Delayed Varenicline Administration Reduces Inflammation and Improves Forelimb Use Following Experimental Stroke

Background: Pharmacological activation of the cholinergic anti-inflammatory pathway (CAP), specifically by activating alpha 7 nicotinic acetylcholine receptors, has been shown to confer short-term improvements in outcome. Most studies have investigated administration within 24 hours of stroke, and few have investigated drugs approved for use in human patients. We investigated whether delayed administration of varenicline, a high-affinity agonist at alpha 7 nicotinic receptors and an established therapy for nicotine addiction, decreased brain inflammation and improved functional performance in a mouse model of experimental stroke. Methods: CSF-1R-EGFP (MacGreen) mice were subjected to transient middle cerebral artery occlusion and administered varenicline (2.5 mg/kg/d for 7 days) or saline (n = 10 per group) 3 days after stroke. Forelimb asymmetry was assessed in the Cylinder test every 2 days after surgery, and structural lesions were quantified at day 10. Enhanced green fluorescent protein (EGFP) and growth associated protein 43 (GAP43) immunohistochemistry were used to evaluate the effect of varenicline on inflammation and axonal regeneration, respectively. Results: Varenicline-treated animals showed a significant increase in impaired forelimb use compared with saline-treated animals 10 days after stroke. Varenicline treatment was associated with reduced EGFP expression and increased GAP43 expression in the striatum of MacGreen mice. Conclusion: Our results show that delayed administration of varenicline promotes recovery of function following experimental stroke. Motor function improvements were accompanied by decreased brain inflammation and increased axonal regeneration in nonpenumbral areas. These results suggest that the administration of an exogenous nicotinic agonist in the subacute phase following stroke may be a viable therapeutic strategy for stroke patients.