Olga Pol

Influence of various acute stressors on the activity of adult male rats in a holeboard and in the forced swim test

The effects of various acute stressors on the activity of adult male rats in a holeboard and in the forced swim test were studied. When tested immediately or 24 h after 1 h exposure to noise, restraint in tubes or tail shock, no changes in either defecation rate or activity in the holeboard were observed. In contrast, immediately after 1 h immobilization in wood-boards, a reduction of the number of areas crossed and the number of head-dips was found. The inhibitory effect of immobilization on head-dips persisted 24 h later. The behavior of the rats in the forced swim test was classified into three categories: struggling, mild swim and immobility. The changes in behavior were critically dependent on the type of stressor, and more specifically on its intensity, that was evaluated with three different physiological parameters (serum prolactin, corticosterone and glucose levels). Thus, if tested immediately after stress, noise did not alter the response of the rats, restraint in tubes and tail shock-reduced immobility, and the latter stressor increased mild swim. In the second experiment, immobilization in wood-boards reduced struggling. Twenty-four hours after stress, noise, restraint in tubes or tail shock were without effect, but immobilized rats showed increased immobility and reduced mild swim activity. The present data clearly indicate that behavior of rats in a holeboard and in a forced swim situation are not related, and that acute stress could have a differential effect on the various categories of behavior in a forced swim situation.

Expression of Opioid Receptors During Peripheral Inflammation

Opioid receptors (OR) and their mRNA are present in the central and peripheral nervous system of mammals. In this review we examine the behavioral effects of opioids and the expression of their receptors during peripheral inflammation in two experimental models: the rat paw and the mouse intestine. Inflammation increased the antinociceptive (paw) and the inhibitory effects of opioids in the gut (transit, permeability and plasma extravasation) by interaction with OR located at peripheral sites. Based on agonist efficacy, micro > delta >> kappa-OR mediate the antinociceptive and antitransit effects of opioids during inflammation. Intestinal permeability is modulated by delta = micro >> kappa-OR, while kappa > delta >> micro-OR are involved in the inhibition of plasma extravasation. Intestinal inflammation increased the transcription of micro and delta-OR (but not kappa) genes in the gut, thus explaining the enhanced antitransit and antisecretory effects of micro and delta-OR agonists; however, the increased inhibitory effects of kappa-OR agonists on plasma extravasation could result from post-transcriptional regulation of the receptor. Similarly, the increased expression of peripheral micro-OR observed in the rat paw during inflammation, occurs at post-transcriptional levels and is related to an increased axonal transport from the dorsal root ganglia to peripheral terminals. The sites and mechanisms implicated in the increased transcription of micro and delta-OR during intestinal inflammation are under investigation.

The Role of Nitric Oxide in the Local Antiallodynic and Antihyperalgesic Effects and Expression of δ-Opioid and Cannabinoid-2 Receptors during Neuropathic Pain in Mice

Both δ-opioid receptor (DOPr) and cannabinoid-2 receptor (CB2R) agonists attenuate neuropathic pain, but the precise mechanism implicated in these effects is not completely elucidated. We investigated whether nitric oxide synthesized by neuronal (NOS1) or inducible (NOS2) nitric-oxide synthases could modulate DOPr and/or CB2R antiallodynic and antihyperalgesic effects through the peripheral nitric oxide-cGMP-protein kinase G (PKG) pathway activation and affect their expression during neuropathic pain. In wild-type (WT) mice at 21 days after chronic constriction of sciatic nerve, we evaluated the effects of [d-Pen2,d-Pen5]-enkephalin (DPDPE); (2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone (JWH-015); and a NOS1 [N-[(4S)-4-amino-5-[(2-aminoethyl)amino]pentyl]-N′-nitroguanidine tris(trifluoroacetate) salt; NANT], NOS2 [l-N(6)-(1-iminoethyl)-lysine; l-NIL], l-guanylate cyclase [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; ODQ], or PKG [(Rp)-8-(para-chlorophenylthio)guanosine-3′,5′-cyclic monophosphorothioate; Rp-8-pCPT-cGMPs] inhibitor administered alone or combined. Expression of DOPr and CB2R mRNA in the spinal cord and dorsal root ganglia of naive and nerve-injured WT, NOS1-knockout (KO), and NOS2-KO mice, also was assessed. The subplantar administration of NANT, l-NIL, ODQ, or Rp-8-pCPT-cGMPs dose-dependently inhibited neuropathic pain and enhanced the local effects of DPDPE or JWH-015. Moreover, although the basal levels of DOPr and CB2R mRNA were similar between WT and NOS-KO animals, nerve injury only decreased (DOPr) or increased (CB2R) their expression in the dorsal root ganglia of WT and NOS2-KO mice, and not in NOS1-KO mice. Results suggest that inactivation of the nitric oxide-cGMP-PKG peripheral pathway triggered by NOS1 and NOS2 enhanced the peripheral actions of DOPr and CB2R agonists and that nitric oxide synthesized by NOS1 is implicated in the peripheral regulation of DOPr and CB2R gene transcription during neuropathic pain.

Carbon Monoxide Reduces Neuropathic Pain and Spinal Microglial Activation by Inhibiting Nitric Oxide Synthesis in Mice

Background Carbon monoxide (CO) synthesized by heme oxygenase 1 (HO-1) exerts antinociceptive effects during inflammation but its role during neuropathic pain remains unknown. Our objective is to investigate the exact contribution of CO derived from HO-1 in the modulation of neuropathic pain and the mechanisms implicated. Methodology/Principal Findings We evaluated the antiallodynic and antihyperalgesic effects of CO following sciatic nerve injury in wild type (WT) or inducible nitric oxide synthase knockout (NOS2-KO) mice using two carbon monoxide-releasing molecules (CORM-2 and CORM-3) and an HO-1 inducer (cobalt protoporphyrin IX, CoPP) daily administered from days 10 to 20 after injury. The effects of CORM-2 and CoPP on the expression of HO-1, heme oxygenase 2 (HO-2), neuronal nitric oxide synthase (NOS1) and NOS2 as well as a microglial marker (CD11b/c) were also assessed at day 20 after surgery in WT and NOS2-KO mice. In WT mice, the main neuropathic pain symptoms induced by nerve injury were significantly reduced in a time-dependent manner by treatment with CO-RMs or CoPP. Both CORM-2 and CoPP treatments increased HO-1 expression in WT mice, but only CoPP stimulated HO-1 in NOS2-KO animals. The increased expression of HO-2 induced by nerve injury in WT, but not in NOS2-KO mice, remains unaltered by CORM-2 or CoPP treatments. In contrast, the over-expression of CD11b/c, NOS1 and NOS2 induced by nerve injury in WT, but not in NOS2-KO mice, were significantly decreased by both CORM-2 and CoPP treatments. These data indicate that CO alleviates neuropathic pain through the reduction of spinal microglial activation and NOS1/NOS2 over-expression. Conclusions/Significance This study reports that an interaction between the CO and nitric oxide (NO) systems is taking place following sciatic nerve injury and reveals that increasing the exogenous (CO-RMs) or endogenous (CoPP) production of CO may represent a novel strategy for the treatment of neuropathic pain.

Isoflurane Requirements During Combined General/Epidural Anesthesia for Major Abdominal Surgery

We evaluated the effects of bupivacaine on the requirements for thiopental and isoflurane during combined general/epidural anesthesia. Sixty patients scheduled for colon resection were randomly distributed into six groups that received, before the induction of anesthesia, an epidural (T9-10) bolus (8 mL) followed by an infusion (8 mL/h) of saline (Groups 1 and 4), bupivacaine 0.0625% plus fentanyl 2 &mgr;g/mL (Groups 2 and 5), or bupivacaine 0.125% plus fentanyl 2 &mgr;g/mL (Groups 3 and 6). We evaluated the amount of thiopental needed to abolish the eyelid reflex and the percentage of isoflurane required to maintain the bispectral index (BIS) between 50 and 60 (Groups 1–3) or the mean arterial blood pressure (MAP) within 20% of basal values (Groups 4–6). All groups required similar doses of thiopental (5 mg/kg); the time of evaluation, but not epidural treatment, had a significant effect (P < 0.0001) on BIS and MAP. After tracheal intubation, MAP and BIS increased by 18% and 49%, respectively (P < 0.05). In the bupivacaine groups, isoflurane requirements similarly decreased by 35% (P < 0.03). For BIS and MAP, the epidural treatment (P < 0.02) and type of evaluation (P < 0.03) had a significant effect; MAP was lower (P < 0.05) with 0.125% bupivacaine. We conclude that epidural bupivacaine does not alter the thiopental dose, but it decreases isoflurane requirements by 35%. This study demonstrates that both doses of bupivacaine and fentanyl induce similar isoflurane-sparing effects. However, patients receiving 0.125% bupivacaine showed lower values of MAP when compared with controls, and thus bupivacaine 0.0625% should be favored during combined anesthesia.

Behavioral and neurochemical changes in response to acute stressors: Influence of previous chronic exposure to immobilization

The effect of daily (2 h) exposure to immobilization (IMO) for 15 days on the behavioral and neurochemical responses of adult male rats to acute stress caused by 2-h IMO or 2-h tail-shock was studied. The brain areas studied were frontal cortex, hippocampus, hypothalamus, midbrain, and pons plus medulla. Chronic exposure to IMO did not alter noradrenaline (NA), 3-methoxy,4-hydroxyphenyletileneglycol-SO4 (MHPG-SO4), serotonin, or 5-hydroxindoleacetic acid (5-HIAA) concentrations in any brain area as measured approximately 20 h after the last exposure to IMO. Exposure to behavioral tests did not modify neurochemical variables except NA levels in the hypothalamus of nonchronically stressed (control) rats. Both exposure to 2-h IMO or 2-h shock significantly decreased NA levels in hypothalamus and midbrain of nonchronically stressed rats. These decreases in response to the two acute stressors were not observed in chronically stressed rats. However, MHPG-SO4 levels increased to the same extent in control and chronically stressed rats after exposure to the acute stressors. Likewise, increased 5-HIAA concentrations observed in response to acute stressors were similar in control and chronically stressed rats. The inhibition of activity (areas crossed and rearing) in the holeboard caused by acute IMO was less marked in rats previously exposed to the same stressor than in control rats, but the response to shock was similar. In the forced swim test, acute IMO decreased struggling in control rats but tended to increase it in chronically stressed rats. The response to shock followed the same pattern as that to IMO, although it was slight.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between metamizol and tramadol in a model of acute visceral pain in rats

Tramadol (TRM) and metamizol (MTZ) are drugs with complex mechanisms of action, extensively used in combination in pain management. In the present investigation we have evaluated the interaction between MTZ:TRM in the ethacrinic acid writhing test in rats. Dose—response curves (s.c.) were obtained for each drug individually, combined in fixed potency ratios (1:0.3, 1:1, 1:3), and for MTZ in presence of a fixed‐dose of TRM (3.5 mg/kg). Interactions were analysed using isobolograms, interaction indexes (INT‐I) and ANOVA. We used naloxone (1 mg/kg s.c.) to determine the opioid‐component of the effects (ED80).

Antinociceptive/Anti-Edema Effects of Liposomal Morphine during Acute Inflammation of the Rat Paw

We evaluated the anti-edema/antinociceptive effects of subcutaneous free and liposomal morphine in rats with carrageenan-induced inflammation of the paw. We assessed antinociception by the paw pressure test and edema by plethysmography. Unilamellar liposomes (150–200 nm) with 0.3% morphine hydrochloride were used; encapsulation signifcantly reduced the rate for release of morphine in vitro. During inflammation, the antinociceptive potency of free, but not liposomal morphine increased 2.5 times; moreover, duration of the effects was prolonged by encapsulation (p < 0.001). The anti-edema effects of liposomal morphine were more pronounced (p < 0.001) and of longer duration (p < 0.05). All the effects were reversed by naloxone. The results show that morphine encapsulation enhances the anti-edema effects and prolongs antinociception.

The Spinal Cord Expression of Neuronal and Inducible Nitric Oxide Synthases and Their Contribution in the Maintenance of Neuropathic Pain in Mice

Background Nitric oxide generated by neuronal (NOS1), inducible (NOS2) or endothelial (NOS3) nitric oxide synthases contributes to pain processing, but the exact role of NOS1 and NOS2 in the maintenance of chronic peripheral neuropathic pain as well as the possible compensatory changes in their expression in the spinal cord of wild type (WT) and NOS knockout (KO) mice at 21 days after total sciatic nerve ligation remains unknown. Methodology/Principal Findings The mechanical and thermal allodynia as well as thermal hyperalgesia induced by sciatic nerve injury was evaluated in WT, NOS1-KO and NOS2-KO mice from 1 to 21 days after surgery. The mRNA and protein levels of NOS1, NOS2 and NOS3 in the spinal cord of WT and KO mice, at 21 days after surgery, were also assessed. Sciatic nerve injury led to a neuropathic syndrome in WT mice, in contrast to the abolished mechanical allodynia and thermal hyperalgesia as well as the decreased or suppressed thermal allodynia observed in NOS1-KO and NOS2-KO animals, respectively. Sciatic nerve injury also increases the spinal cord expression of NOS1 and NOS2 isoforms, but not of NOS3, in WT and NOS1-KO mice respectively. Moreover, the presence of NOS2 is required to increase the spinal cord expression of NOS1 whereas an increased NOS1 expression might avoid the up-regulation of NOS2 in the spinal cord of nerve injured WT mice. Conclusions/Significance These data suggest that the increased spinal cord expression of NOS1, regulated by NOS2, might be responsible for the maintenance of chronic peripheral neuropathic pain in mice and propose these enzymes as interesting therapeutic targets for their treatment.

Treatment with Carbon Monoxide-releasing Molecules and an Ho-1 Inducer Enhances the Effects and Expression of µ-opioid Receptors during Neuropathic Pain

Background:The administration of µ-opioid receptors (MOR) and &dgr;-opioid receptors (DOR) as well as cannabinoid-2 receptor (CB2R) agonists attenuates neuropathic pain. We investigated if treatment with two carbon monoxide-releasing molecules (CORM-2 and CORM-3) or an inducible heme oxygenase inducer (cobalt protoporphyrin IX, CoPP) could modulate the local and systemic effects and expression of MOR, DOR, and CB2R during neuropathic pain. Methods:In C57BL/6 mice, at 10 days after the chronic constriction of sciatic nerve, we evaluated the effects of the intraperitoneal administration of 10 mg/kg of CORM-2, CORM-3, or CoPP on the antiallodynic and antihyperalgesic actions of a locally or systemically administered MOR (morphine), DOR ([d-Pen(2),d-Pen(5)]-enkephalin) or CB2R ((2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone ) agonist. The effects of CORM-2 and CoPP treatments on the expression of MOR, DOR, CB2R, inducible and constitutive heme oxygenases, microglia activation marker (CD11b/c), and neuronal and inducible nitric oxide synthases were also assessed. Results:Treatments with CO-RMs and CoPP reduced the mechanical and thermal hypersensitivity induced by sciatic nerve injury, increased the local, but not systemic, antinociceptive effects of morphine, and decreased those produced by DPDPE and JWH-015. Both CORM-2 and CoPP treatments enhanced MOR and inducible heme oxygenase expression, unaltered DOR and constitutive heme oxygenase expression, and decreased the overexpression of CB2R, CD11b/c, and neuronal and inducible nitric oxide synthases induced by sciatic nerve injury. Conclusions:This study shows that CO-RMs and CoPP treatments increase the local antinociceptive effects of morphine through enhancing MOR peripheral expression and inhibiting spinal microglial activation and overexpression of neuronal/inducible nitric oxide synthases.