MORPHOLOGY AND SPATIAL-DISTRIBUTION OF BEE ANTENNAL LOBE INTERNEURONS RESPONSIVE TO ODORS

Wholemount analysis with optic and confocal microscopy of iontophoretically stained (cobalt or Lucifer Yellow) bee antennal lobe interneurones led us to identify and classify, four main types of olfactory responsive neurones. differing in their morphology and spatial distribution within the glomerular space and amongst the glomeruli in the whole antennal lobe. Two types of local interneurones (LIN), restricted to the antennal lobe were: (i) Homo LIN presenting an apparently similar density of arbors among all the glomeruli where they branch, the fine neurites being limited to the core of the glomeruli; (ii) Hetero LIN, also pluriglomerular, differ from the Homo LIN by a high dense neurite arborization in one particular glomerulus with fine branches invading the core and reaching the outermost part of this glomerulus. Two types of output interneurones (ON) having dendrites in the antennal lobe and axons projecting in other brain parts were: (i) Uni ON with dendrites invading the core and periphery of only one glomerulus; (ii) Pluri ON, pluriglomerular, with dendrites limited to the glomerular cores. The Uni ON axons follow the median tract and project to the mushroom bodies and lateral lobe of the protocerebrum. On the contrary, axons of Pluri ON follow several subtracts of the antenno-glomerular tract and project to various protocerebal structures or to the contralateral antennal lobe. Local interneurones and output interneurones both invade many glomeruli (1/3 to 2/3 and > 50 % of the total number, respectively), most being distributed in the different glomerular populations. The high complexity demonstrated in the architecture of the bee antennal lobe neurones might support the high functional complexity described elsewhere (Fonta et al., 1991; Sun et al., submitted).