In Vitro and In Vivo Pharmacological Characterization of Galanin and Galnon

Abstract

The neuropeptide galanin and its receptors (GAL-R1, GAL-R2, and GAL-R3) are densely localized in areas of the brain thought to regulate stress, fear and anxiety. Several studies suggest a role for galanin in mediating anxiety-like behaviors in rodent models. Here we report that both galanin (0.1 μg, icv) and galnon (0.3, 1.0 and 3.0 mg/kg, ip) show dose-dependent anxiolytic-like activity in the mouse elevated zero maze and four-plate assays. Further, M35 (10 μg, icv), a non-selective galanin receptor antagonist, was able to block galnon’s (0.3 mg/kg, ip) effects in the four-plate model. The in vitro pharmacological basis for these behavioral effects was explored using radioligand binding and a functional calcium mobilization assay. While human galanin was able to displace 125I-galanin in GAL-R1 and human Bowes melanoma cell membranes (Ki = 0.2 nM and 0.17 nM, respectively), galnon only showed affinity for galanin receptors expressed in human Bowes melanoma cells (5.5 μM). Consistent with this finding, galnon only showed functional agonism in Bowes melanoma cells (EC50 = 109 nM). This finding suggests that galnon acts as an agonist at galanin receptors in Bowes melanoma cells but not GALR1 receptors. Taken together, these studies provide further evidence for galaninergic input in anxiety-related behaviors and suggest a functional role for galnon via GAL-R2 or GAL-R3 receptors.