Regulation of the brain dopaminergic system by juvenile hormone in honey bee males (Apis mellifera L.)

Dopamine (DA) and juvenile hormone (JH) are multifunctional regulators of behaviour in social insects, with distinct effects across species and even between different dominance positions within the same species. We examined the effects of JH on the brain dopaminergic system in honey bee males to investigate the potential relationship between JH and DA within Apis mellifera. Both DA content and the expression of three DA receptor genes (Amdop1, Amdop2 and Amdop3) increased in the male honey bee brain from day 4 to day 8 after emergence. Treatment of 4-day-old males with a JH analogue (methoprene, JHA) enhanced brain DA levels. Brain expression of Amdop1 was also enhanced by JHA but not by a DA receptor agonist 2-amino 6,7-dihydroxy-1,2,3,4- tetrahydronaphthalene (6,7-ADTN), indicating that Amdop1 up-regulation was not mediated by increased DA receptor stimulation. Furthermore, Amdop1 expression was still enhanced when JHA was co-applied with the DA receptor antagonist cis-(Z)-flupenthixol. Expression levels of Amdop2 and Amdop3 were not altered by JHA, 6,7-ADTN or by JHA plus the DA receptor antagonist. Regulation of the brain dopaminergic system by JH, as observed in solitary species, is conserved in male honey bees but not in female honey bees and other advanced eusocial insects.