Comparison of effects of bicuculline, strychnine, and picrotoxin with those of pentylenetetrazol on photically evoked afterdischarges

Anxiolytic Action of Taurine via Intranasal Administration in Mice

Taurine has a number of beneficial pharmacological actions in the brain such as anxiolytic and neuroprotective actions. We explored to test whether taurine could be transported to the central nervous system through the intranasal route. Following intranasal administration of taurine in mice, elevated plus maze test, activity cage test and rota rod test were carried out to verify taurine's effect on anxiety. For the characterization of potential mechanism of taurine's anti-anxiety action, mouse convulsion tests with strychnine, picrotoxin, yohimbine, and isoniazid were employed. A significant increase in the time spent in the open arms was observed when taurine was administered through the nasal route in the elevated plus maze test. In addition, vertical and horizontal activities of mice treated with taurine via intranasal route were considerably diminished. These results support the hypothesis that taurine can be transported to the brain through intranasal route, thereby inducing anti-anxiety activity. Taurine's anti-anxiety action may be mediated by the strychnine-sensitive glycine receptor as evidenced by the inhibition of strychnine-induced convulsion.

Phytochemical analysis of Ficus carica L. active compounds possessing anticonvulsant activity

The anticonvulsant potential of Ficus carica methanol-extract (Fc) has been studied. It was found that Fc most active fraction is rich in oligosaccharides (OFG). ¹H, ¹³C NMR and Nano-ESI, MALDI MS, and LC-MS techniques proved that OFG contains alpha-glucopyranoside oligomer in high amounts. Both Fc and OFG reduced strychnine (STR) convulsion-action. Fc and OFG fully protected the experimental-animals from STR-lethality. The intracerebroventricular-administration (ICV) of Fc or OFG in combination with glycine in ethanol-treated mice caused a dose-dependent returning to a 2nd-loss of righting-reflex (LORR), and was antagonized by STR. FC and OFG ICV injection counteracted STR-inhibition, confirming that Fc/OFG anticonvulsant mechanism of action was mediated by potentiation of glycine receptor. These results support Fc and OFG potential anticonvulsant-activity with good safety-profile.

Anticonvulsant Effect of Antiaris toxicaria (Pers.) Lesch. (Moraceae) Aqueous Extract in Rodents

Antiaris toxicaria (Moraceae) was evaluated for anticonvulsant activity in rodents. Animal models used include maximal electroshock test (MEST); pentylenetetrazole-induced (PTZ) convulsions; picrotoxin-induced (PCT) convulsions; strychnine- (STR-) and 4-aminopyridine-induced convulsions. Increase in latency to seizures as well as reduction in duration and frequency of seizures indicated anticonvulsant activity. The extract was more effective in all models used except the maximal electroshock test and strychnine-induced convulsions. Antiaris toxicaria aqueous extract (200, 400, and 800 mg kg(-1)) significantly (P < 0.05 - 0.01) shortened the duration of convulsions in PTZ- and PCT-induced seizures. Delay in the onset of convulsions in the two tests was significant (P < 0.001). Reduction in the frequency of seizures was also significant (P < 0.05 - 0.001) in both tests. Antiaris further delayed the onset of seizures in 4-aminopyridine model while producing 75% protection against death in mice. Diazepam (0.1, 0.3, and 1 mg kg(-1)), carbamazepine (3, 10, and 30 mg kg(-1)), and sodium valproate (100-400 mg kg(-1)) were used as reference anticonvulsant drugs for various models. Flumazenil blocked the effect of the extract in the PTZ test significantly suggesting that Antiaris toxicaria may be acting by enhancing the effects of the GABAergic system. Antiaris toxicaria aqueous extract therefore possesses anticonvulsant activity.

Taurine Induces Anti-Anxiety by Activating Strychnine-Sensitive Glycine Receptor in vivo

Taurine has a variety of actions in the body such as cardiotonic, host-defensive, radioprotective and glucose-regulatory effects. However, its action in the central nervous system remains to be characterized. In the present study, we tested to see whether taurine exerts anti-anxiety effects and to explore its mechanism of anti-anxiety activity in vivo. The staircase test and elevated plus maze test were performed to test the anti-anxiety action of taurine. Convulsions induced by strychnine, picrotoxin, yohimbine and isoniazid were tested to explore the mechanism of anti-anxiety activity of taurine. The Rotarod test was performed to test muscle relaxant activity and the passive avoidance test was carried out to test memory activity in response to taurine. Taurine (200 mg/kg, p.o.) significantly reduced rearing numbers in the staircase test while it increased the time spent in the open arms as well as the number of entries to the open arms in the elevated plus maze test, suggesting that it has a significant anti-anxiety activity. Taurine's action could be due to its binding to and activating of strychnine-sensitive glycine receptor in vivo as it inhibited convulsion caused by strychnine; however, it has little effect on picrotoxin-induced convulsion, suggesting its anti-anxiety activity may not be linked to GABA receptor. It did not alter memory function and muscle activity. Taken together, these results suggest that taurine could be beneficial for the control of anxiety in the clinical situations.

Animal models of the epilepsies

The study of mechanisms of the epilepsies requires employment of animal models. Choice of a model system depends upon several factors, including the question to be studied, the type of epilepsy to be modelled, familiarity and convenience. Over 50 models are reviewed. Major categories of models are those for simple partial seizures: topical convulsants, acute electrical stimulation, cortically implanted metals, cryogenic injury; for complex partial seizures: kainic acid, tetanus toxin, injections into area tempesta, kindling, rodent hippocampal slice, isolated cell preparations, human neurosurgical tissue; for generalized tonic-clonic seizures: genetically seizure-prone strains of mouse, rat, gerbil, fruitfly and baboon, maximal electroshock seizures, systemic chemical convulsants, metabolic derangements; and for generalized absence seizures: thalamic stimulation, bilateral cortical foci, systemic penicillin, gamma-hydroxy-butyrate, intraventricular opiates, genetic rat models. The lithium-pilocarpine, homocysteine and rapid repetitive stimulation models are most useful in studies of status epilepticus. Key findings learned from each of the models, the model's strengths and weaknesses are detailed. Interpretation of findings from each of these models can be difficult. Do results pertain to the epilepsies or to the particular model under study? How important are species differences? Which clinical seizure type is really being modelled? In a model are behavior or EEG findings only similar superficially to epilepsy, or are the mechanisms comparable? The wealth of preparations available to model the epilepsies underscores the need for unifying themes, and for better understanding of basic mechanisms of the epilepsies.

The influence of intermittent light stimulation on potentials evoked by single flashes in photosensitive and non-photosensitive Papio papio

The effects of intermittent light stimulation (ILS) on visual potentials (VEPs), evoked in different cortical areas, were statistically studied in baboons either naturally photosensitive or made photosensitive by allylglycine at a subconvulsant dose, as well as in non-photosensitive animals. VEPs were induced by single flashes (paradigm a) or by flashes preceded by trains of ILS (paradigm b). In every baboon, photosensitive or not, the VEPs induced by paradigm b in the striate area show a decrease of amplitude compared to VEPs induced by paradigm a. The ERG evolves in the same way. Therefore, these effects do not depend on photosensitivity; they depend on the intensity of stimulation. In photosensitive animals the single flash in paradigm b can induce a paroxysmal VEP in the fronto-rolandic (FR) area. In parietal and peristriate areas the VEPs induced by paradigm b show new late components when compared to those induced by paradigm a. These changes are observed even if no FR paroxysmal VEP is induced; they depend on the presence of a train of ILS preceding the single flash and on the predisposition to epilepsy (both natural and due to allylglycine); in the non-photosensitive animals the VEPs recorded in the same areas do not show such differences. We consider that among afferents which could act in inducing FR paroxysmal activities some cortico-cortical visual afferents can come from non-specific cortical areas (parietal or peristriate), but would not directly originate in the striate cortex; anatomical data in this species may support such a hypothesis.

Differential effects of convulsants on visually evoked responses in the albino rat

Visually evoked responses (VERs) were recorded from primary visual cortex in unanesthetized albino rats during pharmacological modulation by one of the following convulsant agents: Physostigmine, picrotoxin, strychnine and Metrazol. The data were analyzed in terms of effects on VER components. The rat VER consists of six distinct waves constituted by three positive peaks (P1--P3) and three negative peaks (N1--N3). Results indicate a differential convulsant action on VER components. The administration of picrotoxin, resulted in a suppression of the peak amplitude of P1--N1 and delayed peak latencies of all components. Strychnine reliably shortened P1, N1 and P2 peak latencies, significantly increased N3 peak latency and only suppressed P3--N3 amplitude. Physostigmine essentially suppressed all component amplitudes but only increased peak latencies for P2 and P3 components. Metrazol, in general, was found to be relatively ineffective in the alteration of any VER component in a systematic manner. The data are discussed in terms of differential modes of convulsant action on the visual system. The results are likewise discussed with respect to their implications for convulsant modulation of photically evoked after-discharges.