A Novel Integrative Mechanism in Anxiolytic Behavior Induced by Galanin 2/Neuropeptide Y Y1 Receptor Interactions on Medial Paracapsular Intercalated Amygdala in Rats

Abstract

Anxiety is evoked by a threatening situation and display adaptive or defensive behaviors, found similarly in animals and humans. Neuropeptide Y (NPY) Y1 receptor (NPYY1R) and Galanin (GAL) receptor 2 (GALR2) interact in several regions of the limbic system, including the amygdala. In a previous study, GALR2 enhanced NPYY1R mediated anxiolytic actions on spatiotemporal parameters in the open field and elevated plus maze, involving the formation of GALR2/NPYY1R heteroreceptor complexes in the amygdala. Moreover, the inclusion of complementary ethological parameters provides a more comprehensive profile on the anxiolytic effects of a treatment. The purpose of the current study is to evaluate the anxiolytic effects and circuit activity modifications caused by coactivation of GALR2 and NPYY1R. Ethological measurements were performed in the open field, the elevated plus-maze and the light-dark box, together with immediate early gene expression analysis within the amygdala-hypothalamus-periaqueductal gray (PAG) axis, as well as in situ proximity ligation assay (PLA) to demonstrate the formation of GALR2/NPYY1R heteroreceptor complexes. GALR2 and NPYY1R coactivation resulted in anxiolytic behaviors such as increased rearing and head-dipping, reduced stretch attend postures and freezing compared to single agonist or aCSF injection. Neuronal activity indicated by cFos expression was decreased in the dorsolateral paracapsular intercalated (ITCp-dl) subregion of the amygdala, ventromedial hypothalamic (VMH) nucleus and ventrolateral part of the periaqueductal gray (vlPAG), while increased in the perifornical nucleus of the hypothalamus (PFX) following coactivation of GALR2 and NPYY1R. Moreover, an increased density of GALR2/NPYY1R heteroreceptor complexes was explicitly observed in ITCp-dl, following GALR2 and NPYY1R coactivation. Besides, knockdown of GALR2 was found to reduce the density of complexes in ITCp-dl. Taken together, these results open up the possibility that the increased anxiolytic activity demonstrated upon coactivation of NPYY1R and GALR2 receptor was related to actions on the ITCp-dl. GALR2-NPYY1R heteroreceptor complexes may inhibit neuronal activity, by also modifying the neuronal networks of the hypothalamus and the PAG. These results indicate that GALR2/NPYY1R interactions in medial paracapsular intercalated amygdala can provide a novel integrative mechanism in anxiolytic behavior and the basis for the development of heterobivalent agonist drugs targeting GALR2/NPYY1R heteromers, especially in the ITCp-dl of the amygdala for the treatment of anxiety.

Galanin and neuropeptide Y interactions elicit antidepressant activity linked to neuronal precursor cells of the dentate gyrus in the ventral hippocampus

“…Furthermore, the effects achieved after the administration of GAL or NPYY1 agonist alone agree with the previous studies and support the prodepressant‐like role of GAL and the antidepressant‐like actions of the NPYY1 agonist in the FST (Kotagale et al, 2013; Kuteeva et al, 2008; Redrobe et al, 2002). These behavioral effects observed in the FST were independent of the motor activity since neither GAL, and NPYY1 agonist nor their coadministration has shown locomotor modifications (Narvaez et al, 2016, 2018, 2015).…”

“…GALR2/NPYY1R heteroreceptor complexes significantly increase in density, as shown with PLA upon combined treatment with GAL and the NPYY1R agonist in the subgranular zone in the ventral hippocampus. The existence of GALR2/NPYY1R heteroreceptor complexes was described in several regions, including the amygdala and the dorsal hippocampus (Narvaez et al, 2016, 2018, 2015). Additionally, we described how heteroreceptor complexes, such as 5HT1A‐FGFR1, promote significant hippocampal plasticity effects linked to hippocampal function changes, including antidepressant actions (Borroto‐Escuela et al, 2012; Narvaez et al, 2020).…”

“…Animals were distributed randomly into five experimental groups: (1) aCSF: control group; (2) GAL-treated group (3 nmol); (3) Y1-treated group receiving an NPYY1R agonist [Leu 31 ,Pro 34 ]NPY (3 nmol); (4) GAL+Y1: group administered with both substances; (5) GAL + Y1 + M871: group injected with GAL, [Leu 31 ,Pro 34 ]NPY and the GALR2 antagonist (M871; 3 nmol; N = 4 in each group). Doses indicated above (Narvaez et al, 2016(Narvaez et al, , 2018(Narvaez et al, , 2015 and the BrdU procedure (Abrial et al, 2014;Pilar-Cuellar et al, 2012) are based on previously published protocols.…”

“…We have described several subtypes of GALR and NPYY1R interactions in distinct regions of the limbic system, with behavioral, region-specific, cellular, and molecular correlations (Diaz-Cabiale et al, 2011;Narvaez et al, 2016Narvaez et al, , 2018Narvaez et al, , 2015. In the DG of the dorsal hippocampus, a facilitatory GALR/NPYY1R interaction was shown, involving the formation of GALR2/NPYY1R heteroreceptor complexes.…”

<p>Galanin Receptors as Drug Target for Novel Antidepressants: Review</p>

“…9,[74][75][76] Narvaez et al confirmed the interaction between GalR2 and NPYY1R in the dentate gyrus (DG) with enhancement of the antidepressive-like behavior mediated by NPY Y1R 77 and anxiolytic behavior. 78 Moreover, GalR1-GalR2 heteromer interaction with Neuropeptide Y Y2 (NPYY2) may be a key molecular mechanism for GAL and its GAL1-15. 79 Furthermore, GAL1-15 fragments facilitate GalR1-5-HT1AR heteroreceptor complexes formation in the raphehippocampal 5-HT neurons and affects serotonin release; GAL1-15 induces stronger effects than GAL to cause depression.…”