Investigation on synaptic architecture of insect deutocerebrum with intracellular staining and imunoelectron microscopical methods.

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Hygro- and thermoreception is closely related to survival of animals, and particularly so in insects. As the ratio of surface area to body size is large, much water evaporates from the body surface and body temperature is much affected by their environment. Therefore hygro- and thermoreception is as important for life as other sensory reception. The hygro- and thermoreceptors are present on antennae of insects. It is well known that most and probably all axons of antennal olfactory receptor cells in the third segment, the flagellum, have terminal arborizations in the antennal lobe. The antennal lobe comprises two types of glomeruli, ordinary glomeruli (OGs) and a macro-glomerulus complex (MGC) in male. Axons of pheromone receptor cells terminate in MGC and other axons of olfactory cells terminate in OGs. However, there were no reliable data about the terminations of axons of the hygro- and thermoreceptors and olfactory receptors other than specific receptors such as pheromone receptors … More . We stained electrophoretically the axons of these receptors and an enanthic acid receptor (olfactory receptor) from the sensilla on Periplaneta antennae. We have found that the axons of the hygro- and thermoreceptors have terminal arborizations in OG specific to each type of receptors. Furthermore, the axon of the enanthic acid receptor also teminates in other specific OG. These results suggest that each receptor axon terminates in specific glomerulus, i.e. sensory information is simultaneously processed in the glomerulus specific to each receptor. Besides primary afferents, there are three types of interneurons in the antennal lobe : local interneurons (LNs), projection neurons (PNs) and centrifugal neurons. The sensory information flows from LNs to PNs in a traditional working hypothesis. However, some LNs reacted to humidity or temperature change with a long delay after stimulations and some PNs reacted quickly in our experiment. This suggests that such PNs are directly connected to some axons of hygro- and thermal receptor cells. Less