Innervation of the Sheep Pineal Gland by Nonsympathetic Nerve Fibers Containing NADPH-diaphorase Activity

sheep. Nerve fibers containing NADPH-diaphorase activity provide dense innervation of the sheep pineal gland. The nerve fibers were located in the pineal capsule, in the connective tissue septae separating the lobuli of the gland, and penetrating between the pinealocytes. The nerve fibers were either smooth or endowed with boutons en passant. After bilateral removal of the superior cervical ganglion, the dense network of NADPH-diaphorasepositive fibers was still present in the gland. Ganglionectomy affected neither the distribution nor the appearance of the NADPH-diaphorase-positive fibers. Most of the NADPH-diaphorasepositive fibers also contained peptide histidine isoleucine and vasoactive intestinal polypeptide, and a comparatively smaller fraction contained neuropeptide Y. Pinealocytes never exhibited NADPH-diaphorase activity. These results demonstrate a major neural input to the sheep pineal gland with NADPH-diaphorase-positive nerve fibers of nonsympathetic origin. (J Histochem Cytochem 45:1121‐1128, 1997) T he pineal gland of mammals is a neuroendocrine organ that exhibits a circadian rhythmicity in its secretion of the hormone melatonin (cf. Reiter 1993). This circadian rhythmicity is generated by the suprachiasmatic nucleus of the hypothalamus (cf. Hastings 1995), which is entrained by photoperiodic signals from the retina (cf. Klein 1985). The neural input to the pineal gland is transmitted from the suprachiasmatic nucleus via caudally projecting neurons (Moller et al. 1991), with the hypothalamic paraventricular nucleus as an important anatomic part of this pathway (Vrang et al. 1995).