local circuit interactions within the neuronal population affected by the penicillin. Penicillin epileptogenesis in striate neocortex evidently is dependent upon both intrinsic neuronal and population interaction abnormalities. Relationships of this unified theory to those of the epileptic neuron and epileptic aggregate are discussed.