[Principles of the pharmacological treatment of drug addiction]. / Principes du traitement pharmacologique de l'addiction.

Treatment of addiction is extremely eomplex Identification of neurobiological mechanisms involved in this disease has made it possible to identify interesting pharmacological targets in the reward circuit and regions associated with this circuit. Current treatments are based on interactions with the acute effects of the drug on dopaminergic transmission, on the reactivation of the reward circuit in the absence of drug, on the reduction of withdrawal symptoms, or on inter-Sactions with systems associated with the reward circuit. In these systems, neurotransmitters such as GABA, glutamate and endogenous opioids play a crucial role in the development of addiction. In this article, we focus on the pharmacological management of addiction to alcohol, nicotine and opiates.

[Pharmacological strategies in the modulation of central nervous system activity]. / Stratégies pharmacologiques de modulation de l'activité du système nerveux central.

There are multiple pharmacological targets in the central nervous system. After reviewing the synaptic physiology and the major neurotransmitter molecules, this article describes the main strategies used in neuropharmacology. The concept of specificity in the central nervous system is discussed, and allows a distinction between drugs according to the degree of specificity of their action. A catalogue of pharmacological targets is presented with therapeutic examples, and an emphasis on new agents having an original mechanism of action or acting on new targets.

[Endocannabinoid system in the brain...and elsewhere]. / Le système endocannabinoïde dans le cerveau...et ailleurs.

The endocannabinoid system is a complex system with endogenous ligands, synthesis and transport processes, specific receptors (CB1 and CB2) and intracellular degrading enzymes. It is widely distributed in the central nervous system, but also in peripheral organs. In the brain, endocannabinoids and CB1 receptors are almost ubiquitous and play a role in synaptic plasticity: they modulate, through an inhibitory retrograde action, the release of classical neurotransmitters such as amines, acetylcholine or amino acids. They may exert a neuroprotective effect, but are also involved in appetite and alcohol/drug dependence. At the periphery, they are present (and overexpressed in case of abdominal obesity) in various organs involved in energy control and metabolic regulation. Furthermore, CB2 receptors are also present in the brain, although less numerous than CB1 receptors. They could attenuate pain and also be neuroprotective. Selective agonists, antagonists and inverse agonists of CB1 and CB2 receptors are currently developed and open new interesting therapeutic perspectives. Rimonabant, a CB1 antagonist, has been recently launched for the treatment of obese or overweight patients at high cardiometabolic risk.

[Regulation of the activity of monoaminergic neurons by ion channels: an opportunity for new therapeutic approaches?]. / Regulation de l'activité des neurones monoaminergiques par des canaux ioniques: une opportunité pour de nouvelles approches thérapeutiques?

Small-conductance ca2+ -activated potassium (SK) channels underlie one component of the afterhyperpolarization which follows one or several action potentials in neurons. Their blockade enhances neuronal excitability and, in some cases, produces a significant depolarization within dendrites. Three subtypes of SK subunits exist and are differentially expressed in the brain. We have developed SK channel blockers, we have characterized their potency and have used some of them as pharmacological tools. Moreover, we have shown that SK channel blockade increases dopaminergic and serotonergic, but not noradrenergic transmission. We believe that this is an original way of modulating brain function. Our next goal is to find subtype-selective blockers, using a variety of approaches, including molecular modelling.

Characterization of 4-(2-hydroxyphenyl)-1-[2'-[N-(2''-pyridinyl)-p-fluorobenzamido]ethyl]piperazine (p-DMPPF) as a new potent 5-HT1A antagonist.

BACKGROUND AND PURPOSE: The identification of potent and selective radioligands for the mapping of 5-HT receptors is interesting both for clinical and experimental research. The aim of this study was to compare the potency of a new putative 5-HT(1A) receptor antagonist, p-DMPPF, (4-(2-hydroxyphenyl)-1-[2'-[N-(2''-pyridinyl)-p-fluorobenzamido]ethyl]piperazine) with that of the well-known 5-HT(1A) antagonists, WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide) and its fluorobenzoyl analogue, p-MPPF (4-(2-methoxyphenyl)-1-[2'-[N-(2''-pyridinyl)-p-fluorobenzamido]ethyl]piperazine). EXPERIMENTAL APPROACH: Single cell extracellular recordings of dorsal raphe (DR) neurones were performed in rat brain slices. The potency of each compound at antagonizing the effect of the 5-HT(1A) agonist, 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)-tetraline], was quantified using the Schild equation. The pharmacological profile of p-DMPPF was defined using competition binding assays. KEY RESULTS: Consistently with a 5-HT(1A) receptor antagonist profile, incubation of slices with an equimolar (10 nM) concentration of each compound markedly reduced the inhibitory effect of 8-OH-DPAT on the firing rate of DR neurones, causing a significant rightward shift in its concentration-response curve. The rank order of potency of the antagonists was WAY-100635>p-DMPPF>or=p-MPPF. The sensitivity of DR neurones to the inhibitory effect of 8-OH-DPAT was found to be heterogeneous. The binding experiments demonstrated that p-DMPPF is highly selective for 5-HT(1A) receptors, with a K(i) value of 7 nM on these receptors. CONCLUSIONS AND IMPLICATIONS: The potency of the new compound, p-DMPPF, as a 5-HT(1A) antagonist is similar to that of p-MPPF in our electrophysiological assay. Its selectivity towards 5-HT(1A) receptors makes it a good candidate for clinical development.

SK channels are on the move.

Small-conductance Ca(2+)-activated K(+) channels (SK channels) underlie the medium duration after hyperpolarization that follows single or trains of action potentials in many types of neurons. Three subtypes of SK subunits, SK1 (K(Ca)2.1), SK2 (K(Ca)2.2) and SK3 (K(Ca)2.3), have been cloned and are expressed differentially within the central nervous system (CNS). A paper in this issue of BJP reports the discovery of the first example of a positive modulator displaying not only selectivity for SK channels over other channels, but also a subtype selectivity among SK and analogous channels (SK3>SK2>>>SK1=IK). Together with other recent progress in the field, this finding enriches the repertoire of tools available to test the hypothesis that SK channels may be targets for future CNS drugs.

[Coenzyme Q10: biochemistry, pathophysiology of its deficiency and potential benefit of an increased intake]. / Le coenzyme Q10: biochimie, physiopathologie de sa carence et intérêt potentiel d'une augmentation de ses apports.

After a brief reminding of the synthesis and function of coenzyme Q10, this article tries to summarise the current state of knowledge about the consequences of its deficiency and about the potential benefits of an increased intake of this coenzyme. We then describe the arguments in favour of such an increase in cardiac diseases and in Parkinson's disease.

Synthesis and biological evaluation of N-methyl-laudanosine iodide analogues as potential SK channel blockers.

Neuronal action potentials are followed by an afterhyperpolarisation (AHP), which is mediated by small conductance Ca2+-activated K+ channels (SK channels or KCa2 channels). This AHP plays an important role in regulating neuronal activity and agents modulating AHP amplitude could have a potential therapeutic interest. It was previously shown that N-methyl-bicuculline iodide blocks SK channels but its GABA) activity represents a serious drawback. In view of the structural analogy between bicuculline and laudanosine 14, several N-quaternary analogues of the latter were developed. It was shown that N-methyl-laudanosine 15 (NML) and N-ethyl-laudanosine 16 induce a reversible and relatively specific blockade of the apamin sensitive AHP in dopaminergic neurones with mean IC50s of 15, and 47 microM, respectively. Laudanosine 14, N-butyl-17 and N-benzyl-18 derivatives were less potent. In order to find pharmacophore elements, modifications were performed at different positions such as C-1, C-6 and C-7. Intracellular recordings on rat midbrain dopaminergic neurones were made in order to evaluate the putative blockade of SK channels by these molecules. Simplified structures such as tetrahydroisoquinoline derivatives with H or Me at C-1 1-6 presented no significant activity at 300 microM. The presence of a 1-(3,4-dimethoxybenzyl) moiety seems an important feature. Indeed, compound 8 showed a blockade of the AHP of only 33% at 300 microM while compound 13 blocked it by 67%, respectively, at the same concentration. Binding experiments were also performed. Binding affinities for SK channels are in good agreement with electrophysiological data. These results indicate that the presence of a charged nitrogen group is an essential point for the affinity on SK channels. Finally, because of the similar activity of both enantiomers of NML 19 and 20, the interaction site may present a symmetrical configuration.

Modulation of small conductance calcium-activated potassium (SK) channels: a new challenge in medicinal chemistry.

Small conductance calcium-activated potassium (SK) channels are found in many types of neurons as well as in some other cell types. These channels are selective for K(+) and open when intracellular Ca(2+) rises to omega 500 nM. In neurons, this occurs during and after an action potential. Activation of SK channels hyperpolarizes the membrane, thus reducing cell excitability for several tens or hundreds of milliseconds. This phenomenon is called a afterhyperpolarization (AHP). Three subtypes of SK channels (SK1, SK2, SK3) have been cloned and exhibit a differential localization in the brain. SK channels may play a role in physiological and pathological conditions. They may be involved in the control of memory and cognition. Moreover, they are heavily expressed in the basal ganglia (in particular in the substantia nigra, pars compacta) and in the limbic system, suggesting that they may modulate motricity and emotional behaviour. Based on these facts, SK channel subtypes may be a suitable target for developing novel therapeutic agents, but more work is needed to validate these targets. Hence, there is a great need for selective ligands. Moreover, although the risk of peripheral side-effects for SK channel modulators appears to be low, some questions remain to be investigated. Currently, different molecules are known as SK channel modulators. Apamin is a very potent peptidic agent; it produces a strong blockade of these targets which is only very slowly reversible and it has limited selectivity. Dequalinium was found to be an effective blocker. Different chemical modulations on the dequalinium structure led to the discovery of highly potent bis-quinolinium derivatives such as UCL 1684. Other bis-(2-amino-benzimidazole) derivatives are in development. On the other hand, quaternary salts of bicuculline were reported to be effective in inhibiting AHPs. More recent developments on structurally-related molecules revealed that methyl-laudanosine is a new interesting tool for exploring SK channel pharmacology. Finally, a family of compounds has been shown to facilitate SK channel opening. Such compounds may be useful in treating disorders involving neuronal hyperexcitability.

[Effects of nicotine and cannabinoids on the central nervous system]. / Effets de la nicotine et du cannabis sur le système nerveux central.

We describe the molecular mechanisms of action of nicotine and delta 9-tetrahydrocannabinol, the most potent component of cannabis. Like other drugs of abuse, these compounds enhance dopamine release in a precise area of the limbic system when administered acutely. It has recently been shown that the cannabinoid receptors on which delta 9-tetrahydrocannabinol acts are also activated by endogenous ligands such as anandamide. This unconventional neurotransmitter appears to have important physiological effects in the central nervous system. Both preclinical and clinical evidence suggests that nicotine is more addictive than delta 9-tetrahydrocannabinol. However, the intimate interactions that exist between cannabinoid and opioid systems within the brain suggest that cannabinoids should not be considered as harmless drugs of abuse.

Dopamine activates noradrenergic receptors in the preoptic area.

Dopamine (DA) facilitates male sexual behavior and modulates aromatase activity in the quail preoptic area (POA). Aromatase neurons in the POA receive dopaminergic inputs, but the anatomical substrate that mediates the behavioral and endocrine effects of DA is poorly understood. Intracellular recordings showed that 100 microm DA hyperpolarizes most neurons in the medial preoptic nucleus (80%) by a direct effect, but depolarizes a few others (10%). DA-induced hyperpolarizations were not blocked by D1 or D2 antagonists (SCH-23390 and sulpiride). Extracellular recordings confirmed that DA inhibits the firing of most cells (52%) but excites a few others (24%). These effects also were not affected by DA antagonists (SCH-23390 and sulpiride) but were blocked by alpha2-(yohimbine) and alpha1-(prazosin) noradrenergic receptor antagonists, respectively. Two dopamine-beta-hydroxylase (DBH) inhibitors (cysteine and fusaric acid) did not block the DA-induced effects, indicating that DA is not converted into norepinephrine (NE) to produce its effects. The pK(B) of yohimbine for the receptor involved in the DA- and NE-induced inhibitions was similar, indicating that the two monoamines interact with the same receptor. Together, these results demonstrate that the effects of DA in the POA are mediated mostly by the activation of alpha2 (inhibition) and alpha1 (excitation) adrenoreceptors. This may explain why DA affects the expression of male sexual behavior through its action in the POA, which contains high densities of alpha2-noradrenergic but limited amounts of DA receptors. This study thus clearly demonstrates the existence of a cross talk within CNS catecholaminergic systems between a neurotransmitter and heterologous receptors.

Pirlindole and dehydropirlindole protect rat cultured neuronal cells against oxidative stress-induced cell death through a mechanism unrelated to MAO-A inhibition.

It has been shown that the MAO (monoamine oxidase)-B inhibitor deprenyl (DPR, selegiline) protects some cell types against oxidative stress. By decreasing H(2)O(2) production, MAO-A inhibitors could also reduce oxidative stress. This study reports the effect of the MAO-A inhibitors, pirlindole (PIR), dehydropirlindole (DHP), brofaromine (BRO) and moclobemide (MCL) on primary-cultured brain cells exposed to iron-mediated toxicity. A comparison with trolox (TRO), a hydrosoluble vitamin-E analogue that protects against such an induced stress, was performed. Rat hippocampal or cortical cultured cells were exposed either to 2 microM FeSO(4) alone or in the presence of PIR, DHP, BRO, DPR, MCL or TRO. Cell survival (lactate-dehydrogenase measurements, 16 h incubation), intracellular peroxide production (DCF-fluorescence, 1 h incubation), lipoperoxidation (TBARS-fluorescence, 6 h incubation) and mitochondrial function (MTT-test, 16 h incubation) were assessed. PIR, DHP and TRO significantly protected cultures (P<0.05) against Fe(2+)-induced toxicity in a concentration-dependent manner. The EC(50s) of these compounds were 6, 12 and 19 microM, respectively, in hippocampal cells. For cortical cell cultures incubated in the presence of iron and PIR or DHP, EC(50s) were 5 and 6 microM respectively. All Hill coefficients were close to unity. BRO, MCL and DPR were not protective in any type of culture. The IC(50s) for the inhibition of MAO-A were 2, 2 and 0.2 microM for PIR, DHP and BRO, respectively. PIR, DHP and TRO, but not DPR, induced a significant decrease in both intracellular peroxide production and lipoperoxidation. They also improved mitochondrial function. These experiments show that PIR and DHP can protect hippocampal and cortical neurons against oxidative stress at pharmacologically relevant concentrations. This protective effect seems unrelated to inhibition of MAO-A, but possibly involves free radical scavenging.

Effect of intermittent and continuous exposure to electromagnetic fields on cultured hippocampal cells.

This study was designed to assess the effect of 50 Hz electromagnetic fields (EMFs) on hippocampal cell cultures in the presence or absence of either sodium nitroprusside (SNP, a NO donor) or Fe2+ induced oxidative stress. One week old cultured rat hippocampal cells were exposed to either intermittent EMFs (IEMFs, 50 Hz, 0-5 mT, 1 min ON/OFF cycles, repeated 10 times every 2 h, 6 times/day during 48 h) or continuous EMFs (CEMFs, 50 Hz, 0-5 mT for 48 h). In a second set of experiments, the effect on such EMFs applied in combination with oxidative stress induced by 0.5 microM Fe2+ or SNP was estimated. At the end of both sets of experiments, cell mortality was assessed by lactate dehydrogenase measurements (LDH). Neither type of exposure to EMFs was observed to modify the basal rate of cell mortality. The exposure to CEMFs in presence of either NO or Fe2+ did not induce any significant increase in cell death. However, when cells were exposed to EMFs in the presence of NO, we observed a significant increase in cell death of 11 and 23% (P<0.001) at 2.5 and 5 mT, respectively. This effect had some specificity because IEMFs did not modify the effect of Fe2+ on cell mortality. Although the effects of IEMFs reported in this study were only observed at very high intensities, our model may prove valuable in trying to identify one cellular target of EMFs.

[Recent progress in the pharmacology of hypnotics and anxiolytics]. / Progrès récents dans la pharmacologie des hypnotiques et anxiolytiques.

Recent studies on the respective contribution of GABAA receptor subunits in the various pharmacological effects of benzodiazepines suggest that the sedative and amnesic properties of diazepam are mediated by enhancement of gabaergic transmission in neurons expressing the alpha 1 subunit while the anxiolytic effect is selectively mediated by alpha 2 subunit. These findings suggest that a separation of the pharmacological properties of benzodiazepines is possible and that drugs with increased clinical specificity could be developed.

Evidence for a modulatory role of Ih on the firing of a subgroup of midbrain dopamine neurons.

A previous investigation has suggested that the hyperpolarization-activated cation current Ih does not contribute to the spontaneous firing of midbrain dopaminergic neurons. This conclusion was reached using Cs(-1). We have re-examined this question with extracellular recordings in slices using the more specific blocker ZD7288. In two-thirds of the cells, low concentrations of ZD7288 induced a decrease of the spontaneous firing. The maximal inhibition was about 40% and the mean IC50 was 1.6 microM. This effect was probably direct because it persisted in the presence of antagonists of various receptors. These concentrations of ZD7288 had no effect in the remaining one third of the examined cells. However, the highest concentration of ZD7288 (300 microM) abolished the firing of all dopaminergic neurons, probably by a mechanism unrelated to the blockade of Ih. We conclude that Ih controls to a certain extent the firing of a majority of midbrain dopaminergic neurons.

The inclusion of fluoxetine into gamma-cyclodextrin increases its bioavailability: behavioral, electrophysiological and pharmacokinetic studies.

The inclusion of a drug into cyclodextrin generally results in the modification of its physical and chemical properties and sometimes can increase its oral bioavailability. The aim of this study was to compare the effects of the fluoxetine HCl/gamma-cyclodextrin complex to that of traditional fluoxetine HCl. In the forced swimming test in mice, fluoxetine HCl/gamma-cyclodextrin was more effective than fluoxetine HCl, the ED30s being, respectively, 9.5 and 16.9 mg/kg PO. Both compounds (10 mg/kg PO) were able to reduce the firing rate of dorsal raphe neurons in the rat. However, between-groups comparisons showed no significant differences between fluoxetine HCl treated animals and the vehicle group, while fluoxetine HCl/gamma-cyclodextrin appeared significantly more effective than vehicle from minute 25 of the measurement period. In healthy volunteers, the relative oral bioavailability, calculated as the ratio AUC 0-infinity fluoxetine HCl/gamma-cyclodextrin on AUC 0-infinity fluoxetine HCl (20 mg PO), was equal to 249.9%. The three experiments taken together suggest that the complexation of fluoxetine HCl into gamma-cyclodextrin increases its pharmacological efficacy in animals, this effect being related to an enhancement of its oral bioavailability as demonstrated in human healthy subjects.

Calcium release from internal stores is required for the generation of spontaneous hyperpolarizations in dopaminergic neurons of neonatal rats.

We recently have demonstrated the existence of spontaneous hyperpolarizations in midbrain dopaminergic neurons of neonatal but not adult rats. These events are mediated by the opening of apamin-sensitive K(+) channels after a rise in the intracellular concentration of Ca(2+). They are resistant to tetrodotoxin in most cases and are probably endogenous (i.e., not synaptically activated). Here their mechanism was investigated. Cyclopiazonic acid (10 microM), a specific inhibitor of endoplasmic reticulum Ca(2+) ATPases, reversibly abolished the events. Caffeine, which promotes Ca(2+) release from intracellular stores, had concentration-dependent effects. At 1 mM, it markedly and steadily increased the frequency and the amplitude of the hyperpolarizations. At 10 mM, it induced a transient increase in their frequency followed by their cessation. All these effects were quickly reversible. Ryanodine (10 microM), which decreases the conductance of Ca(2+) release channels, irreversibly blocked the spontaneous hyperpolarizations. Dantrolene (100 microM), a blocker of Ca(2+) release from sarcoplasmic reticulum of striated muscle, did not affect the events. On the other hand, Cd(2+) (100-300 microM), a broad antagonist of membrane voltage-gated Ca(2+) channels, significantly reduced the amplitude and the frequency of the hyperpolarizations. However, when the frequency of the events was increased by 1 mM caffeine, Cd(2+) affected them to a smaller extent, whereas cyclopiazonic acid still abolished them. We conclude that internal stores are the major source of Ca(2+) ions that induce the K(+) channel openings underlying the spontaneous hyperpolarizations of these neurons.

Effects of JL 3, a putative antidepressant, on rat noradrenergic and serotonergic systems.

Using in vitro electrophysiological procedures, we confirm the inhibitory effect of 10-(4-methylpiperazin-1-yl)pyrido[4,3-b][1, 4]benzothiazepine (JL 3), on dorsal raphe serotonergic (IC(50)=14 microM) and noradrenergic neurons (IC(50)=4.5 microM). The effect on dorsal raphe neurons was reduced by N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl- cyclohexanecarboxamide (WAY-100635), suggesting the importance of 5-HT(1A) receptor stimulation. Yohimbine, and ritanserin, to a lesser extent, blocked the inhibitory effect of JL 3 on locus coeruleus neurons indicating that alpha(2)-adrenoceptors and 5-HT(2A) receptors may be implicated in the effects. Because of its negligible alpha(2)-adrenoceptor affinity, the effect of JL 3 on locus coeruleus neurons, would have to be indirect. JL 3 may interfere with the norepinephrine transporter site (IC(50)=0.34 microM). JL 3 tended to reinforce the hypertensive effect of norepinephrine, while it strongly inhibited the hypertensive effect of tyramine, further indicating an interaction at the norepinephrine transporter site level.

Spontaneous apamin-sensitive hyperpolarizations in dopaminergic neurons of neonatal rats.

Spontaneous apamin-sensitive hyperpolarizations in dopaminergic neurons of neonatal rats. J. Neurophysiol. 80: 3361-3364, 1998. Intracellular recordings from substantia nigra slices revealed the existence of spontaneous hyperpolarizations (amplitude 2-8 mV, duration 100-400 ms) at -60 mV in most dopaminergic neurons of neonatal (9-15 days) but not adult rats. These events were blocked by apamin (300 nM) and bicuculline methochloride (100-300 microM), which blocks apamin-sensitive currents. They were unaffected by the selective gamma-aminobutyric acid-A (GABAA) antagonists SR95531 (100 microM) and picrotoxin (30-50 microM), the GABAB antagonist CGP35348 (300 microM), the D2 antagonist haloperidol (1 microM), and the metabotropic antagonist MCPG (1 mM). The hyperpolarizations were strongly attenuated or abolished when recording electrodes contained 200 mM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. They were resistant to tetrodotoxin in the majority of the cells. They had some voltage dependency and were in some cases transiently potentiated when cells were briefly depolarized by current injection. We conclude that dopaminergic neurons have developmentally regulated physiological properties. These spontaneous hyperpolarizations might affect the firing rate of these cells, which was found to be lower in neonates than in adults.