Effect of chronic clonidine treatment and lesion of the locus coeruleus on the conditioned avoidance behavior in rats.

The effect of chronic clonidine treatment (0.2 mg/kg ip. during 10 consecutive days) on two-way avoidance acquisition was investigated in two groups of rats; sham operated and bilaterally lesioned with the locus coeruleus. Clonidine almost completely blocked the acquisition of avoidance reaction in both groups. In rats injected with saline, lesion of the locus coeruleus significantly decreased the avoidance reaction. The results indicate that destruction of presynaptic sites of clonidine action in neurons of the locus coeruleus failed to change the action of drug.