Structural plasticity of identified glomeruli in the antennal lobes of the adult worker honey bee.

Adult worker honey bees alter their behaviour with age but retain a strong reliance on sensory information from the antennae. The antennae house a diverse array of receptors, including mechanoreceptors, hygroreceptors, olfactory receptors, and contact chemoreceptors, which relay information to the brain. Antennal sensory neurons that project to the antennal lobes of the brain converge onto second-order interneurones to form discrete spheres of neuropil, called glomeruli. The spatial organisation of glomeruli in the antennal lobes of the honey bee is constant, but the central distribution of information from receptors tuned to different sensory modalities is unknown. Here we show that the glomerular neuropil of the antennal lobes undergoes constant modification during the lifetime of the adult worker bee. Changes in morphology are site specific and highly predictable. The total volume of the glomerular neuropil of the antennal lobe increased significantly during the first 4 days of adult life. Each of the five readily identifiable glomeruli examined in this study exhibited a unique pattern of growth. The growth of two of the five glomeruli changed dramatically with the shift to foraging duties. Furthermore, significant differences were identified between the antennal lobes of bees performing nectar- and pollen-foraging tasks. The highly compartmentalized nature of the antennal lobes, the ease with which specific glomeruli can be identified, and the predictability of changes to the antennal lobe neuropil make this an ideal system for examining the mechanisms and behavioural consequences of structural plasticity in primary sensory centres of the brain.