Sevoflurane postconditioning affects post-ischaemic myocardial mitochondrial ATP-sensitive potassium channel function and apoptosis in ageing rats.

This study investigated the effect of sevoflurane postconditioning on post-ischaemic cardiac function, infarct size, myocardial mitochondrial ATP-sensitive potassium channel (mitoKATP) function and apoptosis in ageing rats to determine the possible mechanism underlying the cardioprotective property of sevoflurane. Ageing rat hearts were isolated and attached to a Langendorff apparatus. The hearts were then exposed or not to sevoflurane postconditioning in the presence or absence of 100 µmol/L 5-hydroxydecanoate (5-HD), a selective mitoKATP inhibitor. The infarct size was measured by triphenyltetrazolium chloride (TTC) staining. Mitochondrial morphology was observed by electron microscopy and scored using FlaMeng semiquantitative analysis. In addition, the expression levels of Bax, Bcl-2, and cytochrome-C (Cyt-C) were determined by Western blot analysis at the end of reperfusion. Sevoflurane postconditioning increased coronary flow, improved functional recovery, reduced Bax/Bcl-2 and Cyt-C phosphorylation levels, and decreased mitochondrial lesion severity and the extent of apoptosis. The protective effects of sevoflurane postconditioning were prevented by the mitoKATP inhibitor 5-HD. Sevoflurane postconditioning significantly protected the function of ageing hearts that were subjected to ischaemia and reperfusion, and these protective effects were mediated by mitoKATP opening.

Effect of aquaporin-4 deficiency on intravenous anaesthetic induced hypnotic effects in mice.

The deficiency of aquaporin-4 (AQP4) has been reported to alter release of neurotransmitters in the mouse brain. However, the functional relevance of AQP4 in mediating essential components of the general anaesthetic state is unknown. The aim of the present study was to investigate the role of AQP4 in general anaesthesia in mice lacking AQP4. The hypnotic effects of propofol, ketamine, and pentobarbital in AQP4 knockout (KO) and CD1 control mice were evaluated using the behavioural endpoint of loss of righting reflex (LORR). The effects of propofol on extracellular levels of amino acids in prefrontal cortex of freely moving mice were investigated using microdialysis coupled to high performance liquid chromatography with fluorescent detection. The result showed that, after receiving ketamine or pentobarbital, LORR occurred at earlier time in KO mice than that in control animals. Intraperitoneal injection of ketamine or pentobarbital increased the duration of LORR. After the administration of propofol, the duration of LORR was significantly reduced in KO mice compared with that in controls. Propofol increased the extracellular levels of aspartate, glutamate, and GABA, but not taurine, in prefrontal cortex. There were significant differences of increase patterns of the three kinds of neurotransmitters between KO and WT mice. Notably, the duration of GABA level increase correlated with the duration of LORR in two genotypes of mice. These results provide in vivo evidence of different responses in time-dependent release of excitatory and inhibitory neurotransmitters in prefrontal cortex of the two genotypes of mice. It is suggested that changes in anaesthetic reactions in mice with AQP4 loss may be related to neurotransmitter regulation, and that normal functioning of AQP4 plays an important role in the maintenance of anaesthetic hypnosis.

Perioperative pregabalin reduced fatigue scores after thoracoscopic pneumonectomy in a RCT of NSCLC patients.

Postoperative fatigue is prevalent, but non-small cell lung cancer (NSCLC) patients receive poor treatment after video-assisted thoracoscopic surgery (VATS). The main objective of the present trial is to observe the anti-fatigue function of pregabalin in NSCLC patients after surgery. Patients requiring VATS pneumonectomy were randomized into two groups (n=33): the experimental and control groups. The results showed that the experimental group's Identity-Consequence Fatigue Scale (ICFS) scores on days 1, 3, 7, and 30 after the operation decreased more than those of the control group. On days 1, 2, and 3 following surgery, there were significant differences in the Visual Analog Scale (VAS) scores, the incidence rate of anxiety and depression, and the Athens Insomnia Scale (AIS) scores between the two groups. Furthermore, we discovered that the ICFS scores were positively related to the VAS scores, Hospital Anxiety and Depression Scale (HADS) scores, and AIS scores. Postoperative fatigue and pain, on the other hand, were more closely related. Finally, this analysis suggested that perioperative pregabalin can reduce postoperative fatigue in NSCLC patients by relieving postoperative pain, anxiety, and depression, improving postoperative sleep quality, and promoting early recovery.

Effect of continuous subanesthetic esketamine infusion on postoperative fatigue in patients undergoing laparoscopic radical resection for colorectal cancer: a randomized controlled study.

This study aimed to examine the effect of subanesthetic esketamine on postoperative fatigue in patients who underwent laparoscopic colorectal surgery. A total of 62 patients, including 32 in the esketamine group and 30 in the control group, were analysed in this study. Compared with the control group, the patients in the esketamine group had reduced Identity-Consequence Fatigue Scale (ICFS) on the 3rd and 7th days after surgery (P<0.05). There were also significant differences in the Positive and Negative Affect Schedule (PANAS) scale between the two groups. The positive affect scale was higher on postoperative day 3 (POD3), while the negative affect scale was lower on POD3 and postoperative day 7 (POD7) in the esketamine group than in the control group. However, the scores of postoperative hand grip strength, neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), Numeric Rating Scale (NRS) and Athens Insomnia Scale (AIS) were not significantly different between the two groups. Furthermore, mediation analysis showed that esketamine played an anti-fatigue role through improving emotional heath. Importantly, no adverse reactions occurred at this dosage of esketamine. Finally, our study suggested that subanesthetic esketamine improved postoperative fatigue, stabilized postoperative mood, reduced intraoperative remifentanil consumption, and promoted postoperative intestinal function recovery without increasing adverse reactions.

Expression of TRPM8 in the distal cerebrospinal fluid-contacting neurons in the brain mesencephalon of rats.

BACKGROUND: It has been shown that distal cerebrospinal fluid-contacting neurons (dCSF-CNs) exist near the ventral midline of the midbrain aqueduct and also in the grey matter of the inferior third ventricle and the fourth ventricle floor in the superior segment of the pons. The dCSF-CNs communicate between the cerebrospinal fluid (CSF) and the brain parenchyma and may participate in the transduction and regulation of pain signals. The cold sensation receptor channel, TRPM8 is involved in analgesia for neuropathic pain, but whether the TRPM8 receptor exists on dCSF-CNs remains unknown. However, there is preliminary evidence that TRPM8 is expressed in dCSF-CNs and may participate in the transmission and regulation of sensory information between brain parenchyma and cerebrospinal fluid (CSF) in rats. METHODS: Retrograde tracing of the cholera toxin subunit B labeled with horseradish peroxidase (CB-HRP) injected into the lateral ventricle was used to identify dCSF-CNs. A double-labeled immunofluorescent technique and laser scanning confocal microscopy were used to identify the expression of TRPM8 in dCSF-CNs. Software Image-Pro Plus was used to count the number of neurons in three sections where CB-HRP positive neurons were located in the mesencephalon of six rats. RESULTS: The cell bodies of CB-HRP-positive dCSF-CNs were found in the brain parenchyma near the midline of the ventral Aq, also in the grey of the 3V, and the 4V floor in the superior segment of the pons. In the mesencephalon their processes extended into the CSF. TRPM8 labeled neurons were also found in the same area as were CB-HRP/TRPM8 double-labeled neurons. CB-HRP/TRPM8 double-labeled neurons were found in 42.9 +/- 2.3% of neurons labeled by TRPM8, and all CB-HRP-labeled neurons were also labeled with TPRM8. CONCLUSION: This study has demonstrated that the cold sensation receptor channel, TRPM8, is localised within the dCSF-CNs of the mesencephalon. TRPM8 acts as receptor of dCSF-CNs for sensation transmission and pain regulation.

Protective effects of a heme oxygenase-1-secreting Lactococcus lactis on mucosal injury induced by hemorrhagic shock in rats.

AIM: To investigate the protective effects of a heme oxygenase-1 (HO-1)-secreting Lactococcus lactis (LL-HO-1) on mucosal injury induced by hemorrhagic shock in rats. METHODS: The ability of recombinant LL-HO-1 to secrete biological active HO-1 in the rat intestine was determined in situ after 3 d of daily intragastric administration. The therapeutic potential of LL-HO-1 strain was then evaluated on mucosal injury induced by hemorrhagic shock in rats. After successful resuscitation, mean arterial blood pressure was recorded at 5, 10, 20, and 30 min. One hour after resuscitation, the ileum was harvested for evaluation of mucosal injury by blinded microscopic inflammatory score (Chiu's grade 0-5), myeloperoxidase activity, bacterial translocation, and by the secretion of pro- and anti-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-10, respectively). RESULTS: Intragastric administration of HO-1-secreting L. lactis strain led to bioactive delivery of HO-1 at intestinal mucosa and significantly enhanced mean arterial blood pressure and interleukin-10 levels. Moreover, intragastric administration of LL-HO-1 significantly decreased Chiu's score, myeloperoxidase activity, bacterial translocation, and tumor necrosis factor-alpha levels when compared with rats treated with the wild-type strain. The protective effect of recombinant LL-HO-1 could be abolished by co-administration of a HO-1 inhibitor, the zinc protoporphyrin-IX. CONCLUSION: These results suggest that intragastric administration with HO-1-secreting L. lactis reduces mucosal injury induced by hemorrhagic shock.

Effects of morphine-dependent and withdrawal on activation of the distal cerebrospinal fluid contacting neurons' phosphorylation CREB in rat brain.

OBJECTIVE: To investigate the changes of pCREB protein expression in the distal cerebrospinal fluid contacting neurons induced by chronic morphine dependence and withdrawal. METHODS: Twenty-four Sprague-Dawley rats of both genders were randomly divided into three groups (n=8 each): control (Group I); chronic morphine dependence (Group II); chronic morphine abstinence (Group III). Chronic morphine dependence was induced by increasing doses of morphine, starting from 5 to 260 mg/kg/day in 12 days. The animals were killed 24 hours later. We evaluated morphine dependence by measuring the behavioral expression of morphine withdrawal and pCREB double labeled neuron recordings of dorsal raphe nucleus. The CB-HRP/pCREB double labeling method was used to observe the expression of pCREB in the distal cerebrospinal fluid contacting neurons. RESULTS: The results showed the number of double labeled neuron of distal cerebrospinal fluid contacting neuron in dorsal raphe nucleus with up-regulated expression. CONCLUSION: Morphine-dependent and withdrawal can activate the distal cerebrospinal fluid contacting neurons phosphorylation CREB in rat brain. The cerebrospinal fluid contacting neuron is related to morphine withdrawal and dependence rats.

Intragastric administration with recombinant Lactococcus lactis producing heme oxygenase-1 prevents lipopolysaccharide-induced endotoxemia in rats.

Gut injury is a pivotal initiating event in the dysfunctional inflammatory response that causes postinjury multiple organ failure. Heme oxygenase-1 (HO-1) is an important enzyme that provides cellular protection against oxidative stress in different in vitro and in vivo systems. In this study, we evaluated the protective effects of intragastrically administered live Lactococcus lactis secreting bioactive HO-1 to treat intestinal mucosal injury induced by lipopolysaccharide in rats. Intragastric administration with this recombinant L. lactis strain led to active delivery of HO-1 at the mucosa and significantly decreased morbidity and mortality of lipopolysaccharide -induced endotoxemia as confirmed by blinded macroscopic and microscopic inflammatory scores (Chiu's grade), myeloperoxidase activity, mortality, and tumor necrosis factor-alpha and IL-10 cytokine stimulation. This protective effect could be abolished by an HO-1 inhibitor, the zinc protoporphyrin-IX. Our results suggest that a food-grade bacterium genetically modified to deliver bioactive HO-1 in situ exerts a protective effect against intestinal mucosal injury in rats with endotoxemia via modulation of the immune system. This novel approach may be beneficial for the maintenance of the intestinal barrier and anti-inflammatory response of the lower intestine.

The methodology for labeling the distal cerebrospinal fluid-contacting neurons in rats.

The distal cerebrospinal fluid-contacting neurons (dCSF-CNs) are one special type of neurons, whose bodies are in the parenchyma of the brain and processes extend into the ventricle, which suggested that dCSF-CNs might play the important roles in neuromodulation and neuroendocrinal regulation. Without special tracing method, the dCSF-CNs is hard to identify in parenchyma of the brain. Thus, up to present, these structure and function are seldom investigated. To explore dCSF-CNs, the cholera toxin subunit B conjugated with horseradish peroxidase (CB-HRP) as a tracer was injected into one of the rats' lateral ventricles, 48 h later following tracer injection rats were deeply anesthetized and fixed by intracardiac perfusion of 450 ml fixative at 25-30 ml/min. The brainstem were dissected out and stored in the fixative (postfix) for 4-6 h at 4 degrees C, then cryoprotected by immersion for 24-48 h in gradient sucrose (5%, 10%, 15%, 20%, and 30%) with 0.01 mol/l PBS at 4 degrees C. The brainstem segment was embedded, transverse or horizontal sections were cut with a cryostat and collected in phosphate-buffered saline (PBS). Three methodology were described to label the dCSF-CNs including tetramethylbenzidine-sodium tungstate (TMB-ST) method, CB-HRP-immunofluorescence procedures and CB-HRP-immunoelectron microscopic procedures.

Exogenous hydrogen sulfide postconditioning protects isolated rat hearts against ischemia-reperfusion injury.

Hydrogen sul fi de (H2S) is an endogenous gaseous mediator, produced by cystanthionine-gamma-lysase (CSE) in the cardiovascular system. Hydrogen sulfide given before ischemia can decrease myocardial ischemia and reperfusion injury. The present study investigated: (1) if hydrogen sulfide given at early reperfusion could decrease myocardial ischemia and reperfusion injury; (2) if the protective effects of hydrogen sulfide were related to mitochondrial ATP-sensitive K+ (KATP) channels opening. In isolated rat heart model, treatment of heart with NaHS (H2S donor) at the onset of reperfusion resulted in a concentration-dependent limitation of infarct size and creatine kinase release. The optimal NaHS concentration for cardioprotection is 1 microM. The cardioprotective effects of NaHS (1, 10 microM) were comparable to those of ischemic postconditioning. The KATP channels blocker, Glibenclamide or 5-hydroxydecanoate, reversed the cardioprotective effects of NaHS. The datum provided further evidence that exogenous H2S postconditioning protected rat heart against ischemia and reperfusion injury. Mitochondrial KATP channel opening is implicated in the postconditioning of H2S.

Pergolide protects CA1 neurons from apoptosis in a gerbil model of global cerebral ischemia.

OBJECTIVE: To investigate the effects of dopamine (DA) receptor agonists and antagonists on neuronal apoptosis in hippocampal CA1 region after forebrain ischemia/reperfusion (I/R) injury in gerbils. METHODS: Gerbil forebrain ischemia was induced by occluding bilateral carotid arteries for 5 minutes. The open field test, hematoxylin-eosin staining and in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) methods were used 1, 3 and 7 days after reperfusion. Western blot was used to examine the phosphorylation of c-Jun. RESULTS: Pergolide could significantly reduce the habituation impairments of ischemic gerbils, increase the number of normal neurons and reduce the number of apoptotic neurons in hippocampal CA1 region after reperfusion. SKF38393, SCH23390 and spiperone had no effects on these changes in this transient I/R injury model. Furthermore, pergolide can significantly reduce the phosphorylation of c-Jun induced by transient forebrain ischemia.

Cardioprotection of sevoflurane postconditioning by activating extracellular signal-regulated kinase 1/2 in isolated rat hearts.

AIM: The activation of extracellular signal-regulated kinase (ERK)1/2 protects against ischemic-reperfusion injury. Whether ERK1/2 mediates the cardioprotection of sevoflurane postconditioning is unknown. We tested whether sevoflurane postconditioning produces cardioprotection via an ERK1/2-dependent mechanism. METHODS: In protocol 1, Langendorff-perfused Sprague-Dawley rat hearts (n=84, 12 per group), with the exception of the Sham group, were subjected to 30 min ischemia followed by 90 min reperfusion and were assigned to the untreated (control) group, followed by 4 cycles of ischemic postconditioning (25 s of each), 3% (v/v) sevoflurane postconditioning (for 5 min and 10 min of washout), and the PD98059 solvent DMSO (<0.2%), ERK1/2 inhibitor PD98059 (20 micromol/L), and Sevo+PD administration. Left ventricular hemodynamics and coronary flow at 30 min of equilibrium were recorded at 30, 60, and 90 min of reperfusion, respectively. Acute infarct size was measured by triphenyltetrazolium chloride staining. The configuration of mitochondria was observed by an electron microscope. Western blot analysis was used to determine the contents of cytosolic and mitochondrial cytochrome c at the end of reperfusion. In protocol 2, after 15 min of reperfusion, the expression of total and phosphorylated forms of ERK1/2 and its downstream target p70S6K was determined by Western blotting. RESULTS: No differences in baseline hemodynamics were observed among the experimental groups (P>0.05). After reperfusion, compared with the control group, sevoflurane postconditioning and ischemic postconditioning significantly(P<0.05) improved functional recovery and largely (P<0.05) decreased myocardial infarct size (22.9%+/-4.6% and 21.2%+/-3.8%, vs 39.4%+/- 5.7%, both P<0.05). Sevoflurane-mediated protection was abolished by PD98059. CONCLUSION: Anesthetic postconditioning by sevoflurane effectively protects against reperfusion damage by activating ERK1/2 in vitro.

Sevoflurane post-conditioning protects against myocardial reperfusion injury by activation of phosphatidylinositol-3-kinase signal transduction.

The mechanisms underlying myocardial protection by sevoflurane post-conditioning are unclear. In the present study, we tested two hypotheses: (i) that sevoflurane post-conditioning produces cardioprotection via a phosphatidylinositol-3-kinase (PI3-K)-dependent pathway; and (ii) combining sevoflurane and ischaemic post-conditioning offers an additional benefit against reperfusion injury. Rat isolated perfused hearts were exposed to 25 min ischaemia followed by 90 min reperfusion. Sevoflurane post-conditioning was induced by administration of sevoflurane (3.0 vol%) for 15 min from the onset of reperfusion. In some groups, 15 micromol/L LY294002, a selective PI3-K inhibitor, was coadministrated with sevoflurane. Other groups of hearts were exposed to ischaemic post-conditioning or combined sevoflurane plus ischaemic post-conditioning in the presence and absence of LY294002. After 15 min reperfusion, phosphorylation of Akt and glycogen synthase kinase 3beta (GSK3beta) was determined by Western blot analysis. Infarct size was determined by 2,3,5-triphenyltetrazolium chloride staining and subsarcolemmal mitochondrial lesions were assessed by electron microscopy after 90 min reperfusion. Sevoflurane post-conditioning significantly decreased infarct size compared with control hearts (31 +/- 2 vs 42 +/- 3%, respectively; P < 0.05), diminished mitochondrial lesions and increased phosphorylation of Akt and GSK3beta, as did ischaemic post-conditioning. However, combined sevoflurane plus ischaemic post-conditioning did not further improve the cardioprotective effects compared with either intervention alone. Sevoflurane-mediated cardioprotection was abolished or inhibited by 15 micromol/L LY294002. In conclusion, sevoflurane acts during early reperfusion after ischaemia to salvage the myocardium by activating PI3-K. The combination of sevoflurane plus ischaemic post-conditioning does not offer any additional benefit over either intervention alone.

Protective effect of heme oxygenase-1 on lung injury induced by erythrocyte instillation in rats.

BACKGROUND: Intratracheal instillation of blood induces self-repaired acute lung injury. However, the mechanism of repair has been unclear. Heme-oxygenase (HO)-1, which catalyzes heme breakdown, acts as an inducible defense against oxidative stress and plays an important role in inflammation. The objective of this study was to test the role of HO-1 in lung injury caused by intratracheal instillation of red cells. METHODS: Forty healthy, male Sprague-Dawley rats were randomly divided into five groups: normal group, saline group, erythrocyte group, erythrocyte+zinc-protoporphyrin (ZnPP, HO-1 inhibitor) group and saline+ZnPP group. At 2 days after intratracheal instillation of red cells, lung tissues and lavage samples were isolated for biochemical determinations and histological measurements. RESULTS: Histological analysis revealed that administration of ZnPP worsened the acute lung injury induced by instilled erythrocytes. HO-1 was over-expressed in the erythrocyte group and in the erythrocyte + ZnPP group. Compared with the erythrocyte + ZnPP group, the levels of total protein, lactate dehydrogenase and tumor necrosis factor-alpha in the lavage were lower (P < 0.01), while the level of interleukin-10 was higher in the erythrocyte group (P < 0.01). CONCLUSION: HO-1 protects against erythrocyte-induced inflammatory injury in lung.

[Expression of drebrin in the distal cerebrospinal fluid contacting neurons of rats with chronic constriction injury of sciatic nerve].

To observe the expression of drebrin in the distal cerebrospinal fluid contacting neurons (dCSF-CNs) of rats with chronic constriction injury (CCI) of sciatic nerve by immunofluorescence technique, male Sprague-Dawley rats were randomly divided into three groups: control group, sham surgery group and CCI group. The behavior of rats was scored. After choleratoxin subunit B-conjugated horseradish peroxidase (CB-HRP, 3 muL) was injected into the lateral cerebroventricle to trace dCSF-CNs, the expression of drebrin was observed in the dCSF-CNs through immunofluorescence double staining and laser scanning confocal microscopy technique. The results showed that only the pain threshold of CCI group was decreased. The dCSF-CNs were clearly displayed in three groups. No drebrin expression was observed in the control and sham groups. In CCI group, drebrin was markedly expressed in intracytoplasm. It is suggested that the technique displaying dCSF-CNs with immunofluorescence is successful and the dCSF-CNs are possibly involved in the transmission of nociceptive information under the neuropathic pain state.

Aquaporin-4 knockout mice exhibit increased hypnotic susceptibility to ketamine.

PURPOSE: This study examines anesthetic/hypnotic effects of ketamine in AQP4 knockout (KO) and wild-type (WT) mice with the particular focus on neurotransmission. MATERIALS AND METHODS: Ketamine (100 mg/kg) was intraperitoneally injected in 16 WT and 16 KO mice. The hypnotic potencies were evaluated by the loss of the righting reflex (LORR). The amino acids neurotransmitter levels in prefrontal cortex were measured by microdialysis. RESULTS: This study demonstrated that AQP4 knockout significantly shortened the latency compared with WT mice (98.0 ± 4.2 vs. 138.1 ± 15.0 s, p < .05) and prolonged duration of LORR (884.7 ± 58.6 vs. 562.0 ± 51.7 s, p < .05) compared with WT mice in LORR induced by ketamine. Microdialysis showed that lack of AQP4 markedly decreased glutamate level within 20 min (p < .05) and increased γ-aminobutyric acid (GABA) level within 30-40 min (p < .05) after use of ketamine. Moreover, the levels of taurine were remarkably higher in KO mice than in WT mice, but no obvious differences in aspartate were observed between two genotypes. CONCLUSION: AQP4 deficiency led to more susceptibility of mice to ketamine, which is probably due to the modulation of specific neurotransmitters, hinting an essential maintenance of synaptic activity mediated by AQP4 in the action of ketamine.

Peripheral benzodiazepine receptor ligand, PK11195 induces mitochondria cytochrome c release and dissipation of mitochondria potential via induction of mitochondria permeability transition.

Mitochondrial permeability transition pore plays an important role in the processes of cell apoptosis and necrosis. The peripheral benzodiazepine receptor, a mitochondria outer-membrane protein, is involved in the regulation of mitochondrial permeability transition. In the present study, we test if PK11195, a peripheral benzodiazepine receptor ligand, can lead to the opening of mitochondrial permeability transition pores, and subsequently causes mitochondria cytochrome c loss and mitochondria uncoupling. In isolated cardiac mitochondria, PK11195 (50, 100, 200 microM) caused a dose-dependent mitochondrial swelling, cytochrome c loss, and the dissipation of mitochondrial potential. Cyclosporin A (0.2 microM), a specific inhibitor of mitochondrial permeability transition, completely prevented the mitochondrial swelling induced by PK11195, and maintained the cytochrome c content and membrane potential. These data suggest that peripheral benzodiazepine receptor ligand, PK11195 caused mitochondrial uncoupling and cytochrome c loss via induction of mitochondrial permeability transition.

Involvement of local orphanin FQ in the development of analgesic tolerance induced by morphine microinjections into the dorsal raphe nucleus of rats.

It is well known that dorsal raphe nucleus (DRN) is one of the key structures for the development of opioid analgesia and tolerance. An increased activity of 'antiopioids' like orphanin-FQ (OFQ) has been proposed as a possible mechanism for opioid tolerance. The present study evaluates the role of DRN-located OFQ in the opioid analgesic tolerance induced by repeated microinjections of morphine (MOR) into DRN. Male rats were implanted with chronic guide cannulae aimed at the DRN. Microinjection of MOR (0.5 microg in 0.5 microl) into DRN caused antinociception as quantified with the tail flick and the hot plate tests. When MOR microinjection was repeated twice daily, the antinociceptive effect disappeared within 2 days (tolerance). However, if each MOR microinjection was preceded (within 15 min) by a microinjection of the OFQ receptor antagonist nocistatin (NST) (1 ng in 0.5 microl) into the same DRN site, the microinjections of MOR always produced antinociception and did not induce tolerance. If NST microinjections were suspended, subsequent MOR microinjections induced tolerance. In MOR-tolerant rats, a single NST microinjection into the same DRN site was enough to restore the antinociceptive effect of MOR. On the other hand, if OFQ (1 ng in 0.5 microl) was microinjected into DRN, then MOR microinjection administered 15 min later into the same DRN site did not elicit antinociception. Finally, opioid tolerance induced by repeated systemic MOR injections (5 mg/kg, i.p.) was reversed by a single microinjection of NST into DRN. This emphasizes the central importance of DRN-located OFQ in the MOR analgesic tolerance.

Effects of intrathecal injection of prednisolone acetate on expression of NR2B subunit and nNOS in spinal cord of rats after chronic compression of dorsal root ganglia.

N-methyl-D-aspartate receptor subunit 2B (NR2B) and neuronal nitric oxide synthase (nNOS) play important roles in the mechanism of neuropathic pain. To elucidate how glucocorticoids affect this mechanism, we studied the effects of intrathecal (it) injection of prednisolone acetate (PA) on a nociceptive stimulus and the changes of nNOS and NR2B subunit expression in the spinal dorsal horn of Sprague Dawley rats following chronic compression of the dorsal root ganglia (CCD). Paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were measured for 15 days postoperatively. An it injection of PA (2.0 mg/kg) every 3 days for postoperative days 1 to 15 inhibited the thermal hyperalgesia and tactile allodynia of CCD rats. Chronic compression of the dorsal root ganglia induced time-dependent upregulation of nNOS and NR2B subunits of N-methyl-D-aspartate receptor within the spinal cord dorsal horn ipsilateral to CCD. Both upregulations were significantly diminished by it administration of PA (2.0 mg/kg), but not by lower doses of PA (0.5 or 1.0 mg/kg). The results suggest that PA upregulation of neuronal nitric oxide synthase and NR2B subunit expression in the spinal dorsal horn contributes to PA inhibition of hyperalgesia induced by chronic compression of dorsal root ganglia.