Age-related changes in dopamine receptor densities in the brain of the honey bee, Apis mellifera
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Changes in the levels of binding of 3H-SCH-23390, a vertebrate D1 dopamine receptor ligand, and 3H-spiperone, a vertebrate D2 dopamine receptor ligand were investigated in the brain of the worker honey bee during metamorphic adult development and during the lifetime of the adult bee. Age-related fluctuations in binding levels were markedly different for these two ligands. 3H-SCH-23390 and 3H-spiperone binding sites were present at low levels during metamorphic adult development. After adult emergence, however, 3H-SCH-23390 binding levels, in contrast to those of 3H-spiperone, increased significantly. Within the first 48 h of adult life 3H-SCH-23390 binding reached a level not significantly different from that detected in forager bees. No significant fluctuations in the levels of 3H-spiperone binding were observed during the adult lifetime of the bee. Measurements of dopamine levels in the brains of pupal and adult bees revealed no direct correlation between fluctuations in endogenous amine levels and the amount of binding of either 3H-SCH-23390 or 3H-spiperone. These results provide evidence for subtype-specific patterns of expression of dopamine receptors in the insect brain and show that D1- and D2-like receptors are expressed not only in the adult CNS, but also in the developing brain of the bee.
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