Different plant-derived and synthetic cannabinoids have shown to be neuroprotective in experimental models of Huntington's disease (HD) through cannabinoid receptordependent and/or independent mechanisms. Herein, we studied the effects of cannabigerol (CBG), a nonpsychotropic phytocannabinoid, in 2 different in vivo models of HD. CBG was extremely active as neuroprotectant in mice intoxicated with 3-nitropropionate (3NP), improving motor deficits and preserving striatal neurons against 3NP toxicity. In addition, CBG attenuated the reactive microgliosis and the upregulation of proinflammatory markers induced by 3NP, and improved the levels of antioxidant defenses that were also significantly reduced by 3NP. We also investigated the neuroprotective properties of CBG in R6/2 mice. Treatment with this phytocannabinoid produced a much lower, but significant, recovery in the deteriorated rotarod performance typical of R6/2 mice. Using HD array analysis, we were able to identify a series of genes linked to this disease (e.g., symplekin, Sin3a, Rcor1, histone deacetylase 2, huntingtin-associated protein 1, δ subunit of the gamma-aminobutyric acid-A receptor (GABA-A), and hippocalcin), whose expression was altered in R6/2 mice but partially normalized by CBG treatment. We also observed a modest improvement in the gene expression for brain-derived neurotrophic factor (BDNF), insulinlike growth factor-1 (IGF-1), and peroxisome proliferatoractivated receptor-γ (PPARγ), which is altered in these mice, as well as a small, but significant, reduction in the aggregation of mutant huntingtin in the striatal parenchyma in CBGtreated animals. In conclusion, our results open new research avenues for the use of CBG, alone or in combination with other phytocannabinoids or therapies, for the treatment of neurodegenerative diseases such as HD.

Cannabinoids are promising medicines to slow down disease progression in neurodegenerative disorders including Parkinson's disease (PD) and Huntington's disease (HD), two of the most important disorders affecting the basal ganglia. Two pharmacological profiles have been proposed for cannabinoids being effective in these disorders. On the one hand, cannabinoids like D 9 -tetrahydrocannabinol or cannabidiol protect nigral or striatal neurons in experimental models of both disorders, in which oxidative injury is a prominent cytotoxic mechanism. This effect could be exerted, at least in part, through mechanisms independent of CB1 and CB2 receptors and involving the control of endogenous antioxidant defences. On the other hand, the activation of CB2 receptors leads to a slower progression of neurodegeneration in both disorders. This effect would be exerted by limiting the toxicity of microglial cells for neurons and, in particular, by reducing the generation of proinflammatory factors. It is important to mention that CB2 receptors have been identified in the healthy brain, mainly in glial elements and, to a lesser extent, in certain subpopulations of neurons, and that they are dramatically up-regulated in response to damaging stimuli, which supports the idea that the cannabinoid system behaves as an endogenous neuroprotective system. This CB2 receptor up-regulation has been found in many neurodegenerative disorders including HD and PD, which supports the beneficial effects found for CB2 receptor agonists in both disorders. In conclusion, the evidence reported so far supports that those cannabinoids having antioxidant properties and/or capability to activate CB2 receptors may represent promising therapeutic agents in HD and PD, thus deserving a prompt clinical evaluation. LINKED ARTICLES