Asymmetric dopamine and serotonin metabolism in nigrostriatal and limbic structures of the trained circling rat.

The trained circling rat model was used to investigate dopamine and serotonin metabolism in extrapyramidal and limbic structures during turning behavior. We have previously reported that dopamine turnover is increased during circling in the caudate contralateral to the circling direction in this behavioral model. We have now studied changes in dopamine and serotonin turnover in nucleus accumbens, substantia nigra and amygdala. As in the caudate, dopamine production in nucleus accumbens was selectively increased on the contralateral side after 20 min of circling. By contrast, dopamine turnover in substantia nigra exhibited a relative decline on the contralateral side. Dopamine synthesis in the amygdala was not affected by circling. Selective changes in serotonin metabolism were also seen in these brain regions. In caudate and accumbens, serotonin turnover was unaffected by circling. However, both substantia nigra and amygdala showed significant, progressive increases in serotonin metabolism in the contralateral side after 20 and 70 min of circling. These results show that extrapyramidal and limbic dopamine and serotonin metabolism are involved in turning behavior of normal animals. Multiple transmitters of the nigrostriatal pathway and the limbic system appear to interact to modulate voluntary circling behavior.