Functional assignment of projection interneurons of antennal lobe involved in neural processing of humidity and temperature information in insect brain.

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We have already investigated the hygro-and thermal information processing in the antennal lobe within the deutocerebrum of cockroach Periplaneta and honeybee Apis, showing that the functional and morphological characteristics of some interneurons in the antennal lobe which are involved in neural processing of hygro-and thermal information. In this study we have identified the glomeruli where the axons of the hygro-or thermo-receptors terminated. The receptor axons were ionophoritically stained by cobalt from the sensilla, one of which contained two hygroreceptors, one cold receptor and the other cell and the other contained one cold receptor and a few olfactory receptor cells. An axon of the receptor cell in the hygro-and thermoreceptive sensillum and an axon of the receptor cell in the thermoreceptive and olfactory sensillum terminate in a cluster of glomeruli which located near a dorsal lobe. Two axons of the receptors in the hygro-and thermoreceptive sensilla also terminated in another cluster of glomeruli in the same region. Each of these clusters appear to from 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.