RESUMO
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
RESUMO
The activity of the magnocellular neurons [MCNs] of supraoptic nucleus [SON] is regulated by a variety of excitatory and inhibitory inputs. Opioids are one of the important compounds that affect these inputs at SON synapses. In this study, whole-cell patch clamp recording of SON neurons was used to investigate the effect of acute and repeated morphine administration on spontaneous inhibitory and excitatory post synaptic currents [sIPSCs and sEPSCs] in MCNs. While acute bath application of morphine to brain slice of intact rat produced an increase in sEPSCs frequency and a decrease in sIPSCs frequency, repeated in vivo administration of morphine produced opposite effect. Moreover, repetitive i.c.v. administration of morphine for three consecutive days caused significant increase in urine volume, but had no significant alteration in water consumption compared to control group. The increase in urine volume was consistent with a significant decrease in plasma arginine vasopressin [AVP] levels after repetitive i.p. morphine administration. The results suggest that acute administration of morphine stimulates whereas repeated administration of morphine inhibits the MCNs. Morphine-induced MCN inhibition could result in diminished plasma AVP levels and eventually an increase in urine volume of rats