Differentiating ganglionic function in the earthworm.

Abstract

Traditional formulations of the roles of supra- and subpharyngeal ganglia in the earthworm's behavior were reinvestigated with the use of saline rather than light as the aversive stimulus. Eight different operated groups were tested in a modified T-maze eliciting four classes of unconditioned responses. The factorial design used specifically contrasted a "mass condition" (degree of neural damage) with a "locus condition" (proximity of the ablation to either the supra- or subpharyngeal ganglion); changes over postoperative days were also investigated. The number of changes in head orientations during arm choice were found to be greatest after dorsal anterior ablation and fewest after ventral posterior ablation (both a mass and a locus effect). Contrary to the traditional view, interference with subpharyngeal processing did not reduce backing capacity; rather, backing propensity after aversive stimulation was increased relative to other ablations (a locus effect). In addition, a large, time-dependent increase in nonstarts was found primarily associated with ventral transection of the circumpharyngeal connectives; a 2-day delay in the appearance of this effect suggests that it is of neurohumoral origin.