INTRASEPTAL INJECTIONS OF 192 IGG SAPORIN PRODUCE DEFICITS FOR STRATEGY SELECTION IN SPATIAL-MEMORY TASKS

The involvement of the cholinergic septohippocampal system in strategi es used to reach a spatial goal was examined by functionally inactivat ing this system with infusions of 192 IgG saporin: a potent cholinergi c immunotoxin. Rats were initially trained on a win-shift radial arm m aze (RAM) task and then given injections of either 192 IgG saporin (LE S) or saline vehicle (CON) into the medial septum and vertical limb of the diagonal band. Rats were then retested postoperatively on the RAM to assess whether allocentric spatial strategies used to solve the ta sk were impaired. The results indicated that injections of 192 IgG sap orin into the septum of rats produced deficits in allocentric strategi es used to locate the spatial goal when retested. In addition, place a nd response learning was also examined in a modified version of the Mo rris mater maze task. In this task, rats with cholinergic lesions were mildly impaired in their ability to learn a place response. In order to clarify further whether rats may have been relying on allocentric o r egocentric learning strategies to locate the platform, a probe trial was given on the final test day in which the visible platform was mov ed to a new location. Control rats swam either to the new platform loc ation or the old platform location indicating the use of both an alloc entric and egocentric response. However, rats with the cholinergic sep tal lesions swam to the new platform location indicating an egocentric response. Taken together, these results suggest that selective cholin ergic lesions of the septum produce deficits in spatial strategies use d to locate a spatial goal. (C) 1998 Elsevier Science B.V.