CONSISTENCY OF INTERNEURONAL GROUP FORMATION IN RESPONSE TO STIMULATION OF IDENTIFIED CELLS

In crayfish stimulation of abdominal positioning interneurons (APIs) r ecruits other interneurons producing various abdominal movements. We i nvestigated whether: (1) the same API from different preparations acti vated a similar number or group of interneurons, (2) different APIs ac tivated different groups, and (3) repeated stimulation of an API consi stently affected a similar set of interneurons. To quantify the simila rities and differences of the recruited interneuronal groups we compar ed the number of interneurons affected, their firing frequencies, and motor outputs. Three types of APIs (Curly Q, L and T) were identified and each type was stimulated in three preparations. Our results showed that for the Curly Q and L cells, each cell type activated interneuro nal groups that were statistically similar in number and firing freque ncy. The T cell activated interneuronal groups that were more variable . Some APIs generally provided a repeatable motor output; all did not. The interneuronal groups activated by the Curly Q, L and T cells were very different from each other. Repeated stimulation of one Curly Q c ell affected similar although not identical sets of interneurons. Thes e data suggest that repeated motor outputs could be produced by a simi lar but not identical group of cells.