The action of piracetam on the electrical activity of the hippocampal slice preparation: a field potential analysis.

The action of various doses of piracetam on the electrical responses of in vitro hippocampal slices from the rat was investigated. Piracetam increased dose dependently the amplitude of the population spike response of pyramidal neurons evoked by stimulation of the stratum radiatum. Piracetam began to affect the population spike at a dose of 100 microM and consistently increased it at a dose of 1 mM. The drug had a rapid onset of action and recovery was seen within a few minutes following its removal. The response of the pyramidal neurons to antidromic stimulation was not affected by piracetam at concentrations up to 50 mM. Also, neither the amplitude nor the slope of the dendritic response was changed by the drug.l Piracetam also did not affect either posttetanic or long-term potentiation of synaptic potentials. These findings suggest that the drug does not act through depolarization of the pyramidal cells or potentiation of the synaptic processes located on their dendrites. The action of piracetam on the feedforward- and feedback-mediated inhibition of pyramidal cells by basket cells was investigated in several series of experiments. At concentrations of 1 and 10 mM, piracetam did not change either of the two types of inhibitory mechanisms. Several hypothetical sites of action of piracetam are discussed.