Low frequency electrical stimulation has time dependent improving effect on kindling-induced impairment in long-term potentiation in rats

Application of low-frequency stimulation (LFS) can improve learning and memory in kindled animals (Ghafouri et al., 2016). Considering the important role of long-term potentiation (LTP) in learning and memory, in the present study the effectiveness of LFS on kindling-induced impairment in LTP induction was investigated in hippocampal CA1 area at different times post kindling stimulations. Animals were kindled via electrical stimulation of hippocampal CA1 area in a semi-rapid manner (12 stimulations per day). One group of animals received four trials of LFS at 30 s, 6 h, 24 h, and 30 h following the last kindling stimulation. Each LFS consisted of 4 packages at 5 min intervals; each package contained 200 monophasic square wave pulses of 0.1 ms duration at 1 Hz. The kindled, kindled + LFS and LFS groups were divided into four subgroups in which hippocampal slices were prepared at 48 h, 1 week, 2 weeks, and 1 month following the last kindling stimulation respectively. Extracellular evoked field excitatory postsynaptic potentials (fEPSPs) were recorded in the stratum radiatum of the CA1 area of the slice. Obtained results showed that LTP was not induced in kindled animals. However, application of LFS overcame the kindling-induced impairment in LTP generation in CA1 area of the hippocampus. This improving effect remained up to one week after the last kindling stimulation and extended to one month by increasing the number of applied LFS packages.