A metallic impregnation technique adapted to study the honeybee Apis mellifera L. brain

In order to visualize the distribution pattern of the neuronal bodies and neurofibrils in the honeybee brain, we adapted a metallic impregnation technique first described for vertebrate nervous system by Ramón y Cajal. The honeybee brain constitution plays a key role in the development of learning and memory capacities. The general characteristics observed in the honeybee brain, stained by metallic impregnation, revealed its anatomical and morphological constitution in agreement with studies of other insect brains using different techniques. Metallic impregnation evidenced the optic lobe neuropils, the ocelli fiber cells, the neuron extensions of the calyces, and the axon bundles that involve the antennal glomeruli, as well as the neuron extensions in the alpha lobe. We also observed that the antennal glomeruli were mainly formed by fibers. The optical lobes were impregnated distinctly in the monopolar neuron bodies and in the fibers. In the mushroom bodies, we observed the lip, collar and calyx basal areas. Based on our results, the metallic impregnation technique is effective to visualize neuronal bodies and neurofibrils; moreover, is simpler and faster than other techniques, offering new insights for the investigation of the invertebrate nervous system.