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Innervation of the rat pineal gland by pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive nerve fibres

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Abstract

 Pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive nerve fibres were demonstrated in the rat pineal gland. These fibres entered the pineal gland through the conarian nerve at the distal tip of the gland. A high density of the fibres was observed in the capsule of the gland, from where the immunoreactive elements penetrated into the pineal perivascular spaces and parenchyma. The majority of PACAP-immunoreactive nerve fibres also contained calcitonin gene-related peptide (CGRP). Some PACAP-immunoreactive nerve fibres contained neuropeptide Y (NPY), but only occasionally was PACAP colocalized with vasoactive intestinal peptide (VIP). After removal of both superior cervical ganglia, a high number of PACAP-containing nerve fibres were still present in the gland. In the nervous system PACAP is present in two isoforms, PACAP-38 and PACAP-27. The concentration of PACAP-38 in the superficial pineal gland was determined by radioimmunoassay to be 20.4 pmol/g tissue at midday and 18.9 pmol/g tissue at midnight. The concentration of PACAP-27 was only about 3% of the concentration of PACAP-38. In summary, this study is the first demonstration of a PACAP-containing innervation of the rat pineal gland. The PACAP concentration in the pineal gland does not exhibit a day-night difference. The colocalization of PACAP with calcitonin gene-related peptide in the pinealopetal nerve fibres indicates that the majority of PACAP-immunoreactive nerve fibres might originate from the trigeminal ganglion.

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Received: 14 September 1998 / Accepted: 6 November 1998

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Møller, M., Fahrenkrug, J. & Hannibal, J. Innervation of the rat pineal gland by pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive nerve fibres. Cell Tissue Res 296, 247–257 (1999). https://doi.org/10.1007/s004410051286

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  • Key words Calcitonin gene-related peptide
  • Vasoactive intestinal peptide
  • Neuropeptide Y
  • Colocalization
  • Trigeminal ganglion
  • Rat (Wistar)