RETARDED ACQUISITION OF A TEMPORAL DISCRIMINATION FOLLOWING DESTRUCTION OF NORADRENERGIC NEURONS BY SYSTEMIC TREATMENT WITH DSP4

This experiment examined the effect of destroying central noradrenergi c neurones, using the selective neurotoxin DSP4 (N-(2-chloroethyl)-N-e thyl-2-bromobenzylamine) on the acquisition and performance of discrim ination between two time intervals. Rats that had received systemic tr eatment with DSP4 and vehicle-treated control rats were trained in a s eries of discrete trials to press lever A following a 2-s presentation of a light stimulus and lever B following an 8-s presentation of the same stimulus. Both groups acquired the discrimination (>90% correct c hoices) within 15 sessions; however, the DSP4-treated group showed sig nificantly slower acquisition than the control group. When stable perf ormance had been attained, 'probe' trials were introduced in which the light was presented for intermediate durations. Both groups showed si gmoid functions relating percent choice of lever B to log stimulus dur ation. Neither the bisection point (duration corresponding to 50% choi ce of lever B) nor the Weber fraction differed significantly between t he DSP4-treated and control groups. The levels of noradrenaline were m arkedly reduced in the neocortex and hippocampus of the DSP4-treated g roup, but the levels of dopamine and 5-hydroxytryptamine were not alte red. The results indicate that noradrenaline depletion induced by DSP4 retarded the acquisition of temporal discrimination, but did not impa ir steady-state discriminative precision.