Different types of calcitonin gene-related peptide-immunoreactive neurons in the guinea-pig stellate ganglion as revealed by triple-labelling immunofluorescence.

A triple-labelling immunofluorescence technique was used to study the patterns of coexistence of calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and tyrosine hydroxylase (TH) in the guinea-pig stellate ganglion. CGRP-immunoreactive postganglionic neurons, which all were of the non-catecholaminergic type, could be divided into NPY-positive and NPY-negative populations. Sweat glands, which are a known target of CGRP-immunoreactive sympathetic neurons, exhibited exclusively fibers of the CGRP+/NPY- phenotype. Lack of coexistence of CGRP- and NPY-immunoreactivity was also observed in nerves within skeletal muscle, brown adipose tissue and hairy skin. The findings document a previously unknown diversity of CGRP-immunoreactive postganglionic sympathetic neurons, and indicate the existence of an addition, presently unidentified target of non-catecholaminergic, CGRP-immunoreactive sympathetic neurons.