Cocaine and lidocaine have additive inhibitory effects on the GABAA current of acutely dissociated hippocampal pyramidal neurons

A Hematoma Block in the Wrist for a Displaced Distal Radius Fracture Induces Systemic Neurological Symptoms: A Case Report

Hematoma blocks are considered a relatively simple, safe, and effective technique in the acute setting to provide sufficient anesthesia and allow for closed reduction of displaced distal radius fractures. Complications associated with the utilization of local anesthetics in this setting are rare. We present the case of a patient who had a hematoma block in the wrist and developed short-term systemic neurologic complications likely secondary to systemic absorption of 20 mL of 1% lidocaine without epinephrine via the cancellous bone channels.

Study on influence of external factors on the electrical excitability of PC12 quasi-neuronal networks through Voltage Threshold Measurement Method

The aim of this paper was to investigate the influence of four different external factors (acetylcholine, ethanol, temperature and lidocaine hydrochloride) on PC12 quasi-neuronal networks by multielectrode-array-based Voltage Threshold Measurement Method (VTMM). At first, VTMM was employed to measure the lowest amplitude of the voltage stimulating pulses that could just trigger the action potential from PC12 quasi-neuronal networks under normal conditions, and the amplitude was defined as the normal voltage threshold (VTh). Then the changes of the VTh of PC12 quasi-neuronal networks treated by the four external factors were tested respectively. The results showed the normal VTh of PC12 quasi-neuronal networks was 36 mV. The VTh has negative correlation with the concentration of acetylcholine and has positive correlation with the concentration of ethanol. The curves of the correlation of the VTh with temperature and the concentration of lidocaine hydrochloride were U-shaped and Λ-shaped respectively. Comparing with our earlier studies on hippocampal neuronal networks and hippocampal slices, PC12 quasi-neuronal networks not only had the same typical voltage threshold characteristic, but also had similar changes on electrical excitability when treated by the four external factors mentioned above. Therefore, the rapid-formed PC12 quasi-neuronal networks could replace neuronal networks in proper conditions, and VTMM could be used to analyze the influence of external factors on the electrical excitability of PC12 quasi-neuronal networks.

The interactions of alcohol and cocaine regulate the expression of genes involved in the GABAergic, glutamatergic and endocannabinoid systems of male and female rats

Although the pharmacological and behavioural interactions between cocaine and alcohol are well established, less is known about how polyconsumption of these drugs affects the neurotransmitter systems involved in their psychoactive effects and in particular, in the process of addiction. Here, rats of both sexes at two stages of development were studied under a chronic regime of intravenous cocaine and/or alcohol administration. Brain samples from the medial prefrontal cortex, nucleus accumbens, hippocampus and amygdala were extracted to analyse the mRNA expression of genes encoding subunits of the GABA, NMDA and AMPA receptors, as well as the expression of the CB1 receptor, and that of enzymes related to the biosynthesis and degradation of endocannabinoids. Moreover, two synaptic scaffold proteins related to GABA and NMDA receptors, gephyrin and PSD-95, were quantified in Western blots. Significant interactions between cocaine and alcohol were common, affecting the GABAergic and endocannabinoid systems in the medial prefrontal cortex and amygdala of young adults, whereas such interactions were evident in the glutamatergic and endocannabinoid systems in adults, as well as a more pronounced sex effect. Significant interactions between these drugs affecting the scaffold proteins were evident in the medial prefrontal cortex and nucleus accumbens of young adults, and in the nucleus accumbens and amygdala of adults, but not in the hippocampus. These results highlight the importance of considering the interactions between cocaine and alcohol on neurotransmitter systems in the context of polyconsumption, specifically when treating problems of abuse of these two substances.

Pharmacology of the Equine Foot: Medical Pain Management for Laminitis

One of the biggest challenges in managing laminitis in horses remains the control of pain. The best analgesic approach is a multimodal approach, including nonsteroidal anti-inflammatory drugs, opioids, and/or constant rate infusions of α-2 agonists, ketamine, and lidocaine. Recent literature indicates that amitriptyline and soluble epoxide hydrolase inhibitor might be beneficial. Clinically oriented studies will be needed if they have a place in laminitis pain management. The systemic pain control can be combined with local techniques such as long-acting local anesthetics or epidural catheterization that allows for administration of potent analgesic therapy with a lower risk of negative side effects.

Non-steroidal anti-inflammatory drugs reduce the stress response during sevoflurane anesthesia

BACKGROUND

Non-steroidal anti-inflammatory drugs are analgesics commonly used for post-operative pain. However, their effect on dosages of inhaled anesthetics during surgery is unclear. We investigated the effect of flurbiprofen axetil and parecoxib sodium on the minimum alveolar concentration of sevoflurane required to blunt stress responses to skin incision under general anesthesia.

METHODS

One hundred and five adult patients were randomly allocated to four treatment groups, each receiving sevoflurane: control (sevoflurane only), lidocaine (1 mg/kg bolus, followed by continuous infusion of 20 μg/kg/min after intubation), Intravenous (IV) flurbiprofen (1 mg/kg before skin incision), and IV parecoxib (40 mg before skin incision). Following anesthetic induction and stabilization of end-tidal sevoflurane concentration, mean arterial blood pressure and heart rate were recorded 2 min before and at 5-min intervals after skin incision. The stable end-tidal sevoflurane concentration was calculated using an up-and-down method.

RESULTS

The minimum alveolar concentration of sevoflurane required to blunt the stress responses to skin incision in the control, lidocaine, flurbiprofen, and parecoxib groups was 4.63 ± 0.08%, 2.67 ± 0.08%, 3.33 ± 0.08%, and 3.80 ± 0.11%, respectively. These figures for the later three groups were all significantly less than that of the control group (P = 0.021, P = 0.037, and P = 0.011, respectively); that of the flurbiprofen group was significantly less than the parecoxib (P = 0.034).

CONCLUSION

The non-steroidal anti-inflammatory drugs flurbiprofen axetil and parecoxib sodium decreased the minimum alveolar concentration of sevoflurane required to blunt the stress response to skin incision during general anesthesia.

Depolarizing shift in the GABA-induced current reversal potential by lidocaine hydrochloride

Lidocaine hydrochloride (LC-HCl) is widely used as a local anesthetic, while various adverse effects of LC-HCl, such as seizures have also been reported. Lidocaine is reported to inhibit various channels and receptors including GABA(A) receptors. Although the GABA(A) receptor-mediated response depends on Cl(-) equilibrium potential (E(Cl)), little is known about the effect of LC-HCl on E(Cl). In the present study, we investigated the effect of LC-HCl on GABA-induced currents in cultured rat hippocampal neurons with gramicidin-perforated patch-clamp recording which is known to keep the intracellular Cl(-) concentration intact. LC-HCl inhibited outward GABA-induced currents with depolarizing shift of the GABA reversal potential (E(GABA)). The LC-HCl-induced positive E(GABA) shift was not observed with conventional whole-cell patch-clamp method which cannot retain intact intracellular Cl(-) concentration. The LC-HCl action on E(GABA) was inhibited by either furosemide, a blocker of both Na(+)-K(+)-Cl(-) cotransporter (NKCC) and K(+)-Cl(-) cotransporter (KCC), or an increase in extracellular K(+) concentrations. Neither bumetanide, a specific inhibitor of NKCC, nor Na(+)-free external solution had any effect on the LC-HCl-induced E(GABA) shift. QX-314, a membrane impermeable lidocaine derivative, failed to shift E(GABA) to positive potential. Furthermore, LC-HCl caused a depolarizing shift of E(GABA) in cultured GT1-7 cells expressing KCC2 but failed to change E(GABA) in GT1-7 cells without expression of KCC2. These results suggest that the LC-HCl-induced positive E(GABA) shift is due to a blockade of KCC2. Together with the direct LC-HCl action to GABA(A) receptors, the positive E(GABA) shift induced by LC-HCl reduces the GABAergic inhibition in the central nervous system.

Inhibition by cocaine of G protein-activated inwardly rectifying K+ channels expressed in Xenopus oocytes

Cocaine, a commonly abused psychostimulant, interacts with not only transporters for dopamine, serotonin and norepinephrine but also several receptors and channels. However, the molecular mechanisms underlying the various effects of cocaine remain to be clarified. Using the Xenopus oocyte expression assay, we investigated the effects of cocaine on G protein-activated inwardly rectifying K+ (GIRK) channels, which regulate neuronal excitability and the heart rate. In oocytes injected with mRNAs for GIRK1/GIRK2, GIRK2 or GIRK1/GIRK4 subunits, cocaine reversibly reduced basal GIRK inward currents. The inhibition by cocaine at the toxic levels was concentration-dependent, but voltage-independent and time-independent during each voltage pulse. However, methylphenidate, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) at their toxic concentrations had little effect on the channels. Additionally, Kir1.1 and Kir2.1 channels were insensitive to all of the drugs. The inhibition by cocaine, which exists mainly in a protonated form at pH 7.4, was not affected by extracellular pH 9, at which the proportion of the uncharged form increases, suggesting the inhibition by both forms with similar effectiveness, and at physiological pH the effect being predominantly due to the protonated cocaine. Our results suggest that inhibition of GIRK channels by cocaine may contribute to some of its toxic effects.

Lidocaine, MK-801, and MAC

BACKGROUND

Previous studies have found that the local anesthetic/sodium channel blocker lidocaine decreased MAC by maximum amounts approximately equal to the decreases produced by dizocilpine (MK-801), a N-methyl-d-aspartate (NMDA) receptor antagonist. Blockade of sodium channels by inhaled anesthetics has been suggested as a possible cause for impairment of transmission through NMDA receptors. We postulated that the net effect of lidocaine and MK-801 on MAC would be the same, albeit by affecting NMDA neurotransmission at different points.

METHODS

We measured the effect of various lidocaine infusions on the MAC of cyclopropane, halothane, isoflurane, and o-difluorobenzene in rats. We also measured the effect of concurrent lidocaine-MK-801 infusion on the MAC of isoflurane and o-difluorobenzene.

RESULTS

Our data contradicted our predictions. (a) We found no limit to the effect of lidocaine infusion, in some cases finding that lidocaine, alone, produced immobility; (b) lidocaine infusion did not decrease the MAC of o-difluorobenzene differently from the MAC of other inhaled anesthetics; and (c) the addition of MK-801 equally affected the decrease in MAC produced by lidocaine infusion for isoflurane versus o-difluorobenzene.

CONCLUSION

Lidocaine does not primarily decrease MAC by decreasing the release of glutamate from nerve terminals.

Context-dependent prefrontal cortex regulation of cocaine self-administration and reinstatement behaviors in rats

Evidence of stimulus attribute-specificity within the prefrontal cortex (PFC) suggests that different prefrontal subregions may contribute to cocaine addiction in functionally distinct ways. Thus, the present study examined the effects of lidocaine-induced inactivation of two distinct PFC subregions, the prelimbic (PL) or dorsal agranular insular (AId) cortices, on drug-seeking and drug-taking behaviors under cocaine maintenance and reinstatement testing conditions in rats trained to self-administer 1 mg/kg cocaine under a second-order schedule of drug delivery. Throughout maintenance and reinstatement phases, rats were exposed to conditioned light cues and contextual odor or sound cues. Results showed that PL inactivation during maintenance test sessions significantly reduced drug-seeking and drug-taking behaviors, and disrupted patterns of responding in rats exposed to light-sound, but not light-odor, cues. Moreover, lidocaine-induced inactivation of the PL significantly attenuated drug-seeking behavior during cue-induced and cocaine prime-induced reinstatement in rats exposed to light-sound cues only. In contrast, AId inactivation significantly attenuated cue-induced reinstatement of drug-seeking behavior in rats exposed to light-odor cues only. Drug-seeking and drug-taking behaviors in these rats were not disrupted during maintenance and cocaine prime-induced reinstatement testing regardless of the type of contextual cues used. Together, these data suggest that PL and AId subregions play separate yet overlapping roles in regulating cocaine addiction in rats in ways that are dependent on the presence or absence of cocaine and on the types of contextual cues present in the cocaine self-administration environment.

The Effects of Lidocaine and Bupivacaine on Protein Expression of Cleaved Caspase 3 and Tyrosine Phosphorylation in the Rat Hippocampal Slice

Severe neurologic sequelae have been reported with the use of lidocaine after spinal anesthesia. This is considered a consequence of the high concentrations reached in the cerebrospinal fluid. We have previously shown that lidocaine increases the phosphorylation of focal adhesion kinase (FAK, a nonreceptor tyrosine kinase playing a role in neuronal plasticity and cell death). Here, we compared the effects of lidocaine and bupivacaine on FAK phosphorylation and cleaved caspase 3 expression in rat hippocampal slices. Slices were treated with increasing concentrations of lidocaine (4.3 nM to 4.3 mM) or bupivacaine (3.4 nM to 3.4 mM) in the presence or absence of the specific inhibitor of the FAK tyrosine kinase PP2 (10 microM). Caspase 3 expression and FAK phosphorylation were examined by immunoblotting. Lidocaine induced a concentration-related increase in FAK phosphorylation while the bupivacaine effect was biphasic. The maximal effect observed with millimolar lidocaine concentrations was significantly more than with clinically equipotent bupivacaine concentrations (4.3 x 10(-3) M lidocaine: 168% +/- 20%, mean value +/- sd; 10(-3) M bupivacaine: 145% +/- 19% P < 0.001). The expression of cleaved caspase 3 was increased by lidocaine, but not bupivacaine, at millimolar concentrations and was blocked by PP2. Our results indicate that millimolar concentrations of lidocaine, but not bupivacaine, increase cleaved caspase 3 expression. The role of FAK phosphorylation in this effect remains to be clarified.

Luminal hypotonicity increases duodenal mucosal permeability by a mechanism involving 5-hydroxytryptamine

AIM

To investigate whether 5-hydroxytryptamine (5-HT) participates in the mediation of the hypotonicity-induced increase in duodenal mucosal permeability.

METHODS

Proximal duodenum in anaesthetized rats was perfused in situ with a hypotonic NaCl solution and effects on duodenal motility, net fluid flux, mucosal permeability [blood-to-lumen clearance of (51)Cr-ethylenediaminetetraacetic acid (EDTA)] and the release of 5-HT into the luminal solution studied in the presence of the cyclooxygenase inhibitor indomethacin.

RESULTS

Perfusion of the duodenum with 50 mm NaCl increased mucosal permeability eightfold, increased the luminal output of 5-HT twofold and induced net fluid absorption. This rise in permeability was enhanced 25% by 5-HT (3 x 10(-3) m), reduced by the 5-HT(3)-receptor antagonists granisetron (10(-4)-3 x 10(-4) m) or ondansetron (10(-5)-10(-4) m) or by the 5-HT(4) receptor antagonist SB 203186 (10(-4) m). The 5-HT(3/4) receptor antagonist tropisetron, at 10(-4) m, did not affect while 3 x 10(-4) and 3 x 10(-3) m augmented the hypotonicity-induced increase in mucosal permeability. Lidocaine (1.1 x 10(-3) m) similarly potentiated while tetrodotoxin (TTX) (5 x 10(-5) m) inhibited the hypotonicity-induced increase in mucosal permeability. Compared with animals treated with indomethacin alone ondansetron and granisetron augmented (by 30-40%) while tropisetron and lidocaine reduced (by 60-70%) the hypotonicity-induced net fluid absorption. Tetrodotoxin and all 5-HT receptor antagonists, except tropisetron, depressed duodenal motility.

CONCLUSIONS

Luminal hypotonicity increases duodenal mucosal permeability by a neural mechanism involving 5-HT acting on 5-HT(3) and 5-HT(4) receptors. 5-HT also appears to participate in the regulation of the hypotonicity-induced fluid flux.

Cocaine alters catalase activity in prefrontal cortex and striatum of mice

Catalase is one of the enzymes that convert hydrogen peroxide (H2O2) to H2O presenting a protective role against free radicals. In this study, catalase activity was determined in homogenates of striatum (ST) and prefrontal cortex (PFC) in order to examine the participation of oxidative stress (OS) on cocaine actions in mice brain. Male Swiss mice were injected (i.p.) with cocaine at low (10 and 30 mg/kg) and high doses (90 mg/kg), and observed for 1 h. After cocaine overdose (90 mg/kg) some animals presented only status epilepticus (SE) while others died after seizures. These animals were dissected and divided in two groups, SE and death. Catalase activity was also determined after pretreatment with the anticonvulsant drug, diazepam, alone or injected before cocaine 90 mg/kg, and after seizures induced by a high dose of bupropion, a known inhibitor of NE and DA reuptake used for comparison. Results showed a decrease in catalase activity of the PFC and ST after SE and death induced by cocaine and bupropion overdoses. Cocaine at low doses decreased the enzyme activity only in ST. Diazepam treatment alone and before cocaine overdose did not interfere with catalase activity. This reduction in catalase activity may reflect an increase in H2O2 content in PFC and ST. Previous data reports that H2O2 inhibits dopamine transporter activity, suggesting that the decrease in catalase activity may potentiate the toxic mechanism of drugs that inhibit monoamines reuptake. As far as we know, this is the first report showing an involvement of OS in the cocaine's central mechanism of action.

A pH-sensitive potassium conductance (TASK) and its function in the murine gastrointestinal tract

The excitability of smooth muscles is regulated, in part, by background K+ conductances that determine resting membrane potential. However, the K+ conductances so far described in gastrointestinal (GI) muscles are not sufficient to explain the negative resting potentials of these cells. Here we describe expression of two-pore K+ channels of the TASK family in murine small and large intestinal muscles. TASK-2, cloned from murine intestinal muscles, resulted in a pH-sensitive, time-dependent, non-inactivating K+ conductance with slow activation kinetics. A similar conductance was found in native intestinal myocytes using whole-cell patch-clamp conditions. The pH-sensitive current was blocked by local anaesthetics. Lidocaine, bupivacaine and acidic pH depolarized circular muscle cells in intact muscles and decreased amplitude and frequency of slow waves. The effects of lidocaine were not blocked by tetraethylammonium chloride, 4-aminopyridine, glibenclamide, apamin or MK-499. However, depolarization by acidic pH was abolished by pre-treatment with lidocaine, suggesting that lidocaine-sensitive K+ channels were responsible for pH-sensitive changes in membrane potential. The kinetics of activation, sensitivity to pH, and pharmacology of the conductance in intestinal myocytes and the expression of TASK-1 and TASK-2 in these cells suggest that the pH-sensitive background conductance is encoded by TASK genes. This conductance appears to contribute significantly to resting potential and may regulate excitability of GI muscles.

Discriminative stimulus effects of m-chlorophenylpiperazine as a model of the role of serotonin receptors in anxiety

Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.

Effects of ethanol on cocaine discrimination in rats

Ethanol and cocaine are frequently abused in combination, but little is known about how the subjective effects of the two drugs interact. The ability of ethanol and other GABA(A)-active compounds to alter the discriminative stimulus effects of cocaine was tested. Male Sprague-Dawley rats were trained to discriminate cocaine (10 mg/kg ip) from saline using either single- or cumulative-dosing methods. In single-dose testing, ethanol (0.1-0.5 g/kg) dose-dependently decreased cocaine-appropriate responding following the training dose of cocaine. Ethanol (0.5 g/kg) produced a rightward shift in the cocaine cumulative dose-effect curve. Ethanol (0.1-1.0 g/kg) failed to substitute for the discriminative stimulus effects of cocaine and the higher doses (1-2 g/kg) completely suppressed responding. Indirect GABA(A) agonists diazepam (benzodiazepine site) and pentobarbital (barbiturate site) did not block the discriminative stimulus effects of cumulative doses of cocaine. The GABA(A) antagonist pentylenetetrazol (PTZ) (10-40 mg/kg) did not substitute for cocaine. These findings suggest that ethanol can modulate the discriminative stimulus effects of cocaine, and that these effects may not be mediated by the actions of ethanol at the GABA(A) receptor.

The discriminative stimulus effects of pentylenetetrazol as a model of anxiety: recent developments

Pentylenetetrazol (PTZ), a GABA(A) receptor antagonist and prototypical anxiogenic drug, has been extensively utilized in animal models of anxiety. PTZ produces a reliable discriminative stimulus which is largely mediated by the GABA(A) receptor. Several classes of compounds can modulate the PTZ discriminative stimulus including 5-HT(1A), 5-HT(3), NMDA, glycine, and L-type calcium channel ligands. Spontaneous PTZ-lever responding is seen in trained rats during withdrawal from GABA(A) receptor compounds such as chlordiazepoxide and diazepam, and also ethanol, morphine, nicotine, cocaine, haloperidol, and phencyclidine. This effect is largely mediated by the GABA(A) receptor, which suggests that anxiety may be part of a generalized withdrawal syndrome mediated by the GABA(A) receptor. There are also important hormonal influences on PTZ. Corticosterone plays some role in mediation of its anxiogenic effects. There is a marked sex difference in response to the discriminative stimulus effects of PTZ, and estrogens appear to protect against its anxiogenic effects. Further work with the PTZ drug discrimination is warranted for characterization of anxiety during withdrawal, and the hormonal mechanisms of anxiety.

Lack of allosteric modulation of striatal GABA(A) receptor binding and function after cocaine sensitization

GABA(A) receptor binding after repeated cocaine has been shown to be either increased as indicated by benzodiazepine binding or decreased as indicated by convulsant-site binding. We measured the GABA binding site with [3H]-muscimol binding to GABA(A) receptors and found no differences between saline- and cocaine-sensitized rats. Allosteric modulation of [3H]-muscimol binding with flunitrazepam was also unchanged after cocaine sensitization. In addition, [3H]-flunitrazepam binding and allosteric modulation of [3H]-flunitrazepam binding with GABA was unchanged after 1 day withdrawal from repeated cocaine. GABA(A) receptor function and allosteric modulation of GABA(A) receptor function measured by GABA-stimulated Cl(-) uptake was also unchanged after withdrawal from repeated cocaine. Finally, in vitro cocaine reduced GABA(A) receptor function in striatal microsacs of saline- and cocaine-treated rats. In conclusion, repeated cocaine did not change the coupling of the GABA(A) receptor between the GABA and benzodiazepine (BZD) binding site after 1 day withdrawal.

Cocaine decreases the glycine-induced Cl- current of acutely dissociated rat hippocampal neurons

The effects of cocaine on glycine-induced Cl- current (I(GLY)) of single neurons, freshly isolated from the rat hippocampal CA1 area, were studied with conventional whole-cell recording under voltage-clamp conditions. Cocaine depressed I(GLY) in a concentration-dependent manner, with an IC50 of 0.78 mM. Preincubation with 1 mM cocaine alone had no effect on I(GLY), suggesting that resting glycine channels are insensitive to cocaine. The depression of I(GLY) by cocaine was independent of membrane voltage. Internal cell dialysis with 1 mM cocaine failed to modify I(GLY). Because the depression of I(GLY) was noncompetitive, cocaine may act on the glycine receptor-chloride ionophore complex at a site distinct from that to which glycine binds. The cocaine suppression of I(GLY) was unaffected by 1 microM tetrodotoxin and 1 microM strychnine. Blockers of protein kinase C (Chelerythrine), kinase A (N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide HCl, (H-89)) and Ca-calmodulin-dependent kinase (1-[N,O-bis(5-isoquinoline-sulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperaz ine (KN-62)) were also ineffective, which suggests that these phosphorylating mechanisms do not modulate cocaine-induced suppressant action on I(GLY). This extracellular, strychnine-independent depression of I(GLY) may contribute to cocaine-induced seizures.