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

Amygdala intercalated cells form an evolutionarily conserved system orchestrating brain networks

The amygdala attributes valence and emotional salience to environmental stimuli and regulates how these stimuli affect behavior. Within the amygdala, a distinct class of evolutionarily conserved neurons form the intercalated cell (ITC) clusters, mainly located around the boundaries of the lateral and basal nuclei. Here, we review the anatomical, physiological and molecular characteristics of ITCs, and detail the organization of ITC clusters and their connectivity with one another and other brain regions. We describe how ITCs undergo experience-dependent plasticity and discuss emerging evidence demonstrating how ITCs are innervated and functionally regulated by neuromodulatory systems. We summarize recent findings showing that experience alters the balance of activity between different ITC clusters, thereby determining prevailing behavioral output. Finally, we propose a model in which ITCs form a key system for integrating divergent inputs and orchestrating brain-wide circuits to generate behavioral states attuned to current environmental circumstances and internal needs.

Long-term enhancements in antidepressant efficacy and neurogenesis: Effects of intranasal co-administration of neuropeptide Y 1 receptor (NPY1R) and galanin receptor 2 (GALR2) agonists in the ventral hippocampus

This study evaluates the sustained antidepressant-like effects and neurogenic potential of a 3-day intranasal co-administration regimen of galanin receptor 2 (GALR2) agonist M1145 and neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31, Pro34]NPY in the ventral hippocampus of adult rats, with outcomes analyzed 3 weeks post-treatment. Utilizing the forced swimming test (FST), we found that this co-administration significantly enhances antidepressant-like behaviors, an effect neutralized by the GALR2 antagonist M871, highlighting the synergistic potential of these neuropeptides in modulating mood-related behaviors. In situ proximity ligation assay (PLA) indicated a significant increase in GALR2/NPYY1R heteroreceptor complexes in the ventral hippocampal dentate gyrus, suggesting a molecular basis for the behavioral outcomes observed. Moreover, proliferating cell nuclear antigen (PCNA) immunolabeling revealed increased cell proliferation in the subgranular zone of the dentate gyrus, specifically in neuroblasts as evidenced by co-labeling with doublecortin (DCX), without affecting quiescent neural progenitors or astrocytes. The study also noted a significant uptick in the number of DCX-positive cells and alterations in dendritic morphology in the ventral hippocampus, indicative of enhanced neuronal differentiation and maturation. These morphological changes highlight the potential of these agonists to facilitate the functional integration of new neurons into existing neural circuits. By demonstrating the long-lasting effects of a brief, 3-day intranasal administration of GALR2 and NPY1R agonists, our findings contribute significantly to the understanding of neuropeptide-mediated neuroplasticity and herald novel therapeutic strategies for the treatment of depression and related mood disorders, emphasizing the therapeutic promise of targeting neurogenesis and neuronal maturation processes.

Enhancing Cognitive Functions and Neuronal Growth through NPY1R Agonist and Ketamine Co-Administration: Evidence for NPY1R-TrkB Heteroreceptor Complexes in Rats

This study investigates the combined effects of the neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31-Pro34]NPY at a dose of 132 µg and Ketamine at 10 mg/Kg on cognitive functions and neuronal proliferation, against a backdrop where neurodegenerative diseases present an escalating challenge to global health systems. Utilizing male Sprague-Dawley rats in a physiological model, this research employed a single-dose administration of these compounds and assessed their impact 24 h after treatment on object-in-place memory tasks, alongside cellular proliferation within the dorsal hippocampus dentate gyrus. Methods such as the in situ proximity ligation assay and immunohistochemistry for proliferating a cell nuclear antigen (PCNA) and doublecortin (DCX) were utilized. The results demonstrated that co-administration significantly enhanced memory consolidation and increased neuronal proliferation, specifically neuroblasts, without affecting quiescent neural progenitors and astrocytes. These effects were mediated by the potential formation of NPY1R-TrkB heteroreceptor complexes, as suggested by receptor co-localization studies, although further investigation is required to conclusively prove this interaction. The findings also highlighted the pivotal role of brain-derived neurotrophic factor (BDNF) in mediating these effects. In conclusion, this study presents a promising avenue for enhancing cognitive functions and neuronal proliferation through the synergistic action of the NPY1R agonist and Ketamine, potentially via NPY1R-TrkB heteroreceptor complex formation, offering new insights into therapeutic strategies for neurodegenerative diseases.

Enhanced neuronal survival and BDNF elevation via long-term co-activation of galanin 2 (GALR2) and neuropeptide Y1 receptors (NPY1R): potential therapeutic targets for major depressive disorder

BACKGROUND

Major Depressive Disorder (MDD) is a prevalent and debilitating condition, necessitating novel therapeutic strategies due to the limited efficacy and adverse effects of current treatments. We explored how galanin receptor 2 (GALR2) and Neuropeptide Y1 Receptor (NPYY1R) agonists, working together, can boost brain cell growth and increase antidepressant-like effects in rats. This suggests new ways to treat Major Depressive Disorder (MDD).

RESEARCH DESIGN AND METHODS

In a controlled laboratory setting, adult naive Sprague-Dawley rats were administered directly into the brain's ventricles, a method known as intracerebroventricular (ICV) administration, with GALR2 agonist (M1145), NPYY1R agonist, both, or in combination with a GALR2 antagonist (M871). Main outcome measures included long-term neuronal survival, differentiation, and behavioral.

RESULTS

Co-administration of M1145 and NPYY1R agonist significantly enhanced neuronal survival and maturation in the ventral dentate gyrus, with a notable increase in Brain-Derived Neurotrophic Factor (BDNF) expression. This neurogenic effect was associated with an antidepressant-like effect, an outcome partially reversed by M871.

CONCLUSIONS

GALR2 and NPYY1R agonists jointly promote hippocampal neurogenesis and exert antidepressant-like effects in rats without adverse outcomes, highlighting their therapeutic potential for MDD. The study's reliance on an animal model and intracerebroventricular delivery warrants further clinical exploration to confirm these promising results.

Potentiation of antidepressant effects: NPY1R agonist and ketamine synergy enhances TrkB signaling and neurogenesis in the ventral hippocampus

BACKGROUND

Major Depressive Disorder (MDD) poses a significant challenge to global health, with current treatments often limited by efficacy and onset delays. This study explores the synergistic antidepressant-like effects of an NPY1R agonist and Ketamine, targeting their neurobiological interactions within the ventral hippocampus.

RESEARCH DESIGN AND METHODS

Utilizing a preclinical model, this study administered Neuropeptide Y receptor 1 (NPY1R) agonist and Ketamine, both separately and in combination, through intracerebroventricular (icv) and intranasal (i.n.) routes. The Forced Swimming Test (FST) was employed to assess antidepressant-like activity, while in situ Proximity Ligation Assay and immunohistochemistry were used to examine NPY1R/TrkB heteroreceptor complexes and BDNF expression in the ventral dentate gyrus (DG), along with neurogenesis markers.

RESULTS

The combined treatment significantly reduced immobility in the FST, indicative of enhanced antidepressant-like effects, correlated with increased formation of NPY1R/TrkB complex and brain-derived neurotrophic factor (BDNF) expression in the ventral DG. These molecular alterations were associated with increased neurogenesis.

CONCLUSIONS

The coadministration of an NPY1R agonist and Ketamine in a rodent model demonstrated potentiated antidepressant responses through synergistic neurobiological pathways, including TrkB signaling and hippocampal neurogenesis. This indicates a novel therapeutic strategy for MDD, warranting further clinical investigation to fully understand its implications.

Enhancement of neurogenesis and cognition through intranasal co-delivery of galanin receptor 2 (GALR2) and neuropeptide Y receptor 1 (NPY1R) agonists: a potential pharmacological strategy for cognitive dysfunctions

BACKGROUND

Spatial memory deficits and reduced neuronal survival contribute to cognitive decline seen in the aging process. Current treatments are limited, emphasizing the need for innovative therapeutic strategies. This research explored the combined effects of intranasally co-administered galanin receptor 2 (GALR2) and neuropeptide Y1 receptor (NPY1R) agonists, recognized for their neural benefits, on spatial memory, neuronal survival, and differentiation in adult rats. After intranasal co-delivery of the GALR2 agonist M1145 and a NPY1R agonist to adult rats, spatial memory was tested with the object-in-place task 3 weeks later. We examined neuronal survival and differentiation by assessing BrdU-IR profiles and doublecortin (DCX) labeled cells, respectively. We also used the GALR2 antagonist M871 to confirm GALR2's crucial role in promoting cell growth.

RESULTS

Co-administration improved spatial memory and increased the survival rate of mature neurons. The positive effect of GALR2 in cell proliferation was confirmed by the nullifying effects of its antagonist. The treatment boosted DCX-labeled newborn neurons and altered dendritic morphology, increasing cells with mature dendrites.

CONCLUSIONS

Our results show that intranasal co-delivery of GALR2 and NPY1R agonists improves spatial memory, boosts neuronal survival, and influences neuronal differentiation in adult rats. The significant role of GALR2 is emphasized, suggesting new potential therapeutic strategies for cognitive decline.

Neuropeptide Y receptor 1 and galanin receptor 2 (NPY1R-GALR2) interactions in the dentate gyrus and their relevance for neurogenesis and cognition

INTRODUCTION

This study may unveil novel insights into the interactions between neuropeptide Y receptor 1 (NPY1R) and galanin receptor 2 (GALR2), in the dentate gyrus of the dorsal hippocampus, shedding light on their role in neurogenesis and cognitive functions. Existing literature highlights the potential of these interactions in enhancing learning and memory, yet detailed mechanisms remain underexplored.

METHODS

Utilizing intracerebroventricular injections of GALR2 and NPY1R agonists in Sprague-Dawley male rats, we examined neurogenesis via markers PCNA and DCX, and memory consolidation through the object-in-place task over a three-week period.

RESULTS

Significant increases in NPY1R-GALR2 co-localization and neuroblast proliferation were observed, alongside enhanced memory consolidation. These findings suggest a synergistic effect of NPY1R and GALR2 activation on cognitive functions.

DISCUSSION

Our findings may foster the development of novel heterobivalent or multitargeting drugs, affecting NPY1R-GALR2 interaction, and suggest a future pharmacogical strategy for improving learning and memory found in many brain diseases. Further research is encouraged to explore these mechanisms in pathological models.

Decreased medial prefrontal cortex activity related to impaired novel object preference task performance following GALR2 and Y1R agonists intranasal infusion

Different brain regions' interactions have been implicated in relevant neurological diseases, such as major depressive disorder (MDD), anxiety disorders, age-dependent cognitive decline, Alzheimer's disease (AD) and addiction. We aim to explore the role of the medial prefrontal cortex (mPFC) in the Neuropeptide Y (NPY) and Galanin (GAL) interaction since we have demonstrated specific NPY and GAL interactions in brain areas related to these brain diseases. We performed GALR2 and Y1R agonists intranasal infusion and analyzed the mPFC activation through c-Fos expression. To assess the associated cellular mechanism we studied the formation of Y1R-GALR2 heteroreceptor complexes with in situ proximity ligation assay (PLA) and the expression of the brain-derived neurotrophic factor (BDNF). Moreover, the functional outcome of the NPY and GAL interaction on the mPFC was evaluated in the novel object preference task. We demonstrated that the intranasal administration of both agonists decrease the medial prefrontal cortex activation as shown with the c-Fos expression. These effects were mediated by the decreased formation of Y1R-GALR2 heteroreceptor complexes without affecting the BDNF expression. The functional outcome of this interaction was related to an impaired performance on the novel object preference task. Our data may suggest the translational development of new heterobivalent agonist pharmacophores acting on Y1R-GALR2 heterocomplexes in the medial prefrontal cortex for the novel therapy on neurodegenerative and psychiatric diseases. DATA SHARING AND DATA ACCESSIBILITY: The data that support the findings of this study are openly available in Institutional repository of the University of Malaga (RIUMA) and from the corresponding author upon reasonable request.

GALR2 and Y1R agonists intranasal infusion enhanced adult ventral hippocampal neurogenesis and antidepressant-like effects involving BDNF actions

Dysregulation of adult hippocampal neurogenesis is linked to major depressive disorder (MDD), with more than 300 million people diagnosed and worsened by the COVID-19 pandemic. Accumulating evidence for neuropeptide Y (NPY) and galanin (GAL) interaction was shown in various limbic system regions at molecular-, cellular-, and behavioral-specific levels. The purpose of the current work was to evaluate the proliferating role of GAL2 receptor (GALR2) and Y1R agonists interaction upon intranasal infusion in the ventral hippocampus. We studied their hippocampal proliferating actions using the proliferating cell nuclear antigen (PCNA) on neuroblasts or stem cells and the expression of the brain-derived neurothrophic factor (BDNF). Moreover, we studied the formation of Y1R-GALR2 heteroreceptor complexes and analyzed morphological changes in hippocampal neuronal cells. Finally, the functional outcome of the NPY and GAL interaction on the ventral hippocampus was evaluated in the forced swimming test. We demonstrated that the intranasal infusion of GALR2 and the Y1R agonists promotes neuroblasts proliferation in the dentate gyrus of the ventral hippocampus and the induction of the neurotrophic factor BDNF. These effects were mediated by the increased formation of Y1R-GALR2 heteroreceptor complexes, which may mediate the neurites outgrowth observed on neuronal hippocampal cells. Importantly, BDNF action was found necessary for the antidepressant-like effects after GALR2 and the Y1R agonists intranasal administration. Our data may suggest the translational development of new heterobivalent agonist pharmacophores acting on Y1R-GALR2 heterocomplexes in the ventral hippocampus for the novel therapy of MDD or depressive-affecting diseases.

Amygdala Intercalated Cells: Gate Keepers and Conveyors of Internal State to the Circuits of Emotion

Generating adaptive behavioral responses to emotionally salient stimuli requires evaluation of complex associations between multiple sensations, the surrounding context, and current internal state. Neural circuits within the amygdala parse this emotional information, undergo synaptic plasticity to reflect learned associations, and evoke appropriate responses through their projections to the brain regions orchestrating these behaviors. Information flow within the amygdala is regulated by the intercalated cells (ITCs), which are densely packed clusters of GABAergic neurons that encircle the basolateral amygdala (BLA) and provide contextually relevant feedforward inhibition of amygdala nuclei, including the central and BLA. Emerging studies have begun to delineate the unique contribution of each ITC cluster and establish ITCs as key loci of plasticity in emotional learning. In this review, we summarize the known connectivity and function of individual ITC clusters and explore how different neuromodulators conveying internal state act via ITC gates to shape emotionally motivated behavior. We propose that the behavioral state-dependent function of ITCs, their unique genetic profile, and rich expression of neuromodulator receptors make them potential therapeutic targets for disorders, such as anxiety, schizophrenia spectrum, and addiction.

Melanin-concentrating hormone promotes anxiety and intestinal dysfunction via basolateral amygdala in mice

The limbic system plays a pivotal role in stress-induced anxiety and intestinal disorders, but how the functional circuits between nuclei within the limbic system are engaged in the processing is still unclear. In our study, the results of fluorescence gold retrograde tracing and fluorescence immunohistochemistry showed that the melanin-concentrating hormone (MCH) neurons of the lateral hypothalamic area (LHA) projected to the basolateral amygdala (BLA). Both chemogenetic activation of MCH neurons and microinjection of MCH into the BLA induced anxiety disorder in mice, which were reversed by intra-BLA microinjection of MCH receptor 1 (MCHR1) blocker SNAP-94847. In the chronic acute combining stress (CACS) stimulated mice, SNAP94847 administrated in the BLA ameliorated anxiety-like behaviors and improved intestinal dysfunction via reducing intestinal permeability and inflammation. In conclusion, MCHergic circuit from the LHA to the BLA participates in the regulation of anxiety-like behavior in mice, and this neural pathway is related to the intestinal dysfunction in CACS mice by regulating intestinal permeability and inflammation.

Dysfunctional Heteroreceptor Complexes as Novel Targets for the Treatment of Major Depressive and Anxiety Disorders

Among mental diseases, major depressive disorder (MDD) and anxiety deserve a special place due to their high prevalence and their negative impact both on society and patients suffering from these disorders. Consequently, the development of novel strategies designed to treat them quickly and efficiently, without or at least having limited side effects, is considered a highly important goal. Growing evidence indicates that emerging properties are developed on recognition, trafficking, and signaling of G-protein coupled receptors (GPCRs) upon their heteromerization with other types of GPCRs, receptor tyrosine kinases, and ionotropic receptors such as N-methyl-D-aspartate (NMDA) receptors. Therefore, to develop new treatments for MDD and anxiety, it will be important to identify the most vulnerable heteroreceptor complexes involved in MDD and anxiety. This review focuses on how GPCRs, especially serotonin, dopamine, galanin, and opioid heteroreceptor complexes, modulate synaptic and volume transmission in the limbic networks of the brain. We attempt to provide information showing how these emerging concepts can contribute to finding new ways to treat both MDD and anxiety disorders.

Galanin and Neuropeptide Y Interaction Enhances Proliferation of Granule Precursor Cells and Expression of Neuroprotective Factors in the Rat Hippocampus with Consequent Augmented Spatial Memory

Dysregulation of hippocampal neurogenesis is linked to several neurodegenereative diseases, where boosting hippocampal neurogenesis in these patients emerges as a potential therapeutic approach. Accumulating evidence for a neuropeptide Y (NPY) and galanin (GAL) interaction was shown in various limbic system regions at molecular-, cellular-, and behavioral-specific levels. The purpose of the current work was to evaluate the role of the NPY and GAL interaction in the neurogenic actions on the dorsal hippocampus. We studied the Y1R agonist and GAL effects on: hippocampal cell proliferation through the proliferating cell nuclear antigen (PCNA), the expression of neuroprotective and anti-apoptotic factors, and the survival of neurons and neurite outgrowth on hippocampal neuronal cells. The functional outcome was evaluated in the object-in-place task. We demonstrated that the Y1R agonist and GAL promote cell proliferation and the induction of neuroprotective factors. These effects were mediated by the interaction of NPYY1 (Y1R) and GAL2 (GALR2) receptors, which mediate the increased survival and neurites' outgrowth observed on neuronal hippocampal cells. These cellular effects are linked to the improved spatial-memory effects after the Y1R agonist and GAL co-injection at 24 h in the object-in-place task. Our results suggest the development of heterobivalent agonist pharmacophores, targeting Y1R-GALR2 heterocomplexes, therefore acting on the neuronal precursor cells of the DG in the dorsal hippocampus for the novel therapy of neurodegenerative cognitive-affecting diseases.

Exploring the role of neuropeptides in depression and anxiety

Depression is one of the most prevalent forms of mental disorders and is the most common cause of disability in the Western world. Besides, the harmful effects of stress-related mood disorders on the patients themselves, they challenge the health care system with enormous social and economic impacts. Due to the high proportion of patients not responding to existing drugs, finding new treatment strategies has become an important topic in neurobiology, and there is much evidence that neuropeptides are not only involved in the physiology of stress but may also be clinically important. Based on preclinical trial data, new neuropharmaceutical candidates may target neuropeptides and their receptors and are expected to be essential and valuable tools in the treatment of psychiatric disorders. In the current article, we have summarized data obtained from animal models of depressive disorder and transgenic mouse models. We also focus on previously published research data of clinical studies on corticotropin-releasing hormone (CRH), galanin (GAL), neuropeptide Y (NPY), neuropeptide S (NPS), Oxytocin (OXT), vasopressin (VP), cholecystokinin (CCK), and melanin-concentrating hormone (MCH) stress research fields.

Intranasal Delivery of Galanin 2 and Neuropeptide Y1 Agonists Enhanced Spatial Memory Performance and Neuronal Precursor Cells Proliferation in the Dorsal Hippocampus in Rats

A need for new therapeutic approaches are necessary for dementia conditions and memory deficits of different origins, such as Alzheimer's disease. There is complex pathophysiological mechanisms involved, affecting adult hippocampal neurogenesis, in which neuropeptides and its neurogenesis regulation seem to participate. Neuropeptide Y(NPY) Y1 receptor (Y1R) and galanin (GAL) receptor 2 (GALR2) interact in brain regions responsible for learning and memory processes, emphasizing the hippocampus. Moreover, a significant challenge for treatments involving peptide drugs is bypassing the blood-brain barrier. The current study assesses the sustained memory performance induced by GALR2 and NPYY1R agonists intranasal coadministration and their neurochemical hippocampal correlates. Memory retrieval was conducted in the object-in-place task together with in situ proximity ligation assay (PLA) to manifest the formation of GALR2/Y1R heteroreceptor complexes and their dynamics under the different treatments. We evaluated cell proliferation through a 5-Bromo-2’-deoxyuridine (BrdU) expression study within the dentate gyrus of the dorsal hippocampus. The GalR2 agonist M1145 was demonstrated to act with the Y1R agonist to improve memory retrieval at 24 hours in the object-in-place task. Our data show that the intranasal administration is a feasible technique for directly delivering Galanin or Neuropeptide Y compounds into CNS. Moreover, we observed the ability of the co-agonist treatment to enhance the cell proliferation in the DG of the dorsal hippocampus through 5- Bromo-2’-deoxyuridine (BrdU) expression analysis at 24 hours. The understanding of the cellular mechanisms was achieved by analyzing the GALR2/Y1R heteroreceptor complexes upon agonist coactivation of their two types of receptor protomers in Doublecortin-expressing neuroblasts. Our results may provide the basis for developing heterobivalent agonist pharmacophores, targeting GALR2-Y1R heterocomplexes. It involves especially the neuronal precursor cells of the dentate gyrus in the dorsal hippocampus for the novel treatment of neurodegenerative pathologies as in the Alzheimer’s disease.

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

A need for new antidepressants is necessary since traditional antidepressants have several flaws. Neuropeptide Y(NPY) Y1 receptor (NPYY1R) and galanin (GAL) receptor 2 (GALR2) interact in several regions of the limbic system, including the hippocampus. The current study assesses the antidepressant effects induced by GALR2 and NPYY1R coactivation, together with the evaluation of cell proliferation through 5-Bromo-2'-deoxyuridine expression within the dentate gyrus of the ventral hippocampus (vDG). We employed in situ proximity ligation assay to manifest GALR2/NPYY1R heteroreceptor complexes. Additionally, the expression pattern of GALR2 and the activation of the extracellular-regulated kinases (ERK) pathway after GALR2 and NPYY1R costimulation in cell cultures were examined. GALR2 and NPYY1R coactivation resulted in sustained antidepressant behaviors in the FST after 24 h, linked to increased cell proliferation in the vDG. Moreover, an increased density of GALR2/NPYY1R heteroreceptor complexes was observed in vDG, on doublecortin-expressing neuroblasts. Recruitment of the GALR2 expression to the plasma membrane was observed upon the coactivation of GALR2 and NPYY1R in cell cultures, presumably associated to the enhanced effects on the activation of ERK pathway. GALR2 may promote the GALR2/NPYY1R heteroreceptor complexes formation in the ventral hippocampus. It may induce a transformation of cell proliferation toward a neuronal lineage by enhancement of ERK pathway. Thus, it may give the mechanism for the antidepressant behavior observed. These results may provide the basis for the development of heterobivalent agonist pharmacophores, targeting GALR2/NPYY1R heteromers, especially in the neuronal precursor cells of the dentate gyrus in the ventral hippocampus for the novel treatment of depression.

Galanin Receptors as Drug Target for Novel Antidepressants: Review

Galanin (GAL) is a 29-amino-acid neuropeptide that serves multiple physiological functions throughout the central and peripheral nervous system. Its role involves in a range of physiological and pathological functions including control of food intake, neuro-protection, neuronal regeneration, energy expenditure, reproduction, water balance, mood, nociception and various neuroendocrine functions. The use of currently available antidepressant drugs raises concerns regarding efficacy and onset of action; therefore, the need for antidepressants with novel mechanisms is increasing. Presently, various studies revealed the link between GAL and depression. Attenuation of depressive symptoms is achieved through inhibition of GalR1 and GalR3 and activation of GalR2. However, lack of receptor selectivity of ligands has limited the complete elucidation of effects of different receptors in depression-like behavior. Studies have suggested that GAL enhances the action of selective serotonin reuptake inhibitors (SSRIs) and promotes availability of transcription proteins. This review addresses the role of GAL, GAL receptors (GALRs) ligands including selective peptides, and the mechanism of ligand receptor interaction in attenuating depressive symptoms.