Experimental hypoglycemia is a human model of stress-induced hyperalgesia

Neuropathy of diabetes following initiation of a low-carbohydrate diet: Case report

Introduction

This case study portrays an unusual case of treatment-induced neuropathy of diabetes (TIND) in a patient with uncontrolled type 2 diabetes (T2D) who achieved rapid improvement in glucose control primarily with dietary intervention. Initial presentation was 50-year-old white male with a long-standing history of obesity and a family history of T2D with a screening glucose level >500mg/dL by glucometer, HbA1c of 14.9%, and initial weight 213 lbs.

Methods

The initial intervention included a low-carbohydrate diet, metformin, and a continuous glucose monitor (CGM). Semaglutide was added after seven days.

Results

His glycemia was within the target range within three weeks. Four weeks after initiation of therapy, he developed TIND symptoms consisting of burning, tightness, and numbness of bilateral feet along with 10/10 pain. At three months, his HbA1c dropped to 6.9% and his weight to 195 lbs. Treatment of his TIND reduced his pain from 10/10 to 2/10.

Conclusion

Whereas TIND is commonly associated with the use of insulin or sulfonylureas, this study adds evidence to the paucity of literature regarding TIND precipitated by dietary intervention.

Validity of mental and physical stress models

Different stress models are employed to enhance our understanding of the underlying mechanisms and explore potential interventions. However, the utility of these models remains a critical concern, as their validities may be limited by the complexity of stress processes. Literature review revealed that both mental and physical stress models possess reasonable construct and criterion validities, respectively reflected in psychometrically assessed stress ratings and in activation of the sympathoadrenal system and the hypothalamic-pituitary-adrenal axis. The findings are less robust, though, in the pharmacological perturbations' domain, including such agents as adenosine or dobutamine. Likewise, stress models' convergent- and discriminant validity vary depending on the stressors' nature. Stress models share similarities, but also have important differences regarding their validities. Specific traits defined by the nature of the stressor stimulus should be taken into consideration when selecting stress models. Doing so can personalize prevention and treatment of stress-related antecedents, its acute processing, and chronic sequelae. Further work is warranted to refine stress models' validity and customize them so they commensurate diverse populations and circumstances.

Impact of Intensive Glycemic Treatment on Diabetes Complications-A Systematic Review

Diabetes complications can be related to the long duration of the disease or chronic hyperglycemia. The follow-up of diabetic patients is based on the control of chronic hyperglycemia, although this correction, if obtained rapidly in people living with severe chronic hyperglycemia, can paradoxically interfere with the disease or even induce complications. We reviewed the literature describing the impact of the rapid and intense treatment of hyperglycemia on diabetic complications. The literature review showed that worsening complications occurred significantly in diabetic microangiopathy with the onset of specific neuropathy induced by the correction of diabetes. The results for macroangiopathy were somewhat mixed with the intensive and rapid correction of chronic hyperglycemia having a neutral impact on stroke and myocardial infarction but a significant increase in cardiovascular mortality. The management of diabetes has now entered a new era with new therapeutic molecules, such as gliflozin for patients living with type 2 diabetes, or hybrid insulin delivery systems for patients with insulin-treated diabetes. Our manuscript provides evidence in support of these personalized and progressive algorithms for the control of chronic hyperglycemia.

Fluoxetine reverses hyperactivity of anterior cingulate cortex and attenuates chronic stress-induced hyperalgesia

Somatic symptom disorder (SSD), which occurs in about 5-7 percent of the adult population, involves heightened physical and emotional sensitivity to pain. However, its neural mechanism remains elusive and thus hinders effective clinical intervention. In this study, we employed chronic restraint stress (CRS)-induced hyperalgesia as a mouse model to investigate the neural mechanism underlying SSD and its pharmacological treatment. We found that CRS induced hyperactivity of anterior cingulate cortex (ACC), whereas chemogenetic inhibition of such hyperactivity could prevent CRS-induced hyperalgesia. Systematic application and ACC local infusion of fluoxetine alleviated CRS-induced hyperalgesia. Moreover, we found that fluoxetine exerted its anti-hyperalgesic effects through inhibiting the hyperactivity of ACC and upregulating 5-HT1A receptors. Our study thus uncovers the functional role of 5-HT signaling in modulating pain sensation and provides a neural basis for developing precise clinical intervention for SSD.

Stress, hypoglycemia, and the autonomic nervous system

Stress can be classified as either psychosocial or physiologic. Physiologic stress refers to stresses due to acute illness, trauma, pain, hypoglycemia, and sleep deprivation-much less is known regarding its health consequences. This review focuses on hypoglycemia as a model to further investigate physiological stress. Experimental mild to moderate hypoglycemia is a paradigmatic physiological stress that evokes autonomic, neuroendocrine, and immune responses. Hypoglycemic stress is an ideal model to examine the interactions and consequences of physiological stress on the autonomic nervous system. Acute hypoglycemia has been demonstrated to increase inflammatory markers, prolong QTc, and impair cardiac-vagal baroreflex sensitivity. Some of these consequences may not reverse completely when euglycemia is restored. For example, there is attenuation of the cardiac-vagal baroreflex, attenuation of the vascular sympathetic baroreflex (muscle sympathetic nerve activity response to transient hypotension), and attenuation of the catecholamine response to lower body negative pressure that is present the next day after hypoglycemia has resolved.

The transcription factor CCAAT/enhancer-binding protein β in spinal microglia contributes to pre-operative stress-induced prolongation of postsurgical pain

Prolongation of postsurgical pain caused by pre-operative stress is a clinically significant problem, although the mechanisms are not fully understood. Stress can promote the pro-inflammatory activation of microglia, and the transcription factor CCAAT/enhancer-binding protein (C/EBP) β regulates pro-inflammatory gene expression in microglia. Therefore, we speculated that C/EBPβ in spinal microglia may have critical roles in the development of chronic postsurgical pain. Accordingly, in this study, we used a single prolonged stress (SPS) procedure and plantar incisions to evaluate the roles of C/EBPβ in postsurgical pain. Our experiments showed that SPS exposure prolonged mechanical allodynia, increased the expression of C/EBPβ and pro-inflammatory cytokines, and potentiated the activation of spinal microglia. Subsequently, microinjection of C/EBPβ siRNA attenuated the duration of SPS-prolonged postoperative mechanical allodynia and inhibited microglial activation in the spinal cord. Conversely, mimicking this increase in C/EBPβ promoted microglial activation via pretreatment with a pre-injection of AAV5-C/EBPβ, leading to prolongation of postsurgical pain. Overall, these results suggested that spinal microglia may play key roles in prolongation of postsurgical pain induced by pre-operative stress and that C/EBPβ may be a potential target for disease treatment.

Feasibility, Efficacy, and Safety of Percutaneous Muscle Biopsies in Patients With Chronic Liver Disease

INTRODUCTION

Sarcopenia is present in many chronic disease states including decompensated end stage liver disease (ESLD) and non-cirrhotic non-alcoholic fatty liver disease (NAFLD). Sarcopenia in ESLD can negatively impact quality of life and increase mortality. Despite this, very little is understood about the mechanisms of sarcopenia in these conditions. One key reason for this is the reluctance to undertake percutaneous muscle biopsies due to the perceived increased risks. ESLD can induce thrombocytopaenia and coagulopathy which significantly increases the risk of bleeding. In addition, patients with either NAFLD or ESLD often have co-morbidities that would require additional care and risk assessment. Thus, the aim of this study was to establish an effective and safe protocol for the implementation of percutaneous muscle biopsies in patients with NAFLD and ESLD.

METHODS

A total of 47 patients with ESLD and 9 patients with non-cirrhotic NAFLD were recruited from the Liver Unit, Queen Elizabeth Hospital (Birmingham, United Kingdom). A total of 71 percutaneous vastus lateralis biopsies were attempted over two study visits. A vigorous safety screening occurred prior to and during each visit and a strict protocol was followed to mitigate against complications and risk.

RESULTS

A total of 85% of patients consented to the muscle biopsy at either visit (48/56). A total of 9% of consented biopsies could not occur due to medical considerations, including high international normalised ratio (INR) (n = 3) and the use of aspirin (n = 4). Muscle tissue was obtained from 90% of attempts, with a mean average yield (wet weight tissue) of 98.1 ± 52.9 mg.

CONCLUSION

Percutaneous muscle biopsies are both feasible and yield sufficient tissue in an ESLD population. The procedure is effective for obtaining muscle tissue whilst also safe, with only one adverse event. This study provides evidence for the successful use of muscle biopsies in this population, even in consideration of disease specific complications, medications, and comorbidities.

The Impact of Hypoglycemia on Patients with Diabetes Mellitus: A Cross-Sectional Analysis

The increasing mortality and morbidity in patients with diabetes mellitus constitute a severe public health problem. The condition is recognized as a cause of impaired quality of life, high costs, and diminished productivity. In this study, we performed a cross-sectional analysis among 300 Polish participants with type 1 and type 2 diabetes to determine and classify risk factors associated with increased incidences of hypoglycemia. Including an open-access knowledge about the correlations between diabetes rates and human’s lifestyle, we confirm that the frequency of smoking and drinking alcohol, low BMI, inappropriate diet, low physical activity, lack of vaccination against influenza and pneumococci, and co-existence of other comorbidities such as cardiovascular diseases, thyroid diseases, hyperlipidemia, retinopathy, and asthma elevate the risk of hypoglycemia. Furthermore, hypoglycemic patients were more often malnourished, depressed, irritated, and exposed to stress. In sum, the analysis of the interaction between diabetes and sociodemographic, environmental, or other disease-related risk factors provides strategies to optimize glycemic control and reduce the incidence of hypoglycemia. Furthermore, we believe our findings may constitute a basis for promoting health by adjusting available and implementing new preventive services reducing hypoglycemic episodes in diabetic patients.

GPR30 receptor promotes preoperative anxiety-induced postoperative hyperalgesia by up-regulating GABAA-α4β1δ subunits in periaqueductal gray in female rats

BACKGROUND

G-protein coupled estrogen receptor 30 (GPR30) was proved the specific estrogen receptor relating to mechanical hyperalgesia. Studies have shown that the GABA_A receptor subunits α4, β1, and δ in the periaqueductal gray (PAG) neurons promote the descending facilitation system. This study inquired into whether and how GPR30 and GABA_A-α4β1δ in the PAG promote preoperative anxiety-induced postoperative hyperalgesia in female rats.

METHODS

All the female rats were subjected to the single prolonged stress (SPS) to stimulate preoperative anxiety. Subsequently, mechanical allodynia was evaluated before and after the incision, based on the paw withdrawal mechanical threshold (PWMT). The selective GPR30 agonist G1 and antagonist G15 were locally microinjected into the PAG. The expression of GPR30, protein kinase A (PKA), and GABA_A receptor subunits α4, β1, and δ in the PAG neurons were detected using western blotting and immunofluorescence.

RESULTS

Behavioral testing revealed that Group S and Group I decreased the nociceptive threshold levels of PWMT in female rats. PWMT in Group S + I decreased more than that of Group S and Group I. Further, results of western blotting showed the expression of GPR30, PKA, and GABA_A α4, β1, and δ subunits significantly up-regulated in Group S + I, and immunofluorescence indicated that the neurons of PAG in Group S + I appeared simultaneously immunopositive for GPR30 and GABA_A α4, β1, and δ receptors. After microinjection of G1 into the PAG, female rats with plantar incision continued to exhibit significant hyperalgesia until postoperative 48 h. On the other hand, microinjection of G15 with SPS and plantar incision procedure relieved postoperative hyperalgesia in female rats. Western blotting demonstrated that intra-PAG injection of G15 markedly decreased the GPR30, PKA, and GABA_A α4, β1, and δ levels in Group G15 + I.

CONCLUSIONS

Our results indicate that the GPR30-PKA-GABA_Aα4β1δ pathway in the PAG promotes preoperative anxiety-induced postoperative hyperalgesia in female rats. This mechanism might be a potential novel therapeutic target for hyperalgesia in females.

Treatment induced neuropathy of diabetes

BACKGROUND

Treatment induced neuropathy of diabetes (TIND) is an iatrogenic painful sensory and autonomic neuropathy. Although the prevalence is not known, it is seen in up to 10% of tertiary cases referred for evaluation of diabetic neuropathy.

EVIDENCE

TIND is associated with a decrease in the glycosylated hemoglobin A1C in individuals with longstanding hyperglycemia. TIND is more common in individuals with type 1 diabetes, but can occur in anyone with diabetes through the use of insulin, oral hypoglycemic medications or diet control. There is an acute or subacute onset of neuropathy that is linked to the change in glucose control. Although the primary clinical manifestation is neuropathic pain there is a concurrent development of autonomic dysfunction, retinopathy and nephropathy.

CONCLUSION

TIND is more common than previously suspected. The number of cases reported over the past 10 years is much greater than historical literature predicted. Increased attention to target glucose control as a physician metric could suggest a possible explanation for the increased in TIND cases reported in recent years. At present, supportive care is the only recommended treatment. Future research is necessary to define the underlying mechanism, prevent development and to guide treatment recommendations.

Can oxytocin inhibit stress-induced hyperalgesia?

Stress-induced hyperalgesia is a problematic condition that lacks an effective therapeutic measure, and hence impairs health-related quality of life. The regulation of stress by oxytocin (OT) has overlapping effects on pain. OT can alleviate pain directly mainly at the spinal level and the peripheral tissues. Additionally, OT plays an analgesic role by dealing with stress and fear learning. When OT relieves stress by targeting the prefrontal brain regions and the hypothalamic-pituitary-adrenal axis, the body's sensitivity to pain is attenuated. Meanwhile, OT facilitates fear learning and may, in turn, enhance the anticipatory actions to painful stimulation. The unique therapeutic value of OT in patients suffering from stress and stress-related hyperalgesia conditions is worth considering. We reviewed recent advances in animal and human studies involving the effects of OT on stress and pain, and discussed the possible targets of OT within the descending and ascending pathways in the central nervous system. This review provides an overview of the evidence on the role of OT in alleviating stress-induced hyperalgesia.

Mechanisms of "Cough-Trick" for Pain Relief during Venipuncture: An Experimental Crossover Investigation in Healthy Volunteers

Objectives

The easily performed “cough-trick” (CT) reduces pain during venipuncture (VP), although the underlying mechanism remains unclear. The aim was to investigate the pain-reducing effect of CT during VP in comparison with two distraction methods, as well as under the influence of naloxone.

Methods

54 healthy male volunteers participated in 3 investigations. Pain during standardized VP with CT was compared to a “weak” distraction (squeezing a rubber ball; investigation 1; n=20) and to a “strong” distraction (inflating a tourniquet to a given pressure; investigation 2; n=21). In investigation 3 (n=13), pain at a VP without intervention was compared to pain at VP with CT under naloxone; pressure pain thresholds before and after naloxone administration were also measured. Pain was assessed using a 100 mm visual analogue scale. Data were compared within each sample using Student's t-test for paired samples.

Results

Pain intensity at VP with CT was lower than under “weak” distraction (mean difference 5 mm; 95% CI: 0.5 to 9.6; P=0.03). Pain levels under CT and “strong” distraction were comparable. There was no difference between pain under CT after naloxone infusion and pain without intervention. Pressure pain threshold decreased (mean difference 1 mm; 95% CI: 0.1 to 1.0 mm; P=0.02) after naloxone administration.

Conclusion

Pain-reducing effect of CT during VP is superior to that of simple motor distraction and equivalent to a complex distraction method. This might be due to the activation of segmental pain inhibitory pathways during coughing indicated through the lack of pain reduction due to CT under opioid antagonist blockage.

Chronic stress exacerbates neuropathic pain via the integration of stress-affect-related information with nociceptive information in the central nucleus of the amygdala

Exacerbation of pain by chronic stress and comorbidity of pain with stress-related psychiatric disorders, including anxiety and depression, represent significant clinical challenges. However, the underlying mechanisms still remain unclear. Here, we investigated whether chronic forced swim stress (CFSS)-induced exacerbation of neuropathic pain is mediated by the integration of stress-affect-related information with nociceptive information in the central nucleus of the amygdala (CeA). We first demonstrated that CFSS indeed produces both depressive-like behaviors and exacerbation of spared nerve injury (SNI)-induced mechanical allodynia in rats. Moreover, we revealed that CFSS induces both sensitization of basolateral amygdala (BLA) neurons and augmentation of long-term potentiation (LTP) at the BLA-CeA synapse and meanwhile, exaggerates both SNI-induced sensitization of CeA neurons and LTP at the parabrachial (PB)-CeA synapse. In addition, we discovered that CFSS elevates SNI-induced functional up-regulation of GluN2B-containing NMDA (GluN2B-NMDA) receptors in the CeA, which is proved to be necessary for CFSS-induced augmentation of LTP at the PB-CeA synapse and exacerbation of pain hypersensitivity in SNI rats. Suppression of CFSS-elicited depressive-like behaviors by antidepressants imipramine or ifenprodil inhibits the CFSS-induced exacerbation of neuropathic pain. Collectively, our findings suggest that CFSS potentiates synaptic efficiency of the BLA-CeA pathway, leading to the activation of GluN2B-NMDA receptors and sensitization of CeA neurons, which subsequently facilitate pain-related synaptic plasticity of the PB-CeA pathway, thereby exacerbating SNI-induced neuropathic pain. We conclude that chronic stress exacerbates neuropathic pain via the integration of stress-affect-related information with nociceptive information in the CeA.

Attenuation of pCREB and Egr1 expression in the insular and anterior cingulate cortices associated with enhancement of CFA-evoked mechanical hypersensitivity after repeated forced swim stress

The perception and response to pain are severely impacted by exposure to stressors. In some animal models, stress increases pain sensitivity, which is termed stress-induced hyperalgesia (SIH). The insular cortex (IC) and anterior cingulate cortex (ACC), which are typically activated by noxious stimuli, affect pain perception through the descending pain modulatory system. In the present study, we examined the expression of phospho-cAMP response element-binding protein (pCREB) and early growth response 1 (Egr1) in the IC and ACC at 3h (the acute phase of peripheral tissue inflammation) after complete Freund's adjuvant (CFA) injection in naïve rats and rats preconditioned with forced swim stress (FS) to clarify the effect of FS, a stressor, on cortical cell activities in the rats showing SIH induced by FS. The CFA injection into the hindpaw induced mechanical hypersensitivity and increased the expression of the pCREB and Egr1 in the IC and ACC at 3h after the injection. FS (day 1, 10min; days 2-3, 20min) prior to the CFA injection enhanced the CFA-induced mechanical hypersensitivity and attenuated the increase in the expression of pCREB and Egr1 in the IC and ACC. These findings suggested that FS modulates the CFA injection-induced neuroplasticity in the IC and ACC to enhance the mechanical hypersensitivity. These findings are thought to signify stressor-induced dysfunction of the descending pain modulatory system.

Effects of fluoxetine on changes of pain sensitivity in chronic stress model rats

Exposure to stress could facilitate or inhibit pain responses (stress-induced hyperalgesia or hypoalgesia, respectively). Fluoxetine is a selective serotonin (5-HT) reuptake inhibitor antidepressant. There have been contradictory reports on whether fluoxetine produces antinociceptive effects. The purpose of this study was to elucidate changes in pain sensitivity after chronic stress exposure, and the effects of fluoxetine on these changes. We measured thermal, mechanical, and formalin-induced acute and inflammatory pain by using the tail-flick, von Frey, and formalin tests respectively. The results showed that rats exposed to chronic stress exhibited thermal and formalin-induced acute and inflammatory hypoalgesia and transient mechanical hyperalgesia. Furthermore, fluoxetine promoted hypoalgesia in thermal and inflammatory pain and induced mechanical hyperalgesia. Our results indicate that the 5-HT system could be involved in hypoalgesia of thermal and inflammatory pain and induce transient mechanical hyperalgesia after stress exposure.

Treatment induced neuropathy of diabetes-Long term implications in type 1 diabetes

AIMS/HYPOTHESIS

Aggressive glucose control can result in treatment induced neuropathy of diabetes (TIND) if glycemic control is achieved too quickly. The aim of the present study is to describe the 8-year follow-up data on a cohort of individuals with type 1 diabetes who developed TIND.

METHODS

Twenty-six individuals with type 1 diabetes and TIND were followed longitudinally for 8years with regular quantitative measurement of pain, neurological examinations and evaluation of microvascular complications. Comprehensive neurological testing was performed after TIND and 7-8years later.

RESULTS

Among the 26 individuals with TIND, 19/26 had stable glycemic control and 7/26 had unstable glycemic control in long-term follow up. Those 19/26 with stable glycemic control had improvement in neuropathy, pain and microvascular complications while the 7/26 with unstable glycemic control had significant worsening of neuropathy, pain and microvascular complications (P<0.01, all tests).

CONCLUSION/INTERPRETATION

TIND is a poorly understood iatrogenic complication of aggressive glycemic control, although individuals with stable glycemic control tended to improve, while those with unstable glycemic control worsened. Additional studies of TIND are required to understand potential outcomes in an era of medical 'metrics' where physician reimbursement may be tied to achievement of excessively rapid glycemic control.

Anxious anticipation and pain: the influence of instructed vs conditioned threat on pain

Negative emotions such as anxiety enhance pain perception. However, certain threat characteristics are discussed to have different or even divergent effects on pain (hypoalgesia vs hyperalgesia). In order to investigate the neurobiological basis of different threats, we compared the impact of conditioned threat (CT) vs instructed threat (IT) on pain using fMRI. In two groups, participants underwent either Pavlovian threat conditioning or an instructed threat procedure. Afterwards, in an identical test phase participants watched the same visual cues from the previous phase indicating potential threat or safety, and received painful thermal stimulation. In the test phase, pain ratings were increased in both groups under threat. Group comparisons show elevated responses in amygdala and hippocampus for pain under threat in the CT group, and higher activation of the mid-cingulate gyrus (MCC) in the IT group. Psychophysiological interaction analyses in CT demonstrated elevated connectivity of the amygdala and the insula for the comparison of pain under threat vs safety. In IT, the same comparison revealed elevated functional connectivity of the MCC and the insula. The results suggest a similar pain augmenting effect of CT and IT, which, however, seems to rely on different networks mediating the impact of threat on pain.

Repeated forced swim stress differentially affects formalin-evoked nociceptive behaviour and the endocannabinoid system in stress normo-responsive and stress hyper-responsive rat strains

Repeated exposure to a homotypic stressor such as forced swimming enhances nociceptive responding in rats. However, the influence of genetic background on this stress-induced hyperalgesia is poorly understood. The aim of the present study was to compare the effects of repeated forced swim stress on nociceptive responding in Sprague-Dawley (SD) rats versus the Wistar Kyoto (WKY) rat strain, a genetic background that is susceptible to stress, negative affect and hyperalgesia. Given the well-documented role of the endocannabinoid system in stress and pain, we investigated associated alterations in endocannabinoid signalling in the dorsal horn of the spinal cord and amygdala. In SD rats, repeated forced swim stress for 10 days was associated with enhanced late phase formalin-evoked nociceptive behaviour, compared with naive, non-stressed SD controls. In contrast, WKY rats exposed to 10 days of swim stress displayed reduced late phase formalin-evoked nociceptive behaviour. Swim stress increased levels of monoacylglycerol lipase (MAGL) mRNA in the ipsilateral side of the dorsal spinal cord of SD rats, an effect not observed in WKY rats. In the amygdala, swim stress reduced anandamide (AEA) levels in the contralateral amygdala of SD rats, but not WKY rats. Additional within-strain differences in levels of CB1 receptor and fatty acid amide hydrolase (FAAH) mRNA and levels of 2-arachidonylglycerol (2-AG) were observed between the ipsilateral and contralateral sides of the dorsal horn and/or amygdala. These data indicate that the effects of repeated stress on inflammatory pain-related behaviour are different in two rat strains that differ with respect to stress responsivity and affective state and implicate the endocannabinoid system in the spinal cord and amygdala in these differences.

Pain in Times of Stress

Stress modulates pain perception, resulting in either stress-induced analgesia or stress-induced hyperalgesia, as reported in both animal and human studies. The responses to stress include neural, endocrine, and behavioural changes, and built-in coping strategies are in place to address stressors. Peculiar to humans are additional factors that modulate pain that are experienced in times of stress, notably psychological factors that potentially influence the directionality of pain perception.

Stress induces pain transition by potentiation of AMPA receptor phosphorylation

Chronic postsurgical pain is a serious issue in clinical practice. After surgery, patients experience ongoing pain or become sensitive to incident, normally nonpainful stimulation. The intensity and duration of postsurgical pain vary. However, it is unclear how the transition from acute to chronic pain occurs. Here we showed that social defeat stress enhanced plantar incision-induced AMPA receptor GluA1 phosphorylation at the Ser831 site in the spinal cord and greatly prolonged plantar incision-induced pain. Interestingly, targeted mutation of the GluA1 phosphorylation site Ser831 significantly inhibited stress-induced prolongation of incisional pain. In addition, stress hormones enhanced GluA1 phosphorylation and AMPA receptor-mediated electrical activity in the spinal cord. Subthreshold stimulation induced spinal long-term potentiation in GluA1 phosphomimetic mutant mice, but not in wild-type mice. Therefore, spinal AMPA receptor phosphorylation contributes to the mechanisms underlying stress-induced pain transition.

Diabetic neuropathies

PURPOSE OF REVIEW

This article provides an overview for understanding the diagnosis, pathogenesis, and management of diabetic neuropathy.

RECENT FINDINGS

New information about the pathogenesis of diabetic neuropathy continues to emerge, which will lead to identifying new drug targets. It is clear that the natural history of diabetic neuropathy is changing and the rate of progression is slowing. This is likely because of a combination of earlier diagnosis, improved glycemic management, and improved control of related complications such as hyperlipidemia and hypertension. Early diagnosis is critical, and small fiber neuropathy or subclinical diabetic neuropathy may be reversed or significantly improved with appropriate intervention. The American Academy of Neurology recently published guidelines for the treatment of painful diabetic neuropathy.

SUMMARY

Diabetic neuropathy is common and can present with varied clinical presentations discussed in this article. Although treatment currently focuses on pain management, attention should be paid to potential risk factors for neuropathy. For example, glycemic control, hyperlipidemia, and hypertension should be managed with diet, exercise, and medications. Class I or II clinical studies indicate that pregabalin, duloxetine, amitriptyline, gabapentin, and opioids are effective in the management of diabetic neuropathic pain.

BDNF-trkB-KCC2-GABA pathway may be related to chronic stress-induced hyperalgesia at both the spinal and supraspinal level

Chronic stresses can induce physiological and psychological changes and result in stress-related neuropsychiatry, sometimes they may also contribute to hypersensitivity to pain known as stress-induced hyperalgesia (SIH). Recently it was found that GABAergic disinhibition is closely related to morphine and chronic inflammation pain induced hyperalgesia in the PAG (periaqueductal gray)-RVM (rostral ventromedial medulla) -spinal descending facilitatory system, the changes of potassium-chloride co-transporter 2 (KCC2) function or expression modulated by brain-derived neurotrophic factor (BDNF) are involved in it. Similarly, chronic stress could induce changes of BDNF, KCC2 and a depolarizing shift in the GABA reversal potential (EGABA). Moreover, the descending facilitatory system has been suggested to be related with SIH, but whether it modulates SIH through disinhibition by the downregulation of KCC2 expression and/or transport function remains unknown. We therefore hypothesized that SIH may be owned to disinhibition caused by the activation of BDNF-trkB-KCC2-GABA pathway, which would provide a new understanding for SIH.

Treatment-induced neuropathy of diabetes: an acute, iatrogenic complication of diabetes

Treatment-induced neuropathy in diabetes (also referred to as insulin neuritis) is considered a rare iatrogenic small fibre neuropathy caused by an abrupt improvement in glycaemic control in the setting of chronic hyperglycaemia. The prevalence and risk factors of this disorder are not known. In a retrospective review of all individuals referred to a tertiary care diabetic neuropathy clinic over 5 years, we define the proportion of individuals that present with and the risk factors for development of treatment-induced neuropathy in diabetes. Nine hundred and fifty-four individuals were evaluated for a possible diabetic neuropathy. Treatment-induced neuropathy in diabetes was defined as the acute onset of neuropathic pain and/or autonomic dysfunction within 8 weeks of a large improvement in glycaemic control-specified as a decrease in glycosylated haemoglobin A1C (HbA1c) of ≥2% points over 3 months. Detailed structured neurologic examinations, glucose control logs, pain scores, autonomic symptoms and other microvascular complications were measured every 3-6 months for the duration of follow-up. Of 954 patients evaluated for diabetic neuropathy, 104/954 subjects (10.9%) met criteria for treatment-induced neuropathy in diabetes with an acute increase in neuropathic or autonomic symptoms or signs coinciding with a substantial decrease in HbA1c. Individuals with a decrease in HbA1c had a much greater risk of developing a painful or autonomic neuropathy than those individuals with no change in HbA1c (P < 0.001), but also had a higher risk of developing retinopathy (P < 0.001) and microalbuminuria (P < 0.001). There was a strong correlation between the magnitude of decrease in HbA1c, the severity of neuropathic pain (R = 0.84, P < 0.001), the degree of parasympathetic dysfunction (R = -0.52, P < 0.01) and impairment of sympathetic adrenergic function as measured by fall in blood pressure on tilt-table testing (R = -0.63, P < 0.001). With a decrease in HbA1c of 2-3% points over 3 months there was a 20% absolute risk of developing treatment-induced neuropathy in diabetes, with a decrease in HbA1c of >4% points over 3 months the absolute risk of developing treatment-induced neuropathy in diabetes exceeded 80%. Treatment-induced neuropathy of diabetes is an underestimated iatrogenic disorder associated with diffuse microvascular complications. Rapid glycaemic change in patients with uncontrolled diabetes increases the risk of this complication.

Neurobiology of stress-induced hyperalgesia

The intensity and severity of perceived pain does not correlate consistently with the degree of peripheral or central nervous system tissue damage or with the intensity of primary afferent or spinal nociceptive neurone activity. In this respect, the modulation of pain by emotion and context is now widely recognized. In particular, stress, fear and anxiety exert potent, but complex, modulatory influences on pain. Stress can either suppress pain (stress-induced analgesia) or exacerbate it (stress-induced hyperalgesia; SIH) depending on the nature, duration and intensity of the stressor. Herein, we review the methods and models used to study the phenomenon of SIH in rodents and humans and then present a detailed discussion of our current understanding of neural substrates and neurobiological mechanisms. The review provides perspectives and challenges for the current and future treatment of pain and the co-morbidity of pain with stress-related psychiatric disorders including anxiety and depression.

Stress-induced modulation of nociceptive responses in the rat anterior cingulate cortex

In the limbic system, the anterior cingulate cortex (ACCX) is one of the key areas involved in the close association between pain and emotion. However, neuronal changes in ACCX nociceptive responses after stress conditioning have not yet been quantitatively investigated. We investigated the modulation of nociceptive responses in the ACCX neurons following restraint stress in rats. The present study demonstrated that stress-conditioning enhanced excitatory nociceptive responses in the ACCX following tail stimuli in the mid-term (7 days). Short-term (3 days) and long-term (21 days) of stress conditioning did not affect these responses significantly. Nociceptive responses evoked by other sites of the body (nose, back and four paws) stimulation were not changed by stress-conditioning, indicating that neural information from the tail is important for emotional system modulation. It is suggested that the emotional/affective part of the pain sensation is strongly modified by stress through neuroplasticity in the ACCX.