Calcitonin gene-related peptide containing sympathetic preganglionic and sensory neurons projecting to the superior cervical ganglion of the rat.

The origin of calcitonin gene-related peptide (CGRP)-containing fibers observed in the superior cervical ganglia (SCG) of the rat was investigated by a combined technique of retrograde axonal tracing and indirect immunofluorescence. Following the injection of Fast blue (FB) into the SCG, labeled neurons were observed in the C8-T5 spinal cord segments, with the highest density in T1-T3 (5-8 neurons per section). More than 90% of them were located in the ipsilateral intermediolateral cell column (IML) and the rest were found in the central autonomic area (CA) and intercalated region (IC) between the IML and CA. CGRP-like immunoreactive (IR) neurons were detected in these areas in animals pretreated with colchicine. About one-fourth of FB-labeled cells were CGRP-IR, which corresponded to three-fourths of the CGRP-IR neurons in the above-mentioned autonomic areas of these spinal cord segments. Most of these double-labeled cells were found in the IML (95%). A few FB-labeled cells were also observed in dorsal root ganglia (C8-T5) and 30% of them were CGRP-IR. These findings suggested that the CGRP-IR fibers in the rats SCG are supplied from both sympathetic preganglionic neurons in the spinal cord and sensory ganglion cells, although the latter projection is quite rare.