Methyl-beta-carboline-3-carboxylate attenuates GABA effects in rat brain hippocampus in vivo

The benzodiazepine receptor ligand methyl-beta-carboline-3-carboxylate was applied by micropressure-ejection in the course of extracellular recordings of spontaneously firing rat brain hippocampal pyramidal cells in vivo. Methyl-beta-carboline-3-carboxylate was found to attenuate the depressant effects of GABA, increase the spontaneous firing rate and increase the tendency to fire in bursts. The possibility that both firing rate and burst firing in the hippocampus are controlled by the inhibitory neurotransmitter GABA is discussed. Methyl-beta-carboline-3-carboxylate is a convulsant and this action on GABA could explain the mechanism. Methyl-beta-carboline-3-carboxylate seems to have effects on the firing of CA1 neurons which are similar to the effects reported for ethyl-beta-carboline-3-carboxylate and opposite to those reported for the benzodiazepines midazolam and diazepam.