Peptidergic transmission in sympathetic ganglia of the frog.

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Abstract
A slow synaptic potential recorded in neurons of sympathetic ganglia of bullfrog, the late slow EPSP [excitatory postsynaptic potential] is probably mediated by a peptide resembling LHRH, because a LHRH-like peptide is contained in preganglionic nerve terminals and is released upon nerve stimulation, application of LHRH to ganglion cells mimics the effects of the natural transmitter for the late slow EPSP and the pharmacological properties of LHRH and the natural transmitter for the late slow EPSP are similar. Neurons in frog sympathetic ganglia are also depolarized by substance P. The substance P receptors, unlike the LHRH receptors or the postsynaptic receptors for the late slow EPSP are not blocked by antagonists of LHRH. No cross-desensitization was found between the substance P-induced response and the LHRH-induced response or the late EPSP. Substance P-like immunoreactivity is contained in bundles of axons passing through the ganglia. This distribution is distinct from the distribution of LHRH-like immunoreactivity in preganglionic nerve terminals. Thus, substance P receptors and substance P-containing fibers are distinct from the postsynaptic receptors and preganglionic fibers responsible for the late slow EPSP. Physiological and anatomical evidence is presented which indicates that the peptidergic transmitter for the late slow EPSP can diffuse for many micrometers before acting on ganglion cells.