Diabetic neuropathy

Regulation of increased glutamatergic input to spinal dorsal horn neurons by mGluR5 in diabetic neuropathic pain

Diabetic neuropathic pain is associated with increased glutamatergic input in the spinal dorsal horn. Group I metabotropic glutamate receptors (mGluRs) are involved in the control of neuronal excitability, but their role in the regulation of synaptic transmission in diabetic neuropathy remains poorly understood. Here we studied the role of spinal mGluR5 and mGluR1 in controlling glutamatergic input in a rat model of painful diabetic neuropathy induced by streptozotocin. Whole-cell patch-clamp recordings of lamina II neurons were performed in spinal cord slices. The amplitude of excitatory post-synaptic currents (EPSCs) evoked from the dorsal root and the frequency of spontaneous EPSCs (sEPSCs) were significantly higher in diabetic than in control rats. The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) inhibited evoked EPSCs and sEPSCs more in diabetic than in control rats. Also, the percentage of neurons in which sEPSCs and evoked EPSCs were affected by MPEP or the group I mGluR agonist was significantly higher in diabetic than in control rats. However, blocking mGluR1 had no significant effect on evoked EPSCs and sEPSCs in either groups. The mGluR5 protein level in the dorsal root ganglion, but not in the dorsal spinal cord, was significantly increased in diabetic rats compared with that in control rats. Furthermore, intrathecal administration of MPEP significantly increased the nociceptive pressure threshold only in diabetic rats. These findings suggest that increased mGluR5 expression on primary afferent neurons contributes to increased glutamatergic input to spinal dorsal horn neurons and nociceptive transmission in diabetic neuropathic pain.

Abnormal cold perception in the lower limbs: a sensitive indicator for detection of polyneuropathy in patients with type 1 diabetes mellitus

Diabetic peripheral neuropathy differs in type 1 and type 2 diabetes. The aim of this study was to evaluate how signs and symptoms of neuropathy correlated with defects in motor and sensory nerve conduction velocity (MCV and SCV) and sensory perception thresholds in patients with type 1 diabetes. MCV and SCV in peroneal and sural nerves and vibratory, warm and cold perception thresholds (VPT, WPT, CPT) were evaluated in the lower limbs of 127 patients (42+/-7.9 years old, duration of diabetes, 16+/-11 years and HbA1c, 7.7+/-1.4%). The results were compared with clinical findings (neuropathy impairment assessment, NIA) and sensory symptoms (neurological symptom assessment, NSA). Sensory symptoms were present in 24% of patients, 91% had at least one abnormal finding in the neurological examination and 84% had abnormal nerve conduction. The greatest deviation from normal was observed for CPT on the dorsum of the foot and peroneal MCV. NIA and NSA correlated with all electrophysiological measurements in the foot and big toe. It is concluded that clinical findings correlate well with electrophysiological abnormalities in patients with type 1 diabetic neuropathy. An elevated CPT for the foot was the most pronounced sensory defect.

Metabolism-induced oxidative stress is a mediator of glucose toxicity in HT22 neuronal cells

Oxidative stress has been widely considered as a key player in the adverse effects of hyperglycaemia to various tissues, including neuronal cells. This study examined the participation of oxidative stress in injurious effects of high glucose on HT22 cells along with the activity of proteasome, a proteolytic system responsible for degradation of oxidized proteins. Although 10-fold glucose concentration caused non-significant viability changes, a significant reduction of cell proliferation was found. Moreover, the cell morphology was also altered. These changes were followed by an enhancement of intracellular ROS generation, however without any significant boost of the carbonyl group concentration in proteins. Correspondingly, only a slight decline in the 20S proteasome activity was found in high-glucose-treated cells. On the other hand, substances affecting glucose metabolism or antioxidants partially preserved the oxidative stress in high glucose treated cells. In summary, these results highlight the role of metabolic oxidative stress in hyperglycaemia affecting neurons.

Antinociceptive effects of chronic administration of uncompetitive NMDA receptor antagonists in a rat model of diabetic neuropathic pain

Diabetic neuropathic pain remains an unmet clinical problem and is poorly relieved by conventional analgesics. N-methyl-D-aspartate (NMDA) receptors play an important role in central sensitization in neuropathic pain. Although NMDA antagonists are highly effective in reducing neuropathic pain, these agents cause severe side effects at therapeutic doses, which limit their clinical uses. Neramexane and memantine are uncompetitive NMDA antagonists with minimal side effects at therapeutic doses. Here we determined the antinociceptive effect of chronic administration of neramexane and compared its effect with that of memantine and gabapentin in a rat model of diabetic neuropathic pain. Mechanical hyperalgesia was measured with a noxious pressure stimulus, and tactile allodynia was assessed with von Frey filaments in diabetic rats induced by streptozotocin. Compared with vehicle-treated rats, treatment with neramexane (12.3, 24.6, and 49.2 mg/kg/day) for 2 weeks via an osmotic minipump produced dose-dependent and sustained effects on mechanical hyperalgesia and allodynia. Administration of memantine (20 mg/kg/day) or gabapentin (50 mg/kg/day) for 2 weeks also produced significant and persistent antinociceptive effects on mechanical hyperalgesia and allodynia. The magnitude of the antinociceptive effect produced by the intermediate and high doses of neramexane was comparable to that of gabapentin and memantine. The plasma level achieved by neramexane at 12.3, 24.6, and 49.2 mg/kg/day was 0.26 +/- 0.04, 0.50 +/- 0.05, and 1.21 +/- 0.16 microM, respectively. These data suggest that neramexane at therapeutically relevant doses attenuates diabetic neuropathic pain. Our study provides valuable information about the therapeutic potential of chronic administration of neramexane and memantine for painful diabetic neuropathy.

Evaluation of the efficacy of pulsed electromagnetic field in the management of patients with diabetic polyneuropathy

AIM

The study was carried out to evaluate and compare the effect of low power, low frequency pulsed electromagnetic field (PEMF) of 600 and 800 Hz, respectively, in management of patients with diabetic polyneuropathy.

SETTINGS AND DESIGNS

The study was a randomized controlled trial performed in Guru Nanak Dev University and Medical College, Amritsar, India with different subject experimental design.

MATERIALS AND METHODS

Thirty subjects within an age group of 40-68 years with diabetic polyneuropathy stages N1a, N1b, N2a were randomly allocated to groups 1, 2, 3 with 10 subjects in each. Group 1 and 2 were treated with low power 600 and 800-Hz PEMF for 30 min for 12 consecutive days. Group 3 served as control on usual medical treatment of diabetic polyneuropathy (DPN). The subjects with neuropathy due to any cause other than diabetes were excluded. The pain and motor nerve conduction parameters (distal latency, amplitude, nerve conduction velocity) were assessed before and after treatment.

STATISTICAL ANALYSIS

Related t-test and unrelated t-test were used for data analysis.

RESULTS

Significant reduction in pain and statistically significant (P<0.05) improvement in distal latency and nerve conduction velocity were seen in experimental group 1 and 2.

CONCLUSIONS

Low-frequency PEMF can be used as an adjunct in reducing neuropathic pain as well as for retarding the progression of neuropathy in a short span of time.

Neuronal Targeting in Diabetes Mellitus: A Story of Sensory Neurons and Motor Neurons

Diabetes mellitus targets the peripheral nervous system in unique but disabling ways. Although several mechanisms may target peripheral neurons, they render a degenerative pattern of damage that begins in distal terminals. Moreover, sensory neurons are involved early, motor neurons later. By studying a variety of diabetic neuropathy models in rats, mice, and other species, an overall appreciation of its neurodegeneration emerges. Understanding how mechanisms of diabetes complications target peripheral neurons selectively may offer opportunities to intervene before irretrievable neuron loss develops.NEUROSCIENTIST 14(4):311–318, 2008. DOI: 10.1177/1073858408316175

Blockade of sensory abnormalities and kinin B(1) receptor expression by N-acetyl-L-cysteine and ramipril in a rat model of insulin resistance

Glucose-fed rat is a model of insulin resistance that displays sensory polyneuropathy and hypertension. This study aimed at comparing the beneficial effects of N-acetyl-L-cysteine (NAC, antioxidant) and ramipril (angiotensin-1 converting enzyme inhibitor) on tactile and cold allodynia induced by chronic glucose feeding. Impact of these treatments was also assessed on hypertension, plasma glucose and insulin concentrations, insulin resistance and kinin B(1) receptor expression. Male Wistar rats (50-75 g) were given 10% d-glucose in their drinking water for 11 weeks or tap water (controls). Glucose-fed rats were treated either with NAC (1 g/kg/day, gavage), ramipril (1 mg/kg/day in drinking water) or no drug during the last 5 weeks. Glucose feeding for 6 weeks induced a significant increase in systolic blood pressure and hyperglycaemia which was accompanied by tactile and cold allodynia. At 11 weeks, plasma insulin, insulin resistance (HOMA index), kinin B(1) receptor mRNA in spinal cord and renal cortex and B(1) receptor binding sites in spinal cord were enhanced in glucose-fed rats. NAC and ramipril caused a progressive to complete inhibition of tactile and cold allodynia from 6 to 11 weeks. High systolic blood pressure, hyperinsulinemia, insulin resistance and kinin B(1) receptor expression were also normalized or attenuated in glucose-fed rats by either treatment. Results suggest that chronic treatment with an antioxidant or an ACE inhibitor provides similar beneficial effects on sensory polyneuropathy, hypertension and insulin resistance in glucose-fed rats. Both therapies were associated with a reduction of the expression of the pro-nociceptive kinin B(1) receptor.

Sensitivity of plantar cutaneous sensation and postural stability

BACKGROUND

Impaired plantar cutaneous sensation is often seen clinically and can lead to postural instability. It is not clear if the severity of such sensory loss would be associated with postural stability, and if such an association would be affected by sensory redundancy and task difficulty. The purpose of this study was to investigate the association of the degree of somatosensory loss and postural stability by experimentally induced somatosensory loss in healthy young adults.

METHODS

Twenty-one healthy young adults performed four quiet standing tasks (normal or narrow base, and eyes open or closed) on a force platform under three somatosensory conditions induced by ischemic blocking of afferent conduction below the ankle, normal, partial loss and complete loss. Differences in the standing center of pressure motion between the three sensory loss conditions were compared.

FINDINGS

There was a significant trend of greater center of pressure motion with increasing severity of sensory loss in all task conditions. The differences in the center of pressure motion between partial and total loss conditions were significant only in conditions where vision was removed and the support surface was narrow.

INTERPRETATION

Increased severity of experimentally induced loss of plantar cutaneous sensitivity was associated with greater postural sway. Such an association was affected by the availability of visual input and the size of the support surface. Clinically for patients with somatosensory impairments of the foot, postural stability should be given special attention.

Carpal tunnel syndrome and the "double crush" hypothesis: a review and implications for chiropractic

Upton and McComas claimed that most patients with carpal tunnel syndrome not only have compressive lesions at the wrist, but also show evidence of damage to cervical nerve roots. This "double crush" hypothesis has gained some popularity among chiropractors because it seems to provide a rationale for adjusting the cervical spine in treating carpal tunnel syndrome. Here I examine use of the concept by chiropractors, summarize findings from the literature, and critique several studies aimed at supporting or refuting the hypothesis. Although the hypothesis also has been applied to nerve compressions other than those leading to carpal tunnel syndrome, this discussion mainly examines the original application - "double crush" involving both cervical spinal nerve roots and the carpal tunnel. I consider several categories: experiments to create double crush syndrome in animals, case reports, literature reviews, and alternatives to the original hypothesis. A significant percentage of patients with carpal tunnel syndrome also have neck pain or cervical nerve root compression, but the relationship has not been definitively explained. The original hypothesis remains controversial and is probably not valid, at least for sensory disturbances, in carpal tunnel syndrome. However, even if the original hypothesis is importantly flawed, evaluation of multiple sites still may be valuable. The chiropractic profession should develop theoretical models to relate cervical dysfunction to carpal tunnel syndrome, and might incorporate some alternatives to the original hypothesis. I intend this review as a starting point for practitioners, educators, and students wishing to advance chiropractic concepts in this area.

Muscle fiber conduction abnormalities in early diabetic polyneuropathy

OBJECTIVE

Diabetic polyneuropathy (PNP) has been proposed to be a primary disorder of sensory nerves. At an early stage motor nerve conduction velocity (MNCV) and muscle strength remain preserved due to compensatory mechanisms (axonal sprouting, reinnervation). We evaluated the use of invasive muscle fiber conduction velocity (MFCV) measurements as a method to detect muscle fiber denervation atrophy, as an early sign of motor axonal loss in diabetes mellitus (DM).

METHODS

Twelve selected male patients (8 type 1, 4 type 2; mean age 35.8 years, SD 10.6), without any sign of micro- or macroangiopathy, were studied by systematic clinical and neurophysiological testing including MFCV estimation.

RESULTS

Hand-held dynamometry was normal in all subjects. There were no signs of recent denervation by concentric needle EMG in any of the patients. Sensory nerve conduction velocity (SNCV) was abnormal in 6 subjects, MFCV in 6 subjects (5 had also low SNCV). The ratio of fastest/slowest muscle fibers in MFCV was correlated to SNCV of sural nerve (-.59, p < .05), but not to MNCV.

CONCLUSIONS

Half of the clinically asymptomatic DM subjects showed sensory involvement together with MFCV abnormalities, despite normal needle EMG and force.

SIGNIFICANCE

MFCV estimation offers a sensitive method in detecting early signs of motor axonal dysfunction in DM.

Diabetes mellitus and the peripheral nervous system: manifestations and mechanisms

Diabetes targets the peripheral nervous system with several different patterns of damage and several mechanisms of disease. Diabetic polyneuropathy (DPN) is a common disorder involving a large proportion of diabetic patients, yet its pathophysiology is controversial. Mechanisms considered have included polyol flux, microangiopathy, oxidative stress, abnormal signaling from advanced glycation endproducts and growth factor deficiency. Although some clinical trials have demonstrated modest benefits in disease stabilization or pain therapy in DPN, robust therapy capable of reversing the disease is unavailable. In this review, general aspects of DPN and other diabetic neuropathies are examined, including a summary of recent therapeutic trials. A particular emphasis is placed on the evidence that the neurobiology of DPN reflects a unique yet common and disabling neurodegenerative disorder.

Effect of insulin and its combination with resveratrol or curcumin in attenuation of diabetic neuropathic pain: participation of nitric oxide and TNF-alpha

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, is recognized as one of the most difficult types of pain to treat. The underlying mechanisms of painful symptoms may be closely associated with hyperglycaemia but a lack of the understanding of its proper aetiology, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve this pain. The aim of the present study was to explore the antinociceptive effect of insulin and its combinations with resveratrol and curcumin in attenuating diabetic neuropathic pain. The study also aimed to examine the effect of these combinations on tumour necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) levels in streptozotocin (STZ) induced diabetic mice. Four weeks after a single intraperitoneal injection of streptozotocin (200 mg/kg), mice were tested in the tail immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia along with increased plasma glucose and decreased body weights compared with control mice. Chronic treatment with insulin (10 IU/kg/day, s.c.) and its combinations with antioxidants (resveratrol 20 mg/kg or curcumin 60 mg/kg, p.o.) for 4 weeks starting from the 4th week of STZ injection significantly attenuated thermal hyperalgesia and the hot-plate latencies. There was a significant inhibition of TNF-alpha and NO levels when these drugs were given in combination compared with their effects per se. These results indicate an antinociceptive activity of resveratrol and curcumin and point towards the beneficial effect of these combinations with insulin in attenuating diabetic neuropathic pain, possibly through the participation of NO and TNF-alpha.

Subclinical diabetic neuropathy with normal conventional electrophysiological study

BACKGROUND

For early detection and prevention of diabetic neuropathy, it is important to identify subclinical diabetic neuropathy. Routine nerve conduction study often fails to detect early stage of neuropathy.

OBJECTIVES

The purpose of this study is to evaluate the clinical usefulness of electrophysiological indexes in detecting early diabetic neuropathy with no objective clinical or electrophysiological abnormalities.

MATERIALS AND METHODS

Nerve conduction study of upper/lower limbs was investigated in 31 subclinical diabetic neuropathy patients with normal nerve conduction studies(group I), 38 clinical diabetic neuropathy patients with normal nerve conduction studies(group II) and 31 normal controls. Residual latency (RL), terminal latency index (TLI) and modified F ratio (MFR) were calculated and compared among groups.

RESULTS

Compared with controls, MFR of lower limbs and TLI of both upper/lower limbs were significantly decreased in both group I and II (p<0.05). RL was increased in both groups, but the difference was not statistically significant. Comparing the indexes between group I and II, there was no significant difference.

CONCLUSIONS

RL, TLI and MFR, which reflect distal conduction slowing, may be useful indexes to identify subclinical diabetic neuropathy. The results also suggest that electrophysiological changes that are obscured in routine nerve conduction study are present before the clinical manifestation.

Altered synaptic input and GABAB receptor function in spinal superficial dorsal horn neurons in rats with diabetic neuropathy

Hyperactivity of spinal dorsal horn neurons plays an important role in the development of diabetic neuropathic pain. However, little is known as to whether synaptic input to spinal dorsal horn neurons is altered in diabetic neuropathy. Also, the function of GABAB receptors in the control of synaptic input to dorsal horn neurons in diabetes remains poorly understood. To determine the changes in synaptic input to dorsal horn neurons and the GABAB)receptor function in streptozotocin-induced diabetes, we performed whole-cell recording (GDP-beta-S included in the internal solution) on lamina II neurons in rat spinal cord slices. The frequency of glutamatergic mEPSCs and the amplitude of monosynaptic EPSCs evoked from the dorsal root were significantly higher in diabetic than in control rats. On the other hand, the basal frequency and amplitude of GABAergic spontaneous IPSCs and mIPSCs and those of glycinergic spontaneous IPSCs and mIPSCs did not differ significantly between control and diabetic rats. The GABAB agonist baclofen produced a significantly greater reduction in dorsal root-evoked EPSCs and the frequency of mEPSCs in control than in diabetic rats. However, the inhibitory effect of baclofen on GABAergic and glycinergic spontaneous IPSCs and mIPSCs was not significantly different in the two groups. These findings suggest that increased glutamatergic input from primary afferents to dorsal horn neurons may contribute to synaptic plasticity and central sensitization in diabetic neuropathic pain. Furthermore, the function of presynaptic GABAB receptors at primary afferent terminals, but not that on GABAergic and glycinergic interneurons, in the spinal cord is reduced in diabetic neuropathy.

Conduction slowing in painful versus painless diabetic neuropathy

Motor conduction slowing in diabetic distal symmetrical polyneuropathy (DSP) generally exceeds that in distal axonal polyneuropathy. Additional mechanisms secondary to axonal injury may contribute to motor conduction slowing; however, its clinical and pathophysiological significance has rarely been discussed. The purpose of this study was to evaluate the clinical and pathophysiological significance of conduction slowing in DSP. We analyzed motor conduction in 50 patients with symptomatic painful DSP and 25 patients with asymptomatic painless DSP. Motor conduction data from 40 patients with amyotrophic lateral sclerosis (ALS) were used as controls for pure axonal conduction slowing. Compound muscle action potential amplitude (CMAP), distal motor latency (DL), and conduction velocity (CV) values were converted to a percentage of the upper or lower limits of normal and then presented in square root transformation (SQRT) form. Plots of SQRT-DL and SQRT-CV against SQRT-CMAP were analyzed. Regression analysis showed that DL and CV are amplitude-dependent in both painless DSP and ALS. Changes of DL and CV in painful DSP were not amplitude-dependent except for DL in the lower extremities. Our data support the hypothesis that the mechanism of slowing is similar in both painless DSP and ALS, and that it results from the loss of large, fast-conducting fibres. Lack of amplitude-dependency in conduction slowing in painful DSP may reflect combined axonal and demyelinating changes.

Neurotrophic modulation of myelinated cutaneous innervation and mechanical sensory loss in diabetic mice

Human diabetic patients often lose touch and vibratory sensations, but to date, most studies on diabetes-induced sensory nerve degeneration have focused on epidermal C-fibers. Here, we explored the effects of diabetes on cutaneous myelinated fibers in relation to the behavioral responses to tactile stimuli from diabetic mice. Weekly behavioral testing began prior to streptozotocin (STZ) administration and continued until 8 weeks, at which time myelinated fiber innervation was examined in the footpad by immunohistochemistry using antiserum to neurofilament heavy chain (NF-H) and myelin basic protein (MBP). Diabetic mice developed reduced behavioral responses to non-noxious (monofilaments) and noxious (pinprick) stimuli. In addition, diabetic mice displayed a 50% reduction in NF-H-positive myelinated innervation of the dermal footpad compared with non-diabetic mice. To test whether two neurotrophins nerve growth factor (NGF) and/or neurotrophin-3 (NT-3) known to support myelinated cutaneous fibers could influence myelinated innervation, diabetic mice were treated intrathecally for 2 weeks with NGF, NT-3, NGF and NT-3. Neurotrophin-treated mice were then compared with diabetic mice treated with insulin for 2 weeks. NGF and insulin treatment both increased paw withdrawal to mechanical stimulation in diabetic mice, whereas NT-3 or a combination of NGF and NT-3 failed to alter paw withdrawal responses. Surprisingly, all treatments significantly increased myelinated innervation compared with control-treated diabetic mice, demonstrating that myelinated cutaneous fibers damaged by hyperglycemia respond to intrathecal administration of neurotrophins. Moreover, NT-3 treatment increased epidermal Merkel cell numbers associated with nerve fibers, consistent with increased numbers of NT-3-responsive slowly adapting A-fibers. These studies suggest that myelinated fiber loss may contribute as significantly as unmyelinated epidermal loss in diabetic neuropathy, and the contradiction between neurotrophin-induced increases in dermal innervation and behavior emphasizes the need for multiple approaches to accurately assess sensory improvements in diabetic neuropathy.

Intrathecally administered COX-2 but not COX-1 or COX-3 inhibitors attenuate streptozotocin-induced mechanical hyperalgesia in rats

Members of the cyclooxygenase (COX) family are known to catalyze the rate-limiting steps of prostaglandins synthesis and reported to be involved in neuropathic pain. Diabetic neuropathy is a type of neuropathic pain, though it is not clear if COX is relevant to the condition. Recently, spinal COX-2 protein was found to be increasing in streptozotocin-induced rats as compared to the constitutive expression. We attempted to determine which cyclooxygenase isoforms are involved in streptozotocin-induced mechanical hyperalgesia, which was induced by a single intraperitoneal injection of 75 mg/kg of streptozotocin. Intrathecal administrations of the COX-2 inhibitors SC-58125 (7-100 microg) and NS-398 (7-60 microg), as well as a high dose (100 microg) of the COX-1 inhibitor SC-560 attenuated hyperalgesia, whereas intrathecal administrations of a low dose (10 microg) of SC-560 and the COX-3 inhibitor acetaminophen (1-7 mg) did not. Further, intrathecal administration of SC-58125 (100 microg) did not produce an analgesic effect in normal rats. These results indicate that intrathecal administration of COX-2 inhibitors has an anti-hyperalgesic effect on streptozotocin-induced mechanical hyperalgesia and we concluded that spinal COX-2 is pivotal in streptozotocin-induced hyperalgesia.

Possible involvement of cholinergic and opioid receptor mechanisms in fluoxetine mediated antinociception response in streptozotocin-induced diabetic mice

Clinical and experimental studies have been reported that antidepressant drugs can be used as co-analgesics in the management of neuropathic pain. However, the mechanism through which they alleviate pain still remains unclear. The aim of the present study was to investigate the possible mechanism of action of fluoxetine-induced antinociceptive effect in streptozotocin-induced diabetic mice, especially the involvement of non-serotonergic neurotransmitters and their receptors. Diabetes was induced in male Laka mice with a single intraperitoneal injection of streptozotocin (200 mg/kg). Four weeks after streptozotocin, diabetic mice were tested for pain responses in the tail-immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia as compared with control mice. Fluoxetine (10 and 20 mg/kg, i.p) injected into diabetic mice produced an antinociceptive effect in both tail-immersion and hot-plate assays. The antinociceptive effect of fluoxetine in diabetic mice was significantly lower as compared with that in control mice. Pretreatment with a muscarinic receptor antagonist, atropine (2 and 5 mg/kg, i.p) and an opioid receptor antagonist, naloxone (2 and 5 mg/kg, i.p), but not the alpha(2)-adrenoreceptor antagonist, yohimbine (2 and 5 mg/kg, i.p) reversed the antinociceptive effect of fluoxetine (20 mg/kg). These results suggest that apart from serotonin pathway, muscarinic and opioid receptors also participate in fluoxetine-induced antinociception in diabetic neuropathic pain.

Antinociceptive efficacy of lacosamide in a rat model for painful diabetic neuropathy

Lacosamide was tested in the streptozotocin rat model of diabetic neuropathic pain in comparison to drugs which are commonly used in the treatment of diabetic neuropathic pain, i.e. antidepressants and anticonvulsants. In diabetic rats, lacosamide attenuated cold (10, 30 mg/kg, i.p.), warm (3, 10, 30 mg/kg, i.p.) and mechanical allodynia (30 mg/kg, i.p.). Streptozotocin-induced thermal and mechanical hyperalgesia were reduced by lacosamide at doses of 10 and 30 mg/kg, i.p. Morphine (3 mg/kg) showed similar efficacy on allodynia and hyperalgesia. Amitriptyline (10 mg/kg), venlafaxine (15 mg/kg), levetiracetam (180 mg/kg) and pregabalin (100 mg/kg) exhibited significant effects on thermal allodynia and mechanical hyperalgesia. Only treatment with amitriptyline (30 mg/kg, i.p.) produced full reversal of thermal allodynia comparable to lacosamide. Lamotrigine (45 mg/kg, i.p.) had no effect on both behavioral readouts. Lacosamide's potency and efficacy in reversing pain behavior might be due to its new, yet unknown mechanism of action.

Curcumin attenuates thermal hyperalgesia in a diabetic mouse model of neuropathic pain

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus is recognised as one of the most difficult types of pain to treat. A lack of the understanding of its aetiology, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of the newer agents to relieve this pain. The aim of the present study was to explore the antinociceptive effect of curcumin and its effect on tumour necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) release in streptozotocin induced diabetic mice. Four weeks after a single intraperitoneal injection of streptozotocin (200 mg/kg), mice were tested in the tail immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia along with increased plasma glucose and decreased body weights as compared with control mice. Chronic treatment with curcumin (15, 30 and 60 mg/kg body weight; p.o.) for 4 weeks starting from the 4th week of streptozotocin injection significantly attenuated thermal hyperalgesia and the hot-plate latencies. Curcumin also inhibited the TNF-alpha and NO release in a dose dependent manner. These results indicate an antinociceptive activity of curcumin possibly through its inhibitory action on NO and TNF-alpha release and point towards its potential to attenuate diabetic neuropathic pain.

Characterization of the antinociceptive effects of oxycodone in diabetic mice

We investigated the antinociceptive efficacy of systemic and centrally injected oxycodone on thermal hyperalgesia in streptozotocin-induced diabetic mice. The antinociceptive response was assessed by recording the latency in the tail-flick test using the radiant heat from a 50-W projection bulb on the tail. The tail-flick latency in diabetic mice was significantly shorter than that in non-diabetic mice. Oral (p.o.) and i.t., but not i.c.v., administration of oxycodone prolonged the tail-flick latency in diabetic mice to a level that was considerably longer than the baseline latency in non-diabetic mice. However, morphine did not significantly inhibit the tail-flick response in diabetic mice. The antinociceptive effect of either p.o. or i.t. oxycodone in non-diabetic mice, but not in diabetic mice, was antagonized by pretreatment with a selective mu-opioid receptor antagonist, beta-funaltrexamine. In non-diabetic mice, pretreatment with a selective kappa-opioid receptor antagonist, nor-binaltorphimine, had no effect on the peak antinociceptive effect of either p.o. or i.t. oxycodone at 30 min after administration, however, it slightly but significantly reduced oxycodone-induced antinociception at 60 and 90 min after administration. On the other hand, pretreatment with nor-binaltorphimine practically abolished the antinociceptive effects of both p.o.- and i.t.-administered oxycodone in diabetic mice. Naltrindole, a selective delta-opioid receptor antagonist, had no effects on the antinociceptive effect of oxycodone in either non-diabetic or diabetic mice. These results suggest that the antinociceptive effects of oxycodone may be mediated by spinal kappa-opioid receptors in diabetic mice, whereas it may interact primarily with supraspinal and spinal mu-opioid receptors in non-diabetic mice.

The prevalence of neuropathy and relationship with risk factors in diabetic patients: a single-center experience

OBJECTIVE

To determine the rate of distal symmetrical polyneuropathy (DSP) in patients with type 2 diabetes mellitus, to evaluate the role of history, neurological examination and the electrodiagnostic methods in the diagnosis of DSP, and to determine the association between electromyography-supported neuropathy (ESN), neuropathic complaints (NCs) and risk factors.

SUBJECTS AND METHODS

A total of 191 type 2 DM patients (109 female, 82 male; mean age 58.7 +/- 10 years) were recruited. The NCs were recorded. All patients had electromyographic (EMG) examinations. The relationship between ESN, NCs and risk factors were evaluated.

RESULTS

Of the 191 patients, 83 (43.5%) had DSP on EMG examinations and 92 (48.2%) patients suffered from NCs. Among the ESN patients, a significant relationship existed with HbA1(c) level, illness duration, smoking, male gender or insulin usage (p < 0.05) but not with age, hypertension, hypercholesterolemia or hypertriglyceridemia. The frequency of NCs was higher in patients with ESN. There was also a significant association between NCs and ESN (p < 0.05). The presence of NCs was not related to age, gender, smoking, hypertension, hypercholesterolemia and hypertriglyceridemia (p > 0.05) but NCs were correlated to HbA1(c) level, illness duration and insulin usage (p < 0.05).

CONCLUSION

Our data show that a strong association exists between the presence of DSP and illness duration, HbA1(c), smoking, thereby indicating that cessation of smoking and near normal glycemic control would be additional precautions to delay the beginning or progression of polyneuropathy.

Antinociceptive effect of oxycodone in diabetic mice

The effect of oxycodone on thermal hyperalgesia in streptozotocin-induced diabetic mice was examined. The antinociceptive response was assessed by recording the latency in the tail-flick test using the radiant heat from a 50-W projection bulb on the tail. The tail-flick latency in diabetic mice was significantly shorter than that in non-diabetic mice. When diabetic mice were treated with oxycodone (5 mg/kg, s.c.), the tail-flick latency in diabetic mice was prolonged to the level considerably longer than the baseline latencies of non-diabetic mice. However, s.c. administration of morphine (5 mg/kg) did not produce a significant inhibition of the tail-flick response in diabetic mice. Oxycodone, at doses of 1.25-5.0 mg/kg administered s.c., produced a dose-dependent increase in the tail-flick latencies in both diabetic and non-diabetic mice. The antinociceptive effect of oxycodone was antagonized by pretreatment with a selective delta-opioid receptor antagonist, beta-funaltrexamine (20 mg/kg, s.c.), in both non-diabetic and diabetic mice. In non-diabetic mice, pretreatment with a selective kappa-opioid receptor antagonist, nor-binaltorphimine (20 mg/kg, s.c.) had no effect on the peak antinociceptive effect of oxycodone observed 30 min after administration, however, it slightly but significantly reduced oxycodone-induced antinociception observed 60 and 90 min after administration. On the other hand, pretreatment with nor-binaltorphimine practically abolished the peak (30 min) and persistent (60 and 90 min) antinociceptive effects of oxycodone in diabetic mice. Naltrindole (35 mg/kg, s.c.), a selective delta-opioid receptor antagonist, had no effects on the antinociceptive effect of oxycodone in both non-diabetic and diabetic mice. These results suggest that the antinociceptive effects of oxycodone may be mediated by mu- and kappa-opioid receptors in diabetic mice, whereas it may interact primarily with mu-opioid receptors in non-diabetic mice.

F-wave and H-reflex alterations in recently diagnosed diabetic patients

OBJECTIVE

To explore the frequency of F-wave and H-reflex alterations in recently diagnosed type 2 diabetes mellitus patients and to determine if the alterations are dependent on the levels of glycemia.

METHODS

A cross-sectional study was carried out on 50 asymptomatic patients, with a mean age of 45.4 +/- 9.8 years and a disease evolution of less than 10 years. Patients were classified as either normoglycemic (7 mmol/L; n = 20) or hyperglycemic (7 mmol/L; n = 30). H-reflex (HR), F-wave (FW), and nerve-conduction measurements (NCM) between the diabetic and non-diabetic (control) groups were compared.

RESULTS

The H-reflex was absent in 22% of the patients, while the M-component of this reflex was altered in 58% of patients. The F-wave was altered in 12% of the patients. The motor nerve compound action potential showed a diminution in amplitude (26% of patients, n = 13), area (32%, n = 16), and conduction velocity (20%, n = 10). No positive correlation between glycemia levels and the above alterations was found.

CONCLUSIONS

This study demonstrated that asymptomatic diabetic patients showed a high incidence of subclinical neurophysiological abnormalities.

Bilateral changes in somatosensory sensibility after unilateral below-knee amputation

OBJECTIVE

To evaluate possible alteration in proprioceptive and cutaneous sensibility in the nonamputated leg of unilateral transtibial amputees.

DESIGN

Cross-sectional study with between-subjects (amputees vs controls) and within-subjects (nonamputated vs amputated leg) comparisons.

SETTING

Canadian rehabilitation hospital research laboratory.

PARTICIPANTS

Two groups of amputees (34 due to traumatic causes, 14 due to vascular causes), recruited more than 1 year after their prosthetic training; and 2 groups (n=34, n=14) of age-matched control subjects.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Threshold of movement detection and touch-pressure perception at the knee and foot levels.

RESULTS

In the traumatic group, the sensory thresholds of the nonamputated leg were significantly higher than the control values in the 2 modalities tested. The movement detection was reduced at the knee and ankle levels, whereas a decrease in touch-pressure sensibility was observed only at the plantar site. As expected, a large proportion of the vascular amputees presented with severe sensory deficits in the nonamputated leg, particularly a loss in touch-pressure perception at the foot. The thresholds of movement detection were similar and correlated at both knees in the 2 groups of amputees. For the touch-pressure thresholds, no significant relationship was found between sides at the knee level.

CONCLUSIONS

Sensory changes observed in the nonamputated leg suggest that central sensory adaptations occur after amputation. For movement detection, they were marked by a matching of perception on both sides of the body. Functional significance of these changes remains to be determined.

Spinal orexin-1 receptors mediate anti-hyperalgesic effects of intrathecally-administered orexins in diabetic neuropathic pain model rats

Orexin-A and orexin-B are endogenous ligands of orexin receptors that contain orexin-1 and orexin-2. Activation of the orexinergic system can produce antinociceptive effects in acute inflammatory, mono-neuropathic, and postoperative pain animal models, though the effects of orexins on diabetic neuropathic pain have not been previously investigated. In this study, we studied the anti-hyperalgesic effects of intrathecally administered orexins in a streptozotocin-induced diabetic rat. First, dose-dependent effects were investigated by measuring hind paw withdrawal thresholds in response to noxious-heat and punctate stimuli, after which orexin levels in the cerebrospinal fluid of diabetic rats were measured and compared with those of normal rats using a radioimmunoassay method. The functional role of spinal orexin-1 receptors with the anti-hyperalgesic effects of orexins was also investigated using intrathecal pretreatment with SB-334867, a selective orexin-1 receptor antagonist. Intrathecally administered orexins produced an antinociceptive effect in diabetic rats, however, not in normal rats, though the orexin levels in the cerebrospinal fluid of diabetic rats were similar to those in normal rats. In addition, the anti-hyperalgesic effects of orexins were significantly inhibited by pretreatment with SB-334867. These findings demonstrate that the anti-hyperalgesic effects of orexins in diabetic rats are unlikely due to any direct effect by the supplement on decreased endogenous orexins in the cerebrospinal fluid and that orexin-1 receptors in the spinal cord may be involved in the modulation of nociceptive transmission in diabetic neuropathy. We conclude that the spinal orexinergic system may be a possible target for elucidating the mechanisms of diabetes-induced hyperalgesia.

Experimental diabetic neuropathy with spontaneous recovery: is there irreparable damage?

Progressive diabetic neuropathy has hitherto been irreversible in humans. New approaches raise the question of whether islet cell reconstitution rendering euglycemia can reverse specific features of neuropathy. We evaluated physiological and structural features of experimental neuropathy in a long-term murine model of diabetes induced by streptozotocin. By serendipity, a subset of these diabetic mice spontaneously regained islet function and attained near-euglycemia. Our hypotheses were that this model might better reflect axon loss observed in human disease and that spontaneous recovery from diabetes might identify the features of neuropathy that are reversible. In this model, experimental neuropathy closely modeled that in humans in most critical aspects: declines in motor conduction velocities, attenuation of compound muscle (M waves) and nerve action potentials, axon atrophy, myelin thinning, loss of epidermal axons, and loss of sweat gland innervation. Overt sensory neuron loss in dorsal root ganglia was a feature of this model. In mice with recovery, there was robust electrophysiological improvement, less myelin thinning, and remarkable epidermal and sweat gland reinnervation. There was, however, no recovery of populations of lost sensory neurons. Our findings identify a robust model of human diabetic neuropathy and indicate that overt, irretrievable loss of sensory neurons is one of its features, despite collateral reinnervation of target organs. Sensory neurons deserve unique protective strategies irrespective of islet cell reconstitution.

Symptomatic focal mononeuropathies in diabetic patients: increased or not?

The aim of this study was to investigate whether symptomatic mononeuropathies are more frequent in diabetic patients without symptoms of acute or subacute polyneuropathy than in the general population.For this purpose, six hundred and forty two consecutive outpatients with various acute symptomatic mononeuropathies (radial, ulnar or peroneal neuropathy, Bell's palsy or carpal tunnel syndrome) without symptoms of acute or subacute polyneuropathy were studied. The results showed that in 522 patients with symptomatic carpal tunnel syndrome (CTS) and in 38 patients with Bell's palsy, the rate of diabetes was 7.7% and 10.5%, respectively. These rates do not differ significantly from the anticipated frequency of diabetes in the general population. On the other hand, in 18 patients with radial neuropathy at (or distally to) the spiral groove, in 41 patients with ulnar neuropathy and in 23 patients with peroneal neuropathy at the fibular head, the respective rates were 27.8%, 12.2 % and 30.4%. These rates are significantly higher than those anticipated according to the frequency of diabetes in the general population. The findings of the present study indicate that only focal limb neuropathies due to acute external compression are more frequent in diabetic patients.

Modulatory effect of the PDE-5 inhibitor sildenafil in diabetic neuropathy

Diabetic neuropathy is one of the most frequent peripheral neuropathies associated with hyperalgesia and hyperesthesia. Besides alteration in the levels of neurotransmitter, alteration in the neuronal nitric oxide synthase (nNOS) is a key factor in the pathogenesis of diabetic neuropathy. The present study was aimed at evaluating the role of PDE-5 inhibitor on nociception in streptozotocin-induced diabetes in animal models of nociception (writhing assay in mice and paw hyperalgesia test in rats). Diabetic animals showed a significant decrease in pain threshold as compared to non-diabetic animals in both tests, indicating diabetes induced hyperalgesia in mice and rats. The PDE-5 inhibitor, sildenafil, significantly increased the pain threshold in both diabetic and non-diabetic animals. However, L-NAME, a non-specific NOS inhibitor and methylene blue (MB), a guanylate cyclase inhibitor blocked the antinociceptive effect. The per se administration of L-NAME or MB augmented the hyperalgesic response in diabetic animals with little or no effect in non-diabetic animals, indicating the alteration of NO-cGMP pathway in diabetes. The results in the present study demonstrate that the decreased nNOS-cGMP system may play a crucial role in the pathogenesis of diabetic neuropathy.

Effect of Glycemic Control on Electrophysiologic Changes of Diabetic Neuropathy in Type 2 Diabetic Patients

Diabetic neuropathy is a common complication of diabetes mellitus. Effective blood glucose control retards changes in nerve conduction velocity in type 1 diabetes. This study examined the relationship between glycemic control and electrophysiologic changes in diabetic neuropathy in 57 type 2 diabetic patients. Nerve conduction in the peroneal motor nerve, tibial motor nerve, and sural nerve were measured at study entry and at follow-up 24+/-3.12 months later. Changes in individual nerves are expressed as a percentage change (PC) and overall electrophysiologic changes are expressed as the sum of individual PCs. The PCs for peroneal motor nerve velocity, tibial motor nerve velocity, and sural nerve velocity were all lower in patients with a mean HbA1c of 8.5% or less compared with those in patients with a mean HbA1c of more than 8.5%, and SPCV (sum of PC in velocity) was significantly inversely correlated with mean HbA1c. However, there was no significant difference in SPCV in subjects with or without hypertension, hypertriglyceridemia, or low high-density lipoprotein cholesterol concentration. In conclusion, hyperglycemia is the most important etiology for electrophysiologic progression in type 2 diabetic patients. Furthermore, a mean HbA1c of more than 8.5% will result in significant deterioration in electrophysiology.

Fluoxetine attenuates thermal hyperalgesia through 5-HT1/2 receptors in streptozotocin-induced diabetic mice

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, is recognised as one of the most difficult types of pain to treat. A lack of understanding of its aetiology, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve this pain. The aim of the present study was to explore the antinociceptive effect and possible mechanism of action of a serotonin reuptake inhibitor, fluoxetine, in streptozotocin-induced diabetic mice. Four weeks after a single intraperitoneal injection of streptozotocin (200 mg/kg), mice were tested in the tail-immersion and hot-plate assays. Diabetic mice exhibited significant hyperalgesia compared with control mice. Fluoxetine (10 and 20, but not 5 mg/kg, i.p.) injected into diabetic mice produced an antinociceptive effect in both the tail-immersion and hot-plate assays. The percentage maximum possible effect (% MPE) produced by fluoxetine (20 mg/kg, i.p.) was significantly lower in diabetic mice than in control mice. The antinociceptive effect of fluoxetine (20 mg/kg) in diabetic mice was dose-dependently potentiated by pindolol (5 and 10 mg/kg, i.p., a selective 5-HT(1A/1B) receptor antagonist), attenuated by ritanserin (1 and 2 mg/kg, i.p., a selective 5-HT(2A/2C) receptor antagonist) and remained unaffected by ondansetron (1 and 2 mg/kg, i.p., a selective 5-HT(3) receptor antagonist) in both test systems. These results suggest that fluoxetine-induced antinociception primarily involves serotonin pathway modulation through 5-HT(1) and 5-HT(2) receptors, but not through 5-HT(3) receptors, in the chronic pain associated with streptozotocin-induced diabetic neuropathy. Further, the potentiation of the antinociceptive effect of fluoxetine by pindolol indicates the usefulness of a combination of an antidepressant and a 5-HT(1A/1B) receptor antagonist in the treatment of diabetic neuropathic pain in humans.

Hippocampal synaptic plasticity and glutamate receptor regulation: influences of diabetes mellitus

Diabetes mellitus is an endocrine disorder of carbohydrate metabolism resulting primarily from inadequate insulin release (Type 1 insulin-dependent diabetes mellitus) or insulin insensitivity coupled with inadequate compensatory insulin release (Type 2 non-insulin-dependent diabetes mellitus). Previous studies involving behavioural and electrophysiological analysis indicate that diabetes mellitus induces cognitive impairment and defects of long-term potentiation in the hippocampus. Considered to be an important mechanism of learning and memory in mammals, long-term potentiation is known to require regulation of the glutamate receptor properties. According to many studies, defects of long-term potentiation in the hippocampus of diabetic animals are due to abnormal glutamate receptors. We review here the changes in glutamate receptors that may account for modifications of long-term potentiation in various models of diabetes mellitus. As glutamate receptors are also involved in the appearance of neurodegenerative states, we discuss the possibility that deficits in long-term potentiation during chronic diabetes might arise from dysfunction of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors in early stages of the disease. This review addresses the possible role of hyperglycaemia and insulin in regulating these receptors.

Altered temporal pattern of mechanically evoked C-fiber activity in a model of diabetic neuropathy in the rat

While enhanced nociceptor activity has been demonstrated in models of painful peripheral neuropathy, analyses of activity pattern, which could play a role in the symptoms experienced as well as help elucidate underlying mechanism, are still limited. We evaluated the pattern of C-fiber activity, in response to mechanical and chemical stimuli, in a rat model of diabetes induced by a pancreatic beta-cell toxin, streptozotocin (STZ). In diabetic rats the number of action potentials produced by threshold and suprathreshold (10 g) sustained (60 s) mechanical stimuli was elevated in approximately half of C-fibers. These high-firing C-fibers demonstrated a disproportionate increase in interspike intervals (ISIs) between 100 and 199 ms, compared with low-firing diabetic and control C-fibers. The co-efficient of variability (CV2), a frequency independent measure of ISI variability, was also greater in high-firing fibers, compared with control fibers. Unexpectedly, instantaneous frequency of the initial burst of activity during the first second was lower in high-firing fibers, even though the average frequency over the last 59 s was significantly higher. The number of action potentials evoked by a noxious chemical stimulus, 300 and 600 mM KCl, injected adjacent to the mechanical receptive field was also significantly increased in C-fibers from diabetic rats and mechanically high-firing fibers had more action potentials in response to KCl than control fibers and a disproportionate increase in ISIs between 100 and 199 ms for responses to chemical stimuli appeared only in mechanically high-firing C-fibers, compared with the mechanically low-firing diabetic or control C-fibers. There was, however, no corresponding change in CV2 or instantaneous frequency plots for the response to chemical stimulation in mechanically high-firing fibers, as there was in the response to mechanical stimulation. Our data demonstrate specific changes in firing pattern of high-firing C-fibers in the rat model of painful neuropathy produced by STZ-diabetes that might contribute to the symptoms experienced by patients.

Diabetic neuropathy in children and adolescents

Diabetic neuropathy (DN) represents a major complication of type 1 diabetes mellitus (T1DM) but there is considerable uncertainty as to its incidence, prevalence, diagnosis and prognosis in pediatric population. Generally, DN is classified as polyneuropathy, focal neuropathy and autonomic neuropathy. The latter seems to be detectable even in asymptomatic children and adolescents with diabetes and is associated with the most serious consequences, such as hypoglycemia unawareness and cardiovascular dysfunction. A near-normal control of blood glucose in the early years after onset of diabetes may delay the development of clinically significant nerve impairment and, therefore, children and adolescents with diabetes represent a critical target for primary prevention of this complication. The aim of this review is to focus on the main clinical, epidemiological and prognostic aspects of DN in children and adolescents with T1DM. Etiopathogenetic theories and diagnostic tools are also reviewed from in a pediatric perspective.

Region specific increases in oxidative stress and superoxide dismutase in the hippocampus of diabetic rats subjected to stress

Oxidative stress and modulation of anti-oxidant enzymes may contribute to the deleterious consequences of diabetes mellitus and to the effects of chronic (i.e. 21 day) stress in the CNS. We therefore compared the effects of short- and long-term exposure to diabetes-induced hyperglycemia, restraint stress and the combined effects of restraint stress and diabetes upon parameters of oxidative stress in the rat hippocampus. Whereas 7 days of restraint stress or hyperglycemia, or the combination, produced similar increases in oxidative stress markers 4-hydroxy-2-nonenal (HNE) and malondialdehyde (MDA) throughout the hippocampus, 21 days of stress or hyperglycemia did not increase these markers in the dentate gyrus. In contrast, Ammon's horn still showed elevated levels of these lipid peroxidation products, especially in diabetic rats subjected to 21 days of restraint stress. The expression of two anti-oxidant enzymes, copper/zinc superoxide dismutase (Cu/Zn-SOD) and manganese SOD, was also differentially regulated by stress and hyperglycemia in a time- and region-specific manner in the rat hippocampus. Although long-term stress decreased both SOD isoforms, diabetes increased Cu/Zn-SOD expression in DG with or without 21 days of repeated stress. These increases may account for the finding that protein-conjugated HNE and MDA levels returned to control levels between 7 days and 21 days of hyperglycemia or the combination of diabetes and stress. These results suggest that while other anti-oxidant pathways may account for decreases in oxidative stress in the long-term stress paradigm, increases in Cu/Zn-SOD expression may contribute to the region-specific attenuation of oxidative stress in the diabetic rat hippocampus.

Up-regulation of spinal muscarinic receptors and increased antinociceptive effect of intrathecal muscarine in diabetic rats

Spinally administered muscarinic receptor agonists or acetylcholinesterase inhibitors produce effective pain relief. Intrathecal injection of a small dose of neostigmine produces a profound antiallodynic effect in rats with diabetic neuropathy. However, the mechanisms of increased antinociceptive effect of cholinergic agents on diabetic neuropathic pain are not clear. In the present study, we tested the hypothesis that spinal muscarinic receptors are up-regulated in diabetes. The withdrawal threshold of the hindpaw in response to noxious heat and pressure stimuli was determined in streptozotocin-induced diabetic and age-matched normal rats. Muscarine-stimulated guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding was used to assess the change of functional muscarinic receptors in the spinal cord in diabetes. The [3H]AF-DX 384 membrane binding was performed to determine the number and affinity of spinal cord M2 muscarinic receptors in normal and diabetic rats. We found that the antinociceptive effect of intrathecal 2 to 12 mug muscarine in diabetic animals was potentiated significantly compared with that in normal animals. The maximal muscarine-stimulated [35S]GTPgammaS binding was 112.5 +/- 8.3% in normal rats and 168.8 +/- 12.1% (P < 0.05) in diabetic rats. Although the KD value (2.9 nM) was similar in both groups, the Bmax of [3H]AF-DX 384 membrane binding was significantly higher in diabetic than in normal rats (255.2 +/- 5.9 versus 165.9 +/- 3.5 fmol/mg protein, P < 0.05). Collectively, these data strongly suggest that the muscarinic receptor is up-regulated in the dorsal spinal cord in diabetic rats. This finding probably accounts for the increased efficacy of the antinociceptive effect of intrathecal muscarinic agonists in diabetic neuropathic pain.

Quercetin, a bioflavonoid, attenuates thermal hyperalgesia in a mouse model of diabetic neuropathic pain

Diabetic neuropathic pain, an important microvascular complication in diabetes mellitus, has been recognised as one of the most difficult types of pain to treat. Lack of understanding of etiology involved, inadequate relief, development of tolerance and potential toxicity of classical antinociceptives warrant the investigation of newer agents to relieve pain. The aim of the present study was to explore the antinociceptive effect of a bioflavonoid, quercetin, both in control and streptozotocin (STZ)-induced diabetic mice. After 4 weeks of a single intraperitoneal injection of STZ (200 mg/kg), both control and diabetic mice were subjected to test thermal hyperalgesia by tail-immersion assay (warm water). Diabetic mice exhibited a significant hyperalgesia as compared with control mice. Quercetin (100 but not 50 mg/kg p.o.) produced a marked increase in tail-flick latencies in both diabetic and nondiabetic mice. Quercetin-induced increase in nociceptive threshold was reversed by naloxone (2 mg/kg i.p.), an opioid receptor antagonist. These preliminary results indicate an antinociceptive activity of quercetin, probably through modulation of opioidergic mechanism and point towards its potential to attenuate diabetic neuropathic pain.

Blink reflex alterations in recently diagnosed diabetic patients

OBJECTIVE

The aim of the present study was to determine the frequency of blink reflex alterations and to examine the influence of hyperglycemia in inducing the alterations in recently diagnosed Type 2 diabetes mellitus patients.

METHODS

A cross-sectional study was carried out on patients having asymptomatic diabetes with a period of evolution under 10 years. In all 47 patients (26 women and 21 men), serum glycemia levels were determined and the latency onset of the blink reflex components were measured.

RESULTS

The average patient age was 44.5+/-11.0 (mean+/-SD) years with a diabetes evolution period of 4.3+/-2.9 (mean+/-SD) years. After a fasting serum glucose test, the diabetic patients were catalogued as normoglycemic (< or =126 mg/dl) or as hyperglycemic (> 26 mg/dl) and subjected to a blink reflex test. The results obtained from the diabetic patients were compared with those from a non-diabetic control group. 14.8-31.9% of the diabetic patients showed alterations in blink reflex component latencies. The differences compared with the control group were significant (p<0.05).

CONCLUSIONS

Diabetes, as is well-known, can affect the central and peripheral nervous system and there does not appear to be a link between glycemic levels and blink reflex components. However, blink reflex alterations were present even in diabetic patients with a relatively short period of disease evolution.

Chronic inflammatory demyelinating polyradiculoneuropathy in diabetic patients

This retrospective analysis was undertaken to determine whether a subset of diabetic patients with demyelinating polyneuropathy were similar to patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Ten patients meeting the clinical criteria for idiopathic CIDP were compared to nine patients with diabetes and demyelinating polyneuropathy. The diabetic patients with demyelinating polyneuropathy displayed clinical, electrophysiologic, and histologic features that were similar to those in CIDP patients. All six patients with diabetes and demyelinating polyneuropathy who were treated with immunomodulatory therapy showed a favorable response. Our study highlights the importance of investigating diabetic patients with polyneuropathy in an attempt to identify patients with demyelinating polyneuropathy, because of the likelihood of benefit in these patients from immunomodulatory treatment.

Spinal GABAB receptors mediate antinociceptive actions of cholinergic agents in normal and diabetic rats

Spinally administered muscarinic receptor agonists or acetylcholinesterase inhibitors can produce antinociception. However, the mechanisms of the action of cholinergic agents in the spinal cord are not fully understood. Activation of spinal muscarinic receptors evokes gamma-aminobutyric acid (GABA) release, which reduces the glutamatergic synaptic input to dorsal horn neurons through GABA(B) receptors. In this study, we determined the functional role of spinal GABA(B) receptors in the antinociceptive action of intrathecal cholinergic agents in normal rats and in a rat model of diabetic neuropathic pain. Diabetes was induced by intraperitoneal streptozotocin in rats. The intrathecal catheter was inserted with its tip positioned at the lumbar spinal level. Nociceptive threshold was measured by the paw withdrawal latency in response to a radiant heat stimulus in normal rats. Mechanical allodynia in diabetic rats was determined by von Frey filaments applied to the hindpaw. The effect of intrathecal muscarine or neostigmine was examined through pretreatment with the specific GABA(B) receptor antagonist, CGP55845, or its vehicle. Intrathecal injection of muscarine or neostigmine significantly increased the withdrawal latency in response to a heat stimulus in normal rats and the withdrawal threshold in response to application of von Frey filaments in diabetic rats. Intrathecal pretreatment with CGP55845 significantly attenuated the effect of both muscarine or neostigmine in normal rats. Furthermore, the antiallodynic effect of intrathecal neostigmine and muscarine was largely eliminated by CGP55845 in diabetic rats. These data suggest that the GABA(B) receptors in the spinal cord mediate both the antinociceptive and antiallodynic actions of intrathecal muscarine or neostigmine in normal rats and in a rat model of diabetic neuropathic pain. This study provides new functional evidence that activation of spinal GABA(B) receptors is one of the important mechanisms underlying the antinociceptive action of intrathecal cholinergic agents.

Case report: Myofascial pain syndrome: a double crush-like appearance

OBJECTIVE

To discuss the case of a patient with myofascial pain syndrome that appeared similar to double crush syndrome.

CLINICAL FEATURES

This is a case report of a 45-year old female who presents to the private practice clinic with the same signs and symptoms of carpal tunnel syndrome, 1 year post-carpaltunnel surgery. The history is consistent with injuries that result in double crush syndrome and thoracic outlet syndrome. The patient history includes a motor vehicle accident (MVA) in 1963 that resulted in a prolonged hospital stay and fracture of a cervical vertebral (C4) body. She fractured the olecranon process of the right elbow during a fall in 1970's. She has smoked approximately 1 pack a day for 20 years. Her job involves long periods of sitting at a keyboard and in a car. All of these portions of the patient history are possible factors in the clinical signs and symptoms of double crush syndrome.

INTERVENTION AND OUTCOME

Treatment involved chiropractic manipulation and physical therapy modalities for the elimination of pain and returning the patient's full range of motion in the wrist, elbow, shoulder and cervical spine. After range of motion was restored, a home exercise program was initiated. The home exercise program included a return to past sporting activity and active, resistive (Theraciser band) activities for the elbow and cervical spine. Also a reduction in smoking was initiated as part of the patient's treatment plan.

CONCLUSION

It is our contention that patients who have electromyographic (EMG) demonstrable carpal tunnel syndrome need a cervical spine workup and a period of conservative care to include skilled manipulation, physical therapy and home exercises before surgery is recommended.

Role of primary afferent nerves in allodynia caused by diabetic neuropathy in rats

Both myelinated and unmyelinated afferents are implicated in transmitting diabetic neuropathic pain. Although unmyelinated afferents are generally considered to play a significant role in diabetic neuropathic pain, pathological changes in diabetic neuropathy occur mostly in myelinated A-fibers. In the present study, we first examined the role of capsaicin-sensitive C-fibers in the development of allodynia induced by diabetic neuropathy. We then studied the functional changes of afferent nerves pertinent to diabetic neuropathic pain. Diabetes was induced in rats by i.p. streptozotocin. To deplete capsaicin-sensitive C-fibers, rats were treated with i.p. resiniferatoxin (300 microg/kg). Mechanical and thermal sensitivities were measured using von Frey filaments and a radiant heat stimulus. Single-unit activity of afferents was recorded from the tibial nerve. Tactile allodynia, but not thermal hyperalgesia, developed in diabetic rats. Resiniferatoxin treatment did not alter significantly the degree and time course of allodynia. Post-treatment with resiniferatoxin also failed to attenuate allodynia in diabetic rats. The electrophysiological recordings revealed ectopic discharges and a higher spontaneous activity mainly in Adelta- and Abeta-fiber afferents in diabetic rats regardless of resiniferatoxin treatment. Furthermore, these afferent fibers had a lower threshold for activation and augmented responses to mechanical stimuli. Thus, our study suggests that capsaicin-sensitive C-fiber afferents are not required in the development of allodynia in this rat model of diabetes. Our electrophysiological data provide substantial new evidence that the abnormal sensory input from Adelta- and Abeta-fiber afferents may play an important role in diabetic neuropathic pain.

Treatment of chronic painful diabetic neuropathy with isosorbide dinitrate spray: a double-blind placebo-controlled cross-over study

OBJECTIVE

Considerable evidence implicates impaired nitric oxide (NO) generation in the pathogenesis of diabetic neuropathic pain. We therefore conducted a pilot study to examine the effects of isosorbide dinitrate (ISDN), a NO donor with local vasodilating properties, in spray form in the management of chronic neuropathic pain.

RESEARCH DESIGN AND METHODS

The study was of double-blind, randomized, placebo-controlled, and two-period cross-over design. After a 2-week run-in period, 22 diabetic patients (13 men, 20 with type 2 diabetes, age [mean +/- SE] 63.7 +/- 1.8 years, duration of diabetes 9.1 +/- 1.5 years, duration of painful neuropathy 2.6 +/- 0.4 years) were randomized to receive ISDN or placebo sprays for 4 weeks, exchanging their treatment for a further 4 weeks after a 2-week wash-out period. The patients administered the spray to both feet before bedtime. Biweekly pain and other sensory symptoms were assessed using a visual analog scale (VAS) and the Lickert scale, respectively.

RESULTS

ISDN spray reduced overall neuropathic pain (P = 0.02) and burning sensation (P = 0.006). No treatment difference was observed with other sensory modalities (hot/cold sensation, tingling, numbness, hyperesthesia, and jabbing-like sensation). At study completion, 11 patients (50%) reported benefit and wished to continue using the ISDN spray, 4 (18%) preferred the placebo spray, and the remaining 7 (32%) were undecided.

CONCLUSIONS

ISDN spray offers an alternative and effective pharmacological option in relieving overall pain and burning sensation in the management of painful diabetic neuropathy. The potential of ISDN spray in alleviating other specific sensory symptoms associated with diabetic peripheral neuropathy merits further study.

Morphological changes in the sciatic nerve of diabetic rats treated with low molecular weight heparin OP 2123/parnaparin

This study points out the early alterations that affect the sciatic nerve of rats with experimentally induced diabetes. It emphasizes the advantages deriving from treatment with low molecular weight heparin (LMWH) OP 2123/parnaparin and correlates these findings with observations emerging from a review of the relevant literature. In fact, the number and diameter of the capillaries within the sciatic nerve of diabetic rats appear to be increased consistent with a microangiopathy (the main characteristic of which is the fragility of new vessels), that is related to the evolution of diabetes in humans and animals. Our results suggest a possible therapeutic role for OP 2123/parnaparin in both diabetic neuropathy and microangiopathy, frequent complications of diabetes.

Conduction slowing in diabetic distal polyneuropathy

The pathophysiologic significance of motor conduction slowing observed in diabetic distal symmetrical polyneuropathy (DSP) remains controversial. We have used multiple linear regression analysis of compound muscle action potential (CMAP) amplitude vs. motor conduction velocity (CV) and distal latency (DL) in 57 patients with diabetic DSP and 34 patients with amyotrophic lateral sclerosis (ALS) to determine whether motor conduction slowing in diabetic DSP is due mainly to loss of large axons as in ALS or whether there is an additional demyelinative component. We found amplitude-dependent slowing of CV and DL in both diabetic DSP and ALS in the upper and lower extremities, consistent with a loss of large myelinated fibers. However, in diabetic DSP, there was also significant amplitude-independent slowing in intermediate but not distal nerve segments, supportive of an additional demyelinative component. CMAP amplitude vs. CV and DL regression analyses using ALS as a control group for relatively pure axon loss may provide pathophysiologic information about motor nerves in other neuropathic disorders.

Review: small-fiber neuropathy

BACKGROUND

Most peripheral neuropathies involve large as well as small-fiber dysfunction. A small subset of neuropathies present with restricted or predominant small-fiber involvement.

REVIEW SUMMARY

In this review, we discuss the differential diagnosis, clinical presentation, evaluation, and treatment of small-fiber neuropathies. Although these neuropathies are rare, their differential diagnosis is broad, and includes many disorders, including metabolic, toxic, inflammatory, infectious, and genetic etiologies. As small fibers subserve pain and autonomic functions, these neuropathies usually present with pain and temperature loss, painful dysesthesias, autonomic dysfunction, or a combination. These neuropathies are especially challenging as nerve conductions and EMG, which help guide the evaluation of most peripheral neuropathies, may have normal findings in patients with small-fiber neuropathies. Other specialized studies, including tests of autonomic function, intraepidermal nerve fiber analysis, and quantitative sensory testing, are often required to confirm the presence of a small-fiber neuropathy. In some cases, the underlying etiology can be directly treated. In most, management is limited to symptomatic treatment of sensory and autonomic dysfunction.

CONCLUSION

Small-fiber neuropathies are a heterogeneous group of disorders. They vary in etiologies and require special attention, as many disorders are rare and the differential diagnosis is broad. Evaluation is often extensive and may need pathologic specimen. Many patients respond to symptomatic therapy, but some are difficult to treat.

Hypersensitivity of spinothalamic tract neurons associated with diabetic neuropathic pain in rats

Diabetic neuropathic pain is often considered to be caused by peripheral neuropathy. The involvement of the CNS in this pathological condition has not been well documented. Development of hypersensitivity of spinal dorsal horn neurons is involved in neuropathic pain induced by traumatic nerve injury. In the present study, we determined the functional changes of identified spinothalamic tract (STT) neurons and their correlation to diabetic neuropathic pain. Diabetes was induced in rats by intraperitoneal injection of streptozotocin. Hyperalgesia and allodynia were assessed by the withdrawal responses to pressure, radiant heat, and von Frey filaments applied to the hindpaw. Single-unit activity of STT neurons was recorded from the lumbar spinal cord in anesthetized rats. The responses of STT neurons to mechanical and thermal stimuli and the sensitivity to intravenous morphine were determined in diabetic and normal rats. In 12 diabetic rats, mechanical allodynia and hyperalgesia, but not thermal hyperalgesia, developed within 2 wk after streptozotocin injection and lasted for >/=7 wk. Compared to the 32 STT neurons recorded in normal animals, the 37 STT neurons in diabetic rats displayed a higher spontaneous discharge activity and enlarged receptive fields. Also, the STT neurons in diabetic rats exhibited lower thresholds and augmented responses to mechanical stimulation. Intravenous injection of 2.5 mg/kg of morphine suppressed significantly the responses of STT neurons to noxious stimuli in 12 nondiabetic rats. However, such an inhibitory effect of morphine on the evoked response of STT neurons was diminished in 14 diabetic animals. This electrophysiological study provides new information that development of hypersensitivity of spinal dorsal horn projection neurons may be closely related to neuropathic pain symptoms caused by diabetes. Furthermore, the attenuated inhibitory effects of morphine on evoked responses of STT neurons in diabetes likely accounts for its reduced analgesic efficacy in this clinical form of neuropathic pain.