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The dorsal tegmental noradrenergic projection : an analysis of its role in learning Roberts, David Charles Stephen

Abstract

The hypothesis that the noradrenergic projection from the locus coeruleus (LC) to the cerebral cortex and hippocampus is an important neural substrate for learning was evaluated. Maze performance was studied in rats receiving either electrolytic lesions of the LC, or 6-hydroxydopamine (6-0HDA) injections into the region of the dorsal tegmental noradrenergic projection. In contrast to the results of an earlier report (Anlezark, Crow, and Greenway, 1973), LC lesions did not disrupt the acquisition of a running response for food reinforcement in an L-shaped runway, even though hippocampal-cortical noradrenaline (NA) was reduced to 29%. Greater telencephalic NA depletions (to 6 percent of control levels) produced by 6-0HDA also failed to disrupt the acquisition of this behaviour or impair the acquisition of a food reinforced position habit in a T-maze. Neither locomotor activity nor habituation to a novel environment was affected by the 6-0HDA lesions. Rats with such lesions were, however, „ found to be significantly more distractible than controls during the performance of a previously trained response. In another group of rats with identical 6-OHDA injections, the establishment of a lithium chloride-induced conditioned taste aversion was not affected by the lesions. The hypothesis that telencephalic NA is of fundamental importance in learning was not supported.

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