RESPONSES OF THORACIC INTERNEURONS TO TACTILE STIMULATION IN THE COCKROACH, PERIPLANETA-AMERICANA

Recent findings indicate that cockroaches escape in response to tactil e stimulation as well as they do in response to the classic wind puff stimulus. The thoracic interneurons that receive inputs from ventral g iant interneurons also respond to tactile stimulation and, therefore, represent a potential site of convergence between wind and tactile sti mulation, as well as other sensory modalities. In this article, we cha racterize the tactile response of these interneurons, which are referr ed to as type-A thoracic interneurons (TI(A)s). In response to tactile stimulation of the body cuticle, TI(A)s typically respond with a shor t latency biphasic depolarization which often passes threshold for act ion potentials. The biphasic response is not typical of responses to w ind stimulation nor of tactile stimulation of the antennae. It is also not seen in tactile responses of thoracic interneurons that are not p art of the TIA group. The responses of individual TI(A)s to stimulatio n of various body locations were mapped. The left-right directional pr operties of TI(A)s are consistent with their responses to wind puffs f rom various different directions. Cells that respond equally well to w ind from the left and right side also respond equally well to tactile stimuli on the left and right side of the animal's body. In contrast, cells that are biased to wind on one side are also biased to tactile s timulation on the same side. In general, tactile responses directed at body cuticle are phasic rather than tonic, occurring both when the ta ctile stimulator is depressed and released. The response reflects stim ulus strength and follows repeated stimulation quite well. However, th e first phase of the biphasic response is more robust during high-freq uency stimulation than the second phase. TI(A)s also respond to antenn al stimulation. However, here the response characteristics are complic ated by the fact that movement of either antenna evokes descending act ivity in both left and right thoracic connectives. The data suggest th at the TI(A)s make up a multimodal site of sensory convergence that is capable of generating an oriented escape turn in response to any one of several sensory cues. (C) 1994 John Wiley & Sons, Inc.