Direct synaptic contacts of 5-hydroxytryptamine-, neuropeptide Y-, and somatostatin-immunoreactive nerve terminals on the preganglionic sympathetic neurons of the guinea pig.

Direct synapses from 5-hydroxytryptamine-, neuropeptide Y-, and somatostatin-immunoreactive axon varicosities to the preganglionic sympathetic neurons retrogradely labeled with horseradish peroxidase were observed in the thoracic intermediolateral nucleus of the guinea pig. Symmetric synapses were predominant and both axo-dendritic and axo-somatic contacts were observed.