THE EFFECTS OF AMPA-INDUCED LESIONS OF THE SEPTOHIPPOCAMPAL CHOLINERGIC PROJECTION ON AVERSIVE-CONDITIONING TO EXPLICIT AND CONTEXTUAL CUESAND SPATIAL-LEARNING IN THE WATER MAZE

The environmental context of an animal both subsumes and is associated with the explicit cues that guide its behavioural responses, Recent w ork in this laboratory suggests that learning about the relationship b etween the cues which comprise a context depends on the hippocampus. I n the present study the role of the cholinergic input to the hippocamp us in contextual learning was assessed in rats using a conditioned sti mulus/context conditioning paradigm and spatial learning in the Morris water maze, In the former, a place preference apparatus provided the context. The subject was confined in the black chamber and a 'clicker' conditioned stimulus was presented five times in a 20 min period. A t race interval of 5 or 30 s, depending on the group, was interposed bet ween the end of the clicker and a footshock. Theory predicts that anim als in the 5 s condition will learn more about the clicker as a predic tor of shock and become strongly conditioned, while those in the 30 s condition learn relatively more about the context. Conditioning to the clicker (conditioned stimulus) was measured in a separate lick suppre ssion chamber-presentation of the clicker suppresses drinking, and con textual learning was determined by recording the time spent on the bla ck side of the place preference apparatus when both the black and a fa miliar white chamber were accessible, Lesions of the medial septum/dia gonal band induced by RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazol pro pionic acid (AMPA) enhanced contextual learning in this paradigm but d isrupted conditioned stimulus conditioning in the 30 s condition, Acqu isition of the Morris water maze was largely unimpaired. The results a re suggested to reflect a shift towards the use of hippocampal-depende nt contextual learning strategies in lesioned animals.