ABSTRACT
The dentate gyrus of hippocampus has long been considered as a focal point for studies on mechanisms responsible for the development of temporal lobe epilepsy [TLE]. Change in intrinsic properties of dentate gyrus granule cells [GCs] has been considered as an important factor responsible in temporal lobe seizures. In this study, we evaluated the intrinsic properties of GCs, during acute phase of seizure [24 h after i.p. injection of pilocarpine] compared to sham group using whole cell patch-clamp recordings. Our results showed a significant increase in the number of action potentials [APs] after applying depolarizing currents of 200 pA [p < 0.01] and 250pA [p < 0.05] compared to sham group. The evaluation of AP properties revealed a decrease in half-width of AP in GCs of seizure group [1.27 +/- 0.03 ms] compared to sham group [1.60 +/- 0.11]. Moreover, addition of BAPTA to pipette solution prevented changes in AP half-width in seizure group [1.71 +/- 0.11 ms] compared to sham group [1.91 +/- 0.08 ms]. In contrast, an increase in the amplitude of fast afterhyperpolarization was observed in GCs of seizure group [-11.68 +/- 0.72 mV] compared to sham group [-8.28 +/- 0.59 mV]. Also, GCs of seizure group showed a significant increase in both firing rate and instantaneous firing frequency at depolarizing currents of 200 pA [P < 0.01] and 250 pA [P < 0.05] compared to sham group. The changes in electrophysiological properties of GCs were attenuated after bath application of paxilline suggesting possible involvement of large conductance Ca[2+]- activated K[+] channel [BK channel]. Our results suggested the possible involvement of certain potassium channels in early changes of intrinsic properties of GCs which eventually facilitate TLE development