An electrophysiological study on the common antitussive drug dextromethorphan in hippocampal slices in the rat

Dextromethorphan, a common antitussive drug derived from the opioid class of morphinans, has been reported to have antiepileptic properties in some experimental tests. The effects of dextromethorphan were tested on the synaptic responses of the interconnections between Schaffer collaterals and CA1 pyramidal cells in hippocampal slices of the rat. Dextromethorphan, up to 100-200 microM, did not affect the basal field potentials resulting from electrical stimulation of the radiatum (0.1 Hz, 100-200 microA, 75 mu sec) of CA1 pyramidal cells. Larger concentrations of the drug (300-400 microM) depressed the amplitude and increased the duration of the CA1 basal population spikes. Dextromethorphan, up to 200-300 microM, affected neither the duration nor the incidence of the additional population spikes of the epileptiform bursting, resulting from perfusion of the slice with 1 mM penicillin or in the absence of magnesium ions. The data indicate that: (1) dextromethorphan has an influence on CA1 pyramidal cells, different from that of other opioids; (2) the reported antiepileptic effects of dextromethorphan do not involve the hippocampal area.