Effects of calcium channel blockers on bupivacaine-induced toxicity

The purpose of this study was to investigate the influence of calcium channel blockers on bupivacaine-induced acute toxicity. For each of the three tested calcium channel blockers (diltiazem, verapamil and bepridil) 6 groups of mice were treated by two different doses, i.e. 2 and 10 mg/kg/i.p., or an equal volume of saline for the control group (n=20); 15 minutes later, all the animals were injected with a single 50 mg/kg/i.p. dose of bupivacaine. The convulsant activity, the time of latency to convulse and the mortality rate were assessed in each group. The local anesthetic-induced mortality was significantly increased by the three different calcium channel blockers. The convulsant activity of bupivacaine was not significantly modified but calcium channel blockers decreased the time of latency to obtain bupivacaine-induced convulsions; this effect was less pronounced with bepridil.     

Flumazenil and bupivacaine-induced toxicity: inverse agonist type activity

The purpose of this study was to investigate the influence of flumazenil on bupivacaine-induced acute toxicity, 10 groups of mice were previously treated by a 1, 0.5, 0.25 and 0.125 mg/kg single dose of flumazenil or saline 15 minutes before an injection of bupivacaine (50 mg/kg: exp. 1 and 60 mg/kg: exp.2). The convulsant activity, the period of latency to convulse and the induced mortality were assessed in each group. The bupivacaine-induced mortality was increased by flumazenil. Also, the convulsant activity was increased by flumazenil and the period of latency to convulse was proportionally decreased with increasing doses of flumazenil for the two tested doses of bupivacaine.     

Circadian Phase-Dependent Protein and Tissular Binding of Three Local Anesthetics (Bupivacaine,Etidocaine, and Mepivacaine) in Mice: A Possible Mechanismof Their Chronotoxicokinetics?

The aim of this study was to investigate the possible influence of the time of administration on bupivacaine (B), etidocaine (E), and mepivacaine (M) protein and tissue (brain and heart) binding. For each anesthetic agent, a single dose of B (20 mg/kg), E (40 mg/kg), or M (60 mg/kg) was administered intraperito-neally at 10:00,16:00,22:00, and 04:00 h. Blood and tissue samples were collected 15 min after drug administration. This study documents significant circadian variations in protein and tissue binding of the three local anesthetic agents. We did not demonstrate a temporal relationship between the respective free and tissue levels. Thus, the temporal variations of free plasma, brain, and heart levels do not seem to be involved in the temporal changes of induced mortality.     

Circadian Phase-Dependent Protein and Tissular Binding of Three Local Anesthetics (Bupivacaine, Etidocaine, and Mepivacaine) in Mice: A Possible Mechanismof Their Chronotoxicokinetics?

The aim of this study was to investigate the possible influence of the time of administration on bupivacaine (B), etidocaine (E), and mepivacaine (M) protein and tissue (brain and heart) binding. For each anesthetic agent, a single dose of B (20 mg/kg), E (40 mg/kg), or M (60 mg/kg) was administered intraperito-neally at 10:00,16:00,22:00, and 04:00 h. Blood and tissue samples were collected 15 min after drug administration. This study documents significant circadian variations in protein and tissue binding of the three local anesthetic agents. We did not demonstrate a temporal relationship between the respective free and tissue levels. Thus, the temporal variations of free plasma, brain, and heart levels do not seem to be involved in the temporal changes of induced mortality.     

Inhibition of fast axonal transport in vitro by the local anesthetics prilocaine, mepivacaine, and bupivacaine

The aim of the present study was to establish the concentrations of prilocaine, mepivacaine, and bupivacaine which are effective at blocking fast axonal transport, to determine whether prilocaine and mepivacaine offer a better prospect of dissociating conduction block and transport block in vivo than does lidocaine and whether bupivacaine offers a better prospect than etidocaine in the same context. Fast axonal transport of [3H]leucine-labeled proteins was studied in vitro in bullfrog spinal nerves and quantitated by liquid scintillation counting. Exposure of spinal nerves to 14 mM prilocaine reduced the quantity of 3H-labeled proteins which accumulated at a ligature by 86%, and exposure to 14 mM mepivacaine reduced it by 70%; 10 mM prilocaine reduced this same parameter by 54%, a degree of inhibition close to the 44% reduction caused by 14 mM lidocaine. The D(-) and L(+) stereoisomers of mepivacaine each reduced transport to the ligature by approximately 50% at a concentration of 14 mM. Bupivacaine reduced the accumulation of 3H-labeled proteins at the ligature by 49% at a 10 mM concentration (pH 6.2); its potency is close to that found for etidocaine in a previous study. Since prilocaine and mepivacaine are at least as potent as lidocaine as transport inhibitors and at blocking impulse conduction, these two anesthetics offer no advantage over lidocaine to achieve dissociation of conduction block from transport block in vivo. Bupivacaine appears to offer no advantage over etidocaine in the same context, as the two agents have a similar potency as local anesthetics and a similar potency as inhibitors of fast axonal transport.     

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.     

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.     

Effect of combined treatment of thioperamide with some antiepileptic drugs on methionine-sulfoximine induced convulsions in mice

Methionine-sulfoximine (MSO), a convulsant is known to increase the activity of histamine N-methyl transferase. The effect of a selective H3 receptor agonist R- (alpha) methylhistamine (RAMH) and antagonist (thioperamide, THP) and some antiepileptic drugs (gabapentin and sodium valproate) have been evaluated on MSO-induced convulsions in mice. The effect of THP was also evaluated in combination with these antiepileptic drugs. Sodium valproate (300 mg/kg, po) and gabapentin (400 mg/kg, po) offered protection against MSO-induced convulsions as evidenced by a significant prolongation of latency to abnormal dorsoflexion and complete protection against mortality within 6 h of administration. THP (15 mg/kg, ip) alone and in combination with sub-effective doses of gabapentin (75 mg/kg, po) and sodium valproate (75 mg/kg, po) revealed no significant differences from the control group or either drug alone. Hence, the convulsant action of MSO does not appear to be mediated via histaminergic mechanisms.     

Central nervous system depressant activity of Russelia equisetiformis.

The central nervous system depressant activity of the crude methanol extract (REC) and fractions (RE1, RE2, and RE3) of Russelia equisetiformis were evaluated in mice using the following models: amphetamine-induced stereotypy, picrotoxin-induced convulsion and phenobarbitone sleeping time. At 200-400 mg/kg, REC significantly increased phenobarbitone-sleeping time [P < 0.05] in a dose- dependent manner and also reduced the sleep latency significantly [P < 0.05]. The fractions, at doses 1.5 mg/kg for RE1 and 20 mg/kg for RE2 and RE3 also significantly prolonged Phenobarbitone sleeping time and sleep latency [P < 0.05]. Picrotoxin-induced convulsion was not prevented by 100-400 mg/kg of REC but this dose range significantly prolonged seizure latency. A significant reduction [P < 0.05] in amphetamine-induced stereotype behavior was observed with 200 mg/kg REC, but there was no protection against amphetamine-induced mortality. The results of this study suggest that Russelia equisetiformis methanol extract possesses central nervous system depressant activities.     

Beneficial effect of trimebutine and N-monodesmethyl trimebutine on trinitrobenzene sulfonic acid-induced colitis in rats

The use of local anesthetics, such as lidocaine, has been proposed in the treatment of distal ulcerative colitis. Trimebutine maleate (TMB) displays a local anesthetic activity higher than that of lidocaine in rabbit corneal reflex. TMB and nor-TMB its main metabolite in human show similar affinity to that of bupivacaine toward sodium channel labeled by [3H]batrachotoxin and block sodium currents in sensory neurons from rat dorsal root ganglia. The aim of this study was to evaluate the effects of TMB and nor-TMB in comparison to lidocaine and bupivacaine in a rat model of acute colonic inflammation induced by trinitrobenzene sulfonic acid (TNBS). A single intracolonic instillation of TNBS (50 mg/kg dissolved in ethanol 30%) led to early plasma extravasation then macroscopic damage (hyperemia and necrosis), increased colonic weight and tissular MPO, a marker of neutrophilic infiltration. Local administration of TMB at dose of 3 to 60 mg/kg, 30 min before, 24 and 48 h after colitis induction, significantly reduced the severity of colitis. Nor-TMB (1, 3, 10, 30 mg/kg) as well as lidocaine (1, 3, 10 mg/kg) dose-dependently reduced colitis while bupivacaine at 10 mg/kg did not affect it significantly. In contrast systemic administration of TMB, nor-TMB and lidocaine at 10 mg/kg had no significant effect. Furthermore, local administration of TMB (30 mg/kg) and lidocaine (10 mg/kg) significantly reduced plasmatic extravasation. In conclusion, intracolonic treatment with TMB and nor-TMB improved acute experimental TNBS-induced colitis in rat and these effects could be explained by their local anesthetic activity.     

Differential effects of uncharged aminoamide local anesthetics on phospholipid bilayers, as monitored by 1H-NMR measurements

We have collected evidences of a "transient site" for the local anesthetics (LA) lidocaine, etidocaine, bupivacaine and mepivacaine in sonicated egg phosphatidylcholine (EPC) vesicles. The effects of the uncharged anesthetic species at a fixed LA/EPC ratio inside the bilayer were measured by chemical shifts (C.S.) and longitudinal relaxation times (T(1)) of the lipid hydrogens. Two sort of changes were detected: (I) decrease, indicating specific orientation of the LA aromatic ring (measured as up-field C.S. changes by the short-range ring-current effect) and less rotational freedom (smaller T(1) values) for EPC hydrogens such as the two glycerol-CH(2) and the choline-CH(2) bound to the PO(4-) group, probably due to the nearby presence of the LA; (II) increase, indicating the aromatic ring is now perpendicular to the orientation observed before (causing down-field changes in C.S.) and larger T(1) values for all the choline and glycerol hydrogens, as a result of LA insertion behind these well-organized bilayer regions. The less hydrophobic, linear and nonlinear (lidocaine and mepivacaine, respectively) aminoamide analogs provide similar effects-described in I; their hydrophobic counterparts (etidocaine and bupivacaine) also produced comparable effects (depicted in II). The preferential positioning and orientation of each LA inside the bilayer is then determined by its hydrophobic and steric properties. We propose that this "transient site" in the lipid milieu exists also in biological membranes, where it can modulates the access of the uncharged LA species to its site(s) of action in the voltage-gated sodium channel.     

Anticonvulsant effects of thymoquinone, the major constituent of Nigella sativa seeds, in mice.

The anticonvulsant effects of thymoquinone, the major constituent of Nigella sativa seeds, were investigated using pentylenetetrazole (PTZ)- and maximal electroshock (MES)-induced seizure models. We also studied the effect of thymoquinone on pentobarbital-induced hypnosis, locomotor activity, and motor coordination. In PTZ-induced seizure, the intraperitoneally injection of thymoquinone with doses of 40 and 80 mg/kg, prolonged the onset of seizures and reduced the duration of myoclonic seizures. The protective effect of thymoquinone against mortality was 71.4% and 100% in the mentioned doses, respectively. In MES model, thymoquinone failed to reduce the duration of seizure, whereas exhibited a complete protection against mortality. In PTZ model, flumazenil (10 mg/kg, i.p.), an antagonist of benzodiazepine (BZD) site in the GABAA-BZD receptor complex, inhibited the prolongation of seizure latency, but did not show any effect on the duration of myoclonic seizures. Also, pretreatment with naloxone (0.1 and 03 mg/kg, i.p.) inhibited the prolongation of myoclonic seizure latency and antagonized the reduction of myoclonic seizure duration induced by thymoquinone (40 and 80 mg/kg) in the PTZ model. Moreover, thymoquinone (40 and 80 mg/kg) did not have any hypnosis effect in the pentobarbital-induced hypnosis, but impaired the motor coordination and reduced the locomotor activity. These results indicate that thymoquinone may have anticonvulsant activity in the petit mal epilepsy probably through an opioid receptor-mediated increase in GABAergic tone.     

Local anesthetics potently block a potential insensitive potassium channel in myelinated nerve

Effects of some local anesthetics were studied in patch clamp experiments on enzymatically demyelinated peripheral amphibian nerve fibers. Micromolar concentrations of external bupivacaine depolarized the excised membrane considerably. The flicker K+ channel was found to be the most sensitive ion channel to local anesthetics in this preparation. Half-maximum inhibiting concentrations (IC50) for extracellular application of bupivacaine, ropivacaine, etidocaine, mepivacaine, lidocaine, and QX-314 were 0.21, 4.2, 8.6, 56, 220, and > 10,000 microM, respectively. The corresponding concentration-effect curves could be fitted under the assumption of a 1:1 reaction. Application from the axoplasmic side resulted in clearly lower potencies with IC50 values of 2.1, 6.6, 16, 300, 1,200, and 1,250 microM, respectively. The log(IC50)-values of the local anesthetics linearly depended on the logarithm of their octanol:buffer distribution coefficients with two regression lines for the piperidine derivatives and the standard amino-amides indicating an inherently higher potency of the cyclic piperidine series. Amide-linked local anesthetics did not impair the amplitude of the single-channel current but prolonged the time of the channel to be in the closed state derived as time constants tau c from closed-time histograms. With etidocaine and lidocaine tau c was 133 and 7.2 ms, and proved to be independent of concentration. With the most potent bupivacaine time constants of wash in and wash out were 1.8 and 5.2 s for 600 nM bupivacaine. After lowering the extracellular pH from 7.4 to 6.6, externally applied bupivacaine showed a reduced potency, whereas at higher pH of 8.2 the block was slightly enhanced. Intracellular pH of 6.4, 7.2, 8.0 had almost no effect on internal bupivacaine block. It is concluded that local anesthetics block the flicker K+ channel by impeding its gating but not its conductance. The slow blocker bupivacaine and the fast blocker lidocaine compete for the same receptor. Lipophilic interactions are of importance for blockade but besides a hydrophobic pathway, there exists also a hydrophilic pathway to the binding site which could only be reached from the cytoplasmic side of the membrane. Under physiological conditions, blockade of the flicker K+ channel which is more sensitive to bupivacaine than the Na+ channel might lead via membrane depolarization and the resulting sodium channel inactivation to a pronounced block of conduction in thin fibers.     

Partition coefficients (n-octanol/water) of N-butyl-p-aminobenzoate and other local anesthetics measured by reversed-phase high-performance liquid chromatography

For the determination of the logarithmic partition coefficients between n-octanol and water (log P_o/w) of local anesthetics, the pH of the aqueous phase needs to be adjusted to high values to ensure that the local anesthetics are in the unionized form. Using the shake-flask or the stir-flask method, this high pH may catalyze hydrolysis, leading to increasing amounts of impurities in time. These impurities exclude non-selective quantification methods like UV spectrometry and require repetitive quantitative analysis of both liquid phases resulting in a tedious and time-consuming method. A rapid reversed-phase HPLC method was developed to measure log P_o/w of the local anesthetics N-butyl-p-aminobenzoate, methyl-p-aminobenzoate, benzocaine, procaine, mepivacaine, prilocaine, lidocaine, bupivacaine, etidocaine, tetracaine and oxubuprocaine.     

Melatonin Accelerates Reentrainment After Phase Advance of the Light-dark Cycle in Syrian Hamsters: Antagonism by Flumazenil

The objective of this study was to assess whether melatonin injections accelerated reentrainment of locomotor activity and body temperature rhythms of Syrian hamsters after phase-advancing the light-dark (L:D) cycle and to what extent the effect can be modified by the benzodiazepine (BZP) receptor antagonist flumazenil. After a baseline recording of rhythms, a 6-h phase advance of the L:D cycle was made (day D). Groups of hamsters were subjected, on days D -2, D -1, and D, to one of the following treatments: two injections of vehicle 15 min apart; vehicle followed 15 min later by melatonin (1 mg/kg); flumazenil (5 mg/kg) followed 15 min later by vehicle; or flumazenil (5 mg/kg) followed 15 min later by melatonin (1 mg/kg). Injections were given at the expected time of lights off after the phase shift. In vehicle-injected and untreated controls, ～ 1 day per hour of phase advance was needed to resynchronize the rhythms. The administration of melatonin brought about a significant decrease of resynchronization time to 66% of vehicle-injected controls. The effect of melatonin was prevented by first administering flumazenil. Flumazenil, injected alone, did not modify resynchronization after the shift. The results agree with the view that melatonin activity on circadian rhythmicity is sensitive to central-type BZP antagonism.     

Protective effect of safranal on pentylenetetrazol-induced seizures in the rat: Involvement of GABAergic and opioids systems

The aim of the present study was to evaluate the effects of safranal, an active constituent of Crocus sativus L. stigmas, on seizures induced by pentylenetetrazol. Intracerebroventricular (i.c.v.) microinjection of safranal (4.84, 9.68 and 24.2 micromol) had no effects on tonic and clonic phases as well as mortality upon seizures induced by PTZ (90mg/kg body wt., i.p.). Peripheral administration of safranal (72.75, 145.5 and 291 mg/kg body wt., i.p.), however, induced a dose-dependent decrease in the incidence of both minimal clonic seizures (MCS) (145.5 mg/kg body wt., p<0.01) and generalized tonic-clonic seizures (GTCS) (145.5 mg/kg body wt., p<0.001) following PTZ administration. Safranal also increased MCS and GTCS latency, significantly. Percent of protection against GTCS was 30%, 100% and 100% and mortality protection percent was 40%, 100% and 100% for the mentioned doses, respectively. Pretreatment with flumazenil (5 nmol, i.c.v.) and naloxone (5.5 nmol, i.c.v. and 2 mg/kg body wt., i.p.), 15 min prior to safranal administration (145.5 mg/kg body wt., i.p.), abolished the protective effect of safranal on MCS. Flumazenil also decreased the effect of safranal on incidence as well as latency of GTCS, significantly. These effects were not, however, significant for naloxone (5.5 nmol, i.c.v. and 2mg/kg body wt., i.p.). Results of this study demonstrated that safranal could exert anticonvulsant activity in the PTZ model and this effect may be mediated, at least partly, through GABA(A)-benzodiazepine receptor complex.     

Melatonin Accelerates Reentrainment After Phase Advance of the Light-dark Cycle in Syrian Hamsters: Antagonism by Flumazenil

The objective of this study was to assess whether melatonin injections accelerated reentrainment of locomotor activity and body temperature rhythms of Syrian hamsters after phase-advancing the light-dark (L:D) cycle and to what extent the effect can be modified by the benzodiazepine (BZP) receptor antagonist flumazenil. After a baseline recording of rhythms, a 6-h phase advance of the L:D cycle was made (day D). Groups of hamsters were subjected, on days D -2, D -1, and D, to one of the following treatments: two injections of vehicle 15 min apart; vehicle followed 15 min later by melatonin (1 mg/kg); flumazenil (5 mg/kg) followed 15 min later by vehicle; or flumazenil (5 mg/kg) followed 15 min later by melatonin (1 mg/kg). Injections were given at the expected time of lights off after the phase shift. In vehicle-injected and untreated controls, ∼ 1 day per hour of phase advance was needed to resynchronize the rhythms. The administration of melatonin brought about a significant decrease of resynchronization time to 66% of vehicle-injected controls. The effect of melatonin was prevented by first administering flumazenil. Flumazenil, injected alone, did not modify resynchronization after the shift. The results agree with the view that melatonin activity on circadian rhythmicity is sensitive to central-type BZP antagonism.     

Evaluation of the Role of Chronic Daily Melatonin Administration and Pinealectomy on Penicillin-Induced Focal Epileptiform Activity and Spectral Analysis of ECoG in Rats: An In Vivo Electrophysiological Study

In the present study, we aimed to investigate the effects of pinealectomy and chronic melatonin administration on focal epileptiform activity induced by penicillin in the rat cortex and to determine the relation between melatonin levels and electrocorticogram (ECoG) power spectrum. For this purpose, male Sprague-Dawley rats were divided into six groups: control, sham operated, ethanol, melatonin, pinealectomy and pinealectomy + melatonin group. Melatonin-treated rats was intraperitoneally injected with a daily single dose of 10 mg/kg melatonin for 14 days, but the last dose was given 30 min after local application of penicillin as a convulsant agent. Focal epileptiform activity was produced by intracortical administration of penicillin (200 units/1 μl). While chronic melatonin application did not affect either the onset latency or the spike frequency of epileptiform activity, pinealectomy significantly reduced latency to onset of initial epileptiform discharges and increased cortical epileptiform activity. However, acute melatonin administration decreased the epileptiform activity. The results also indicated that exogenously applied melatonin did not change the spectral analysis of ECoG, but pinealectomy led to a reduction in the power of the fast bands (gamma) power in ECoG. We conclude that endogenous melatonin signaling seem to have a tonic inhibitory action on neuronal excitability and epileptiform activity, and also a certain concentration of melatonin required for normal cortical excitability.     

The effect of a novel pentadecapeptide BPC 157 on development of tolerance and physical dependence following repeated administration of diazepam

A novel gastric pentadecapeptide BPC 157 with different beneficial activities and anticonvulsant effect interacting with GABAergic system could improve diazepam efficacy coadministered (10 microg/kg, 10 ng/kg i.p.) with diazepam (5.0 mg/kg i.p.) twice daily for 10 days, since diazepam chronic medication would otherwise predispose for diazepam- tolerance/withdrawal development (shorter latency to convulsion after convulsant). In diazepam chronically treated mice, it attenuated diazepam tolerance (provoked by later acute administration of diazepam together with convulsant) and postponed physical dependence/withdrawal effects (provoked by later administration of isoniazid). In tolerance assay, at 42 h after the end of conditioning regimen, shorter preconvulsive latencies than in healthy (non-diazepam conditioned) mice following isoniazid (800 mg/kg i.p.) (as hallmark of tolerance) were observed if diazepam (5.0 mg/kg i.p.) was again given acutely to mice previously conditioned with diazepam alone (use of picrotoxin 3.0 mg/kg i.p., as convulsant, with acute application of diazepam in previously diazepam conditioned mice did not lead to tolerance hallmark). This was completely avoided in diazepam+BPC 157 10 microg or diazepam+BPC 157 10 ng chronically treated animals. In physical dependence assay (isoniazid challenge assessed at 6, 14, 42 and 72 h after conditioning medication), when compared to diazepam non-conditioned healthy mice, in diazepam conditioned mice residual anticonvulsive activity was not present already at the earliest post-conditioning interval (i.e., not different latency to isoniazid-convulsions), whereas shorter preconvulsive latencies (as physical dependence/withdrawal hallmark) were noted in diazepam conditioned mice following isoniazid challenge at 42 h and at 72 h after end of conditioning treatment. In diazepam+BPC 157 10 microg- conditioned mice, a residual anticonvulsive activity (i.e., longer latency to isoniazid convulsion) was noted at 6 h post-conditioning, whereas shorter preconvulsive latencies appeared only at 72 h-post-conditioning period. In conclusion, taken together these data (lack of tolerance development (tolerance studies), prolonged residual anticonvulsive activity, and postponed physical dependence/withdrawal hallmark in diazepam+BPC 157 chronically treated mice) with common benzodiazepines tolerance/withdrawal knowledge, it could be speculated that BPC 157 acts favoring the natural homeostasis of the GABA receptor complex as well as enhancing the GABAergic transmission, and having a mechanism at least partly different from those involved in diazepam tolerance/withdrawal, it may be likely used in further therapy of diazepam tolerance and withdrawal.     

Serotonin mediation of the protective effect of clonidine against pentylenetetrazol-induced seizures in rats

An intraperitoneal injection of 0.5 mg/kg clonidine significantly increased the latency to the first convulsion and reduced tonic seizures and mortality caused by pentylenetetrazol (PTZ), 90 mg/kg, administered subcutaneously to rats. 1 mg/kg clonidine produced similar effects except that tonic seizures were not significantly affected. No effect was observed with 0.01 or 0.1 mg/kg clonidine. Metergoline (1 mg/kg) and methysergide (10 mg/kg), administered intraperitoneally, completely prevented the effect of 0.5 mg/kg clonidine on PTZ-induced seizures. An intraperitoneal injection of 5 mg/kg of d-fenfluramine, a releaser of 5HT from nerve terminals, significantly reduced tonic seizures and completely blocked mortality caused by PTZ but did not significantly modify the latency to the first convulsion. The results suggest that serotonin plays an important role in the protective effect of 0.5 mg/kg clonidine against PTZ-induced seizures. Possible reasons for the different effects of clonidine on different experimental seizures are discussed.