Effects of enadoline on the development of pentylenetetrazol kindling, learning performance, and hippocampal morphology

Effect of U50488, a selective kappa opioid receptor agonist and levetiracetam against lithium-pilocarpine-induced status epilepticus, spontaneous convulsive seizures and related cognitive impairment

PURPOSE

Kappa opioid receptor (KOR) agonists have anticonvulsant effect but their antiepileptogenic effect is unknown. U50488, a selective KOR agonist is used to determine its effect on status epilepticus (SE), spontaneous convulsive seizures (SS) and cognitive impairment in rat lithium-pilocarpine SE model. Effect of an antiepileptic drug levetiracetam is also studied.

METHOD

Male Wistar rats with SE were divided into three groups namely, LiP, LiP + U50488 (10 mg/kg, i.p.) and LiP + levetiracetam (400 mg/kg, i.p.) group. SE was terminated after 90 min of its onset with diazepam (15 mg/kg, i.p.) and phenobarbitone (25 mg/kg, i.p.). Drug treatment was started after 15 min of onset of SE and repeated once after 4 h. Rats were video monitored 12 h daily (9 AM to 9 PM) to determine severity of SE using modified Racine scale and onset and frequency of SS from day 0 to day 21. Morris water maze (MWM) test was done at baseline i.e. day -1 (before lithium administration) and day 22, to assess cognitive impairment.

RESULTS

As compared to LiP, U50488 decreased the severity of SE (1.98 ± 0.13 vs 2.95 ± 0.12; p-value < 0.0001) but not levetiracetam (2.62 ± 0.09; p-value = 0.3112). Survival increased with both U50488 (90%, n = 10) and levetiracetam (81.8%, n = 11) as compared to NS (56.2%, n = 16). No effect on onset and frequency of SS was found in U50488/levetiracetam group. U50488 improved seizures-induced cognitive impairment. Levetiracetam group showed thigmotactic (wall hugging) behaviour in MWM in 8 out of 9 rats.

CONCLUSION

Acute treatment with U50488, a kappa opioid receptor agonist has a beneficial effect on SE, SE-related mortality and memory impairment. The dual protective effect of U50488 on seizures and related cognitive impairment is advantageous over currently used antiseizure drugs which are known to cause cognitive impairment.

Salvinorin A Does Not Affect Seizure Threshold in Mice

The κ-opioid receptor has recently gained attention as a new molecular target in the treatment of many psychiatric and neurological disorders including epilepsy. Salvinorin A is a potent plant-derived hallucinogen that acts as a highly selective κ-opioid receptor agonist. It has unique structure and pharmacological properties, but its influence on seizure susceptibility has not been studied so far. Therefore, the aim of the present study was to investigate the effect of salvinorin A on seizure thresholds in three acute seizure tests in mice. We also examined its effect on muscular strength and motor coordination. The obtained results showed that salvinorin A (0.1-10 mg/kg, i.p.) did not significantly affect the thresholds for the first myoclonic twitch, generalized clonic seizure, or forelimb tonus in the intravenous pentylenetetrazole seizure threshold test in mice. Likewise, it failed to affect the thresholds for tonic hindlimb extension and psychomotor seizures in the maximal electroshock- and 6 Hz-induced seizure threshold tests, respectively. Moreover, no changes in motor coordination (assessed in the chimney test) or muscular strength (assessed in the grip-strength test) were observed. This is a preliminary report only, and further studies are warranted to better characterize the effects of salvinorin A on seizure and epilepsy.

Anticonvulsant Effects of Aerial Parts of Verbena officinalis Extract in Mice: Involvement of Benzodiazepine and Opioid Receptors

To evaluate the anticonvulsant activity of the aerial parts of Verbena officinalis used traditionally by local Iranians for the treatment of convulsion. The anticonvulsant activity of the extract was assessed in pentylenetetrazole (PTZ) and maximal electroshock (MES) induced seizures in mice. Diazepam was used as reference drug. In addition, for investigating the mechanism of V officinalis in PTZ model, flumazenil and naloxone were injected before V officinalis. The extract showed no toxicity and significantly increased the period taken before the onset and decreased the duration of the seizures induced by PTZ. In the MES test, V officinalis displayed significant reduction in hind limb tonic extension duration in a dose-dependent manner. The results propose that V officinalis ethanolic extract has anticonvulsant activity against seizure. It seems that these effects may be related to potentiating of GABAergic system. Moreover, this study supports the use of this plant by local Iranians in order to treat convulsion.

Garcinol Upregulates GABAA and GAD65 Expression, Modulates BDNF-TrkB Pathway to Reduce Seizures in Pentylenetetrazole (PTZ)-Induced Epilepsy

BACKGROUND Epilepsy is the most predominant neurological disorder characterized by recurrent seizures. Despite treatment with antiepileptic drugs, epilepsy still is a challenge to treat, due to the associated adverse effects of the drugs. Previous investigations have shown critical roles of BDNF-TrkB signalling and expression of glutamic acid decarboxylase 65 (GAD65) and GABAA in the brain during epilepsy. Thus, drugs that could modulate BDNF-TrkB signal and expression of GAD65 and GABAA could aid in therapy. Recent experimental data have focussed on plant-derived compounds in treatments. Garcinol (camboginol), is a polyisoprenylated benzophenone derived from the fruit of Garcinia indica. We investigated the effects of garcinol in pentylenetetrazole (PTZ)-induced epileptic models. MATERIAL AND METHODS Seizure scores were measured in epilepsy kindled mice. Neuronal degeneration and apoptosis were assessed by Nissl staining, TUNEL assay, and Fluoro-Jade B staining. Immunohistochemistry was performed to evaluate cleaved caspase-3 expressions. Expression of BDNF, TrkB, GABAA, GAD65, Bad, Bcl-2, Bcl-xL, and Bax were determined by western blots. RESULTS Significantly reduced seizure scores and mortality rates were observed with pretreatment with garcinol. Elevated expression of apoptotic proteins and caspase-3 in kindled mice were effectively downregulated by garcinol. Epileptogenic mice presented increased BDNF and TrkB with considerably decreased GABAA and GAD65 expression. Garcinol significantly enhanced GABAA and GAD65 while it suppressed BDNF and TrkB. Garcinol enhanced the performance of mice in Morris water maze tests. CONCLUSIONS Garcinol exerts neuroprotective effects via supressing apoptosis and modulating BDNF-TrkB signalling and GAD65/GABAA expressions and also enhanced cognition and memory of the mice.

Methanol extract of Ficus platyphylla ameliorates seizure severity, cognitive deficit and neuronal cell loss in pentylenetetrazole-kindled mice

Decoctions of Ficus plathyphylla are used in Nigeria's folk medicine to manage epilepsy for many years and their efficacies are widely acclaimed among the rural communities of Northern Nigeria. In this study, we examined the ameliorative effects of the standardized methanol extract of Ficus platyphylla (FP) stem bark on seizure severity, cognitive deficit and neuronal cell loss in pentylenetetrazole-kindled mice. The (35)S-GTPγS, glutamate and γ-aminobutyric acid receptors binding properties of the extract were also evaluated. Male CD-1 mice were kindled with an initial subeffective dose of pentylenetetrazole (PTZ, 37.5mg/kg, i.p.) for a total of 13 convulsant injections and the treatment groups concurrently received FP (100 and 200mg/kg). Control animals received the same number of saline injections. Twenty-four h after kindling completion the animals' learning performance was tested in a two-way shuttle-box. The animals were challenged with another subeffective dose of PTZ (32.5mg/kg, i.p.) on day 7 after kindling completion. Animals were sacrificed a day after the challenged experiment and the brains were processed for histological investigation. FP ameliorates seizure severity, cognitive deficits and neuronal cell loss in PTZ kindled mice. Components of the extract showed affinity for GABAergic and glutamatergic receptors. Glutamate release was diminished and the (35)S-GTPγS binding assay revealed no intrinsic activity at glutamatergic receptors. Our results revealed that FP contains psychoactive secondary metabolites with anticonvulsant properties, thus supporting the isolation and development of the biologically active components of this medicinal plant as antiepileptic agents.

Effect of minocycline on pentylenetetrazol-induced chemical kindled seizures in mice

Inflammation is one of the mechanisms involved in seizure induction. In this study, the effect of minocycline, an anti-inflammatory drug, was investigated on kindling acquisition. Chemical kindling was induced by injection of a subthreshold dose of pentylenetetrazol (PTZ; 37.5 mg/kg) in mice on every other day. Two groups of animals received minocycline (25 mg/kg) at 1 h before or 1 h after PTZ injection. Following the last PTZ injection, the changes in gene expression of TNF-α receptor, γ2 subunit of GABAA receptor and NR2A subunit of NMDA receptor were assessed in the hippocampus and piriform cortex. Injection of minocycline before PTZ increased the latency to stage 4 seizure, and decreased the duration of stages 4 and 5 seizure. It also prevented the increase in the mRNA of NR2A subunit of NMDA receptor in the hippocampus and removed the PTZ-induced increase in mRNA of γ2 subunit of GABAA receptor in piriform cortex of PTZ kindled mice. Minocycline also prevented the increase in TNF-α receptor gene expression in both hippocampus and piriform cortex. Injection of minocycline after PTZ had no significant effect on measured parameters. Therefore, it can be concluded that minocycline may exert an anticonvulsant effect through preventing the increase in GABAA and NMDA receptor subunits. These effects are accompanied by a reduction in an important inflammation index, TNF-α receptor.

A single pentylenetetrazole-induced clonic-tonic seizure episode is accompanied by a slowly developing cognitive decline in rats

According to different studies, between 5% and 10% of people suffer a single isolated seizure episode at some time in their life. However, little is known about the effects of a single seizure episode on cognitive function, and clinical investigations of this issue are not easy to perform. In this situation, animal models may be a reasonable choice. The aim of our study was to follow the time course of delayed effects of generalized clonic-tonic convulsions on learning and memory functions in rats. A clonic-tonic seizure episode was induced by a single i.p. injection of pentylenetetrazole (70 mg/kg). Different behavioral tests were performed between days 10 and 100 after the convulsant administration. A single seizure episode resulted in a gradual decline in short-term memory function as assessed by novel object recognition and social recognition tests. The seizure episode induced a quick increase in hippocampal cell proliferation; however, the excessive newly generated cells seemed to be eliminated by the time of obvious cognitive impairment. These observations are indicative of a slowly developing and long-lasting influence of a single seizure episode on cognitive function. A rather long time period between the seizure episode and the manifestations of cognitive decline provides a window for a possible therapeutic intervention, and an elaboration of such "post-conditioning" treatments may be a promising opportunity to prevent subsequent mental impairments in patients.

The effects of rutin on the development of pentylenetetrazole kindling and memory retrieval in rats

Individuals with epilepsy often complain about memory deficits. Various synthetic derivatives of natural flavonoids are known to have neuroactive properties. Rutin is a flavonoid that is an important dietary constituent of foods and plant-based beverages. The aim of the present study was to investigate the effects of rutin on memory retrieval in pentylenetetrazole (PTZ)-kindled rats using a step-through passive avoidance task. We administered rutin and PTZ intraperitoneally every other day prior to the start of training. Two retention tests were subsequently performed to assess memory in these rats. The results suggest that pretreatment with rutin at 50 and 100mg/kg can attenuate seizure severity during the kindling procedure. Furthermore, rutin administration significantly increased the step-through latency in the passive avoidance paradigm. Taken together, these results indicate that rutin has a potential role in enhancing memory retrieval in kindled rats.

Anticonvulsant effects of aerial parts of Passiflora incarnata extract in mice: involvement of benzodiazepine and opioid receptors

Background

Passion flower (Passiflora incarnata) is used in traditional medicine of Europe and South America to treat anxiety, insomnia and seizure. Recently, it has shown antianxiety and sedative effects in human.

Methods

In this study, anticonvulsant effects of hydro- alcoholic extract of Passiflora, Pasipay, were examined by using pentylentetrazole model (PTZ) on mice. Pasipay, diazepam, and normal saline were injected intraperitoneally at the doses 0.4–0.05 mg/kg, 0.5–1 mg/kg and 10 ml/kg respectively 30 minutes before PTZ (90 mg/kg, i.p). The time taken before the onset of clonic convulsions, the duration of colonic convulsions, and the percentage of seizure and mortality protection were recorded. For investigating the mechanism of Pasipay, flumazenil (2 mg/kg, i.p) and naloxone (5 mg/kg, i.p) were also injected 5 minutes before Pasipay.

Results

An ED₅₀ value of Pasipay in the PTZ model was 0.23 mg/kg (%95 CL: 0.156, 0.342). Pasipay at the dose of 0.4 mg/kg prolonged the onset time of seizure and decreased the duration of seizures compared to saline group (p < 0.001). At the dose of 0.4 mg/kg, seizure and mortality protection percent were 100%. Flumazenil and naloxone could suppress anticonvulsant effects of Pasipay.

Conclusion

It seems that Pasipay could be useful for treatment absence seizure and these effects may be related to effect of it on GABAergic and opioid systems. More studies are needed in order to investigate its exact mechanism.

The price of seizure control: dynorphins in interictal and postictal psychosis

Postictal and interictal psychoses are relatively common complicating factors in the clinical course of epilepsy, yet their neurobiological substrates are poorly understood. Recent evidence shows that kappa opioid receptor (KOR) activation elicits anticonvulsant and psychotomimetic effects. In view of this background, here we introduce the hypothesis that epilepsy-related psychoses may partially result from excessive hippocampal dynorphin release and kappa opioid receptor overstimulation aimed at seizure control.

Pharmacological and genetic manipulation of kappa opioid receptors: Effects on cocaine- and pentylenetetrazol-induced convulsions and seizure kindling

The present study used pharmacological and gene ablation techniques to examine the involvement of kappa opioid receptors (KOPr) in modulating the convulsant effects of two mechanistically different drugs: cocaine and pentylenetetrazol (PTZ; GABA-A receptor antagonist) in mice. Systemic administration of the selective KOPr-1 agonist, U69593 (0.16-0.6mg/kg; s.c.), failed to modify cocaine-evoked convulsions or cocaine kindling. Similarly, no alteration in responsiveness to cocaine was observed in wild-type mice that received the selective KOPr-1 antagonist, nor-binaltorphimine (nor-BNI; 5mg/kg) or in mice lacking the gene encoding KOPr-1. In contrast to cocaine, U69593 attenuated the seizures induced by acute or repeated PTZ administration. Nor-BNI decreased the threshold for PTZ-evoked seizures and increased seizure incidence during the initial induction of kindling relative to controls. Decreased thresholds for PTZ-induced seizures were also observed in KOPr-1 knock out mice. Together, these data demonstrate an involvement of endogenous KOPr systems in modulating vulnerability to the convulsant effects of PTZ but not cocaine. Furthermore, they demonstrate that KOPr-1 activation protects against acute and kindled seizures induced by this convulsant. Finally, the results of our study suggest that KOPr-1 antagonists will not have therapeutic utility against cocaine-induced seizures, while they may prove beneficial in attenuating several actions of cocaine that have been linked to its abuse.

Pentylenetetrazol-kindling in mice overexpressing heat shock protein 70

Kindling induced by the convulsant pentylenetetrazol (PTZ) is an accepted model of primary generalized epilepsy. Because seizures represent a strong distressing stimulus, stress-induced proteins such as heat shock proteins might counteract the pathology of increased neuronal excitation. Therefore, the aim of the present study was to determine whether PTZ kindling outcome parameters are influenced by heat shock protein 70 (Hsp70) overexpression in Hsp70 transgenic mice as compared to the respective wild-type mice. Kindling was performed by nine intraperitoneal injections of PTZ (ED(16) for induction of clonic-tonic seizures, every 48 h); control animals received saline instead of PTZ. Seven days after the final injection, all mice received a PTZ challenge dose. Outcome parameters included evaluation of seizure stages and overall survival rates. In addition, histopathological findings such as cell number in hippocampal subfields CA1 and CA3 were determined. The onset of the highest convulsion stage was delayed in Hsp70 transgenic mice as compared to wild-type mice, and overall survival during kindling was improved in Hsp70 transgenic mice as compared to wild-type mice. In addition, a challenge dose after termination of kindling produced less severe seizures in Hsp70 transgenic mice than in wild-type mice. PTZ kindling did not result in significant subsequent neuronal cell loss in CA1 or CA3 neither in wild-type mice nor in the Hsp70 transgenic mice. The results of the present experiments clearly demonstrate that overexpression of Hsp70 exerts protective effects regarding seizure severity and overall survival during PTZ kindling. In addition, the decreased seizure severity in Hsp70 transgenic mice after a challenge dose suggests an interference of Hsp70 with the developmental component of kindling.

Pentylenetetrazol-induced seizures affect the levels of prolyl oligopeptidase, thimet oligopeptidase and glial proteins in rat brain regions, and attenuation by MK-801 pretreatment

The regulatory mechanisms of neuropeptide-metabolizing enzymes often play a critical role in the pathogenesis of neuronal damage. A systemic administration of pentylenetetrazol (PTZ), an antagonist of GABA(A) receptor ion channel binding site, causes generalized epilepsy in an animal model. In the present study, we examined the involvement of prolyl oligopeptidase (POP), thimet oligopeptidase/neurolysin (EP 24.15/16) and glial proteins in PTZ-treated rat brain regions, and the suppressive effect of MK-801, a non-competitive NMDA receptor antagonist, pretreatment for their proteins. The activity of POP significantly decreased in the hippocampus at 30min and 3h, and in the frontal cortex at 3h after PTZ treatment, and pretreatment with MK-801 recovered the activity in the cortex at 3h. The activity of EP 24.15/16 significantly decreased in the hippocampus at 3h and 1 day, and in the cortex at 3h after the PTZ administration, whereas pretreatment with MK-801 recovered the change of the activity. The Western blot analysis of EP 24.15 showed significant decrease of the protein level in the hippocampus 3h after the PTZ treatment, whereas pretreatment with MK-801 recovered. The expression of GFAP and CD11b immunohistochemically increased in the hippocampus of the PTZ-treated rat as compared with controls. Pretreatment with MK-801 also recovered the GFAP and CD11b expression. These data suggest that PTZ-induced seizures of the rats cause indirect activation of glutamate NMDA receptors, then decrease POP and EP 24.15/16 enzyme activities and EP 24.15 immunoreactivity in the neuronal cells of the hippocampal formation. We speculate that changes of those peptidases in the brain may be related to the levels of the neuropeptides regulating PTZ-induced seizures.

Endogenous opiates: 1999

This paper is the twenty-second installment of the annual review of research concerning the opiate system. It summarizes papers published during 1999 that studied the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress; tolerance and dependence; learning, memory, and reward; eating and drinking; alcohol and other drugs of abuse; sexual activity, pregnancy, and development; mental illness and mood; seizures and other neurologic disorders; electrical-related activity; general activity and locomotion; gastrointestinal, renal, and hepatic function; cardiovascular responses; respiration and thermoregulation; and immunologic responses.

Primed-burst potentiation occludes the potentiation phenomenon and enhances the epileptiform activity induced by transient pentylenetetrazol in the CA1 region of rat hippocampal slices

The effects of pentylenetetrazol (PTZ) following induction of long-term potentiation (LTP) on population spikes in CA1 of hippocampal slices were investigated. Population spikes were evoked by activation of Schaffer collaterals with a range of stimulation intensities. LTP was induced using &theta;-pattern primed burst tetanic stimulation. Changes in the population spike amplitude and number of population spikes were used as indices to quantify the effects of PTZ exposure in the control (non-tetanized) and LTP (tetanized) conditions. The amplitude of population spike was measured 20 min before, during 20 min chemical application (3 mM), and also after 30 or 60 min washout period. In non-tetanized slices, the population spike input-output curve was significantly increased 20 min after PTZ application and persisted at least for 60 min. Multiple population spikes or after potentials also appeared, but did not persist. When PTZ was applied on tetanized slices, 60 min after LTP induction, the amplitude increase produced by PTZ was smaller than the increase seen in the control condition. Also LTP induction preceding PTZ exposure increased the number of population spikes evoked by stimulation of Schaffer collaterals. It is concluded that a transient PTZ application produces a long-lasting increase in population spike amplitude. Primed burst LTP occludes PTZ-induced potentiation while also increasing the epileptogenic effect of PTZ.

Kindling induced by pentylenetetrazole in rats is not directly associated with changes in the expression of NMDA or benzodiazepine receptors

Repeated injections of a subconvulsant dose of pentylenetetrazole (PTZ, 30 mg/kg IP three times weekly for 13 injections) in Wistar and hooded Lister rats resulted in kindled seizures, the extent of which varied between strains. Wistar rats achieved stage 4 of clonic-tonic seizures, whereas hooded Lister rats only reached stage 2 of convulsive waves axially through the body. Rats were killed 10 days after their final injection, and radioligand binding was used to measure the expression of NMDA receptors in cortex and hippocampus using [3H]MK-801 and [3H]L-689,560, the latter binding specifically to the NR1 subunit. [3H]Ro 15-1788 measured expression of GABA(A)-benzodiazepine binding sites containing alpha1, alpha2, alpha3, or alpha5 subunits. Specific analysis of GABA(A) receptors containing the alpha5 subunit, which are preferentially localized in the hippocampus, was assessed with [3H]L-655,708. In the cortex, there was no effect of strain or treatment on the K(D) or B(max) of any of the ligands. Similarly, there was no effect of strain or treatment on hippocampal [3H]L-689,560 or [3H]Ro 15-1788 binding. However, in the hippocampus there was a significant, albeit modest, effect of treatment on the B(max) of [3H]MK-801 binding and the B(max) and K(D) of [3H]L-655,708 binding, i.e., PTZ-treated rats had fewer [3H]MK-801 and [3H]L-655,708 binding sites (NMDA and alpha5-containing GABA(A) receptors, respectively), but, these reductions were significant only in the relatively seizure-insensitive hooded Lister strain. This suggests that the increased susceptibility to kindling in Wistar rats is not directly related to alterations in the expression of NMDA or GABA(A) receptors.