CHARACTERIZATION OF TACTILE-SENSITIVE INTERNEURONS IN THE ABDOMINAL GANGLIA OF THE COCKROACH, PERIPLANETA-AMERICANA

Tactile stimulation of an insect's abdomen evokes various behaviors in cluding grooming and vigorous escape responses, We tested a sample of 37 tactile-sensitive abdominal interneurons for various morphological and physiological characteristics, including their ability to excite t horacic interneurons that are known to integrate wind information cond ucted by giant interneurons in the classical escape response, The resu lts suggest that abdominal tactile-sensitive interneurons are heteroge neous both in anatomical and physiological properties, In general, the se cells are very small interganglionic interneurons that respond to t actile stimulation at more than one abdominal segment, However, the la rger population contained virtually all types of cells, Some projected anteriorly, others posteriorly, and still others projected in both di rections. For most cells, the soma was on the side opposite to their a xons, but in 24% of the cells it was on the same side, Patterns of den dritic arbors also varied among cells, However, tactile sensitivity wa s in general consistent with the morphological bias noted in dendritic branch patterns, We were able to document the existence of tactile ab dominal interneurons that connect directly to thoracic interneurons in volved in escape (TI(A)s). However, instances of demonstrated connecti vity were rare, One cell that did show connectivity (AI652) was charac terized in detail, and its properties were appropriate for conducting tactile signals in a directional escape system, The dendritic arbors w ere biased to the side that was ipsilateral to the cell's soma and axo n, As a result, this cell's abdominal inputs and thoracic outputs are on the same side, This pattern is appropriate for generating the senso ry fields recorded previously in TI(A)s. Its axon was located in the v entral median tract, which should bring it close to the integrating re gion of the TI(A)s. (C) 1998 John Wiley & Sons, Inc.