Discriminative stimulus effects of midazolam and abecarnil in rats treated chronically with diazepam or abecarnil

Abecarnil (ABC) is a beta-carboline that acts as an agonist at benzodiazepine (BZD) receptors. It possesses anxiolytic and anticonvulsant properties, but produces little sedation and is without muscle relaxant effects. To explain this unusual profile of activity, two hypotheses have been advanced: either 1) ABC acts as a partial agonist or 2) ABC acts as a full agonist, but only at a sub-population of BZD receptors. The present experiment used cross-tolerance profiles between BZDs and ABC to differentiate these hypotheses based upon predictions of receptor theory: tolerance produced to a full agonist should confer even greater cross-tolerance to a partial agonist. Rats were trained in a three-choice drug discrimination procedure to detect the benzodiazepine, midazolam (MDZ, 1.0 mg/kg) from pentylenetetrazole (PTZ, 20 mg/kg) from saline. Tested acutely, MDZ and ABC substituted for MDZ with similar potencies. Following chronic treatment with the BZD-agonist diazepam (DZP; 20 mg/kg per 8 h for 7 days), both the MDZ and ABC dose-effect curves were significantly shifted to the right, and both drugs showed a comparable three-fold decrease in potency. The chronic administration of ABC (4.0 mg/kg per 8 h for 7 days) produced a different spectrum of results. No significant shift occurred in the MDZ dose-effect curve, but there was a significant seven-fold shift to the right of the ABC dose-effect curve. Throughout all tests, PTZ-lever responding rarely occurred and did not account for more than 20% of lever selections for any individual test. These data support the hypothesis that ABC acts as a full agonist at a sub-population of BZD receptors, which mediate its substitution for MDZ.     

Differential pharmacological reactivity of aversion induced by stimulation of periaqueductal gray or mesencephalic locomotor region

Rats were trained to switch-off aversive electrical brain stimulations applied to the periaqueductal gray (PAG) or mesencephalic locomotor region (MLR) by pressing a bar (switch-off behavior). We investigated the effects of IP injections of the benzodiazepine (BZ) receptor inverse agonist FG 7142 (2.5, 5, 10 mg/kg) or BZ receptor agonist chlordiazepoxide (CDP: 5 mg/kg) on the switch-off latency, i.e., the time elapsed between the onset of the stimulation and its offset by a press of the bar. It was found that FG 7142 decreased, whereas CDP increased the mean switch-off latency for electrical stimulation of the PAG, which is interpreted as a potentiating effect of FG 7142 and a reducing effect of CDP on the electrically induced aversive state. By contrast, neither FG 7142 nor CDP were found to affect the mean switch-off latency for MLR stimulations. These results suggest a difference in the pharmacological sensitivity to BZ receptor ligands between aversive states elicited by electrical stimulation of the PAG or MLR.     

Ethopharmacological analysis of the unstable elevated exposed plus maze,a novel model of extreme anxiety: predictive validity and sensitivity to anxiogenic agents

RATIONALE AND OBJECTIVES: The unstable elevated exposed plus maze (UEEPM) has been proposed as a novel model of anxiety which elicits unconditioned escape-related behaviour in rats thought to mimic the persistent "fight/flight" state exhibited by patients suffering from extreme anxiety disorders. This study investigated the predictive validity of the UEEPM by examining the behaviour of rats exposed to the test following administration of drugs known to induce panic and anxiety in panic disorder and post-traumatic stress disorder patients, namely m-chlorophenylpiperazine (mCPP), caffeine and yohimbine. The sensitivity of the UEEPM to two further putative anxiogenic agents, the benzodiazepine partial inverse agonist FG 7142 and pentylenetetrazole (PTZ), was also assessed. METHODS: Male Hooded Lister rats received a single dose of mCPP (0.5-2.0 mg/kg; ip), caffeine (3.0-30.0 mg/kg; ip), yohimbine (1.25-5.0 mg/kg; ip), FG 7142 (3.0-30.0 mg/kg; ip) or PTZ (3.0-30.0 mg/kg; ip) before being exposed to the UEEPM for a period of 5 min. Subjects' behaviour was analysed to determine the effects of each compound on unconditioned escape. RESULTS: mCPP (1.0 and 2.0 mg/kg), caffeine (30 mg/kg), FG 7142 (3.0 and 30.0 mg/kg) and PTZ (30.0 mg/kg) significantly increased animals' propensity to escape from the UEEPM, i.e. they had a clear anxiogenic effect, whilst yohimbine had no effect on escape. CONCLUSIONS: The UEEPM is sensitive to the behavioural effects of anxiogenic agents. Furthermore, pharmacological similarities exist between symptoms of panic and anxiety in patients and escape from the UEEPM in rats. The UEEPM may therefore represent a paradigm to facilitate investigation into the neurochemical basis of extreme anxiety disorders.     

Behavioral and genotoxic evaluation of rosmarinic and caffeic acid in acute seizure models induced by pentylenetetrazole and pilocarpine in mice

The goal of this study was to investigate the effects of rosmarinic acid (RA) and caffeic acid (CA) in the acute pentylenetetrazole (PTZ) and pilocarpine (PIL) seizure models. We also evaluated the effect of RA and CA on the diazepam (DZP)-induced sleeping time test and its possible neuroprotective effect against the genotoxic damage induced by PTZ and PIL. Mice were treated intraperitoneally (i.p.) with saline, RA (2 or 4 mg/kg), or CA (4 or 8 mg/kg) alone or associated to low-dose DZP. After, mice received a single dose of PTZ (88 mg/kg) or PIL (250 mg/kg) and were monitored for the percentage of seizures and the latency to first seizure (LFS) >3 s. Vigabatrin and DZP were used as positive controls. In the DZP-induced sleeping time test, mice were treated with RA and CA and 30 min after receiving DZP (25 mg/kg, i.p.). The alkaline comet assay was performed after acute seizure tests to evaluate the antigenotoxic profiles of RA and CA. The doses of RA and CA tested alone did not reduce the occurrence of seizures induced by PTZ or PIL. The association of 4 mg/kg RA + low-dose DZP was shown to increase LFS in the PTZ model, compared to the group that received only the DZP. In the DZP-induced sleeping time test, the latency to sleep was reduced by 4 mg/kg RA and 8 mg/kg CA. The PTZ-induced genotoxic damage was not prevented by RA or CA, but the PIL-induced genotoxic damage was decreased by pretreatment with 4 mg/kg RA (in cortex) and 4 mg/kg CA (in hippocampus). In conclusion, RA and CA presented neuroprotective effect against PIL-induced genotoxic damage and reduced the latency to DZP-induced sleep. Of the rosmarinic acid, 4 mg/kg enhanced the DZP effect in the increase of latency to clonic PTZ-induced seizures.     

A behavioral and electrocorticographic comparison of diazepam and pentylenetetrazol in rat pups

This experiment assessed the possibility suggested by previous research that benzodiazepines cause convulsions in infant rats. Seven-day-old Wistar rats were randomly assigned to receive either diazepam (DZP) (0, 0.5 or 2.5 mg/kg), the convulsogen pentylenetetrazol (PTZ) (50 mg/kg), or DZP followed 30 minutes later by PTZ. The amount of paddling and wall progression and head and body tremors was recorded for each group. Both DZP and PTZ elevated paddling and wall progression, but only PTZ elevated head and body tremor scores. DZP antagonized the PTZ-induced increases in head and body tremors. In a second experiment, seven-day-old pups were implanted with cortical electrodes. The following day, baseline electrocorticograms (ECoGs) were taken for each animal. Each pup subsequently received either DZP vehicle, 0.5 mg/kg DZP, 50 mg/kg PTZ, or 0.5 mg/kg DZP followed 30 minutes later by 50 mg/kg PTZ. Neither the vehicle nor the DZP injections altered ECoG activity. In contrast, PTZ-treated pups showed continuous, high-amplitude, spiking activity. Pretreatment with DZP eliminated these PTZ-induced alterations in ECoG activity. We conclude that in infant rats, the behavioral and electrophysiological effects of DZP and PTZ are distinct from one another. Furthermore, both the behavioral and the electrocorticographic effects of PTZ are blocked by DZP. It is unlikely that DZP causes seizures in neonatal rats.     

Assessment of zolpidem and Cl-966 for anxiolytic and anxiogenic properties by using the discrimination of pentylenetetrazole by rats

This experiment determined if two novel compounds, zolpidem and CI-966, would show anxiogenic or anxiolytic activity in an animal model of anxiety based upon the discrimination of pentylentetrazole (PTZ). Rats were trained to detect the anxiogenic drug PTZ, 20 mg/kg, and tested with zolpidem (an agonist at omega [benzodiazepine] receptors) and CI-966 (a GABA-uptake inhibitor). Zolpidem did not substitute for PTZ. This drug blocked the PTZ stimulus in a dose-related manner (0.32–5.0 mg/kg), although only partial blockade was obtained even at the highest dose that could be tested. These data suggest that zolpidem may have weak efficacy as an anxiolytic drug. CI-966 partially substituted for PTZ at 3 to 6 hr post injection of doses of 16.0 and 32.0 mg/kg. Lower doses of CI-966 produced a slight, but non-significant, blockade of the PTZ stimulus, which appeared to be additive with the blocking effects of diazepam upon this discrimination. Because CI-966 has been shown to block PTZ seizures in mice, the present data suggest that the discriminative stimulus produced by PTZ is not related to its ability to produce convulsions. The partial substitution of CI-966 given in high doses is consistent with clinical reports that this compound may produce anxiogenic effects.     

Inverse agonist properties of the FG 7142 discriminative stimulus.

A two-lever, food-motivated discrimination was established between the benzodiazepine receptor partial inverse agonist FG 7142 (5.0 mg/kg) and its vehicle. The FG 7142 discriminative stimulus was pharmacologically characterized by testing trained rats with a variety of benzodiazepine receptor ligands. Administration of the inverse agonist DMCM (0.15-0.30 mg/kg) dose-dependently mimicked the FG 7142 stimulus. In contrast, the benzodiazepine receptor agonist chlordiazepoxide, partial agonist ZK 91 296, mixed agonist/antagonist CGS 9896 and antagonist RO 15-1788 blocked the FG 7142 cue. These results indicate that the FG 7142 discriminative stimulus is based on its inverse agonist activity. The generalization of FG 7142 to the anxiogenic/convulsant compound pentylenetetrazole (PTZ), but not to the anorectic agent norfenfluramine, indicates that the anxiogenic properties of FG 7142, rather than its anorectic actions, may underlie the FG 7142 discriminative stimulus.     

The long-term effects of diazepam and pentylenetetrazol on the potentiated startle response

Stress desensitization is observed as a decrease in the disruptive effects of a stressor on behavior when the organism is repeatedly exposed to the stressor. For instrumental behavior, stress desensitization was also reported for rats preexposed to anxiogenic drugs; stress sensitization was reported for rats preexposed to an anxiolytic compound. The present study investigated whether similar effects are found in a noninstrumental task situation. First, rats received 12 daily injections of pentylenetetrazol (PTZ, 20 mg/kg, IP), diazepam (DZP, 5 mg/kg, IP) or saline. After each injection the effect of the drugs on the acoustic startle reflex was measured. No drugs were given during the remainder of the experiment. Eight days later rats were given 5 days of Pavlovian fear conditioning to establish a light as a shock signal. During the next 3 days, potentiation of the startle response by the light was measured. None of the drug treatments had an effect on startle potentiation, indicating that stress sensitivity is not affected by previous administration of PTZ and DZP in a noninstrumental task. An explanation for the different effects found for instrumental and noninstrumental tasks is suggested.     

The influence of diazepam on learning processes impaired by pentylenetetrazol kindling

Repeated administration of pentylenetetrazol (PTZ) induces kindling and impairs shuttle-box learning. The available literature suggesting a close connection between seizure frequency and mental deficits in human epileptics allows us to hypothesize that seizure inhibition prevents the progressive mental retardation associated with kindling. In order to investigate the effect of motor seizure inhibition on mental impairment we administered diazepam (DZP) doses of 0.5 and 2.5 mg/kg, respectively 60 min prior to the 10 convulsant injections. After completion of kindling the learning performance of the rats was tested in the shuttle-box. PTZ kindling resulted in diminished shuttle-box learning. In control rats treated with DZP no significant changes in their learning ability occurred. Although DZP was found to suppress kindling development effectively a worsened shuttle-box learning could be observed in all PTZ groups treated with DZP. Correspondence to: A. Becker at the above address     

Effects of social defeat and of diazepam on behavior in a resident-intruder test in male DBA/2 mice

Social stress induces robust behavioral and physiological changes, some of which may alter the responsiveness to pharmacological agents, including diazepam (DZP). We used a resident-intruder paradigm to (1) develop a comprehensive ethogram of behavioral changes following social defeat (SD) in the socially reactive strain, DBA/2 male mice, (2) determine whether acute exposure of DBA/2 mice to low-dose DZP would induce flight or aggressive behavior, both of which have been observed in other rodent models and (3) to test whether prior social stress affects responses to DZP. Behavioral responses to a nonaggressive intruder (NAI) mouse 24 h post-SD were measured in resident subject mice exposed to DZP (0, 0.5, 2.0 mg/kg, ip) either prior to the resident-intruder test (Experiment 1) or immediately post-SD (Experiment 2); control mice were not defeated (NOSD). In general, SD mice displayed increased passive and active avoidance, defense, immobility, and risk assessment relative to NOSD mice. In Experiment 1, mice treated acutely with 0.5 mg/kg DZP had more approach and flight behavior, while those treated with 2.0 mg/kg DZP had more avoidance than vehicle-treated mice, independent of SD. In Experiment 2, acute DZP (2 mg/kg) induced effects 24 h later, possibly secondary to withdrawal. In a nonsocial context (Experiment 3), DZP increased exploratory activity.     

Effects of fluoxetine on hippocampal rhythmic slow activity and behavioural inhibition

Anxiolytics that act as GABAA agonists and those that act as 5-HT1A receptor agonists all reduce the frequency of hippocampal rhythmic slow activity (RSA). Changes in RSA have been linked to changes in behavioural inhibition and therefore anxiety - but this has not been tested with specific serotonin reuptake inhibitors, which are antidepressant and anxiolytic; therefore we tested the effects of fluoxetine on RSA and behavioural inhibition. Fluoxetine (FLU; 10 and 20 mg/kg, intraperitoneally) produced a dose-related reduction in the frequency of reticular-elicited RSA. Groups of rats received, intraperitoneally, either (i) saline, or 5 mg/kg fluoxetine, or 10 mg/kg fluoxetine; or (ii) saline, or 20 mg/kg fluoxetine, or 6.6 mg/kg of the 5-HT1A agonist buspirone (BUS) and were tested on a fixed interval 60-s schedule and a differential reinforcement of low rates 15-s schedule. FLU at 5 mg/kg produced effects similar to low doses of BUS and other anxiolytics. FLU (10 and 20 mg/kg) produced effects more like those reported earlier for higher doses of BUS. These results continue to link anxiolysis, RSA and behavioural inhibition, and suggest that serotonergic anxiolytics share some of the central actions of GABAergic anxiolytics, but at higher doses, administered acutely, have distinct side effects that can obscure their anxiolytic action in behavioural tasks.     

Fluoxetine-induced anxiety and nervousness

The aim of this study was to model fluoxetine-induced increase in anxiety appearing in the initial phase of the treatment with this antidepressant drug. The effects of acute administration of fluoxetine given alone and co-administered with a subthreshold dose of pentetrazole (PTZ), a proconvulsant agent with well recognized anxiogenic properties, were examined in the open field test of neophobia in rats. It was found that a single injection of fluoxetine at the dose of 5 and 10 mg/kg did not change motor and exploratory behavior of rats. Furthermore, fluoxetine (10.0 mg/kg) co-administered with a subthreshold dose of PTZ (10.0 mg/kg) had a strong and selective inhibitory influence on rat exploratory behavior. Pharmacokinetic study did not show any changes in brain concentration of PTZ in fluoxetine-pretreated animals. The central mechanism of the reported effects might involve stimulation of 5-HT2C receptors by fluoxetine in animals with PTZ-induced decrease in the threshold for emotional arousal. The present data describe a new animal model to study the central action of antidepressants reflecting dysphoric-like effects observed in the initial phase of the treatment.     

A behavioural and pharmacological evaluation of the discriminative stimulus induced by pentylenetetrazole in the pig

The anxiogenic nature of the interoceptive discriminative stimulus induced by pentylenetetrazole (PTZ) was investigated by examining the discriminatory behaviour of PTZ conditioned pigs during a conditioned emotional response (CER). A CER was induced in a non-operant situation, by pairing a tone stimulus with the application of a mild, non-injurious electric shock. Subsequent presentation of the conditioned tone stimulus alone produced a generalisation to the PTZ cue. This generalisation of the conditioned emotional state (CES) to the PTZ cue was antagonised by pretreatment with diazepam (0.5 mg/kg, PO; 30 min). The PTZ stimulus was also antagonised by diazepam (0.5 mg/kg, PO; 30 min) but not by an anticonvulsant dose of ethosuximide (30 mg/kg, PO; 1–3 h), providing further confirmation of the anxiogenic nature of the PTZ cue. Our results demonstrate the validity of the PTZ discrimination paradigm in pigs as a test of anxiety.     

Anxiogenic beta-carboline FG 7142 produces activation of noradrenergic neurons in specific brain regions of rats.

By measuring the levels of two major metabolites of rat brain noradrenaline (NA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), we investigated the effects of anxiogenic beta-carboline FG 7142, an inverse agonist of benzodiazepine (BZD) receptors, on brain noradrenergic activity of rats. Thirty min after treatment with FG 7142 (15 mg/kg IP), levels of both MHPG and DHPG in the hypothalamus, amygdala and thalamus, but not in the hippocampus and cerebral cortex, significantly increased. These increases were significantly antagonized by pretreatment with BZD receptor antagonist Ro 15-1788 (15 mg/kg, IP). Sixty min after treatment with FG 7142 at the same dose, significant increases in both metabolite levels occurred in the hypothalamus, amygdala, thalamus and cerebral cortex, and increases in MHPG levels only were observed in the hippocampus. These increases were significantly blocked by pretreatment with alpha 2-adrenoreceptor agonist clonidine (100 microgram/kg, IP). The present findings suggest that FG 7142 can produce increases in brain noradrenergic activity in specific brain regions by interacting with BZD receptors, and may support the hypothesis that hyperactivity of brain noradrenergic systems may be one neural mechanism in provocation of aversive emotional changes (anxiety, fear or panic).     

Anti-seizure efficacy of nimodipine in pentylenetetrazole and kainic acid combined seizure models in mice

The present study aimed at establishing two models of experimental seizures by combination treatment with subconvulsive doses of PTZ and kainic acid in adult male mice and evaluating the modulatory role of cerebroselective dihydropyridine calcium channel blocker, nimodipine. The CD50 +/- SEM value for PTZ was found to be 20.00 +/- 0.92 mg/kg, ip in kainic acid (administered at per se subconvulsive dose of 1.00 mg/kg, ip) pretreated mice while CD50 +/- SEM value for kainic acid was found to be 0.30 +/- 0.08 mg/kg, ip in PTZ (administered at per se subconvulsive dose of 30.00 mg/kg, ip) pretreated mice. Nimodipine (5.00 mg/kg, ip) significantly protected the mice from seizure in both of the combination in vivo seizure models. The results suggested synergistic interaction between PTZ and kainic acid at subconvulsive dose combination while the protective efficacy of nimodipine suggested the role of calcium ion as an important mediator for the genesis of seizures.     

Evidence for noradrenergic involvement in mediating the FG 7142 discriminative stimulus.

Rats were trained to discriminate the stimulus properties of the benzodiazepine receptor partial inverse agonist beta-carboline-3-carboxylate acid methyl amide (FG 7142) (5.0 mg/kg) or the alpha 2-adrenergic receptor antagonist 17 alpha-hydroxyyohimban-16 alpha-carboxylic acid methyl ester (yohimbine) (3.0 mg/kg) from vehicle in a two-lever, food-motivated operant task. These compounds have in common a beta-carboline structure and anxiogenic behavioral profiles. The yohimbine discriminative stimulus was mimicked by the alpha 2-adrenergic receptor antagonist idazoxan and antagonized by the alpha 2-adrenergic receptor agonist clonidine, indicating that the yohimbine stimulus was mediated through the alpha 2-adrenergic receptor. The anxiogenic beta-carbolines FG 7142, 1,2,3,4-tetrahydro-beta-carboline (THBC), and norharmane, the anxiogenic/convulsant agent pentylenetetrazole (PTZ), and two physiological stressors failed to mimic the yohimbine discriminative stimulus. In contrast, both yohimbine and idazoxan dose responsively mimicked the anxiogenic FG 7142 stimulus. The present results demonstrate that an asymmetrical generalization exists between the discriminative stimuli produced by yohimbine and FG 7142. Furthermore, these data suggest that yohimbine can produce a multicomponent discriminative stimulus, part of which may be anxiogenic in nature. The ability of alpha 2-adrenergic receptor antagonists to mimic the FG 7142 cue suggests that activation of the noradrenergic system may underlie cues produced by benzodiazepine receptor inverse agonists.     

Discriminative stimulus properties of β-carbolines characterized as agonists and inverse agonists at central benzodiazepine receptors

The discriminative stimulus properties of three -carboline derivatives were studied in three groups of rats trained, respectively, to discriminate diazepam (2.5 mg/kg IP), chlordiazepoxide (CDP, 5 mg/kg IP) or pentylenetetrazol (PTZ, 15 mg/kg IP) from saline in standard procedures employing two-lever operant chambers. Two -carbolines, ZK 91296 and ZK 93423, substituted for the benzodiazepines in both CDP- and diazepam-trained rats. The neutral benzodiazepine antagonist Ro 15-1788 blocked the diazepam discriminative stimulus and the ability of ZK 91296 to substitute for diazepam. A third -carboline, FG 7142, was not identified as benzodiazepine-like in generalization tests in either diazepam- or CDP-trained rats, but when administered together with CDP antagonized the benzodiazepine discriminative stimulus. In rats trained to discriminate PTZ from saline (a discrimination which is thought to depend on the anxiogenic properties of PTZ) the PTZ cue was antagonized by diazepam and ZK 93423, and partially antagonized by ZK 91296. The PTZ cue generalized to FG 7142 and this generalization was partially antagonized by Ro 15-1788. These results suggest that the three -carbolines provide more than one kind of discriminative stimulus, consistent with the classification of ZK 93423 as an agonist at central benzodiazepine receptors, with ZK 91 296 as a partial agonist, and with FG 7142 as an inverse agonist. Pharmacologically, ZK 93 423 and ZK 91 296 may exhibit anxiolytic qualities, whereas FG 7142 produces anxiogenic effects.     

Acute or chronic effects of cannabinoids on spontaneous or pharmacologically induced yawning in rats

Yawning is a reflex or event that is not fully understood. It is controlled by many neurotransmitters and neuropeptides and can be induced pharmacologically by cholinergic or dopaminergic agonists. Amongst their many actions, cannabinoids acting on cannabinoid (CB(1) or CB(2)) receptors can alter cholinergic and/or dopaminergic activity. This study examined the effects of Delta(8)-tetrahydrocannabinol (Delta(8)-THC) administered acutely (2.5 mg/kg intraperitoneally [ip], 15 min before test) or chronically (5 mg/kg for 30 days followed by 24 h or 7 days of discontinuation) on yawning induced by pilocarpine, a cholinergic agonist (0, 1, 2, 4 or 8 mg/kg ip), or apomorphine, a dopaminergic agonist (0, 20, 40 or 80 microg/kg subcutaneously [sc]). Acute effects of different doses of Delta(9)-tetrahydrocannabinol (Delta(9)-THC: 0, 0.5, 1.25 or 2.5 mg/kg ip) on yawning induced by pilocarpine (2 mg/kg ip) or apomorphine (40 microg/kg sc) were also investigated. Both pilocarpine and apomorphine produced yawning in a dose-related manner. Acute administration of Delta(8)-THC and Delta(9)-THC significantly reduced yawning induced by both pilocarpine and apomorphine. Chronic administration of Delta(8)-THC did not change yawning induced by either agonist 24 h or 7 days after discontinuation of Delta(8)-THC. However, a high frequency of spontaneous yawning was observed 7 days after Delta(8)-THC discontinuation. These results suggest that cannabinoid agonists inhibited yawning induced by cholinergic or dopaminergic agonists. In addition, the increased frequency of spontaneous yawning following cessation of chronic administration of a cannabinoid agonist may be of importance as a withdrawal sign for these drugs.     

Hesperidin potentiates the neuroprotective effects of diazepam and gabapentin against pentylenetetrazole-induced convulsions in mice: Possible behavioral,biochemical and mitochondrial alterations

Aim:

Epilepsy is a chronic neurological disorder with complex pathophysiology. Several evidences suggest a role of oxidative stress and mitochondrial dysfunction in pathophysiology of epilepsy. Hesperidin (Hesp) acts as a powerful anti-oxidant agent against superoxide, singlet oxygen, and hydroxyl radicals. Thus, this study was undertaken to evaluate the possible neuroprotective mechanism of Hesp against pentylenetetrazole (PTZ)-induced convulsions in mice.

Materials and Methods:

Sixty males Laca mice (20-25 g) were randomly divided into 10 treatment groups (n = 6). Seven days pretreatment of Hesp (100, 200 mg/kg, p.o.) was carried out before PTZ (80 mg/kg, intraperitoneal [i.p.]) challenge, whereas diazepam (DZP) (0.2, 0.5 mg/kg) and gabapentin (Gbp) (10, 20 mg/kg) were administered i.p. 30 min before PTZ administration, that is, on 7^th day. Following PTZ challenge, severity of convulsions (onset of jerks, myoclonic seizures, extensor phase and death), brain anti-oxidant enzyme levels and mitochondrial complex enzymes activities were estimated.

Results:

Single i.p. PTZ (80 mg/kg) challenge demonstrated severe convulsions, oxidative damage (raised lipid peroxidation [LPO], nitrite concentration as well as depleted reduced glutathione, superoxide dismutase and catalase levels), and depletion of mitochondrial enzyme Complex (I, II, IV) activities. Hesp (200 mg/kg), DZP (0.5 mg/kg) and Gbp (20 mg/kg) pretreatments attenuated PTZ induced behavioral, biochemical and mitochondrial alterations. However, administration of Hesp (100 mg/kg) in combination with DZP (0.2 mg/kg) or Gbp (10 mg/kg) potentiated their neuroprotective effect, which was significant as compared to their effects in PTZ treated animals.

Conclusion:

Hesp possesses potent anticonvulsant activity which might be mediated through modulation of gamma-amino butyric acid/benzodiazepine receptor action.KEY WORDS: Mitochondrial dysfunction, myoclonic jerks, oxidative stress, seizure     

Adenosinergic mechanisms in anticonvulsant action of diazepam and sodium valproate

The effects of adenosine receptor agonists and antagonists were studied in pentylenetetrazole (PTZ)-induced seizures in rats. Animals were pretreated with the non-specific adenosine receptor antagonist, theophylline (50 and 100 mg/kg, i.p.), or the specific A₁ adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), in a dose of 1 mg/kg, i.p., followed by 100% anticonvulsant doses of diazepam (4 mg/kg)/sodium valproate (300 mg/kg, i.p.). Subsequently, they were challenged with convulsant doses of PTZ i.e. 60 mg/kg, i.p. It was seen that while DPCPX could not reverse the protection of both the antiepileptic drugs, theophylline significantly reversed this protection, as assessed by percent incidence of seizures and change in latency parameters. In another set of experiments, the rats were pretreated with a combination of subanticonvulsant doses of adenosine (500 mg/kg) or specific adenosine A₁ receptor agonist, cyclopentyladenosine (CPA) and diazepam (0.5 and 1 mg/kg)/sodium valproate (150 mg/kg), prior to PTZ challenge. We observed a decrease in incidence and increase in latency of seizures following either combination. The protection observed was independent of the hypothermic and hypotensive effects of adenosine and CPA. These results indicate that though A₁ agonist enhances the protection of diazepam and sodium valproate, a direct involvement of adenosine A₁ receptor in anticonvulsant action of these drugs is doubtful.