Date on Master's Thesis/Doctoral Dissertation

5-2013

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Anatomical Sciences and Neurobiology

Committee Chair

Moore, Joseph P.

Author's Keywords

PACAP; Pre-puberty male; Pituitary gonadotrophs; Follicle-stimulating hormone

Subject

Pituitary hormone releasing factors; Pituitary hormones; Pituitary gland

Abstract

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid C-terminally a-amidated peptide that was first isolated from ovine hypothalamic extracts on the basis of its ability to stimulate cAMP production in anterior pituitary cells. As a member of the vasoactive intestinal polypeptide (VIP)/secretin/growth hormone-releasing hormone/glucagon superfamily, PACAP has been well conserved during evolution from sea squirt to humans, which suggests important biological functions. Two types of PACAP receptors have been characterized. PAC1-R is the only one PACAP-specific receptor with high affinity. Although PACAP was first found in hypothalamus, it is also expressed in the pituitary. In the research to be presented, PACAP and PAC1-R mRNA expression in the rodent pituitary and in gonadotroph cell lines were explored using semi-quantitative PCR, laser capture micro-dissection (LCM) and single cell PCR. The level of pituitary PACAP expression is high in the fetus and declines after birth. Most of pituitary PACAP is from gonadotrophs. PAC1-R in fetal pituitary exists as the Hop and short forms, and the level of the short form decreases after birth. The effects of PACAP on gonadotropins synthesis and secretion were studied in vivo and in vitro. The action of PACAP on LH and FSH was investigated utilizing micro-pump implanted, containing PACAP38 or the antagonist, PACAP 6-38, in pre-pubertal male rats. Protein and mRNA analysis revealed that PACAP suppresses FSH presumably through increased follistatin, but had no significant influence on LH. The existence of PACAP, therefore, likely contributes to maintain an appropriate gonadotropin environment during sexual development. We also studied pituitary cell cultures and gonadotroph cell lines to understand why PACAP expression in pituitary is high in the fetus, and declines at birth. PACAP was found to stimulate its own expression in that the PACAP 6-38 antagonist reduced the PACAP mRNA level in primary cell cultures, and PACAP38 induced high activity of PACAP promoter in gonadotroph cell lines. Furthermore, we found preliminary evidence to support the ideal that dopamine receptor 2 (Drd2) signaling may explain the neonatal decrease in pituitary PACAP mRNA levels. Finally, we propose that the decrease in PACAP results in a fall in pituitary follistatin, allowing for increased activin signaling which increases FSHß facilitates the sexual maturation of the gonads.

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