GAL3 receptor knockout mice exhibit an alcohol-preferring phenotype.

Galanin is a neuropeptide which mediates its effects via three G-protein coupled receptors (GAL1-3 ). Administration of a GAL3 antagonist reduces alcohol self-administration in animal models while allelic variation in the GAL3 gene has been associated with an increased risk of alcohol use disorders in diverse human populations. Based on the association of GAL3 with alcoholism, we sought to characterize drug-seeking behavior in GAL3 -deficient mice for the first time. In the two-bottle free choice paradigm, GAL3 -KO mice consistently showed a significantly increased preference for ethanol over water when compared to wildtype littermates. Furthermore, male GAL3 -KO mice displayed significantly increased responding for ethanol under operant conditions. These differences in alcohol seeking behavior in GAL3 -KO mice did not result from altered ethanol metabolism. In contrast to ethanol, GAL3 -KO mice exhibited similar preference for saccharin and sucrose over water, and a similar preference for a high fat diet over a low fat diet as wildtype littermates. No differences in cognitive and locomotor behaviors were observed in GAL3 -KO mice to account for increased alcohol seeking behavior. Overall, these findings suggest genetic ablation of GAL3 in mice increases alcohol consumption.

Effects of galanin receptor 2 and receptor 3 knockout in mouse models of acute seizures.

There exists solid evidence that endogenous galanin and galanin agonists exert anticonvulsive actions mediated both by galanin 1 receptor (GAL1-R) and galanin 2 receptor (GAL2-R). We have now investigated whether depletion of the recently identified third galanin receptor, GAL3-R, and that of GAL2-R, alters the threshold to the systemically applied γ-aminobutyric acid (GABA) antagonist pentylenetetrazole (PTZ) or to intrahippocampally administered kainic acid (KA). In neither model, GAL3-KO mice differed in their latency to the first seizure, mean seizure duration, total number of seizures, or time spent in seizures compared to wild-type controls. In addition, consistent with previous data, the response to PTZ was not altered in GAL2-KO mice. In contrast, intrahippocampal KA resulted in a significantly increased number of seizures and time spent in seizures in GAL2-KO mice, although the latency to the first seizure and the duration of individual seizures was not altered. These results are consistent with the previous data showing that GAL2-R knockdown does not affect the number of perforant path stimulations required for initiating status epilepticus but significantly increases the seizure severity during the ongoing status. In conclusion, our data support a specific role of GAL2-R but not of GAL3-R in mediating the anticonvulsive actions of endogenous galanin.

Lack of Galanin 3 Receptor Aggravates Murine Autoimmune Arthritis.

Neurogenic inflammation mediated by peptidergic sensory nerves has a crucial impact on the pathogenesis of various joint diseases. Galanin is a regulatory sensory neuropeptide, which has been shown to attenuate neurogenic inflammation, modulate neutrophil activation, and be involved in the development of adjuvant arthritis, but our current understanding about its targets and physiological importance is incomplete. Among the receptors of galanin (GAL1-3), GAL3 has been found to be the most abundantly expressed in the vasculature and on the surface of some immune cells. However, since there are minimal in vivo data on the role of GAL3 in joint diseases, we analyzed its involvement in different inflammatory mechanisms of the K/BxN serum transfer-model of autoimmune arthritis employing GAL 3 gene-deficient mice. After arthritis induction, GAL3 knockouts demonstrated increased clinical disease severity and earlier hindlimb edema than wild types. Vascular hyperpermeability determined by in vivo fluorescence imaging was also elevated compared to the wild-type controls. However, neutrophil accumulation detected by in vivo luminescence imaging or arthritic mechanical hyperalgesia was not altered by the lack of the GAL3 receptor. Our findings suggest that GAL3 has anti-inflammatory properties in joints by inhibiting vascular hyperpermeability and consequent edema formation.