Noradrenaline acting on astrocytic β2-adrenoceptors induces neurite outgrowth in primary cortical neurons

Estrogen-immuno-neuromodulation disorders in menopausal depression

A significant decrease in estrogen levels puts menopausal women at high risk for major depression, which remains difficult to cure despite its relatively clear etiology. With the discovery of abnormally elevated inflammation in menopausal depressed women, immune imbalance has become a novel focus in the study of menopausal depression. In this paper, we examined the characteristics and possible mechanisms of immune imbalance caused by decreased estrogen levels during menopause and found that estrogen deficiency disrupted immune homeostasis, especially the levels of inflammatory cytokines through the ERα/ERβ/GPER-associated NLRP3/NF-κB signaling pathways. We also analyzed the destruction of the blood-brain barrier, dysfunction of neurotransmitters, blockade of BDNF synthesis, and attenuation of neuroplasticity caused by inflammatory cytokine activity, and investigated estrogen-immuno-neuromodulation disorders in menopausal depression. Current research suggests that drugs targeting inflammatory cytokines and NLRP3/NF-κB signaling molecules are promising for restoring homeostasis of the estrogen-immuno-neuromodulation system and may play a positive role in the intervention and treatment of menopausal depression.

Ablation of specific long PDE4D isoforms increases neurite elongation and conveys protection against amyloid-β pathology

Inhibition of phosphodiesterase 4D (PDE4D) enzymes has been investigated as therapeutic strategy to treat memory problems in Alzheimer's disease (AD). Although PDE4D inhibitors are effective in enhancing memory processes in rodents and humans, severe side effects may hamper their clinical use. PDE4D enzymes comprise different isoforms, which, when targeted specifically, can increase treatment efficacy and safety. The function of PDE4D isoforms in AD and in molecular memory processes per se has remained unresolved. Here, we report the upregulation of specific PDE4D isoforms in transgenic AD mice and hippocampal neurons exposed to amyloid-β. Furthermore, by means of pharmacological inhibition and CRISPR-Cas9 knockdown, we show that the long-form PDE4D3, -D5, -D7, and -D9 isoforms regulate neuronal plasticity and convey resilience against amyloid-β in vitro. These results indicate that isoform-specific, next to non-selective, PDE4D inhibition is efficient in promoting neuroplasticity in an AD context. Therapeutic effects of non-selective PDE4D inhibitors are likely achieved through actions on long isoforms. Future research should identify which long PDE4D isoforms should be specifically targeted in vivo to both improve treatment efficacy and reduce side effects.

Clenbuterol Treatment Is Safe and Associated With Slowed Disease Progression in a Small Open-Label Trial in Patients With Amyotrophic Lateral Sclerosis

OBJECTIVE

Clenbuterol, a beta-agonist, has plausible mechanisms for treating amyotrophic lateral sclerosis (ALS). In this highly inclusive open-label trial (NCT04245709), we aimed to study the safety and efficacy of clenbuterol in patients with ALS.

METHODS

All participants received clenbuterol starting at 40 μg daily and increased to 80 μg twice daily. Outcomes included safety, tolerability, ALS Functional Rating Score (ALSFRS-R) progression, forced vital capacity (FVC) progression, and myometry. ALSFRS-R and FVC slopes measured during treatment were compared with slopes before treatment (calculated by assuming ALSFRS-R was 48 and FVC was 100% at ALS onset).

RESULTS

The 25 participants had a mean age of 59, mean disease duration of 43 months, ALSFRS-R score at enrollment 34, and FVC at enrollment 77%. Forty-eight percent were female, 68% were taking riluzole, and none were taking edaravone. Two participants experienced severe adverse events, neither related to the study. Twenty-four participants experienced adverse events, most commonly tremors/jitters, cramps/spasms, insomnia, and stiffness/spasticity. Fourteen participants withdrew early from the trial, 13 due to adverse events. Patients who withdrew early were significantly older and more likely to be male. Per-protocol and intention-to-treat analyses showed meaningfully slower ALSFRS-R and FVC progression during treatment. Hand grip dynamometry and myometry changes were highly variable between participants; most declined slowly, but some showed improvements.

CONCLUSIONS

Clenbuterol was safe but less tolerable at the doses we selected compared with an earlier Italian case series. Consistent with that series, our study suggested benefits on ALS progression. However, the latter result should be interpreted with caution as our study is limited by small sample size, large drop out, lack of randomization, and blinding and placebo controls. A larger, more traditional trial now seems warranted.

GDNF promotes the proliferation and osteogenic differentiation of jaw bone marrow mesenchymal stem cells via the Nr4a1/PI3K/Akt pathway

How to efficiently regenerate jawbone defects caused by trauma, jaw osteomyelitis, tumors, or intrinsic genetic diseases is still challenging. Ectoderm-derived jawbone defect has been reported to be regenerated by selectively recruiting cells from its embryonic origin. Therefore, it is important to explore the strategy for promoting ectoderm-derived jaw bone marrow mesenchymal stem cells (JBMMSCs) on the repair of homoblastic jaw bone. Glial cell-derived neurotrophic factor (GDNF) is an important growth factor and is essential in the process of proliferation, migration and differentiation of nerve cells. However, whether GDNF promoting the function of JBMMSCs and the relative mechanism are not clear. Our results showed that activated astrocytes and GDNF were induced in the hippocampus after mandibular jaw defect. In addition, the expression of GDNF in the bone tissue around the injured area was also significantly increased after injury. Data from in vitro experiments demonstrated that GDNF could effectively promote the proliferation and osteogenic differentiation of JBMMSCs. Furthermore, when implanted in the defected jaw bone, JBMMSCs pretreated with GDNF exhibited enhanced repair effect compared with JBMMSCs without treatment. Mechanical studies found that GDNF induced the expression of Nr4a1 in JBMMSCs, activated PI3K/Akt signaling pathway and then enhanced the proliferation and osteogenic differentiation capacities of JBMMSCs. Our studies reveal that JBMMSCs are good candidates for repairing jawbone injury and pretreated with GDNF is an efficient strategy for enhancing bone regeneration.

The β-adrenergic hypothesis of synaptic and microglial impairment in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease originating partly from amyloid β protein-induced synaptic failure. As damaging of noradrenergic neurons in the locus coeruleus (LC) occurs at the prodromal stage of AD, activation of adrenergic receptors could serve as the first line of defense against the onset of the disease. Activation of β₂ -ARs strengthens long-term potentiation (LTP) and synaptic activity, thus improving learning and memory. Physical stimulation of animals exposed to an enriched environment (EE) leads to the activation of β₂ -ARs and prevents synaptic dysfunction. EE also suppresses neuroinflammation, suggesting that β₂ -AR agonists may play a neuroprotective role. The β₂ -AR agonists used for respiratory diseases have been shown to have an anti-inflammatory effect. Epidemiological studies further support the beneficial effects of β₂ -AR agonists on several neurodegenerative diseases. Thus, I propose that β₂ -AR agonists may provide therapeutic value in combination with novel treatments for AD.

Effect of risperidone on serum IL-6 levels in individuals with schizophrenia: a systematic review and meta-analysis

BACKGROUND

Risperidone has been significant correlated with a direct effect of interleukin-6 (IL-6) levels in patients with schizophrenia. This fact allows the opportunity to link the probable immunomodulatory effect of antipsychotic medication. Specially, a proper functioning of IL-6 pathway plays a potential role in the treatment or development of schizophrenia.

OBJECTIVE

Our primary aim was to perform a systematic review and meta-analysis to determine the effect of risperidone on IL-6 levels in individuals with schizophrenia.

METHODS

Studies were identified through a systematic search using PubMed, Scopus, and Web of Science databases. The articles found were subjected to the inclusion and exclusion criteria; then, the mean and standardised differences were extracted to calculate the standardised mean differences using the CMA software.

RESULTS

IL-6 levels in individuals with schizophrenia were compared before and after receiving risperidone as treatment. Increased levels of IL-6 levels were observed in individuals with schizophrenia who received risperidone (point estimate 0.249, lower limit 0.042, upper limit 0.455, p-value 0.018). In the Asian population sub-analysis, no statistically significant differences were observed (point estimate 0.103, lower limit -0.187, upper limit 0.215, p value 0.890). When we compared individuals with schizophrenia to the control groups, a significant increase of IL-6 levels was observed in the group with schizophrenia (point estimate 0.248, lower limit 0.024, upper limit 0.472, p-value 0.30).

CONCLUSIONS

Risperidone appears to play an important role in IL-6 levels in schizophrenia. Potential implications of increased IL-6 levels in people with schizophrenia should be considered in future studies.KEY POINTSIncreased levels of IL-6 levels were observed in individuals with schizophrenia who received risperidone.Risperidone appears to play an important role in IL-6 levels in schizophrenia.This study could serve for future research focussed on IL-6.

Dopamine regulates astrocytic IL-6 expression and process formation via dopamine receptors and adrenoceptors

Dopamine levels in the central nervous system change under pathological conditions such as Parkinson's disease, Huntington's disease, and addiction. Under those pathological conditions, astrocytes become reactive astrocytes characterized by morphological changes and the release of inflammatory cytokines involved in pathogenesis. However, it remains unclear whether dopamine regulates astrocytic morphology and functions. Elucidating these issues will help us to understand the pathogenesis of neurodegenerative diseases caused by abnormal dopamine signaling. In this study, we investigated the effects of dopamine on IL-6 expression and process formation in rat primary cultured astrocytes and acute hippocampal slices. Dopamine increased IL-6 expression in a concentration-dependent manner, and this was accompanied by CREB phosphorylation. The effects of a low dopamine concentration (1 μM) were inhibited by a D1-like receptor antagonist, whereas the effects of a high dopamine concentration (100 μM) were inhibited by a β-antagonist and enhanced by a D2-like receptor antagonist. Furthermore, dopamine (100 μM) promoted process formation, which was inhibited by a β-antagonist and enhanced by both an α-antagonist and a D2-like receptor antagonist. In acute hippocampal slices, both a D1-like receptor agonist and β-agonist changed astrocytic morphology. Together, these results indicate that dopamine promotes IL-6 expression and process formation via D1-like receptors and β-adrenoceptors. Furthermore, bidirectional regulation exists; namely, the effects of D1-like receptors and β-adrenoceptors were negatively regulated by D2-like receptors and α₂-adrenoceptors.

Noradrenaline in Alzheimer's Disease: A New Potential Therapeutic Target

A growing body of evidence demonstrates the important role of the noradrenergic system in the pathogenesis of many neurodegenerative processes, especially Alzheimer’s disease, due to its ability to control glial activation and chemokine production resulting in anti-inflammatory and neuroprotective effects. Noradrenaline involvement in this disease was first proposed after finding deficits of noradrenergic neurons in the locus coeruleus from Alzheimer’s disease patients. Based on this, it has been hypothesized that the early loss of noradrenergic projections and the subsequent reduction of noradrenaline brain levels contribute to cognitive dysfunctions and the progression of neurodegeneration. Several studies have focused on analyzing the role of noradrenaline in the development and progression of Alzheimer’s disease. In this review we summarize some of the most relevant data describing the alterations of the noradrenergic system normally occurring in Alzheimer’s disease as well as experimental studies in which noradrenaline concentration was modified in order to further analyze how these alterations affect the behavior and viability of different nervous cells. The combination of the different studies here presented suggests that the maintenance of adequate noradrenaline levels in the central nervous system constitutes a key factor of the endogenous defense systems that help prevent or delay the development of Alzheimer’s disease. For this reason, the use of noradrenaline modulating drugs is proposed as an interesting alternative therapeutic option for Alzheimer’s disease.

Stress-Induced Depression and Alzheimer's Disease: Focus on Astrocytes

Neurodegenerative diseases and depression are multifactorial disorders with a complex and poorly understood physiopathology. Astrocytes play a key role in the functioning of neurons in norm and pathology. Stress is an important factor for the development of brain disorders. Here, we review data on the effects of stress on astrocyte function and evidence of the involvement of astrocyte dysfunction in depression and Alzheimer's disease (AD). Stressful life events are an important risk factor for depression; meanwhile, depression is an important risk factor for AD. Clinical data indicate atrophic changes in the same areas of the brain, the hippocampus and prefrontal cortex (PFC), in both pathologies. These brain regions play a key role in regulating the stress response and are most vulnerable to the action of glucocorticoids. PFC astrocytes are critically involved in the development of depression. Stress alters astrocyte function and can result in pyroptotic death of not only neurons, but also astrocytes. BDNF-TrkB system not only plays a key role in depression and in normalizing the stress response, but also appears to be an important factor in the functioning of astrocytes. Astrocytes, being a target for stress and glucocorticoids, are a promising target for the treatment of stress-dependent depression and AD.

Alpha and beta adrenoceptors activate interleukin-6 transcription through different pathways in cultured astrocytes from rat spinal cord

In brain astrocytes, noradrenaline (NA) has been shown to up-regulate IL-6 production via β-adrenoceptors (ARs). However, the underlying intracellular mechanisms for this regulation are not clear, and it remains unknown whether α-ARs are involved. In this study, we investigated the AR-mediated regulation of IL-6 mRNA levels in the cultured astrocytes from rat spinal cord. NA, the α1-agonist phenylephrine, and the β-agonist isoproterenol increased IL-6 mRNA levels. The phenylephrine-induced IL-6 increase was accompanied by an increase in ERK phosphorylation, and these effects were blocked by inhibitors of PKC and ERK. The isoproterenol-induced IL-6 increase was accompanied by an increase in CREB phosphorylation, and these effects were blocked by a PKA inhibitor. Our results indicate that IL-6 increases by α1- and β-ARs are mediated via the PKC/ERK and cAMP/PKA/CREB pathways, respectively. Moreover, conditioned medium collected from astrocytes treated with the α2-AR agonist dexmedetomidine, increased IL-6 mRNA in other astrocytes. In this study, we elucidate that α1- and α2-ARs, in addition to β-ARs, promote IL-6 transcription through different pathways in spinal cord astrocytes.

On inflammatory hypothesis of depression: what is the role of IL-6 in the middle of the chaos?

Many patients with major depressive disorder (MDD) are reported to have higher levels of multiple inflammatory cytokines including interleukin 6 (IL-6). Recent studies both pre-clinical and clinical have advocated for the functional role of IL-6 in development of MDD and suggested a great potential for targeting this cytokine to open new avenues in pharmacotherapy of depression. The purpose of the present narrative review was to provide an integrated account of how IL-6 may contribute to development of depression. All peer-reviewed journal articles published before July 2020 for each area discussed were searched by WOS, PubMed, MEDLINE, Scopus, Google Scholar, for original research, review articles, and book chapters. Publications between 1980 and July 2020 were included. Alterations in IL-6 levels, both within the periphery and the brain, most probably contribute to depression symptomatology in numerous ways. As IL-6 acts on multiple differing target tissues throughout the body, dysregulation of this particular cytokine can precipitate a multitude of events relevant to depression and blocking its effects can prevent further escalation of inflammatory responses, and potentially pave the way for opening new avenues in diagnosis, treatment, and prevention of this debilitating disorder.

Dl-3-n-butylphthalide promotes neurite outgrowth of primary cortical neurons by Sonic Hedgehog signaling via upregulating Gap43

Neurite outgrowth is the basis for wiring during the development of the nervous system. Dl-3-n-butylphthalide (NBP) has been recognized as a promising treatment to improve behavioral, neurological and cognitive outcomes in ischemic stroke. However, little is known about the effect and mechanism of NBP on the neurite outgrowth. In this study, we used different methods to investigate the potential effects of NBP on the neurite extension and plasticity of immature and mature primary cortical neurons and explored the underlying mechanisms. Our results demonstrated that in immature and mature cortical neurons, NBP promoted the neurite length and intersections, increased neuritic arborization, elevated numbers of neurite branch and terminal points and improved neurite complexity and plasticity of neuronal development processes. Besides, our data revealed that NBP promoted neurite extension and branching partly by activating Shh signaling pathway via increasing Gap43 expression both in immature and mature primary cortical neurons. The present study provided new insights into the contribution of NBP in neuronal plasticity and unveiled a novel pathway to induce Gap43 expression in primary cortical neurons.

Neonatal therapy with clenbuterol and salmeterol restores spinogenesis and dendritic complexity in the dentate gyrus of the Ts65Dn model of Down syndrome

Down syndrome (DS), a neurodevelopmental disorder caused by triplication of chromosome 21, is characterized by intellectual disability. In DS, defective neurogenesis causes an overall reduction in the number of neurons populating the brain and defective neuron maturation causes dendritic hypotrophy and reduction in the density of dendritic spines. No effective therapy currently exists for the improvement of brain development in individuals with DS. Drug repurposing is a strategy for identifying new medical use for approved drugs. A drug screening campaign showed that the β2-adrenergic receptor (β2-AR) agonists clenbuterol hydrochloride (CLEN) and salmeterol xinafoate (SALM) increase the proliferation rate of neural progenitor cells from the Ts65Dn model of DS. The goal of the current study was to establish their efficacy in vivo, in the Ts65Dn model. We found that, at variance with the in vitro experiments, treatment with CLEN or SALM did not restore neurogenesis in the hippocampus of Ts65Dn mice treated during the postnatal (P) period P3-P15. In Ts65Dn mice treated with CLEN or SALM, however, dendritic spine density and dendritic arborization of the hippocampal granule cells were restored and the lowest dose tested here (0.01 mg/kg/day) was sufficient to elicit these effects. CLEN and SALM are used in children as therapy for asthma and, importantly, they pass the blood-brain barrier. Our study suggests that treatment with these β2-AR agonists may be a therapy of choice in order to correct dendritic development in DS but is not suitable to rescue neurogenesis.

Norepinephrine upregulates the expression of tyrosine hydroxylase and protects dopaminegic neurons against 6-hydrodopamine toxicity

As a classic neurotransmitter in the brain, norepinephrine (NE) also is an important modulator to other neuronal systems. Using primary cultures from rat ventral mesencephalon (VM) and dopaminergic cell line MN9D, the present study examined the neuroprotective effects of NE and its effects on the expression of tyrosine hydroxylase (TH). The results showed that NE protected both VM cultures and MN9D cells against 6-hydroxydopamine-caused apoptosis, with possible involvement of adrenal receptors. In addition, treatment with NE upregulated TH protein levels in dose- and time-dependent manner. Further experiments to investigate the potential mechanisms underlying this NE-induced upregulation of TH demonstrated a marked increase in protein levels of the brain-derived neurotrophic factor (BDNF) and the phosphorylated extracellular signal-regulated protein kinase 1 and 2 (pERK1/2) in VM cultures treated with NE. In MN9D cells, a significantly increase of TH and pERK1/2 protein levels were observed after their transfection with BDNF cDNA or exposure to BDNF peptides. Treatment of VM cultures with K252a, an antagonist of the tropomyosin-related kinase B, blocked the upregulatory effects of NE on TH, BDNF and pERK1/2. Administration of MEK1 & MEK2 inhibitors also reversed NE-induced upregulation of TH and pERK1/2. Moreover, ChIP assay showed that treatment with NE or BDNF increased H4 acetylation in the TH promoter. These results suggest that the neuroprotection and modulation of NE on dopaminergic neurons are mediated via BDNF and MAPK/ERK pathways, as well as through epigenetic histone modification, which may have implications for the improvement of therapeutic strategies for Parkinson's disease.

Inhibitors of the NMDA-Nitric Oxide Signaling Pathway Protect Against Neuronal Atrophy and Synapse Loss Provoked by l-alpha Aminoadipic Acid-treated Astrocytes

The impact of treating astrocytes with the astrocytic toxin l-alpha amino adipic acid (L-AAA) on neuronal outgrowth, complexity and synapse formation was assessed, using a model of astrocyte-neuronal interaction. Treatment of rat primary cortical neurons with conditioned media (CM) derived from astrocytes treated with L-AAA reduced neuronal complexity and synapse formation. L-AAA provoked a reduction in the expression of glial fibrillary acid protein (GFAP) and a reduction in ATP-linked mitochondrial respiration in astrocytic cells. As the NMDA-R/PSD-95/NOS signaling pathway is implicated in regulating the structural plasticity of neurons, treatment of neuronal cultures with the neuronal nitric oxide synthase (nNOS) inhibitor 1-[2-(trifluoromethyl)phenyl] imidazole (TRIM) [100 nM] was assessed and observed to protect against L-AAA-treated astrocytic CM-induced reduction in neuronal complexity and synapse loss. Treatment with the NMDA-R antagonist ketamine protected against the CM-induced loss of synapse formation whereas the novel PSD-95/nNOS inhibitors 2-((1H-benzo[d] [1,2,3]triazol-5-ylamino) methyl)-4,6-dichlorophenol (IC87201) and 4-(3,5-dichloro-2-hydroxy-benzylamino)-2-hydroxybenzoic acid (ZL006) protected against synapse loss with partial protection against reduced neurite outgrowth. Furthermore, L-AAA delivery to the pre-limbic cortex (PLC) of mice was found to increase dendritic spine density and treatment with ZL006 reduced this effect. In summary, L-AAA-induced astrocyte impairment leads to a loss of neuronal complexity and synapse loss in vitro and increased dendritic spine density in vivo that may be reversed by inhibitors of the NMDA-R/PSD-95/NOS pathway. The results have implications for understanding astrocytic-neuronal interaction and the search for drug candidates that may provide therapeutic approaches for brain disorders associated with astrocytic histopathology.

Interleukin-6 in Schizophrenia-Is There a Therapeutic Relevance?

Renewing interest in immune aspects of schizophrenia and new findings about the brain-fat axis encourage us to discuss the possible role of interleukin-6 (IL-6) in schizophrenia. Previously, it was suggested that a primary alteration of the innate immune system may be relevant in schizophrenia. Functional dichotomy of IL-6 suggests that this chemical messenger may be responsible for regulating the balance between pro- and anti-inflammatory responses, with tissue-specific properties at the periphery and in the central nervous system. Specific phase of this chronic and deteriorating disorder must be considered, which can involve IL-6 in acute or possible chronic inflammation and/or autoimmunity. We give an overview of IL-6 role in the onset and progression of this disorder, also considering cognitive impairment and metabolic changes in patients with schizophrenia. Data suggest that decreased serum level of IL-6 following antipsychotic therapy could be predisposing factor for the development of obesity and obesity-related metabolic disorders in schizophrenia. As we reviewed, the IL-6 plays significant role in disease genesis and progression, so the use of specific inhibitors may not only be beneficial for exacerbation and alleviation of positive symptoms, but may attenuate cognitive impairment in patients with schizophrenia.

Dopamine cross-reacts with adrenoreceptors in cortical astrocytes to induce BDNF expression, CREB signaling and morphological transformation

Expression of brain-derived neurotrophic factor (BDNF) is induced in cultured rat cortical astrocytes by catecholamines norepinephrine and dopamine as well as selective α1 and β adrenergic agonists. However, it has remained unknown which receptors mediate dopamine-induced BDNF upregulation in astrocytes. Here, we demonstrate that β adrenoreceptors are the main mediators of this effect in cultured cortical astrocytes, while α1 adrenoreceptors and D1 dopamine receptors contribute to a lesser extent. We show that in cortical astrocytes BDNF exon IV and exon VI containing mRNAs are induced by dopamine and norepinephrine via CREB-dependent signaling and that this regulation is mediated by a mechanism that is distinct from activity-dependent CREB-mediated activation of BDNF transcription in neurons. We also show that regulation of BDNF promoters IV and VI by catecholamines requires a distal regulatory element in the BDNF locus. Finally, we demonstrate that dopamine-induced astrocyte stellation and induction of CREB signaling are mediated by cross-reaction of dopamine with β adrenoreceptors.

Noradrenergic antagonists mitigate amphetamine-induced recovery

Brain injury, including that due to stroke, leaves individuals with cognitive deficits that can disrupt daily aspect of living. As of now there are few treatments that shown limited amounts of success in improving functional outcome. The use of stimulants such as amphetamine have shown some success in improving outcome following brain injury. While the pharmacological mechanisms for amphetamine are known; the specific processes responsible for improving behavioral outcome following injury remain unknown. Understanding these mechanisms can help to refine the use of amphetamine as a potential treatment or lead to the use of other methods that share the same pharmacological properties. One proposed mechanism is amphetamine's impact upon noradrenaline (NA). In the current, study noradrenergic antagonists were administered prior to amphetamine to pharmacologically block α- and β-adrenergic receptors. The results demonstrated that the blockade of these receptors disrupted amphetamines ability to induce recovery from hemispatial neglect using an established aspiration lesion model. This suggests that amphetamine's ability to ameliorate neglect deficits may be due in part to noradrenaline. These results further support the role of noradrenaline in functional recovery. Finally, the development of polytherapies and combined therapeutics, while promising, may need to consider the possibility that drug interactions can negate the effectiveness of treatment.

Inhibition of the kynurenine pathway protects against reactive microglial-associated reductions in the complexity of primary cortical neurons

Brain glia possess the rate limiting enzyme indoleamine 2, 3-dioxygenase (IDO) which catalyses the conversion of tryptophan to kynurenine. Microglia also express kynurenine monooxygenase (KMO) and kynureninase (KYNU) which lead to the production of the free radical producing metabolites, 3-hydroxykynurenine and 3-hydroxyanthranillic acid respectively and subsequently production of the NMDA receptor agonist quinolinic acid. The aim of this study was to examine the effect of IFNγ-stimulated kynurenine pathway (KP) induction in microglia on neurite outgrowth and complexity, and to determine whether alterations could be abrogated using pharmacological inhibitors of the KP. BV-2 microglia were treated with IFNγ (5ng/ml) for 24h and conditioned media (CM) was placed on primary cortical neurons 3 days in vitro (DIV) for 48h. Neurons were fixed and neurite outgrowth and complexity was assessed using fluorescent immunocytochemistry followed by Sholl analysis. Results show increased mRNA expression of IDO, KMO and KYNU, and increased concentrations of tryptophan, kynurenine, and 3-hydroxykynurenine in the CM of IFNγ-stimulated BV-2 microglia. The IFNγ-stimulated BV-2 microglial CM reduced neurite outgrowth and complexity with reductions in various parameters of neurite outgrowth prevented when BV-2 microglia were pre-treated with either the IDO inhibitor, 1-methyltryptophan (1-MT) (L) (0.5mM; 30min), the KMO inhibitor, Ro 61-8048 (1μM; 30min), the synthetic glucocorticoid, dexamethasone (1μM; 2h) -which suppresses IFNγ-induced IDO - and the N-methyl-D-aspartate (NMDA) receptor antagonist, MK801 (0.1μM; 30min). Overall this study indicates that inhibition of the KP in microglia may be targeted to protect against reactive microglial-associated neuronal atrophy.

The Proliferation Enhancing Effects of Salidroside on Schwann Cells In Vitro

Derived from Rhodiola rosea L., which is a popular plant in Eastern Europe and Asia, salidroside has pharmacological properties including antiviral, anticancer, hepatoprotective, antidiabetic, and antioxidative effects. Recent studies show that salidroside has neurotrophic and neuroprotective effects. However, the effect of salidroside on Schwann cells (SCs) and the underlying mechanisms of the salidroside-induced neurotrophin secretion have seldom been studied. In this study, the effect of salidroside on the survival, proliferation, and gene expression of Schwann cells lineage (RSC96) was studied through the examinations of the cell viability, proliferation, morphology, and expression of neurotrophic factor related genes including BDNF, GDNF, and CDNF at 2, 4, and 6 days, respectively. These results showed that salidroside significantly enhanced survival and proliferation of SCs. The underlying mechanism might involve that salidroside affected SCs growth through the modulation of several neurotrophic factors including BDNF, GDNF, and CDNF. As for the concentration, 0.4 mM, 0.2 mM, and 0.1 mM of salidroside were recommended, especially 0.2 mM. This investigation indicates that salidroside is capable of enhancing SCs survival and function in vitro, which highlights the possibility that salidroside as a drug agent to promote nerve regeneration in cellular nerve scaffold through salidroside-induced neurotrophin secretion in SCs.

Dammarane Sapogenins Ameliorates Neurocognitive Functional Impairment Induced by Simulated Long-Duration Spaceflight

Increasing evidence indicates the occurrence of cognitive impairment in astronauts under spaceflight compound conditions, but the underlying mechanisms and countermeasures need to be explored. In this study, we found that learning and memory abilities were significantly reduced in rats under a simulated long-duration spaceflight environment (SLSE), which includes microgravity, isolation confinement, noises, and altered circadian rhythms. Dammarane sapogenins (DS), alkaline hydrolyzed products of ginsenosides, can enhance cognition function by regulating brain neurotransmitter levels and inhibiting SLSE-induced neuronal injury. Bioinformatics combined with experimental verification identified that the PI3K-Akt-mTOR pathway was inhibited and the MAPK pathway was activated during SLSE-induced cognition dysfunction, whereas DS substantially ameliorated the changes in brain. These findings defined the characteristics of SLSE-induced cognitive decline and the mechanisms by which DS improves it. The results provide an effective candidate for improving cognitive function in spaceflight missions.

Role of glial cell line-derived neurotrophic factor in the pathogenesis and treatment of mood disorders

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a survival factor for dopaminergic neurons, but GDNF has also been shown to promote development, differentiation, and protection of other central nervous system neurons and was thought to play an important role in various neuropsychiatric disorders. Severe mood disorders, such as primarily major depressive disorder and bipolar affective disorder, attract particular attention. These psychopathologies are characterized by structural alterations accompanied by the dysregulation of neuroprotective and neurotrophic signaling mechanisms required for the maturation, growth, and survival of neurons and glia. The main objective of this review is to summarize the recent findings and evaluate the potential role of GDNF in the pathogenesis and treatment of mood disorders. Specifically, it describes (1) the implication of GDNF in the mechanism of depression and in the effect of antidepressant drugs and mood stabilizers and (2) the interrelation between GDNF and brain neurotransmitters, playing a key role in the pathogenesis of depression. This review provides converging lines of evidence that (1) brain GDNF contributes to the mechanism underlying depressive disorders and the effect of antidepressants and mood stabilizers and (2) there is a cross-talk between GDNF and neurotransmitters representing a feedback system: GDNF-neurotransmitters and neurotransmitters-GDNF.

Modulation of neuroinflammation and pathology in the 5XFAD mouse model of Alzheimer's disease using a biased and selective beta-1 adrenergic receptor partial agonist

Degeneration of noradrenergic neurons occurs at an early stage of Alzheimer's Disease (AD). The noradrenergic system regulates arousal and learning and memory, and has been implicated in regulating neuroinflammation. Loss of noradrenergic tone may underlie AD progression at many levels. We have previously shown that acute administration of a partial agonist of the beta-1 adrenergic receptor (ADRB1), xamoterol, restores behavioral deficits in a mouse model of AD. The current studies examined the effects of chronic low dose xamoterol on neuroinflammation, pathology, and behavior in the pathologically aggressive 5XFAD transgenic mouse model of AD. In vitro experiments in cells expressing human beta adrenergic receptors demonstrate that xamoterol is highly selective for ADRB1 and functionally biased for the cAMP over the β-arrestin pathway. Data demonstrate ADRB1-mediated attenuation of TNF-α production with xamoterol in primary rat microglia culture following LPS challenge. Finally, two independent cohorts of 5XFAD and control mice were administered xamoterol from approximately 4.0-6.5 or 7.0-9.5 months, were tested in an array of behavioral tasks, and brains were examined for evidence of neuroinflammation, and amyloid beta and tau pathology. Xamoterol reduced mRNA expression of neuroinflammatory markers (Iba1, CD74, CD14 and TGFβ) and immunohistochemical evidence for microgliosis and astrogliosis. Xamoterol reduced amyloid beta and tau pathology as measured by regional immunohistochemistry. Behavioral deficits were not observed for 5XFAD mice. In conclusion, chronic administration of a selective, functionally biased, partial agonist of ADRB1 is effective in reducing neuroinflammation and amyloid beta and tau pathology in the 5XFAD model of AD.

Locus Ceruleus Norepinephrine Release: A Central Regulator of CNS Spatio-Temporal Activation?

Norepinephrine (NE) is synthesized in the Locus Coeruleus (LC) of the brainstem, from where it is released by axonal varicosities throughout the brain via volume transmission. A wealth of data from clinics and from animal models indicates that this catecholamine coordinates the activity of the central nervous system (CNS) and of the whole organism by modulating cell function in a vast number of brain areas in a coordinated manner. The ubiquity of NE receptors, the daunting number of cerebral areas regulated by the catecholamine, as well as the variety of cellular effects and of their timescales have contributed so far to defeat the attempts to integrate central adrenergic function into a unitary and coherent framework. Since three main families of NE receptors are represented-in order of decreasing affinity for the catecholamine-by: α2 adrenoceptors (α2Rs, high affinity), α1 adrenoceptors (α1Rs, intermediate affinity), and β adrenoceptors (βRs, low affinity), on a pharmacological basis, and on the ground of recent studies on cellular and systemic central noradrenergic effects, we propose that an increase in LC tonic activity promotes the emergence of four global states covering the whole spectrum of brain activation: (1) sleep: virtual absence of NE, (2) quiet wake: activation of α2Rs, (3) active wake/physiological stress: activation of α2- and α1-Rs, (4) distress: activation of α2-, α1-, and β-Rs. We postulate that excess intensity and/or duration of states (3) and (4) may lead to maladaptive plasticity, causing-in turn-a variety of neuropsychiatric illnesses including depression, schizophrenic psychoses, anxiety disorders, and attention deficit. The interplay between tonic and phasic LC activity identified in the LC in relationship with behavioral response is of critical importance in defining the short- and long-term biological mechanisms associated with the basic states postulated for the CNS. While the model has the potential to explain a large number of experimental and clinical findings, a major challenge will be to adapt this hypothesis to integrate the role of other neurotransmitters released during stress in a centralized fashion, like serotonin, acetylcholine, and histamine, as well as those released in a non-centralized fashion, like purines and cytokines.

Clenbuterol activates the central IL-1 system via the β2-adrenoceptor without provoking inflammatory response related behaviours in rats

The long-acting, highly lipophilic, β2-adrenoceptor agonist clenbuterol may represent a suitable therapeutic agent for the treatment of neuroinflammation as it drives an anti-inflammatory response within the CNS. However, clenbuterol is also known to increase the expression of IL-1β in the brain, a potent neuromodulator that plays a role in provoking sickness related symptoms including anxiety and depression-related behaviours. Here we demonstrate that, compared to the immunological stimulus lipopolysaccharide (LPS, 250μg/kg), clenbuterol (0.5mg/kg) selectively up-regulates expression of the central IL-1 system resulting in a mild stress-like response which is accompanied by a reduction in locomotor activity and food consumption in rats. We provide further evidence that clenbuterol-induced activation of the central IL-1 system occurs in a controlled and selective manner in tandem with its negative regulators IL-1ra and IL-1RII. Furthermore, we demonstrate that peripheral β2-adrenoceptors mediate the suppression of locomotor activity and food consumption induced by clenbuterol and that these effects are not linked to the central induction of IL-1β. Moreover, despite increasing central IL-1β expression, chronic administration of clenbuterol (0.03mg/kg; twice daily for 21days) fails to induce anxiety or depressive-like behaviour in rats in contrast to reports of the ability of exogenously administered IL-1 to induce these symptoms in rodents. Overall, our findings suggest that clenbuterol or other selective β2-adrenoceptor agonists could have the potential to combat neuroinflammatory or neurodegenerative disorders without inducing unwanted symptoms of depression and anxiety.

Causes, consequences, and cures for neuroinflammation mediated via the locus coeruleus: noradrenergic signaling system

Aside from its roles in as a classical neurotransmitter involved in regulation of behavior, noradrenaline (NA) has other functions in the CNS. This includes restricting the development of neuroinflammatory activation, providing neurotrophic support to neurons, and providing neuroprotection against oxidative stress. In recent years, it has become evident that disruption of physiological NA levels or signaling is a contributing factor to a variety of neurological diseases and conditions including Alzheimer's disease (AD) and Multiple Sclerosis. The basis for dysregulation in these diseases is, in many cases, due to damage occurring to noradrenergic neurons present in the locus coeruleus (LC), the major source of NA in the CNS. LC damage is present in AD, multiple sclerosis, and a large number of other diseases and conditions. Studies using animal models have shown that experimentally induced lesion of LC neurons exacerbates neuropathology while treatments to compensate for NA depletion, or to reduce LC neuronal damage, provide benefit. In this review, we will summarize the anti-inflammatory and neuroprotective actions of NA, summarize examples of how LC damage worsens disease, and discuss several approaches taken to treat or prevent reductions in NA levels and LC neuronal damage. Further understanding of these events will be of value for the development of treatments for AD, multiple sclerosis, and other diseases and conditions having a neuroinflammatory component. The classical neurotransmitter noradrenaline (NA) has critical roles in modulating behaviors including those involved in sleep, anxiety, and depression. However, NA can also elicit anti-inflammatory responses in glial cells, can increase neuronal viability by inducing neurotrophic factor expression, and can reduce neuronal damage due to oxidative stress by scavenging free radicals. NA is primarily produced by tyrosine hydroxylase (TH) expressing neurons in the locus coeruleus (LC), a relatively small brainstem nucleus near the IVth ventricle which sends projections throughout the brain and spinal cord. It has been known for close to 50 years that LC neurons are lost during normal aging, and that loss is exacerbated in neurological diseases including Parkinson's disease and Alzheimer's disease. LC neuronal damage and glial activation has now been documented in a variety of other neurological conditions and diseases, however, the causes of LC damage and cell loss remain largely unknown. A number of approaches have been developed to address the loss of NA and increased inflammation associated with LC damage, and several methods are being explored to directly minimize the extent of LC neuronal cell loss or function. In this review, we will summarize some of the consequences of LC loss, consider several factors that likely contribute to that loss, and discuss various ways that have been used to increase NA or to reduce LC damage. This article is part of the 60th Anniversary special issue.

Amitriptyline protects against TNF-α-induced atrophy and reduction in synaptic markers via a Trk-dependent mechanism

Neuritic degeneration and synaptic loss are features of both neuroinflammation and neurodegenerative disease. The tricyclic antidepressant amitriptyline has neurotrophic and anti-inflammatory properties and acts as a novel agonist of the neurotrophin Trk receptors. Primary cortical neurons were treated with amitriptyline, nortriptyline and NGF and tested for neuronal complexity by Sholl analysis, protein expression by Western immunoblotting, and synapse number by colocalization of pre and postsynaptic makers. Amitriptyline (500 nmol/L) and its active metabolite nortriptyline (50 nmol/L) are found to induce neurite outgrowth in rat primary cortical neurons. Amitriptyline-induced neurite outgrowth is blocked by inhibition of Trk signaling using Trk antagonist K252a (200 nmol/L) but not by the neurotrophin inhibitor Y1036 (40 μmol/L), indicating that amitriptyline binds directly to the Trk receptor to initiate neurite outgrowth. MEK inhibitor PD98059 (10 μmol/L) also blocks amitriptyline-induced neurite outgrowth, implicating activation of the MAPK signaling pathway downstream of Trk receptor activation. Furthermore, pretreatment of primary cortical neurons with amitriptyline and nortriptyline prevents the effects of the proinflammatory cytokine TNF-α (10 ng/mL) on neurite outgrowth and colocalization of synaptic proteins. These findings suggest that amitriptyline and nortriptyline can exert neurotrophic effects in primary cortical neurons via activation of a Trk/MAPK signaling pathway. These compounds therefore have significant potential to be used in the treatment of neurodegenerative conditions where atrophy and loss of synaptic connections contribute to progression of disease.

Astrocyte plasticity induced by emotional stress: A new partner in psychiatric physiopathology?

A growing body of evidence has demonstrated that astrocytes play a pivotal role in the normal functioning of the nervous system. This new conceptual framework has set the groundwork to be able to hypothesize that astrocytes could underlie signs and symptoms of mental diseases. Stress is a major risk factor in the etiology of several psychiatric diseases, such as anxiety disorders and depression. Hence, understanding the effects of stress on astrocytes and how these changes contribute to the development of psychiatric endophenotypes is crucial for both a better comprehension of mental illness and for potential targeted treatment of stress-related mental disorders. Here, we describe the currently used approaches and recent evidence showing astrocyte alterations induced by chronic and acute stress in animals. In addition, the relevance of these changes in stress-induced behavioral sequelae and human data linking astrocytes with neuropsychiatric disorders related to stress are also discussed. All together, the data indicate that astrocytes are also an important target of stress, with both chronic and acute stressors being able to alter the morphology or the expression of several astrocyte specific proteins in brain areas that are known to play a critical role in emotional processing, such as the prefrontal cortex, hippocampus and amygdala. Furthermore, different lines of evidences suggest that these changes may contribute, at less in part, to the behavioral consequences of stress.

Upregulation of p‑Akt by glial cell line‑derived neurotrophic factor ameliorates cell apoptosis in the hippocampus of rats with streptozotocin‑induced diabetic encephalopathy

The loss of neurotrophic factor support has been shown to contribute to the development of the central nervous system. Glial cell line‑derived neurotrophic factor (GDNF), a potent neurotrophic factor, is closely associated with apoptosis and exerts neuroprotective effects on numerous populations of cells. However, the underlying mechanisms of these protective effects remain unknown. In the present study, a significant increase in Bax levels and DNA fragmentation was observed in the hippocampus obtained from the brains of diabetic rats 60 days after diabetes had been induced. The apoptotic changes were correlated with the loss of GDNF/Akt signaling. GDNF administration was found to reverse the diabetes‑induced Bax and DNA fragmentation changes. This was associated with an improvement in the level of p‑Akt/Akt. In addition, combination of GDNF with a specific inhibitor of the phosphoinositide 3‑kinase (PI3K)/Akt pathway, Wortmannin, significantly abrogated the effects of GDNF on the levels of p‑Akt/Akt, Bax and DNA fragmentation. However, a p38 mitogen‑activated proten kinase (MAPK) inhibitor, SB203580, had no effect on the expression of p‑Akt/Akt, Bax or DNA fragmentation. These results demonstrate the pivotal role of GDNF as well as the PI3K/Akt pathway, but not the MAPK pathway, in the prevention of diabetes‑induced neuronal apoptosis in the hippocampus.

β2-Adrenoceptor agonists as novel, safe and potentially effective therapies for Amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a chronic and progressive neuromuscular disease for which no cure exists and better treatment options are desperately needed. We hypothesize that currently approved β2-adrenoceptor agonists may effectively treat the symptoms and possibly slow the progression of ALS. Although β2-agonists are primarily used to treat asthma, pharmacologic data from animal models of neuromuscular diseases suggest that these agents may have pharmacologic effects of benefit in treating ALS. These include inhibiting protein degradation, stimulating protein synthesis, inducing neurotrophic factor synthesis and release, positively modulating microglial and systemic immune function, maintaining the structural and functional integrity of motor endplates, and improving energy metabolism. Moreover, stimulation of β2-adrenoceptors can activate a range of downstream signaling events in many different cell types that could account for the diverse array of effects of these agents. The evidence supporting the possible therapeutic benefits of β2-agonists is briefly reviewed, followed by a more detailed review of clinical trials testing the efficacy of β-agonists in a variety of human neuromuscular maladies. The weight of evidence of the potential benefits from treating these diseases supports the hypothesis that β2-agonists may be efficacious in ALS. Finally, ways to monitor and manage the side effects that may arise with chronic administration of β2-agonists are evaluated. In sum, effective, safe and orally-active β2-agonists may provide a novel and convenient means to reduce the symptoms of ALS and possibly delay disease progression, affording a unique opportunity to repurpose these approved drugs for treating ALS, and rapidly transforming the management of this serious, unmet medical need.

Robust Neuritogenesis-Promoting Activity by Bis(heptyl)-Cognitin Through the Activation of alpha7-Nicotinic Acetylcholine Receptor/ERK Pathway

AIMS

Neurodegenerative disorders are caused by progressive neuronal loss in the brain, and hence, compounds that could promote neuritogenesis may have therapeutic values. In this study, the effects of bis(heptyl)-cognitin (B7C), a multifunctional dimer, on neurite outgrowth were investigated in both PC12 cells and primary cortical neurons.

METHODS

Immunocytochemical staining was used to evaluate the proneuritogenesis effects, and Western blot and short hairpin RNA assays were applied to explore the underlying mechanisms.

RESULTS

B7C (0.1-0.5 μM) induced robust neurite outgrowth in PC12 cells, as evidenced by the neurite-bearing morphology and upregulation of growth-associated protein-43 expression. In addition, B7C markedly promoted neurite outgrowth in primary cortical neurons as shown by the increase in the length of β-III-tubulin-positive neurites. Furthermore, B7C rapidly increased ERK phosphorylation. Specific inhibitors of alpha7-nicotinic acetylcholine receptor (α7-nAChR) and MEK, but not those of p38 or JNK, blocked the neurite outgrowth as well as ERK phosphorylation induced by B7C. Most importantly, genetic depletion of α7-nAChR significantly abolished B7C-induced neurite outgrowth in PC12 cells.

CONCLUSION

B7C promoted neurite outgrowth through the activation of α7-nAChR/ERK pathway, which offers novel insight into the potential application of B7C in the treatment of neurodegenerative disorders.

Volume Transmission in Central Dopamine and Noradrenaline Neurons and Its Astroglial Targets

Already in the 1960s the architecture and pharmacology of the brainstem dopamine (DA) and noradrenaline (NA) neurons with formation of vast numbers of DA and NA terminal plexa of the central nervous system (CNS) indicated that they may not only communicate via synaptic transmission. In the 1980s the theory of volume transmission (VT) was introduced as a major communication together with synaptic transmission in the CNS. VT is an extracellular and cerebrospinal fluid transmission of chemical signals like transmitters, modulators etc. moving along energy gradients making diffusion and flow of VT signals possible. VT interacts with synaptic transmission mainly through direct receptor-receptor interactions in synaptic and extrasynaptic heteroreceptor complexes and their signaling cascades. The DA and NA neurons are specialized for extrasynaptic VT at the soma-dendrtitic and terminal level. The catecholamines released target multiple DA and adrenergic subtypes on nerve cells, astroglia and microglia which are the major cell components of the trophic units building up the neural-glial networks of the CNS. DA and NA VT can modulate not only the strength of synaptic transmission but also the VT signaling of the astroglia and microglia of high relevance for neuron-glia interactions. The catecholamine VT targeting astroglia can modulate the fundamental functions of astroglia observed in neuroenergetics, in the Glymphatic system, in the central renin-angiotensin system and in the production of long-distance calcium waves. Also the astrocytic and microglial DA and adrenergic receptor subtypes mediating DA and NA VT can be significant drug targets in neurological and psychiatric disease.

Application of Sholl analysis to quantify changes in growth and development in rat mammary gland whole mounts

Studies that utilize the rodent mammary gland (MG) as an endpoint for assessing the developmental toxicity of chemical exposures typically employ either basic dimensional measurements or developmental scoring of morphological characteristics as a means to quantify MG development. There are numerous means by which to report these developmental changes, leading to inconsistent translation across laboratories. The Sholl analysis is a method historically used for quantifying neuronal dendritic patterns. The present study describes the use of the Sholl analysis to quantify MG branching characteristics. Using this method, we were able to detect significant differences in branching density in MG of peripubertal female Sprague Dawley rats that had been exposed to vehicle or a potent estrogen. These data suggest the Sholl analysis can be an effective tool for quantitatively measuring an important characteristic of MG development and for examining associations between MG growth and density and adverse effects in the breast.

Evidence for fibroblast growth factor-2 as a mediator of amphetamine-enhanced motor improvement following stroke

Previously we have shown that addition of amphetamine to physical therapy results in enhanced motor improvement following stroke in rats, which was associated with the formation of new motor pathways from cortical projection neurons of the contralesional cortex. It is unclear what mechanisms are involved, but amphetamine is known to induce the neuronal release of catecholamines as well as upregulate fibroblast growth factor-2 (FGF-2) expression in the brain. Since FGF-2 has been widely documented to stimulate neurite outgrowth, the present studies were undertaken to provide evidence for FGF-2 as a neurobiological mechanism underlying amphetamine-induced neuroplasticity. In the present study rats that received amphetamine plus physical therapy following permanent middle cerebral artery occlusion exhibited significantly greater motor improvement over animals receiving physical therapy alone. Amphetamine plus physical therapy also significantly increased the number of FGF-2 expressing pyramidal neurons of the contralesional cortex at 2 weeks post-stroke and resulted in significant axonal outgrowth from these neurons at 8 weeks post-stroke. Since amphetamine is a known releaser of norepinephrine, in vitro analyses focused on whether noradrenergic stimulation could lead to neurite outgrowth in a manner requiring FGF-2 activity. Primary cortical neurons did not respond to direct stimulation by norepinephrine or amphetamine with increased neurite outgrowth. However, conditioned media from astrocytes exposed to norepinephrine or isoproterenol (a beta adrenergic agonist) significantly increased neurite outgrowth when applied to neuronal cultures. Adrenergic agonists also upregulated FGF-2 expression in astrocytes. Pharmacological analysis indicated that beta receptors and alpha1, but not alpha2, receptors were involved in both effects. Antibody neutralization studies demonstrated that FGF-2 was a critical contributor to neurite outgrowth induced by astrocyte-conditioned media. Taken together the present results suggest that noradrenergic activation, when combined with physical therapy, can improve motor recovery following ischemic damage by stimulating the formation of new neural pathways in an FGF-2-dependent manner.