D1 and D2 dopamine receptor messenger ribonucleic acid in brain and pituitary during the reproductive cycle of the turkey hen

The regulation of prolactin secretion during the reproductive cycle of seas onal breeding birds appears to be largely under the stimulatory influence o f hypothalamic vasoactive intestinal peptide (VIP). However, the factors in fluencing VIP secretion, and hence prolactin release, in birds remain large ly unexplored, Recent evidence has demonstrated that dopamine and dopamine receptors may affect VIP and prolactin release in birds, The differential e xpression of dopamine receptors on hypothalamic VIP-releasing neurons may a ffect the degree of prolactinemia observed during the reproductive cycle of birds. In order to examine this hypothesis, we used reverse transcription- polymerase chain reaction to quantitate the levels of D1 and D2 dopamine re ceptor subtype mRNAs in the brain of the domestic turkey hen during the rep roductive cycle, No significant difference in hypothalamic expression of D1 or D2 dopamine receptor subtypes during the reproductive cycle was observe d, However, pronounced differences in D1, and D2 mRNAs were detected in cor tex and cerebellum, Interestingly, there was a dramatic increase in pituita ry D1, receptor mRNA during the reproductive stages of laying and incubatio n of eggs, which paralleled the hyperprolactinemic state of the turkey repr oductive cycle. In addition, pituitary D2 receptor mRNA steadily increased throughout the reproductive cycle. In light of these observations, a modifi ed hypothesis regarding the effects of dopamine on prolactin secretion is d iscussed.