Expression of D1 and D2 dopamine receptors in the hypothalamus and pituitary during the turkey reproductive cycle: Colocalization with vasoactive intestinal peptide

Yupaporn Chaiseha, Orlan Youngren, Khaled Al-Zailaie, M E Elhalawani

Research output: Contribution to journalArticle

34 Scopus citations

Abstract

The regulation of avian prolactin (PRL) secretion and PRL gene expression is influenced by hypothalamic vasoactive intestinal peptide (VIP), the PRL-releasing factor in avian species. Recent evidence indicates that D1 and D2 dopamine (DA) receptors play a pivotal role in VIP and PRL secretion. The differential expression of DA receptors located on hypothalamic VIP neurons and anterior pituitary cells may affect the degree of prolactinemia observed during the turkey reproductive cycle. The relative expression of D1D and D2 DA receptor subtype mRNA was quantitated using in situ hybridization histochemistry (ISH). D1D and D2 DA receptor mRNA was found expressed throughout the hypothalamus and pituitary. The expression of D1D DA receptor mRNA in the hypothalamus was found to be 6.8-fold greater than that of D2 DA receptor mRNA. Higher D1D DA receptor mRNA content was found in the anterior hypothalamus (3.6-fold), the ventromedial nucleus (2.0-fold), the infundibular nuclear complex (INF; 1.9-fold), and the medial preoptic nucleus (1.5-fold) of laying hens as compared to that of reproductively quiescent non-photostimulated hens. The levels seen in incubating hyperprolactinemic hens were essentially the same as in laying hens, except for the INF where levels were 52% higher. During the photorefractory stage (hypoprolactinemia), the D1D DA receptor mRNA was at its lowest level in all areas tested. No differences were observed in hypothalamic D2 DA receptor mRNA abundance throughout the reproductive cycle, except for an increase in D2 DA receptor mRNA within the INF of photorefractory hens. Also, a marked reduction in D2 DA receptor mRNA was observed in the pituitary of incubating hens. Pituitary D1D DA receptor levels did not change when birds entered the incubating phase. Double ISH revealed that D1D and D2 DA receptor mRNAs were co-expressed within neurons expressing VIP mRNA, predominantly within the lateral hypothalamus and INF. D1D DA receptor mRNA was more highly expressed than D2 DA receptor mRNA. The present findings clearly demonstrate that the expression of stimulatory D1 DA receptor mRNA in the hypothalamus increases in hyperprolactinemic incubating hens, whereas inhibitory D2 DA receptor mRNA increases in the pituitary of hypoprolactinemic photorefractory hens.

Original languageEnglish (US)
Pages (from-to)105-118
Number of pages14
JournalNeuroendocrinology
Volume77
Issue number2
DOIs
StatePublished - Jan 1 2003

Keywords

  • Arcuate nucleus
  • Birds
  • Catecholamine receptors
  • In situ hybridization
  • Preoptic nucleus
  • Prolactin
  • Vasoactive intestinal peptide
  • Ventromedial nucleus

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