The selective α1 adrenoceptor antagonist HEAT reduces L‐DOPA‐induced dyskinesia in a rat model of Parkinson's disease

In Parkinson's disease (PD), the long term use of L‐DOPA results in major adverse effects including dyskinesia or abnormal involuntary movements. The present study focuses on the effect of the selective α₁ adrenoceptor antagonist HEAT (2‐[[β‐(‐4‐hydroxyphenyl)ethyl]aminomethyl]‐1‐tetralone) in the 6‐hydroxydopamine rat model of L‐DOPA‐induced dyskinesia. We demonstrate that the selective α₁ adrenoceptor antagonist HEAT (1 and 2 mg kg^?1), the α₂ adrenoceptor antagonist idazoxan (9 mg kg^?1), and the nonselective β₁/β₂ adrenoceptor antagonist propranolol (20 mg kg^?1) alleviate dyskinetic movements induced by L‐DOPA. Furthermore, the adrenoceptor antagonists at the doses used did not influence exploratory behavior in the open field system indicating that the antidyskinetic effect is not due to a reduction in general motor activity. Intrastriatal administration of the selective α₁ adrenoceptor agonist cirazoline via reverse in vivo microdialysis did not induce dyskinesia. Additionally, we measured plasma, brain, and CSF levels of HEAT. HEAT is a CNS active compound with a brain/plasma and CSF/plasma ratio of 4.29 and 0.15, respectively, which is appropriate for the investigation of α₁‐mediated mechanisms in CNS disorders. In conclusion, these results demonstrated for the first time that a α₁ adrenoceptor antagonist reduced L‐DOPA‐induced dyskinesia in a rat model. Further studies assessing the risk benefit in comparison to existing therapies are needed before considering α₁ adrenoceptor antagonists as a target for the development of new antidyskinetic compounds. Synapse 64:117–126, 2010. © 2009 Wiley‐Liss, Inc.