Effect of δ-opioid receptor activation on BDNF-TrkB vs. TNF-α in the mouse cortex exposed to prolonged hypoxia

Assessment of corticospinal tract remodeling based on diffusion tensor imaging in the treatment of motor dysfunction after ischemic stroke by acupuncture: A meta-analysis

BACKGROUND

To investigate the efficacy of acupuncture in improving motor dysfunction after ischemic stroke (IS) and to investigate the effect of acupuncture on corticospinal tract (CST) remodeling using diffusion tensor imaging.

METHODS

Published literature on the effect of acupuncture on CST remodeling after IS using diffusion tensor imaging in the form of randomized controlled trials (RCTs) were systematically retrieved and screened from Cochrane Library, Web of Science, PubMed, Embase, CNKI, CBM, VIP, and Wanfang databases from inception to December 2022. The methodological quality of the included studies was critically and independently evaluated by 2 reviewers using the Cochrane Risk of Bias Assessment Tool for RCTs. The correlated data were extracted using the pre-designed form, and all analyses were performed using Reviewer Manager version 5.4.

RESULTS

Eleven eligible RCTs involving 459 patients were eventually included. The combined evidence results showed that the acupuncture group significantly improved patients' National Institute of Health stroke scale, Fugl-Meyer Assessment Scale, and Barthel index compared with conventional medical treatment. The acupuncture group significantly promoted remodeling of the CST, as reflected by an increase in fractional anisotropy (FA) throughout the CST [MD = 0.04, 95% CI (0.02, 0.07), P = .001], and in addition, subgroup analysis showed that the acupuncture group significantly improved FA in the infarct area compared with conventional medical treatment at around 4 weeks [MD = 0.04, 95% CI (0.02, 0.06), P = .0002] and FA of the affected cerebral peduncle [MD = 0.03, 95% CI (0.00, 0.07), P = .02]. Also, compared with conventional medical treatment, the acupuncture group significantly increased average diffusion coefficient of the affected cerebral peduncle [MD = -0.21, 95% CI (-0.28, -0.13), P < .00001].

CONCLUSION

The results of the meta-analysis suggest that acupuncture therapy can improve the clinical manifestations of motor dysfunction in patients after IS and advance a possibly beneficial effect on CST remodeling. However, due to the number and quality of eligible studies, these findings need to be further validated in more standardized, rigorous, high-quality clinical trials.

Neuromodulation in Parkinson's disease targeting opioid and cannabinoid receptors, understanding the role of NLRP3 pathway: a novel therapeutic approach

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta, resulting in motor and non-motor symptoms. Although levodopa is the primary medication for PD, its long-term use is associated with complications such as dyskinesia and drug resistance, necessitating novel therapeutic approaches. Recent research has highlighted the potential of targeting opioid and cannabinoid receptors as innovative strategies for PD treatment. Modulating opioid transmission, particularly through activating µ (MOR) and δ (DOR) receptors while inhibiting κ (KOR) receptors, shows promise in preventing motor complications and reducing L-DOPA-induced dyskinesia. Opioids also possess neuroprotective properties and play a role in neuroprotection and seizure control. Similar to this, endocannabinoid signalling via CB1 and CB2 receptors influences the basal ganglia and may contribute to PD pathophysiology, making it a potential therapeutic target. In addition to opioid and cannabinoid receptor targeting, the NLRP3 pathway, implicated in neuroinflammation and neurodegeneration, emerges as another potential therapeutic avenue for PD. Recent studies suggest that targeting this pathway holds promise as a therapeutic strategy for PD management. This comprehensive review focuses on neuromodulation and novel therapeutic approaches for PD, specifically highlighting the targeting of opioid and cannabinoid receptors and the NLRP3 pathway. A better understanding of these mechanisms has the potential to enhance the quality of life for PD patients.

Electroacupuncture ameliorates inflammatory response induced by retinal ischemia-reperfusion injury and protects the retina through the DOR-BDNF/Trkb pathway

Objectives: Retinal ischemia-reperfusion injury (RIRI) is the common pathological basis of many ophthalmic diseases in the later stages, and inflammation is the primary damage mechanism of RIRI. Our study aimed to assess whether electroacupuncture (EA) has a protective effect against RIRI and to elucidate its related mechanisms. Methods: A high-intraocular pressure (HIOP) model was used to simulate RIRI in Wistar rats. EA was applied to the EA1 group [Jingming (BL1) + Shuigou (GV26)] and the EA2 group [Jingming (BL1) + Hegu (LI4)] respectively for 30 min starting immediately after the onset of reperfusion and repeated (30 min/time) at 12 h and then every 24 h until days 7 after reperfusion. The pathological changes in the retina were observed by H and E staining after HIOP. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was utilized to observe retinal cell apoptosis. The mRNA expression of IL1-β, TNF-α, IL-4, IL-10, δ-opioid receptor (DOR), brain-derived neurotrophic factor (BDNF), and tropomyosin-related kinase B (TrkB) in the retina was measured by quantitative real-time PCR. Results: HIOP caused structural disorders of the retina, decreased RGCs, and increased retinal cell apoptosis. At 1 and 3 days of RIRI, retinal apoptotic cells in the EA group were significantly reduced, while there was no distinct difference in the EA group compared with the HIOP group at 7 days of RIRI. Compared with that in the HIOP group, the expression of anti-inflammatory factors, DOR and TrkB was increased, and the expression of pro-inflammatory factors was decreased in the EA group. In contrast, HIOP had no appreciable effect on BDNF expression. Conclusion: EA at Jingming (BL1) and Shuigou (GV26) or at Jingming (BL1) and Hegu (LI4) may inhibit RIRI induced inflammation through activating the DOR-BDNF/TrkB pathway to protect the retina, especially the pair of Jingming (BL1) and Shuigou (GV26) has better inhibitory effects on inflammation.

Synergistic Effect in Neurological Recovery via Anti-Apoptotic Akt Signaling in Umbilical Cord Blood and Erythropoietin Combination Therapy for Neonatal Hypoxic-Ischemic Brain Injury

Our previous clinical studies demonstrated the synergistic therapeutic effect induced by co-administering recombinant human erythropoietin (rhEPO) in human umbilical cord blood (hUCB) therapy for children with cerebral palsy. However, the cellular mechanism beyond the beneficial effects in this combination therapy still needs to be elucidated. A hypoxic–ischemic encephalopathy (HIE) model of neonates, representing cerebral palsy, was prepared and randomly divided into five groups (hUCB+rhEPO combination, hUCB, and rhEPO treatments over HIE, HIE control, and sham). Seven days after, hUCB was administered intraperitoneally and the rhEPO injections were started. Neurobehavioral tests showed the best outcome in the combination therapy group, while the hUCB and rhEPO alone treatments also showed better outcomes compared with the control (p < 0.05). Inflammatory cytokines were downregulated by the treatments and attenuated most by the combination therapy (p < 0.05). The hUCB+rhEPO treatment also showed remarkable increase in phosphorylation of Akt and potentiation of anti-apoptotic responses with decreased Bax and increased Bcl-2 (p < 0.05). Pre-treatment of MK-2206, an Akt inhibitor, for the combination therapy depressed the anti-apoptotic effects. In conclusion, these findings suggest that the therapeutic effect of hUCB therapy might be potentiated by co-administration of rhEPO via augmentation of anti-inflammatory and anti-apoptotic responses related to the phosphorylation of Akt.

Preservation of spatial memory and neuroprotection by the fatty acid amide hydrolase inhibitor URB597 in a rat model of vascular dementia

Background

Chronic cerebral hypoperfusion (CCH) is a major risk factor for vascular dementia (VaD). There are currently no broadly effective prevention or treatment strategies for VaD, but recent studies have reported promising results following vascular bypass surgery and pharmacomodulation of the brain endocannabinoid system (ECS). In this study, early effects of encephalomyosynangiosis (EMS) bypass surgery and augmented endocannabinoid signaling on CCH-induced cognitive dysfunction and neuronal damage were investigated.

Methods

An animal model of VaD was established by bilateral common carotid artery occlusion (BCCAO). Cannabinoid signaling was upregulated by treatment with the fatty acid amide hydrolase inhibitor URB597 (URB). Spatial learning and memory, cerebral blood flow (CBF), revascularization, brain-derived neurotrophic factor (BDNF)-tropomyosin receptor kinase B (TrkB) signaling, and apoptosis were compared among Sham, BCCAO, BCCAO + EMS, BCCAO + URB, and BCCAO + URB + EMS groups. Spatial learning and memory were evaluated using the Morris water maze (MWM). The CBF in cortex and hippocampus was evaluated by 3-dimensional arterial spin labeling. The neovascularization was visualized by CD34 immunofluorescence staining, and BDNF-TrkB signaling protein expression levels were assessed by Western blotting.

Results

Treatment with URB597 but not EMS alone reversed the spatial learning and memory deficits induced by BCCAO. Neovascularization was enhanced after EMS surgery but not by URB597. Alternatively, there were no significant differences in CBF among treatment groups. Expression levels of BDNF and TrkB were significantly reduced by CCH compared to Sham treatment, and downregulation of both proteins was reversed by URB597 treatment but not EMS. BCCAO enhanced neuronal apoptosis, which was also reversed by URB597.

Conclusions

Augmentation of endogenous cannabinoid signaling but not EMS protects against CCH-induced neurodegeneration and preserves spatial learning and memory, possibly by activating BDNF-TrkB signaling.

Naringenin improves depressive- and anxiety-like behaviors in mice exposed to repeated hypoxic stress through modulation of oxido-inflammatory mediators and NF-kB/BDNF expressions

Oxidative and inflammatory signaling pathways have been identified as important targets for mitigating hypoxic stress-induced neurological complications. Thus, the effects of naringenin, a potent antioxidant, anti-inflammatory and neuroprotective bioflavonoid on hypoxic stress-induced depressive-like and anxiety-related behaviors in mice, and the underlying molecular mechanisms were evaluated in this study. Thirty-five male Swiss mice were distributed into 5 groups (n = 7). Mice in group I (non-stress control) and group 2 (stress-control) both had vehicle (5 % DMSO), while groups 3-5 received naringenin (10, 25 and 50 mg/kg), intraperitonally. Thirty minutes later, mice in groups 2-5 were subjected to 15 min hypoxic stress, daily for 14 days. Locomotor activity, anxiety and depression were evaluated on day 15. The mice brains were processed for malondialdehyde, glutathione, superoxide-dismutase (SOD), catalase, tumor necrosis factor-alpha (TNF-α) and interleukin-1β assays. The serum corticosterone concentration and expressions of the brain immunopositive cells of inducible nitric oxide synthase (iNOS), nuclear factor kappa-B (NF-kB) and brain derived neurotrophic factor (BDNF) as well as histomorphological changes of the amygdala were also determined. Naringenin (25-50 mg/kg) ameliorated the hypolocomotion, depressive- and anxiety-like behaviors in hypoxic mice. The increased brain contents of malondialdehyde, TNF-α, interleukin-1β, and decreased antioxidant (glutathione and SOD) status were attenuated by naringenin. Naringenin (10 mg/kg) increases BDNF expression but did not significantly (p < 0.05) alter corticosterone and catalase contents. The increased expressions of iNOS and NF-kB as well as loss of amygdala neuronal cells were reduced by naringenin (10 mg/kg). Overall, these findings suggest that naringenin improves depressive- and anxiety-like behaviors in mice exposed to hypoxic stress by modulating oxido-inflammatory insults and NF-kB/BDNF expressions.

Alleviation of TGF-β1 induced tubular epithelial-mesenchymal transition via the δ-opioid receptor

Renal fibrosis is a common pathological feature of progressive chronic kidney disease (CKD). It is indicated that transforming growth factor-β1 (TGF-β1) plays as a central mediator in renal fibrosis. The present study aimed to investigate the role of δ-opioid receptor (DOR) on renal fibrosis of the rat renal proximal tubular epithelial cell line (NRK-52E) induced by TGF-β1 and to elucidate its underlying mechanism, as well as its involvement in signaling pathways. Cells were treated with TGF-β1 (10 ng·mL^-1 ), along with a specific DOR agonist (UFP-512) or naltrindole (a DOR antagonist). Cell viability and morphology, as well as cell migration, were measured after drug administration. Western blotting was employed to examine the extracellular matrix (ECM) protein Fibronectin, and the tubular epithelial-mesenchymal transition (EMT) markers (E-cadherin and α-smooth muscle actin (α-SMA)), signal transducer (p-Smad3), and EMT-regulatory gene (Snail). The expression level of phosphorylated Akt and p38 was also examined. Our results showed that TGF-β1 induced fibroblastic appearance and increased the expression of Fibronectin, α-SMA, P-Smad3, and Snail, while it decreased the expression of E-cadherin in NRK-52E cells. Moreover, TGF-β1 induced the activation of Akt and p38 MAPK signaling pathways. DOR activation was found to efficiently block morphological changes and cell migration, as long as the expression changes of Fibronectin, E-cadherin, α-SMA, P-Smad3, Snail, P-Akt, and P-p38 were induced by TGF-β1. These findings suggest that DOR may serve as an antifibrotic factor for renal proximal tubule cells by inhibiting the fibrosis process via TGF-β/Smad, Akt, and p38 MAPK signaling pathways.

δ-Opioid Receptors, microRNAs, and Neuroinflammation in Cerebral Ischemia/Hypoxia

Hypoxia and ischemia are the main underlying pathogenesis of stroke and other neurological disorders. Cerebral hypoxia and/or ischemia (e.g., stroke) can lead to neuronal injury/death and eventually cause serious neurological disorders or even death in the patients. Despite knowing these serious consequences, there are limited neuroprotective strategies against hypoxic and ischemic insults in clinical settings. Recent studies indicate that microRNAs (miRNAs) are of great importance in regulating cerebral responses to hypoxic/ischemic stress in addition to the neuroprotective effect of the δ-opioid receptor (DOR). Moreover, new discovery shows that DOR can regulate miRNA expression and inhibit inflammatory responses to hypoxia/ischemia. We, therefore, summarize available data in current literature regarding the role of DOR and miRNAs in regulating the neuroinflammatory responses in this article. In particular, we focus on microglia activation, cytokine production, and the relevant signaling pathways triggered by cerebral hypoxia/ischemia. The intent of this review article is to provide a novel clue for developing new strategies against neuroinflammatory injury resulting from cerebral hypoxia/ischemia.

Electroacupuncture Ameliorates Cerebral I/R-Induced Inflammation through DOR-BDNF/TrkB Pathway

The beneficial effects of electroacupuncture (EA) at Shuigou (GV26) and Neiguan (PC6) on poststroke rehabilitation are critically related to the activation of the delta-opioid receptor (DOR). The underlying anti-inflammatory mechanisms in DOR activation and EA-mediated neuroprotection in cerebral ischemia/reperfusion (I/R) injury were investigated in the current study. Cell proliferation and apoptosis were detected by morphological changes, cell counting kit-8 (CCK-8) assay, lactate dehydrogenase (LDH) release, and TUNEL staining. The mRNA levels were evaluated by using real-time quantitative polymerase chain reaction (RT-qPCR), and the protein expression was measured by western blot or enzyme-linked immunosorbent assay (ELISA) in vitro. Infarct volume was examined by cresyl violet (CV) staining, neurologic recovery was assessed by neurological deficit scores, and pro- and anti-inflammatory cytokines were determined by immunofluorescence in vivo. DOR activation greatly ameliorated morphological injury, reduced LDH leakage and apoptosis, and increased cell viability. It reversed the oxygen-glucose deprivation/reoxygenation- (OGD/R-) induced downregulation of DOR mRNA and protein, as well as BDNF protein. DOR activation also reduced proinflammatory cytokine gene expression, including TNF-α, IL-1β, and IL-6, and at the same time, increased anti-inflammatory cytokines IL-4 and IL-10 in OGD/R challenged PC12 cells. EA significantly reduced middle cerebral artery occlusion/reperfusion- (MCAO/R-) induced infarct volume and attenuated neurologic deficit scores. It markedly increased the expression of IL-10 and decreased IL-1β, while sham EA did not have any protective effect in MCAO/R-injured rats. DOR activation plays an important role in neuroprotection against OGD/R injury by inhibiting inflammation via the brain-derived neurotrophic factor/tropomyosin-related kinase B (BDNF/TrkB) pathway. The neuroprotective efficacy of EA at Shuigou (GV26) and Neiguan (PC6) on cerebral I/R injury may be also related to the inhibition of inflammatory response through the DOR-BDNF/TrkB pathway.

δ Opioid Receptor Agonism Preserves the Retinal Pigmented Epithelial Cell Tight Junctions and Ameliorates the Retinopathy in Experimental Diabetes

Purpose

Outer blood retinal barrier breakdown is a neglected feature of diabetic retinopathy (DR). We demonstrated that the agonism of the δ opioid receptor (DOR) by epicatechin preserves the tight junction proteins in ARPE-19 cells under diabetic conditions. Presently, we aimed to evaluate the possible role of the DOR on the maintenance of tight junction of RPE layer and on the early markers of experimental DR.

Methods

DR markers and external retinal tight junction proteins were evaluated in CL57B diabetic mice submitted to intravitreous injection of short hairpin RNA (shRNA)-DOR (108 transducing units [TU]/mL) treated or not with DOR agonist (0.05 g/animal/d of epicatechin in drinking water) for 16 weeks. The presence of DOR in human retina from postmortem eyes from diabetic and nondiabetic donors were also performed.

Results

DOR is present in RPE layer and in neuro retina. The treatment with DOR agonist prevented the upregulation of the early markers of retinopathy (glial fibrillary acidic protein, VEGF) and the downregulation of pigment epithelium-derived factor, occludin, claudin-1, and zonula occludens-1 tight junction expressions. The silencing of DOR in retina of diabetic mice partially abolished the protective effects of epicatechin. In human retina specimens, DOR is present throughout the retina, similarly in nondiabetic and diabetic donors.

Conclusions

This set of experiments strongly indicates that the DOR agonism preserves RPE tight junctions and reduces the early markers of retinopathy in model of diabetes. These novel findings designate DOR as a potential therapeutic tool to treat DR with preservation of the RPE tight junction proteins.

δ-Opioid Receptor-Nrf-2-Mediated Inhibition of Inflammatory Cytokines in Neonatal Hypoxic-Ischemic Encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) causes serious neurological disability; there are, however, currently few promising therapies for it. We have recently shown that δ-opioid receptor (DOR) is neuroprotective by downregulating TNF-α. Since hypoxia-ischemia (HI) triggers a robust inflammatory response, which exacerbates HI brain damage, we investigated, in this study, whether DOR activation could regulate inflammatory cytokine expression, thereby playing a protective effect on the neonatal brain under HI. Twenty-five neonatal rats were randomly divided into five groups: (1) control (control); (2) HI; (3) HI with saline (HI + NS); (4) DOR activation with UFP-512 (a potent and specific DOR agonist) under HI conditions (HI + U); and (5) DOR inhibition using NT treatment under HI conditions (HI + NT). The rats were sacrificed by decapitation at 24 h after HI, and their brains were rapidly removed for measurements. The protein expression of TNF-α, IL-6, ICAM-1, IL-10, IL-18, NQO-1, Nrf-2, and HO-1 was measured using Western blot. In the hemispheres exposed to HI, DOR activation significantly decreased the expressions of TNF-α, IL-6, and ICAM-1 in the cortex, while it significantly increased IL-10 and had no effect on IL-18 in the same region. In contrast, DOR had no appreciable effect on inflammatory cytokine expression in non-cortical tissues including hippocampal, subcortical, and cerebellar tissues. Moreover, HI stress triggered an upregulation of Nrf-2 nuclear protein as well as some of its downstream anti-inflammatory genes such as HO-1 and NQO-1 in the cortex, while DOR activation further augmented such a protective reaction against HI injury. DOR plays an important role in protecting against HI by regulating the expression of inflammatory and anti-inflammatory cytokines in the cortex, which is likely mediated by the Nrf-2/HO-1/NQO-1 signaling.

The delta-opioid receptor and Parkinson's disease

Parkinson's disease (PD) is a common degenerative neurological disease leading to a series of familial, medical, and social problems. Although it is known that the major characteristics of PD pathophysiology are the dysfunction of basal ganglia due to injury/loss of dopaminergic neurons in the substantia nigra pars compacta dopaminergic and exhaustion of corpus striatum dopamine, therapeutic modalities for PD are limited in clinical settings up to date. It is of utmost importance to better understand PD pathophysiology and explore new solutions for this serious neurodegenerative disorder. Our recent work and those of others suggest that the delta-opioid receptor (DOR) is neuroprotective and serves an antiparkinsonism role in the brain. This review summarizes recent progress in this field and explores potential mechanisms for DOR-mediated antiparkinsonism.

Mu-opioid receptor and delta-opioid receptor differentially regulate microglial inflammatory response to control proopiomelanocortin neuronal apoptosis in the hypothalamus: effects of neonatal alcohol

BACKGROUND

Opioid receptors are known to control neurotransmission of various peptidergic neurons, but their potential role in regulation of microglia and neuronal cell communications is unknown. We investigated the role of mu-opioid receptors (MOR) and delta-opioid receptors (DOR) on microglia in the regulation of apoptosis in proopiomelanocortin (POMC) neurons induced by neonatal ethanol in the hypothalamus.

METHODS

Neonatal rat pups were fed a milk formula containing ethanol or control diets between postnatal days 2-6. Some of the alcohol-fed rats additionally received pretreatment of a microglia activation blocker minocycline. Two hours after the last feeding, some of the pups were sacrificed and processed for histochemical detection of microglial cell functions or confocal microscopy for detection of cellular physical interaction or used for gene and protein expression analysis. The rest of the pups were dissected for microglia separation by differential gradient centrifugation and characterization by measuring production of various activation markers and cytokines. In addition, primary cultures of microglial cells were prepared using hypothalamic tissues of neonatal rats and used for determination of cytokine production/secretion and apoptotic activity of neurons.

RESULTS

In the hypothalamus, neonatal alcohol feeding elevated cytokine receptor levels, increased the number of microglial cells with amoeboid-type circularity, enhanced POMC and microglial cell physical interaction, and decreased POMC cell numbers. Minocycline reversed these cellular effects of alcohol. Alcohol feeding also increased levels of microglia MOR protein and pro-inflammatory signaling molecules in the hypothalamus, and MOR receptor antagonist naltrexone prevented these effects of alcohol. In primary cultures of hypothalamic microglia, both MOR agonist [D-Ala 2, N-MePhe 4, Gly-ol]-enkephalin (DAMGO) and ethanol increased microglial cellular levels and secretion of pro-inflammatory cell signaling proteins. However, a DOR agonist [D-Pen2,5]enkephalin (DPDPE) increased microglial secretion of anti-inflammatory cytokines and suppressed ethanol's ability to increase microglial production of inflammatory signaling proteins and secretion of pro-inflammatory cytokines. In addition, MOR-activated inflammation promoted while DOR-suppressed inflammation inhibited the apoptotic effect of ethanol on POMC neurons.

CONCLUSIONS

These results suggest that ethanol's neurotoxic action on POMC neurons results from MOR-activated neuroinflammatory signaling. Additionally, these results identify a protective effect of a DOR agonist against the pro-inflammatory and neurotoxic action of ethanol.

Naloxone exacerbates memory impairments and depressive-like behavior after mild traumatic brain injury (mTBI) in mice with upregulated opioid system activity

The neuroprotective role of the endogenous opioid system in the pathophysiological sequelae of brain injury remains largely ambiguous. Noteworthy, almost no data is available on how its genetically determined activity influences the outcome of mild traumatic brain injury. Thus, the aim of our study was to examine the effect of opioid receptor blockage on cognitive impairments produced by mild traumatic brain injury in mice selectively bred for high (HA) and low (LA) swim-stress induced analgesia that show innate divergence in opioid system activity. Mild traumatic brain injury was induced with a weight-drop device on anaesthetized mice. Naloxone (5mg/kg) was intraperitoneally delivered twice a day for 7days to non-selectively block opioid receptors. Spatial memory performance and manifestations of depressive-like behavior were assessed using the Morris Water Maze and tail suspension tests, respectively. Mild traumatic brain injury resulted in a significant deterioration of spatial memory performance and severity of depressive-like behavior in the LA mouse line as opposed to HA mice. Opioid receptor blockage with naloxone unmasked cognitive deficits in HA mice but was without effect in the LA line. The results suggest a protective role of genetically predetermined enhanced opioid system activity in suppression of mild brain trauma-induced cognitive impairments. Mice selected for high and low swim stress-induced analgesia might therefore be a useful model to study the involvement of the opioid system in the pathophysiology and neurological outcome of traumatic brain injury.

Repeated activation of delta opiod receptors counteracts nerve injury-induced TNF-α up-regulation in the sciatic nerve of rats with neuropathic pain: A possible correlation with delta opiod receptors-mediated antiallodinic effect

Despite mu opioid receptor agonists are the cornerstones of moderate-to-severe acute pain treatment, their effectiveness in chronic pain conditions is controversial. In contrast to mu opioid receptor agonists, a number of studies have reported the effectiveness of delta opioid receptor agonists on neuropathic pain strengthening the idea that delta opioid receptors gain importance when chronic pain develops. Among other effects, it has been shown that delta opioid receptor activation in optic nerve astrocytes inhibits tumor necrosis factor-α-mediated inflammation in response to severe hypoxia. Considering the involvement of tumor necrosis factor-α in the development and maintenance of neuropathic pain, with this study we sought to correlate the effect of delta opioid receptor agonist on the development of mechanical allodynia to tumor necrosis factor-α expression at the site of nerve injury in rats subjected to chronic constriction injury of the sciatic nerve. To this aim, we measured the levels of tumor necrosis factor-α in the sciatic nerve of rats with neuropathic pain after repeated injections with a delta opioid receptor agonist. Results obtained demonstrated that repeated administrations of the delta opioid receptor agonist SNC80 (10 mg/kg, i.p. for seven consecutive days) significantly inhibited the development of mechanical allodynia in rats with neuropathic pain and that the improvement of neuropathic symptom was timely related to the reduced expression of tumor necrosis factor-α in the rat sciatic nerve. We demonstrated also that when treatment with the delta opioid receptor agonist was suspended both allodynia and tumor necrosis factor-α up-regulation in the sciatic nerve of rats with neuropathic pain were restored. These results show that persistent delta opioid receptor activation significantly attenuates neuropathic pain and negatively regulates sciatic nerve tumor necrosis factor-α expression in chronic constriction injury rats.

Recurrent Moderate Hypoglycemia Suppresses Brain-Derived Neurotrophic Factor Expression in the Prefrontal Cortex and Impairs Sensorimotor Gating in the Posthypoglycemic Period in Young Rats

Recurrent hypoglycemia is common in infants and children. In developing rat models, recurrent moderate hypoglycemia leads to neuronal injury in the medial prefrontal cortex. To understand the effects beyond neuronal injury, 3-week-old male rats were subjected to 5 episodes of moderate hypoglycemia (blood glucose concentration, approx. 30 mg/dl for 90 min) once daily from postnatal day 24 to 28. Neuronal injury was determined using Fluoro-Jade B histochemistry on postnatal day 29. The effects on brain-derived neurotrophic factor (BDNF) and its cognate receptor, tyrosine kinase receptor B (TrkB) expression, which is critical for prefrontal cortex development, were determined on postnatal day 29 and at adulthood. The effects on prefrontal cortex-mediated function were determined by assessing the prepulse inhibition of the acoustic startle reflex on postnatal day 29 and 2 weeks later, and by testing for fear-potentiated startle at adulthood. Recurrent hypoglycemia led to neuronal injury confined primarily to the medial prefrontal cortex. BDNF/TrkB expression in the prefrontal cortex was suppressed on postnatal day 29 and was accompanied by lower prepulse inhibition, suggesting impaired sensorimotor gating. Following the cessation of recurrent hypoglycemia, the prepulse inhibition had recovered at 2 weeks. BDNF/TrkB expression in the prefrontal cortex had normalized and fear-potentiated startle was intact at adulthood. Recurrent moderate hypoglycemia during development has significant adverse effects on the prefrontal cortex in the posthypoglycemic period.

Effect of dexmedetomidine on hippocampal neuron development and BDNF-TrkB signal expression in neonatal rats

The study aimed to explore the effect of dexmedetomidine (DEX) on hippocampal neuron development process and on molecular expression of brain-derived neurotrophic factor (BDNF)-tyrosine receptor kinase B (TrkB) signaling pathway in neonatal rats. The hippocampal neuron cells were isolated from newborn neonatal rats and cultured in vitro. One control group and three treated groups with 1, 10, and 100 μmol/L DEX were used for the study. Cell activity and apoptosis were detected by the MTT and terminal deoxynucleotidyl transferase-mediated biotinylated uridine triphosphate (UTP) nick end labeling assays. The synaptophysin (SYN) and postsynaptic density 95 (PSD95) were detected by quantitative polymerase chain reaction. There was no difference in the viability of neuron cells among the different dose groups of DEX and the control group during days 2-10 (P>0.05). Compared to the control group, there was no significant difference (P>0.05) in the expressions of SYN and PSD95 in the groups treated with 1 and 10 μmol/L DEX, whereas significant difference in the expression was observed in the group treated with 100 μmol/L DEX (P<0.01). Compared with the control group, the expression of BDNF was significantly upregulated (P<0.05) in the group treated with 100 μmol/L DEX. There were no significant differences in TrkB expression among the four groups. The expression of p-N-methyl-D-aspartate receptor increased with an increase in the concentration of DEX; however, only the high dose revealed a significant upregulation compared with the control group. The neuroprotective effect of DEX may be achieved by upregulating the expression of BDNF and phosphorylation level of N-methyl-D-aspartate receptor.

In vitro and in vivo efficacy of a potent opioid receptor agonist, biphalin, compared to subtype-selective opioid receptor agonists for stroke treatment

To meet the challenge of identification of new treatments for stroke, this study was designed to evaluate a potent, nonselective opioid receptor (OR) agonist, biphalin, in comparison to subtype selective OR agonists, as a potential neuroprotective drug candidate using in vitro and in vivo models of ischemic stroke. Our in vitro approach included mouse primary neuronal cells that were challenged with glutamate and hypoxic/aglycemic (H/A) conditions. We observed that 10nM biphalin, exerted a statistically significant neuroprotective effect after glutamate challenge, compared to all selective opioid agonists, according to lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Moreover, 10nM biphalin provided superior neuroprotection after H/A-reoxygenation compared to selective opioid agonists in all cases. Our in vitro investigations were supported by in vivo studies which indicate that the nonselective opioid agonist, biphalin, achieves enhanced neuroprotective potency compared to any of the selective opioid agonists, evidenced by reduced edema and infarct ratios. Reduction of edema and infarction was accompanied by neurological improvement of the animals in two independent behavioral tests. Collectively these data strongly suggest that concurrent agonist stimulation of mu, kappa and delta ORs with biphalin is neuroprotective and superior to neuroprotection by activation of any single OR subtype.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Recent advances on the δ opioid receptor: from trafficking to function

Within the opioid family of receptors, δ (DOPrs) and μ opioid receptors (MOPrs) are typical GPCRs that activate canonical second-messenger signalling cascades to influence diverse cellular functions in neuronal and non-neuronal cell types. These receptors activate well-known pathways to influence ion channel function and pathways such as the map kinase cascade, AC and PI3K. In addition new information regarding opioid receptor-interacting proteins, downstream signalling pathways and resultant functional effects has recently come to light. In this review, we will examine these novel findings focusing on the DOPr and, in doing so, will contrast and compare DOPrs with MOPrs in terms of differences and similarities in function, signalling pathways, distribution and interactions. We will also discuss and clarify issues that have recently surfaced regarding the expression and function of DOPrs in different cell types and analgesia.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Non-pharmaceutical therapies for stroke: mechanisms and clinical implications

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases and transcranial laser therapy. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

Deep brain stimulation: are astrocytes a key driver behind the scene?

Despite its widespread use, the underlying mechanism of deep brain stimulation (DBS) remains unknown. Once thought to impart a "functional inactivation", there is now increasing evidence showing that DBS actually can both inhibit neurons and activate axons, generating a wide range of effects. This implies that the mechanisms that underlie DBS work not only locally but also at the network level. Therefore, not only may DBS induce membrane or synaptic plastic changes in neurons over a wide network, but it may also trigger cellular and molecular changes in other cells, especially astrocytes, where, together, the glial-neuronal interactions may explain effects that are not clearly rationalized by simple activation/inhibition theories alone. Recent studies suggest that (1) high-frequency stimulation (HFS) activates astrocytes and leads to the release of gliotransmitters that can regulate surrounding neurons at the synapse; (2) activated astrocytes modulate synaptic activity and increase axonal activation; (3) activated astrocytes can signal further astrocytes across large networks, contributing to observed network effects induced by DBS; (4) activated astrocytes can help explain the disparate effects of activation and inhibition induced by HFS at different sites; (5) astrocytes contribute to synaptic plasticity through long-term potentiation (LTP) and depression (LTD), possibly helping to mediate the long-term effects of DBS; and (6) DBS may increase delta-opioid receptor activity in astrcoytes to confer neuroprotection. Together, the plastic changes in these glial-neuronal interactions network-wide likely underlie the range of effects seen, from the variable temporal latencies to observed effect to global activation patterns. This article reviews recent research progress in the literature on how astrocytes play a key role in DBS efficacy.

Cytokines, chaperones and neuroinflammatory responses in heroin-related death: what can we learn from different patterns of cellular expression?

Heroin (3,6-diacetylmorphine) has various effects on the central nervous system with several neuropathological alterations including hypoxic-ischemic brain damage from respiratory depressing effects and neuroinflammatory response. Both of these mechanisms induce the release of cytokines, chemokines and other inflammatory mediators by the activation of many cell types such as leucocytes and endothelial and glial cells, especially microglia, the predominant immunocompetent cell type within the central nervous system. The aim of this study is to clarify the correlation between intravenous heroin administration in heroin related death and the neuroinflammatory response. We selected 45 cases among autopsies executed for heroin-related death (358 total cases); immunohistochemical studies and Western blotting analyses were used to investigate the expression of brain markers such as tumor necrosis factor-α, oxygen-regulated protein 150, (interleukins) IL-1β, IL-6, IL-8, IL-10, IL-15, cyclooxygenase-2, heat shock protein 70, and CD68 (MAC387). Findings demonstrated that morphine induces inflammatory response and cytokine release. In particular, oxygen-regulated protein 150, cyclooxygenase-2, heat shock protein 70, IL-6 and IL-15 cytokines were over-expressed with different patterns of cellular expression.