Synaptic and non-synaptic actions of benzodiazepines on the crayfish sensory neuron

On the stretch-induced discharge activity of the isolated crayfish sensory neuron flurazepam (less than or equal to 3 X 10(-4) M) and Ro 15-1788 (less than or equal to 10(-3) M) produced reversible concentration-dependent excitation, but oxazepam only produced depression (less than or equal to 5 X 10(-4) M). Similar divergent effects on the membrane properties were observed. Oxazepam increased the threshold to firing without changing resting potential, membrane resistance or the GABA-mediated IPSP. In contrast flurazepam and Ro 15-1788 produced a concentration-dependent decrease in threshold. Flurazepam did not alter membrane resistance or resting potential but facilitated GABA transmission. Ro 15-1788 had the opposite effect on the GABA synapse, and also depolarized the resting potential but did not alter membrane resistance. The change in spike threshold appeared to be an important component in producing discharge excitation or depression. These results not only demonstrate the capability of the sensory neuron to discriminate between structures of benzodiazepines, but also that these agents can produce divergent effects on synaptic and non-synaptic properties of a single neuron.