Damage to ceruleo-cortical noradrenergic projections impairs locally cued but enhances spatially cued water maze acquisition

Abstract

A series of 4 experiments tested the effects of central catecholamine depletion on acquisition of an escape response in a spatial water maze. In Expt. 1, local infusions of 6-hydroxydopamine (6-OHDA) into the dorsal noradrenergic bundle (DNAB) enhanced efficient acquisition of the spatial water maze in a stressful condition (cold water), but had no effect in warm water. In Expt. 2, lesions of the ventral noradrenergic bundle did not affect acquisition of the maze, indicating that the changes observed in Expt. 1 were unlikely to have been the result of incidental damage to the noradrenergic innervation of the hypothalamus. Measures of core body temperature and plasma corticosterone were taken in parallel with the behavioral experiments and revealed that central noradrenaline (NA) depletion did not alter these responses to cold or warm water swims. Expt. 3 revealed a contrasting pattern of effects following dopamine (DA) depletion from the caudate-putamen: swimming speed was reduced in warm, but not cold water and maze acquisition was impaired, to an equal extent in warm and cold water. Finally, in Expt. 4, rats with 6-OHDA lesions of the DNAB were impaired in discriminating local cues in a simultaneous visual discrimination water maze. These results support the hypothesis that ceruleo-cortical NA depletion broadens the span of attention, particularly under stressful circumstances. In contrast, the results also indicate that striatal DA depletion mainly affects vigour of responding, as measured by swim speed, and that this effect can be reversed by the stressful effects of cold water.