The influence of endogenous dopamine levels on the density of [ [formula omitted]]SCH23390-binding sites in the brain of the honey bee, Apis mellifera L

Abstract

This paper examines the relationship between endogenous dopamine (DA) levels and the density of [ 3 H ]SCH23390-binding sites in the brain of the adult worker honey bee. DA levels were reduced pharmacologically using a single 10 μl injection of either α-methyl- dl- p-tyrosine (AMT; 250 μg or 500 μg) or α-methyl- dl-tryptophan (AMTP; 250 or 500 μg) into the haemolymph of the bee. In all cases, maximum depletion of DA was observed 3 h after treatment, but in bees treated with AMTP (250 or 500 μg) or with 250 μg AMT, DA levels returned to normal within 24 h of treatment. Neither AMT nor AMTP was selective for DA: both drugs also reduced serotonin (5-hydroxytryptamine, 5HT) levels in the brain. However, AMTP was more effective than AMT at depleting 5HT, whereas for DA, the reverse was true. Depletion of DA levels, using 250 μg AMT, led to a dramatic decline in the levels of specific binding of [ 3 H ]SCH23390, defined in this study as binding in the presence of 5×10 −6 M cis-( Z)-flupentixol (see Ref. [28]). In contrast, naturally occurring diel fluctuations in DA levels, identified in the optic lobes of the brain, and changes in brain DA levels resulting from queenlessness, had no significant effect on the density of [ 3 H ]SCH23390-binding sites in the brain of the bee. Overall, these results indicate that under normal physiological conditions, there is no direct link in honey bees between changes in endogenous brain DA levels and the density of D 1-like receptors labelled by [ 3 H ]SCH23390.