A role for the cerebellum in motor-triggered alleviation of anxiety.

Physical exercise is known to reduce anxiety, but the underlying brain mechanisms remain unclear. Here, we explore a hypothalamo-cerebello-amygdalar circuit that may mediate motor-dependent alleviation of anxiety. This three-neuron loop, in which the cerebellar dentate nucleus takes center stage, bridges the motor system with the emotional system. Subjecting animals to a constant rotarod engages glutamatergic cerebellar dentate neurons that drive PKCδ+ amygdalar neurons to elicit an anxiolytic effect. Moreover, challenging animals on an accelerated rather than a constant rotarod engages hypothalamic neurons that provide a superimposed anxiolytic effect via an orexinergic projection to the dentate neurons that activate the amygdala. Our findings reveal a cerebello-limbic pathway that may contribute to motor-triggered alleviation of anxiety and that may be optimally exploited during challenging physical exercise.

Dynorphin promotes stress-induced depressive behaviors by inhibiting ventral pallidal neurons in rats.

AIM: Endogenous dynorphin signaling via kappa opioid receptors (KORs) plays a key role in producing the depressive and aversive consequences of stress. We investigated the behavioral effects of the dynorphin/KOR system in the ventral pallidum (VP) and studied the underlying mechanisms. METHODS: To investigate the effects of dynorphin on the VP, we conducted behavioral experiments after microinjection of drugs or shRNA and brain-slice electrophysiological recordings. Histological tracing and molecular biological experiments were used to identify the distribution of KORs and the possible sources of dynorphin projections to the VP. RESULTS: An elevated dynorphin concentration and increased KOR activity were observed in the VP after acute stress. Infusion of dynorphin-A into the VP produced depressive-like phenotypes including anhedonia and despair and anxiety behaviors, but did not alter locomotor behavior. Mechanistically, dynorphin had an inhibitory effect on VP neurons-reducing their firing rate and inhibiting excitatory transmission-through direct activation of KORs and modulation of downstream G-protein-gated inwardly rectifying potassium (GIRK) channels and high-voltage gated calcium channels (VGCCs). Tracing revealed direct innervation of VP neurons by dynorphin-positive projections; potential sources of these dynorphinergic projections include the nucleus accumbens, amygdala, and hypothalamus. Blockade of dynorphin/KOR signaling in the VP by drugs or viral knock-down of KORs significantly reduced despair behavior in rats. CONCLUSIONS: Endogenous dynorphinergic modulation of the VP plays a critical role in mediating depressive reactions to stress.

Detecting Amyloid-ß Accumulation via Immunofluorescent Staining in a Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disease that contributes to 60-70% dementia around the world. One of the hallmarks of AD undoubtedly lies on accumulation of amyloid-ß (Aß) in the brain. Aß is produced from the proteolytic cleavage of the beta-amyloid precursor protein (APP) by ß-secretase and γ-secretase. In pathological circumstances, the increased ß-cleavage of APP leads to overproduction of Aß, which aggregates into Aß plaques. Since Aß plaques are a characteristic of AD pathology, detecting the amount of Aß is very important in AD research. In this protocol, we introduce the immunofluorescent staining method to visualize Aß deposition. The mouse model used in our experiments is 5×FAD, which carries five mutations found in human familial AD. The neuropathological and behavioral deficits of 5xFAD mice are well-documented, which makes it a good animal model to study Aß pathology. We will introduce the procedure including transcardial perfusion, cryosectioning, immunofluorescent staining and quantification to detect Aß accumulation in 5×FAD mice. With this protocol, researchers can investigate Aß pathology in an AD mouse model.

The Role of the Kappa Opioid System in Comorbid Pain and Psychiatric Disorders: Function and Implications.

Both pain and psychiatric disorders, such as anxiety and depression, significantly impact quality of life for the sufferer. The two also share a strong pathological link: chronic pain-induced negative affect drives vulnerability to psychiatric disorders, while patients with comorbid psychiatric disorders tend to experience exacerbated pain. However, the mechanisms responsible for the comorbidity of pain and psychiatric disorders remain unclear. It is well established that the kappa opioid system contributes to depressive and dysphoric states. Emerging studies of chronic pain have revealed the role and mechanisms of the kappa opioid system in pain processing and, in particular, in the associated pathological alteration of affection. Here, we discuss the key findings and summarize compounds acting on the kappa opioid system that are potential candidates for therapeutic strategies against comorbid pain and psychiatric disorders.

An updated pharmacological insight of resveratrol in the treatment of diabetic nephropathy.

As one of the most common complications of diabetes, nephropathy develops in approximately 40% of diabetic individuals. Although end stage kidney disease is known as one of the most consequences of diabetic nephropathy, the majority of diabetic individuals might die from cardiovascular diseases and infections before renal replacement treatment. Moreover, the routine medical treatments for diabetes hold undesirable side effects. The explosive prevalence of diabetes urges clinicians and scientists to investigate the complementary or alternative therapies. Phytochemicals are emerging as alternatives with a wide range of therapeutic effects on various pathologies, including diabetic kidney disease. Of those phytochemicals, resveratrol, a natural polyphenolic stilbene, has been found to exert a broad spectrum of health benefits via various signaling molecules. In particular, resveratrol has gained a great deal of attention because of its anti-oxidative, anti-inflammatory, anti-diabetic, anti-obesity, cardiovascular-protective, and anti-tumor properties. In the renal system, emerging evidence shows that resveratrol has already been used to ameliorate chronic or acute kidney injury. This review critically summarizes the current findings and molecular mechanisms of resveratrol in diabetic renal damage. In addition, we will discuss the adverse and inconsistent effects of resveratrol in diabetic nephropathy. Although there is increasing evidence that resveratrol affords great potential in diabetic nephropathy therapy, these results should be treated with caution before its clinical translation. In addition, the unfavorable pharmacokinetics and/or pharmacodynamics profiles, such as poor bioavailability, may limit its extensive clinical applications. It is clear that further research is needed to unravel these limitations and improve its efficacy against diabetic nephropathy. Increasing investigation of resveratrol in diabetic kidney disease will not only help us better understand its pharmacological actions, but also provide novel potential targets for therapeutic intervention.

Orexin prevents depressive-like behavior by promoting stress resilience.

Hypothalamic neuropeptide orexin has been implicated in the pathophysiology of psychiatric disorders and accumulating clinical evidence indicates a potential link between orexin and depression. However, the exact role of orexin in depression, particularly the underlying neural substrates and mechanisms, remains unknown. In this study, we reveal a direct projection from the hypothalamic orexinergic neurons to the ventral pallidum (VP), a structure that receives an increasing attention for its critical position in rewarding processing, stress responses, and depression. We find that orexin directly excites GABAergic VP neurons and prevents depressive-like behaviors in rats. Two orexin receptors, OX1R and OX2R, and their downstream Na+-Ca2+ exchanger and L-type Ca2+ channel co-mediate the effect of orexin. Furthermore, pharmacological blockade or genetic knockdown of orexin receptors in VP increases depressive-like behaviors in forced swim test and sucrose preference test. Intriguingly, blockage of orexinergic inputs in VP has no impact on social proximity in social interaction test between novel partners, but remarkably strengthens social avoidance under an acute psychosocial stress triggered by social rank. Notably, a significantly increased orexin level in VP is accompanied by an increase in serum corticosterone in animals exposed to acute stresses, including forced swimming, food/water deprivation and social rank stress, rather than non-stress situations. These results suggest that endogenous orexinergic modulation on VP is especially critical for protecting against depressive reactions to stressful events. The findings define an indispensable role for the central orexinergic system in preventing depression by promoting stress resilience.

Histamine Excites Rat GABAergic Ventral Pallidum Neurons via Co-activation of H1 and H2 Receptors.

The ventral pallidum (VP) is a crucial component of the limbic loop of the basal ganglia and participates in the regulation of reward, motivation, and emotion. Although the VP receives afferent inputs from the central histaminergic system, little is known about the effect of histamine on the VP and the underlying receptor mechanism. Here, we showed that histamine, a hypothalamic-derived neuromodulator, directly depolarized and excited the GABAergic VP neurons which comprise a major cell type in the VP and are responsible for encoding cues of incentive salience and reward hedonics. Both postsynaptic histamine H1 and H2 receptors were found to be expressed in the GABAergic VP neurons and co-mediate the excitatory effect of histamine. These results suggested that the central histaminergic system may actively participate in VP-mediated motivational and emotional behaviors via direct modulation of the GABAergic VP neurons. Our findings also have implications for the role of histamine and the central histaminergic system in psychiatric disorders.

Hippocampal PPARδ Overexpression or Activation Represses Stress-Induced Depressive Behaviors and Enhances Neurogenesis.

BACKGROUND: Emerging data have demonstrated that peroxisome proliferator-activated receptor δ (PPARδ) activation confers a potentially neuroprotective role in some neurodegenerative diseases. However, whether PPARδ is involved in depression is unknown. METHODS: In this study, PPARδ was firstly investigated in the chronic mild stress (CMS) and learned helplessness (LH) models of depression. The changes in depressive behaviors and hippocampal neurogenesis were investigated after PPARδ overexpression by microinfusion of the lentiviral vector, containing the coding sequence of mouse PPARδ (LV-PPARδ), into the bilateral dentate gyri of the hippocampus or PPARδ activation by repeated systemic administration of PPARδ agonist GW0742 (5 or 10mg/kg.d, i.p., for 21 d). RESULTS: We found that both CMS and LH resulted in a significant decrease in the PPARδ expression in the hippocampi of mice, and this change was reversed by treatment with the antidepressant fluoxetine. PPARδ overexpression and PPARδ activation each suppressed the CMS- and LH-induced depressive-like behavior and produced an antidepressive effect. In vivo or in vitro studies also showed that both overexpression and activation of PPARδ enhanced proliferation or differentiation of neural stem cells in the hippocampi of mice. CONCLUSIONS: These results suggest that hippocampal PPARδ upregulation represses stress-induced depressive behaviors, accompanied by enhancement of neurogenesis.

Protective effect of pranlukast on Aß1₋42-induced cognitive deficits associated with downregulation of cysteinyl leukotriene receptor 1.

Deposition of extracellular amyloid-ß (Aß) peptide is one of the pathological hallmarks of Alzheimer's disease (AD). Accumulation of Aß is thought to associate with cognition deficits, neuroinflammation and apoptosis observed in AD. However, effective neuroprotective approaches against Aß neurotoxicity are unavailable. In the present study, we analysed the effects of pranlukast, a selective cysteinyl leukotriene receptor 1 (CysLT1R) antagonist, on the impairment of learning and memory formation induced by Aß and the probable underlying electrophysiological and molecular mechanisms. We found that bilateral intrahippocampal injection of Aß1₋42 resulted in a significant decline of spatial learning and memory of mice in the Morris water maze (MWM) and Y-maze tests, together with a serious depression of in vivo hippocampal long-term potentiation (LTP) in the CA1 region of the mice. Importantly, this treatment caused significant increases in CysLT1R expression and subsequent NF-κB signaling, caspase-3 activation and Bcl-2 downregulation in the hippocampus or prefrontal cortex. Oral administration of pranlukast at 0.4 or 0.8 mg/kg for 4 wk significantly reversed Aß1₋42-induced impairments of cognitive function and hippocampal LTP in mice. Furthermore, pranlukast reversed Aß1₋42-induced CysLT1R upregulation, and markedly suppressed the Aß1₋42-triggered NF-κB pathway, caspase-3 activation and Bcl-2 downregulation in the hippocampus and prefrontal cortex in mice. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay confirmed its presence in the brain after oral administration of pranlukast in mice. These data disclose novel findings about the therapeutic potential of pranlukast, revealing a previously unknown therapeutic possibility to treat memory deficits associated with AD.

Involvement of cysteinyl leukotriene receptor 1 in Aß1-42-induced neurotoxicity in vitro and in vivo.

Accumulation of amyloid-ß (Aß) is thought to be associated with the progressive neuronal death observed in Alzheimer's disease, but the mechanisms underlying neurotoxicity triggered by Aß remain elusive. In the current study, we investigated the roles of cysteinyl leukotriene receptor 1 (CysLT1R) in Aß1-42-induced neurotoxicity in vitro or in vivo. In vitro exposure of mouse primary neurons to Aß1-42 caused a gradual increases in CysLT1R expression. In vivo bilateral intrahippocampal injection of Aß1-42 also elicited time-dependent increases of CysLT1R expression in the hippocampus and cortex of mice. The CysLT1R antagonist pranlukast not only reversed Aß1-42-induced upregulation of CysLT1R, but also suppressed Aß1-42-triggered neurotoxicity evidenced by enhanced nuclear factor-kappa B p65, activated caspase-3, decreased B-cell lymphoma-2 and cell viability and impaired memory. Furthermore, chronic treatment with pranlukast produced similar beneficial effects on memory behavior and hippocampal long-term potentiation to memantine or donepezil in intrahippocampal Aß1-42-injected mice. Our data indicate that CysLT1R is involved in Aß1-42-induced neurotoxicity, and that blockade of CysLT1R, such as application of CysLT1R antagonist, could be a novel and promising strategy for the treatment of Alzheimer's disease.