Effects of histamine on acetylcholine release in bullfrog sympathetic ganglia

The effects of histamine on the release of acetylcholine (ACh) from bullfrog sympathetic preganglionic nerve terminals were examined by means of intracellular microelectrode techniques. Low concentrations of histamine (1, 3 muM) increased the amplitude of fast excitatory postsynaptic potentials (fast EPSPs) and ACh quantal content, while high concentrations (100, 300 muM) decreased the amplitude and content. Amplitudes of miniature EPSPs and ACh potentials were not affected by histamine (0.3-300 muM). The facilitatory effect of histamine on fast EPSPs disappeared in the presence of mepyramine, whereas the depressant effect of histamine on fast EPSPs disappeared in the presence of cimetidine. These results suggest that histamine has facilitatory and depressant actions on ACh release. The facilitatory action is probably mediated by the H1-receptor and the depressant action by the H2-receptor, both of which are located at the presynaptic nerve terminals of bullfrog sympathetic ganglia.