Evaluation of an anxiety-related phenotype in galanin overexpressing transgenic mice

Understanding the role of neuropeptides in mediating emotional behaviors is an important avenue for discovering novel drug targets for anxiety disorders. A role for galanin in mediating anxiety-related behavior is suggested by the pattern of distribution in the CNS and the coexistence of galanin with norepinephrine in the locus coeruleus. Studies in rats have shown that central administration of galanin modulates anxiety-related behaviors, and galanin release blocks the proanxiety effects of noradrenergic activation in prestressed rats. To further investigate the role of galanin in anxiety behaviors, we conducted a comprehensive behavioral phenotyping of galanin overexpressing transgenic mice (GAL-tg). GAL-tg mice were normal on measures of general health, neurological reflexes, home cage social behaviors, sensory functions, motor coordination, and exploratory locomotor activity. In three separate tests for anxiety-related behaviors, the elevated plus-maze, light <--> dark exploration, and open field center time, GAL-tg mice showed no anxiety-like phenotype. GAL-tg mice and wild-type littermate controls were equally responsive to the anxiolytic effects of chlordiazepoxide (10 mg/kg) in the light <--> dark exploration test, indicating normal benzodiazepine receptor function in GAL-tg mice. Stimulation of noradrenergic cells via administration with an alpha2 adrenoreceptor antagonist, yohimbine (2.5 mg/kg), produced proanxiety effects in wild type mice in the light <--> dark exploration test, but not in the GAL-tg mice. These data suggest that galanin contributes to the modulation of anxiety states induced by high levels of noradrenergic activation, but is silent under less challenging situations. A specific role for galanin in extreme anxiety states represents an attractive target for the development of novel anxiolytic treatments.