Neuropeptide Y (NPY)-like immunoreactivity in the guinea pig pineal organ

Relatively little is known about mammalian pineal neuropeptides. In the present study neuropeptide Y-like immunoreactivity (NPY-LI) was examined in the guinea pig pineal gland. NPY-LI was restricted to few intrapineal nerve fibers of faint fluorescence intensity. They showed no preferential localization with regard to the different pineal portions. As catecholaminergic fibers are abundant in the guinea pig pineal gland, the scarcity of NPY-LI fibers indicates that in the pineal colocalization of noradrenaline and NPY-LI is not a regular feature, in contrast to other organs. The possibility exists that in the pineal NPY-LI fibers are not of peripheral sympathetic but of central origin.