Comparative Studies of VIP-, PHI-, and NPY- Immunoreactive Nerve Fibers in the Pineal Gland of the Sheep

The mammalian pineal gland is innervated by orthosympathetic nerve fibers coming from the superior cervical ganglia. These fibers probably represent the last step of a chain starting in the retina and reaching the suprachiasmatic nuclei, the paraventricular nuclei and the superior cervical ganglia (Moore, 1978; Klein, 1985; Moore and Card, 1985). From the superior cervical ganglia, sympathetic nerve fibers travel close to blood vessels (for trajectories see TamamaKi and Nojyo, 1987), and penetrate the pineal from the posterodorsal tip, spreading into the connective capsule and in the parenchyma of the organ (Bowers et al., 1984). Additional to the classical orthosympathetic innervation, a number of anatomical reports indicates the existence of other pathways of innervation of the pineal gland (Korf and Moller, 1984,1985; Moller et al., 1987b).