WIN55,212-2, a Cannabinoid Receptor Agonist, Protects Against Nigrostriatal Cell Loss in the MPTP Mouse Model of Parkinson’s Disease

Parkinson’s disease (PD) is characterized by the progressive loss of nigrostriatal dopamine (DA) neurons leading to motor disturbances and cognitive impairment. Current pharmacotherapies relieve PD symptoms temporarily but fail to prevent or slow down the disease progression. In this study, we investigated the molecular mechanisms by which the non-selective cannabinoid receptor agonist WIN55,212-2 (WIN) protects mouse nigrostriatal neurons from 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity and neuroinflammation. Stereological analyses showed that chronic treatment with WIN (4 mg/kg, i.p.), initiated 24 hr after MPTP administration, protected against MPTP-induced loss of tyrosine hydroxylase positive (TH+) neurons in the substantia nigra pars compacta (SNc) independently of CB1 cannabinoid receptor activation. The neuroprotective effect of WIN was accompanied by increased DA and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the SNc and dorsal striatum of MPTP-treated mice. Three days post-MPTP, we found significant microglial activation and up-regulation of CB2 cannabinoid receptors in the ventral midbrain. Treatment with WIN or the CB2 receptor agonist JWH015 (4 mg/kg, i.p.) reduced MPTP-induced microglial activation, whereas genetic ablation of CB2 receptors exacerbated MPTP systemic toxicity. Furthermore, chronic WIN reversed MPTPassociated motor deficits, as revealed by the analysis of forepaw step width and percentage of faults using the inverted grid test. In conclusion, our data indicate that agonism at CB2 cannabinoid receptors protects against MPTP-induced nigrostriatal degeneration by inhibiting microglial activation/infiltration and suggest that CB2 receptors represent a new therapeutic target to slow the degenerative process occurring in PD. Corresponding Author: Andrea Giuffrida, Ph.D., University of Texas Health Science Center at San Antonio, Department of Pharmacology, 7703 Floyd Curl Drive MC 6205, San Antonio, Texas 78229-3900, Phone: (210) 567-8533, Fax: (210) 567-8024, [email protected]. *Current address: Department of Pharmacology, University of Colorado Denver, Denver, Colorado NIH Public Access