Sevoflurane suppresses noxious stimulus-evoked expression of Fos-like immunoreactivity in the rat spinal cord via activation of endogenous opioid systems

Effects of anesthetic depth on postoperative pain and delirium: a meta-analysis of randomized controlled trials with trial sequential analysis

BACKGROUND

Whether anesthetic depth affects postoperative outcomes remains controversial. This meta-analysis aimed to evaluate the effects of deep vs. light anesthesia on postoperative pain, cognitive function, recovery from anesthesia, complications, and mortality.

METHODS

PubMed, EMBASE, and Cochrane CENTRAL databases were searched until January 2022 for randomized controlled trials comparing deep and light anesthesia in adult surgical patients. The co-primary outcomes were postoperative pain and delirium (assessed using the confusion assessment method). We conducted a meta-analysis using a random-effects model. We assessed publication bias using the Begg's rank correlation test and Egger's linear regression. We evaluated the evidence using the trial sequential analysis and Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology. We conducted subgroup analyses for pain scores at different postoperative time points and delirium according to cardiac or non-cardiac surgery.

RESULTS

A total of 26 trials with 10,743 patients were included. Deep anesthesia compared with light anesthesia (a mean difference in bispectral index of -12 to -11) was associated with lower pain scores at rest at 0 to 1 h postoperatively (weighted mean difference = -0.72, 95% confidence interval [CI] = -1.25 to -0.18, P  = 0.009; moderate-quality evidence) and an increased incidence of postoperative delirium (24.95% vs. 15.92%; risk ratio = 1.57, 95% CI = 1.28-1.91, P  < 0.0001; high-quality evidence). No publication bias was detected. For the exploratory secondary outcomes, deep anesthesia was associated with prolonged postoperative recovery, without affecting neurocognitive outcomes, major complications, or mortality. In the subgroup analyses, the deep anesthesia group had lower pain scores at rest and on movement during 24 h postoperatively, without statistically significant subgroup differences, and deep anesthesia was associated with an increased incidence of delirium after non-cardiac and cardiac surgeries, without statistically significant subgroup differences.

CONCLUSIONS

Deep anesthesia reduced early postoperative pain but increased postoperative delirium. The current evidence does not support the use of deep anesthesia in clinical practice.

Expressions of spinal microglia activation, BDNF, and DREAM proteins correlated with formalin-induced nociceptive responses in painful and painless diabetic neuropathy rats

The complications of diabetic polyneuropathy (DN) determines its level of severity. It may occur with distinctive clinical symptoms (painful DN) or appears undetected (painless DN). This study aimed to investigate microglia activation and signalling molecules brain-derived neurotrophic factor (BDNF) and downstream regulatory element antagonist modulator (DREAM) proteins in spinal cord of streptozotocin-induced diabetic neuropathy rats. Thirty male Sprague-Dawley rats (200-230 g) were randomly assigned into three groups: (1) control, (2) painful DN and (3) painless DN. The rats were induced with diabetes by single intraperitoneal injection of streptozotocin (60 mg/kg) whilst control rats received citrate buffer as a vehicle. Four weeks post-diabetic induction, the rats were induced with chronic inflammatory pain by intraplantar injection of 5% formalin and pain behaviour responses were recorded and assessed. Three days later, the rats were sacrificed and lumbar enlargement region of spinal cord was collected. The tissue was immunoreacted against OX-42 (microglia), BDNF and DREAM proteins, which was also quantified by western blotting. The results demonstrated that painful DN rats exhibited increased pain behaviour score peripherally and centrally with marked increase of spinal activated microglia, BDNF and DREAM proteins expressions compared to control group. In contrast, painless DN group demonstrated a significant reduction of pain behaviour score peripherally and centrally with significant reduction of spinal activated microglia, BDNF and DREAM proteins expressions. In conclusions, the spinal microglia activation, BDNF and DREAM proteins correlate with the pain behaviour responses between the variants of DN.

Genetic Reporters of Neuronal Activity: c-Fos and G-CaMP6

The majority of 20th century investigations into anesthetic effects on the nervous system have used electrophysiology. Yet some fundamental limitations to electrophysiologic recordings, including the invasiveness of the technique, the need to place (potentially several) electrodes in every site of interest, and the difficulty of selectively recording from individual cell types, have driven the development of alternative methods for detecting neuronal activation. Two such alternative methods with cellular scale resolution have matured in the last few decades and will be reviewed here: the transcription of immediate early genes, foremost c-fos, and the influx of calcium into neurons as reported by genetically encoded calcium indicators, foremost GCaMP6. Reporters of c-fos allow detection of transcriptional activation even in deep or distant nuclei, without requiring the accurate targeting of multiple electrodes at long distances. The temporal resolution of c-fos is limited due to its dependence upon the detection of transcriptional activation through immunohistochemical assays, though the development of RT-PCR probes has shifted the temporal resolution of the assay when tissues of interest can be isolated. GCaMP6 has several isoforms that trade-off temporal resolution for signal to noise, but the fastest are capable of resolving individual action potential events, provided the microscope used scans quickly enough. GCaMP6 expression can be selectively targeted to neuronal populations of interest, and potentially thousands of neurons can be captured within a single frame, allowing the neuron-by-neuron reporting of circuit dynamics on a scale that is difficult to capture with electrophysiology, as long as the populations are optically accessible.

Nicotine-prevented learning and memory impairment in REM sleep-deprived rat is modulated by DREAM protein in the hippocampus

INTRODUCTION

REM sleep deprivation is associated with impairment in learning and memory, and nicotine treatment has been shown to attenuate this effect. Recent studies have demonstrated the importance of DREAM protein in learning and memory processes. This study investigates the association of DREAM protein in REM sleep-deprived rats hippocampus upon nicotine treatment.

METHODS

Male Sprague Dawley rats were subjected to normal condition, REM sleep deprivation and control wide platform condition for 72 hr. During this procedure, saline or nicotine (1 mg/kg) was given subcutaneously twice a day. Then, Morris water maze (MWM) test was used to assess learning and memory performance of the rats. The rats were sacrificed and the brain was harvested for immunohistochemistry and Western blot analysis.

RESULTS

MWM test found that REM sleep deprivation significantly impaired learning and memory performance without defect in locomotor function associated with a significant increase in hippocampus DREAM protein expression in CA1, CA2, CA3, and DG regions and the mean relative level of DREAM protein compared to other experimental groups. Treatment with acute nicotine significantly prevented these effects and decreased expression of DREAM protein in all the hippocampus regions but only slightly reduce the mean relative level of DREAM protein.

CONCLUSION

This study suggests that changes in DREAM protein expression in CA1, CA2, CA3, and DG regions of rat's hippocampus and mean relative level of DREAM protein may involve in the mechanism of nicotine treatment-prevented REM sleep deprivation-induced learning and memory impairment in rats.

Differential effects of general anesthetics on anxiety-like behavior in formalin-induced pain: involvement of ERK activation in the anterior cingulate cortex

RATIONALE

Pain-related anxiety and depression are well known to be comorbid with chronic pain and adversely affect patient quality of life. Recent studies have shown that anxiety-like behaviors also develop with acute surgical pain, but the effects of general anesthetics on acute pain-related anxiety are unknown.

OBJECTIVE

The present study aimed to compare the effects of different general anesthetics on anxiety-like behaviors that follow formalin-induced acute pain in a rat model.

METHODS

Formalin-induced acute inflammatory pain was established by intraplantar injection of 1% formalin without anesthesia or with anesthesia using the clinical anesthetics sevoflurane, propofol, or pentobarbital sodium. Anxiety-like behaviors were studied using the open-field test and elevated plus maze. Phosphorylated extracellular signal-regulated kinase (p-ERK) 1/2 expression in the anterior cingulate cortex (ACC) and spinal cord was examined using immunohistochemistry.

RESULTS

Anxiety-like behaviors were observed at 24 and 72 h post-formalin injection. Concomitantly, p-ERK 1/2 expression was upregulated in the ACC at 1 and 24 h post-formalin injection. While all three general anesthetics effectively blocked nociceptive responses and activation of ERK in the rat ACC following formalin injection during anesthesia, only sevoflurane inhibited ERK activation in the spinal cord and ACC at 24 h post-injection.

CONCLUSIONS

This study suggests that sevoflurane, but not intravenous anesthetics, inhibits pain-related anxiety, along with ERK activation in the ACC, probably through inhibition of spinal nociceptive transmission. Intraoperative application of inhaled anesthetics may be a better choice to reduce postoperative anxiety.

The Effects of Pre-emptive Administration of Ketamine and norBNI on Pain Behavior, c-Fos, and Prodynorphin Protein Expression in the Rat Spinal Cord after Formalin-induced Pain Is Modulated by the DREAM Protein

Background

We investigated the effects of pre-emptive administration of ketamine and norBNI on pain behavior and the expression of DREAM, c-Fos, and prodynorphin proteins on the ipsilateral side of the rat spinal cord at 2 and 4 hours after formalin injection.

Methods

Eighty-four male Sprague Dawley rats were divided into 4 major groups consisting of control rats (C) (n = 12), rats given only formalin injections (F) (n = 24), and rats treated with pre-emptive administration of either ketamine (K+F) (n = 24) or norBNI (N+F) (n = 24). The non-control groups were further divided into subgroups consisting of rats that were sacrificed at 2 and 4 hours (n = 12 for each group) after formalin injection. Pain behavior was recorded for 1 hour. After 2 and 4 hours, the rats were sacrificed and the spinal cords (L4-L5 sections) were removed for immunohistochemistry and Western blot analysis.

Results

The pain behavior response was reduced in the K+F group compared to the other groups during the second phase of the formalin pain response. We detected an increase in the nuclear DREAM protein level in the K+F group at 2 and 4 hours and a transient decrease in the N+F group at 2 hours; however, it increased at 4 hours after injection. Fos-like immunoreactivity (FLI) and Prodynorphin-like immunoreactivity (PLI) neurons decreased in the K+F group but increased in the N+F group at 2 hours after injection. While FLI decreased, PLI increased in all groups at 4 hours after injection.

Conclusions

We suggest that NMDA and kappa opioid receptors can modulate DREAM protein expression, which can affect pain behavior and protein transcriptional processes at 2 hours and bring about either harmful or protective effects at 4 hours after formalin injection.

Sevoflurane versus propofol anesthesia in patients undergoing lumbar spondylodesis: a randomized trial

BACKGROUND

Spondylodesis is a procedure aiming at providing stability in one or more spinal segments. The aim of our study was to compare sevoflurane and propofol as induction and maintenance agents, focusing on hemodynamic stability, recovery characteristics, postoperative nausea and vomiting, and pain intensity.

MATERIALS AND METHODS

Seventy patients, with a physical status according to American Society of Anesthesiologists (ASA) I-II, 50-72 y old, undergoing selective lumbar spondylodesis were enrolled.

RESULTS

There was no statistically significant difference between groups in overall mean hemodynamic parameters. No differences in fluid administration and vasoactive substances used were noted. Postoperatively, there was a significant difference in overall mean visual analog score at rest and at cough, with the sevoflurane group showing lower values. No differences in the incidence of nausea, vomiting, shivering, postoperative sedation scores, and orientation to place were revealed. Orientation to time exhibited a statistically significant difference at the time just after transfer to the post-anesthesia care unit, where more patients of the sevoflurane group seemed to be well oriented.

CONCLUSIONS

Sevoflurane and propofol anesthesia for lumbar spondylodesis surgery provide safe and comparable results.

The role of TNFα in the periaqueductal gray during naloxone-precipitated morphine withdrawal in rats

Tolerance and dependence are common complications of long-term treatment of pain with opioids, which substantially limit the long-term use of these drugs. The mechanisms underlying these phenomena are poorly understood. Studies have implicated the midbrain periaqueductal gray (PAG) in the pathogenesis of morphine withdrawal, and recent evidence suggests that proinflammatory cytokines in the PAG may play an important role in morphine withdrawal. Here we report that chronic morphine withdrawal-induced upregulation of glial fibrillary acidic protein (GFAP), tumor necrosis factor alpha (TNFα) and phosphorylation of ERK1/2 (pERK1/2) in the caudal ventrolateral PAG (vlPAG). Microinjection of recombinant TNFα into the vlPAG followed by intraperitoneal naloxone resulted in morphine withdrawal-like behavioral signs, and upregulation of pERK1/2, expression of Fos, and phosphorylation of cAMP response element binding (pCREB) protein. We used a herpes simplex virus (HSV)-based vector expressing p55 soluble TNF receptor (sTNFR) microinjected into the PAG to examine the role of the proinflammatory cytokine TNFα in the PAG in the naloxone-precipitated withdrawal response. Microinjection of HSV vector expressing sTNFR into the PAG before the start of morphine treatment significantly reduced the naloxone-precipitated withdrawal behavioral response and downregulated the expression of GFAP and TNFα in astrocytes of the PAG. TNFR type I colocalized with neuronal pERK1/2. Microinjection of HSV vector expressing sTNFR into the PAG also significantly reduced the phosphorylation of both ERK1/2 and CREB, and reduced Fos immunoreactivity in neurons of the PAG following naloxone-precipitated withdrawal. These results support the concept that proinflammatory cytokines expressed in astrocytes in the PAG may play an important role in the pathogenesis of morphine withdrawal response.

Effects of transgene-mediated endomorphin-2 in inflammatory pain

We examined the analgesic properties of endomorphin-2 expressed in DRG neurons transduced with a non-replicating herpes simplex virus (HSV)-based vector containing a synthetic endomorphin-2 gene construct. HSV-mediated endomorphin-2 expression reduced nocisponsive behaviors in response to mechanical and thermal stimuli after injection of complete Freund's adjuvant (CFA) into the paw, and reduced peripheral inflammation measured by paw swelling after injection of CFA. The analgesic effect of the vector was blocked by either intraperitoneal or intrathecal administration of naloxone methiodide, blocking peripheral and central mu opioid receptors, respectively. Endomorphin-2 vector injection also reduced spontaneous pain-related behaviors in the delayed phase of the formalin test and in both CFA and formalin models suppressed spinal c-fos expression. The magnitude of the vector-mediated analgesic effect on the delayed phase of the formalin test was similar in naïve animals and in animals with opiate tolerance induced by twice daily treatment with morphine, suggesting that there was no cross-tolerance between vector-mediated endomorphin-2 and morphine. These results suggest that transgene-mediated expression of endomorphin-2 in transduced DRG neurons in vivo acts both peripherally and centrally through mu opioid receptors to reduce pain perception.

Minimum alveolar concentration of halogenated volatile anaesthetics in left ventricular hypertrophy and congestive heart failure in rats

BACKGROUND

Although many physiological and pathological conditions affect minimal alveolar concentration (MAC), there are no reliable data on the MAC for halogenated anaesthetics during left ventricular hypertrophy (LVH) and congestive heart failure (CHF). The aim of this experimental study was to determine the MAC values of halothane, isoflurane, and sevoflurane in rats, at early and later stages of cardiomyopathic hypertrophy.

METHODS

LVH was induced by ascending aortic stenosis in 3-4-week-old rats. LVH and CHF in each animal were assessed weekly by echocardiography. MAC of halothane, isoflurane, and sevoflurane was determined using the tail-clamp technique in spontaneously breathing rats from each group. Response vs no-response data were analysed using logistic regression analysis. Data are medians (95% confidence interval).

RESULTS

The MAC of halothane [1.30% (1.26-1.34)], isoflurane [1.52% (1.48-1.57)], and sevoflurane [2.93% (2.78-3.07)] in rats with LVH was not different from sham-operated rats [respectively, 1.23% (1.20-1.26), 1.52% (1.47-1.56), and 2.90% (2.79-3.00)]. Conversely, the MAC of halothane [1.44 (1.39-1.50)] and isoflurane [1.74 (1.69-1.78)], but not sevoflurane [2.99 (2.93-3.06)], was significantly increased in rats with CHF.

CONCLUSIONS

MAC values for halothane, isoflurane, and sevoflurane were unchanged in rats with pressure-induced overload LVH. Conversely, the MAC for halothane and isoflurane, but not sevoflurane, was significantly increased in rats with CHF.

Gene transfer to interfere with TNFalpha signaling in neuropathic pain

We examined the role of spinal tumor necrosis factor-alpha (TNFalpha) in neuropathic pain of peripheral nerve origin. Two weeks after selective L5 spinal nerve ligation (SNL), rats exhibiting mechanical allodynia and thermal hyperalgesia showed a marked increase in full-length membrane-associated TNFalpha (mTNFalpha) in the dorsal horn of spinal cord, in the absence of detectable soluble TNFalpha peptide. Local release of the soluble p55 TNF receptor, achieved by herpes simplex virus vector-based gene transfer to dorsal root ganglion, resulted in a reduction of mTNFalpha and concomitant reductions in interleukin-1beta and phosphorylated p38 MAP kinase. Subcutaneous inoculation of soluble p55 TNF receptor expressing HSV vector into the plantar surface of the hind foot ipsilateral to the ligation 1 week before SNL delayed the development of both mechanical allodynia and thermal hyperalgesia; subcutaneous inoculation into the hind foot ipsilateral to the ligation 1 week after SNL resulted in a statistically significant reduction in mechanical allodynia and thermal hyperalgesia that was apparent 1 week after inoculation. These results suggest a novel 'reverse signaling' through glial mTNFalpha, which may be exploited to downregulate the neuroimmune reaction in spinal cord to reduce chronic neuropathic pain.

Propofol's effects on nociceptive behavior and spinal c-fos expression after intraplantar formalin injection in mice with a mutation in the gamma-aminobutyric acid-type(A) receptor beta3 subunit

We investigated whether propofol affected nociceptive behavior and fos-like immunoreactivity (FLI) in the lumbo-sacral spinal cord after intraplantar formalin injection in wild-type (WT) mice and in mutant mice harboring a point mutation of the gamma-aminobutyric acid type(A) receptor, which renders them resistant to propofol. Bolus injection of propofol (30 mg/kg IV) in WT mice reduced phase 1 formalin-evoked behavior over the initial 2-3 min but did not alter phase 2 behavior or spinal FLI (64 +/- 19 cells/section) compared with WT mice receiving intralipid vehicle plus intraplantar formalin (57 +/- 19 cells/section). Most FLI was restricted to superficial dorsal horn laminae ipsilateral to the formalin injection. WT mice receiving a 60-min propofol infusion were anesthetized throughout and did not display nociceptive behavior but had FLI (58 +/- 11 cells/section) that did not differ significantly from the other WT groups. Mutant mice receiving bolus injection of propofol (30 mg/kg) and intraplantar formalin were not anesthetized and exhibited nociceptive behavior. The total FLI in the spinal cord was 47 +/- 29 cells/section. These data indicate that although propofol produces anesthesia, it does not prevent the FLI that is associated with nociception, a finding consistent with propofol lacking analgesic properties.

Naloxone Does Not Increase the Minimum Alveolar Anesthetic Concentration of Sevoflurane in Mice

Several previous studies concluded that opioid receptors do not mediate the capacity of inhaled anesthetics to produce immobility in the face of noxious stimulation because administration of naloxone (a nonspecific opioid receptor antagonist) does not increase the minimum alveolar anesthetic concentration (MAC) of inhaled anesthetic that produces immobility in 50% of subjects given a noxious stimulation. In contrast, a recent study found that 0.1 mg/kg naloxone given intraperitoneally increased sevoflurane MAC in mice by 18% (P < 0.01). We repeated the recent study with sevoflurane in the same strain of mice, administering nothing (control), 0.1 mg/kg, and 1.0 mg/kg of naloxone. Our study differed in that we also tested a parallel group given saline rather than naloxone. We were blinded to drug administration. MAC decreased 4.8% +/- 11.0% (mean+/- sd) and 2.4% +/- 12.5% with the first and second administrations of saline. Similarly, MAC decreased 4.7% +/- 7.1% and 5.5% +/- 10.0% with the administration of 0.1 mg/kg and 1.0 mg/kg of naloxone. We do not find that naloxone increases MAC. Opioid receptors do not underlie a portion of the capacity of inhaled anesthetics to produce immobility.

HSV-mediated expression of interleukin-4 in dorsal root ganglion neurons reduces neuropathic pain

BACKGROUND

To examine the role of inflammatory mediators in neuropathic pain, we used a replication-defective genomic herpes simplex virus (HSV)-based vector containing the coding sequence for the anti-inflammatory peptide interleukin (IL)-4 under the transcriptional control of the HSV ICP4 immediate early promoter, vector S4IL4, to express IL-4 in dorsal root ganglion (DRG) neurons in vivo.

RESULTS

Subcutaneous inoculation of S4IL4 in the foot transduced lumbar DRG to produce IL-4. Transgene-mediated expression of IL-4 did not alter thermal latency or tactile threshold in normal animals, but inoculation of S4IL4 1 week after spinal nerve ligation (SNL) reduced mechanical allodynia and reversed thermal hyperalgesia resulting from SNL. Inoculation of S4IL4 1 week before SNL delayed the development of thermal hyperalgesia and tactile allodynia, but did not prevent the ultimate development of these manifestations of neuropathic pain. S4IL4 inoculation suppressed non-noxious-induced expression of c-Fos immunoreactivity in dorsal horn of spinal cord and reversed the upregulation of spinal IL-1beta, PGE2, and phosphorylated-p38 MAP kinase, characteristic of neuropathic pain.

CONCLUSION

HSV-mediated expression of IL-4 effectively reduces the behavioral manifestations of neuropathic pain, and reverses some of the biochemical and histologic correlates of neuropathic pain at the spinal level.

Clinical actions of subarachnoid sevoflurane administration in vivo : a study in dogs

BACKGROUND

Halogenated ethers produce clinical effects at spinal sites. Nevertheless, in vitro and in vivo studies have not determined whether the immobilizing effect in the spinal cord is due to inhibition of nociceptive or motor transmission or both. Our goal was to characterize the clinical effects of direct spinal sevoflurane administration.

METHODS

Five adult beagle dogs completed the study. In a randomized and blinded manner each animal received placebo (saline 0.1 ml kg(-1)) and three concentrations of pure sevoflurane administered intrathecally (0.05, 0.075 and 0.1 ml kg(-1)) by means of a permanent spinal catheter. Sensory and motor block and state of consciousness were determined at baseline and at predetermined regular intervals until at least 2 h after total recovery.

RESULTS

None of the dogs presented a decrease in consciousness with either 0.05 or 0.075 ml kg(-1) of sevoflurane. Administration of 0.1 ml kg(-1) produced light sedation (2 on a four-point sedation scale) in three of the five dogs. A comparison of the duration of the sensory and motor blocks among the three sevoflurane dosages shows a significant dose-dependent increase that is greater in all cases than that for the saline solution.

CONCLUSIONS

Spinal administration of pure sevoflurane resulted in a dose-related and totally reversible motor and sensory regional block without any signs of clinical neurotoxicity or significant decrease in consciousness. Therefore the model allows us to comment on the analgesic effects at the spinal level in addition to the direct immobilizing effects of sevoflurane.

Gene transfer of glutamic acid decarboxylase reduces neuropathic pain

We tested whether transfer of the gene coding for glutamic acid decarboxylase to dorsal root ganglion using a herpes simplex virus vector to achieve release of GABA in dorsal horn would attenuate nociception in this condition. Subcutaneous inoculation of a replication-defective herpes simplex virus vector expressing glutamic acid decarboxylase (vector QHGAD67) 7 days after selective L5 spinal nerve ligation reversed mechanical allodynia and thermal hyperalgesia; the antiallodynic effect lasted 6 weeks and was reestablished by reinoculation. QHGAD67 inoculation also suppressed induction of c-Fos and phosphorylated extracellular signal-regulated kinase 1 and 2 in the spinal cord.

Nociceptin system does not affect MAC of volatile anaesthetics

BACKGROUND

Nociceptin is the endogenous agonist of the opioid receptor-like (ORL) 1 receptor (NOP), and both nociceptin and NOP are widely expressed in the brain and spinal cord, which are target organs of general anaesthetics. As nociceptin has been reported to be involved in modulating pain mechanisms and stress responses, it is possible that the activity of the nociceptin system affects the anaesthetic potency of general anaesthetics. To address this possibility, we investigated the minimum alveolar concentrations (MACs) of various volatile anaesthetics in nociceptin receptor knockout mice (NOP-/-) and wild-type mice (NOP+/+).

METHODS

We used male NOP-/- mice and NOP+/+ mice. MACs for halothane, isoflurane and sevoflurane were determined by the tail-clamp method.

RESULTS

MACs for halothane, isoflurane and sevoflurane in NOP-/- mice were 1.60 (SD 0.06), 1.68 (0.08) and 3.36 (0.07)%, respectively. In NOP+/+ mice, MACs for halothane, isoflurane and sevoflurane were 1.59 (SD 0.07), 1.72 (0.07) and 3.38 (0.09)%, respectively.

CONCLUSION

MACs in NOP-/- mice did not significantly differ from those in NOP+/+ mice for halothane, isoflurane and sevoflurane. This result suggests that the nociceptin system does not affect the anaesthetic potency of volatile anaesthetics.

Effects of intrathecal BAM22 on noxious stimulus-evoked c-fos expression in the rat spinal dorsal horn

The effects of bovine adrenal medulla 22 (BAM22), a cleaved product of proenkephalin A, were investigated on the noxious stimulus-evoked expressions of spinal c-fos-like immunoreactivity (FLI). Heat (51 degrees C) applied to the tail evoked FLI predominantly in laminae I-II of the sacral spinal cord. Intrathecal (i.t.) BAM22 at a dose of 7 nmol decreased the expressions of the heat-evoked FLI by 68%, 64% and 56% in laminae I-II, III-IV and V-VI, respectively, and the decrease pattern was comparable to that induced by i.t. morphine (10 mug). Naloxone (1 mg/kg, i.p.) significantly enhanced the heat-evoked FLI in laminae III-VI, prevented the morphine-induced inhibition, and decreased the potencies of BAM22 in laminae I-II and V-VI by 23-40%. Higher dose of naloxone (10 mg/kg, i.p.) also partially reduced the BAM22-induced suppression. Following intraplantar injection of formalin (2.5%), FLI neurons were preferentially distributed not only in laminae I-II but also in laminae III-IV and V-VI of segments L4-L5. Pretreatment with BAM22 (7 nmol, i.t.) reduced the formalin-evoked FLI neurons by 72%, 61% and 58%, in laminae I-II, III-IV and V-VI, respectively. Naloxone (1 mg/kg. i.p.) enhanced the formalin-evoked expressions of FLI in laminae III-VI and decreased the potencies of BAM22 by 22-38% in laminae I-II and V-VI. The present study provided evidence at a cellular level showing that opioid and non-opioid effects of BAM22 on nociceptive processing in acute and persistent pain models were associated with modulation of noxious stimulus-evoked activity of the spinal dorsal horn neurons.

Dual effects of intrathecal BAM22 on nociceptive responses in acute and persistent pain--potential function of a novel receptor

Bovine adrenal medulla 22 (BAM22) peptide is one of the cleavage products of proenkephalin A. It binds with high affinity to both opioid receptors and a newly discovered receptor in vitro. This latter receptor was first named sensory neuron-specific receptor and is here named BAM peptide-activated receptor with non-opioid activity (BPAR). BPAR is uniquely distributed in small-diameter DRG neurons, most of which are associated with the IB4 class of nociceptor afferent. The present study examined the effects of intrathecal administration of BAM22 on formalin-induced nocifensive behaviors and tail-withdrawal latency in the rat. Intrathecal (i.t.) administration of BAM22 decreased nocifensive behavior scores, measured as the sum of flinching and lifting/licking, in the first and second phases of the formalin test. This decrease was partially attenuated by systemic injection of naloxone. In the presence of naloxone, i.t. BAM22 produced a dose-dependent suppression of the nocifensive behaviors observed during the formalin test. The ratio of the efficacy of BAM22 (5 nmol) in the presence of naloxone over that in the absence of naloxone was 0.65 for flinching and 0.74 for lifting/licking in the second phase. BAM22 at a dose of 5 nmol increased the tail-withdrawal latency by 193 and 119% of baseline in the absence and presence of naloxone, respectively. Systemic administration of naloxone alone enhanced the nocifensive behaviors in the second, but not in the first phase of the formalin test. Naloxone treatment did not alter the tail-withdrawal latency. These data confirm earlier in vitro data showing that BAM22 has both opioid and non-opioid biological actions. The non-opioid action of BAM22 involves inhibition of acute and persistent nociceptive behaviors at the spinal level, presumably mediated via BPAR. The name suggested for this novel receptor, its potential physiological function and its ligand are discussed. British Journal of Pharmacology (2004) 141, 423-430. doi:10.1038/sj.bjp.0705637

HSV-mediated gene transfer of the glial cell-derived neurotrophic factor provides an antiallodynic effect on neuropathic pain

Neuropathic pain is a difficult clinical problem that is often refractory to medical management. Glial-derived neurotrophic factor (GDNF) administered intrathecally has been shown to prevent or reduce pain in an animal model of neuropathic pain, but cannot be delivered in the required doses to treat human pain. We have previously demonstrated that peripheral subcutaneous inoculation of a replication-incompetent herpes simplex virus (HSV)-based vector can be used to transduce neurons of the dorsal root ganglion. To examine whether HSV-mediated expression of GDNF could be used to ameliorate neuropathic pain, we constructed a replication-incompetent HSV vector expressing GDNF. Subcutaneous inoculation of the vector 1 week after spinal nerve ligation resulted in a continuous antiallodynic effect that was maintained for 3-4 weeks. Reinoculation of the vector reestablished the antiallodynic effect with a magnitude that was at least equivalent to the initial effect. Vector-mediated GDNF expression blocked the nonnoxious touch-induced increase in c-fos expression in dorsal horn characteristic of the painful state. Gene transfer to produce a trophic factor offers a novel approach to the treatment of neuropathic pain that may be appropriate for human therapy.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

The effects of dexmedetomidine and halothane on Fos expression in the spinal dorsal horn using a rat postoperative pain model

We investigated the effect of an intrathecal injection of a selective alpha2 adrenergic receptor agonist, dexmedetomidine (Dex), and halothane anesthesia on Fos expression in the lumbar spinal dorsal horn after skin incision of the plantar surface of the hind paw, a postoperative pain model using rats. Fos immunoreactivity was induced particularly in the superficial layers of the spinal cord 2 h after surgery. Halothane anesthesia (0.5-1.5%) partially reversed Fos induction, but not in a dose-dependent manner. Preoperative spinal Dex (0.1-10 microg) dose-dependently reduced Fos immunoreactivity, while a relatively high dose of Dex (10 microg) was necessary to produce a profound effect. When used with halothane anesthesia, relatively low doses of Dex (1-3 microg) completely suppressed Fos induction in the superficial spinal layers. These findings indicate that preoperative Dex treatment may provide anesthesia that does not induce stress on spinal neurons.