Temperature- and concentration-dependence of kainate-induced gamma oscillation in rat hippocampal slices under submerged condition

Aim: Fast neuronal network oscillation at the gamma frequency band (gamma oscillation: 30-80 Hz) has been studied extensively in hippocampal slices under interface recording condition. The aim of this study is to establish a method for recording gamma oscillation in submerged hippocampal slices that allows simultaneously monitoring gamma oscillation and the oscillation-related intracellular events, such as intracellular Ca2+ concentration or mitochondrial membrane potentials. Methods: Horizontal hippocampal slices (thickness: 300 mu m) of adult rats were prepared and placed in a submerged or an interface chamber. Extracellular field recordings were made in the CA3c pyramidal layer of the slices. Kainate, an AMPA/kainate receptor agonist, was applied via perfusion. Data analysis was performed off-line. Results: Addition of kainate (25-1000 nmol/L) induced gamma oscillation in both the submerged and interface slices. Kainate increased the gamma power in a concentration-dependent manner, but the duration of steady state oscillation was reduced at higher concentrations of kainate. Long-lasting gamma oscillation was maintained at the concentrations of 100-300 nmol/L. Under submerged condition, gamma oscillation was temperature-dependent, with the maximum power achieved at 29 degrees C. The induction of gamma oscillation under submerged condition also required a fast rate of perfusion (5-7 mL/min) and showed a fast dynamic during development and after the washout. Conclusion: The kainite-induced gamma oscillation recorded in submerged rat hippocampal slices is useful for studying the intracellular events related to neuronal network activities and may represent a model to reveal the mechanisms underlying the normal neuronal synchronizations and diseased conditions.