Suppression of a ligand operated membrane current by the epileptogenic agent pentylenetetrazol in oocytes of Xenopus laevis after injection of rat brain RNA

Triterpene 3β, 6β, 16β trihidroxilup-20(29)-ene protects against excitability and oxidative damage induced by pentylenetetrazol: the role of Na(+),K(+)-ATPase activity

Administration of the compound triterpene 3β, 6β, 16β-trihidroxilup-20(29)-ene (TTHL) resulted in antinociceptive activity in several pain models in mice. Because pain and epilepsy have common mechanisms, and several anticonvulsants are clinically used to treat painful disorders, we investigated the anticonvulsant potential of TTHL. Behavioral and electrographic recordings revealed that pretreatment with TTHL (30 mg/kg; i.g.) increased the latencies to the first clonic seizure to the tonic-clonic and reduced the duration of the generalized seizures induced by the GABA(A) receptor antagonist PTZ (80 g; i.p.). The TTHL pretreatment also protected against PTZ-induced deleterious effects, as characterized by protein carbonylation, lipid peroxidation, [(3)H] glutamate uptake and the inhibition of Na(+),K(+)-ATPase (subunits α(1) and α(2)/α(3)). Although TTHL did not exhibit DPPH, ABTS radical scavenging activity per se and does not alter the binding of [(3)H]flunitrazepam to the benzodiazepinic site of the GABA(A) receptor, this compound was effective in preventing behavioral and EEG seizures, as well as the inhibition of Na(+),K(+)-ATPase induced by ouabain. These results suggest that the protection against PTZ-induced seizures elicited by TTHL is due to Na(+),K(+)-ATPase activity maintenance. In fact, experiments in homogenates of the cerebral cortex revealed that PTZ (10 mM) reduced Na(+),K(+)-ATPase activity and that previous incubation with TTHL (10 μM) protected against this inhibition. Collectively, these data indicate that the protection exerted by TTHL in this model of convulsion is not related to antioxidant activity or GABAergic activity. However, these results demonstrated that the effective protection of Na(+),K(+)-ATPase elicited by this compound protects against the damage due to neuronal excitability and oxidation that is induced by PTZ.

Study of epileptiform activity in cerebral ganglion of mud crab Scylla serrata

An attempt is made to induce in mud crab (Scylla serrata) epileptiform activities that resemble the generalized epileptic seizures. Cerebral ganglion of crab was exposed in situ, to a convulsant drug pentylenetetrazole (PTZ) 100 mM, for induction of seizures. Also, crabs were pretreated with antiepileptic drug viz sodium valproate (120 μmol/l) to inhibit epileptiform activities. The surface electrical discharges of cerebral ganglion were recorded using Unkelscope (MIT, USA) in control as well as experimental animals. The cerebral ganglion of crab showed a pattern of high cerebral electrical discharges after PTZ treatment compared to control. The sodium valproate promoted sedative action in control and prevented PTZ-mediated epileptiform discharges. Glutamate and GABA contents in cerebral ganglion were assayed. Glutamate level increased (31.45%) during PTZ treatment with concomitant decrease (43.93%) in GABA. Sodium valproate had no effect on glutamate concentration, but it decreased GABA by 24.75%. The present study shows that epileptiform activities can be induced in crabs.

Pentylenetetrazol elicits epileptiform activity in the dentate gyrus of the urethane anesthetized rat by activation of the entorhinal cortex

Pentylenetetrazol is a chemical convulsant, often used to generate experimental seizures, that is thought to act as a GABA antagonist. In the urethane anesthetized rat, pentylenetetrazol produces a characteristic epileptiform discharge in the dentate gyrus. The hypothesis that this discharge is generated by activity in the entorhinal cortex was examined in this study. Recording electrodes were placed in the dentate gyrus bilaterally and neuronal activity was recorded after administration of pentylenetetrazol. A laminar analysis of the convulsant-induced activity was compared to responses evoked by angular bundle stimulation (n = 6). Both convulsant-induced and evoked activity were negative-going in the molecular layer of the dentate gyrus. In other animals tetrodotoxin (TTX) was injected into the right entorhinal cortex before the onset of epileptiform activity (n = 5). The TTX prevented epileptiform activity in the right dentate gyrus. Injection of TTX after the onset of epileptiform activity caused the epileptiform activity to cease on the side of injection (n = 5). These experiments support the hypothesis that pentylenetetrazol specifically activates the entorhinal cortex to produce the epileptiform activity recorded in the dentate gyrus. This selective activation suggests that the mechanism of action of pentylenetetrazol, as a convulsant, is not simply as an antagonist of GABA receptors.