Monoamines are implicated in cognitive processes in variety of brain regions including the hippocampal formation, where storage and retrieval of information is facilitated by synchronous network activities. We have investigated the effects of norepinephrine, serotonin and dopamine on carbachol-, kainate- and stimulus-induced hippocampal γ-oscillations employing extra and intracellular recordings. Monoamines dose-dependently and reversibly suppressed kainate- and carbachol-induced γ-oscillations. The effect of serotonin was mimicked by fenfl uramine, which releases serotonin from presynaptic terminals. Forskolin also suppressed kainate- and carbachol-induced γ-oscillations. This effect was mimicked by 8-Br-cAMP and isoproteronol, an agonist of noradrenergic β-receptor suggesting that the monoamines-mediated suppression of these oscillations could involve intracellular cyclic AMP. By contrast, stimulus-induced γ-oscillations were dose-dependently augmented in power and duration after monoamines application. Intracellular recordings from pyramidal cells revealed that monoamines prolonged the stimulus-induced depolarization and membrane potential oscillations. Stimulus-induced γ-oscillations were also suppressed by isoproteronol, the D1 agonist SKF-38393 forskolin and 8-BrcAMP. This suggests that the augmentation of stimulus induced γ-oscillations by monoamines involves – at least in part – different classes of cells than in case of carbachol- and kainate-induced γ-oscillations.
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