ACTIVITY OF GIANT INTERNEURONS AND OTHER WIND-SENSITIVE ELEMENTS OF THE TERMINAL GANGLION IN THE WALKING CRICKET

Using intracellular recording techniques in stationary walking cricket s (Gryllus bimaculatus), we have investigated the relationship between locomotion and the activity of interneurones ascending from the termi nal ganglion. Nine different types of giant interneurones (GI) were ch aracterized during walking and standing. One third of them reduced the ir activity, while the others enhanced their spike rate, during walkin g. These physiological properties were strictly correlated with morpho logical characteristics such as axon position in the longitudinal trac ts of the terminal ganglion. In general, ventral GIs reduced and dorsa l GIs increased their spike frequency during walking. In some of them, there was a weak but significant correlation between the spike rate a nd translational speed, but no correlation with rotational speed. In a ll GIs except 10-3a, the changes in activity occurred at the start of walking. In GI 10-3a, an increase in membrane potential and spike rate was observed before the start of locomotion. Therefore, an intrinsic mechanism within the central nervous system operating on GI 10-3a is s uggested. Additionally, the activities of filiform hair receptors and of previously undescribed small ascending interneurones (SAI) have bee n studied during walking. About 80 % of the receptors slightly increas ed their spike rate during walking, while one SAI became more active d uring walking and another one was hardly affected. The physiological p roperties of ascending interneurones are discussed with respect to the ir modulation and particular function during walking.