Ultrastructural observation of nerve fibers containing both substance P and calcitonin gene-related peptide in the nucleus tractus solitarii of the rat: a combination of immunofluorescence and PAP methods.

Nerve fibers and their axon terminals with substance P (SP)-like and calcitonin gene-related peptide (CGRP)-like immunoreactivity in the nucleus tractus solitarii were ultrastructurally characterized by a combination of immunofluorescent double staining and the PAP method. The axon terminals formed asymmetrical synaptic contacts with other non-reactive neuronal elements (perikarya, dendritic shafts and dendritic spines). Some terminals received synaptic inputs from non-reactive axon terminals. This suggests that some, if not all, afferents containing SP and CGRP are affected presynaptically by other afferents.