Galanin subtype 1 and subtype 2 receptors mediate opposite anxiety-like effects in the rat dorsal raphe nucleus

•We tested galanin (GAL) agonists infused in the dorsal raphe nucleus (DRN) on anxiety.•Activation of GAL1 receptors enhances anxiety in rats tested in the elevated T-maze.•Activation of DRN GAL2 receptors by AR-M1896 decreases rat’s anxiety.•A 5-HT1A antagonist attenuates the anxiolytic effect of a...

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Published in:	Behavioural brain research Vol. 314; pp. 125 - 133
Main Authors:	Morais, J.S., Souza, M.M., Campanha, T.M.N., Muller, C.J.T., Bittencourt, A.S., Bortoli, V.C., Schenberg, L.C., Beijamini, V.
Format:	Journal Article
Language:	English
Published:	Netherlands Elsevier B.V 01-11-2016
Subjects:	5-HT Animals Anti-Anxiety Agents - pharmacology Anxiety Anxiety - drug therapy Anxiety - metabolism Anxiety Disorders - drug therapy Dorsal raphe nucleus Dorsal Raphe Nucleus - drug effects Dorsal Raphe Nucleus - metabolism GAL1 GAL2 Galanin Galanin - metabolism Galanin - pharmacology Male Periaqueductal Gray - drug effects Rats, Wistar Receptor, Galanin, Type 1 - drug effects Receptor, Galanin, Type 1 - metabolism Receptor, Galanin, Type 2 - drug effects Receptor, Galanin, Type 2 - metabolism Serotonin 5-HT1 Receptor Antagonists - pharmacology GAL2 Anxiety Galanin 5-HT Dorsal raphe nucleus GAL1 GAL
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Summary:	•We tested galanin (GAL) agonists infused in the dorsal raphe nucleus (DRN) on anxiety.•Activation of GAL1 receptors enhances anxiety in rats tested in the elevated T-maze.•Activation of DRN GAL2 receptors by AR-M1896 decreases rat’s anxiety.•A 5-HT1A antagonist attenuates the anxiolytic effect of a GAL2 agonist in the DRN.•GAL infused in the DRN reduces panic behaviours evoked by the DPAG stimulation. About 40% of the dorsal raphe nucleus (DRN) neurons co-express serotonin (5-HT) and galanin. Serotonergic pathways from the DRN to the amygdala facilitate learned anxiety, while those from the DRN to the dorsal periaqueductal grey matter (DPAG) impair innate anxiety. Previously, we showed that galanin infusion in the DRN of rats induces anxiolytic effect by impairing inhibitory avoidance without changing escape behaviour in the elevated T-maze (ETM). Here, we evaluated: (1) which galanin receptors would be involved in the anxiolytic effect of galanin in the DRN of rats tested in the ETM; (2) the effects of galanin intra-DRN on panic-like behaviours evoked by electrical stimulation of the DPAG. The activation of DRN GAL1 receptors by M617 (1.0 and 3.0nmol) facilitated inhibitory avoidance, whereas the activation of GAL2 receptors by AR-M1896 (3.0nmol) impaired the inhibitory avoidance in the ETM, suggesting an anxiogenic and an anxiolytic-like effect respectively. Both agonists did not change escape behaviour in the ETM or locomotor activity in the open field. The anxiolytic effect of AR-M1896 was attenuated by the prior administration of WAY100635 (0.18nmol), a 5-HT1A antagonist. Galanin (0.3nmol) administered in the DRN increased discreetly flight behaviours induced by electrical stimulation of the DPAG, suggesting a panicolytic effect. Together, our results showed that galanin mediates opposite anxiety responses in the DRN by activation of GAL1 and GAL2 receptors. The anxiolytic effect induced by activation of Gal2 receptors may depend on serotonergic tone. Finally, the role of galanin in panic related behaviours remains uncertain.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0166-4328 1872-7549
DOI:	10.1016/j.bbr.2016.08.007