Benzodiazepine selectively antagonize kainate-induced activation in the rat hippocampus

Low intravenous doses of two benzodiazepines, lorazepam and diazepam, antagonized the activation of dorsal hippocampus CA1 pyramidal neurons by kainate to a greater extent than the activations produced by glutamate and acetylcholine. A similar effect was obtained with microiontophoretic application of two water-soluble benzodiazepines, flurazepam and chlordiazepoxide. Chlorpromazine and phenobarbital did not exert any consistent effect on kainate-induced activation. RO 15-1788, a benzodiazepine antagonist, prevented the effect of lorazepam on kainate-induced activation. The regional selectivity of this effect was indicated by the failure of lorazepam to produce a sustained reduction of kainate action in the CA3 hippocampal region and in the cerebral cortex. This selective antagonism by benzodiazepines of the excitation of selected limbic neurons via 'kainate-sensitive' receptors might be related to their anxiolytic effect.