Neuropeptide Y-containing neurons in the rat superior cervical ganglion: projections to the pineal gland.

The aim of this study was to investigate the localization in the superior cervical ganglia (SCG) of neuropeptide Y-containing neurons innervating the pineal gland. Following injection of the fluorescent tracer Fluoro-Gold (FG) into the superficial part of the pineal gland and retrograde axonal transport, labeled cells were observed predominantly in the rostral third to half of SCG sections (average number 239 per ganglion). Incubation of the sections with neuropeptide Y (NPY) antiserum showed that the vast majority of neurons exhibit NPY-like immunoreactivity (NPY-LI). The comparison of cells labeled with FG and those containing NPY revealed that nearly three fourths of retrogradely labeled neurons also exhibit NPY-LI. Incubation of pineal gland sections with NPY antiserum showed immunoreactive axons, relatively sparse and scattered throughout the superficial part of the organ and the pineal stalk. The present results confirm the assumption that, in rodents, pineal NPY originates from the superior cervical ganglia.