Impaired acquisition in a 14-unit T-maze following medial septal lesions in rats is correlated with lesion size and hippocampal acetylcholinesterase staining.

Septohippocampal cholinergic system involvement in acquisition of an aversively motivated 14-unit T-maze was evaluated in 4-month-old male Fischer-344 rats. Each rat was assigned to one of two groups that received either a bilateral electrolytic lesion to the medial septal area (MSA) or a sham operation. One week after surgery, each rat began pretraining in one-way active avoidance (footshock = 0.8 mA) consisting of 10 trials per day on each of 3 consecutive days. Criterion for successful completion of pretraining was 8/10 avoidances on the third day. On the day following completion of pretraining, each rat received 10 trials in a shock-motivated 14-unit T-maze. The performance requirement was to move through each of five maze segments within 10 s to avoid footshock (0.8 mA). A second 10-trial session was provided 24 h later. Performance measures included errors, alternation errors, runtime, shock frequency, and duration. Following maze training, each rat was sacrificed, and formalin-fixed brains were frozen for histology, which included procedures for thionin Nissl and acetylcholinesterase (AChE) staining. MSA-lesioned rats were observed to be significantly impaired on all measures of maze performance compared to sham-operated controls. Densitometric analysis of hippocampal AChE staining revealed a 30% reduction in relative AChE staining of MSA-lesioned rats compared to sham-operated controls. Lesion size was observed to be highly positively correlated with maze errors. A negative correlation of mean error score with density of AChE staining was observed for MSA-lesioned rats, but not for sham-operated rats.(ABSTRACT TRUNCATED AT 250 WORDS)