Scopolamine in rats impairs acquisition but not retention in a 14-unit T-maze

To follow up a previous report noting that scopolamine impaired acquisition performance of young rats in a shock-motivated 14-unit T-maze, the present study assessed the effects of muscarinic antagonism on retention aspects of the same task. The broader objective was to further the investigation of possible defects in cholinergic neurotransmission that might underlie the age-related impairements previously observed in this task. Young (3-month) male F-344 rats were given preliminary training to criterion in one-way active avoidance in a straight runaway. Then on the first day of complex maze training, each rat received 5 acquisition (AQ) trials followed by a second 10-trial retention (RET) session conducted the following day. Subjects were assigned to one of eight groups receiving an intraperitoneal injection of either scopolamine hydrochloride (1.0 mg/kg) or saline as follows: (a) 30 min prior to training on the first day (PRE-AQ); (b) 30 min prior to training on both the first and second day (PRE-AQ-RET); (c) immediately after completing the trial on the first day (POST-AQ); (d) 30 min prior to testing on the second day (PRE-RET). Dependent measures included errors, alternation errors, run time, number of shocks, and total shock received. On the first day of maze training, all performance measures except for alternation errors were significantly higher for the two acquisition groups (PRE-AQ and PRE-AQ-RET) compared to all other groups which did not differ significantly. While on the second day the PRE-AQ group recovered on all measures to levels comparable to other groups, the PRE-AQ-RET group remained impaired throughout training on all performance measures and appeared to maintain an alternation strategy for maze acquisition. Retention aspects of this task appeared unaffected as none of the other groups differed significantly in performance. Thus, further evidence of a scopolamine-induced cognitive impairment in acquisition of this task was noted but was manifested only when given throughout training. These results suggest that the dose of scopolamine used impaired encoding processes while leaving storage and retrieval mechanisms intact.