Pentobarbital: differential postsynaptic actions on sympathetic ganglion cells.

The frog sympathetic ganglion has been used as a model to elucidate the cellular mechanism of barbiturate anesthesia. Anesthetic concentrations of pentobarbital markedly reduced the fast nicotinic excitatory postsynaptic potential while having no effect on the slow excitatory postsynaptic potential or slow inhibitory postsynaptic potential, even though all three synaptic potentials depend on the presynaptic release of acetylcholine. A similar differential effect was seen for nicotinic and muscarinic responses to exogenously applied agonists, while the depolarizing action of gamma-aminobutyric acid (GABA) was enhanced. These results indicate that pentobarbital has remarkably selective actions on the sympathetic ganglion and further indicate that blockade of ganglionic transmission by anesthetic concentrations of pentobarbital can be entirely explained by a postsynaptic action. The present results strengthen the concept that pentobarbital anesthesia results from a postsynaptic blockade of central excitatory synapses which increase sodium conductance coupled with a postsynaptic enhancement of GABA-mediated synaptic inhibition.