Immunocytochemical localisation of substance P-like nerves in the cardiac ganglia of the monkey (Macaca fascicularis).

Substance P-like immunoreactive (SP-IR) nerves formed 2 types of relationships with nerve cells in the cardiac ganglia of the monkey (Macaca fascicularis). The first type consisted of varicose SP-IR nerve fibres that ramified throughout the cardiac ganglia, forming a loose network with several nerve cell bodies. The second type consisted of several nerve cell bodies enwrapped by a dense pericellular (basket-like) investment of varicose SP-IR nerve fibres. Numerous SP-IR nerve fibres formed perivascular networks around the walls of the blood vessels within the cardiac ganglia and the muscle. The cardiac muscle cells were also innervated either by an isolated single varicose SP-IR nerve fibre or by complex networks. At the ultrastructural level, the substance P reaction product appeared to be associated with the microtubules and the outer mitochondrial membranes of labelled axons. Substance P reaction product was also localised on the membranes of small agranular vesicles of the labelled axon terminals. The SP-IR axons and axon terminals were closely related to the nerve cell bodies and they occurred either singly or in small groups. Most of the axons were enwrapped by a sheath from the adjacent Schwann cells which often exhibited pseudopodia-like processes. None of the axon terminals was observed to make synaptic contact with the cell bodies. However, a few axoaxonal contacts involving SP-IR and non-SP-IR axon terminals were present, the significance of which is not understood. Several axon terminals lay close to blood vessels, and may modulate the activity of these vessels.(ABSTRACT TRUNCATED AT 250 WORDS)