Experience- and age-related outgrowth of intrinsic neurons in the mushroombodies of the adult worker honeybee

A worker honeybee performs tasks within the hive for approximately the firs t 3 weeks of adult life. After this time, it becomes a forager, flying repe atedly to collect food outside of the hive for the remainder of its 5-6 wee k life. Previous studies have shown that foragers have an increased volume of neuropil associated with the mushroom bodies, a brain region involved in learning, memory, and sensory integration. We report here that growth of t he mushroom body neuropil in adult bees occurs throughout adult life and co ntinues after bees begin to forage. Studies using Golgi impregnation asked whether the growth of the collar region of the mushroom body neuropil was a result of growth of the dendritic processes of the mushroom body intrinsic neurons, the Kenyon cells. Branching and length of dendrites in the collar region of the calyces were strongly correlated with worker age, but when a ge-matched bees were directly compared, those with foraging experience had longer, more branched dendrites than bees that had foraged less or not at a ll. The density of Kenyon cell dendritic spines remained constant regardles s of age or behavioral state. Older and more experienced foragers therefore have a greater total number of dendritic spines in the mushroom body neuro pil. Our findings indicate that, under natural conditions, the cytoarchitec tural complexity of neurons in the mushroom bodies of adult honeybees incre ases as a function of increasing age, but that foraging experience promotes additional dendritic branching and growth.