Dopamine Modulation of Honey Bee (Apis mellifera) Antennal-Lobe Neurons

Abstract

Primary olfactory centers [antennal lobes (ALs)] of the honey bee brain are invaded by dopamine (DA)-immunoreactive neurons early in development (pupal stage 3), immediately before a period of rapid growth and compartmentalization of the AL neuropil. Here we examine the modulatory actions of DA on honey bee AL neurons during this period. Voltage-clamp recordings in whole cell configuration were used to determine the effects of DA on ionic currents in AL neurons in vitro from pupal bees at stages 4-6 of the nine stages of metamorphic adult development. In approximately 45% of the neurons tested, DA (5-50 x 10(-5) M) reduced the amplitude of outward currents in the cells. In addition to a slowly activating, sustained outward current, DA reduced the amplitude of a rapidly activating, transient outward conductance in some cells. Both of the currents modulated by DA could be abolished by the removal of Ca2+ from the external medium or by treatment of cells with charybdotoxin (2 x 10(-8) M), a blocker of Ca2+-dependent K+ currents in the cells. Ca2+ currents were not affected by DA, nor were A-type K+ currents (I(A)). Results suggest that the delayed rectifier-like current (I(KV)) also remains intact in the presence of DA. Taken together, our data indicate that Ca2+-dependent K+ currents are targets of DA modulation in honey bee AL neurons. This study lends support to the hypothesis that DA plays a role in the developing brain of the bee.