Ultrastructural evidence of synaptic contacts between substance p‐, enkephalin‐, and serotonin‐immunoreative terminals and retrogradely labeled sympathetic preganglionic neurons in the Rat: A Study using a double‐peroxidase procedure

A double‐peroxidase procedure was used to study the ultrastructural relationship between terminals and fibers containing three putative neurotranasmitters and retrogradely identified sympathetic preganglionic neurons (SPNS) located in the intermediolateral cell column (IML) of the rat. SPNS with axons in the cervical sympathetic trunk were retrogradely labeled with horseradish peroxidase. In addition, terminals and fibers containing substance P, enkejphalin, and serotonin were detected using immunohistochemistry. Sections containing both retrogradely labeled SPNS and immunoreactive processes were processed for electron microscopy. Ultrastructural examination revealed synaptic contacts between terminals containing each of these three neurotransmitters and labeled dendrites from SPNS. Also, immunoreactive terminals were apposed to retrogradely labeled cell bodies. Therefore, these transmitters may alter sympathetic function by their direct action on SPNS.