DIFFERENTIAL-EFFECTS OF SELECTIVE IMMUNOTOXIC LESIONS OF MEDIAL SEPTAL CHOLINERGIC CELLS ON SPATIAL WORKING AND REFERENCE

The effect of injection into the medial septum of a toxin selective fo r cholinergic neurons, 192 IgG-saporin, was examined in rats trained t o perform 2 versions of the radial 8-arm maze task. Rats were first tr ained to perform a task with varying delays (0, 1, 2 min) imposed betw een the 4th correct arm choice and access to all 8 arms. Lesioned rats made significantly more errors in the first 4 choices compared with c ontrols and significantly more errors after delays; however, this effe ct was not delay dependent. Rats were then trained on a different vers ion of this B-arm maze task in which they learned to avoid 2 arms that were never baited. There was no treatment effect on acquisition of th is task. These data are consistent with the hypothesis that the cholin ergic projection to the hippocampus facilitates the acquisition of inf ormation into the system responsible for short-term memory for locatio ns visited (spatial working memory) but is not involved in retention o f this information. It also appears to play no role in either the acqu isition or retention of place-nonreward associations (spatial referenc e memory).