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Keywords:

  • acetylcholine;
  • basal forebrain;
  • hippocampus;
  • immunotoxin;
  • medial septum

Abstract

Rats solving a simple spatial discrimination task in a plus maze initially employ a place-learning strategy, then switch to a motor response strategy. The hippocampus is required for the use of a place-learning strategy in this task. Rats with 192 IgG-saporin lesions of the medial septum/vertical limb of the diagonal band (MS/VDB), that selectively removed cholinergic neurons projecting to the hippocampus, were significantly facilitated in acquisition of the spatial discrimination, and switched from place to response strategies just as control rats did. Rats with ibotenic acid lesions of the MS/VDB, that produced cell loss in the MS/VDB but little damage to cholinergic neurons, were significantly impaired in acquiring the spatial discrimination and did not reliably employ either a place or response strategy at any point in training. This suggests that the MS/VDB modulates hippocampal involvement in place learning, but that cholinergic MS/VDB neurons are neither necessary nor sufficient for using a place strategy to solve a spatial discrimination.