Selective lesion of septal cholinergic neurons in rats impairs acquisition of a delayed matching to position T-maze task by delaying the shift from a response to a place strategy

Abstract

This study tested the hypothesis that septal cholinergic lesions impair acquisition of a delayed matching to position (DMP) T-maze task in male rats by affecting learning strategy. Rats received either the selective cholinergic immunotoxin, 192 IgG-saporin (SAP) or artificial cerebrospinal fluid directly into the medial septum. Two weeks later, animals were trained to acquire the DMP task. SAP-treated rats took significantly longer to acquire the task than corresponding controls. Both SAP-treated and control rats adopted a persistent turn and utilized a response strategy during early periods of training. By the time rats reached criterion the persistent turn was no longer evident, and all rats had shifted to an allocentric strategy, i.e., were relying on extramaze cues to a significant degree. During the acquisition period, SAP-treated rats spent significantly more days showing a persistent turn and using a response strategy than corresponding controls. The added time spent using a response strategy accounted entirely for the added days required to reach criterion among the SAP-treated rats. This suggests that the principal mechanism by which septal cholinergic lesions impair DMP acquisition in male rats is by increasing the predisposition to use a response vs. a place strategy, thereby affecting the ability to switch from one strategy to another.