Scopolamine into the anterior cingulate cortex diminishes nociception in a neuropathic pain model in the rat: an interruption of ‘nociception‐related memory acquisition’?

The cingulate cortex plays a key role in the affective component related to pain perception. This structure receives cholinergic projections and also plays a role in memory processing. Therefore, we propose that the cholinergic system in the anterior cingulate cortex is involved in the nociceptive memory process. We used scopolamine (10 microg in 0.25 mircrol/saline) microinjected into the anterior cingulate cortex, either before thermonociception followed by a sciatic denervation, between thermonociception and denervation or after both procedures (n=10 each). The vehicle group (saline solution 0.9%, n=14) was microinjected before thermonociception. Chronic nociception was measured by the autotomy score, which onset and incidence were also determined. Group scopolamine-thermonociception-denervation (STD) presented the lowest autotomy score as compared to vehicle and group thermonociception-denervation-scopolamine (TDS) (vehicle vs. STD, p=0.002, STD vs. TDS, p=0.001). Group thermonociception-scopolamine-denervation (TSD) showed a diminished autotomy score when compared to TDS (p=0.053). STD group showed a delay in the onset of AB as compared to the rest of the groups. Group TSD presented a significative delay (p=0.048) in AB onset when compared to group TDS. There were no differences in the incidence between groups. The results show that nociception-related memory processed in the anterior cingulate cortex is susceptible of being modified by the cholinergic transmission blockade. When scopolamine is microinjected prior to the nociceptive stimuli, nociception-related memory acquisition is prevented. The evidence obtained in this study shows the role of the anterior cingulate cortex in the acquisition of nociception-related memory.     

Lesion of the rostral anterior cingulate cortex eliminates the aversiveness of spontaneous neuropathic pain following partial or complete axotomy

Neuropathic pain is often “spontaneous” or “stimulus-independent.” Such pain may result from spontaneous discharge in primary afferent nociceptors in injured peripheral nerves. However, whether axotomized primary afferent nociceptors give rise to pain is unclear. The rostral anterior cingulate cortex (rACC) mediates the negative affective component of inflammatory pain. Whether the rACC integrates the aversive component of chronic spontaneous pain arising from nerve injury is not known. Here, we used the principle of negative reinforcement to show that axotomy produces an aversive state reflecting spontaneous pain driven from injured nerves. Additionally, we investigated whether the rACC contributes to the aversiveness of nerve injury-induced spontaneous pain. Partial or complete hind paw denervation was produced by sciatic or sciatic/saphenous axotomy, respectively. Conditioned place preference resulting from presumed pain relief was observed following spinal clonidine in animals with sciatic axotomy but not in sham-operated controls. Similarly, lidocaine administration into the rostral ventromedial medulla (RVM) produced place preference selectively in animals with sciatic/saphenous axotomy. In rats with spinal nerve ligation (SNL) injury, lesion of the rACC blocked the reward elicited by RVM lidocaine but did not alter acute stimulus-evoked hypersensitivity. Lesion of the rACC did not block cocaine-induced reward, indicating that rACC blockade did not impair memory encoding or retrieval but did impair spontaneous aversiveness. These data indicate that spontaneous pain arising from injured nerve fibers produces a tonic aversive state that is mediated by the rACC. Identification of the circuits mediating aversiveness of chronic pain should facilitate the development of improved therapies.     

Hemispheric asymmetry in cognitive division of anterior cingulate cortex: A resting-state functional connectivity study

The cognitive division of anterior cingulate cortex (ACC-cd) plays an important role in cognitive control via a distributed attention network. The structural hemispheric asymmetries of ACC have been revealed by several neuroimaging studies. However potential functional hemispheric asymmetries of ACC remain less clear. Investigating the functional hemispheric asymmetries of ACC helps for a better understanding of ACC function. The aim of this study was to use resting-state functional magnetic resonance imaging (fMRI) to examine hemispheric differences in the functional networks associated with ACC-cd in the two hemispheres. ROI-based functional connectivity analysis was performed on a group of 49 right-handed healthy volunteers. The left and right ACC-cd showed significant differences in their patterns of connectivity with a variety of brain regions, including the dorsolateral prefrontal cortex, inferior parietal lobule, superior parietal lobule and dorsal posterior cingulate cortex in their ipsilateral cerebral cortex, as well as cerebellar tonsil and inferior semilunar lobule in their contralateral cerebellar hemisphere. Specifically, for these areas, we found significantly greater connectivity strength with ACC-cd in the right hemisphere than the left, regardless of whether the connection was positive or negative. The current results highlight the presence of clear asymmetries in functional networks associated with ACC-cd. Future functional imaging studies are needed to give greater attention to the lateralized ACC functional networks which are observed.     

Activation of anterior cingulate cortex produces inhibitory effects on noxious mechanical and electrical stimuli‐evoked responses in rat spinal WDR neurons

In present study, in vivo electrophysiological techniques were applied to examine the effects of anterior cingulate cortex (ACC) activation on mechanical and electrical stimuli‐evoked responses in rat spinal cord wide‐dynamic‐range (WDR) neurons. We found that bilateral ACC electrical stimulation (100 Hz, 20 V, 20 s) had different effects on neuronal responses to brush, pressure and pinch stimuli (10 s). The brush‐evoked neuronal responses at baseline, post 1 min and post 5 min were 60.8±15.0, 59.2±15.4 and 60.0±19.3 spikes/10 s, respectively (n =10, P >0.05 vs. baseline). The pressure‐evoked neuronal responses at baseline, post 1 min and post 5 min were 77.8±11.9, 38.0±7.8 and 45.8±7.6 spikes/10 s, respectively (n =10, P <0.05 vs. baseline). The pinch‐evoked neuronal responses at baseline, post 1 min and post 5 min were 137.6±16.7, 62.6±17.5 and 68.8±15.0 spikes/10 s, respectively (n =10, P <0.05 vs. baseline). Furthermore, ACC stimulation generated distinct effects on the different components of wind‐up response. The total numbers of late response (LR) and after‐discharge (AD), but not early response (ER), significantly decreased. Collectively, the present study demonstrated that short‐term ACC activation could generate long‐term inhibitory effects on the responses of WDR neurons to noxious mechanical (pressure and pinch) and electrical stimuli. The results indicated that ACC activation could negatively regulate noxious information ascending from spinal cord with long‐term effect, providing potential neuronal substrate for the modulation of ACC activation on nociception.     

Impairment of long-term depression in the anterior cingulate cortex of mice with bone cancer pain

The anterior cingulate cortex (ACC) has been shown to play an important role in pain-related perception and chronic pain. However, little is known about the molecular mechanisms involved. To address this issue, we analyzed excitatory synaptic transmission and long-term synaptic plasticity in layer II/III pyramidal neurons within the rostral ACC (rACC) from mice with bone cancer pain induced by intra-tibia implantation of osteolytic fibrosarcoma cells. Ex vivo whole-cell patch-clamp recordings from rACC neurons showed no significant alterations in presynaptic glutamate release probability and postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated synaptic responses in mice with bone cancer pain. However, mechanical allodynia occurred in conjunction with decreased N-methyl-d-aspartate (NMDA)/AMPA ratio of synaptic currents elicited in bilateral rACC neurons. In addition, the induction of NMDA receptor-dependent long-term depression (LTD) at rACC synapses was impaired in rACC neurons of tumor-bearing mice. Western blot analysis revealed a significant decrease in the levels of NR1, NR2A, and NR2B subunits of NMDA receptors in the rACC under bone cancer pain condition. No significant changes in overall mRNA levels for any of the NMDA receptor subunits or calpain activity were observed in the rACC of tumor-bearing mice. These results indicate that tumor-induced injury or remodeling of primary afferent sensory nerve fibers that innervate the tumor-bearing bone may cause a persistent decrease in NMDA receptor expression in rACC neurons, resulting in a loss of LTD induction, thereby leading to long-term alterations of rACC activity and creating exaggerated pain behaviors.     

1H-MRS检测儿童及青少年创伤后应激障碍大脑前扣带回代谢物改变

目的 探讨儿童及青少年创伤后应激障碍（PTSD）患者¹H-MRS中大脑前扣带回区代谢物水平的变化。方法 纳入汶川地震幸存者57人,包括10例PTSD患者、23名PTSD康复者和24名健康者。对所有研究对象行¹H-MRS检查,检测大脑前扣带回区N-乙酰天门冬氨酸（NAA）、肌酸（Cr）、胆碱（Cho）、肌醇（MI）和谷氨酸和谷氨酰胺复合物（Glx）水平,计算并比较NAA/Cr、Glx/Cr、Cho/Cr、MI/Cr的差异。结果 Glx/Cr：PTSD患者（1.16±0.15）、PTSD患者+PTSD康复者（1.31±0.07）均明显低于健康者（1.59±0.10）,PTSD患者明显低于PTSD康复者+健康者（1.48±0.07）,差异均有统计学意义（P均<0.05）,PTSD康复者（1.37±0.08）与健康者和PTSD患者间差异均无统计学意义（P均>0.05）。NAA/Cr、Cho/Cr和MI/Cr差异均无统计学意义（P均>0.05）。结论 ¹H-MRS中儿童及青少年PTSD患者大脑前扣带回区Glx明显下降,其改变可能在PTSD病理生理机制中发挥重要作用。     

Met carriers of BDNF Val66Met genotype show increased N-acetylaspartate concentration in the anterior cingulate cortex

Decreased levels of N-acetylaspartate (NAA) and brain-derived neurotrophic factor (BDNF) in the anterior cingulate cortex (ACC) have been linked to neuronal loss and psychiatric disorders like schizophrenia and bipolar disorder.We previously found that BDNF serum concentration was predicted by the concentration of NAA in the ACC, indicating that neuronal integrity and vitality of a cortical region like the ACC, as reflected by a high concentration of NAA, might be related to high concentrations of BDNF in serum. Moreover, our recent finding that Val66Met genotype appears to predict the BDNF serum level in healthy human volunteers suggests the Met allele to be connected to higher concentrations of BDNF in serum.We examined absolute NAA concentrations in the ACC and hippocampus of 40 male and 42 female healthy volunteers (age: 33.3 ± 9 years).We found NAA in the ACC to be significantly increased in Met carriers (F = 5.2, df = 1, p = 0.025). On the other hand, the concentration of creatine + phosphocreatine in the hippocampus was significantly decreased in Met carriers.We hypothesize that higher NAA levels in the ACC might contribute to the protection of Met allele carriers against major psychiatric disorders as schizophrenia and bipolar disorder.     

NMDA NR2A and NR2B receptors in the rostral anterior cingulate cortex contribute to pain-related aversion in male rats

NMDA receptors, which are implicated in pain processing, are highly expressed in forebrain areas including the anterior cingulate cortex (ACC). The ACC has been implicated in the affective response to noxious stimuli. Using a combination of immunohistochemical staining, Western blot, electrophysiological recording and formalin-induced conditioned place avoidance (F-CPA) rat behavioral model that directly reflects the affective component of pain, the present study examined formalin nociceptive conditioning-induced changes in the expressions of NMDA receptor subunits NR1, NR2A, and NR2B in the rostral ACC (rACC) and its possible functional significance. We found that unilateral intraplantar (i.pl.) injection of dilute formalin with or without contextual conditioning exposure markedly increased the expressions of NMDA receptor subunits NR2A and NR2B but not of NR1 in the bilateral rACC. NMDA-evoked currents in rACC neurons were significantly greater in formalin-injected rats than in naïve or normal saline-injected rats. Selectively blocking either NR2A or NR2B subunit in the rACC abolished the acquisition of F-CPA and formalin nociceptive conditioning-induced Fos expression, but it did not affect formalin acute nociceptive behaviors and non-nociceptive fear stimulus-induced CPA. These results suggest that both NMDA receptor subunits NR2A and NR2B in the rACC are critically involved in pain-related aversion. Thus, a new strategy targeted at NMDA NR2A or NR2B subunit might be raised for the prevention of pain-related emotional disturbance.     

Descending facilitatory modulation of a behavioral nociceptive response by stimulation in the adult rat anterior cingulate cortex.

It is well documented that the descending endogenous analgesia system, including the periaqueductal gray (PAG) and the rostral ventral medulla (RVM), play an important role in modulation of nociceptive transmission and morphine- and cannabinoid-produced analgesia. Neurons in the PAG receive inputs from different nuclei of higher structures, including the anterior cingulate cortex (ACC). However, it is unclear if stimulation of neurons in the ACC modulates spinal nociceptive transmission. The present study has examined the effects of electrical stimulation and chemical activation of metabotropic glutamate receptors (mGluRs) in the ACC on a spinal nociceptive tail-flick (TF) reflex induced by noxious heating. Activation of the ACC at high intensities (up to 500 microA) of electrical stimulation did not produce any antinociceptive effect. Instead, at most sites within the ACC (n = 36 of 41 sites), electrical stimulation produced significant facilitation of the TF reflex (i.e. decreases in TF latency). Chemical activation of mGluRs within the ACC also produced a facilitatory effect. Descending facilitation from the ACC apparently relays at the RVM. Electrical stimulation in the RVM produces a biphasic modulatory effect, showing facilitation at low intensities and inhibition at higher intensities. The present study provides evidence that activation of mGluRs within the ACC can facilitate spinal nociception.     

Altered functional connectivity between the insula and the cingulate cortex in patients with temporomandibular disorder: a pilot study

Background.— Among the most common chronic pain conditions, yet poorly understood, are temporomandibular disorders (TMDs), with a prevalence estimate of 3‐15% for Western populations. Although it is increasingly acknowledged that central nervous system mechanisms contribute to pain amplification and chronicity in TMDs, further research is needed to unravel neural correlates that might abet the development of chronic pain. Objective.— The insular cortex (IC) and cingulate cortex (CC) are both critically involved in the experience of pain. The current study sought specifically to investigate IC–CC functional connectivity in TMD patients and healthy controls (HCs), both during resting state and during the application of a painful stimulus. Methods.— Eight patients with TMD, and 8 age‐ and sex‐matched HCs were enrolled in the present study. Functional magnetic resonance imaging data during resting state and during the performance of a pressure pain stimulus to the temple were acquired. Predefined seed regions were placed in the IC (anterior and posterior insular cortices) and the extracted signal was correlated with brain activity throughout the whole brain. Specifically, we were interested whether TMD patients and HCs would show differences in IC–CC connectivity, both during resting state and during the application of a painful stimulus to the face. Results.— As a main finding, functional connectivity analyses revealed an increased functional connectivity between the left anterior IC and pregenual anterior cingulate cortex (ACC) in TMD patients, during both resting state and applied pressure pain. Within the patient group, there was a negative correlation between the anterior IC–ACC connectivity and clinical pain intensity as measured by a visual analog scale. Conclusions.— Since the pregenual region of the ACC is critically involved in antinociception, we hypothesize that an increase in anterior IC–ACC connectivity is indicative of an adaptation of the pain modulatory system early in the chronification process. (Headache 2012;52:441‐454)     

Upregulation of presynaptic proteins and protein kinases associated with enhanced glutamate release from axonal terminals (synaptosomes) of the medial prefrontal cortex in rats with neuropathic pain

Although nerve injury-induced long-term postsynaptic changes have been investigated, less is known regarding the molecular mechanisms within presynaptic axonal terminals. We investigated the molecular changes in presynaptic nerve terminals underlying chronic pain-induced plastic changes in the medial prefrontal cortex (mPFC). After neuropathic pain was induced by spared nerve injury (SNI) in rats, we assessed the release of the excitatory neurotransmitter glutamate by using in vitro synaptosomal preparations from the mPFC. We also measured the levels of synaptic proteins and protein kinases in synaptosomes using Western blotting. The results showed that unilateral long-term SNI augmented depolarization-evoked glutamate release from synaptosomes of the bilateral mPFC. This result was confirmed by a rapid destaining rate of FM1-43 dye in SNI-operated rats. Unilateral long-term nerve injury also significantly increased synaptic proteins (including synaptophysin, synaptotagmin, synaptobrevin, syntaxin, and 25-kDa synaptosome-associated protein) in synaptosomal fractions from the bilateral mPFC, and ultrastructure images demonstrated increased synaptic vesicular profiles in synaptosomes from SNI animals. Chronic pain upregulated the phosphorylation of endogenous protein kinases, including extracellular signal-regulated kinases 1 and 2 (ERK1/2) and Ca²⁺/calmodulin-dependent kinase II (CaMKII), and synapsin I, the primary presynaptic target of ERK1/2 and CaMKII. Both presynaptic proteins and protein kinases were upregulated after SNI in a time-dependent manner. These results indicate that the long-term neuropathic pain-induced enhancement of glutamate release in the mPFC is linked to increased synaptic vesicle proteins and the activation of the ERK1/2- and CaMKII-synapsin signaling cascade in presynaptic axonal terminals.     

N-formylpeptides induce two distinct concentration optima for mouse neutrophil chemotaxis by differential interaction with two N-formylpeptide receptor (FPR) subtypes. Molecular characterization of FPR2, a second mouse neutrophil FPR.

The N-formylpeptide receptor (FPR) is a G protein-coupled receptor that mediates mammalian phagocyte chemotactic responses to bacterial N-formylpeptides. Here we show that a mouse gene named Fpr-rs2 encodes a second N-formylpeptide receptor subtype selective for neutrophils which we have provisionally named FPR2. The prototype N-formylpeptide fMLF induced calcium flux and chemotaxis in human embryonic kidney (HEK) 293 cells stably transfected with FPR2. The EC(50)s, approximately 5 microM for calcium flux and chemotaxis, were approximately 100-fold greater than the corresponding values for mouse FPR-transfected HEK 293 cells. Consistent with this, fMLF induced two distinct concentration optima for chemotaxis of normal mouse neutrophils, but only the high concentration optimum for chemotaxis of neutrophils from FPR knockout mice. Based on these data, we hypothesize that high- and low-affinity N-formylpeptide receptors, FPR and FPR2, respectively, may function in vivo as a relay mediating neutrophil migration through the high and low concentration portions of N-formylpeptide gradients.     

Treatment of chronic pain with millimetre wave therapy (MWT) in patients with diffuse connective tissue diseases: a pilot case series study.

BACKGROUND: Pain relief is reported to be the most common clinical application of electromagnetic millimetre waves. AIM: To evaluate safety and pain relief effect of millimetre wave therapy (MWT) for treatment of chronic joint pain in a group of patients with diffuse connective tissue diseases. METHODS: Twelve patients with diffuse connective tissue diseases received MWT in addition to their analgesic medication with non-steroidal anti-inflammatory drugs. MWT procedure included the exposure of tender points around the painful joints to electromagnetic waves with frequency 54-78GHz and power density of 2.5mW/cm(2). The time of exposure was 35 +/-5 min and the total number of sessions ranged from 5 to 10 (median 6). Intensity of pain, medication requirement, joint stiffness and subjective assessment of therapy success were measured before, during and immediately after the treatment, and after a 6-months follow-up. RESULTS: No adverse effects of MWT were noted. Pain intensity and required medication decreased significantly after the treatment (p<0.05) and remained at the same level throughout the follow-up period. The joint stiffness decreased and the subjective assessment of the treatment success after 6 month did not change except in only one patient. CONCLUSION: MWT applied to tender points around the affected joints was safe under the conditions of our study and after an appropriate full-scale double-blind clinical study, may be recommended as an effective adjunct therapy for chronic pain treatment in patients with diffuse connective tissue diseases.     

A diminished response to formalin stimulation reveals a role for the glutamate transporters in the altered pain sensitivity of mice with experimental autoimmune encephalomyelitis (EAE)

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) in which neuropathic pain is now recognized as a major symptom. To date, few studies have examined the underlying mechanisms of neuropathic pain in MS. Recently we showed that in a chronic-relapsing animal model of MS, experimental autoimmune encephalomyelitis (EAE), characteristic neuropathic behaviours develop. However, responses to persistent noxious stimuli in EAE remain unexplored. We, therefore set out to characterize the changes in pain sensitivity in our EAE model to subcutaneous injection of formalin. We show here that female C57BL/6 mice immunized with myelin oligodendrocyte glycoprotein (MOG_35–55) display a significant decrease in elicited pain behaviours in response to formalin injection. These effects were found to involve dysregulation of the glutamatergic system in EAE. We show here that these effects are mediated by decreased glutamate transporter expression associated with EAE. Our findings demonstrate that dysregulation of glutamate transporter function in EAE mice is an important mechanism underlying the abnormal pain sensitivity in response to persistent noxious stimulation of mice with EAE and also sheds light on a potential mechanism underlying neuropathic pain behaviours in this model.     

Tocilizumab: A novel humanized anti-interleukin 6 (IL-6) receptor antibody for the treatment of patients with non-RA systemic,inflammatory rheumatic diseases

Abstract

Tocilizumab is a highly effective therapeutic agent for the treatment of rheumatoid arthritis and systemic juvenile idiopathic arthritis. Furthermore, a large amount of case study data reveals that tocilizumab can be an effective therapy for not only rheumatoid arthritis but also for other mostly rare inflammatory rheumatic diseases. By blocking the interleukin-6 pathway tocilizumab can be a useful therapeutic alternative when conventional treatment fails. It is successful in treating diseases such as the adult-onset Still's disease, amyloidosis, giant cell arteritis, multiple myeloma, polymyalgia rheumatica, relapsing polychondritis, remitting seronegative symmetrical synovitis with pitting edema-syndrome, systemic lupus erythematosus, systemic sclerosis, and Takayasu arteritis. Studies underway are now recruiting patients to acquire further data on treating patients with non-rheumatic arthritis, inflammatory diseases. This review focuses on tocilizumab as a promising agent for treating rare and orphan diseases in rheumatology for which no satisfactory treatment is yet available.     

A comparative study between angiotensin receptor neprilysin inhibitor (thiorphan/irbesartan) with each of nitrate and carvedilol in a rat model of myocardial ischemic reperfusion injury

The combined angiotensin receptor neprilysin inhibitor is a promising cardioprotective pharmacological agent. This study investigated the beneficial effects of thiorphan (TH)/irbesartan (IRB), in myocardial ischemia–reperfusion (IR) injury, compared to each of nitroglycerin and carvedilol. Male Wistar rats were divided into five groups (10 rats/group): Sham, untreated I/R, TH/IRB + IR (0.1/10 mg/kg), nitroglycerin + IR (0.2 mg/kg), and carvedilol + IR (10 mg/kg). Mean arterial blood pressure, cardiac functions and arrhythmia incidence, duration and score were assessed. Cardiac levels of creatine kinase-MB (CK-MB), oxidative stress, endothelin-1, ATP, Na⁺/K⁺ ATPase pump activity and mitochondria complexes activities were measured. Histopathological examination, Bcl/Bax immunohistochemistry studies and electron microscopy examination of left ventricle were performed. TH/IRB preserved the cardiac functions and mitochondrial complexes activities, mitigated cardiac damage, reduced oxidative stress and arrhythmia severity, improved the histopathological changes and decreased cardiac apoptosis. TH/IRB showed a comparable effect to each of nitroglycerin and carvedilol in alleviating the IR injury consequences. TH/IRB showed significant preservation of mitochondrial complexes activity I and II compared to nitroglycerin. TH/IRB significantly increased LVdP/dtmax and decreased oxidative stress, cardiac damage and endothelin-1 along with increasing the ATP content, Na⁺/K⁺ ATPase pump activity and mitochondrial complexes activity when compared to carvedilol. TH/IRB showed a cardioprotective effect in reducing IR injury that is comparable to each of nitroglycerin and carvedilol that could be explained in part by its ability to preserve mitochondrial function, increase ATP, decrease oxidative stress as well as endothelin 1.