Dorsal hippocampal galanin modulates anxiety-like behaviours in rats

Galanin, a peptide expressed in mammalian brain regions, has been implicated in anxiety and depression. Galanin signalling occurs through three G protein-linked receptors (GAL1, GAL2 and GAL3). Galanin regulates the release of neurotransmitters in some brain regions related to anxiety, including the hippocampus. GAL2 is the most abundant galanin receptor in the dorsal hippocampus. In this study, we evaluated whether galanin administered in the dorsal hippocampus affected anxiety-like behaviours of rats. We also investigated if GAL2 receptors are involved in the anxiogenic-like effect of galanin using a GAL2 antagonist, M871. To achieve these objectives, male adult Wistar rats received intra-dorsal hippocampal delivery of galanin (0.3 and 1.0 nmol/0.5 µl) or vehicle in experiment 1 and GAL2 antagonist M871 (1.0 and 3.0 nmol/0.5 µl) or vehicle in experiment 2. Twenty min after administration of drugs, the animals were tested in the elevated plus-maze (EPM). Galanin (1.0 nmol) induced anxiogenic-like behaviours, while the GAL2 receptor antagonist M871 (3.0 nmol) induced anxiolytic-like behaviours in rats exposed to the EPM, indicating a tonic effect of galanin. In experiment 3, we evaluated whether previous infusion of the GAL2 antagonist M871 (1 or 2 nmol) in the dorsal hippocampus would block the anxiogenic-like effect of galanin in rats tested in the EPM. We showed that M871 (2.0 nmol) counteracted the anxiogenic-like effect of galanin infused in the dorsal hippocampus of rats. Altogether, our results provide evidence that galanin promotes pharmacological and tonic anxiogenic-like effects in the dorsal hippocampus, possibly mediated by GAL2 receptors.