PARVALBUMIN-CONTAINING AND CALBINDIN-CONTAINING NEURONS EXPRESS C-FOSPROTEIN IN PRIMARY AND SECONDARY (MIRROR) EPILEPTIC FOCI OF THE RAT NEOCORTEX

The present experiments aimed at the description and further immunocyt ochemical characterization of activated neocortical neurons expressing the c-fos gene. Focal seizures were induced by the topical applicatio n of isotonic, isohydric 4-aminopyridine solution to the frontal neoco rtex of adult anesthetized Wistar rats. The EEG of both hemispheres wa s recorded from the surface of the skull. The animals were perfused wi th fixative, coronal plane vibratome sections were cut and stained wit h cocktails containing polyclonal c-fos and monoclonal calbindin or pa rvalbumin antibodies. The polyclonal c-fos antibody was tested with We stern blotting and the diffusion of 4-aminopyridine investigated with autoradiography of [H-3]4-aminopyridine. The c-fos protein was detecte d in every layer of the neocortex (primary focus) and in some allocort ical areas of the treated hemisphere. Scattered immunostained nuclei w ere observed in layers II, III, IV and VI of the contralateral neocort ex (mirror focus), Several parvalbumin- and calbindin-positive neurons contained the c-fos protein in both foci. The medium-sized non-pyrami dal parvalbumin neurons were found in layers II-IV and VI of the neoco rtex and in stratum multiforme of the prepiriform cortex. The c-fos pr otein was colocalized with calbindin mainly in layers II and III in sm all and medium-sized non-pyramidal neurons. The results prove that foc al epileptiform activity of the neocortex activates diverse inhibitory neuronal populations. As concluded, the inhibitory control is probabl y more effective in the contralateral hemisphere (mirror focus) than o n the side of 4-APY treatment (primary focus). (C) 1997 Elsevier Scien ce B.V.