A quantitative ultrastructural study of the honeybee antennal lobe.

This paper describes the ultrastructural organization of the honeybee antennal lobe, including the distribution of synapses within the antennal lobe neuropile and the distribution of the afferent fibres in the antennal nerve and its afferent tracts. We show that: 1) The antennal nerve and tracts T3-T6 are composed of a heterogeneous population of fibres, with respect to their diameters, whereas two afferent tracts (T1 and T2) are composed of fibres of almost homogeneous diameter. 2) Synapses are mainly localized in the glomeruli with a higher frequency in the cortical layer than in the core of the glomerulus. Nevertheless a few synapses are found in the coarse neuropile. 3) Reciprocal synapses have been identified in the cortical layer. At the ultrastructural level, the organization of the bee antennal lobe was largely unknown and these results bring the anatomical background needed in order to carry out a developmental study related to the bee antennal lobe structures.