RECEPTIVE-FIELDS OF CRICKET GIANT INTERNEURONES ARE RELATED TO THEIR DENDRITIC STRUCTURE

The structural relationship between the afferent projection and the dendrites of the interneurons was examined in the cercal-to-giant interneuron system of the cricket using intracellular recording and dye injection techniques. The physiology of the sensory neurons beneath the cercal filiform hairs was investigated by placing a recording pipette over the end of a cut hair and using movements of the pipette to characterize the directionality of the receptor. Most of the filiform receptors could be classified as belonging to 1 of 4 major types. Each type is sensitive to a different wind direction and is confined to particular regions of the cercus. The location of the terminal arborizations of each type of sensory cell was revealed by staining with CoCl. single cells were stained reliably by placing a dye-filled pipette over a cut hair. Each physiological receptor type arborizes in a different region of the CNS. The neuropile is functionally divided according to wind direction. The dendrites of 3 identified interneurons were examined in the context of this afferent projection. Each of these neurons has dendrites in regions of neuropile corresponding to different wind directions. By searching for unitary synaptic potentials in identified interneurons, it was possible to show a strong correlation between anatomical overlap of primary afferent and interneuron and the existence of a synaptic connection. When there was no overlap, no synaptic potentials were seen. The over-all excitatory receptive field of an interneuron could be predicted by examining its dendritic structure. Each of the 3 identified interneurons examined in this study was found to have a directional response that matched the response predicted on the basis of its anatomy.