Neuropeptide Y reduces expression of social fear via simultaneous activation of Y1 and Y2 receptors

Dipeptidyl peptidase-4 inhibitors enhance memory retention via neuropeptide Y

We have previously shown that neuropeptide Y (NPY) prolongs the retention of memory in the object discrimination test in mice. In this study, we investigated the potential memory-enhancing effects of dipeptidyl peptidase-4 (DPP4) inhibitors, commonly referred to as gliptins, which are known to prevent the degradation of NPY, thereby increasing its concentration. We show that administration of sitagliptin (50 and 100 mg/kg/day) and linagliptin (5 and 10 mg/kg/day) via the drinking water facilitates the retention of object memory in male CD1 mice, extending memory retention to time points when control mice no longer retain memory. Similar to gliptin-treated mice, male and female homozygous and heterozygous DPP4 deficient mice displayed intact object memory at time points when wild-type littermates showed no memory. Sitagliptin treatment, however, did not facilitate the retention of memory in male and female homozygous NPY deficient mice, indicating that NPY is essential for the memory-enhancing effects of sitagliptin. These results indicate that sitagliptin exerts memory-enhancing effects through an NPY-dependent mechanism and highlight the potential of gliptins as cognitive enhancers in healthy individuals.

Differential suppression of hippocampal network oscillations by neuropeptide Y

Neuropeptide Y (NPY) is the most abundant neuropeptide in the brain. It exerts anxiolytic and anticonvulsive actions, reduces stress and suppresses fear memory. While its effects at the behavioral and cellular levels have been well studied, much less is known about the modulation of physiological activity patterns at the network level. We therefore studied the impact of NPY on two prominent, memory-related hippocampal activity patterns, gamma oscillations and sharp wave-ripple complexes in C57BL/6 male mice. Using established in vitro brain slice models for both patterns, we assessed the effects of NPY and receptor-specific agonists and antagonists on network activity in the CA3 and CA1 subnetworks. We report that NPY strongly suppresses sharp waves, and has significant, but much weaker effects on the power of carbachol-induced gamma oscillations. Both effects are primarily mediated via Y2 receptors. Additionally, NPY effects are much more prominent in the CA1 region compared to CA3. Our results show pattern- and region-specific effects of NPY on hippocampal networks, which suggest specific modulatory actions on hippocampus-dependent memory processes.

Valence-dependent effects of neuropeptide Y on the expression of conditioned fear and anxiety-like behavior: Involvement of the bed nucleus of the stria terminalis

Neuropeptide Y (NPY) has anxiolytic-like effects and facilitates the extinction of cued and contextual fear in rodents. We have previously shown that intracerebroventricular administration of NPY reduces the expression of social fear via simultaneous activation of Y1 and Y2 receptors in a mouse model of social fear conditioning (SFC). In the present study, we investigated whether the anteroventral bed nucleus of the stria terminalis (BNSTav) mediates these effects of NPY, given the important role of BNSTav in regulating anxiety- and fear-related behaviors. We show that while NPY (0.1 nmol/0.2 μl/side) did not reduce the expression of SFC-induced social fear in male CD1 mice, it reduced the expression of both cued and contextual fear by acting on Y2 but not on Y1 receptors within the BNSTav. Prior administration of the Y2 receptor antagonist BIIE0246 (0.2 nmol/0.2 μl/side) but not of the Y1 receptor antagonist BIBO3304 trifluoroacetate (0.2 nmol/0.2 μl/side) blocked the effects of NPY on the expression of cued and contextual fear. Similarly, NPY exerted non-social anxiolytic-like effects in the elevated plus maze test but not social anxiolytic-like effects in the social approach avoidance test by acting on Y2 receptors and not on Y1 receptors within the BNSTav. These results suggest that administration of NPY within the BNSTav exerts robust Y2 receptor-mediated fear-reducing and anxiolytic-like effects specifically in non-social contexts and add a novel piece of evidence regarding the neural underpinnings underlying the effects of NPY on conditioned fear and anxiety-like behavior.

Neuropeptide Y gene variants and Agreeableness: interaction effect with the birth cohort and the serotonin transporter promoter polymorphism

OBJECTIVE

Neuropeptide Y (NPY) is a powerful regulator of anxious states, including social anxiety, but evidence from human genetic studies is limited. Associations of common gene variants with behaviour have been described as subject to birth cohort effects, especially if the behaviour is socially motivated. This study aimed to examine the association of NPY rs16147 and rs5574 with personality traits in highly representative samples of two birth cohorts of young adults, the samples having been formed during a period of rapid societal transition.

METHODS

Both birth cohorts (original n = 1238) of the Estonian Children Personality Behaviour and Health Study (ECPBHS) self-reported personality traits of the five-factor model at 25 years of age.

RESULTS

A significant interaction effect of the NPY rs16147 and rs5574 and birth cohort on Agreeableness was found. The T/T genotype of NPY rs16147 resulted in low Agreeableness in the older cohort (born 1983) and in high Agreeableness in the younger cohort (born 1989). The C/C genotype of NPY rs5574 was associated with higher Agreeableness in the younger but not in the older cohort. In the NPY rs16147 T/T homozygotes, the deviations from average in Agreeableness within the birth cohort were dependent on the serotonin transporter promoter polymorphism.

CONCLUSIONS

The association between the NPY gene variants and a personality domain reflecting social desirability is subject to change qualitatively in times of rapid societal changes, serving as an example of the relationship between the plasticity genes and environment. The underlying mechanism may involve the development of the serotonergic system.

Development of Comorbid Depression after Social Fear Conditioning in Mice and Its Effects on Brain Sphingolipid Metabolism

Currently, there are no animal models for studying both specific social fear and social fear with comorbidities. Here, we investigated whether social fear conditioning (SFC), an animal model with face, predictive and construct validity for social anxiety disorder (SAD), leads to the development of comorbidities at a later stage over the course of the disease and how this affects the brain sphingolipid metabolism. SFC altered both the emotional behavior and the brain sphingolipid metabolism in a time-point-dependent manner. While social fear was not accompanied by changes in non-social anxiety-like and depressive-like behavior for at least two to three weeks, a comorbid depressive-like behavior developed five weeks after SFC. These different pathologies were accompanied by different alterations in the brain sphingolipid metabolism. Specific social fear was accompanied by increased activity of ceramidases in the ventral hippocampus and ventral mesencephalon and by small changes in sphingolipid levels in the dorsal hippocampus. Social fear with comorbid depression, however, altered the activity of sphingomyelinases and ceramidases as well as the sphingolipid levels and sphingolipid ratios in most of the investigated brain regions. This suggests that changes in the brain sphingolipid metabolism might be related to the short- and long-term pathophysiology of SAD.

Social Fear Affects Limbic System Neuronal Activity and Gene Expression

Social anxiety disorder (SAD) is a highly prevalent and comorbid anxiety disorder with rather unclear underlying mechanisms. Here, we aimed to characterize neurobiological changes occurring in mice expressing symptoms of social fear and to identify possible therapeutic targets for SAD. Social fear was induced via social fear conditioning (SFC), a validated animal model of SAD. We assessed the expression levels of the immediate early genes (IEGs) cFos, Fosl2 and Arc as markers of neuronal activity and the expression levels of several genes of the GABAergic, serotoninergic, oxytocinergic, vasopressinergic and neuropeptide Y (NPY)-ergic systems in brain regions involved in social behavior or fear-related behavior in SFC+ and SFC− mice 2 h after exposure to a conspecific. SFC+ mice showed a decreased number and density of cFos-positive cells and decreased expression levels of IEGs in the dorsal hippocampus. SFC+ mice also showed alterations in the expression of NPY and serotonin system-related genes in the paraventricular nucleus of the hypothalamus, basolateral amygdala, septum and dorsal raphe nucleus, but not in the dorsal hippocampus. Our results describe neuronal alterations occurring during the expression of social fear and identify the NPY and serotonergic systems as possible targets in the treatment of SAD.

Roles of Neuropeptides in Sleep-Wake Regulation

Sleep and wakefulness are basic behavioral states that require coordination between several brain regions, and they involve multiple neurochemical systems, including neuropeptides. Neuropeptides are a group of peptides produced by neurons and neuroendocrine cells of the central nervous system. Like traditional neurotransmitters, neuropeptides can bind to specific surface receptors and subsequently regulate neuronal activities. For example, orexin is a crucial component for the maintenance of wakefulness and the suppression of rapid eye movement (REM) sleep. In addition to orexin, melanin-concentrating hormone, and galanin may promote REM sleep. These results suggest that neuropeptides play an important role in sleep–wake regulation. These neuropeptides can be divided into three categories according to their effects on sleep–wake behaviors in rodents and humans. (i) Galanin, melanin-concentrating hormone, and vasoactive intestinal polypeptide are sleep-promoting peptides. It is also noticeable that vasoactive intestinal polypeptide particularly increases REM sleep. (ii) Orexin and neuropeptide S have been shown to induce wakefulness. (iii) Neuropeptide Y and substance P may have a bidirectional function as they can produce both arousal and sleep-inducing effects. This review will introduce the distribution of various neuropeptides in the brain and summarize the roles of different neuropeptides in sleep–wake regulation. We aim to lay the foundation for future studies to uncover the mechanisms that underlie the initiation, maintenance, and end of sleep–wake states.

Neuropeptide Y in the amygdala contributes to neuropathic pain-like behaviors in rats via the neuropeptide Y receptor type 2/mitogen-activated protein kinase axis

Neuropeptide Y (NPY) is a highly conserved endogenous peptide in the central and peripheral nervous systems, which has been implicated in nociceptive signaling in neuropathic pain. However, downstream mechanistic actions remain uncharacterized. In this study, we sought to investigate the mechanism of NPY and its receptor NPY2R in the amygdala in rats with neuropathic pain-like behaviors induced by chronic constriction injury (CCI) of the sciatic nerve. The expression of NPY and NPY2R was found to be aberrantly up-regulated in neuropathic pain-related microarray dataset. Further, NPY was found to act on NPY2R in the basolateral amygdala (BLA). As reflected by the decrease in mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) as well as the increase of NPY expression in the amygdala of rats with neuropathic pain-like behaviors, NPY was closely related to the effect of amygdala nerve activity in neuropathic pain. Subsequently, mechanistic investigations indicated that NPY2R activated the MAPK signaling pathway in the amygdala. NPY2R-induced decrease of MWT and TWL were also restored in the presence of MAPK signaling pathway antagonist. Moreover, it was revealed that NPY2R overexpression promoted the viability while inhibiting the apoptosis of microglia. Taken together, NPY in the amygdala interacts with NPY2R to activate the MAPK signaling pathway, thereby promoting the occurrence of neuropathic pain.

Neuropeptide Y Reduces Social Fear in Male Mice: Involvement of Y1 and Y2 Receptors in the Dorsolateral Septum and Central Amygdala

Neuropeptide Y (NPY) has anxiolytic-like effects and facilitates the extinction of cued and contextual fear in rodents. We previously showed that intracerebroventricular administration of NPY reduces the expression of social fear in a mouse model of social fear conditioning (SFC) and localized these effects to the dorsolateral septum (DLS) and central amygdala (CeA). In the present study, we aimed to identify the receptor subtypes that mediate these local effects of NPY. We show that NPY (0.1 nmol/0.2 µL/side) reduced the expression of SFC-induced social fear in a brain region- and receptor-specific manner in male mice. In the DLS, NPY reduced the expression of social fear by acting on Y2 receptors but not on Y1 receptors. As such, prior administration of the Y2 receptor antagonist BIIE0246 (0.2 nmol/0.2 μL/side) but not the Y1 receptor antagonist BIBO3304 trifluoroacetate (0.2 nmol/0.2 μL/side) blocked the effects of NPY in the DLS. In the CeA, however, BIBO3304 trifluoroacetate but not BIIE0246 blocked the effects of NPY, suggesting that NPY reduced the expression of social fear by acting on Y1 receptors but not Y2 receptors within the CeA. This study suggests that at least two distinct receptor subtypes are differentially recruited in the DLS and CeA to mediate the effects of NPY on the expression of social fear.

Brain Region-Dependent Effects of Neuropeptide Y on Conditioned Social Fear and Anxiety-Like Behavior in Male Mice

Neuropeptide Y (NPY) has anxiolytic-like effects and facilitates the extinction of cued and contextual fear in rodents. We have previously shown that the intracerebroventricular administration of NPY reduces the expression of social fear in a mouse model of social fear conditioning (SFC). In the present study, we aimed to identify the brain regions that mediate these effects of NPY. We show that NPY (0.1 nmol/0.2 µL/side) reduces the expression of SFC-induced social fear in a brain-region-dependent manner. In more detail, NPY reduced the expression of social fear when administered into the dorsolateral septum (DLS) and central amygdala (CeA), but not when administered into the dorsal hippocampus (DH), medial amygdala (MeA) and basolateral amygdala (BLA). We also investigated whether the reduced expression of social fear might partly be due to a reduced anxiety-like behavior, and showed that NPY exerted anxiolytic-like effects when administered into the DH, DLS, CeA and BLA, but not when administered into the MeA. This study identifies the DLS and the CeA as brain regions mediating the effects of NPY on the expression of social fear and suggests that partly distinct neural circuitries mediate the effects of NPY on the expression of social fear and on anxiety-like behavior.

Neuropeptide Y as Alternative Pharmacotherapy for Antidepressant-Resistant Social Fear

In many social anxiety disorder (SAD) patients, the efficacy of antidepressant therapy is unsatisfactory. Here, we investigated whether mice deficient for the lysosomal glycoprotein acid sphingomyelinase (ASM−/−) represent an appropriate tool to study antidepressant-resistant social fear. We also investigated whether neuropeptide Y (NPY) reduces this antidepressant-resistant social fear in ASM−/− mice, given that NPY reduced social fear in a mouse model of SAD, namely social fear conditioning (SFC). We show that neither chronic paroxetine nor chronic amitriptyline administration via drinking water were successful in reducing SFC-induced social fear in ASM−/− mice, while the same treatment reduced social fear in ASM+/− mice and completely reversed social fear in ASM+/+ mice. This indicates that the antidepressants paroxetine and amitriptyline reduce social fear via the ASM-ceramide system and that ASM−/− mice represent an appropriate tool to study antidepressant-resistant social fear. The intracerebroventricular administration of NPY, on the other hand, reduced social fear in ASM−/− mice, suggesting that NPY might represent an alternative pharmacotherapy for antidepressant-resistant social fear. These results suggest that medication strategies aimed at increasing brain NPY concentrations might improve symptoms of social fear in SAD patients who fail to respond to antidepressant treatments.

Social Fear Memory Requires Two Stages of Protein Synthesis in Mice

It is well known that long-term consolidation of newly acquired information, including information related to social fear, require de novo protein synthesis. However, the temporal dynamics of protein synthesis during the consolidation of social fear memories is unclear. To address this question, mice received a single systemic injection with the protein synthesis inhibitor, anisomycin, at different time-points before or after social fear conditioning (SFC), and memory was assessed 24 h later. We showed that anisomycin impaired the consolidation of social fear memories in a time-point-dependent manner. Mice that received anisomycin 20 min before, immediately after, 6 h, or 8 h after SFC showed reduced expression of social fear, indicating impaired social fear memory, whereas anisomycin caused no effects when administered 4 h after SFC. These results suggest that consolidation of social fear memories requires two stages of protein synthesis: (1) an initial stage starting during or immediately after SFC, and (2) a second stage starting around 6 h after SFC and lasting for at least 5 h.

Neuropeptide Y prolongs non-social memory in a brain region- and receptor-specific way in male mice

Neuropeptide Y (NPY) and its receptors are highly expressed in brain regions involved in learning and memory processes. We have previously shown that intracerebroventricular administration of NPY prolongs the retention of non-social memory in the object discrimination test. Here, we aimed to identify the brain regions which mediate these memory-enhancing effects of NPY. We show that NPY (0.1 nmol/0.2 μl/side) prolongs retention of non-social memory when administered into the dorsolateral septum (DLS) and medial amygdala (MeA), but not when administered into the dorsal hippocampus, central amygdala and basolateral amygdala. In the DLS, the effects of NPY were blocked by the Y1 receptor antagonist BIBO3304 trifluoroacetate (0.2 nmol/0.2 μl/side), but not by the Y2 receptor antagonist BIIE0246 (0.2 nmol/0.2 μl/side). In the MeA, on the other hand, BIIE0246, but not BIBO3304 trifluoroacetate blocked the effects of NPY. This study demonstrates that NPY exerts Y1 receptor-mediated memory-enhancing effects in the DLS and Y2 receptor-mediated memory-enhancing effects in the MeA, and suggests that distinct brain regions and receptor subtypes are recruited to mediate the effects of NPY on non-social memory.