Proconvulsant actions of intrahippocampal botulinum neurotoxin B in the rat.

Botulinum neurotoxins (BoNTs) may affect the excitability of brain circuits by inhibiting neurotransmitter release at central synapses. There is evidence that local delivery of BoNT serotypes A and E, which target SNAP-25, a component of the release machinery specific to excitatory synapses, can inhibit seizure generation. BoNT serotype B (BoNT/B) targets VAMP2, which is expressed in both excitatory and inhibitory terminals. Here we assessed the effects of unilateral intrahippocampal infusion of BoNT/B in the rat on intravenous pentylenetetrazol (PTZ) seizure thresholds, and on the expression of spontaneous behavioral and electrographic seizures. Infusion of BoNT/B (500 and 1,000 unit) by convection-enhanced delivery caused a reduction in myoclonic twitch and clonic seizure thresholds in response to intravenous PTZ beginning about 6 days after the infusion. Handling-evoked and spontaneous convulsive seizures were observed in many BoNT/B-treated animals but not in vehicle-treated controls. Spontaneous electrographic seizure discharges were recorded in the dentate gyrus of animals that received local BoNT/B infusion. In addition, there was an increased frequency of interictal epileptiform spikes and sharp waves at the same recording site. BoNT/B-treated animals also exhibited tactile hyperresponsivity in comparison with vehicle-treated controls. This is the first demonstration that BoNT/B causes a delayed proconvulsant action when infused into the hippocampus. Local infusion of BoNT/B could be useful as a focal epilepsy model.

L-histidine is a beneficial adjuvant for antiepileptic drugs against maximal electroshock-induced seizures in mice.

Endogenous histamine has been reported to be involved in regulation of seizure susceptibility. Enhancement of histamine neurotransmission engendered by L-histidine treatment produces anticonvulsant effects in experimental animals. The present study investigated the influence of L-histidine on the protective effects of carbamazepine and phenytoin against maximal electroshock-induced seizures in mice.L-Histidine, administered at the doses that did not influence the threshold for electroconvulsions (250-500 mg/kg), enhanced by nearly 30% the protective effects of carbamazepine against maximal electroshock-induced seizures. D-Histidine (1000 mg/kg), an inactive isomer of histidine, was without any effect in this regard. L-Histidine (500 mg/kg) also augmented the protective effects of phenytoin. Importantly, the enhancement of the anticonvulsant effects of these antiepileptic drugs produced by L-histidine co-administration was not associated with augmentation of their unwanted effects on memory and motor performance. A pharmacokinetic interaction was also excluded since the free plasma levels of these antiepileptics remained unchanged in the presence of L-histidine. It may be suggested that L-histidine could serve as a beneficial adjuvant for selected antiepileptic drugs.

Effects of antiepileptic drugs on rat platelet aggregation: ex vivo and in vitro study.

The influence of conventional antiepileptic drugs (valproate, phenobarbital, diazepam, clonazepam, carbamazepine and diphenylhydantoin) on rat platelet activation induced by arachidonic acid (AA) or adenosine-5'-diphosphate (ADP) was investigated both ex vivo and in vitro on platelet-rich plasma (PRP). It was found that only diazepam, and to a smaller extent clonazepam, impaired rat platelet function. These benzodiazepines did not affect ex vivo platelet aggregation induced by ADP but dose-dependent inhibition of platelet aggregation and malondialdehyde (MDA) synthesis were observed, when the platelets were stimulated with AA (ED(50) of diazepam for aggregation was 2.7 mg/kg and that for MDA synthesis - 3.9 mg/kg). In in vitro study, diazepam was found to be a potent inhibitor of AA-induced platelet aggregation (IC(50) 1.2 microg/ml) and MDA synthesis (IC(50) 4.0 microg/ml). Higher concentrations of diazepam were required to inhibit ADP-induced aggregation (IC(50) 29.0 microg/ml). Clonazepam also exhibited a concentration-dependent inhibitory effect on AA-induced platelet aggregation and MDA synthesis but this effect was weaker when compared to diazepam. The present data demonstrate that diazepam possesed a strong inhibitory effect on rat platelet activation. The correlation between the reduction of platelet aggregation and the synthesis of MDA may suggest that the observed effect of diazepam is due to the inhibition of the cyclooxygenase pathway of the AA metabolism in platelet.

Pharmacological properties of some xanthone derivatives.

A series of aminoalkanolic derivatives of xanthone were examined in some experimental models of epilepsia, i.e., pilocarpine, aminophylline and pentetrazole-induced seizures. A final objective of this research was to examine the action of these compounds on the central nervous system, namely on spontaneous locomotor activity, amphetamine-induced hyperactivity and narcotic sleep induced by hexobarbital, as well as their influence on the gamma-aminobutyric acid (GABA) level and glutamic acid decarboxylase (GAD) activity in mice brain. The most interesting were the pharmacological results of (R)-2-N-methylamino-1-butanol derivative of 7-chloro-2-methylxanthone [Id], which displayed protective activity against the seizures induced by maximum electroshock and pentetrazole induced seizures; moreover, this compound had a relatively low toxicity and did not exhibit a neurotoxic effect. The influence on the locomotor activity as well as on the amphetamine-induced locomotor hyperactivity in mice was also seen for Id. Compound Id did not decrease the GABA level in mice brain.

Antiplatelets activity of some xanthone derivatives.

The effects of twelve aminoalkanolic derivatives of xanthone on platelet aggregation have been evaluated. Five from them inhibited thrombin-induced platelet aggregation. The most active compound was R-(+)-2-N-(7-chloro-2-xanthonemethyl)-2-N-methylamino-1-butanol [IV] which, at a concentration of 40 micrograms/ml, nearly completely inhibited the aggregation concentration (TAC) of thrombin.

Transformation of some pyrido[2,3-d]pyrimidine derivatives into other di- and triheterocyclic systems.

It was stated that three analogous ethyl 2,4-dioxo-1,2,3,4-tetrahydropyrido[2,3-d]pyrimidine-5-carboxylates (7-9) react with hydrazine hydrate giving derivatives of the new heterocyclic system pyrido[2,3,4-ef]pyridazino[3,4-e]-1,2,4-triazepine (10-12), pyrido[3,4-d]pyridazine (16-18) and pentaazaphenalene (13-15). The latters were formed in low yields. The results of the preliminary pharmacological study of 2 of these compounds are reported.

Investigations on the synthesis and properties of some N-[4-phenyl(2-pyrimidinyl)-1-piperazinyl]alkyl (hydroxyalkyl)-3,4-pyridinedicarboximides.

Synthesis of 2-substituted N-(4-phenyl-1 piperazinyl)propyl(butyl)- and N-2-hydroxy-3[4-phenyl(2-pyrimidinyl)-1-piperazinyl]propyl-6-methyl-3,4- pyridinedicarboximides [VI-XIV] is described. Some of them displayed depressive action on the central nervous system.

NG-nitro-L-arginine sensitizes mice to 4-aminopyridine-induced seizures.

We investigated the influence of NG-nitro-L-arginine (NNA), the inhibitor of nitric oxide synthese, on seizures induced by 4-aminopyridine (4-AP), the K+ channel antagonist, in mice NNA (5, 10 and 40 mg/kg, i.p.) significantly reduced the respectives CD50 of 4-AP from 9.0 to 7.6, 7.5 and 6.8 for clonic seizures, and from 9.2 to 7.7, 7.5 and 6.9 for tonic seizures and death. Lower doses of NNA (1.0 and 2.5 mg/kg) had no effect on 4-AP-induced convulsions and lethality. Our results indicate that 4-AP-induced seizures may be, at least in part, dependent on nitric oxide level.