Dopamine released from dendrites in the substantia nigra controls the nigral and striatal release of serotonin.

Using push--pull cannulae, the release of endogenously synthesized [3H]serotonin was estimated in both substantia nigra and caudate nuclei of 'encéphale isolé' cats. The unilateral nigral application of dopamine (10(-7) M) reduced [3H]serotonin release in ipsilateral structures whereas alpha-methylparatyrosine (10(-4) M) induced opposite effects. Both treatments decreased [3H]serotonin release in the contralateral caudate nucleus but not in the contralateral substantia nigra. As a working hypothesis it is suggested that the effects observed are related to changes in the activity of nigroraphe neurons regulated by dopamine release from dendrites of the nigrostriatal dopaminergic neurons. However it cannot yet be excluded that the local changes in [3H]serotonin release induced by the nigral application of dopamine or alpha-methylparatyrosine result from presynaptic modulation.