Peptidergic transmitters in synaptic boutons of sympathetic ganglia

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Abstract
In sympathetic ganglia of the bullfrog, a slow synaptic potential lasting for minutes, the late slow excitatory postsynaptic potential (e.p.s.p.), was discovered. This slow response, unlike other previously known synaptic potentials in the autonomic nervous system, is not mediated by acetylcholine or monoamines. Similar non-cholinergic, non-adrenergic slow synaptic potentials have since been found in several other vertebrate autonomic ganglia. The late slow e.p.s.p. is probably mediated by a peptide that is identical to, or closely resembles, mammalian luteinizing hormone releasing hormone (LHRH) because when applied directly to sympathetic neurons, LHRH and its agonists elicit a slow depolarization, associated with similar changes in membrane conductance and excitability as those occurring during the late slow e.p.s.p. Peptide-induced and nerve-evoked responses are blocked by antagonists of LHRH; and radioimmunoassays indicate that a chain of sympathetic ganglia contains 100-800 pg of a LHRH-like peptide. Its distribution among spinal nerves, the great reduction of this substance following denervation and its release from ganglia following isotonic KCl treatment or nerve stimulation suggest that the LHRH-like material is contained in preganglionic nerve fibers. Immunohistochemical staining of sympathetic ganglia shows that LHRH-like immunoreactivity is indeed present in synaptic boutons. The 2 types of ganglion cells (B cells and C cells) receive strikingly different patterns of peptidergic innervation.