The vigilance promoting drug modafinil increases extracellular glutamate levels in the medial preoptic area and the posterior hypothalamus of the conscious rat: prevention by local GABAA receptor blockade.

The effects of modafinil on glutamatergic and GABAergic transmission in the rat medial preoptic area (MPA) and posterior hypothalamus (PH), are analysed. Modafinil (30-300 mg/kg) increased glutamate and decreased GABA levels in the MPA and PH. Local perfusion with the GABAA agonist muscimol (10 microM), reduced, while the GABAA antagonist bicuculline (1 microM and 10 microM) increased glutamate levels. The modafinil (100 mg/kg)-induced increase of glutamate levels was antagonized by local perfusion with bicuculline (1 microM). When glutamate levels were increased by the local perfusion with the glutamate uptake inhibitor L-trans-PDC (0.5 mM), modafinil produced an additional enhancement of glutamate levels. Modafinil (1-33 microM) failed to affect [3H]glutamate uptake in hypothalamic synaptosomes and slices. These findings show that modafinil increases glutamate and decreases GABA levels in MPA and PH. The evidence that bicuculline counteracts the modafinil-induced increase of glutamate levels strengthens the evidence for an inhibitory GABA/glutamate interaction in the above regions controlling the sleep-wakefulness cycle.

Lack of pre-synaptic dopaminergic involvement in modafinil activity in anaesthetized mice: in vivo voltammetry studies.

Modafinil was compared to the indirect dopaminergic drugs, dexamphetamine and methylphenidate, using in vivo differential normal pulse voltammetry with carbon fibre electrodes located in the caudate nucleus to study extracellular catechol level in anaesthetized mice. Modafinil (16-256 mg kg-1) failed to modify the catechol oxidation peak height (peak 2). Dexamphetamine at low doses (2 and 4 mg kg-1) decreased, while at a higher dose (8 mg kg-1) did not modify peak 2 height. A low dose of methylphenidate (16 mg kg-1) did not display any effect, while higher doses (32 and 64 mg kg-1) increased peak 2 height. Pargyline-induced monoamine oxidase inhibition elicited a rapid and dramatic decrease in peak 2 height (related to the decrease of catechol levels). In these conditions modafinil (64 and 256 mg kg-1) did not modify, while dexamphetamine (2, 4 and 8 mg kg-1) and methylphenidate (16, 32 and 64 mg kg-1) increased peak 2 height in relation to synaptic dopamine level increase. This study, in mice, demonstrated the lack of effects of modafinil on nigro-striatal function, at the pre-synaptic level, as opposed to dexamphetamine and methylphenidate.

Amplification of cortical serotonin release: a further neurochemical action of the vigilance-promoting drug modafinil.

The present in vitro and in vivo studies examined the effects of modafinil on serotonergic transmission in the rat frontal cortex. In the in vitro study modafinil (0.3-30 microM) increased electrically-evoked, but not spontaneous, serotonin ([(3)H]5-HT) efflux from cortical slices in a concentration-dependent manner while the indirect serotonin agonist dl-fenfluramine (1-15 microM) enhanced both spontaneous and evoked [(3)H]5-HT efflux. The effects of modafinil were more pronounced when the 5-HT reuptake was blocked by paroxetine. Contrary to paroxetine (0.3-3 microM) and dl-fenfluramine (1-5 microM), modafinil failed to influence the [(3)H]5-HT uptake. In the in vivo study modafinil (3-100 mg/kg i.p.) increased 5-HT dialysate levels, the maximal effect being already reached at the 30 mg/kg dose. dl-fenfluramine (5 mg/kg) induced an increase in 5-HT levels which was significantly higher than that displayed by modafinil at 30 mg/kg. In the presence of paroxetine (3 microM), the effect of modafinil at 30 mg/kg was higher than that observed in the absence of 5-HT reuptake inhibition. Finally, in the presence of the selective 5-HT(1A) receptor agonist 8-OH-DPAT, modafinil at 100 mg/kg failed to affect 5-HT dialysate levels. These results demonstrate that modafinil regulates cortical serotonergic transmission and suggest that the drug preferentially acts by amplifying the electro-neurosecretory coupling mechanisms and via mechanisms which do not involve the reuptake process.

Awakening properties of modafinil: effect on nocturnal activity in monkeys (Macaca mulatta) after acute and repeated administration.

Single oral administration of modafinil (16-64 mg/kg) in monkeys induced an increase in nocturnal activity and in behavioural arousal without stereotyped behaviour. Modafinil-induced increase in nocturnal activity was prevented by the centrally acting alpha 1 adrenoceptor antagonist prazosin. After repeated oral administration of modafinil, b.i.d. for 5 days, nocturnal activity was still increased, but was lower than after a single administration; the gradual decrease appeared on the second night. No rebound of sleep and no residual effect on night 5 (when modafinil was administered for 4 days and placebo on day 5) were seen after the withdrawal of the drug. Therefore, modafinil appeared to produce strong behavioural stimulation and awakening in a non-human primate species, after single, as well as after repeated administration, without other obvious side-effects (no sign of anxiety, no behavioural trouble). These awakening properties involved a modulation (stimulation) of a central alpha 1 adrenergic system.

Modafinil prevents glutamate cytotoxicity in cultured cortical neurons.

The ability of modafinil (Modiodal) to protect cortical neurons from glutamate-induced degeneration was evaluated by measuring electrically evoked [3H]GABA release and [3H]GABA uptake in primary cerebral cortical cultures. In normal cells, electrical stimulation (10 Hz, 2 min) increased [3H]GABA release (FR-NER St1 = 0.77+/-0.14; St2/St1 ratio = 0.94+/-0.02). The exposure of sister cells to glutamate, reduced electrically evoked [3H]GABA release (FR-NER St1 = 0.40+/-0.05; St2/St1 ratio = 0.60+/-0.08). Modafinil (0.3-1 microM) prevented the glutamate-induced reduction of the St2/St1 ratio (0.85+/-0.11; 0.88+/-0.05, respectively). A similar protective effect was observed for [3H]GABA uptake. These findings suggest that modafinil may be neuroprotective in that it attenuates glutamate-induced excitotoxicity in cortical neurons.

Modafinil does not affect serotonin efflux from rat frontal cortex synaptosomes: comparison with known serotonergic drugs.

Modafinil did not affect spontaneous and K(+)-evoked [3H]5-HT efflux from cortical synaptosomes while it increased K(+)-evoked tritium efflux from cortical slices, an action that became stronger in the presence of paroxetine. In contrast, DL-fenfluramine and fluoxetine were able to enhance spontaneous and/or K(+)-evoked tritium efflux from synaptosomes and slices. These results suggest that modafinil does not affect 5-HT transmission from cortical synaptosomes and that its 5-HT releasing action is different from that of DL-fenfluramine and fluoxetine.

A possibe alpha-adrenergic mechanism for drug (CRL 40028)-induced hyperactivity.

CRL 40028 (benzhydryl sulfinyl acetohydroxamic acid)-induced stimulation in mice, measured as an increase in locomotor activity was studied following an intraperitoneal injection of drugs known to block alpha-adrenergic receptors. Phenoxybenzamine (20 mg/kg), prazosin (0.5-1 mg/kg) and yohimbine (2 mg/kg) prevented the development of CRL 40028-induced hyperactivity. These results suggest that stimulation of an alpha-adrenergic postsynaptic receptor is of importance for the stimulant effect of CRL 40028.

Central alpha 1-adrenergic stimulation in relation to the behaviour stimulating effect of modafinil; studies with experimental animals.

Single administration of the new drug modafinil was followed by an increase in locomotor activity in mice and in nocturnal activity in monkeys. Stereotyped behaviour in mice and rats, and potentiation of amphetamine-induced stereotyped behaviour were not observed; however, at the highest dose used, a slight potentiation of apomorphine-induced stereotyped behaviour was observed in rats. The modafinil-induced increase in locomotor activity in mice was prevented by the centrally acting alpha 1-adrenoceptor antagonists, prazosin and phenoxybenzamine, and by reserpine but not by the mixed dopamine D-1/D-2 antagonist, haloperidol, the dopamine D-2 antagonist, sulpiride, the peripherally acting alpha 1-adrenoceptor antagonist, phentolamine, the alpha 2-adrenoceptor antagonist, yohimbine, the beta-adrenoceptor antagonist, propranolol, or by the catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine. Likewise, the modafinil-induced increase in nocturnal activity in monkeys was prevented by prazosin. Interestingly, modafinil did not produce obvious peripheral sympathetic effects in mice and rats (no salivation, no contraction of the pilomotor muscles, slight mydriasis only at high doses). Therefore, modafinil appears to produce a strong stimulating effect in rodents and in primates. These effects could be linked to modulation (stimulation) of central alpha 1-adrenoceptors unaccompanied by peripheral sympathetic effects, which is unexpected.

Modafinil and cortical gamma-aminobutyric acid outflow. Modulation by 5-hydroxytryptamine neurotoxins.

The acute or chronic administration of modafinil, (diphenyl-methyl-sulfinyl-2-acetamide, 30 mg/kg s.c.) decreased gamma-amino-butyric acid (GABA) outflow from the cerebral cortex of freely moving guinea pigs and rats. In 5,7-dihydroxytryptamine intracerebroventricularly pretreated guinea pigs, the effect of modafinil on GABA outflow was reversed and the noradrenaline cortical levels increased. Prazosin (35.8 ng/kg i.p.) blocked the drug-induced increase in GABA efflux. In vitro experiments, performed in rat cortical slices, showed that modafinil failed to affect [3H]GABA release and uptake as well as glutamic acid decarboxylase activity. In conclusion, our results suggest that the balance between central noradrenaline and 5-hydroxytryptamine transmission is important for the regulation by modafinil of the GABAergic release in the cerebral cortex.

The effects of modafinil on striatal, pallidal and nigral GABA and glutamate release in the conscious rat: evidence for a preferential inhibition of striato-pallidal GABA transmission.

The effects of the anti-narcoleptic drug modafinil (30-300 mg/kg i.p.) on GABA and glutamate release were evaluated in the basal ganglia of the conscious rat, by using the microdialysis technique. Modafinil (100 mg/kg) inhibited striatal (85+/-4% of basal values) and pallidal (85+/-2%) GABA release without influencing local glutamate release. At the highest dose (300 mg/kg), modafinil induced a further reduction of pallidal (75+/-2%) but not striatal (82+/-7%) GABA release and increased striatal (134+/-11%) but not pallidal glutamate release. On the contrary, in the substantia nigra modafinil reduced GABA release only at the 300 mg/kg dose (59+/-5%) without affecting glutamate release. The preferential reduction in striato-pallidal GABA release at the 100 mg/kg dose of modafinil suggests that modafinil may be useful in the treatment of Parkinsonian diseases.

A stereological study on the neuroprotective actions of acute modafinil treatment on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced nigral lesions of the male black mouse.

The effect of an acute administration of the vigilance-promoting drug modafinil ((+/-)(diphenyl-methyl)-sulfinyl-2 acetamide; Modiodal) on the nigrostriatal dopamine system was studied after damage induced by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) by means of immunohistochemistry for tyrosine hydroxylase (TH) and a stereological method. MPTP (40 mg/kg) reduced from 24,380 +/- 902 to 13,501 +/- 522 and from 37,868 +/- 3300 to 20,568 +/- 1270, respectively, the number of TH immunoreactive (IR) and non-TH IR nigral neurons. Co-administration of Modafinil restored to normal the number of these neuronal populations. MPTP treatment induced also a reduction in the volume of TH IR neurons, which was counteracted by Modafinil administration. The data provide morphological evidence, based on unbiased stereological analysis, for a potential neuroprotective role of Modafinil, not only in dopaminergic neurons, but also with a similar magnitude in the non-DA nerve cell population of the substantia nigra after MPTP lesion. These results suggest that Modafinil has a neuroprotective role in the substantia nigra via a still undefined mechanism in which a crucial role of DA uptake blockade should be excluded. Modafinil may therefore have a therapeutic potential in neurodegenerative processes such as those occurring in Parkinson's disease.

Flerobuterol: a potential antidepressant drug related to beta-adrenergic agonists. Experimental profile in mice.

The potential antidepressant effect of flerobuterol (dl-(fluoro-2 phenyl)-1 t-butylamino-2 ethanol), a new drug related to beta-adrenoceptor agonists, was evaluated and compared with imipramine and salbutamol using classical psychopharmacological tests in mice. Like imipramine and salbutamol, flerobuterol (0.5-32 mg kg-1, ip) fully prevented apomorphine (16 mg kg-1, sc)- and partly reversed reserpine- and oxotremorine-induced hypothermia. At higher doses (16-32 mg kg-1), flerobuterol enhanced the toxic effects of yohimbine. Unlike imipramine, flerobuterol and salbutamol did not reduce immobility duration in the behavioural despair test. Salbutamol and flerobuterol decreased locomotor activity. Flerobuterol did not induce mydriasis, did not prevent oxotremorine-induced tremors or salivary and lacrimal gland secretion and did not reduce reserpine-induced palpebral ptosis. Propranolol (8 mg kg-1, ip) but not alpha-methyl-paratyrosine (75 mg kg-1, ip) prevented the flerobuterol-induced antagonism of apomorphine-induced hypothermia. Our results suggest that flerobuterol demonstrates potential antidepressant activity, which could be related to beta-adrenoceptor activation in mice.

[Safety pharmacology: central nervous system]. / Pharmacologie de sécurité: système nerveux central.

Some of the results formerly included in the dossiers under the heading of 'General Pharmacology: Central Nervous System' were intended to document most of the information now covered by the CNS Safety Pharmacology. This paper allows to point out some general experimental conditions relating to the choice of (1) suitable animal species whose use should be advocated, (2) the route by which the effects of the drugs should be studied and (3) the controls of the experimental context (surroundings, temperature, schedules of the trials, interference with food-intake episodes, influence of noises and smells, expertise of the experimental staff) likely to optimize the predictive value of the trials. Besides the core of investigations recommended by most of the regulatory authorities (changes in gross behaviour, motor coordination, locomotor activity, interaction with hypnotics, convulsant potential), the need to include or not some investigations such as EEG studies and the prediction of adverse events, such as anxiolytic and amnesia potentials, is considered. The place, within the scope of CNS Safety Pharmacology, of studies intended to document the potential for drug abuse and dependence is mentioned and some information given about the methods generally used.

[A unique psychopharmacologic profile of adrafinil in mice]. / Profil psychopharmacologique original de l'adrafinil chez la souris.

The following psychopharmacological effects of adrafinil have been observed in mice: increase in locomotor activity (64-256 mg.kg-1), antagonism (16-128 mg.kg-1) of the hypnotic effects of barbitone but not of pentobarbitone, reduction of immobility duration in the forced swimming test (16-256 mg.kg-1); slight antagonism (256 mg.kg-1) of electroshock-induced convulsions; no modification of rectal temperature; no stereotyped or climbing behaviour; no increase in lethality in aggregated mice (LD50 isolated = 1022 mg.kg-1, LD50 aggregated = 859 mg.kg-1); lack of effects on the provisional tests for antidepressants: no interaction with reserpine-, oxotremorine-, or apomorphine-induced hypothermia but potentiation of yohimbine-induced toxicity; lack of peripheral sympathetic effects (no mydriasis, no salivation, no contraction of the pilomotor muscles, no antagonism of reserpine-induced ptosis); lack of peripheral anticholinergic effects (no mydriasis, no antagonism of oxotremorine-induced salivation or lacrimation). As compared to no analeptic, anticholinergic or antidepressant drugs, adrafinil shows a unique behavioural profile in mice defined on the one hand by a specific stimulant activity associated with antidepressant-like effects that do no seem related to a beta-adrenergic mechanism and on the other hand by a lack of dopaminergic effects. Most adrafinil-induced effects (increase in locomotor activity, reduction of immobility duration in the forced swimming test) may correspond to a central alpha 1-adrenergic stimulation, but the unexpected lack of peripheral sympathetic effects remains unexplained.