The inhibitory effect of different patterns of low frequency stimulation on neuronal firing following epileptiform activity in rat hippocampal slices.

Low frequency stimulation (LFS) has inhibitory effect on hyperexcitability during epileptic states. However, knowledge is lacking about LFS patterns that can exert an optimal antiepileptic effect. In this study, the effect of different numbers of pulses and current intensities of 1 Hz LFS applied at various time points of epileptiform activity was evaluated in high-K+ model of epileptiform activity (EA). LFS was applied to the Schaffer collaterals, and changes in the excitability of CA1 pyramidal neurons were measured using whole-cell patch-clamp recording. Six hundred and 900 pulses of LFS at two current intensities (equal to and 1.5 times greater than the current intensity sufficient to elicit a 5 mV EPSP) administered at the beginning of EA revealed a stronger LFS inhibitory effect on EA-induced neuronal hyperexcitability when applied at higher pulse number and current intensity. LFS900 (high intensity) significantly hyperpolarized the membrane potential after a high-K+ ACSF washout, reduced the frequency of spontaneous action potentials during EA, and attenuated neuronal firing frequency after high-K+ ACSF washout. Moreover, applying LFS900 (high intensity) before EA induction and 8-10 min after EA initiation could not significantly affect neuronal hyperexcitability, compared to its application at the beginning of EA. This study's findings also offered long-term depression (LTD) as a probable mechanism for LFS' inhibitory role on EA-induced neuronal hyperexcitability. Therefore, the application of LFS (1 Hz) at 900 pulses and greater current intensity at the beginning of EA can exert a strong inhibitory effect on EA-induced neuronal hyperexcitability.

Phasic and tonic type A γ-Aminobutryic acid receptor mediated effect of Withania somnifera on mice hippocampal CA1 pyramidal Neurons.

BACKGROUND: In Nepali and Indian system of traditional medicine, Withania somnifera (WS) is considered as a rejuvenative medicine to maintain physical and mental health and has also been shown to improve memory consolidation. OBJECTIVE: In this study, a methanolic extract of WS (mWS) was applied on mice hippocampal CA1 neurons to identify the receptors activated by the WS. MATERIALS AND METHODS: The whole cell patch clamp recordings were performed on CA1 pyramidal neurons from immature mice (7-20 postnatal days). The cells were voltage clamped at -60 mV. Extract of WS root were applied to identify the effect of mWS. RESULTS: The application of mWS (400 ng/µl) induced remarkable inward currents (-158.1 ± 28.08 pA, n = 26) on the CA1 pyramidal neurons. These inward currents were not only reproducible but also concentration dependent. mWS-induced inward currents remained persistent in the presence of amino acid receptor blocking cocktail (AARBC) containing blockers for the ionotropic glutamate receptors, glycine receptors and voltage-gated Na(+) channel ( CONTROL: -200.3 ± 55.42 pA, AARBC: -151.5 ± 40.58 pA, P > 0.05) suggesting that most of the responses by mWS are postsynaptic events. Interestingly, these inward currents were almost completely blocked by broad GABAA receptor antagonist, bicuculline- 20 µM (BIC) (BIC: -1.46 ± 1.4 pA, P < 0.001), but only partially by synaptic GABAA receptor blocker gabazine (1 µM) (GBZ: -18.26 ± 4.70 pA, P < 0.01). CONCLUSION: These results suggest that WS acts on synaptic/extrasynaptic GABAA receptors and may play an important role in the process of memory and neuroprotection via activation of synaptic and extrasynaptic GABAA receptors.