Development of dopamine-immunoreactive neurons associated with the antennal lobes of the honey bee,Apis mellifera

Abstract

This report examines the development of the dopaminergic system in the primary antennosensory centres (antennal lobes) of the brain of the honey bee, Apis mellifera, and the effects of dopamine on neurite outgrowth of antennal-lobe neurons in vitro. Antibodies raised against dopamine were used to follow the development of a small population of dopamine-immunoreactive neurons that invade the antennal lobes during metamorphic adult development. Immunopositive somata associated with the antennal lobes were first detected at stage 2 of the nine stages of metamorphic adult development, but processes of these neurons within the antennal-lobe neuropil did not exhibit immunostaining until pupal stage 3. Severe depletion of primary sensory input to the right antennal lobe early in metamorphic adult development or removal of the right antenna from newly emerged bees did not alter the expression of dopamine immunoreactivity in the antennal-lobe neuropil. The presence of dopamine in developing antennal lobes was confirmed by using high performance liquid chromatography with electrochemical detection. Levels of dopamine were significantly higher at pupal stage 4 than at all other stages examined. This surge in dopamine levels coincided with rapid growth and compartmentalisation of the antennal-lobe neuropil. Exogenously applied dopamine (50 microM) enhanced the growth of antennal-lobe neurons in vitro, but only in cells derived from pupae at stage 5 of metamorphic adult development. The early appearance of dopamine-immunoreactive neurons and the effects of dopamine on stage 5 antennal-lobe neurons in vitro support the view that dopamine plays a role in the developing brain of the honey bee.