The effects of cannabinoids on the brain

Cannabinoids have a long history of consumption for recreational and medical reasons. The primary active constituent of the hemp plant Cannabis sativa is delta9-tetrahydrocannabinol (delta9-THC). In humans, psychoactive cannabinoids produce euphoria, enhancement of sensory perception, tachycardia, antinociception, difficulties in concentration and impairment of memory. The cognitive deficiencies seem to persist after withdrawal. The toxicity of marijuana has been underestimated for a long time, since recent findings revealed delta9-THC-induced cell death with shrinkage of neurons and DNA fragmentation in the hippocampus. The acute effects of cannabinoids as well as the development of tolerance are mediated by G protein-coupled cannabinoid receptors. The CB1 receptor and its splice variant CB1A, are found predominantly in the brain with highest densities in the hippocampus, cerebellum and striatum. The CB2 receptor is found predominantly in the spleen and in haemopoietic cells and has only 44% overall nucleotide sequence identity with the CB1 receptor. The existence of this receptor provided the molecular basis for the immunosuppressive actions of marijuana. The CB1 receptor mediates inhibition of adenylate cyclase, inhibition of N- and P/Q-type calcium channels, stimulation of potassium channels, and activation of mitogen-activated protein kinase. The CB2 receptor mediates inhibition of adenylate cyclase and activation of mitogen-activated protein kinase. The discovery of endogenous cannabinoid receptor ligands, anandamide (N-arachidonylethanolamine) and 2-arachidonylglycerol made the notion of a central cannabinoid neuromodulatory system plausible. Anandamide is released from neurons upon depolarization through a mechanism that requires calcium-dependent cleavage from a phospholipid precursor in neuronal membranes. The release of anandamide is followed by rapid uptake into the plasma and hydrolysis by fatty-acid amidohydrolase. The psychoactive cannabinoids increase the activity of dopaminergic neurons in the ventral tegmental area-mesolimbic pathway. Since these dopaminergic circuits are known to play a pivotal role in mediating the reinforcing (rewarding) effects of the most drugs of abuse, the enhanced dopaminergic drive elicited by the cannabinoids is thought to underlie the reinforcing and abuse properties of marijuana. Thus, cannabinoids share a final common neuronal action with other major drugs of abuse such as morphine, ethanol and nicotine in producing facilitation of the mesolimbic dopamine system.

Effects of the endogeneous cannabinoid, anandamide, on neuronal activity in rat hippocampal slices

1. The arachidonic acid derivative arachidonylethanolamide (anandamide) is an endogeneous ligand of cannabinoid receptors that induces pharmacological actions similar to those of cannabinoids such as delta9-tetrahydrocannabinol (THC). We examined whether anandamide can influence excessive neuronal activity by investigating stimulation-induced population spikes and epileptiform activity in rat hippocampal slices. For this purpose, the effects of anandamide were compared with those of the synthetic cannabinoid agonist WIN 55,212-2 and its inactive S(-)-enantiomer WIN 55,212-3. 2. Both anandamide (1 and 10 microM) and WIN 55,212-2 (0.1 and 1 microM) decreased the amplitude of the postsynaptic population spike and the slope of the field excitatory postsynaptic potential (field e.p.s.p.) without affecting the presynaptic fibre spike of the afferents. At a concentration of 1 microM, WIN 55,212-2 completely suppressed the postsynaptic spike, whereas the S(-)-enantiomer WIN 55,212-3 produced only a slight depression. The CB1 receptor antagonist SR 141716 blocked the inhibition evoked by the cannabinoids. SR 141716 had a slight facilitatory effect on neuronal excitability by itself. 3. Anandamide shifted the input-output curve of the postsynaptic spike and the field e.p.s.p. to the right and increased the magnitude of paired-pulse facilitation indicating a presynaptic mechanism of action. 4. Anandamide and WIN 55,212-2, but not WIN 55,212-3, attenuated both stimulus-triggered epileptiform activity in CA1 elicited by omission of Mg2+ and spontaneously occurring epileptiform activity in CA3 elicited by omission of Mg2+ and elevation of K+ to 8 mM. The antiepileptiform effect of these cannabinoids was blocked by SR 141716. 5. In conclusion, cannabinoid receptors of the CB1 type as well as their endogeneous ligand, anandamide, are involved in the control of neuronal excitability, thus reducing excitatory neurotransmission at a presynaptic site, a mechanism which might be involved in the prevention of excessive excitability leading to epileptiform activity.

Frequency- and structure-dependent inhibition of normal and epileptiform activity by 6-benzoyldeltamine in rat hippocampal slices

The present study investigated the effects of the Aconitum alkaloids 6-benzoyldeltamine and the structurally related eldeline on neuronal activity in rat hippocampal slices. 6-Benzoyldeltamine (1-30 microM) decreased the orthodromic field potentials recorded in area CA1 in a concentration-dependent manner. The inhibitory effect of eldeline (3-100 microM) was lower. The attenuation of the postsynaptic population spike was accompanied by a simultaneous decrease in the presynaptic fibre spike evoked by electrical stimulation of the Schaffer collaterals. The input-output relationship of the presynaptic fibre spike as function of the stimulation intensity, and for the postsynaptic population spike as function of the presynaptic fibre spike was shifted to the right. Thus, electrophysiologically, these alkaloids seem to inhibit predominantly the excitability of the afferent fibres and, in consequence, neurotransmission between Schaffer collaterals and the CAI neurons, thereby suppressing the firing of the latter. The inhibitory action of 6-benzoyldeltamine revealed use-dependence as obvious by an enhanced attenuation of the antidromic spike when stimulation frequency was increased. 6-Benzoyldeltamine inhibited stimulus-triggered epileptiform population bursts in area CA1 elicited by omission of Mg2+, as well as spontaneously occurring epileptiform discharges in area CA3 elicited by omission of Mg2+ and elevation of K+. Complete suppression of spontaneous activity was observed at 1 microM 6-benzoyldeltamine, which reduced the population spike only by about 20% of control. It is concluded that the inhibitory and antiepileptiform effect of 6-benzoyldeltamine is mediated by a frequency-dependent decrease in excitability, which might be important for filtering high frequency bursts of action potentials characteristic for epileptiform activity in the hippocampus.

Intermediate syndrome with delayed distal polyneuropathy from ethyl parathion poisoning

An acute poisoning in a 44-y-old female who ingested 50 ml of ethyl parathion concentrate (25 g) is described. She was treated by gastric lavage, administration of pralidoxime and atropine, and mechanical ventilation. As signs of intoxication disappeared at day 3, treatment was discontinued. The patient had a relapse of acute cholinergic crisis at day 4, and the same treatment was applied again. The acute poisoning phase was followed by an intermediate syndrome and delayed distal polyneuropathy. The clinical course of this severe ethyl parathion poisoning was favorable after 40 d.

The effects of Aconitum alkaloids on the central nervous system

Preparations of Aconitum roots are employed in Chinese and Japanese medicine for analgesic, antirheumatic and neurological indications. The recent surge in use of phytomedicine derived from traditional Chinese medicine as well as increasing concerns about possible toxic effects of these compounds have inspired a great deal of research into the mechanisms by which certain Aconitum alkaloids may act on the central nervous system. The pharmacological effects of preparations of Aconitum roots are attributed to several diterpenoid alkaloids. The main alkaloid of these plants is aconitine, a highly toxic diterpenoid alkaloid which is known to suppress the inactivation of voltage-dependent Na+ channels by binding to neurotoxin binding site 2 of the alpha-subunit of the channel protein. In this article the pharmacology of several structurally related Aconitum alkaloids is highlighted and their therapeutic vs toxic potential is discussed. Neurochemical and neurophysiological studies will be reviewed with emphasis on the effects of the alkaloids in regions of the brain that have been implicated in pain transmission and generation of epileptic activity. Considering the chemical structure of the Aconitum alkaloids as well as their mechanism of action, a subdivision in three groups becomes obvious: the first group comprises such alkaloids which possess high toxicity due to two ester boundings at the diterpene skeleton. The members of this group activate voltage-dependent sodium channels already at resting potential and inhibit noradrenaline reuptake. Activation of sodium channels and in consequence excessive depolarization with final inexcitability and suppression of pain transmission account for their antinociceptive properties. The second group comprises less toxic monoesters which have been shown to possess strong antinociceptive, antiarrhythmic and antiepileptiform properties due to a blockade of the voltage-dependent sodium channel. Electrophysiological studies have revealed a use-dependent inhibition of neuronal activity by these alkaloids. They seem to be competitive antagonists of the group I-alkaloids. The third group of Aconitum alkaloids are lacking an ester side chain in the molecule. Toxicity is markedly reduced when compared with the two other groups. They fail to affect neuronal activity, but are reported to have antiarrhythmic actions suggesting that they may have different affinities to various subtypes of the alpha-subunit of the Na+ channel in brain and heart.

Effects of the Aconitum alkaloid songorine on synaptic transmission and paired-pulse facilitation of CA1 pyramidal cells in rat hippocampal slices

1. The present study investigated the electrophysiological effects of songorine (1 100 microM), an alkaloid occurring in plants of the Aconitum genus, in rat hippocampal slices. 2. Songorine (10-100 microM) evoked a concentration-dependent increase in the amplitude of the orthodromic population spike and in the slope of the field e.p.s.p. The enhancement was long-lasting and was not reversed by up to 90 min of washout. Songorine failed to affect size and shape of the presynaptic fiber spike which represents the compound action potential of the Schaffer collaterals. This indicates that enhancement of the synaptic response is no consequence of an increased afferent excitability. 3. The antidromically evoked population spike was not affected by songorine at concentrations up to 100 microM suggesting that the enhancement of the orthodromic population spike and of the field e.p.s.p. was not due to an increase in pyramidal cell excitability. 4 The input-output curve for the postsynaptic population spike was shifted to the left implying that a presynaptic fiber spike of the same size elicited a larger postsynaptic response, indicating a decrease in threshold for generation of the population spike. 5. The songorine-evoked increase in excitability was not affected by the NMDA receptor antagonist, D-AP5. However, the effect of songorine was completely abolished by the selective dopamine D2 receptor antagonist sulpiride (0.1 microM) as well as by haloperidol (10 microM) and was mimicked by application of the dopamine releaser, amantadine (100 mM). In contrast, the selective D1 receptor antagonist, SCH23390, did not block the action of songorine. 6. The results indicate that the plant alkaloid songorine enhances excitatory synaptic transmission which may be due to an agonistic action at D2 receptors.

Effects of mesaconitine on [3H]noradrenaline uptake and neuronal excitability in rat hippocampus

Mesaconitine, one of the main alkaloids contained in Aconiti tubers, is a centrally acting analgesic without affinity to opioid receptors. It has been reported that the antinociception is due to an interaction with the noradrenergic system. In the present study, the effect of mesaconitine on the uptake of noradrenaline and on neuronal activity was examined in rat hippocampus. Experiments were performed as a study of [3H]noradrenaline uptake into rat hippocampal synaptosomes. Mesoconitine inhibited [3H]noradrenaline uptake in a concentration-dependent manner with a Ki of 111.95+/-18 nM. In a further series of experiments, the effects of mesaconitine on the extracellularly recorded population spike were investigated in rat hippocampal slices. At a concentration of 10 nM, mesaconitine increased the amplitude of the postsynaptic population spike by 31.10%+/-6.7% of control and elicited one or two additional spikes. The presynaptic fiber spike and the field excitatory postsynaptic potential were not affected by this alkaloid. The enhancement of neuronal activity was abolished by 1 microM propranolol as well as by 1 microM timolol. It is concluded that mesoconitine increased the excitability in rat hippocampal pyramidal cells by an involvement of the noradrenergic system, with at least one mechanism being inhibition of noradrenaline uptake leading to an enhanced extraneuronal noradrenaline level.

Frequency of the 20210 G-->A mutation in the 3'-untranslated region of the prothrombin gene in 35 cases of cerebral venous thrombosis

BACKGROUND AND PURPOSE

A novel sequence variation in the 3'-untranslated region of the prothrombin (factor II) gene (nucleotide 20210 G-->A) has been recently described as a risk factor for deep vein thrombosis and pulmonary embolism. It is found in approximately 1% to 4% of healthy subjects. We studied the frequency of this factor II variant in patients with cerebral venous thrombosis.

METHODS

The 20210A allele of the prothrombin gene was studied after DNA extraction, polymerase chain reaction amplification, and HindIII digestion in 35 patients with magnetic resonance imaging or angiographically confirmed cerebral venous thrombosis (23 women and 12 men, aged 11 to 71 years).

RESULTS

Two patients (5.7%) had the 20210A allele of the prothrombin gene. Both had other risk factors for thrombosis (use of oral contraceptives and of intrathecal steroids).

CONCLUSIONS

The 20210A allele of the prothrombin gene in association with other prothrombic factors may increase the risk of cerebral venous thrombosis, but case-control studies will be necessary to clarify these associations.

Structure-dependent inhibitory action of the Aconitum alkaloids 14-benzoyltalitasamine and talitasamine in rat hippocampal slices

In the present study the effects of the two Aconitum alkaloids 14-benzoyltalitasamine and talitasamine on neuronal activity were investigated in order to obtain further insight into structure-dependent effects of this group of alkaloids on central nervous activity. Both alkaloids are closely related to aconitine, the main alkaloid of plants of Aconitum species. However, they have shortened side chains at position C3 and C8 of the molecule. The experiments were performed as extracellular recordings of orthodromically and antidromically evoked population spikes as well as of field excitatory potentials (EPSPs) from the CA1 region of rat hippocampal slices. 14-Benzoyltalitasamine exerted a reversible inhibition of the field potentials in a concentration-dependent manner. The orthodromic population spike was attenuated at concentrations higher than 1 microM, while the field EPSP was already affected at a concentration of at least 0.3 microM. Both responses were completely blocked at a concentration of 30 microM. The alkaloid failed to affect the presynaptic fiber spike at concentrations less than 10 microM. There was only a up to 30% decrease in the antidromic population spike (10-100 microM). The inhibition of the antidromic spike was increased by using a higher stimulus frequency. In contrast to 14-benzoyltalitasamine, the alkaloid talitasamine which is lacking the benzoylester side chain was a less effective inhibitor of the orthodromic population spike and even failed to affect the antidromic spike. Furthermore, the effects of the alkaloids on experimentally induced epileptiform activity was examined. While talitasamine was lacking any significant effect at concentrations less than 100 microM, 14-benzoyltalitasamine reversibly reduced both stimulus-triggered epileptiform activity in area CA1 elicited by omission of Mg2+ from the bathing medium as well as spontaneously occurring epileptiform activity in CA3 elicited by omission of Mg2+ and elevation of K+ to 5 or 8 mM. The antiepileptiform efficacy of this compound was concentration-dependent (0.3-10 microM) and manifested itself as a decrease in burst frequency as well as in burst amplitude and was significantly increased by the higher K+ concentration.

Different effects on [3H]noradrenaline uptake of the Aconitum alkaloids aconitine, 3-acetylaconitine, lappaconitine, and N-desacetyllappaconitine in rat hippocampus

The effect of the Aconitum alkaloids aconitine, 3-acetylaconitine, lappaconitine, and N-desacetyllappaconitine to inhibit [3H]noradrenaline uptake was investigated in rat hippocampal synaptosomes. Aconitine and 3-acetylaconitine, which are known to activate sodium channels, had comparable inhibitory potencies and yielded Ki (inhibitor constant) values of 230 +/- 66 nM and 316 +/- 96 nM, respectively. In contrast, lappaconitine and N-desacetyllappaconitine failed to inhibit [3H]noradrenaline uptake. When either lappaconitine or N-desacetyllappaconitine was applied in combination with aconitine, [3H]noradrenaline uptake was not affected. The sodium channel blocker tetrodotoxin enhanced [3H]noradrenaline uptake, whereas uptake was completely blocked in sodium-free incubation medium. The inhibitory action of aconitine and 3-acetylaconitine on [3H]noradrenaline uptake was blocked by addition of tetrodotoxin. Patch clamp studies performed on cultured rat hippocampal neurons revealed an inhibitory action of lappaconitine and N-desacetyllappaconitine on whole cell sodium currents. It is concluded that the blockade of [3H]noradrenaline uptake evoked by aconitine and 3-acetylaconitine is mediated indirectly by an increased sodium concentration in the synaptosomes.

Inhibition of stimulus-triggered and spontaneous epileptiform activity in rat hippocampal slices by the Aconitum alkaloid mesaconitine

The aim of the present study was to investigate if the plant alkaloid, mesaconitine, which has been reported to have antinociceptive effects via stimulation of the noradrenergic system, inhibits epileptiform field potentials. The experiments were performed as extracellular recordings on rat hippocampal slices. Epileptiform activity was induced by omission of Mg2+ from the bathing medium or by addition of bicuculline and stimulus-evoked population bursts were recorded in the CA1 region. Spontaneous epileptiform activity was elicited by perfusing a nominally Mg2+-free bathing medium with high K+ concentration (5 mM). Both stimulus-triggered and spontaneous epileptiform activity was attenuated in a concentration-dependent manner by mesaconitine (30 nM-1 microM). The inhibitory effect was rather variable in appearance when lower concentrations (30 and 100 nM) of mesaconitine were applied. Pretreatment of the slices with the alpha-adrenoceptor antagonist yohimbine (1 microM) prevented the effect of mesaconitine. It is concluded that the inhibitory action of mesaconitine at low concentration is mediated via alpha-adrenoceptors.

Effects of the Aconitum alkaloid mesaconitine in rat hippocampal slices and the involvement of alpha- and beta-adrenoceptors

1 The effects of mesaconitine, the main alkaloid contained in Aconiti tuber, were investigated by use of extracellular recordings of stimulus-evoked population spikes and field excitatory postsynaptic potentials (e.p.s.ps) in the CA1 region of rat hippocampal slices. 2 At a concentration of 10 nM, mesaconitine evoked excitations, which were manifested as an increase in the amplitude of the orthodromic spike and the appearance of multiple spikes following the first postsynaptic spike, without affecting the magnitude of paired-pulse facilitation. The increase in spike amplitude was persistent and was not reversed by up to 90 min of washout. At concentrations of 30 and 100 nM, the alkaloid produced a biphasic effect, that is an excitation followed by an inhibition without having any effect upon the field e.p.s.p. At concentrations above 100 nM, mesaconitine suppressed the orthodromic population spike and the field e.p.s.p. 3 The excitatory effect was also observed when electrical stimulation was stopped completely during the application of mesaconitine (10 nM) and during the first 15 min of washout. 4 The enhancement of the population spike and the appearance of multiple spikes induced by mesaconitine (10-100 nM) were blocked by pretreatment with the beta-adrenoceptor antagonists propranolol (1 microM) and timolol (1 microM), whereas the inhibitory effect was blocked by the alpha-adrenoceptor antagonists yohimbine (1 microM) and phentolamine (10 microM). However, when the beta-adrenoceptor antagonist timolol was added 10 min after the application of mesaconitine, it failed to block the long-lasting enhancement of the spike amplitude and the appearance of multiple population spikes. 5 Application of the selective beta-adrenoceptor agonist isoprenaline (500 nM) to the hippocampal slices induced an increase in the amplitude of the orthodromic population spike and elicited 2-3 additional spikes. Mesaconitine (10 nM) did not further potentiate this enhancement of the spike amplitude when added after a 15 min pretreatment with isoprenaline. 6 Perfusion of forskolin, which directly activates adenylate cyclase, enhanced the population spike. Mesaconitine had no additional effect when applied after pretreatment with forskolin. 7 It is concluded that the excitatory effects evoked by lower concentrations of the plant alkaloid mesaconitine are mediated by stimulation of beta-adrenoceptors and the consequent activation of intracellular processes which lead to the long-lasting changes in excitability.

Inhibition of rat hippocampal excitability by the Aconitum alkaloid, 1-benzoylnapelline, but not by napelline

The effects of the two structurally related Aconitum alkaloids, 1-benzoylnapelline and napelline, were investigated by extracellular recording of the stimulus-evoked population spike in the CA1 region of rat hippocampal slices in vitro. 1-Benzoylnapelline (1-100 microM) exerted a depressant action on the orthodromic as well as on the antidromic population spike. Napelline failed to evoke a significant effect at concentrations up to 100 microM. The inhibitory action induced by 1-benzoylnapelline was enhanced when the frequency of electrical stimulation was increased. In contrast, reversal of the inhibitory effect was accelerated when stimulation frequency was decreased. The activity-dependent mode of action of 1-benzoylnapelline raised the question of whether the drug is effective to suppress epileptiform activity. The results obtained from experiments on epileptiform hippocampal slices revealed a reduction of the burst duration and of the number of spikes in the burst as well as attenuation of the amplitude of the population spikes. These data support the conclusion that 1-benzoylnapelline, in contrast to the structurally related compound, napelline, has an activity-dependent inhibitory action on central neurons.

Structure-dependent differences in the effects of the Aconitum alkaloids lappaconitine, N-desacetyllappaconitine and lappaconidine in rat hippocampal slices

Lappaconitine, a C19 diterpenoid alkaloid from Aconitum sinomontanum has been reported to possess analgesic and antiinflammatory properties in vivo and to inhibit neuronal activity in brain slices. In the present study the effect of lappaconitine has been compared with the effects of its main metabolite N-desacetyllappaconitine and the structurally related alkaloid lappaconidine. For comparison of drug effects population spikes and field excitatory postsynaptic potentials (EPSPs) evoked by stimulation of stratum radiatum or the alveus were studied in normal rat hippocampal slices and in slices treated with low Mg2+-medium. At concentrations of 3-100 microM, both lappaconitine and N-desacetyllappaconitine inhibited population spikes elicited by stratum radiatum and alvear stimulation as well as the field EPSP recorded in CA1 stratum radiatum. The drug-induced depression of field potential responses was increased with rising stimulus frequency, indicating an activity-dependent mode of action. The effect of N-desacetyllappaconitine on each parameter investigated was significantly stronger than the effect of lappaconitine. Despite the structural relationship, lappaconidine failed to affect neuronal excitability in concentration below 100 microM, and an increase in stimulus frequency did not potentiate its effect. Moreover, lappaconitine and N-desacetyllappaconitine suppressed epileptiform activity induced by bicuculline or by omission of Mg2+ from the bathing medium.

Relaxation of evoked contractile activity of isolated guinea-pig ileum by (+/-)-kavain

Kava pyrones are the pharmacologically active compounds of Piper methysticum Forst. In the present study, the effect of the synthetic kava pyrone (+/-)-kavain was investigated on evoked contractile activity of isolated guinea-pig ileum. (+/-)-Kavain (1 microM-1 mM) dose-dependently reduced contractions of ileum evoked by carbachol (10 microM), by BAY K 8644 (0.3 microM), or by substance P (0.05 microM). (+/-)-Kavain also inhibited the contractile responses induced by raising the extracellular K+ concentration from 4 to 20 mM and by blocking the K+ channel by barium chloride (1 mM) or 4-aminopyridine (0.3 mM). After pre-incubation with 1 microM nifedipine, carbachol (1 microM) evoked 18.2 +/- 14.3% of contraction at control (i.e. prior pre-incubation with nifedipine). This remaining response was completely abolished by high concentrations of (+/-)-kavain (400 microM). After treatment of the longitudinal ileum strips with pertussis toxin (PTX), carbachol (1 microM) evoked 27.0 +/- 6.2% of the control response in untreated ileum. These contractions were also blocked by (+/-)-kavain (400 microM). However, (+/-)-kavain had no effect on the caffeine-induced (20 mM) contractions of ileum strips, which were permeabilized with digitonin or beta-escin. Moreover, it failed to affect Ca(2+)-evoked contractions of skinned muscles. These results suggest that the kava pyrone (+/-)-kavain may act in a non-specific musculotropic way on the smooth muscle membrane.

Effects of the alkaloids 6-benzoylheteratisine and heteratisine on neuronal activity in rat hippocampal slices

Alkaloids of different Aconitum species are employed as analgesics in traditional Chinese folk medicine. The present study was designed in order to investigate the effects of the structurally related alkaloids 6-benzoylheteratisine and heteratisine on neuronal activity in rat hippocampus. Experiments were performed as extracellular recordings of stimulus evoked population spikes in rat hippocampal slices. 6-Benzoylheteratisine (0.01-10 microM) inhibited the ortho- and antidromic population spike as well as the field EPSP in a concentration- and frequency-dependent manner. Heteratisine (1-100 microM) was a less potent inhibitor. It exerted a depression of the orthodromic spike, but failed to affect the antidromic population spike. 6-Benzoylheteratisine (10 microM) diminished epileptiform activity induced by bicuculline. In hippocampal neurons, this compound reduced the peak amplitude of the sodium current. There was no effect of heteratisine on the sodium current in concentrations up to 100 microM. It is concluded that the frequency-dependent action of 6-benzoylheteratisine suggests an inhibition of neuronal activity which underlies epileptiform burst discharges. The predominant effect is a suppression of neuronal activity due to a blockade of sodium channels.

Bicuculline-induced epileptiform activity in rat hippocampal slices: suppression by Aconitum alkaloids

Alkaloids of Aconitum spec. (Ranunculaceae) are employed in traditional Chinese folk medicine as analgesics. The present study was designed in order to investigate the effects of the structurally related alkaloids aconitine, lappaconitine, and 6-benzoylheteratisine on experimentally induced epileptiform activity. Experiments were performed as extracellular recordings of stimulus evoked population spikes in rat hippocampal slices. Epileptiform activity was induced by bicuculline. All three alkaloids exerted an inhibitory action on excitability of hippocampal pyramidal cells in a frequency-dependent manner. The onset of inhibition was accelerated by increasing the frequency of electrical stimulation. Aconitine (1 microM) evoked a complete suppression of both normal and epileptiform activity, whereas lappaconitine (10 microM) and 6-benzoylheteratisine (10 microM) selectively diminished the epileptiform afterdischarges and the duration of the bursts, but spared the normal activity. The present findings suggest that the structurally related Aconitum alkaloids aconitine, lappaconitine, and 6-benzoylheteratisine possess an anticonvulsive potential. The predominant effect of these alkaloids is to suppress the spread of seizure activity, and they may therefore tend to distort epileptic events. However, despite their similar structure, they exert qualitatively and quantitatively different inhibitory effects.

Calcium-dependent, sustained enhancement of excitability during washout of aconitine in rat hippocampal slices

Extracellular recording of the stimulus-evoked population spike was performed in the CA1 area of rat hippocampal slices in order to investigate delayed effects of the plant alkaloids aconitine and veratridine. Veratridine (1 microM and 10 microM) suppressed the orthodromic and antidromic population spike. After washout of the drug, only a partial recovery was obtained. Aconitine (1 microM) exerted the same inhibitory action as veratridine. However, after washout, the spike amplitude was enhanced compared with the control. This enhancement of the spike amplitude was dependent on the concentration of aconitine and was maintained during the observation period of at least 2 h. Lowering the Ca2+ concentration of the bathing medium from 2.5 mM to 1.25 mM during application of aconitine attenuated recovery and prevented the enhancement observed during washout of the drug. Application of aconitine in the presence of CdCl2 as well as in the presence of inhibitors of protein kinase C and Ca2+/calmodulin-dependent protein kinase II prevented the increase in spike amplitude during washout with standard artificial cerebrospinal fluid. In contrast, the N-methyl-D-aspartate (NMDA) receptor antagonists D-AP5 and MK-801 as well as the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione were ineffective in abolishing the aconitine-induced enhancement. These data support the conclusion that different modes of action are involved in the effects of aconitine but not veratridine. It is concluded that the aconitine-induced increase in neuronal activity is mediated by intracellular Ca2+-dependent mechanisms leading to an activation of Ca2+-dependent protein kinases. This effect is independent of Ca2+ entrance through NMDA and non-NMDA receptors.

Electrophysiological actions of the plant alkaloid 6-benzoylheteratisine in rat hippocampal slices

The effects of the Aconitum alkaloid 6-benzoylheteratisine on neuronal activity was investigated in the in vitro slice preparation of rat hippocampus by extracellular recording of the stimulus-evoked population spike. 6-Benzoylheteratisine (0.01-10 microM) depressed the orthodromic and antidromic population spike in a concentration-dependent manner. The action of the drug was activity-dependent. The latency of onset of the inhibition was accelerated when the frequency of electrical stimulation had been increased. Furthermore, the effect of 6-benzoylheteratisine was evaluated in two different models of epileptiform activity induced either by blockade of GABA receptors by bicuculline (10 microM) or by a nominal Mg2+-free bathing medium. Due to the activity-dependent mode of action, this drug effectively reduced the number and the size of the synaptically evoked population spikes in the presence of bicuculline or nominal Mg2+-free bathing medium, respectively.

Treatment of recurrent malignant supratentorial gliomas with the association of carboplatin and etoposide: a phase II study

Thirty one patients previously treated with surgery, radiation therapy and chemotherapy with a nitrosourea for malignant supratentorial gliomas received a combination of carboplatin (CBDCA) and etoposide (VP16) at tumor progression. Carboplatin and etoposide (CE) were given, each at a dose of 100 mg/m2/day from day 1 to 3. The response was evaluated at each course and a minimum of three course was required to definite stable patient. Tolerance was evaluated in 31 patients. None had renal or auditory toxicity. Side effects consisted of grade III hematologic toxicity in 6 patients (19%), and grade III hepatic toxicity in one patient. No grade IV WHO toxicity was observed. All 31 patients could be evaluated for therapeutic response. A partial response was noted in 4 patients during 13, 34 +, 35 + and 51 + weeks. Ten patients had stable disease after a minimum of 3 courses (19 to 37 weeks). The rate of partial response (PR) and stabilisation (S) was 45% (14/31). The median time to tumor progression (MTTP) for responding and stable patients was 28 weeks. The median survival time (ST) for the entire group was 45 weeks and over 51 weeks for PR and S patients.

Antithrombotic action of the kava pyrone (+)-kavain prepared from Piper methysticum on human platelets

(+)-Kavain, a 4-methoxy-alpha-pyrone prepared from Piper methysticum Forst. (Piperaceae), was investigated regarding its assumed antithrombotic action on human platelets which was deduced from its ability to suppress arachidonic acid (AA)-induced aggregation, exocytosis of ATP, and inhibition of cyclooxygenase (COX) and thromboxane synthase (TXS) activity, the latter two effects being estimated from the generation of prostaglandin E2 (PGE2) and thromboxane A2 (TXA2), respectively. Exogenously applied AA (100 mumol/l) provoked a 90% aggregation of platelets, the release of 14 pmol ATP, and the formation of either 220 pg TXA2 or 43 pg PGE2, each parameter being related to 10(6) platelets. An application of (+)-kavain 5 min before AA, dose-dependently diminished aggregation, ATP-release, and the synthesis of TXA2 and PGE2 with IC50 values of 78, 115, 71, and 86 mumol/l, respectively. The similarity of the IC50 values suggest an inhibition of COX by (+)-kavain as primary target, thus suppressing the generation of TXA2 which induces aggregation of platelets and exocytosis of ATP by its binding on TXA2-receptors.

Inhibition of rat hippocampal excitability by the plant alkaloid 3-acetylaconitine mediated by interaction with voltage-dependent sodium channels

The effects of the Aconitum alkaloid 3-acetylaconitine on neuronal activity were investigated in the slice preparation and on cultivated neurons of rat hippocampus by extracellular and patch-clamp recordings, respectively. 3-Acetylaconitine (0.01-1 microM) diminished the orthodromic and antidromic population spike in a concentration-dependent manner. The inhibitory action of the drug was preceded by a transiently enhanced excitability. The latency of onset of the inhibition was accelerated by increased stimulation frequency, whereas recovery during washout of the alkaloid was accelerated by decreased stimulation frequency. Moreover, the inhibitory effect of 3-acetylaconitine was evaluated in two different models of epileptiform activity induced either by blockade of GABA receptors by bicuculline (10 microM) or by a nominal Mg(2+)-free bathing medium. In accordance with the activity-dependent mode of action, this compound abolished the synaptically evoked population spikes in the presence of bicuculline or nominal Mg(2+)-free bathing medium, respectively. Whole-cell patch-clamp recordings revealed an interaction of 3-acetylaconitine with the voltage-dependent sodium channel. At a concentration of 1 microM, 3-acetylaconitine did not affect the peak amplitude of the sodium current, but shifted the current-voltage relationship in the hyperpolarized direction such that sodium currents were already activated at the resting potential.

Kavain inhibits non-stereospecifically veratridine-activated Na+ channels

The action of the natural kava pyrone, (+)-kavain, and its synthetic racemate, (+/-)-kavain, on voltage-dependent Na+ channels was investigated, while considering their stereospecific properties, on veratridine-induced increases in cytosolic free Na+ and Ca2+ ([Na+]i, [Ca2+]i) and the release of endogenous glutamate from cerebrocortical synaptosomes. Both compounds dose-dependently suppressed the veratridine-induced increase in [Na+]i, [Ca2+]i and glutamate release with IC50 values (+/- S.D.) of 71 +/- 22, 72 +/- 7, 120 +/- 37 micromol/l (+)-kavain and 77 +/- 21, 90 +/- 14, 92 +/- 23 micromol/l (+/-)-kavain, respectively. As judged from the dose-dependency, IC50 values, velocity and time course of action, both kava pyrones were equally effective suggesting a non-stereospecific inhibition of veratridine-activated Na+ channels.

Treatment of recurrent malignant supratentorial gliomas with ifosfamide, carboplatin and etoposide: a phase II study

Thirty-six patients previously treated with surgery, radiation therapy and chemotherapy with a nitrosourea for malignant supratentorial gliomas received a combination of ifosfamide, carboplatin and etoposide (ICE) at tumour progression. Carboplatin and etoposide were both given at a dose of 75-100 mg/m2/day for 3 days, whereas ifosfamide doses ranged from 750 mg/m2/day to 1500 mg/m2/ day for 3 days, according to haematological tolerance. Treatment was repeated every 4 weeks. A minimum of three courses was required to evaluate the response unless the patient had rapid tumour progression. Grade III and IV haematological toxicity occurred in 15 patients (42%) and was lethal in one patient. Grade II hepatic toxicity was observed in one patient. Five complete (CR) and five partial responses (PR) were noted. 9 patients had stable disease (SD) after a minimum of three courses. CR + PR + SD was 53% (19/36). The median time to tumour progression (MTTP) was 13 weeks. Median survival (MST) was 29 weeks (44 weeks for R + S patients and 17 weeks for patients with progressing disease). This study suggests that the ICE combination is active in recurrent supratentorial malignant gliomas after failure of surgery, radiation therapy and chemotherapy, but at the cost of substantial haematological toxicity.