Functional gene expression of dopamine receptors in the male reproductive organ during sexual maturation in the honey bee (Apis mellifera L.)

Dopamine is a potential integrator between the central nervous system and reproductive system in insects. To test for a possible action of dopamine on the male reproductive organ via hemolymph in honey bees, relative expression levels of dopamine receptor genes and second messenger levels responding to dopamine in the reproductive organ were quantified. Protein content of the three parts of the reproductive organ (testes, seminal vesicles, and mucus glands) differed depending on the age of bees: the protein content of the testes decreased, whereas that of the seminal vesicles and mucus glands increased as males aged. Relative expression levels of dopamine receptor genes (Amdop1 , Amdop2, Amdop3 and Amgper19) in each part of the reproductive organ were detected and were lower than those in the brain. Expression of all these genes was significantly higher in the seminal vesicles than in testes and mucus glands. Expression of Amgper19 was significantly higher in testes of 8-day-old males than in males of other ages, and was highest in the seminal vesicles of 4-day-old males. Cyclic adenosine monophosphate (cAMP) levels responding to dopamine in seminal vesicles were significantly higher in 10(-3) M dopamine immersion than in 10(-4) M, 10(-5) M dopamine, and controls. However, no significant differences in cAMP levels between control and dopamine immersion were detected in testes and mucus glands. These results suggest that the dopamine receptors in seminal vesicles can be driven by dopamine for reproduction, including sperm transfer and storage in the male reproductive organ.