Role of the 5-HT1A receptors in the effect of Galanin(1-15) on Fluoxetine-mediated action in the forced swimming test

Galanin N-terminal fragment (1-15) [GAL(1-15)] modulates the antidepressant effects induced by the 5-HT1A receptor (5-HT1AR) agonist in the forced swimming test (FST) and the binding characteristics and mRNA levels of 5-HT1AR in the dorsal hippocampus and dorsal raphe (DR). Recently, we observed that GAL(1-15) enhanced the antidepressant-like effects induced by Fluoxetine (FLX) in the FST. In this work, we have studied whether the effects of GAL(1–15) on FLX action were mediated via 5-HT1AR, analyzing the effect of the 5-HT1AR antagonist WAY100635 in this effect and if the binding characteristics and mRNA levels of 5-HT1AR in the DR and dorsal hippocampus are modified by GAL(1-15)+FLX. Groups of rats (n=6-8) received three injections of sc FLX(10mg/kg) and 15 minutes before the FST a single icv injection of GAL(1-15) (1nmol) and 5HT1AR antagonist WAY100635(6nmol) icv alone or in combination. We also analyzed the effects of GAL(1-15)+FLX in the binding characteristics of the 5-HT1AR agonist [H3]-8-OH-DPAT and 5-HT1A mRNA levels in the DR, CA1 and Dentate Gyrus (DG). WAY100635 significantly blocked the reduction in immobility time (p<0.05), and the increase in swimming time (p<0.01) induced by GAL(1-15)+FLX in the FST. GAL(1-15)+FLX produced a significant increase in the 5HT1AR mRNA levels in CA1 (p<0.05) and DG (p<0.05). This effect was not observed in the DR. Moreover, GAL(1-15)+FLX produced a significant decrease in the Kd value (p<0.01) and in the Bmax value (p<0.05) of [3H]-8-OH-DPAT in the DG. These effects were not observed in the CA1 or in the DR. These results indicate that 5HT1AR participates in the GAL(1-15)/FLX interactions in the FST and the mechanism underlying affected the binding characteristics and the mRNA levels of 5-HT1AR specifically in the dorsal hippocampus. The heteroreceptor 5-HT1AR-GALR1-GALR2 located in the dorsal hippocampus may be the target for GAL(1-15). This work was supported by SAF2016-79008-P; PSI2013-44901-P.SAF2016-79008-P; PSI2013-44901-P. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Antidepressant-like effects induced by galanin 2/neuropeptide Y Y1 heterodimers in the dentate gyrus of the hippocampus

Previously, we have described the Galanin (GAL) and Neuropeptide Y Y1 (NPYY1) interactions through GAL receptor 2 and NPYY1 receptor 1 (GALR2/NPYY1R) heterodimers in the Dentate Gyrus (DG) of the Hippocampus, using autoradiographic, in situ hybridization and in situ proximity ligation assay(PLA) (1,2). The current work is to evaluate GALR2 and NPYY1R interactions in relation to depression-like behaviour and c-Fos expression in the Hippocampal DG. Rats (n=6-8) were forced to swim for a 15-min period (pre-test) and 24 h later were subjected to a 5-min swimming session (test) 15 min after the administration alone or in combination of GAL, the NPYY1R agonist [Leu31,Pro34]NPY and the GALR2 antagonist M871. The total duration of immobility, swimming, and climbing periods were scored during the test. For c-Fos immunohistochemistry, experimental groups of rats were anesthetized with sodium pentobarbital (100 mg/kg, i.p.) and perfused with 4 % Paraformaldehyde 90 min after icv injections. Then, brains were coronally sliced and immunostained. As primary antibodies, an antibody against c-Fos protein (1:5000, sc- 52, Santa Cruz Biotechnology, CA, USA), revealed with 3,3´-Diaminobenzidine (DAB) plus nickel, was used as an indirect marker of neural activity. The antibody to Calbindin-D28 k (1:1000, Santa Cruz Biotecnology, CA, USA), revealed with DAB, was used to outline the granular region since it marks mainly hippocampal granule cells. Sections were analyzed using the optical fractionator stereological method. We observed that icv injection of GAL and NPYY1R agonist significantly enhanced the decrease in the immobility (p<0,001) and the increase in the swimming behaviour (p<0,001) compared with the NPYY1R agonist alone. Moreover, a significant enhancement of the decrease in climbing behavior (p<0.05) was also observed. Furthermore, GALR2 is involved in this GALR/NPYY1R interaction, since the presence of the GALR2 antagonist M871 counteracted the enhancement of the decrease in immobility (p<0.01) and in climbing behavior (p<0.05) as well as the increase in swimming time (p<0.001) induced by the coadministration of GAL and NPYY1R agonist in the FST. Specific cells populations within DG subregions may be involved in this behavioural effect since the coadministration of GAL and NPYY1 agonist enhances the NPYY1R-mediated reduction (p<0.05) in the number of c-Fos immunoreactive nuclei in the polymorphic region. In this region, the GABA interneurons could be involved in the interaction since c-Fos IR colocalized with a GABAergic marker (GAD65/67) after NPYY1R agonist injection. Moreover, within the granular cells layer, GAL and NPYY1 agonist coadministration significantly increased c-Fos IR expression in the entire granular cell layer compared with GAL (p<0.05) and [Leu31,Pro34]NPY (p<0.01) alone. Again, the co-treatment with the GALR2 antagonist M871 completely reversed the GAL contribution to the responses in both regions, the polymorphic and the granular layer of the DG, demonstrating the involvement of GALR2 in the GAL actions. These results indicate that GALR2/NPYY1R interactions can provide a novel integrative mechanism in DG in depression-related behavior and may give the basis for the development of drugs targeting GALR2/NPYY1R heteroreceptor complexes in the DG of the hippocampus for the treatment of depression. Study supported by Junta de Andalucia CVI6476 and Proyecto Puente-Universidad de Málaga. 1. Galanin receptor 2-neuropeptide Y Y1 receptor interactions in the dentate gyrus are related with antidepressant-like effects. Narváez M, Borroto-Escuela DO, Millón C, Gago B, Flores-Burgess A, Santín L, Fuxe K, Narváez JA, Díaz-Cabiale Z. Brain Struct Funct 2016 Nov. 221(8):4129-4139. 2. Galanin receptor 2-neuropeptide Y Y1 receptor interactions in the amygdala lead to increased anxiolytic actions. Narváez M, Millón C, Borroto-Escuela D, Flores-Burgess A, Santín L, Parrado C, Gago B, Puigcerver A, Fuxe K, Narváez JA, Díaz-Cabiale Z. Brain Struct Funct. 2015 Jul;220(4):2289-301.Study supported by Junta de Andalucia CVI6476 and Proyecto Puente. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Galanin (1-15) enhancement of the behavioral effects of a 5-HT1AR agonist and fluoxetine in the forced swimming test gives a new therapeutic strategy against depression: possible role of GALR1-GALR2-5-HT1AR heteroreceptor complexes

Major Depression is the most frequent mood disorder, with a lifetime prevalence that has been reported to range from 7% to 21%. It is associated with a substantial functional impairment, diminished quality of life, increased burden both for patients and caregivers, as well as with a higher risk of mortality. Although the underlying mechanisms have not yet been clearly defined in the last decade the importance of the role of neuropeptides, including Galanin (GAL) and the N-terminal fragment GAL(1-15) and/or their receptors in the treatment of stress-related mood disorders is becoming increasingly apparent. We have described that GAL(1-15) induces strong depression-related and anxiogenic-like effects in rats and these effects were significantly stronger than the ones induced by GAL. The GALR1-GALR2 heteroreceptor complexes in the dorsal hippocampus and dorsal raphe (DR) were involved in these effects and demonstrated also in cellular models. Although several neurotransmitter systems and brain areas have been implicated in depression, the pharmacological treatment of major depression is mainly based on drugs elevating serotonergic (5-HT) activity. Specifically, selective 5-HT reuptake inhibitors (SRRIs) are the most commonly used for treatment of major depression. In particular, Fluoxetine (FLX) is usually chosen for the treatment of symptoms of depression In view of these results the purpose of the current study was to assess the ability of GAL(1–15) to modulate the behavioral effects of the 5-HT1AR agonist 8-OH-DPAT and FLX. We have analyzed the effect of GAL (1–15) on the 5-HT1AR agonist 8-OH-DPAT and FLX-mediated responses in a behavioral test of depression.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by SAF2016-79008-P, PSI2017-82604-R (Grant BES-2014-068426)

Receptor-Receptor Interactions in Multiple 5-HT1A Heteroreceptor Complexes in Raphe-Hippocampal 5-HT Transmission and Their Relevance for Depression and Its Treatment

Due to the binding to a number of proteins to the receptor protomers in receptor heteromers in the brain, the term "heteroreceptor complexes" was introduced. A number of serotonin 5-HT1A heteroreceptor complexes were recently found to be linked to the ascending 5-HT pathways known to have a significant role in depression. The 5-HT1A-FGFR1 heteroreceptor complexes were involved in synergistically enhancing neuroplasticity in the hippocampus and in the dorsal raphe 5-HT nerve cells. The 5-HT1A protomer significantly increased FGFR1 protomer signaling in wild-type rats. Disturbances in the 5-HT1A-FGFR1 heteroreceptor complexes in the raphe-hippocampal 5-HT system were found in a genetic rat model of depression (Flinders sensitive line (FSL) rats). Deficits in FSL rats were observed in the ability of combined FGFR1 and 5-HT1A agonist cotreatment to produce antidepressant-like effects. It may in part reflect a failure of FGFR1 treatment to uncouple the 5-HT1A postjunctional receptors and autoreceptors from the hippocampal and dorsal raphe GIRK channels, respectively. This may result in maintained inhibition of hippocampal pyramidal nerve cell and dorsal raphe 5-HT nerve cell firing. Also, 5-HT1A-5-HT2A isoreceptor complexes were recently demonstrated to exist in the hippocampus and limbic cortex. They may play a role in depression through an ability of 5-HT2A protomer signaling to inhibit the 5-HT1A protomer recognition and signaling. Finally, galanin (1-15) was reported to enhance the antidepressant effects of fluoxetine through the putative formation of GalR1-GalR2-5-HT1A heteroreceptor complexes. Taken together, these novel 5-HT1A receptor complexes offer new targets for treatment of depression