Autoradiographic localisation of [3H]-SCH23390 and [3H]-spiperone binding sites in honey bee brain

In the brain of the honey bee, dopamine receptors have been identified by using the vertebrate D1 dopamine antagonist [3H]-SCH23390 and the vertebrate D2 dopamine antagonist [3H]-spiperone. This study uses light microscope autoradiography to investigate the anatomical distributions of the binding sites labelled by [3H]-SCH23390 and [3H]-spiperone in tissue sections cut at three depths from the anterior surface of the brain. The binding of these radioligands differed significantly, in both density and distribution. Specific binding of [3H]-SCH23390, defined by using 5 x 10(-6) M cis-(Z)-flupentixol, was densest in regions of somata, such as the deutocerebral somatal rind, the somatal layer beneath the calyces of the mushroom bodies and the ventral protocerebral somatal group. High levels of [3H]-SCH23390 binding were also measured in the lateral protocerebrum. [3H]-Spiperone binding site density estimates were consistently lower than those of [3H]-SCH23390. Specific binding of [3H]-spiperone, determined by subtracting binding in the presence of 10(-4) M domperidone from the total binding, was highest in the alpha lobes, beta lobes, and calyces of the mushroom body neuropil. Relatively high binding was also measured in the central body and lateral protocerebral neuropil. These results suggest that the distribution of dopamine receptors in the brain of the bee is subtype specific, and they support the view that dopamine plays many roles in the insect central nervous system.