Functional assignment of glomeruli and projection interneurons of antennal lobe in insect brain

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We have identified the regions where the hygro- and thermoreceptor neurons and mechanoreceptor neurons terminated. For the hygro- and thermoreceptor neurons the neurons were ionophoritically stained by cobalt from the sensilla, one of which contained two hygroreceptors, one cold receptor and the fourth cell and the other contained one cold receptor and a few olfactory receptor cells. A neuron in the hygro- and thermoreceptive sensillum and a neuron in the thermoreceptive and olfactory sensillum terminate in a cluster of glomeruli which located near a dorsal lobe. Two other neurons in the hygro- and thermoreceptive sensilla also terminated in another cluster of glomeruli in the same region. Each of these clusters appears to form a complex of glomeruli similar to the macroglomerular complex of male moths. On the other hand, the projection neurons that respond strongly to hygro- or thermal stimulations have dendritic arborizations in these glomerular clusters but the projection neurons show weak responses to these stimulations appear to terminate in other glomeruli. Therefore, humidity and temperature information appears to be primarily transmitted to the particular projection interneurons through these glomerular clusters, respectively. The mechanoreceptor neurons were also stained in the same method from mechanoreceptive sensilla. The neurons passed through the dorsal lobe and the tritocerebrum and terminated in suboesophageal ganglion. This pass way was very similar to that of the fourth neuron in the hygro- and thermoreceptive sensilla.