Chronic environmental or genetic elevation of galanin in noradrenergic neurons confers stress resilience in mice

Abstract

ABSTRACTThe neuropeptide galanin has been implicated in stress-related neuropsychiatric disorders in both humans and rodent models. While pharmacological treatments for these disorders are ineffective for many individuals, physical activity is beneficial for stress-related symptoms. Galanin is highly expressed in the noradrenergic system, particularly the locus coeruleus (LC), which is dysregulated in stress-related disorders and activated by exercise. Galanin expression is elevated in the LC by chronic exercise, and blockade of galanin transmission attenuates exercise-induced stress resilience. However, most research on this topic has been done in rats, so it is unclear whether the relationship between exercise and galanin is species-specific. Moreover, use of intracerebroventricular galanin receptor antagonists in prior studies precluded defining a causal role for LC-derived galanin specifically. Therefore, the goals of this study were twofold. First, we investigated whether physical activity (chronic voluntary wheel running) increases stress resilience and galanin expression in the LC of mice. Next, we used transgenic mice that overexpress galanin in noradrenergic neurons (Gal OX) to determine how chronically elevated noradrenergic-derived galanin, alone, alters anxiogenic-like responses to stress. We found that three weeks of ad libitum access to a running wheel in their home cage increased galanin mRNA in the LC of mice and conferred resilience to a stressor. The effects of exercise were phenocopied by galanin overexpression in noradrenergic neurons, and Gal OX mice were resistant to the anxiogenic effect of optogenetic LC activation. Together, these findings support a role for chronically increased noradrenergic galanin in mediating resilience to stress.Significance statementUnderstanding the neurobiological mechanisms underlying behavioral responses to stress is necessary to improve treatments for stress-related neuropsychiatric disorders. Increased physical activity is associated with stress resilience in humans, but the neurobiological mechanisms underlying this effect are not clear. Here we investigate the anxiolytic potential of the neuropeptide galanin from the main noradrenergic nucleus, the locus coeruleus (LC). We show that chronic voluntary wheel running in mice galanin expression in the LC and stress resilience. Furthermore, we show that genetic overexpression of galanin in noradrenergic neurons confers resilience to the anxiogenic effects of foot shock and optogenetic LC activation. These findings support a role for chronically increased noradrenergic galanin in mediating resilience to stress.