Target Specificity of Projections from Postganglionic Sympathetic Neurons Innervated by Enkephalin Containing Preganglionic Fibers.

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It has been known that neurons of sympathetic nervous system contain many kinds of neuropeptides in addition to the classical neurotransmitter such Noradrenaline (NA) or acetylcholine. In the present study we investigated specific connections coded with certain neuropeptides between sympathetic nerve cells and their targets in the dog. By use of the fast blue tracing technique and immunohistochemistry, it was revealed that :1. Enkephalin (ENK)-Immunoreactive (IR) fibers were selectively distributed in the stellate and L_6-S_1 sympathetic ganglia, and were originated from preganglionic neurons in the intermediolateral nucleus of spinal cord.2. The ENK-1R fibers surrounded Vasoactive Intestinal Peptide (VIP)/Calcitonin Gene-Related Peptide (CCRP)/Substance P (SP)-IR non-NA ganglionic cells and formed a basket-like terminal.3. Many ENK-1R terminals formed direct contacts with somata of postganglionic neurons and also made asymmetrical axo-dendritic synapses.4. The VIP/CGRP/SP-IR postganglionic neurons in the stellate ganglion innervated selectively to the sweat glands of the footpads.Thus, a target specific connection, i. e., the ENK containing preganglionic neurons -> VIP/CGRP/SP containing postganglionic neurons -> sweat glands, was demonstrated.In another experiment, we demonstrated target-specific projections of intrinsic ganglionic neurons with different chemical codes in the canine larynx.