The general anesthetic propofol increases brain N-arachidonylethanolamine (anandamide) content and inhibits fatty acid amide hydrolase

The antinociceptive and antihyperalgesic effects of topical propofol on dorsal horn neurons in the rat

BACKGROUND

Propofol (2,6-diisopropylphenol) is an IV anesthetic used for general anesthesia. Recent evidence suggests that propofol-anesthetized patients experience less postoperative pain, and that propofol has analgesic properties when applied topically. We presently investigated the antinociceptive effects of topical propofol using behavioral and single-unit electrophysiological methods in rats.

METHODS

In behavioral experiments with rats, we assessed the effect of topical hindpaw application of propofol (1%-25%) on heat and mechanically evoked paw withdrawals. In electrophysiological experiments, we recorded from lumbar dorsal horn wide dynamic range (WDR)-type neurons in pentobarbital-anesthetized rats. We assessed the effect of topical application of propofol to the ipsilateral hindpaw on neuronal responses elicited by noxious heat, cold, and mechanical stimuli. We additionally tested whether propofol blocks heat sensitization of paw withdrawals and WDR neuronal responses induced by topical application of allyl isothiocyanate (AITC; mustard oil).

RESULTS

Topical application of propofol (1%-25%) significantly increased the mean latency of the thermally evoked hindpaw withdrawal reflex on the treated (but not opposite) side in a concentration-dependent manner, with no effect on mechanically evoked hindpaw withdrawal thresholds. Propofol also prevented shortening of paw withdrawal latency induced by AITC. In electrophysiological experiments, topical application of 10% and 25% propofol, but not 1% propofol or vehicle (10% intralipid), to the ipsilateral hindpaw significantly attenuated the magnitude of responses of WDR neurons to noxious heating of glabrous hindpaw skin with no significant change in thermal thresholds. Maximal suppression of noxious heat-evoked responses was achieved 15 minutes after application followed by recovery to the pre-propofol baseline by 30 minutes. Responses to skin cooling or graded mechanical stimuli were not significantly affected by any concentration of propofol. Topical application of AITC enhanced the noxious heat-evoked response of dorsal horn neurons. This enhancement of heat-evoked responses was attenuated when 10% propofol was applied topically after application of AITC.

CONCLUSIONS

The results indicate that topical propofol inhibits responses of WDR neurons to noxious heat consistent with analgesia, and reduced AITC sensitization of WDR neurons consistent with an antihyperalgesic effect. These results are consistent with clinical studies demonstrating reduced postoperative pain in surgical patients anesthetized with propofol. The mechanism of analgesic action of topical propofol is not clear, but may involve desensitization of TRPV1 or TRPA1 receptors expressed in peripheral nociceptive nerve endings, engagement of endocannabinoids, or activation of peripheral γ-aminobutyric acid A receptors.

Changes of blood endocannabinoids during anaesthesia: a special case for fatty acid amide hydrolase inhibition by propofol?

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Available data from animal studies suggest that the narcotic drug propofol interacts with the endocannabinoid system. Inhibition of enzymatic degradation of anandamide could explain some of the characteristics of propofol. Direct measurements have not been reported yet in humans.

WHAT THIS STUDY ADDS

• Propofol does not change the time course of anandamide plasma concentrations during anaesthesia. Furthermore, propofol does not inhibit fatty acid amide hydrolase activity ex vivo or in vitro. Thus, specific characteristics of the narcotic drug propofol cannot be explained by peripheral inhibition of anandamide degradation in humans.

AIMS

The aim of our study was to describe the time course of endocannabinoids during different anaesthesia protocols in more detail, and to challenge the hypothesis that propofol acts as a FAAH inhibitor.

METHODS

Endocannabinoids were measured during the first hour of anaesthesia in 14 women and 14 men undergoing general anaesthesia with propofol and in 14 women and 14 men receiving thiopental/sevoflurane. We also incubated whole human blood samples ex vivo with propofol and the known FAAH inhibitor oloxa and determined FAAH enzyme kinetics.

RESULTS

Plasma anandamide decreased similarly with propofol and thiopental/sevoflurane anaesthesia, and reached a nadir after 10 min. Areas under the curve for anandamide (mean and 95% CI) were 53.3 (47.4, 59.2) nmol l(-1) 60 min with propofol and 48.5 (43.1, 53.8) nmol l(-1) 60 min with thiopental/sevoflurane (P= NS). Anandamide and propofol plasma concentrations were not correlated at any time point. Ex vivo FAAH activity was not inhibited by propofol. Enzyme kinetics (mean ± SD) of recombinant human FAAH were K(m) = 16.9 ± 8.8 µmol l(-1) and V(max) = 44.6 ± 15.8 nmol mg(-1) min(-1) FAAH without, and K(m) = 16.6 ± 4.0 µmol l(-1) and V(max) = 44.0 ± 7.6 nmol mg( 1 ) min(-1) FAAH with 50 µmol l(-1) propofol (P= NS for both).

CONCLUSIONS

Our findings challenge the idea that propofol anaesthesia and also propofol addiction are directly mediated by FAAH inhibition, but we cannot exclude other indirect actions on cannabinoid receptors.

Potential impact of propofol immediately after motor vehicle accident on later symptoms of posttraumatic stress disorder at 6-month follow up: a retrospective cohort study

INTRODUCTION

Critically injured patients are at risk of developing posttraumatic stress disorder (PTSD). Propofol was recently reported to enhance fear memory consolidation retrospectively. Thus, we investigated here whether administration of propofol within 72 h of a motor vehicle accident (MVA) affects the subsequent development of PTSD symptoms.

METHODS

We examined data obtained from a prospective cohort study of MVA-related injured patients, admitted to the intensive care unit of a general hospital. We investigated the effect of propofol administration within 72 h of MVA on outcome. Primary outcome was diagnosis of full or partial PTSD as determined by the Clinician-Administered PTSD Scale (CAPS) at 6 months. Secondary outcomes were diagnosis of full or partial PTSD at 1 month and CAPS score indicating PTSD at 1 and 6 months. Multivariate analysis was conducted adjusting for being female, age, injury severity score (ISS), and administration of ketamine or midazolam within 72 h of MVA.

RESULTS

Among 300 patients recruited (mean ISS, 8.0; median Glasgow Coma Scale (GCS) score, 15.0; age, 18 to 69 years), propofol administration showed a higher risk for full or partial PTSD as determined by CAPS at 6 months (odds ratio = 6.13, 95% confidence interval (CI): 1.57 to 23.85, P = 0.009) and at 1 month (odds ratio = 1.31, 95% CI: 0.41 to 4.23, P = 0.647) in the multivariate logistic regression. Multivariate regression analysis showed a trend toward adverse effects of propofol on PTSD symptom development at 6 months after MVA (β = 4.08, 95% CI: -0.49 to 8.64, P = 0.080), but not at 1 month after MVA (β = -0.42, 95% CI: -6.34 to 5.51, P = 0.890).

CONCLUSIONS

These findings suggest that using propofol in the acute phase after MVA might be associated with the development of PTSD symptoms 6 months later. However, since the design of this study was retrospective, these findings should be interpreted cautiously and further study is warranted.

A review of the interactions between alcohol and the endocannabinoid system: implications for alcohol dependence and future directions for research

Over the past fifty years a significant body of evidence has been compiled suggesting an interaction between the endocannabinoid (EC) system and alcohol dependence. However, much of this work has been conducted only in the past two decades following the elucidation of the molecular constituents of the EC system that began with the serendipitous discovery of the cannabinoid 1 receptor (CB1). Since then, novel pharmacological and genetic tools have enabled researchers to manipulate select components of the EC system, to determine their contribution to the motivation to consume ethanol. From these preclinical studies, it is evident that CB1 contributes the motivational and reinforcing properties of ethanol, and chronic consumption of ethanol alters EC transmitter levels and CB1 expression in brain nuclei associated with addiction pathways. These results are augmented by in vitro and ex vivo studies showing that acute and chronic treatment with ethanol produces physiologically relevant alterations in the function of the EC system. This report provides a current and comprehensive review of the literature regarding the interactions between ethanol and the EC system. We begin be reviewing the studies published prior to the discovery of the EC system that compared the behavioral and physiological effects of cannabinoids with ethanol in addition to cross-tolerance between these drugs. Next, a brief overview of the molecular constituents of the EC system is provided as context for the subsequent review of more recent studies examining the interaction of ethanol with the EC system. These results are compiled into a summary providing a scheme for the known changes to the components of the EC system in different stages of alcohol dependence. Finally, future directions for research are discussed.

Exogenous and endogenous cannabinoids suppress inhibitory neurotransmission in the human neocortex

Activation of CB(1) receptors on axon terminals by exogenous cannabinoids (eg, Δ(9)-tetrahydrocannabinol) and by endogenous cannabinoids (endocannabinoids) released by postsynaptic neurons leads to presynaptic inhibition of neurotransmission. The aim of this study was to characterize the effect of cannabinoids on GABAergic synaptic transmission in the human neocortex. Brain slices were prepared from neocortical tissues surgically removed to eliminate epileptogenic foci. Spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs) were recorded in putative pyramidal neurons using patch-clamp techniques. To enhance the activity of cannabinoid-sensitive presynaptic axons, muscarinic receptors were continuously stimulated by carbachol. The synthetic cannabinoid receptor agonist WIN55212-2 decreased the cumulative amplitude of sIPSCs. The CB(1) antagonist rimonabant prevented this effect, verifying the involvement of CB(1) receptors. WIN55212-2 decreased the frequency of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin, but did not change their amplitude, indicating that the neurotransmission was inhibited presynaptically. Depolarization of postsynaptic pyramidal neurons induced a suppression of sIPSCs. As rimonabant prevented this suppression, it is very likely that it was due to endocannabinods acting on CB(1) receptors. This is the first demonstration that an exogenous cannabinoid inhibits synaptic transmission in the human neocortex and that endocannabinoids released by postsynaptic neurons suppress synaptic transmission in the human brain. Interferences of cannabinoid agonists and antagonists with synaptic transmission in the cortex may explain the cognitive and memory deficits elicited by these drugs.

Propofol protects against anandamide-induced injury in human umbilical vein endothelial cells

Endocannabinoid anandamide, arachidonylethanolamine (AEA), is considered to be a causative mediator of hemorrhagic or septic shock, inducing death of several types of cells by producing free radicals such as reactive oxygen species (ROS). Propofol contains a phenolic hydroxyl group that donates electrons to the free radicals, and thus functions as an antioxidant. The purpose of this study was to investigate the protective effect of propofol against AEA-induced cell injury. After incubation with propofol at concentrations of 10, 50 or 100 µM, human umbilical vein endothelial cells (HUVECs) were stimulated with 10 µM of AEA for 24 h. ROS production, caspase-3 activity, and cell viability were evaluated 1, 8, and 24 h after the administration of 10 µM of AEA, respectively. Propofol (50 µM) significantly attenuated cell death induced by AEA, showing a protective effect against ROS production and caspase-3 activity. These results suggest that propofol at concentrations used during clinical anesthesia protects HUVECs against AEA-induced injury, in part by suppressing apoptosis.

The abused inhalant toluene differentially modulates excitatory and inhibitory synaptic transmission in deep-layer neurons of the medial prefrontal cortex

Volatile organic solvents such as toluene are voluntarily inhaled for their intoxicating effects. Solvent use is especially prevalent among adolescents, and is associated with deficits in a wide range of cognitive tasks including attention, behavioral control, and risk assessment. Despite these findings, little is known about the effects of toluene on brain areas mediating these behaviors. In this study, whole-cell patch-clamp recordings were used to determine the effect toluene on neurons within the medial PFC, a region critically involved in cognitive function. Toluene had no effect on measures of intrinsic excitability, but enhanced stimulus-evoked γ-amino butyric acid A-mediated inhibitory postsynaptic currents (IPSCs). In the presence of tetrodotoxin (TTX) to block action potentials, toluene increased the frequency and amplitude of miniature IPSCs. In contrast, toluene induced a delayed but persistent decrease in evoked or spontaneous AMPA-mediated excitatory postsynaptic currents (EPSCs). This effect was prevented by an intracellular calcium chelator or by the ryanodine receptor and SERCA inhibitors, dantrolene or thapsigargin, respectively, suggesting that toluene may mobilize intracellular calcium pools. The toluene-induced reduction in AMPA EPSCs was also prevented by a cannabinoid receptor (CB1R) antagonist, and was occluded by the CB1 agonist WIN 55,212-2 that itself induced a profound decrease in AMPA-mediated EPSCs. Toluene had no effect on the frequency or amplitude of miniature EPSCs recorded in the presence of TTX. Finally, toluene dose-dependently inhibited N-methyl-D-aspartate (NMDA)-mediated EPSCs and the magnitude and reversibility of this effect was CB1R sensitive indicating both direct and indirect actions of toluene on NMDA-mediated responses. Together, these results suggest that the effect of toluene on cognitive behaviors may result from its action on inhibitory and excitatory synaptic transmission of PFC neurons.

Molecular approaches to improving general anesthetics

Over the last several decades, the average age of patients has steadily increased, whereas the use of general anesthesia and deep sedation has grown largely outside the operating room environment. Currently available general anesthetics and delivery models represent limitations in addressing these trends. At the same time, research has tremendously expanded the knowledge of how general anesthetics produce their beneficial effects and also revealed evidence of previously unappreciated general anesthetic toxicities. The goal of this review is to highlight these important developments and describe translational research on new general anesthetics with the potential to improve and reshape clinical care.

LC–MS/MS-ESI method for simultaneous quantitation of three endocannabinoids and its application to rat pharmacokinetic studies

An LC–MS/MS-ESI method has been validated for simultaneous estimation of the three endocannabinoids; N-arachidonoylethanolamine (AEA), N-oleoylethanolamine (OEA) and palmitoylethanolamide (PEA), in surrogate matrix using AEA-d 4 as an internal standard with highest sensitivity over the existing methods. Simple precipitation was used to extract analytes and these were subsequently analyzed on a monolithic column. Linear response function was established over the concentration range 12.3 to 1225 pg/ml for AEA (r > 0.994); 0.70 to 641 ng/ml for OEA (r > 0.999) and 0.54 to 321 ng/ml (r > 0.998) for PEA. The intra- and inter-day precision values met the acceptance to criteria as per US FDA guidelines. Analytes were found to be stable in the battery of stability studies. The method was applied to quantify endogenous levels of analytes in rat plasma.

The misuse and abuse of propofol

Media attention on the misuse of propofol increased significantly when the drug was implicated in the death of pop music superstar Michael Jackson in 2010. The misuse and abuse of propofol among healthcare providers has been reported worldwide, with some misuse resulting in death. Propofol policies guiding healthcare worker re-entry into the workplace after misusing propofol have received rare attention in the research literature. The paucity of information regarding propofol-specific re-entry policies suggests that little research has addressed this problem and the lack of research and policy guidance can contribute to unsafe re-entry and even death. This paper focuses on healthcare providers because they have an easy access to propofol and therefore are vulnerable to misusing or abusing the drug. To accomplish this, the pharmacology and misuse/abuse potential of propofol and the influence of the 12-step recovery paradigm in the re-entry literature are reviewed. In conclusion, existing research and policy are drawn upon to suggest employment re-entry guidelines for healthcare workers.

Inhibition of monoacylglycerol lipase by troglitazone, N-arachidonoyl dopamine and the irreversible inhibitor JZL184: comparison of two different assays

BACKGROUND AND PURPOSE

Drugs used clinically usually have a primary mechanism of action, but additional effects on other biological targets can contribute to their effects. A potentially useful additional target is the endocannabinoid metabolizing enzyme monoacylglycerol lipase (MGL). We have screened a range of drugs for inhibition of MGL and compared the observed potencies using different MGL enzyme assays.

EXPERIMENTAL APPROACH

MGL activity was screened using recombinant human MGL (cell lysates and purified enzyme) with 4-nitrophenyl acetate (NPA) as substrate. 2-Oleolyglycerol metabolism by rat cerebellar cytosolic MGL and by recombinant MGL was also investigated.

KEY RESULTS

Among the 96 compounds screened in the NPA assay, troglitazone, CP55,940, N-arachidonoyl dopamine and AM404 inhibited NPA hydrolysis by the lysates with IC(50) values of 1.1, 4.9, 0.78 and 3.1µM, respectively. The potency for troglitazone is in the same range as its primary pharmacological activity, activation of peroxisome proliferator-activated receptor (PPAR) γ. Among PPARγ ligands, the potency order towards human MGL was troglitazone > ciglitazone > rosiglitazone > 15-deoxy-Δ(12,14) -prostaglandin J(2) ≈ CAY 10415 > CAY 10514. In contrast to the time-dependent inhibitor JZL184, the potency of troglitazone was dependent upon the enzyme assay system used. Thus, troglitazone inhibited rat cytosolic 2-oleoylglycerol hydrolysis less potently (IC(50) 41µM) than hydrolysis of NPA by the human MGL lysates.

CONCLUSIONS AND IMPLICATIONS

'Hits' in screening programmes for MGL inhibitors should be assessed in different MGL assays. Troglitazone may be a useful lead for the design of novel, dual action MGL inhibitors/PPARγ activators.

Fast feedback inhibition of the HPA axis by glucocorticoids is mediated by endocannabinoid signaling

Glucocorticoid hormones are secreted in response to stimuli that activate the hypothalamo-pituitary-adrenocortical (HPA) axis and self-regulate through negative feedback. Negative feedback that occurs on a rapid time scale is thought to act through nongenomic mechanisms. In these studies, we investigated fast feedback inhibition of HPA axis stress responses by direct glucocorticoid action at the paraventricular nucleus of the hypothalamus (PVN). Local infusion of dexamethasone or a membrane-impermeant dexamethasone-BSA conjugate into the PVN rapidly inhibits restraint-induced ACTH and corticosterone release in a manner consistent with feedback actions at the cell membrane. The dexamethasone fast feedback response is blocked by the cannabinoid CB1 receptor antagonist AM-251, suggesting that fast feedback requires local release of endocannabinoids. Hypothalamic tissue content of the endocannabinoid 2-arachidonoyl glycerol is elevated by restraint stress, consistent with endocannabinoid action on feedback processes. These data support the hypothesis that glucocorticoid-induced fast feedback inhibition of the HPA axis is mediated by a nongenomic signaling mechanism that involves endocannabinoid signaling at the level of the PVN.

Effect of anaesthesia and cardiopulmonary bypass on blood endocannabinoid concentrations during cardiac surgery

BACKGROUND

The endocannabinoid system (ECS) is an endogenous signalling system which includes the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) and specific G-protein-coupled endocannabinoid receptors (CB1 and CB2). Recent studies have described important roles of the peripheral ECS in human atherosclerosis, cardiometabolic disorders, heart failure, and systemic inflammation. We sought to study changes in plasma endocannabinoid concentrations during cardiac surgery (CS) under general anaesthesia with isoflurane/sufentanil, and during cardiopulmonary bypass (CPB).

METHODS

We studied 30 patients undergoing CS with CPB. All patients received midazolam and sufentanil for induction and isoflurane and sufentanil for maintenance of general anaesthesia. Blood samples were drawn before and after induction of general anaesthesia, after the beginning of surgery, during and after weaning from CPB, and after admission to intensive care unit (ICU) after surgery. Endocannabinoid measurements were performed by HPLC-tandem mass spectrometry.

RESULTS

Induction of general anaesthesia led to a significant decline in plasma AEA concentrations [from mean (sd) 0.39 (0.03) to 0.27 (0.03) ng ml(-1), P<0.01]. CPB induced a pronounced increase in 2-AG concentrations [from 112.5 (163.5) to 321.0 (120.4) ng ml(-1), P<0.01], whereas AEA concentrations remained persistently low until admission to the ICU. 2-AG concentrations returned to preoperative values after surgery.

CONCLUSIONS

General anaesthesia with isoflurane significantly reduces plasma AEA concentrations. This could be a consequence of stress reduction after loss of consciousness. The significant increase in 2-AG after initiation of CPB may be part of an inflammatory response. These findings suggest that anaesthesia and surgery have differential effects on the ECS which could have substantial clinical consequences.

Microinjection of propofol into the perifornical area induces sedation with decreasing cortical acetylcholine release in rats

BACKGROUND

Among many neurotransmitter systems in the central nervous system, the cholinergic system has been shown to contribute to propofol's sedative/anesthetic effects, because it has been shown that cholinesterase inhibitor reverses the level of propofol-induced unconsciousness in humans. It has been reported that intraperitoneal injection of propofol induced sedative/anesthetic actions and decreased the release of acetylcholine (Ach) from the rat cortex. However, the sites of action of propofol in the cholinergic pathway and its related pathways remain unresolved. We studied whether microinjection of propofol into the nuclei in the cholinergic pathway and its related pathways may induce sedation and decrease Ach from the cortex.

METHODS

Thirty-seven male Wistar rats weighing 270 to 320 g were used. Almost 5 days before the experiments, 23 rats anesthetized with pentobarbital (50 mg/kg) were outfitted with an electroencephalogram (EEG) socket, a microdialysis cannula in the cortex, and an intraperitoneal tube or a microinjection tube into the basal forebrain (BF), the perifornical area (Pef), or the striatum. The Ach effluxes in the somatosensory cortex were detected using in vivo intracerebral microdialysis in freely moving rats. Once basal levels of Ach were stabilized, samples were collected every 20 minutes and measured by high-performance liquid chromatography. In the intraperitoneal group, propofol was cumulatively administered (10, 30, and 100 mg/kg) into the peritoneal cavity. In the microinjection groups, propofol (40 ng in 0.2 microL) was administered into the BF, the Pef, or the striatum (control), and the cortical changes in Ach efflux and EEG were observed for 2 hours. In another 14 rats, the sedative/anesthetic score was obtained after intraperitoneal, Pef, or striatal injection of propofol. The placement of the tip of the microdialysis probe and the microinjection tube was confirmed by histological examination.

RESULTS

Intraperitoneal injection of propofol dose-dependently decreased the Ach efflux and induced light sedative to moderate anesthetic states. Loss of righting reflex was observed with significant increases in the relative alpha-power band at 100 mg/kg propofol. Microinjection of propofol into the BF significantly decreased the cortical Ach efflux to -40.2% + or - 19.9% at 40 to 60 minutes. However, there was no difference in the total Ach efflux for 2 hours between BF and control groups. In contrast, microinjection of propofol into the Pef immediately decreased the Ach efflux at 0 to 20 min and maximally to -59.3 + or - 20.4 at 100 to 120 minutes. The total Ach efflux in the Pef microinjection group was significantly less than that in the control group. The same dose of propofol injected into the Pef induced light to deep sedation. There was no significant change in the relative EEG power band between BF or Pef and control groups.

CONCLUSION

The nuclei in the Pef are, at least in part, responsible for the sedative action of propofol in rats.

Propofol: neuroprotection in an in vitro model of traumatic brain injury

Introduction

The anaesthetic agent propofol (2,6-diisopropylphenol) has been shown to be an effective neuroprotective agent in different in vitro models of brain injury induced by oxygen and glucose deprivation. We examined its neuroprotective properties in an in vitro model of traumatic brain injury.

Methods

In this controlled laboratory study organotypic hippocampal brain-slice cultures were gained from six- to eight-day-old mice pups. After 14 days in culture, hippocampal brain slices were subjected to a focal mechanical trauma and subsequently treated with different molar concentrations of propofol under both normo- and hypothermic conditions. After 72 hours of incubation, tissue injury assessment was performed using propidium iodide (PI), a staining agent that becomes fluorescent only when it enters damaged cells via perforated cell membranes. Inside the cell, PI forms a fluorescent complex with nuclear DNA.

Results

A dose-dependent reduction of both total and secondary tissue injury could be observed in the presence of propofol under both normo- and hypothermic conditions. This effect was further amplified when the slices were incubated at 32°C after trauma.

Conclusions

When used in combination, the dose-dependent neuroprotective effect of propofol is additive to the neuroprotective effect of hypothermia in an in vitro model of traumatic brain injury.

Simultaneous Quantification of Anandamide and Other Endocannabinoids in Dorsal Vagal Complex of Rat Brainstem by LC-MS

A quantitative method has been developed and validated for the simultaneous determination of anandamide (AEA), docosatetraenylethanolamide (DEA) and N-arachidonyldopamine (NADA) in dorsal vagal complex (DVC) of rat brainstem by liquid chromatographic-electrospray ionization mass spectrometry. The analytes were extracted from the tissue samples of rat brainstem by a single step liquid extraction technique using acetonitrile. The chromatographic separation was conducted on a C18 column using a gradient mobile phase consisting of methanol and water at a flow rate of 0.3 mL min(-1). The analytes were quantified by positive electrospray ionization mass spectrometry with selected ion monitoring (SIM) mode. The limits of detection (LOD) for AEA, DEA and NADA were 0.5, 1 and 0.5 ng mL(-1), respectively. This method required only simple processing of the samples and could be applied to monitor the change in the level of these compounds in DVC of the rat brain tissue. Time dependent (10-70 min) accumulation of the endocannabinoids (AEA, DEA, and NADA) in brain tissue was also studied, which included a novel examination of the accumulation of DEA as a function of time in rat brain tissue after decapitation.

Anandamide and neutrophil function in patients with fibromyalgia

Fibromyalgia (FM) is a common stress-related painful disorder. There is considerable evidence of neuroimmunologic alterations in FM which may be the consequence of chronic stress and pain or causally involved in the development of this disorder. The endocannabinoid system has been shown to play a pivotal role in mammalian nociception, is activated under stressful conditions and can be an important signaling pathway for immune modulation. The endocannabinoid system could therefore be involved in the complex pathophysiology of FM. We tested this hypothesis by evaluating the effects of stress hormones and the endocannabinoid anandamide on neutrophil function in patients with FM. We determined plasma levels of catecholamines, cortisol and anandamide in 22 patients with primary FM and 22 age- and sex-matched healthy controls. Neutrophil function was characterized by measuring the hydrogen peroxide (H2O2) release (oxidative stress) and the ingestion capabilities of neutrophils (microbicidal function). FM patients had significantly higher norepinephrine and anandamide plasma levels. Neutrophils of FM patients showed an elevated spontaneous H2O2 production. The ability of neutrophils to adhere was negatively correlated with serum cortisol levels. Adhesion and phagocytosis capabilities of neutrophils correlated positively with anandamide plasma levels. In conclusion, patients with FM might benefit from pharmacologic manipulation of endocannabinoid signaling which should be tested in controlled studies.

Volatile anesthetics and endogenous cannabinoid anandamide have additive and independent inhibitory effects on alpha(7)-nicotinic acetylcholine receptor-mediated responses in Xenopus oocytes

In earlier studies, the volatile anesthetics and the endogenous cannabinoid anandamide have been shown to inhibit the function of alpha(7)-nicotinic acetylcholine receptors. In the present study, interactions between the effects of volatile anesthetics and anandamide on the function of alpha(7)-nicotinic acetylcholine receptors expressed in Xenopus oocytes were investigated using the two-electrode voltage-clamp technique. Anandamide and volatile anesthetics isoflurane and halothane inhibited currents evoked with acetylcholine (100 microM) in a reversible and concentration-dependent manner. Coapplication of anandamide and volatile anesthetics caused a significantly greater inhibition of alpha(7)-nicotinic acetylcholine receptor function than anandamide or volatile anesthetics alone. Analyses of oocytes by matrix-assisted laser desorption/ionization mass spectroscopy indicated that volatile anesthetics did not alter the lipid profile of oocytes. Results of studies with chimeric alpha(7)-nicotinic acetylcholine-5-HT(3) receptors comprised of the N-terminal domain of the alpha(7)-nicotinic acetylcholine receptor and the transmembrane and carboxyl-terminal domains of 5-HT(3) receptors suggest that while isoflurane inhibition of the alpha(7)-nicotinic acetylcholine receptor is likely to involve the N-terminal region of the receptor, the site of action for anandamide involves transmembrane and carboxyl-terminal domains of the receptors. These data indicate that endocannabinoids and isoflurane have additive inhibitory effects on alpha(7)-nicotinic acetylcholine receptor function through allosteric binding sites located on the distinct regions of the receptor.

Neuroprotective effects of propofol in acute cerebral injury

Propofol (2,6-diisopropylphenol) is one of the most popular agents used for induction of anesthesia and long-term sedation, owing to its favorable pharmacokinetic profile, which ensures a rapid recovery even after prolonged administration. A neuroprotective effect, beyond that related to the decrease in cerebral metabolic rate for oxygen, has been shown to be present in many in vitro and in vivo established experimental models of mild/moderate acute cerebral ischemia. Experimental studies on traumatic brain injury are limited and less encouraging. Despite the experimental results and the positive effects on cerebral physiology (propofol reduces cerebral blood flow but maintains coupling with cerebral metabolic rate for oxygen and decreases intracranial pressure, allowing optimal intraoperative conditions during neurosurgical operations), no clinical study has yet indicated that propofol may be superior to other anesthetics in improving the neurological outcome following acute cerebral injury. Therefore, propofol cannot be indicated as an established clinical neuroprotectant per se, but it might play an important role in the so-called multimodal neuroprotection, a global strategy for the treatment of acute injury of the brain that includes preservation of cerebral perfusion, temperature control, prevention of infections, and tight glycemic control.

Endocannabinoids and related compounds: walking back and forth between plant natural products and animal physiology

Cannabis sativa has been known, used, and misused by mankind for centuries, and yet only over the last two decades has research stemming from the chemical constituents specific to this plant, the cannabinoids, started to provide fundamental insights into animal physiology and pathology, resulting in the development of new therapeutics. The discovery of the endocannabinoid system, and its targeting with two new pharmaceutical preparations now on the market in several countries, represent the most recent example of how studies on medicinal plants and on the mechanism of their biological effects can reveal, through a chain of breakthroughs, new systems of endogenous signals and physiological phenomena that can become the source of novel strategies for unmet therapeutic challenges.

Tonic endovanilloid facilitation of glutamate release in brainstem descending antinociceptive pathways

Activation of transient receptor potential vanilloid-1 (TRPV1) channels in the periaqueductal gray (PAG) activates OFF antinociceptive neurons of the rostral ventromedial medulla (RVM). We examined in rats the effect of intra-ventrolateral (VL)-PAG injections of TRPV1 agonists and antagonists on the nocifensive response to heat in the plantar test, neurotransmitter (glutamate and GABA) release in the RVM, and spontaneous and tail flick-related activities of RVM neurons. The localization of TRPV1 in VL-PAG and RVM neurons was examined using various markers of glutamatergic and GABAergic neurons. Intra-VL-PAG injection of capsaicin increased the threshold of thermal pain sensitivity, whereas the selective TRPV1 antagonist 5'-iodo-resiniferatoxin (I-RTX) facilitated nociceptive responses, and blocked capsaicin analgesic effect at a dose inactive per se. Intra-VL PAG capsaicin evoked a robust release of glutamate in RVM microdialysates. I-RTX, at a dose inactive per se, blocked the effect of capsaicin, and inhibited glutamate release at a higher dose. Antinociception and hyperalgesia induced by capsaicin and I-RTX, respectively, correlated with enhanced or reduced activity of RVM OFF cells. Immunohistochemical analyses suggested that several TRPV1-immunoreactive (ir) neurons in both the VL-PAG and RVM are glutamatergic and surrounded by glutamatergic and GABAergic terminals. Our data suggest that VL-PAG neurons respond to TRPV1 stimulation by releasing glutamate into the RVM, thereby activating OFF cells and producing analgesia. The results obtained with the TRPV1 antagonist alone suggest that this pathway is tonically activated by endovanilloids.

Pharmacological and clinical evidences on the potential for abuse and dependence of propofol: a review of the literature

Propofol (2,6-diisopropylphenol) is an intravenous short-acting anaesthetic widely used for inducing and maintaining anaesthesia. Propofol is also being increasingly used for sedation. Beside medical use, propofol is abused for recreational purpose, mostly in medical professionals who are not informed of the risk of dependence to this compound. The aim of this review was to provide an overview of molecular, animal and clinical pharmacological data of the literature evidencing the potential for abuse and dependence of propofol.

Fatty acid amide hydrolase: from characterization to therapeutics

Fatty acid amide hydrolase (FAAH) is an integral membrane enzyme within the amidase-signature family that terminates the action of several endogenous lipid messengers, including oleamide and the endocannabinoid anandamide. The hydrolysis of such messengers leads to molecules devoid of biological activity, and, therefore, modulates a number of neurobehavioral processes in mammals, including pain, sleep, feeding, and locomotor activity. Investigations into the structure and function of FAAH, its biological and therapeutic implications, as well as a description of different families of FAAH inhibitors are the topic of this review.

Correlating the clinical actions and molecular mechanisms of general anesthetics

PURPOSE OF REVIEW

To summarize recent in-vitro and in-vivo research on molecular mechanisms of general anesthetics' actions.

RECENT FINDINGS

Classes of general anesthetics with distinct clinical profiles appear to induce amnesia, hypnosis, and immobility via different molecular targets. Propofol, etomidate, and barbiturates produce profound amnesia and hypnosis, but weak immobility, by enhancing the activity of specific gamma-aminobutyric acid typeA receptors. In contrast, nitrous oxide, xenon, and ketamine produce analgesia, but weak hypnosis and amnesia, by inhibiting glutamate and nicotinic receptors and activating potassium 'leak' channels such as TREK-1. Volatile halogenated anesthetics show little selectivity for molecular targets. They act on all the channels mentioned above, and other targets such as glycine receptors and mediators of neurotransmitter release.

SUMMARY

Several clinically distinct 'anesthetic states' are induced by different classes of drugs acting on neuronal circuits via different molecular targets. Understanding the mechanisms underlying the therapeutic and toxic actions of general anesthetics helps us reframe the 'art' of anesthesia into more of a 'science'. These studies also enhance efforts to develop new drugs with improved clinical utility.

The Antinociceptive Effects of Local Injections of Propofol in Rats Are Mediated in Part by Cannabinoid CB1 and CB2 Receptors

BACKGROUND

Propofol can inhibit fatty acid amidohydrolase, the enzyme responsible for the metabolism of anandamide (an endocannabinoid). To study the potential antinociceptive effect of propofol, we administered different doses (0.005, 0.05, 0.5, 5, and 500 microg) of the anesthetic in the hind paw of animals to determine an ED50. To further investigate the mechanisms by which propofol produced its antinociceptive effect, we used specific antagonists for the cannabinoid CB1 (AM251) and CB2 (AM630) receptors and measured fatty-acid amide/endocannabinoid (anandamide, 2-arachidonylglycerol, and palmitoylethanolamide) concentrations in skin paw tissues.

METHODS

Formalin tests were performed on 65 Wistar rats allocated to six different groups: 1) control (Intralipidtrade mark 10%); 2) propofol (ED50 dose); 3) AM251; 4) AM251 + propofol; 5) AM630; 6) AM630 + propofol. Drugs were injected subcutaneously in the dorsal surface of the hind paw (50 microL) 15 min before 2.5% formalin injection into the same paw. Fatty-acid amide/endocannabinoid levels were measured by high performance liquid chromatography/mass spectrometry analysis.

RESULTS

Propofol produced a dose-dependent antinociceptive effect for the early and late phases of the formalin test with an ED50 of 0.08 +/- 0.061 microg for the latter phase. This effect was antagonized by AM251 and AM630. It was locally mediated, since a higher dose of propofol given in the contralateral paw was not antinociceptive. Finally, only paw concentrations of palmitoylethanolamide were significantly increased.

CONCLUSION

In a test of inflammatory pain, locally injected propofol decreased pain behavior in a dose-dependent manner. This antinociceptive effect was mediated, in part, by CB1 and CB2 receptors.

The 'specific' tyrosine kinase inhibitor genistein inhibits the enzymic hydrolysis of anandamide: implications for anandamide uptake

BACKGROUND AND PURPOSE

The cellular uptake of anandamide is reduced by inhibitors of fatty acid amide hydrolase (FAAH) and by agents disrupting endocytotic mechanisms. However, it is not clear if these events occur over the same time frame and if they occur to the same extent in different cells. We have therefore investigated the effects of such compounds in three cell lines of different origins using different assay incubation times and temperatures.

EXPERIMENTAL APPROACH

FAAH activity and cellular uptake of anandamide was measured using anandamide, radio-labelled either in the ethanolamine or arachidonoyl part of the molecule.

KEY RESULTS

The FAAH inhibitor URB597 inhibited the uptake of anandamide into C6 glioma, RBL2H3 basophilic leukaemia cells and P19 embryonic carcinoma cells at incubation time 4 min. However, a time-dependent and temperature-sensitive residual uptake remained after URB597 treatment. The combination of progesterone and nystatin reduced the uptake, but also decreased the amount of anandamide retained by the wells. Genistein inhibited anandamide uptake in a manner that was not additive to that of URB597. However, genistein was a potent competitive inhibitor of FAAH (K(i) value 8 microM).

CONCLUSIONS AND IMPLICATIONS

The reduction of anandamide uptake by genistein can be explained by its ability to inhibit FAAH with a potency which overlaps that for inhibition of tyrosine kinase. The FAAH- resistant but time-dependent uptake of anandamide is seen in all three cell lines studied and is thus presumably a generally occurring process.

Fatty acids and sleep in depressed inpatients

Sleep disturbances belong to the most frequent symptoms of depression. Low concentrations of n-3-fatty acids might represent one determinant within that process. Therefore, the aim of the study was to examine the relationships between serum fatty acid concentrations and severity of sleep disturbances in depressives. Serum fatty acids were measured gaschromatographically in 118 depressive inpatients (51 males; 67 females; age 45.4+/-12.0 years), divided into subgroups according to three degrees of sleep disturbances (BDI-item). At admission and discharge, we found significant negative correlations between the degree of sleep disturbances and fatty acid concentrations (myristic, palmitic, palmitoleic, oleic, linoleic, eicosadienoic and docosahexaenoic acid). At both assessments palmitoleic and eicosadienoic acids had the strongest connections with sleep performance. Palmitoleic and oleic acid seem to be especially important for sleep disorders, may be due to their function as precursors of the sleep inducing oleamide. Linoleic and eicosadienoic acid could be helpful for maintaining sleep because they are precursors of the sleep mediator PGD2. In contrast to our hypothesis, there is not only a significant lack of n-3 fatty acids but also of special monoenoic and n-6 fatty acids in sleep-disturbed depressives.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

Upregulation of cerebrospinal fluid and peripheral prostaglandin E2 in a rat postoperative pain model

Analgesic management of postoperative pain associated with thoracic surgery remains a difficult clinical challenge. In the present study we used a thoracic muscle incision model to characterize pain-related behavior and changes in prostaglandin E2 (PGE2) in both thoracic cerebrospinal fluid (CSF) and incision site tissues. A deep muscle incision was made in the left thoracic region of rats anesthetized with isoflurane, propofol, or spinal bupivacaine. Thoracic CSF and incision site tissue concentrations of PGE2 were monitored for 6 h using microdialysis loop catheters. Postoperative pain-related behavior was assessed by recording exploratory locomotive activity. Thoracic muscle surgery decreased rearing and ambulation. Oral ketorolac or rofecoxib 3 mg/kg restored normal rearing and ambulation. Postoperative CSF PGE2 concentration increased most (threefold) with spinal anesthesia, and not at all with propofol. With surgery under isoflurane or spinal bupivacaine, presurgical oral administration of ketorolac or rofecoxib 3 mg/kg reduced postsurgical CSF PGE2 levels and tissue PGE2 levels. Intrathecal ketorolac (4 microg) reduced CSF PGE2 after surgery without affecting tissue PGE2 levels, whereas intrathecal L-745,337 (80 microg) did not reduce CSF PGE2. Thoracic surgical wounds increase pain-related behavior and CSF and tissue PGE2 levels, all of which can be attenuated by oral cyclooxygenase inhibitors.

Determination of the endocannabinoid anandamide in human plasma by high-performance liquid chromatography

Anandamide (N-arachidonylethanolamine) is an endogenous cannabinoid receptor ligand that has been implicated in various physiological and pathophysiological functions. In the present study, a liquid-liquid extraction-based reversed-phase HPLC method with fluorometric detection was validated and applied for the analysis of anandamide in human plasma. Following derivatization with the fluorogenic reagent 4-(N,N-dimethylaminosulfonyl)-7-(N-chloroformylmethyl-N-methyl-amino)-2,1,3-benzoxadiazole (DBD-COCl), the analyte was separated using an acetonitrile-water gradient at a flow rate of 0.8 mL/min, and spectrophotometric detection at 560 nm with an excitation wavelength of 450 nm. The retention times for anandamide and R+-methanandamide (internal standard) were 27.1 and 30.7 min, respectively. The validated quantification range was 1-15 ng/mL. The developed procedure was applied to determine anandamide levels in human plasma following a 24 h incubation of human whole blood at 37 degrees C in the presence or absence of phenylmethylsulfonyl fluoride, an inhibitor of the anandamide-degrading enzyme fatty acid amide hydrolase. Anandamide levels determined under both conditions were within the validated concentration range with anandamide levels being 2.3-fold higher in plasma from PMSF-treated blood.

Interactions of anesthetics with their targets: non-specific, specific or both?

What makes a general anesthetic a general anesthetic? We shall review first what general anesthesia is all about and which drugs are being used as anesthetics. There is neither a unique definition of general anesthesia nor any consensus on how to measure it. Diverse drugs and combinations of drugs generate general anesthetic states of sometimes very different clinical quality. Yet the principal drugs are still considered to belong to the same class of 'general anesthetics'. Effective concentrations of inhalation anesthetics are in the high micromolar range and above, and even for intravenous anesthetics they do not go below the micromolar range. At these concentrations, many molecular and higher level targets are affected by inhalation anesthetics, fewer probably by intravenous anesthetics. The only physicochemical characteristic shared by anesthetics is the correlation of their anesthetic potencies with hydrophobicity. These correlations depend on the group of general anesthetics considered. In this review, anesthetic potencies for many different targets are plotted against octanol/water partition coefficients as measure of hydrophobicity. Qualitatively, similar correlations result, suggesting several but weak interactions with proteins as being characteristic of anesthetic actions. The polar interactions involved are weak, being roughly equal in magnitude to hydrophobic interactions. Generally, intravenous anesthetics are noticeably more potent than inhalation anesthetics. They differ considerably more between each other in their interactions with various targets than inhalation anesthetics do, making it difficult to come to a decision which of these should be used in future studies as representative 'prototypical general anesthetics'.

Modulators of endocannabinoid enzymic hydrolysis and membrane transport

Tissue concentrations of the endocannabinoids N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) are regulated by both synthesis and inactivation. The purpose of this review is to compile available data regarding three inactivation processes: fatty acid amide hydrolase, monoacylglycerol lipase, and cellular membrane transport. In particular, we have focused on mechanisms by which these processes are modulated. We describe the in vitro and in vivo effects of inhibitors of these processes as well as available evidence regarding their modulation by other factors.

Cannabinoids in anaesthesia and pain therapy

PURPOSE OF REVIEW

Cannabinoids have been known for their analgesic, anxiolytic, antiemetic and antispastic properties for many centuries. Since an endogenous cannabinoid system has been identified in the past two decades, cannabinoids have also become the focus of interest in western medicine. This review summarizes preclinical and clinical studies on the role of the endocannabinoid system and exogenous cannabinoids in anaesthesia and pain management.

RECENT FINDINGS

It has recently been shown that the endocannabinoid system is involved in the effects of the widely used anaesthetic drug propofol. In terms of nociception, preclinical data suggest that the endocannabinoid system plays an important role in the control of synaptic transmission and synaptic plasticity in pain pathways. In patients, the treatment of acute pain often requires relatively high doses of cannabinoids, which are associated with considerable side-effects such as dizziness and sedation. In contrast, preclinical and clinical data suggest that lower doses of cannabinoids may be effective for the treatment of allodynia and hyperalgesia in neuropathic pain. In multiple sclerosis, cannabinoids have been shown to have beneficial effects on spasticity, pain, tremor and bladder dysfunction.

SUMMARY

In general, the results of the very few well-conducted clinical trials often diverge from the highly interesting and promising findings of preclinical studies. Taken together, the most recent preclinical and clinical data suggest that cannabinoids should be applied as low-dose co-analgesics to inhibit neuroplasticity and central sensitization rather than as analgesics in acute pain.

Inhibition of restraint stress-induced neural and behavioural activation by endogenous cannabinoid signalling

The role of endocannabinoid (eCB) signalling in restraint stress-induced neuronal activation was studied. Male mice exposed to 30 min of restraint exhibit increased Fos protein within prefrontal cortex (PFC), lateral septum (LS), nucleus accumbens (Acb) and medial amygdala. SR141716 (2 mg/kg) itself had no effect on Fos but pretreatment with SR141716 significantly potentiated restraint-induced Fos expression in cingulate, LS and Acb. SR141716 also significantly increased the time spent in active escape behaviours during the restraint. In restraint-habituated mice (mice exposed to four previous restraint episodes), the fifth restraint exposure resulted in decreased expression of active escape behaviours compared to the first exposure and only induced Fos protein in the central and medial amygdala. Administration of SR141716 prior to the fifth restraint episode resulted in greater potentiation of restraint-induced Fos induction than the first; significant increases occurred within all regions of PFC examined, LS and Acb. Brain regional eCB content was measured immediately after restraint. N-arachidonylethanolamine content within the amygdala was significantly decreased after both restraint episodes. 2-Arachidonylglycerol content was significantly increased in both the limbic forebrain and amygdala after the fifth restraint but not the first. Restraint had no effect on cerebellar eCB content. These data suggest that eCB activation of CB(1) receptors opposes the behavioural and neuronal responses to aversive stimuli. Because repeated homotypic stress increased both limbic 2-AG and resulted in a greater effect of SR141716 on limbic Fos expression, we hypothesize that increased CB(1) receptor activity contributes to the expression of habituation to homotypic stress.

Cyclooxygenation of the arachidonoyl side chain of 1-arachidonoylglycerol and related compounds block their ability to prevent anandamide and 2-oleoylglycerol metabolism by rat brain in vitro

In the present study, the abilities of cyclooxygenated derivatives of 1-arachidonoylglycerol and related compounds to prevent the metabolism of [3H]2-oleoylglycerol and [3H]anandamide by cytosolic and membrane fractions, respectively, have been investigated. For each compound, nine concentrations (range 0.2-100 microM) were tested. 1-Arachidonoylglycerol inhibited the hydrolysis of [3H]2-oleoylglycerol with a pI50 value of 5.17+/-0.04 (maximum attainable inhibition 88%). In contrast, the 1-glyceryl esters of prostaglandin D2, E2 and F2alpha were very weak inhibitors of this hydrolysis. Similarly, prostaglandin D2, prostaglandin D2 ethanolamide and prostaglandin D2 serinol amide produced <20% inhibition of [3H]2-oleoylglycerol metabolism at any concentration tested, in contrast to previous data with arachidonic acid, anandamide and arachidonoyl serinol which are all able to inhibit metabolism of this substrate under the assay conditions used here. A similar pattern was seen for all the compounds with respect to the inhibition of [3H]anandamide hydrolysis by the membrane fractions. Thus, cyclooxygenation of the arachidonoyl side chain greatly reduces the ability of 1-arachidonoylglycerol and related compounds to inhibit the hydrolysis of [3H]2-oleoylglycerol and [3H]anandamide.

Intrathecal propofol has analgesic effects on inflammation-induced pain in rats

PURPOSE

Propofol is thought to act on gamma-aminobutyric acid receptors, which have some role in pain transmission in the spinal cord. In this study, we examined the effects of intrathecal propofol on acute thermally- or inflammation-induced pain in rats.

METHODS

Lumbar intrathecal catheters were implanted in Male Sprague-Dawley rats. The tail withdrawal response to thermal stimulation (tail flick test) or paw flinching and shaking response by sc formalin injection into the hind paw (formalin test) were tested. Propofol 1000, 300 or 100 microg or saline (control) was administered as 10 microL intrathecally. Motor disturbance and behavioural side effects were also monitored in the rats during the tail flick test. Eight rats were used for each dose in each test.

RESULTS

No analgesic effects were observed in the tail flick test. In the formalin test, 50% of effective doses were 449 mug (95% confidence interval, 80-3180 microg) in phase 1 and 275 microg (146-519 microg) in phase 2. Motor disturbance was observed in one rat with 100 microg and agitation and allodynia were seen in one rat with 300 microg. However, both were reversible in 120 min.

CONCLUSIONS

Intrathecal administration of propofol had analgesic effects on inflammation-induced acute and facilitated pain but not on thermally-induced acute pain. Transient motor and sensory disturbance could not rule out the possibility of neurotoxicity.