C-fiber mechanical stimulus-response functions are different in inflammatory versus neuropathic hyperalgesia in the rat

Kv7 Channel Activators Flupirtine and ML213 Alleviate Neuropathic Pain Behavior in the Streptozotocin Rat Model of Diabetic Neuropathy

Background & Objective

Chronic peripheral neuropathic pain (PNP) is a debilitating condition that is associated with many types of injury/diseases, including diabetes mellitus. Patients with longstanding diabetes develop diabetic PNP (DPNP), which is resilient to currently available drugs. The underlying molecular mechanisms of DPNP are still illusive, but Kv7 channels that have been implicated in the pathogenesis of various types of chronic pain are likely to be involved. Indeed, using the streptozotocin (STZ) rat model of DPNP, we have previously shown that Kv7 activation with their non-selective activator retigabine attenuated neuropathic pain behavior suggesting that these channels are implicated in DPNP pathogenesis. Here, we evaluated, in the same STZ model, whether the more potent and more selective Kv7 channel openers flupirtine and ML213 attenuate STZ-induced pain hypersensitivity.

Methods

Male Sprague Dawley rats (250-300 g) were used. The STZ model involved a single injection of STZ (60 mg/kg, i.p.). Behavioral testing for mechanical and heat pain sensitivity was performed using a dynamic plantar aesthesiometer and Hargreaves analgesiometer, respectively.

Results

STZ rats exhibited behavioral signs of mechanical and heat hypersensitivity as indicated by significant decreases in the mean paw withdrawal threshold (PWT) and mean paw withdrawal latency (PWL), respectively, at 35 days post-STZ treatment. Single injections of flupirtine (10 mg/kg, i.p.) and ML213 (5 mg/kg, i.p.) to STZ rats (35-days after STZ treatment) caused significant increases in the mean PWT, but not PWL, indicating attenuation of mechanical, but not heat hypersensitivity. Both flupirtine and ML213 were as effective as the positive control gabapentin (10/kg, i.p.), and their anti-allodynic effects were prevented by the Kv7 channel-specific blocker XE991 (3 mg/kg, i.p.).

Conclusion

The findings suggest that Kv7 channels are involved in the mechanisms of mechanical but not heat hypersensitivity associated with DPNP, and that their activation may prove to be effective in alleviating DPNP symptoms.

Expression of Piezo1 in the Trigeminal Neurons and in the Axons That Innervate the Dental Pulp

Information on the neurons and axons that express the mechanosensitive channel Piezo1 and its expression in axons innervating the dental pulp may help understand the nature of the Piezo1-mediated mechanosensation and the underlying mechanism of dentin sensitivity elicited by mechanical stimuli. For this, we here investigated the neurochemical properties of the neurons in the rat trigeminal ganglion (TG) and their axons in its sensory root that express Piezo1 and the expression of Piezo1 in the rat and human dental pulp by light and electron microscopic immunohistochemistry and quantitative analysis. Piezo1 was expressed mainly in medium-sized and large TG neurons. Piezo1-immunopositive (+) neurons frequently coexpressed the marker for neurons with myelinated axons, NF200, but rarely the markers for neurons with unmyelinated axons, CGRP or IB4. In the sensory root of TG, Piezo1 was expressed primarily in small myelinated axons (Aδ, 60.2%) but also in large myelinated (Aβ, 24.3%) and unmyelinated (C, 15.5%) axons. In the human dental pulp, Piezo1 was expressed in numerous NF200+ axons, which formed a network in the peripheral pulp and often “ascended” toward the dentin. Most Piezo1+ myelinated axons in the radicular pulp became unmyelinated in the peripheral pulp, where Piezo1 immunoreaction product was associated with the axonal plasma membrane, suggesting a functional role of Piezo1 in the peripheral pulp. These findings suggest that Piezo1 is involved primarily in mediating the acute pain elicited by high-threshold mechanical stimuli, and that the Piezo1-mediated dental mechanotransduction occurs primarily in the axons in the peripheral pulp.

The Assessment of Prolonged Inferior Alveolar Nerve Blockade for Postoperative Analgesia in Mandibular Third Molar Surgery by a Perineural Addition of Dexamethasone to 0.5% Ropivacaine: A Randomized Comparison Study

Background: Perineurally adding dexamethasone to local anesthetics could enable postoperative analgesia. Our aim was to investigate the efficacy of 4 mg dexamethasone and 0.5% ropivacaine on the prolonged duration of mandibular anesthesia for postoperative analgesia during third molar surgery. Materials and method: The patients of both sexes, and in the age range of 17 to 50 yrs of age, received the Gow-Gates anesthesia. Group I received 4 mL of plain 0.5% ropivacaine, with perineurally added 1 mL/4 mg of dexamethasone; group II received 4 mL of plain 0.5% ropivacaine with perineurally added 1 mL of 0.9% saline; group III received 4 mL of plain 0.5 bupivacaine with perineurally added 1 mL of 0.9% saline. The prime anesthesia outcome was the duration of conduction anesthesia (DCA); the secondary outcome was the duration of analgesia (DAN) and analgesia before analgesic intake. Results: In 45 randomly selected subjects (mean age 27.06 ± 8.20), DCA was statistically longest in group I (n = 15) (592.50 ± 161.75 min, p = 0.001), collated with groups II (n = 15) and III (n = 15) (307.40 ± 84.71 and 367.07 ± 170.52 min, respectively). DAN was significantly the longest in group I (mean: 654.9 ± 198.4 min, p = 0.001), compared with group II (345.4 ± 88.0 min) and group III (413.7 ± 152.3 min), with insignificant adverse reactions. One-third of the operated patients absented from the use of analgesics. Conclusion: A amount 0.5% ropivacaine with dexamethasone usefully served as an analgesic with a success rate of 93.4% of the given anesthesia.

Analgesic efficacy of dexamethasone versus dexmedetomidine as an adjuvant to ropivacaine in ultrasound-guided transversus abdominis plane block for post-operative pain relief in caesarean section: A prospective randomised controlled study

Background and Aims:

Transversus abdominis plane (TAP) block is commonly used to treat post-operative pain after lower abdominal surgeries. The aim of this randomised controlled study was to assess the efficacy of addition of dexmedetomidine or dexamethasone to ropivacaine in TAP block and compare the two for post-operative pain relief in caesarean section.

Methods:

A hundred parturients (18–45 years) undergoing caesarean section under spinal anaesthesia received ultrasound-guided (USG) bilateral TAP block with 50ml of 3mg/kg ropivacaine along with 0.1mg/kg dexamethasone (Group A) or 1μg/kg dexmedetomidine (Group B) in this prospective, randomised, double-blind study. Time to initial self-reporting of post-operative pain, time to first rescue analgesic demand, visual analogue scale (VAS) for pain haemodynamic parameters and adverse effects if any were noted, anda P value < 0.005 was considered as statistically significant.

Results:

Time to initial self-reporting of post-operative pain (411.35 vs. 338.20 min, P < 0.005) and time to first rescue analgesic (474.30 vs. 407.30 min, P < 0.005) were significantly longer in group B as compared to group A. VAS score at the time of initial self-reporting of pain was significantly lower in group B. No significant haemodynamic changes or side-effects were noted.

Conclusion:

Addition of dexmedetomidine to ropivacaine as compared with dexamethasone in bilateral TAP block following caesarean section prolongs the time to initial post-operative pain and time to first rescue analgesic consumption.

Prospective Randomized Control Trial Comparing Effect of Dexamethasone Versus Fentanyl as Adjuvants to Intrathecal Bupivacaine for Orthopedic Surgery

Introduction Spinal anesthesia is the most consistent block for lower limb orthopedic surgeries. We conducted this randomized prospective study to evaluate comparative efficacy of intrathecal dexamethasone with fentanyl and normal saline as adjuvants to hyperbaric bupivacaine in spinal anesthesia administered to patients scheduled for lower limb orthopedic surgery. Materials and methods 105 patients scheduled for lower limb orthopedic surgeries under spinal anesthesia were included in this clinical trial. After randomization, patients received an intrathecal injection of hyperbaric bupivacaine (12.5 mg) with 4 mg of dexamethasone in group I, hyperbaric bupivacaine (12.5 mg) with 25 ug fentanyl with 0.5 ml of normal saline in group II and hyperbaric bupivacaine (12.5 mg) with normal saline (1 ml) in group III, so as to make volume of drug equal in all three groups. The observer evaluated the sensory and motor blocks and other parameters like time to self-void, stay in post-anesthesia care unit (PACU) and complications.  Results The total duration of sensory blockade was found to be 311.43, 197.86 and 115.29 minutes and motor blockade of 223.43, 163.86 and 83.0 minutes in groups I, II and III respectively. The PACU stay was 233.14, 173.86 and 93.00 minutes in groups I, II and III, respectively. The average time to self-void was 400.00, 315.29 and 203.00 in three groups, respectively. Conclusion Intrathecal dexamethasone seemed to be an effective adjuvant to spinal bupivacaine as it prolongs the duration of analgesia, stable hemodynamic profile with minimal side effects. Further studies are required to evaluate the optimum dose and long-term safety of intrathecal dexamethasone.

The Future Directions of Research in Cardiac Anesthesiology

This article provides an overview of knowledge gaps that need to be addressed in cardiac anesthesia, including mitigating the inflammatory effects of cardiopulmonary bypass, defining myocardial infarction after cardiac surgery, improving perioperative neurologic outcomes, and the optimal management of patients undergoing valve replacement. In addition, emerging approaches to research conduct are discussed, including the use of new analytical techniques like machine learning, pragmatic trials, and adaptive designs.

Changes in expression of Kv7.5 and Kv7.2 channels in dorsal root ganglion neurons in the streptozotocin rat model of painful diabetic neuropathy

Diabetic peripheral neuropathic pain (DPNP), the most debilitating complication of diabetes mellitus, is resistant to current therapy. The pathogenesis of DPNP is still elusive, but several mechanisms have been proposed including abnormal hyperexcitability of dorsal root ganglion (DRG) neurons. The underlying molecular mechanisms of such aberrant hyperexcitability are incompletely understood. Using the streptozotocin (STZ) rat model of DPNP, we have recently provided evidence implicating neuronal K_v7 channels that normally exert a powerful stabilizing influence on neuronal excitability, in the abnormal hyperexcitability of DRG neurons and in pain hypersensitivity associated with DPNP. In the present immunohistochemical study, we sought to determine whether K_v7.2 and/or K_v7.5 channel expression is altered in DRG neurons in STZ rats. We found 35 days post-STZ: (1) a significant decrease in K_v7.5-immunoreactivity in small (<30 μm) DRG neurons (both IB4 positive and IB4 negative) and medium-sized (30-40 μm) neurons, and (2) a significant increase in K_v7.2-immunoreactivity in small (<30 μm) neurons, and a non-significant increase in medium/large neurons. The decrease in K_v7.5 channel expression in small and medium-sized DRG neurons in STZ rats is likely to contribute to the mechanisms of hyperexcitability of these neurons and thereby to the resulting pain hypersensitivity associated with DPNP. The upregulation of K_v7.2 subunit in small DRG neurons may be an activity dependent compensatory mechanism to limit STZ-induced hyperexcitability of DRG neurons and the associated pain hypersensitivity. The findings support the notion that K_v7 channels may represent a novel target for DPNP treatment.

The Future Directions of Research in Cardiac Anesthesiology

This article provides an overview of knowledge gaps that need to be addressed in cardiac anesthesia, including mitigating the inflammatory effects of cardiopulmonary bypass, defining myocardial infarction after cardiac surgery, improving perioperative neurologic outcomes, and the optimal management of patients undergoing valve replacement. In addition, emerging approaches to research conduct are discussed, including the use of new analytical techniques like machine learning, pragmatic trials, and adaptive designs.

Microbial biotransformation of bioactive and clinically useful steroids and some salient features of steroids and biotransformation

Steroids are perhaps one of the most widely used group of drugs in present day. Beside the established utilization as immunosuppressive, anti-inflammatory, anti-rheumatic, progestational, diuretic, sedative, anabolic and contraceptive agents, recent applications of steroid compounds include the treatment of some forms of cancer, osteoporosis, HIV infections and treatment of declared AIDS. Steroids isolated are often available in minute amounts. So biotransformation of natural products provides a powerful means in solving supply problems in clinical trials and marketing of the drug for obtaining natural products in bulk amounts. If the structure is complex, it is often an impossible task to isolate enough of the natural products for clinical trials. The microbial biotransformation of steroids yielded several novel metabolites, exhibiting different activities. The metabolites produced from pregnenolone acetate by Cunning hamella elegans and Rhizopus stolonifer were screened against tyrosinase and cholinesterase showed significant inhibitory activities than the parent compound. Diosgenin and its transformed sarsasapogenin were screened for their acetyl cholinesterase and butyryl cholinesterase inhibitory activities. Sarsasapogenin was screened for phytotoxicity, and was found to be more active than the parent compound. Diosgenin, prednisone and their derivatives were screened for their anti-leishmanial activity. All derivatives were found to be more active than the parent compound. The biotransformation of steroids have been reviewed to a little extent. This review focuses on the biotransformation and functions of selected steroids, the classification, advantages and agents of enzymatic biotransformation and examines the potential role of new enzymatically transformed steroids and their derivatives in the chemoprevention and treatment of other diseases. tyrosinase and cholinesterase inhibitory activities, severe asthma, rheumatic disorders, renal disorders and diseases of inflammatory bowel, skin, gastrointestinal tract.

Adjuvants to local anesthetics: Current understanding and future trends

Although beneficial in acute and chronic pain management, the use of local anaesthetics is limited by its duration of action and the dose dependent adverse effects on the cardiac and central nervous system. Adjuvants or additives are often used with local anaesthetics for its synergistic effect by prolonging the duration of sensory-motor block and limiting the cumulative dose requirement of local anaesthetics. The armamentarium of local anesthetic adjuvants have evolved over time from classical opioids to a wide array of drugs spanning several groups and varying mechanisms of action. A large array of opioids ranging from morphine, fentanyl and sufentanyl to hydromorphone, buprenorphine and tramadol has been used with varying success. However, their use has been limited by their adverse effect like respiratory depression, nausea, vomiting and pruritus, especially with its neuraxial use. Epinephrine potentiates the local anesthetics by its antinociceptive properties mediated by alpha-2 adrenoreceptor activation along with its vasoconstrictive properties limiting the systemic absorption of local anesthetics. Alpha 2 adrenoreceptor antagonists like clonidine and dexmedetomidine are one of the most widely used class of local anesthetic adjuvants. Other drugs like steroids (dexamethasone), anti-inflammatory agents (parecoxib and lornoxicam), midazolam, ketamine, magnesium sulfate and neostigmine have also been used with mixed success. The concern regarding the safety profile of these adjuvants is due to its potential neurotoxicity and neurological complications which necessitate further research in this direction. Current research is directed towards a search for agents and techniques which would prolong local anaesthetic action without its deleterious effects. This includes novel approaches like use of charged molecules to produce local anaesthetic action (tonicaine and n butyl tetracaine), new age delivery mechanisms for prolonged bioavailability (liposomal, microspheres and cyclodextrin systems) and further studies with other drugs (adenosine, neuromuscular blockers, dextrans).

The Analgesic Efficacy of Dexamethasone Added to Ropivacaine in Transversus Abdominis Plane Block for Transabdominal Hysterectomy under Subarachnoid Block

Background and Aims:

Ultrasound-guided transversus abdominis plane (TAP) block has been proven as a safe and effective analgesic technique for several lower abdominal surgeries. Various adjuvants have been used to intensify the quality and prolong the local anesthetic effect. We evaluated the analgesic efficacy of dexamethasone addition to ropivacaine in TAP block following open abdominal hysterectomy.

Materials and Methods:

After clearance from the Institutional Ethics Committee, a double-blind, prospective, randomized study was carried out on sixty patients aged 40–60 years posted for elective open abdominal hysterectomy comparing bilateral TAP block using 20 ml of 0.5% ropivacaine + 1 ml of 0.9% saline (control Group R) or 20 ml of 0.5% ropivacaine + 4 mg dexamethasone (Group RD). The aim of our study was to observe postoperative pain score (visual analog scale [VAS]), time for first analgesic (TFA) demand, total analgesic consumption, and incidence of nausea or vomiting.

Statistical Analysis:

Chi-square test and Student's t-test were used, and P < 0.05 was considered as statistically significant.

Results:

Postoperative VAS pain scores were significantly lower at 4, 6, and 12 h in Group RD as compared to Group R (P < 0.05). Significantly longer TFA (13.2 ± 7.6 vs. 7.1 ± 4.6 h, P < 0.001) with lesser tramadol requirement in first 24 h (50.2 ± 34 vs. 94 ± 35 mg, P < 0.001) were observed in Group RD as compared to Group R. Incidence of nausea or vomiting was statistically insignificant between the groups (P > 0.05).

Conclusions:

Addition of dexamethasone to ropivacaine TAP block prolonged the postoperative analgesia and reduced analgesic requirement following abdominal hysterectomy.

Painful neuropathy: Mechanisms

Painful neuropathy, like the other complications of diabetes, is a growing healthcare concern. Unfortunately, current treatments are of variable efficacy and do not target underlying pathogenic mechanisms, in part because these mechanisms are not well defined. Rat and mouse models of type 1 diabetes are frequently used to study diabetic neuropathy, with rats in particular being consistently reported to show allodynia and hyperalgesia. Models of type 2 diabetes are being used with increasing frequency, but the current literature on the progression of indices of neuropathic pain is variable and relatively few therapeutics have yet been developed in these models. While evidence for spontaneous pain in rodent models is sparse, measures of evoked mechanical, thermal and chemical pain can provide insight into the pathogenesis of the condition. The stocking and glove distribution of pain tantalizingly suggests that the generator site of neuropathic pain is found within the peripheral nervous system. However, emerging evidence demonstrates that amplification in the spinal cord, via spinal disinhibition and neuroinflammation, and also in the brain, via enhanced thalamic activity or decreased cortical inhibition, likely contribute to the pathogenesis of painful diabetic neuropathy. Several potential therapeutic strategies have emerged from preclinical studies, including prophylactic treatments that intervene against underlying mechanisms of disease, treatments that prevent gains of nociceptive function, treatments that suppress enhancements of nociceptive function, and treatments that impede normal nociceptive mechanisms. Ongoing challenges include unraveling the complexity of underlying pathogenic mechanisms, addressing the potential disconnect between the perceived location of pain and the actual pain generator and amplifier sites, and finding ways to identify which mechanisms operate in specific patients to allow rational and individualized choice of targeted therapies.

Do Corticosteroids Still Have a Role in the Management of Third Molar Surgery?

INTRODUCTION

The use of corticosteroids to reduce the post-operative sequelae of lower third molar surgery, namely pain, swelling and trismus, has been well studied by many researchers over the past 6 decades. This study reviewed the reported outcome of corticosteroids used in controlling the above sequalae after third molar surgery.

MATERIALS AND METHODS

A PubMed, Medline, EMBASE and Google search was undertaken of all controlled clinical trials on the effects of corticosteroids on pain, swelling and trismus after lower third molar surgery. The review was limited to studies published over the last 10 years (2006-2015).

RESULTS

Of the 46 initially retrieved articles, 34 were finally included. Eleven studies compared the effect of 2 similar (but different dose) or different group of corticosteroids. Thirty-one studies reported the effects of corticosteroids on all sequale, 2 reported the outcome on swelling and trismus and another 1 on swelling and pain only. In 16 of the studies, corticosteroid use resulted in significant reductions in pain after third molar removal. Twenty-two out of 29 studies reported reduced swelling against negative control while 18 out of 25 studies reported improved mouth opening. Fourteen studies reported the benefit of corticosteroids on all 3 sequelae, with 71.4% resulted from the use of methylprednisolone.

CONCLUSION

Although there are some conflicting effects, the results of this analysis shows in general the benefits derived from short-term use of corticosteroids in relation to pain, swelling and trismus following third molar surgical extraction, with no side effects observed.

FUNDING

This work was supported by the University of Malaya's High Impact Research grant UM.C/625/1/HIR/MOHE/05.

A double-blind randomized controlled trial comparing dexamethasone and clonidine as adjuvants to a ropivacaine sciatic popliteal block for foot surgery

Background and aims

A popliteal block is effective in managing postoperative pain for foot surgery, but since the duration of analgesia is limited following a single-shot popliteal fossa block technique, methods to prolong effective postoperative analgesia are mandatory. The aim of this study was to assess the effect of adjuvants to ropivacaine on the duration of sensory and motor block.

Methods

In this double-blind randomized placebo-controlled study, we evaluated the analgesic effect of clonidine or dexamethasone (DXM) when added to ropivacaine for hallux valgus surgery. After obtaining institutional ethics research board approval and written informed consent, a total of 72 patients were randomly allocated. Fifty-seven of these patients were statistically analyzed. All patients received an ultrasound-guided single-shot popliteal fossa block with 30 mL of ropivacaine 0.75%, supplemented with saline, clonidine 100 µg, or DXM 5 mg. The primary end point was time to first pain sensation. Secondary end points were time to complete sensory and motor block regression.

Results

Compared to saline, duration to first pain sensation was prolonged by 9 hours (mean ± standard deviation: 31±9 hours) (42%) in the DXM group (P=0.024) and by 6 hours (28±10 hours) (27%) in the clonidine group (P=0.024). Compared to saline, DXM prolonged both complete sensory and motor blockade by 12 hours (25±7 hours) (46%) and 13 hours (36±6 hours) (55%), respectively, while clonidine prolonged complete sensory and motor blockade by 7 hours (30±7 hours) (27%) and 2 hours (22±5 hours) (10%), respectively. DXM prolonged sensory block regression time by 6 hours (21±7 hours) (41%) and clonidine by 2 hours (17±6 hours) (13%) compared to the control group (P=0.006). Similarly, DXM prolonged motor block regression by 7 hours (25±7 hours) (46%) and clonidine by 4 hours (21±4 hours) (19%) (P<0.0001).

Conclusion

Addition of DXM and clonidine to ropivacaine significantly prolonged the duration of postoperative sensory and motor block.

Comparison of caudal and intravenous dexamethasone as adjuvants for caudal epidural block: A double blinded randomised controlled trial

Background and Aims:

Dexamethasone has a powerful anti-inflammatory action with significant analgesic benefits. The aim of this study was to compare the efficacy of dexamethasone administered through intravenous (IV) and caudal route on post-operative analgesia in paediatric inguinal herniotomy patients.

Methods:

One hundred and five paediatric patients undergoing inguinal herniotomy were included and divided into three groups. Each patient received a single caudal dose of ropivacaine 0.15%, 1.5 mL/kg combined with either corresponding volume of normal saline (Group 1) or caudal dexamethasone 0.1 mg/kg (Group 2) or IV dexamethasone 0.5 mg/kg (Group 3). Baseline, intra- and post-operative haemodynamic parameters, pain scores, time to rescue analgesia, total analgesic consumption and adverse effects were evaluated for 24 h after surgery. Unpaired Student's t-test and analysis of variance were applied for quantitative data and Chi-square test for qualitative data. Time to first analgesic administration was analysed by Kaplan–Meier survival analysis and log-rank test.

Results:

Duration of analgesia was significantly longer (P < 0.001), and total consumption of analgesics was significantly lower (P < 0.001) in Group II and III compared to Group I. The incidence of nausea and vomiting was higher in Group I (31.4%) compared to Group II and III (8.6%).

Conclusions:

Addition of dexamethasone both caudally or intravenously as an adjuvant to caudal 0.15% ropivacaine significantly reduced the intensity of post-operative pain and prolonged the duration of post-operative analgesia with the significant advantage of caudal over IV route.

Comparative evaluation of ropivacaine and ropivacaine with dexamethasone in supraclavicular brachial plexus block for postoperative analgesia

BACKGROUND

Mixing of various adjuvants has been tried with local anesthetics in an attempt to prolong anesthesia from peripheral nerve blocks but have met with inconclusive success. More recent studies indicate that 8 mg dexamethasone added to perineural local anesthetic injections augment the duration of peripheral nerve block analgesia.

AIMS

Evaluating the hypothesis that adding dexamethasone to ropivacaine significantly prolongs the duration of analgesia in supraclavicular brachial plexus block compared with ropivacaine alone.

PATIENTS AND METHODS

It was a randomized, prospective, and double-blind clinical trial. Eighty patients of ASA I and II of either sex, aged 16-60 years, undergoing elective upper limb surgeries were equally divided into two groups and given supraclavicular nerve block. Group R patients (n = 40) received 30 ml of 0.5% ropivacaine with distilled water (2 ml)-control group whereas Group D patients (n = 40) received 30 ml of 0.5% ropivacaine with 8 mg dexamethasone (2 ml)-study group. The primary outcome was measured as duration of analgesia that was defined as the interval between the onset of sensory block and the first request for analgesia by the patient. The secondary outcome included maximum visual analogue scale (VAS), total analgesia consumption, surgeon satisfaction, and side effects.

RESULTS

Group R patients required first rescue analgesia earlier (557 ± 58.99 min) than those of Group D patients (1179.4 ± 108.60 min), which was found statistically significant in Group D (P < 0.000). The total dose of rescue analgesia was higher in Group R as compared to Group D, which was statistically significant (P < 0.00).

CONCLUSION

Addition of dexamethasone (8 mg) to ropivacaine in supraclavicular brachial plexus approach significantly and safely prolongs motor blockade and postoperative analgesia (sensory) that lasted much longer than that produced by local anesthetic alone.

Interscalene brachial plexus block for shoulder arthroscopic surgery: Prospective randomised controlled study of effects of 0.5% ropivacaine and 0.5% ropivacaine with dexamethasone

BACKGROUND AND AIMS

Various adjuvants have been used to prolong the duration of local anaesthetic action after peripheral and regional nerve blocks. We evaluated the effect of dexamethasone on the duration of pain relief in shoulder arthroscopic surgeries performed under interscalene brachial plexus using ropivacaine as local anaesthetic.

METHODS

After Ethical Committee approval and informed consent from patients we performed a prospective, randomised, comparative study on patients scheduled for arthroscopic shoulder surgery under interscalene block (ISB). Patients in ropivacaine group (Group R) received 30 ml of 0.5% ropivacaine plus 2 ml normal saline (n = 50) and dexamethasone-ropivacaine (Group RD) received 0.5% ropivacaine 30 ml plus 8 mg dexamethasone (4 mg/ml) (n = 50). Duration of analgesia, onset of sensory and motor block, success and failure of block, and complications were recorded and compared. Computer software SPSS version-16 (SPSS Inc., Chicago, Illinois, USA) was used for statistical analysis. Chi-square test and Student's t-test were used and P < 0.05 was considered as significant.

RESULTS

The mean duration of analgesia in Group RD was 1103.72 ± 296.027 min and in Group R it was 551.54 ± 166.92 min (P = 0.0001). Onset of sensory block in Group RD was 12.24 ± 1.88 min and in Group R was 13.48 ± 1.81 min (P = 0.5170). Onset of motor block in Group RD was 16.24 ± 2.04 min and in Group R was 17.76 ± 2.21 min (P = 0.2244). Onset of surgical anaesthesia in Group RD was19.46 ± 1.86 min and in Group R was 20.84 ± 1.71 min (P = 0.0859).

CONCLUSION

Dexamethasone significantly prolonged duration of analgesia of ropivacaine during ISB used for arthroscopic surgeries of shoulder. Dexamethasone when mixed with ropivacaine had no effect on the onset of sensory and motor effects of ISB with ropivacaine.

Transient receptor potential ankyrin 1 (TRPA1) ion channel in the pathophysiology of peripheral diabetic neuropathy

Background

Transient receptor potential ankyrin 1 (TRPA1) is a non-selective cation channel permeable to calcium that is expressed on pain-mediating primary afferent nerve fibers. Here we review recent experimental evidence supporting the hypothesis that activation of the TRPA1 channel by reactive compounds generated in diabetes mellitus, such as 4-hydroxynonenal and methylglyoxal, exerts an important role in the pathophysiology of peripheral diabetic neuropathy (PDN). The hypothesis includes development of the early diabetic pain hypersensitivity and the later loss of cutaneous nerve endings of pain fibers and their dysfunction, which are hallmarks of peripheral diabetic neuropathy (PDN).

Methods

The evidence for a role of the TRPA1 channel in PDN consists of in vitro patch clamp and calcium imaging data and assessments of pain behavior, axon reflex measurements, and immunohistochemical analyses of cutaneous innervation in an experimental animal model of diabetes. The experiments were combined with blocking the TRPA1 channel with selective antagonists Chembridge-5861528 or A-967079.

Results

In vitro studies indicate that under physiological concentration of Ca2+, methylglyoxal and 4-hydroxynonenal produce sustained activation of the TRPA1 channel and sustained inflow of calcium. In vivo studies indicate that diabetic pain hypersensitivity is maintained by the TRPA1 channel as indicated by the antihypersensitivity effect induced by acute blocking of the TRPA1 channel. Moreover, TRPA1 channel is involved in the development of diabetic hypersensitivity as indicated by prevention of the development of pain hypersensitivity in diabetic animals treated daily with Chembridge-5861528. The diabetes-induced loss of substance P-like cutaneous innervation and that of the TRPA1 channel-mediated cutaneous axon reflex function during the later phase of diabetes were also prevented or delayed by prolonged blocking of the TRPA1 channel. No motor impairment or other obvious side-effects were observed following block of the TRPA1 channel.

Conclusions

Together the in vitro and in vivo results indicate that reactive compounds generated in diabetes exert, through action on the TRPA1 channel, an important role in the pathophysiology of PDN. Sustained activation of the TRPA1 channel is a plausible mechanism that contributes to the early diabetic pain hypersensitivity and the later loss of cutaneous pain fiber endings and their dysfunction with prolonged diabetes.

Implications

Blocking the TRPA1 channel with a selective antagonist provides a promising disease-modifying treatment for PDN, with only minor, if any, side-effects.

Sensory and signaling mechanisms of bradykinin, eicosanoids, platelet-activating factor, and nitric oxide in peripheral nociceptors

Peripheral mediators can contribute to the development and maintenance of inflammatory and neuropathic pain and its concomitants (hyperalgesia and allodynia) via two mechanisms. Activation or excitation by these substances of nociceptive nerve endings or fibers implicates generation of action potentials which then travel to the central nervous system and may induce pain sensation. Sensitization of nociceptors refers to their increased responsiveness to either thermal, mechanical, or chemical stimuli that may be translated to corresponding hyperalgesias. This review aims to give an account of the excitatory and sensitizing actions of inflammatory mediators including bradykinin, prostaglandins, thromboxanes, leukotrienes, platelet-activating factor, and nitric oxide on nociceptive primary afferent neurons. Manifestations, receptor molecules, and intracellular signaling mechanisms of the effects of these mediators are discussed in detail. With regard to signaling, most data reported have been obtained from transfected nonneuronal cells and somata of cultured sensory neurons as these structures are more accessible to direct study of sensory and signal transduction. The peripheral processes of sensory neurons, where painful stimuli actually affect the nociceptors in vivo, show marked differences with respect to biophysics, ultrastructure, and equipment with receptors and ion channels compared with cellular models. Therefore, an effort was made to highlight signaling mechanisms for which supporting data from molecular, cellular, and behavioral models are consistent with findings that reflect properties of peripheral nociceptive nerve endings. Identified molecular elements of these signaling pathways may serve as validated targets for development of novel types of analgesic drugs.

Addition of intrathecal Dexamethasone to Bupivacaine for spinal anesthesia in orthopedic surgery

OBJECTIVES

Spinal anesthesia has the advantage that profound nerve block can be produced in a large part of the body by the relatively simple injection of a small amount of local anesthetic. Intrathecal local anesthetics have limited duration. Different additives have been used to prolong spinal anesthesia. The effect of corticosteroids in prolonging the analgesic effects of local anesthetics in peripheral nerves is well documented. The purpose of this investigation was to determine whether the addition of dexamethasone to intrathecal bupivacaine would prolong the duration of sensory analgesia or not.

METHODS

We conducted a randomized, prospective, double-blind, case-control, clinical trial. A total of 50 patients were scheduled for orthopedic surgery under spinal anesthesia. The patients were randomly allocated to receive 15 mg hyperbaric bupivacaine 0.5% with 2 cc normal saline (control group) or 15 mg hyperbaric bupivacaine 0.5% plus 8 mg dexamethasone (case group) intrathecally. The patients were evaluated for quality, quantity, and duration of block; blood pressure, heart rate, nausea, and vomiting or other complications.

RESULTS

There were no signification differences in demographic data, sensory level, and onset time of the sensory block between two groups. Sensory block duration in the case group was 119±10.69 minutes and in the control group was 89.44±8.37 minutes which was significantly higher in the case group (P<0.001). The duration of analgesia was 401.92±72.44 minutes in the case group; whereas it was 202±43.67 minutes in the control group (P<0.001). The frequency of complications was not different between two groups.

CONCLUSION

This study has shown that the addition of intrathecal dexamethasone to bupivacaine significantly improved the duration of sensory block in spinal anesthesia without any changes in onset time and complications.

Addition of intrathecal Dexamethasone to Bupivacaine for spinal anesthesia in orthopedic surgery

Objectives:

Spinal anesthesia has the advantage that profound nerve block can be produced in a large part of the body by the relatively simple injection of a small amount of local anesthetic. Intrathecal local anesthetics have limited duration. Different additives have been used to prolong spinal anesthesia. The effect of corticosteroids in prolonging the analgesic effects of local anesthetics in peripheral nerves is well documented. The purpose of this investigation was to determine whether the addition of dexamethasone to intrathecal bupivacaine would prolong the duration of sensory analgesia or not.

Methods:

We conducted a randomized, prospective, double-blind, case-control, clinical trial. A total of 50 patients were scheduled for orthopedic surgery under spinal anesthesia. The patients were randomly allocated to receive 15 mg hyperbaric bupivacaine 0.5% with 2 cc normal saline (control group) or 15 mg hyperbaric bupivacaine 0.5% plus 8 mg dexamethasone (case group) intrathecally. The patients were evaluated for quality, quantity, and duration of block; blood pressure, heart rate, nausea, and vomiting or other complications.

Results:

There were no signification differences in demographic data, sensory level, and onset time of the sensory block between two groups. Sensory block duration in the case group was 119±10.69 minutes and in the control group was 89.44±8.37 minutes which was significantly higher in the case group (P<0.001). The duration of analgesia was 401.92±72.44 minutes in the case group; whereas it was 202±43.67 minutes in the control group (P<0.001). The frequency of complications was not different between two groups.

Conclusion:

This study has shown that the addition of intrathecal dexamethasone to bupivacaine significantly improved the duration of sensory block in spinal anesthesia without any changes in onset time and complications.

Applications of Steroid in Clinical Practice: A Review

Steroids are perhaps one of the most widely used group of drugs in present day anaesthetic practice, sometimes with indication and sometimes without indications. Because of their diverse effects on various systems of the body, there has been renewed interest in the use of steroids in modern day anaesthetic practice. This paper focuses on the synthesis and functions of steroids and risks associated with their supplementation. This paper also highlights the recent trends, relevance, and consensus issues on the use of steroids as adjunct pharmacological agents in relation to anaesthetic practice and intensive care, along with emphasis on important clinical aspects of perioperative usefulness and supplementation.

Inflammation reduces mechanical thresholds in a population of transient receptor potential channel A1-expressing nociceptors in the rat

Inflammatory hypersensitivity is characterized by behavioural reductions in withdrawal thresholds to noxious stimuli. Although cutaneous primary afferent neurones are known to have lowered thermal thresholds in inflammation, whether their mechanical thresholds are altered remains controversial. The transient receptor potential channel A1 (TRPA1) is a receptor localized to putative nociceptive neurones and is implicated in mechanical and thermal nociception. Herein, we examined changes in the properties of single primary afferents in normal and acutely inflamed rats and determined whether specific nociceptive properties, particularly mechanical thresholds, are altered in the subpopulation of afferents that responded to the TRPA1 agonist cinnamaldehyde (TRPA1-positive afferents). TRPA1-positive afferents in normal animals belonged to the mechanonociceptive populations, many of which also responded to heat or capsaicin but only a few of which responded to cold. In acute inflammation, a greater proportion of afferents responded to cinnamaldehyde and an increased proportion of dorsal root ganglion neurones expressed TRPA1 protein. Functionally, in inflammation, TRPA1-positive afferents showed significantly reduced mechanical thresholds and enhanced activity to agonist stimulation. Inflammation altered thermal thresholds in both TRPA1-positive and TRPA1-negative afferents. Our data show that a subset of afferents is sensitized to mechanical stimulation by inflammation and that these afferents are defined by expression of TRPA1.

Marked attenuation of inflammatory mediator-induced C-fiber sensitization for mechanical and hypotonic stimuli in TRPV4-/- mice

Inflammatory mediators can directly sensitize primary afferent nociceptors to mechanical and osmotic stimuli. Sensitized nociceptors have a lowered threshold of activation and increased spontaneous activity, which result in symptoms of hyperalgesia and pain, respectively. The transient receptor potential vanilloid 4 (TRPV4) ligand-gated ion channel has been implicated in the hyperalgesia for mechanical and osmotic stimuli associated with inflammatory states. To investigate whether TRPV4 directly contributes to the mechanisms of inflammatory mediator sensitization of C-fiber nociceptors, we compared the effect of the injection of simplified inflammatory soup (prostaglandin E₂ and serotonin) into the mechanical receptive fields of C-fibers in TRPV4^+/+ and TRPV4^-/- mice in vivo. Following the injection of the soup, the percentage of C-fibers responding to a hypotonic stimulus and the magnitude of the response was significantly greater in TRPV4^+/+ mice compared to TRPV4^-/- mice. Moreover, in response to simplified inflammatory soup only C-fibers from TRPV4^+/+ mice exhibited increased spontaneous activity and decreased mechanical threshold. These marked impairments in the response of C-fibers in TRPV4^-/- mice demonstrate the importance of TRPV4 in nociceptor sensitization; we suggest that TRPV4, as TRPV1, underlies the nociceptive effects of multiple inflammatory mediators on primary afferent.

Mechanically-evoked C-fiber activity in painful alcohol and AIDS therapy neuropathy in the rat

While altered activities in sensory neurons were noticed in neuropathic pain, caused by highly diverse insults to the peripheral nervous system, such as diabetes, alcohol ingestion, cancer chemotherapy and drugs used to treat AIDS, other infections and autoimmune diseases, as well as trauma, our understanding of how these various peripheral neuropathies manifest as altered neuronal activity is still rudimentary. The recent development of models of several of those neuropathies has, however, now made it possible to address their impact on primary afferent nociceptor function. We compared changes in mechanically-evoked C-fiber activity, in models of painful peripheral neuropathy induced by drinking ethanol (alcohol) or administering 2',3'-dideoxycytidine (ddC), a nucleoside reverse transcriptase inhibitor for AIDS therapy, two co-morbid conditions in which pain is thought to be mediated by different second messenger signaling pathways. In C-fiber afferents, ddC decreased conduction velocity. In contrast, alcohol but not ddC caused enhanced response to mechanical stimulation (i.e., decrease in threshold and increase in response to sustained threshold and supra-threshold stimulation) and changes in pattern of evoked activity (interspike interval and action potential variability analyses). These marked differences in primary afferent nociceptor function, in two different forms of neuropathy that produce mechanical hyperalgesia of similar magnitude, suggest that optimal treatment of neuropathic pain may differ depending on the nature of the causative insult to the peripheral nervous system, and emphasize the value of studying co-morbid conditions that produce painful peripheral neuropathy by different mechanisms.

Intrathecal betamethasone for cancer pain in the lower half of the body: a study of its analgesic efficacy and safety

BACKGROUND

Sufficient analgesia for cancer pain is sometimes difficult to achieve with conventional treatments. We aimed at investigating the analgesic efficacy and safety of intrathecal betamethasone in patients with uncontrollable cancer pain.

METHODS

Betamethasone 1 mg mixed with saline was injected into the lumbar intrathecal space once a week in 10 patients with persistent cancer pain in the lower half of the body. During the 4-week study period, the analgesic efficacy and adverse effects related to intrathecal betamethasone were observed.

RESULTS

Long-lasting analgesia (mean numerical pain score < or = 5) for 7 days, after immediate analgesia within 10 min, was obtained without the need to increase the morphine dose in 5 of 10 patients. In almost all of the patients, not only pain, but also uncomfortable symptoms were improved. Adverse effects related to neurotoxicity of intrathecal betamethasone, such as sensory and motor dysfunctions, were not observed in any patients.

CONCLUSION

When conventional cancer pain treatments are not successful, intrathecal betamethasone may be useful, as it probably induces long-lasting analgesia without adverse effects and improves activities of daily living, especially in patients with vertebral bone metastases.

Dexamethasone Added to Lidocaine Prolongs Axillary Brachial Plexus Blockade

Different additives have been used to prolong regional blockade. We designed a prospective, randomized, double-blind study to evaluate the effect of dexamethasone added to lidocaine on the onset and duration of axillary brachial plexus block. Sixty patients scheduled for elective hand and forearm surgery under axillary brachial plexus block were randomly allocated to receive either 34 mL lidocaine 1.5% with 2 mL of isotonic saline chloride (control group, n = 30) or 34 mL lidocaine 1.5% with 2 mL of dexamethasone (8 mg) (dexamethasone group, n = 30). Neither epinephrine nor bicarbonate was added to the treatment mixture. We used a nerve stimulator and multiple stimulations technique in all of the patients. After performance of the block, sensory and motor blockade of radial, median, musculocutaneous, and ulnar nerves were recorded at 5, 15, and 30 min. The onset time of the sensory and motor blockade was defined as the time between last injection and the total abolition of the pinprick response and complete paralysis. The duration of sensory and motor blocks were considered as the time interval between the administration of the local anesthetic and the first postoperative pain and complete recovery of motor functions. Sixteen patients were excluded because of unsuccessful blockade. The duration of surgery and the onset times of sensory and motor block were similar in the two groups. The duration of sensory (242 +/- 76 versus 98 +/- 33 min) and motor (310 +/- 81 versus 130 +/- 31 min) blockade were significantly longer in the dexamethasone than in the control group (P < 0.01). We conclude that the addition of dexamethasone to lidocaine 1.5% solution in axillary brachial plexus block prolongs the duration of sensory and motor blockade.

Spontaneous discharge and increased heat sensitivity of rat C-fiber nociceptors are present in vitro after plantar incision

Postoperative pain is characterized by spontaneous pain at the surgical site and increased pain due to movements. To study postoperative pain mechanisms, we investigated discharge properties of mechano-heat sensitive C-fiber afferents innervating the rat glabrous hindpaw skin 1 day after plantar incision. Behaviors indicating spontaneous pain, heat and mechanical hyperalgesia were present 1 day after incision. Recording of afferents using in vitro glabrous skin-nerve preparation showed that more C-fibers from the incision had spontaneous discharge than control rats. The spontaneously discharging fibers from incised rats had lower heat response threshold compared with fibers without spontaneous activity. In all fibers less than 2 mm from the incision, an increased percentage responded to lower temperatures (35-41 degrees C), the mean heat response threshold was 3.1 degrees C less, the stimulus-response function for heat evoked response was shifted to the left and the total number of impulses in response to a 33-48 degrees C heat stimulus was increased. Heat responses of C-fibers more than 2 mm from the incision, however, were not different from control. The mean mechanical response thresholds, measured by a servo force-controlled stimulator, were not different between groups. The total spikes evoked at supra-threshold mechanical stimulation were not increased in afferents from the incision. In conclusion, 1 day after incision, when behaviors indicating spontaneous pain, heat and mechanical hyperalgesia are present, C-fibers close to incision showed spontaneous discharge and sensitization to heat but not to mechanical stimuli, in vitro.

Early painful diabetic neuropathy is associated with differential changes in tetrodotoxin-sensitive and -resistant sodium channels in dorsal root ganglion neurons in the rat

Diabetic neuropathy is a common form of peripheral neuropathy, yet the mechanisms responsible for pain in this disease are poorly understood. Alterations in the expression and function of voltage-gated tetrodotoxin-resistant (TTX-R) sodium channels have been implicated in animal models of neuropathic pain, including models of diabetic neuropathy. We investigated the expression and function of TTX-sensitive (TTX-S) and TTX-R sodium channels in dorsal root ganglion (DRG) neurons and the responses to thermal hyperalgesia and mechanical allodynia in streptozotocin-treated rats between 4-8 weeks after onset of diabetes. Diabetic rats demonstrated a significant reduction in the threshold for escape from innocuous mechanical pressure (allodynia) and a reduction in the latency to withdrawal from a noxious thermal stimulus (hyperalgesia). Both TTX-S and TTX-R sodium currents increased significantly in small DRG neurons isolated from diabetic rats. The voltage-dependent activation and steady-state inactivation curves for these currents were shifted negatively. TTX-S currents induced by fast or slow voltage ramps increased markedly in neurons from diabetic rats. Immunoblots and immunofluorescence staining demonstrated significant increases in the expression of Na(v)1.3 (TTX-S) and Na(v) 1.7 (TTX-S) and decreases in the expression of Na(v) 1.6 (TTX-S) and Na(v)1.8 (TTX-R) in diabetic rats. The level of serine/threonine phosphorylation of Na(v) 1.6 and In Na(v)1.8 increased in response to diabetes. addition, increased tyrosine phosphorylation of Na(v)1.6 and Na(v)1.7 was observed in DRGs from diabetic rats. These results suggest that both TTX-S and TTX-R sodium channels play important roles and that differential phosphorylation of sodium channels involving both serine/threonine and tyrosine sites contributes to painful diabetic neuropathy.

Sexual dimorphism in the contribution of protein kinase C isoforms to nociception in the streptozotocin diabetic rat

The contribution of second messenger signaling, glucose level and sex hormones to sexual dimorphism in the streptozotocin model of diabetic painful peripheral neuropathy was evaluated. Streptozotocin induced elevation of blood glucose and mechanical hyperalgesia (measured by the Randall-Selitto paw-withdrawal test) were both greater in female rats. Ovariectomy abolished and estrogen implants reconstituted this sexual dimorphism; gonadectomy in males had no effect. An inhibitor of protein kinase Cepsilon attenuated hyperalgesia in males and ovariectomized females, but not in normal females or in ovariectomized females with estrogen implants, whereas inhibitors of protein kinase Cdelta attenuated hyperalgesia in females but not in males. Inhibitors of protein kinase A, protein kinase C (non-selective), protein kinase G and nitric oxide synthase attenuated hyperalgesia equally in both sexes. Higher blood glucose levels in diabetic females were also sex hormone dependent, and magnitude of hyperalgesia correlated with blood glucose level in diabetic male and female rats. These results demonstrate sexual dimorphism in diabetic hyperalgesia, mediated by sex hormone dependent differences in protein kinase Cepsilon and protein kinase Cdelta signaling and blood glucose levels and suggest that sex may be an important factor to be considered in the treatment of symptomatic diabetic neuropathy.

Potential mechanisms of neuropathic pain in diabetes

Abnormal sensations and pain are features of approximately 10% of all cases of diabvetic neuropathy and can cause marked diminution in the quality of life for these patients. The quality and distribution of pain are variable, although descriptions of burning pain in the hands and feet are commonly reported. Like other neuropathic pain states, painful diabetic neuropathy has an unknown pathogenesis and, in many cases, is not alleviated by nonsteriodal anti-inflammatory drugs or opiates. In the last decase, a number of behavioral and physiologic studies have revealed indices of sensory dysfunction in animal models of diabetes. These include hyperalgesia to mechanical and noxious chemical stimuli and allodynia to light touch. Animal models of painful diabetic neuropathy have been used to investigate the therapeutic potential of a range of experimental agents and also to explore potential etiologic mechanisms. There is relatively little evidence to suggest that the peripheral sensory nerves of diabetic rodents exhibit spontaneous activity or increased responsiveness to peripheral stimuli. Indeed, the weight of eveidence suggests that sensory input to the spinal cord is decreased rather than increased in diabetic rodents. Aberrant spinal or supraspinal modulation of sensory processing may therefore be involved in generating allodynia and hyperalgesia in these models. Studies have supported a role for spinally mediated hyeralgesia in diabetic rats that may reflect either a response to diminished peripheral input or a consequence of hyperglycemia on local or descending modulatory systems. Elucidating the affects of diabetes on spinal sensory processing may assist development of novel therapeutic strategies for preventing and alleviating painful diabetic neuropathy.

Analgesia for pelvic and perineal cancer pain by intrathecal steroid injection

BACKGROUND

Corticosteroids are used systemically in patients with advanced cancer to alleviate pain. Intrathecal administration of steroids is rarely performed but analgesic effects of intrathecal steroids have been reported in animal studies. We administered betamethasone intrathecally in three cancer patients with uncontrollable pain.

CASE REPORT

Intrathecal injection of betamethasone (1-4 mg) with saline (total volume = 2 mL) was performed in three patients with advanced pelvic or perineal cancer, in whom pain could not be controlled in spite of various analgesic therapies. After obtaining the patient's informed consent for the procedure, betamethasone was administered intrathecally through the L4/5 intervertebral space. Intrathecal betamethasone produced rapid analgesia within 10 min and subsequent long-lasting analgesia for 5 days or more. Sleep, appetite and activity improved. No adverse effects were observed in any of the patients.

CONCLUSIONS

Intrathecal injection of betamethasone may be a useful approach in some patients with intractable cancer pain.

Characterization of Adelta- and C-fibers innervating the plantar rat hindpaw one day after an incision

Primary hyperalgesia after tissue injury is suggested to result from sensitization of primary afferent fibers, but sensitization to mechanical stimuli has been difficult to demonstrate. In the companion study, sensitization of mechano-responsive Adelta- and C-fibers did not explain pain behaviors 45 min after an incision in the rat hindpaw. In the present study, we examined mechanical response properties of Adelta- and C-fibers innervating the glabrous skin of the plantar hindpaw in rats 1 day after an incision or sham procedure. In behavioral experiments, median withdrawal thresholds to von Frey filaments were reduced from 522 mN before to 61 mN 2 and 20 h after incision; median withdrawal thresholds after sham procedure were stable (522 mN). Responses to a nonpunctate mechanical stimulus were increased after incision. In neurophysiological experiments in these same rats, 67 single afferent fibers were characterized from the left tibial nerve 1 day after sham procedure (n = 39) or incision (n = 28); electrical stimulation was used as the search stimulus to identify a representative population of Adelta- and C-fibers. In the incision group, 11 fibers (39%) had spontaneous activity with frequencies ranging from 0.03 to 39.3 imp/s; none were present in the sham group. The median response threshold of Adelta-fibers was less in the incision (56 mN, n = 13) compared with sham (251 mN, n = 26) group, mainly because the proportion of mechanically insensitive afferents (MIAs) was less (8 vs. 54% after sham procedure). Median C-fiber response thresholds were similar in incised (28 mN, n = 15) and sham rats (56 mN, n = 13). Responsiveness to monofilaments was significantly enhanced in Adelta-fibers 1 day after incision; stimulus response functions of C-fibers after incision and after sham procedure did not differ significantly. Only Adelta-fibers but not C-fibers sensitized to the nonpunctate mechanical stimulus. The size of receptive fields was increased in Adelta- and C-fibers 1 day after incision. The results indicate that sensitization of Adelta- and C-fibers is apparent 1 day after incision. Because sensitization of afferent fibers to mechanical stimuli correlated with behavioral results, sensitization may contribute to the reduced withdrawal threshold after incision. Spontaneous activity in Adelta- and C-fibers may account for nonevoked pain behavior and may also contribute to mechanical hyperalgesia by amplifying responses centrally.

Distinct sensitizing effects of the cAMP-PKA second messenger cascade on rat dural mechanonociceptors

Activation of the cAMP/protein kinase A (PKA) second messenger cascade has been implicated in the induction of mechanical hyperalgesia by inflammatory mediators. We examined the role of this cascade in mechanical sensitization of nociceptive neurons that innervate the meninges, a process thought to be involved in the pathophysiology of headache syndromes such as migraine. Single unit activity was recorded in the trigeminal ganglion from 40 mechanosensitive dural afferents (conduction velocitity: 0.3-6.6 m s(-1)) and nine mechanically insensitive dural afferents (MIAs) (conduction velocitity: 0.3-2.8 m s(-1)) while stimulating the dura with a servo force-controlled stimulator or von Frey monofilaments, respectively. Local application to the dura of dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP, 100 microM), a stable membrane-permeant cAMP analogue, produced mechanical sensitization in the majority of mechanosensitive units (19/29, 66 %). Two distinct patterns of mechanical sensitization were observed. Thirty-eight per cent of the units exhibited only a decrease in threshold (TH group), while 28 % showed only an increase in suprathreshold responses (STH group). dbcAMP also induced mechanosensitivity in the majority of MIA units (6/9, 67 %). dbcAMP-induced sensitization was blocked by the PKA inhibitors, Rp-cAMP (1 mM) and H-89 (100 microM). A mixture of inflammatory mediators induced both components of sensitization in the majority of mechanosensitive units tested. However, in each unit, PKA inhibitors blocked only one of the two effects (either TH or STH). Units that were classified as TH or STH also differed in their baseline stimulus-response slopes, thresholds and conduction velocities. These findings implicate the cAMP-PKA cascade in sensitization of dural mechanonociceptors and suggest that this cascade may produce sensitization through at least two different mechanisms operating in separate neuronal populations.

Tachykinins and neuro-immune interactions in asthma

Excitatory non-adrenergic-non-cholinergic neuropeptides, such as the tachykinins substance P and neurokinin A, and its receptors are present in human and animal airways. Tachykinins are biologically active at extremely low concentrations. These peptides can cause potent inflammatory effects and can affect airway function in a way that resembles features of asthma. Local release of tachykinins affects blood vessels (vasodilatation and increased vascular permeability) and bronchial smooth muscle (bronchoconstrition and hyperresponsiveness). Neuropeptide research has revealed that tachykinins also play an important modulatory role in immune reactions. Tachykinins stimulate immune cells, such as mast cells, lymphocytes, and macrophages and are chemotactic for neutrophils and eosinophils. Vice versa, a range of immune cell mediators can also induce the release of tachykinins from excitatory NANC nerve endings in the airways. In the last 20 years, significant advances have been made in investigations of the interaction between immune cells and nervous systems in chronic inflammatory diseases such as asthma.

The effect of electroacupuncture on pain behaviors and noxious stimulus-evoked Fos expression in a rat model of neuropathic pain

Chronic-constriction injury (CCI) of the sciatic nerve causes mechanical and heat hyperalgesia and mechanical allodynia in the plantar surface of the hindpaw. The underlying mechanism thought to account for these phenomena include central sensitization induced by peripheral nerve injury, ie, the increase in neuronal activity of spinal dorsal horn neurons. As a marker of neuronal activation of the central nervous system, Fos expression has been used widely to monitor the change in neuronal activity evoked by peripheral input. In this study, we examined the antinociceptive effect of electroacupuncture (EA) on pain behavior and noxious stimulus-evoked Fos expression in dorsal horn neurons of the spinal cord in CCI rats 14 days after injury. Male Sprague-Dawley rats (180 to 200 g) received loose ligation of the left sciatic nerve. Heat and mechanical hyperalgesia and mechanical allodynia were examined by the plantar foot test, the pin-prick test, and the von Frey test before and after the EA treatment (100 Hz, 0.3 millisecond, 3 or 1 mA, 20 minutes) into the Zusanli point (S36). When EA stimulation to the Zusanli point was applied, the mechanical and heat hyperalgesia were significantly suppressed; however, mechanical allodynia was not affected. The EA stimulation to nonacupuncture point did not show any significant effect. Next, pinch stimulation was applied to the plantar surface of the operated hindpaw of the CCI rats for 10 minutes, and the stimulus-evoked Fos expression in dorsal horn neurons in L4-L6 spinal cord levels was then examined by using immunohistochemistry. The number of noxious stimulus-evoked Fos-labeled neurons in both the superficial and deep laminae of the dorsal horn in the CCI rats was increased significantly compared with those in sham-operated rats, suggesting an increased excitability of dorsal horn neurons to noxious stimuli. Concurrent EA treatment to the Zusanli point with the pinch stimulus suppressed the increase in the number of Fos-labeled cells in the spinal dorsal horn in the CCI rats. The present results show that EA treatment has antinociceptive effects on both pain behavior and neuronal activation of the spinal dorsal horn neurons in CCI rats.

Hyper-responsivity in a subset of C-fiber nociceptors in a model of painful diabetic neuropathy in the rat

While clinical characteristics of diabetic painful neuropathy are well described, the underlying electrophysiological basis of the exaggerated painful response to stimuli, as well as the presence of spontaneous pain, are poorly understood. In order to elucidate peripheral contributions to painful diabetic neuropathy, we quantitatively evaluated the function of C-fibers in a rat model of painful diabetic neuropathy, diabetes induced by the pancreatic beta-cell toxin streptozotocin. While there was no significant effect of diabetes on conduction velocity, mechanical threshold or spontaneous activity, the number of action potentials in response to sustained threshold and suprathreshold mechanical stimuli was significantly increased in the diabetic rats. Moreover, there was a clustering of responses of C-fibers in diabetic rats; while two-thirds of C-fibers fired at the same mean frequency as C-fibers in control rats, one-third of C-fibers in diabetic rats were markedly hyper-responsive, demonstrating a threefold increase in firing frequency. The high-firing-frequency C-fibers in rats with diabetes also had faster conduction velocity than the low-firing-frequency C-fibers in rats with diabetes or in C-fibers in control rats. The hyper-responsiveness was characterized by a selective increase of the shortest interspike intervals (<100ms) in the burst component (first 10s) of the response to a sustained suprathreshold stimulus; in the plateau phase (last 50s) of the response to a 60-s suprathreshold stimulus, we found a selective increase of interspike intervals between 100 and 300ms in hyper-responsive C-fibers in rats with diabetes. The hyper-responsiveness did not correlate with mechanical threshold, presence of spontaneous activity or location of the fiber's receptive field. In summary, in an established model of painful diabetic neuropathy in the rat, a subset of C-fibers demonstrated a marked hyper-responsiveness to mechanical stimuli. The subset was also found to have a greater mean conduction velocity than the fibers not demonstrating this hyper-responsivity. The present findings suggest that study of individual neurons in vitro may allow elucidation of the ionic basis of enhanced nociception in diabetic neuropathy.

A selective increase in Fos expression in spinal dorsal horn neurons following graded thermal stimulation in rats with experimental mononeuropathy

In order to clarify the central mechanisms of thermal hyperalgesia produced by peripheral nerve injury, Fos protein-like immunoreactive (Fos-LI) cells in spinal dorsal horn neurons were studied in rats with chronic constriction nerve injury (CCI) following graded thermal stimulation of the hind paw. The graded thermal stimuli (cold: 5, 10 and 15 degrees C, heat: 42, 46 and 54 degrees C) were applied to the plantar surface of the operated hind paw 14 days after CCI or sham operation, and the number of Fos-LI cells in the spinal dorsal horn was quantified. Many Fos-LI cells were expressed in the superficial laminae of the spinal dorsal horn both in sham-operated and CCI rats following thermal stimulation. Fos-LI cells were mainly restricted to the medial half of the superficial laminae of the spinal dorsal horn, and were sparsely distributed in the deeper laminae. The number of Fos-LI cells in the superficial laminae (laminae I--II) of the dorsal horn was significantly higher in CCI rats after stimulation at 10 and 46 degrees C, but not at the other stimulating temperatures (5, 15, 42, and 54 degrees C) as compared to that in sham-operated rats. In laminae III-IV, the number of Fos-LI cells was significantly higher at all stimulus temperatures in CCI rats when compared to the sham-operated rats. No distribution difference of Fos-LI cells was observed between CCI and sham-operated rats in laminae V--VI. Thus, in the spinal dorsal horn of the CCI rats, there was a selective increase in thermal stimulus-induced Fos-LI cells in the superficial dorsal horn after stimulating at near noxious threshold intensities and a non-selective increase in Fos-LI cells in laminae III--IV after both noxious and innocuous thermal stimuli. The increase of Fos-LI cells in the superficial laminae may be related to hypersensitivity to noxious stimuli while the increase of Fos-LI cells in laminae III--IV may be related to an increased sensitivity to both noxious and innocuous stimuli that leads to increased reflex activity following nerve injury.

Pain behavior and response properties of spinal dorsal horn neurons following experimental diabetic neuropathy in the rat: modulation by nitecapone, a COMT inhibitor with antioxidant properties

We attempted to characterize a spinal neuronal correlate of painful neuropathy induced by diabetes mellitus (DM). Pain behavior and response properties of spinal dorsal horn neurons were determined in rats with a streptozocin-induced DM. A catechol-O-methyltransferase inhibitor with potent antioxidant properties, nitecapone, was used in an attempt to attenuate neuropathic symptoms. Behaviorally DM induced mechanical hypersensitivity that was markedly attenuated by oral treatment with nitecapone. The antihyperalgesic effect of nitecapone was not reversed by naloxone, an opioid antagonist, or atipamezole, an alpha-2-adrenoceptor antagonist. Electrophysiological recordings performed in pentobarbitone-anesthetized animals revealed that the most distinct abnormality in response properties of spinal dorsal horn wide-dynamic range (WDR) neurons was the increase in their spontaneous activity observed in untreated but not in nitecapone-treated DM rats. Conditioning electrical stimulation and a lidocaine block of the rostroventromedial medulla (RVM) had a similar modulatory effect on evoked responses of spinal dorsal horn WDR neurons in all experimental groups. The response properties of spinal dorsal horn nociceptive-specific or low-threshold mechanoreceptive neurons were not markedly different between the experimental groups. The results indicate that increased spontaneous activity in spinal dorsal horn WDR neurons may be causally related to behaviorally observed mechanical hypersensitivity in DM. Attenuation of the increased spontaneous activity in WDR neurons may explain the antihyperalgesic effect by nitecapone, due to naloxone- and alpha-2-adrenoceptor-insensitive mechanisms. DM or nitecapone treatment did not produce significant changes in phasic or tonic descending pain regulation originating in the RVM.

Effect of intrathecal administration of serotonin in chronic pain models in rats

The present study examined the effects of intrathecal (i.t.) administration of 5-hydroxytryptamine (5-HT; 0.1-100 microg) on mechanical hyperalgesia associated with neuropathic pain (chronic constriction of the sciatic nerve model and diabetic model) and inflammatory pain (carrageenan and polyarthritic models) in rats. Results demonstrated that the hyperalgesia observed in the mononeuropathic and diabetic rats was attenuated by 5-HT; the active dose, however, was 100- to 1000-fold higher than that required in normal rats, and was moderately effective. In the two experimental models of inflammatory pain, 5-HT was not markedly or similarly active. In the carrageenan model, 5-HT at the highest dose was only weakly effective whereas in the polyarthritic model it was inactive. Together, these results show that 5-HT has antinociceptive effects in several rat pain models, except in the model of diffuse pain (polyarthritic rats). Its antinociceptive effects in these models, however, are slight and differ from those observed in normal rats.

Excitatory non-adrenergic-non-cholinergic neuropeptides: key players in asthma

Professor David de Wied first introduced the term 'neuropeptides' at the end of 1971. Later peptide hormones and their fragments, endogenous opioid (morphine-like) peptides and a large number of other biogenic peptides became classified as neuropeptides. All of these peptides are united by a number of common features including their origin (nervous system and peptide-secreting cells found in various organs such as skin, gut, lungs), biosynthesis, secretion, metabolism, and enormous effectiveness. Neuropeptides are biologically active at extremely low concentrations. The past decade, neuropeptide research has revealed that neuropeptides also participate strongly in immune reactions. The neuro-immune concept has opened up a whole new research area. In the last 20 years, significant advances have been made in investigations of the interaction between immune and nervous systems in chronic inflammatory diseases such as asthma. The goal of this review is to bring together the functional relevance of excitatory non-adrenergic-non-cholinergic (NANC) nerves and the interaction with the immune system in asthma.

Evidence for an involvement of tachykinins in allodynia in streptozocin-induced diabetic rats

A better knowledge of the pathophysiology of chronic pain could help to improve the treatment of patients with such syndrome. The aim of the present work was to elucidate the possible involvement of spinal substance P and neurokinin A in the mechanical and thermal allodynia observed in streptozocin-induced diabetic rats. A tachykinin NK(1) receptor antagonist, RP-67,580 ((3aR,7aR) -7, 7-diphenyl-2-(1-imino-2(2-methoxy phenyl)-ethyl) perhydroisoindol-4-one hydrochloride), a tachykinin NK(2) receptor antagonist, SR-48,968 ((S)-N-methyl (4-(acetylamino-4phenylpiperidino)-2-(3, 4-dichlorophenyl) butyl) benzamide) and their respective enantiomers were intrathecally administered 4 weeks after the induction of diabetes. Mechanical and thermal allodynia were evaluated before and up to 60 min after injection. The tachykinin receptor antagonists at the highest doses (10 and 25 microgram) significantly reduced allodynia, their enantiomers being inactive. Both of these data suggest the involvement of substance P and neurokinin A in the neuropathy-induced allodynia and offer a novel hypothesis to treat chronic pain due to diabetes.

Peripheral demyelination and neuropathic pain behavior in periaxin-deficient mice

The Prx gene in Schwann cells encodes L- and S-periaxin, two abundant PDZ domain proteins thought to have a role in the stabilization of myelin in the peripheral nervous system (PNS). Mice lacking a functional Prx gene assemble compact PNS myelin. However, the sheath is unstable, leading to demyelination and reflex behaviors that are associated with the painful conditions caused by peripheral nerve damage. Older Prx-/- animals display extensive peripheral demyelination and a severe clinical phenotype with mechanical allodynia and thermal hyperalgesia, which can be reversed by intrathecal administration of a selective NMDA receptor antagonist We conclude that the periaxins play an essential role in stabilizing the Schwann cell-axon unit and that the periaxin-deficient mouse will be an important model for studying neuropathic pain in late onset demyelinating disease.