Effect of serotonergic lesion on "anxious" behaviour measured in the elevated plus-maze test in the rat.

5,7-Dihydroxytryptamine (250 micrograms) was administered intracerebroventricularly to rats to lesion central serotonergic neurones. Fourteen days later the rats were tested in the elevated plus-maze "anxiety" model in comparison to sham lesioned animals. Twenty-four hours later, the rats were killed and serotonin levels and [3H]paroxetine binding measured in cortical and hippocampal membranes. The lesion destroyed 81% of the serotonergic innervation in the cortex and 99% in the hippocampus as determined by endogenous serotonin levels. Lesioned rats had an increased ratio of open/total arm entries in the elevated plus-maze, reflecting a decreased level of "anxiety". These results are compatible with the implication of serotonin in the control of anxiety and suggest that an anxiolytic effect may be induced by lowering the level of serotonergic activation.