Behavioral effects of neurotoxic lesions of the ascending monoamine pathways in the rat brain.

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Abstract
Intracranial microinjections of 6-hydroxydopamine or 5,6-dihydroxytryptamine into 6 ascending monoamine pathways produced the expected patterns of depletion of telencephalic serotonin, and norepinephrine. Serotonin level was specifically lowered after dorsal or median raphe lesions but, not after mesolimbic or nigrostriatal system lesions which lowered both norepinephrine and dopamine. Lesions in the locus coeruleus or ventral noradrenergic bundle lowered only norepinephrine, and locus coeruleus lesions elevated serotonin level. Behavior was examined in an open field, 1 way active avoidance, and 2 passive avoidance tasks, and measures were taken of water consumption and body weight. Dorsal raphe lesions had no effect on any of the measures; the other 5 lesion groups exhibited deficient acquisition of the 1 way active avoidance task. In the appetitive passive avoidance task, only the substantia nigra lesion group exhibited a deficiency. In the step-through passive avoidance task, both the substantia nigra and the median raphe groups exhibited a deficit, with the median raphe group exhibiting hyperactivity in the start box during testing. Water consumption was decreased by lesions in the ventral noradrenergic bundle during the 1st postoperative week and was increased in the median raphe group by the 4th postoperative week. Lesions in the locus coeruleus dramatically decreased activity in the open field. The results are discussed in regard to the search for specificity of behavioral functions of the distinct ascending monoamine pathways.

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