CURRENT INJECTION INTO INTERNEURONS OF THE TERMINAL GANGLION MODIFIESTURNING BEHAVIOR OF WALKING CRICKETS

Ascending interneurones of the terminal ganglion of orthopterous insec ts are known to carry information on wind stimuli perceived by cereal receptors to thoracic and cephalic ganglia. Neurones of these anterior ganglia control evasive walking behaviour. We demonstrate that curren t injection into individual wind-sensitive local non-spiking interneur ones and ascending giant inter neurones of the terminal ganglion call influence the orientation behaviour of walking crickets. To induce a c hange of turning during ''wind puff stimulation'' by current injection into the lateral giant interneurone, its spike activity has to be mod ified by at least 100%. In 5 of 12 different types of non-spiking inte rneurones a moderate shift of the membrane potential results in a chan ge of the mean speed of rotation and/or the frequency of turns. All pr eparations tested with different amounts of current injection showed a proportional change of turning frequency. Normally, the turning behav iour is evasive with respect to the wind source. During current inject ion this dependence is preserved, but the general orientation is readj usted. Taking into account known connections between some of these int erneurones and ascending neurones the tested wind-sensitive local non- spiking interneurones of the terminal ganglion are likely to impose an offset on the mean direction of orientation controlled by cephalic an d thoracic neuronal networks.