Pharmacological modulation of amphetamine-induced dyskinesia in transplanted hemi-parkinsonian rats.

Foetal cell transplantation in patients with Parkinson's disease can induce motor complications independent of L-DOPA administration, known as graft-induced dyskinesia. In the 6-OHDA lesioned rat model of Parkinson's disease, post-transplantation abnormal movements can develop in response to an amphetamine challenge, a behaviour which is used to model graft-induced dyskinesia. Although L-DOPA-induced dyskinesia has been well characterised pharmacologically, we lack knowledge on the modulation of post-transplantation amphetamine-induced dyskinesia which may shed light on the mechanisms underlying graft-induced dyskinesia. We assessed a series of drugs effective at reducing L-DOPA-induced dyskinesia against post-transplantation amphetamine-induced dyskinesia. Agents include: dopaminergic antagonists (D₁: CP94253; D₂: SCH-22390; D₃: nafadotride), serotonergic agonists (5-HT(1A): 8-OH-DPAT; 5-HT(1B): CP94253), opioid antagonist (μ: naloxone), cannabinoid agonist (CB₁: WIN55, 212-2), adrenergic antagonist (α₁ and α₂: yohimbine) and glutamatergic antagonists (NMDA: amantadine and MK-801; mGluR5: MTEP; AMPA: IEM1460). Abnormal involuntary movements in response to amphetamine were decreased by SCH-22390, raclopride, CP94253 and 8-OH-DPAT, yet were unaltered by naloxone, WIN55, 212-2, yohimbine, amantadine, MTEP and IEM1460. Unusually, MK-801 increased the appearance of amphetamine-induced dyskinesia. The results suggest that dopaminergic, serotoninergic and glutamatergic systems are likely to have a fundamental role in the development of graft-induced dyskinesias, which are mechanistically distinct from L-DOPA-induced behvaviours. Importantly, the expression of D₁ and D₂ receptors was unrelated to the severity of AIMs.