Phenotypic assessment of galanin overexpressing and galanin receptor R1 knockout mice in the tail suspension test for depression-related behavior.

Rationale: Galanin and its receptors exert inhibitory neuromodulatory control over brain monoamines. Rat studies revealed that galanin expression is upregulated by exposure to stressors and that galanin manipulations modify neuroendocrine and behavioral responses to stress, leading to the hypothesis that galanin mediates depression-related behaviors.

Methods: In the present study, we examined the role of galanin in modulating antidepressant-related behavior in galanin overexpressing transgenic (GAL-tg) mice and galanin receptor R1 knockout (GAL-R1 KO) mice, using the tail suspension test (TST). Quantitative autoradiography for 5-HT(1A)-R and serotonin transporter binding density tested for changes in these two major regulatory components of the 5-HT system in galanin mutant mice.

Results: Baseline TST behavior was normal in GAL-tg and GAL-R1 KO mice, and intracerebroventricular administration of galanin failed to alter TST behavior in normal C57BL/6J mice. The TST anti-immobility effects of acute treatment with the serotonin reuptake inhibitor, fluoxetine (0-30 mg/kg), and the norepinephrine reuptake inhibitor, desipramine (0-30 mg/kg), were unaltered in galanin mutant mice. Hippocampal 5-HT(1A)-R density was significantly elevated in GAL-tg and GAL-R1 KO mice, while hippocampal 5-HTT density was reduced in GAL-R1 KO mice, relative to controls.

Conclusion: Neither pharmacological nor molecular genetic manipulations of galanin altered depression-related profiles in the TST. Possible functional alterations in hippocampal 5-HT neurotransmission may have contributed to these negative results. These preliminary findings provide evidence against the hypothesis that galanin plays a central role in mouse depression-related behaviors. It remains possible that galanin modulates depression-related responses in other experimental paradigms and species.