Serotonin 5-HT1A agonist improves motor complications in rodent and primate parkinsonian models

Serotoninergic transmission in the basal ganglia is known to influence dopaminergic mechanisms and motor function.

To evaluate the possibility that serotoninergic 5-HT1A autoreceptors (by regulating the release of serotonin as well as dopamine formed from exogenous levodopa) affect the response alterations complicating levodopa treatment of PD.

The 5-HT1A receptor agonist sarizotan (EMD128130) was systemically administered alone and together with levodopa to parkinsonian rats and nonhuman primates.

In 6-hydroxydopamine-lesioned rats, sarizotan (2.5 mg/kg PO) had no effect on the acute rotational response to levodopa but did attenuate the shortening in motor response duration induced by chronic levodopa treatment. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned monkeys, sarizotan (2 mg/kg PO) alone had no effect on parkinsonian severity or on the antiparkinsonian response to levodopa. In contrast, the same dose of sarizotan reduced levodopa-induced choreiform dyskinesias by 91 +/- 5.9%. In both species, the motoric effects of sarizotan were blocked by the selective 5-HT1A antagonist WAY100635 (0.1 mg/kg SC), indicating that the observed sarizotan responses were probably mediated at the 5-HT1A autoreceptor.

Pharmaceuticals acting to stimulate 5-HT1A receptors could prove useful in the treatment of the motor response complications in parkinsonian patients.