Electrophysiological study of amygdale-induced changes in the excitability of CA1 hippocampal pyramidal neurons in male adult rats

Introduction: Many studies have shown that amygdala kindling produces synaptic potentiation by induction of changes in the neuronal electrophysiological properties and inward currents both in epileptic focus and in the areas which are in connection with the epileptic focus and have important role in seizure development and progression such as hippocampal CA1 region. However, cellular mechanisms of these processes are not clear. In the present study, changes in the electrophysiological properties of hippocampal CA1 pyramidal neurons following amygdala kindling were examined in rat. Methods: Animals were rapidly kindled by stimulation of right amygdala (12 stimulation per day, 1 ms pulse duration at 50Hz). Twenty-four hours after amygdala kindling, electrophysiological properties and inward currents of CA1 pyramidal neurons were assessed by using whole-cell patch clamp technique. Results: Amygdala kindling findings show that percentage broadening of the last spike compared to the first spike during a trains of action potentials was significantly increased in kindled rats (p<0.05). The number of rebound action potential was significantly increased from 1±1 in control rats to 6±1 in kindled rats (p<0.01). The amplitude of post stimulus afterhyperpolarization potential (Post AHP) following a trains of action potential was also significantly (p<0.05) increased in kindled group (-5±2mV) compared to normal rats (-3±1mV). Under voltage clamp condition, amygdala kindling produced a significantly larger inward current (-5344.25±33.19 pA, p<0.001) in CA1 pyramidal neurons compared to normal cells (-9203.6±44.99pA). Conclusion: The present findings show that amygdala kindling resulted in neuronal hyperexcitability through alteration of the electrophysiological characteristics possibly by increasing the inward currents in hippocampal CA1 pyramidal neurons.