Postnatal changes in adrenergic and neuropeptide Y-containing nerve fibres in pineal gland of the pig. An immunohistochemical study.

Postnatal development of the innervation of the porcine pineal gland by tyrosine hydroxylase-(TH-), dopamine-beta-hydroxylase-(D beta H), phenylethanolamine-N-methyltransferase-(PNMT-) and neuropeptide Y- (NPY-) immunoreactive (IR) nerve fibres was examined using the double-labelling immunohistochemical technique. TH-IR nerve fibres appeared in the pineal gland of new-born piglets and formed plexus in the capsula and connective tissue septa of the gland. In 20-day-old pigs and older ones, the nerve terminals branched off from the plexus and penetrated into adjacent parenchyma. The nerve fibres formed network; its density increased with age and depended on the region of the gland. In mature pigs, some differences in the innervation pattern between cortex and medulla were also observed. Most of TH-IR fibres were also D beta H- and NPY-positive. Some PNMT-positive fibres were noted in new-born piglets, but not in older animals. NPY-IR fibres were distributed in pattern overlapping that observed in the case of TH- and D beta H-IR fibres. Most of NPY-IR fibres were also positive for TH.