Applicability of capillary electrophoresis-frontal analysis for displacement studies: Effect of several drugs on l-tryptophan and lidocaine binding to human serum albumin.

The effective concentration of a drug in the blood, i.e. the concentration of a free drug in the blood, is influenced by the strength of drug binding onto plasma proteins. Besides its efficacy, these interactions subsequently influence the liberation, absorption, distribution, metabolism, excretion, and toxicological properties of the drug. It is important to not only determine the binding strength and stoichiometry, but also the binding site of a drug on the plasma protein molecule, because the co-administration of drugs with the same binding site can affect the above-mentioned concentration and as a result the pharmacological behavior of the drugs and lead to side effects caused by the change in free drug concentration, its toxicity. In this study, the binding characteristics of six drugs with human serum albumin, the most abundant protein in human plasma, were determined by capillary electrophoresis-frontal analysis, and the obtained values of binding parameters were compared with the literature data. The effect of several drugs and site markers on the binding of l-tryptophan and lidocaine to human serum albumin was investigated in subsequent displacement studies which thus demonstrated the usability of capillary electrophoresis as an automated high-throughput screening method for drug-protein binding studies.

Lidocaine relaxation in isolated rat aortic rings is enhanced by endothelial removal: possible role of Kv, KATP channels and A2a receptor crosstalk.

BACKGROUND: Lidocaine is an approved local anesthetic and Class 1B antiarrhythmic with a number of ancillary properties. Our aim was to investigate lidocaine's vasoreactivity properties in intact versus denuded rat thoracic aortic rings, and the effect of inhibitors of nitric oxide (NO), prostenoids, voltage-dependent Kv and KATP channels, membrane Na+/K+ pump, and A2a and A2b receptors. METHODS: Aortic rings were harvested from adult male Sprague Dawley rats and equilibrated in an organ bath containing oxygenated, modified Krebs-Henseleit solution, pH 7.4, 37 °C. The rings were pre-contracted sub-maximally with 0.3 µM norepinephrine (NE), and the effect of increasing lidocaine concentrations was examined. Rings were tested for viability after each experiment with maximally dilating 100 µM papaverine. The drugs 4-aminopyridine (4-AP), glibenclamide, 5-hydroxydecanoate, ouabain, 8-(3-chlorostyryl) caffeine and PSB-0788 were examined. RESULTS: All drugs tested had no significant effect on basal tension. Lidocaine relaxation in intact rings was biphasic between 1 and 10 µM (Phase 1) and 10 and 1000 µM (Phase 2). Mechanical removal of the endothelium resulted in further relaxation, and at lower concentrations ring sensitivity (% relaxation per µM lidocaine) significantly increased 3.5 times compared to intact rings. The relaxing factor(s) responsible for enhancing ring relaxation did not appear to be NO- or prostacyclin-dependent, as L-NAME and indomethacin had little or no effect on intact ring relaxation. In denuded rings, lidocaine relaxation was completely abolished by Kv channel inhibition and significantly reduced by antagonists of the MitoKATP channel, and to a lesser extent the SarcKATP channel. Curiously, A2a subtype receptor antagonism significantly inhibited lidocaine relaxation above 100 µM, but not the A2b receptor. CONCLUSIONS: We show that lidocaine relaxation in rat thoracic aorta was biphasic and significantly enhanced by endothelial removal, which did not appear to be NO or prostacyclin dependent. The unknown factor(s) responsible for enhanced relaxation was significantly reduced by Kv inhibition, 5-HD inhibition, and A2a subtype inhibition indicating a potential role for crosstalk in lidocaine's vasoreactivity.

In-practice evaluation of OraVerse for the reversal of soft-tissue anesthesia after dental procedures.

This study investigated the pattern of use, dentist evaluation, and patient assessment of OraVerse (OV), a solution of phentolamine mesylate formulated for intraoral submucosal injection and used for the reversal of soft anesthesia after dental procedures. Participants were provided the drug for treatment of up to 10 patients each and agreed to complete a 26-item evaluation questionnaire at the end of the clinical assessment. Data were available from 51 dentists reporting on 390 patients 4 to 90 years of age. A total of 394 dental procedures were performed: 224 (57%) in the mandible and 170 (43%) in the maxilla. Local anesthetics most frequently used were lidocaine/epinephrine (66.4%) and articaine/epinephrine (23.6%). In 81.5% of cases, OV was administered after restorative procedures. This OV dose was given as one-half, one, and two cartridges in 11.8%, 76.7%, and 10.3% of patients, respectively. An adverse reaction at the injection site was reported in 19 patients (4.9%). The median times to return to normal after injection were 60 minutes for lip sensation, 57.5 minutes for tongue sensation, and 60 minutes for oral function. Patients reported reduced duration of oral numbness (92%) and improved dental experiences (84%) after use. A total of 83% of patients said they would recommend the medication to others and 79% said they would opt for OV in the future. Dentists reported that the medication addressed an existing need (86%), met expectations (82%), was a practice differentiator (55%) and a practice builder (45%), and improved scheduling (29%). In this in-practice clinical evaluation, times to return to normal oral sensation and function after OV administration were consistent with those reported in randomized clinical studies. Both patient and dentist satisfaction rates were high.

The use of phentolamine mesylate to evaluate mandibular nerve damage following implant placement.

High success rates and long-term predictability of implant therapy have been well documented in the literature. However, complications in implant treatment can arise and include sensory disturbances, especially in the posterior mandible in areas close to the inferior alveolar nerve. Treatment efficacy of sensory disturbances caused by implant placement in this area relies on the expeditious diagnosis of an induced paresthesia. Recently, phentolamine mesylate has been introduced as a reversal agent of local anesthesia with the ability to decrease the requisite time for a patient to return to normal sensation. This article introduces a method for faster detection of a potential paresthesia induced by implant placement in the posterior mandible.

Dexmedetomidine protects against lidocaine-induced neurotoxicity through SIRT1 downregulation-mediated activation of FOXO3a.

Lidocaine, a typical local anesthetic, has been shown to directly induce neurotoxicity in clinical settings. Dexmedetomidine (DEX) is an alpha-2-adrenoreceptor agonist that has been used as anxiolytic, sedative, and analgesic agent which has recently found to protect against lidocaine-induced neurotoxicity. Nicotinamide adenine dinucleotide-dependent deacetylase sirtuin-1 (SIRT1)/forkhead box O3 (FOXO3a) signaling is critical for maintaining neuronal function and regulation of the apoptotic pathway. In the present study, we designed in vitro and in vivo models to investigate the potential effects of lidocaine and DEX on SIRT1 and FOXO3a and to verify whether SIRT1/FOXO3a-mediated regulation of apoptosis is involved in DEX-induced neuroprotective effects against lidocaine. We found that in both PC12 cells and brains of mice, lidocaine decreased SIRT1 level through promoting the degradation of SIRT1 protein. Lidocaine also increased FOXO3a protein level and increased the acetylation of SIRT1 through inhibiting SIRT1. Upregulation of SIRT1 or downregulation of FOXO3a significantly inhibited lidocaine-induced changes in both cell viability and apoptosis. DEX significantly inhibited the lidocaine-induced decrease of SIRT1 protein level and increase of FOXO3a protein level and acetylation of FOXO3a. Downregulation of SIRT1 or upregulation of FOXO3a suppressed DEX-induced neuroprotective effects against lidocaine. The data suggest that SIRT1/FOXO3a is a potential novel target for alleviating lidocaine-induced neurotoxicity and provide more theoretical support for the use of DEX as an effective adjunct to alleviate chronic neurotoxicity induced by lidocaine.

Curcumin exerts protective effect on PC12 cells against lidocaine-induced cytotoxicity by suppressing the formation of NLRP3 inflammasome.

OBJECTIVE: To explore the protective effect of curcumin on lidocaine-insulted PC12 cells. MATERIALS AND METHODS: We first treated PC12 cells with different doses of lidocaine, and then treated the cells with curcumin or Nod-like receptor pyrin domain3 (NLRP3) inhibitor (MCC950). Subsequently, the cell viability, apoptosis, reactive oxygen species (ROS) production and NLRP3 inflammasome were detected by cell counting kit-8 (CCK8), Annexin V/PI staining, FCM and Western blot analysis, respectively, and the level of IL-1ß in PC12 cells was determined by an enzyme-linked immunosorbent assay (ELISA) kit. RESULTS: Lidocaine inhibited the viability of PC12 cells, and it induced cell apoptosis, promoted ROS release and activated NLRP3 inflammasome in PC12 cells, but its effects were reversed by the treatment of curcumin. Moreover, NLRP3 over-expression also induced cytotoxicity in PC12 cells, which was also rescued by the treatment of curcumin. CONCLUSIONS: Our study indicates that curcumin exerts protective effect against lidocaine-induced cytotoxicity on PC12 cells by suppressing the activity of NLRP3 inflammasome, which provides new ideas on screening natural product for neurological damage therapy.

Dexmedetomidine protects PC12 cells from lidocaine-induced cytotoxicity via downregulation of Stathmin 1.

Background: Understanding of lidocaine-induced neurotoxicity is not complete, resulting in the unsuccessful treatment in some clinical settings. Dexmedetomidine (DEX) has been shown to alleviate lidocaine-induced neurotoxicity in our previous cell model. However, the rationale for DEX combined with lidocaine to reduce lidocaine-induced neurotoxicity in the clinical setting remains to be further clarified in the detailed molecular mechanism. Methods: In this study, we established a cellular injury model by lidocaine preconditioning. Cell Counting Kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) proliferation assay kit were used to analyze cell proliferation. Cell apoptosis was measured by flow cytometry and Hoechst 33342 staining. Cell cycle progression was detected by flow cytometry. The protein expression levels were detected by Western blotting and immunofluorescence staining. Results: Our results showed that DEX dose-dependently restored impaired proliferation of PC12 cells induced by lidocaine，as reflected by the increased cell viability and EdU positive cells, which were consistent with the decreased expression of tumor suppressor protein p21 and increased expression of cell cycle-related cyclin D1 and CDK1. In addition, DEX dose-dependently reduced apoptotic PC12 cells induced by lidocaine，as reflected by the decreased expression of apoptosis-related Bax, caspase-3 and caspase-9 and increased expression of anti-apoptotic Bcl-2 compared to the cells only treated with lidocaine. Mechanistically, with gain-or-loss-of-function of STMN1, we showed that DEX-mediated neuroprotection by lidocaine-induced damage is associated with downregulation of STMN1 which might be an upstream molecule involved in regulation of mitochondria death pathway. Conclusion: Our results reveal that DEX is likely to be an effective adjunct to alleviate chronic neurotoxicity induced by lidocaine.

Effects of clonidine on lidocaine-induced inhibition of axonal transport in cultured mouse dorsal root ganglion neurones.

BACKGROUND: The alpha(2)-adrenoceptor agonist clonidine is used in combination with lidocaine for anaesthesia. Lidocaine inhibits axonal transport and neurite growth, whereas alpha(2)-adrenoceptor agonists have neurotrophic effects. Here we have investigated whether clonidine reduces lidocaine-induced inhibition of axonal transport in cultured mouse dorsal root ganglion neurones. METHODS: Axonal transport of organelles and neurite growth were assessed by video microscopy in cells treated with clonidine and lidocaine for 1 h. Stable responses were achieved within this period. RESULTS: Clonidine (10 and 100 microM) increased and lidocaine (10, 100 microM, and 1 mM) decreased axonal transport. The inhibitory effects of lidocaine were reduced by simultaneous treatment with clonidine. The actions of clonidine were antagonized by the alpha(2)-adrenoceptor antagonist yohimbine. Since clonidine was reported to block N-type channels, we further investigated the role of ion channels in the antagonistic action of clonidine on the lidocaine response. The action of lidocaine on axonal transport was not mimicked by the Na+ channel blocker tetrodotoxin and not blocked by the Na+ channel activator veratridine. The action of lidocaine was not blocked by the L-type Ca2+ channel blocker nifedipine, but was blocked by the N-type channel blocker omega-conotoxin MVIIA. These effects on axonal transport correlated with the effects on neurite growth. CONCLUSIONS: Inhibition of axonal transport induced by lidocaine, which may be mediated by N-type channel activation, can be blocked by clonidine. Clonidine may alleviate the effects of lidocaine on neuronal dysfunction.

Reversal of soft-tissue local anesthesia with phentolamine mesylate in adolescents and adults.

BACKGROUND: The authors conducted two multicenter, randomized, double-blinded, controlled Phase III clinical trials to study the efficacy and safety of phentolamine mesylate (PM) in shortening the duration and burden of soft-tissue anesthesia. The study involved 484 subjects who received one of four commercially available local anesthetic solutions containing vasoconstrictors for restorative or scaling procedures. METHODS: On completion of the dental procedure, subjects randomly received a PM or a sham injection (an injection in which a needle does not penetrate the soft tissue) in the same site as the local anesthetic injection. The investigators measured the duration of soft-tissue anesthesia by using standardized lip- and tongue-tapping procedures every five minutes for five hours. They also evaluated functional measures and subject-perceived altered function, sensation, appearance and safety. RESULTS: Median recovery times in the lower lip and tongue for subjects in the PM group were 70 minutes and 60 minutes, respectively. Median recovery times in the lower lip and tongue for subjects in the sham group were 155 minutes and 125 minutes, respectively. Upper lip median recovery times were 50 minutes for subjects in the PM group and 133 minutes for subjects in the sham group. These differences were significant (P < .0001). Recovery from actual functional deficits and subject-perceived altered function, sensation and appearance also showed significant differences between the PM and the sham groups. CONCLUSIONS: PM was efficacious and safe in reducing the duration of local anesthetic- induced soft-tissue numbness and its associated functional deficits. CLINICAL IMPLICATIONS: Clinicians can use PM to accelerate reversal of soft-tissue anesthesia and the associated functional deficits.

Reversal of soft-tissue local anesthesia with phentolamine mesylate in pediatric patients.

BACKGROUND: The authors evaluated the safety and efficacy of a formulation of phentolamine mesylate (PM) as a local anesthesia reversal agent for pediatric patients. METHODS: A total of 152 pediatric subjects received injections of local anesthetic with 2 percent lidocaine and 1:100,000 epinephrine before undergoing dental procedures. The authors then randomized subjects to receive a PM injection or a control injection (sham injection in which a needle does not penetrate the tissue) in the same sites as the local anesthetic was administered in a 1:1 cartridge ratio after the procedure was completed. Over a two- to-four-hour period, they measured the duration of soft-tissue anesthesia and evaluated vital signs, pain and adverse events. RESULTS: The median recovery time to normal lip sensation was 60 minutes for the subjects in the PM group versus 135 minutes for subjects in the control group. The authors noted no differences in adverse events, pain, analgesic use or vital signs, and no subjects failed to complete the study. CONCLUSIONS: PM was well-tolerated and safe in children 4 to 11 years of age, and it accelerated the reversal of soft-tissue local anesthesia after a dental procedure in children 6 to 11 years of age. CLINICAL IMPLICATIONS: PM can help dental clinicians shorten the post-treatment duration of soft-tissue anesthesia and can reduce the number of posttreatment lip and tongue injuries in children.

Reversing the effects of 2% Lidocaine: A randomized controlled clinical trial.

OBJECTIVES: Prolonged soft tissue anesthesia following a dental appointment is a complaint that is frequently reported by patients. Soft tissue anesthesia generally exceeds the duration of pulpal anesthesia by a few hours. This can lead to difficulties with smiling, drinking, speaking and lip/cheek biting following dental appointments. Phentolamine Mesylate (PM) is a pharmacological agent capable of reducing the duration of soft tissue anesthesia following dental treatments. Many clinical trials supporting its efficacy have used sham injections compared to injections with PM. The present study aims to evaluate the effect of PM on the duration of soft tissue anesthesia compared to a control injection of saline water. METHODS: This randomized controlled trial recruited 40 participants above 18 years of age. Following an inferior alveolar nerve block using 1.8 ml of Lidocaine 2%, 1:100 000 epinephrine, participants were randomized into one of 2 groups. The test group received an injection of 0.4 mg PM (OraVerse). Participants in the control group received an injection of sterile saline water. Participants were trained in self-assessing their anesthesia, which they did until return to normal sensation. RESULTS: Thirty-six participants completed the study. PM significantly reduced the duration of soft tissue anesthesia in the lower lip (104 vs 170 min, p = .001), and tongue (83 vs 134 min, p = .004) compared to the control injection. No serious adverse events were encountered. The only adverse events observed were post-operative pain and discomfort. CONCLUSIONS: Phentolamine Mesylate hastens the return to normal soft tissue sensation and function by approximately one hour compared to a control injection of water. CLINICAL SIGNIFICANCE: Phentolamine Mesylate can be considered a safe and effective way of reducing the duration of soft tissue anesthesia following a dental appointment. This controlled clinical trial is registered at the National Institutes of Health (ClinicalTrials.gov) #NCT02861378.

Reversal of lidocaine effects on sodium currents by isoproterenol in rabbit hearts and heart cells.

We demonstrated recently that isoproterenol enhanced the cardiac voltage-dependent sodium currents (INa) in rabbit ventricular myocytes through dual G-protein regulatory pathways. In this study, we tested the hypothesis that isoproterenol reverses the sodium channel blocking effects of class I antiarrhythmic drugs through modulation of INa. The experiments were performed in rabbit ventricular myocytes using whole-cell patch-clamp techniques. Reversal of lidocaine suppression of INa by isoproterenol (1 microM) was significant at various concentrations of lidocaine (20, 65, and 100 microM, P < 0.05). The effects of isoproterenol were voltage dependent, showing reversal of INa suppression by lidocaine at normal and hyperpolarized potentials (negative to -80 mV) but not at depolarized potentials. Isoproterenol enhanced sodium channel availability but did not alter the steady state activation or inactivation of INa nor did it improve sodium channel recovery in the presence of lidocaine. The physiological significance of the single cell INa findings were corroborated by measurements of conduction velocities using an epicardial mapping system in isolated rabbit hearts. Lidocaine (10 microM) significantly suppressed epicardial impulse conduction in both longitudinal (theta L, 0.430 +/- 0.024 vs. 0.585 +/- 0.001 m/s at baseline, n = 7, P < 0.001) and transverse (theta T, 0.206 +/- 0.012 vs. 0.257 +/- 0.014 m/s at baseline, n = 8, P < 0.001) directions. Isoproterenol (0.05 microM) significantly reversed the lidocaine effects with theta L of 0.503 +/- 0.027 m/s and theta T of 0.234 +/- 0.015 m/s (P = 0.014 and 0.004 compared with the respective lidocaine measurements). These results suggest that enhancement of INa is an important mechanism by which isoproterenol reverses the effects of class I antiarrhythmic drugs.

Dexmedetomidine Protects PC12 Cells from Lidocaine-Induced Cytotoxicity Through Downregulation of COL3A1 Mediated by miR-let-7b.

Safety concerns of some local anesthetics, such as lidocaine, have been raised in recent years due to potential neurological impairment. Dexmedetomidine may protect humans from neurotoxicity, and miR-let-7b is activated by nerve injury; however, the roles of miR-let-7b and its target gene in lidocaine-induced cytotoxicity are not well known. Through bioinformatics and a luciferase reporter assay, COL3A1 was suggested as a direct target gene of miR-let-7b. Here, we confirmed by measuring mRNA and protein levels that miR-let-7b was downregulated and COL3A1 was upregulated in lidocaine-treated cells, an observation that was reversed by dexmedetomidine. Similar to miR-let-7b mimics or knockdown of COL3A1, dexmedetomidine treatment reduced the expression of COL3A1, suppressed cell apoptosis and cell migration/invasion ability, and induced cell cycle progression and cell proliferation in PC12 cells, effects that were reversed by the miR-let-7b inhibitor. Meanwhile, proteins involved in cell apoptosis, such as Bcl2 and caspase 3, were impacted as well. Taken together, dexmedetomidine may protect PC12 cells from lidocaine-induced cytotoxicity through miR-let-7b and COL3A1, while also increasing Bcl2 and inhibiting caspase 3. Therefore, miR-let-7b and COL3A1 might play critical roles in neuronal injury, and they are potential therapeutic targets.

Caspase-2 and microRNA34a/c regulate lidocaine-induced dorsal root ganglia apoptosis in vitro.

Epidural administration of lidocaine may cause neurotoxicity in spinal cord dorsal root ganglia neurons (DRGNs). In this study, we explored the underling mechanisms of apoptotic pathways of lidocaine-induced apoptosis in DRGNs. Neonatal rat DRGNs were treated with lidocaine to induced apoptosis in vitro. Western blot showed caspase- (casp-) 2/3/9 proteins were all upregulated by lidocaine in DRGNs. However, inhibition of casp-2 protected lidocaine-induced apoptosis in DRGNs, whereas Casp3/9 inhibition did not. The possible upstream epigenetic regulators of casp-2, microRNA-34 (miR-34) family, including miR-34a/b/c, were evaluated by dual-luciferase reporter assay and qRT-PCR. We found miR-34a/c, but not miR-34b, were down-regulated in lidocaine-induced DRGN apoptosis. Subsequent upregulation of miR-34 family showed miR-34a/c were able to inhibit casp-2 and protect lidocaine-induced apoptosis in DRGNs, whereas miR-34b did not. Thus, out study shows that casp-2, in association with miR-34a/c was actively involved in lidocaine-induced apoptosis in DRGNs. Inhibiting casp-2 or upregulating miR-34a/c may provide novel meanings to protect local anesthetic-induced neurotoxicity.

Kinetic analysis of mutual metabolic inhibition of lidocaine and propranolol in rat liver microsomes.

The metabolic interaction between lidocaine (LD) and propranolol (PL) was analysed kinetically in rat liver microsomes. Employing a very short incubation time of 30 sec, we demonstrated that PL competitively inhibited liver microsomal 3-hydroxylation of LD, but did not affect either the formation of monoethylglycinexylidide or methylhydroxylidocaine from LD in PL concentrations up to 1 microM. On the other hand, LD competitively inhibited PL 4-, 5- and 7-hydroxylations, but the inhibition type of LD for PL N-desisopropylation could not be clarified. Comparison of the kinetic data for liver microsomes from Wistar and Dark Agouti rats indicated that among the primary metabolic pathways of LD, the Vmax value for 3-hydroxylation was markedly less in female Dark Agouti rats. The results suggest that LD 3-hydroxylation and PL ring hydroxylations are mediated by the same isozyme(s) belonging to the CYP2D subfamily.

Specific contribution of lumbar spinal mechanisms to persistent nociceptive responses in the formalin test.

To determine whether a lumbar spinal mechanism mediates the late phase of the nociceptive response in the formalin test, we compared the effects of intrathecal (i.t.) lidocaine given pre- or post-formalin at the lumbar or thoracic level. Pre- but not post-formalin administration of lidocaine to the lumbar level significantly attenuated late phase nociceptive responses. In contrast, neither pre- nor post-formalin administration of lidocaine to the mid-thoracic level altered nociceptive responses. In rats chronically spinalized at the mid-thoracic level, nociceptive responses to formalin were observed which were blocked by i.t. pre-treatment with lidocaine at the lumbar level. These results suggest that a specific lumbar spinal mechanism is involved in the initiation of persistent nociception in the formalin test.

Intravenously administered lidocaine in therapeutic doses increases the intraspinal release of acetylcholine in rats.

The local anesthetic lidocaine suppresses different pain conditions when administered systemically. Part of the antinociceptive effect appears to be mediated via receptor mechanisms. We have previously shown that muscarinic and nicotinic agonists that produce antinociception increase the intraspinal release of acetylcholine. In the present study it was hypothesized that systemically administered lidocaine is acting through the same mechanisms as cholinergic agonists and affects the intraspinal release of acetylcholine. Microdialysis probes were placed in anesthetized rats for sampling of acetylcholine. Ten and 30 mg/kg lidocaine injected intravenously significantly increased the intraspinal release of acetylcholine. The effect of lidocaine could be reduced by pretreatment with intraspinally administered atropine or mecamylamine. Our results suggest that the antinociceptive effect produced by systemically administered lidocaine is mediated through an action on muscarinic and nicotinic receptors.

Local anesthetic-induced toxicity may be modified by low doses of flumazenil.

The purpose of this study was to investigate the influence of flumazenil on local anesthetic-induced acute toxicity. For each of the three tested anesthetics (etidocaine, mepivacaine and lidocaine) 6 groups of mice were treated by a single dose of flumazenil (0.125, 0.25, 0.5, 1 and 2 mg/kg), or an equal volume of saline, 15 minutes before the injection of the anesthetic (etidocaine: 50 mg/kg, mepivacaine: 110 mg/kg and lidocaine: 115 mg/kg). The convulsant activity, the time of latency to convulse and the mortality rate were assessed in each group. The local anesthetic-induced mortality was not significantly modified by flumazenil. The convulsant activity of lidocaine and mepivacaine was significantly increased by flumazenil but not for etidocaine. Also, increasing doses of flumazenil decreased the time of latency to obtain lidocaine-induced convulsions. This effect was not obtained with etidocaine or mepivacaine.

Facilitation and antagonism of lidocaine-kindled seizures: the behavioral feature.

The role of the purinergic system in the genesis of lidocaine-kindled seizures has been studied. At the same time, in order to assess the behavioral changes in lidocaine-kindled rats, the animals were rated on an Albert and Richmond scale on the 7th, 14th and 21st day. Pretreatment with aminophylline (a blocker of adenosine receptors), in doses of 40 mg/kg, 30 minutes prior to lidocaine, potentiated seizure development and the manifestations of irritable-aggressive behavior in experimental animals. On the contrary, pretreatment with papaverine (a blocker of adenosine uptake) in doses of 40 mg/kg, also 30 minutes prior to lidocaine, was effective in preventing the appearance of lidocaine kindling phenomenon. These results demonstrated that purinergic modulation of synaptic transmission in the central nervous system in mammalia might play a significant role in the genesis of lidocaine-kindled seizures and behavioral changes.

Lidocaine toxicity to rat retinal ganglion cells.

PURPOSE: To examine the effects of the local anesthetic, lidocaine, on rat retinal ganglion cells (RGC) in vitro and in a modified in vivo assay. METHODS: For in vitro experiments, RGC were dissociated from freshly harvested Long Evan's rat pup retinas. The RGC were incubated overnight with varying concentrations of lidocaine (0.5-12.0 mM). Surviving cells were assayed at 24 hours. In an in vivo assay, 7-day-old Long-Evans rat pups were anesthetized and 2 microl of lidocaine (final intraocular concentration: 0.03-15 mM) or vehicle was injected intravitreally. Intravitreal coinjection of nimodipine or MK801 (dizocilpine) were also performed in a subset of animals. A week after injection, rat pups were sacrificed and each retina removed, dissociated and plated separately. RGC survival was immediately assessed. Living RGC were identified on the basis of morphology and counted in a masked fashion. RESULTS: Lidocaine is toxic in a dose dependent fashion to RGC in vitro. Lower concentrations (0.5 mM and 1.0 mM) were non-toxic; 2.0, 6.0 and 12.0 mM lidocaine killed 25%, 88% and 99% of the RGC respectively. Intravitreal lidocaine was also toxic to RGC in a dose dependent fashion. Lidocaine concentrations of 3.0 mM, 7.5 mM and 15 mM killed 25%, 38% and 44% of the RGC. This effect was blocked by the simultaneous administration of either nimodipine or MK801. CONCLUSIONS: Lidocaine is toxic to RGC both in vitro and in vivo. This effect is blocked in vivo by the simultaneous administration of agents known to block glutamate mediated neuronal death, suggesting that excitotoxicity may be involved in this process.