Serotonin neuron-dependent and -independent reduction of dyskinesia by 5-HT1A and 5-HT1B receptor agonists in the rat Parkinson model

To unveil the relative contribution of these mechanisms, we have investigated the effect of increasing doses of 5-HT1A and 5-HT1B receptor agonists on AIMs induced by either l-DOPA or apomorphine. In contrast to l-DOPA-induced AIMs, which were dampened already at low doses of 5-HT1 agonists, reduction of apomorphine-induced AIMs required higher doses. Removal of the serotonin innervation suppressed l-DOPA-induced AIMs, but neither affected apomorphine-induced AIMs nor the inhibiting effect of 5-HT1 agonists on AIMs induced by the direct dopamine agonist, suggesting that such effect is independent on activation of pre-synaptic 5-HT1 receptors.