The antipsychotic drug loxapine is an opener of the sodium-activated potassium channel slack (Slo2.2).

Sodium-activated potassium (K(Na)) channels have been suggested to set the resting potential, to modulate slow after-hyperpolarizations, and to control bursting behavior or spike frequency adaptation (Trends Neurosci 28:422-428, 2005). One of the genes that encodes K(Na) channels is called Slack (Kcnt1, Slo2.2). Studies found that Slack channels were highly expressed in nociceptive dorsal root ganglion neurons and modulated their firing frequency (J Neurosci 30:14165-14172, 2010). Therefore, Slack channel openers are of significant interest as putative analgesic drugs. We screened the library of pharmacologically active compounds with recombinant human Slack channels expressed in Chinese hamster ovary cells, by using rubidium efflux measurements with atomic absorption spectrometry. Riluzole at 500 µM was used as a reference agonist. The antipsychotic drug loxapine and the anthelmintic drug niclosamide were both found to activate Slack channels, which was confirmed by using manual patch-clamp analyses (EC(50) = 4.4 µM and EC(50) = 2.9 µM, respectively). Psychotropic drugs structurally related to loxapine were also evaluated in patch-clamp experiments, but none was found to be as active as loxapine. Loxapine properties were confirmed at the single-channel level with recombinant rat Slack channels. In dorsal root ganglion neurons, loxapine was found to behave as an opener of native K(Na) channels and to increase the rheobase of action potential. This study identifies new K(Na) channel pharmacological tools, which will be useful for further Slack channel investigations.

Behavioral effects of phenelzine in an experimental model for screening anxiolytic and anti-panic drugs: correlation with changes in monoamine-oxidase activity and monoamine levels.

This study investigated the effects of acute and chronic (one daily i.p. injection for 14 days) treatments with the non-selective irreversible monoamine-oxidase (MAO) inhibitor phenelzine (10 and 30 mg/kg) on defensive behaviors of Swiss mice in the mouse defense test battery (MDTB) which has been designed for screening anxiolytic and anti-panic drugs. In the MDTB, subjects were confronted with a natural threat (a rat) and situations associated with this threat. MAO-A and MAO-B activities and levels of brain monoamines (serotonin (5-HT), dopamine (DA) and norepinephrine (NE)) and their deaminated metabolites were subsequently measured. Behavioral results showed that acute administration of phenelzine did not specifically modify defensive behaviors. By contrast, after chronic treatment, phenelzine produced a significant reduction in avoidance distance when the rat was approaching, an effect which is consistent with an anti-panic-like action. In addition, phenelzine displayed weak anxiolytic-like effects as it increased risk assessment responses when mice were constrained in one part of the apparatus facing the rat which remained at a constant distance. No other specific drug effect was observed. These behavioral changes were associated with a dramatic increase in 5-HT levels, in particular after chronic treatment, while levels of DA and NE increased only slightly. Importantly, no significant differences in DA and NE levels between acute and chronic regimens were observed. Levels of deaminated metabolites of monoamines were markedly decreased. Measurements of MAO activity revealed substantial reductions in both type A and B forms with a full inhibition of both forms being observed only after chronic treatment with phenelzine. These results suggest that the effects of phenelzine may be due mainly to its effects on the 5-HT system and presumably related to the full inhibition of MAO-A and/or MAO-B.

Tandospirone and its metabolite, 1-(2-pyrimidinyl)-piperazine--II. Effects of acute administration of 1-PP and long-term administration of tandospirone on noradrenergic neurotransmission.

1-(2-Pyrimidinyl)-piperazine (1-PP) is a common metabolite of the antidepressant/anxiolytic 5-HT1A agonists, tandospirone (SM-3997), gepirone, buspirone and ipsapirone. The present electrophysiological studies were undertaken to characterize in vivo the effect of 1-PP on noradrenergic (NE) neurotransmission in rat brain. At small doses, 1-PP (ED50 = 80 micrograms/kg, i.v.) reversed the depressant effect of the alpha 2-adrenoceptor agonist, clonidine (20 micrograms/kg, i.v.) on the firing activity of NE neurones of the locus coeruleus. After long-term treatment with tandospirone (10 mg/kg/day, s.c. x 14 days), the responsiveness of these NE neurones to intravenous administration of clonidine was decreased but their mean firing frequency remained within the control range. The effect of 1-PP on the postsynaptic alpha 2-adrenoceptor of pyramidal neurones in the hippocampus was investigated: intravenous administration of 1-PP (2-8 mg/kg, i.v.) reduced the effect of microiontophoretically-applied NE on CA3 pyramidal neurones of the dorsal hippocampus, without affecting their responsiveness to GABA and 5-HT. The effect of the electrical stimulation of NE neurones of the locus coeruleus in reducing firing activity of pyramidal neurones, which is mediated by postsynaptic alpha 1-adrenoceptors, was increased by 47% after acute administration of 1-PP (4 mg/kg, i.v.), presumably as a result of blockade of terminal alpha 2-autoreceptors. The effectiveness of these stimulations remained unchanged after long-term treatment with tandospirone. Furthermore, the decrease in the effectiveness of stimulation of the locus coeruleus, obtained by increasing the frequency from 1 to 5 Hz, a phenomenon due to an increased activation of terminal alpha 2-adrenergic autoreceptors by endogenous NE, remained unaltered after long-term treatment with tandospirone. In addition to the initial depressant effect, stimulation of the locus coeruleus induces a late activation of these neurones which is mediated by a beta-adrenoceptor. The degree of activation induced by stimulation of the locus coeruleus was similar in controls and in long-term tandospirone-treated rats. It is concluded that 1-PP acts as an antagonist at somatodendritic and terminal alpha 2-adrenergic autoreceptors, as well as at postsynaptic alpha 2-adrenoceptors, in the central nervous system of the rat. However, the levels of 1-PP attained after long-term administration of tandospirone were not sufficient to modify NE neurotransmission.

Selective and potent monoamine oxidase type B inhibitors: 2-substituted 5-aryltetrazole derivatives.

Twenty new 2-(cyanoalkyl)tetrazoles (15 and 16) and twenty new 2-(hydroxyalkyl)tetrazoles (17 and 18) were synthesized and investigated in vitro for their abilities to inhibit selectively rat brain monoamine oxidase (MAO) B over MAO A. Most of them were MAO B inhibitors and those bearing a substituted 4-(arylmethoxy)phenyl group in the position 5 of the tetrazole ring had IC50 values between 8 microM for 18d and 2 nM for 16a (30 nM for lazabemide) with a selectivity toward MAO B of 37,000 for 16a. The reversibility of their inhibitory activity was demonstrated by in vitro dialysis tests. The 5-[4-(phenylmethoxy)phenyl]-2-(2-cyanoethyl)tetrazole (16a) its derivative 16h and the 5-[4-(phenylmethoxy)phenyl]-2-(2-hydroxyethyl)tetrazole (18a) and its derivative 18h were found to be potent, in vitro selective, and competitive MAO B inhibitors. Tetrazole 16a can be considered one of the most active and selective competitive MAO B inhibitors known up to now. This compound was selected for ex vivo experiments and was shown to be a strong and reversible MAO B inhibitor with a short duration of action after oral administration at 5 mg/kg. The structure-activity approach gives rise to the great importance of lipophilicity over electronic effects of the compounds in these series.

Autoradiographic distribution of the D1 agonist [3H]SKF 38393, in the rat brain and spinal cord. Comparison with the distribution of D2 dopamine receptors.

The regional distribution of the specific D1 agonist [3H]SKF 38393 (SKF 38393, 2,3,4,5-tetra-hydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine) has been studied autoradiographically in the rat CNS. The binding of [3H]SKF 38393 to striatal sections was saturable, stereospecific, reversible, of high affinity (Kd = 9.9 nM) and partly sodium sensitive; it occurred at a single population of sites and possessed the pharmacological characteristics of the dopamine D1 receptor. The highest levels of [3H]SKF 38393 binding sites were found in the caudate-putamen, nucleus accumbens, olfactory tubercle and substantia nigra. Moderately high concentrations of the [3H]ligand were observed in the amygdala, endopyriform nucleus, nucleus olfactorius anterior, lateral septum, primary olfactory cortex, cerebellum (molecular layer) and spinal cord. An intermediate labelling was found in the thalamus, habenula, subthalamic nucleus, hypothalamus, ventral tegmental area, superior colliculus, hippocampus and cerebral cortex. Moderate levels of [3H]SKF 38393 binding were observed in the globus pallidus and arcuate nucleus. The autoradiographic distribution of [3H]SKF 38393 overlapped with that of [3H]N,n-propylnorapomorphine, a radioligand which labels the D2 dopamine receptors, in a number of dopamine-rich brain areas but there were several areas which exhibited a high density of [3H]SKF 38393 binding sites but undetectable concentrations of [3H]N,n-propylnorapomorphine. Moreover, in the spinal cord, the subregional localization of these [3H]ligands clearly differed. Intrastriatal injection of ibotenic acid caused a large decrease in [3H]SKF 38393 and [3H]N,n-propylnorapomorphine binding in the striatum and provoked a reduction of [3H]SKF 38393 but not [3H]N,n-propylnorapomorphine binding in the substantia nigra confirming the view that nigral D1 but not D2 receptors are located on striatonigral fibres.

Pharmacodynamics and pharmacokinetics of two dose regimens of befloxatone, a new reversible and selective monoamine oxidase inhibitor, at steady state in healthy volunteers.

The pharmacodynamic equipotency of 2 dose regimens (5 mg twice daily versus 10 mg once daily) of befloxatone, a new reversible and selective monoamine oxidase A (MAO-A) inhibitor, after single and multiple doses for 6 days was examined in a randomized, double-blind, three-way crossover, placebo-controlled trial of 12 healthy volunteers. Plasma levels of the deaminated metabolite 3-4 dihydroxyphenylglycol (DHPG), as measured by high-performance liquid chromatography (HPLC) with coulometric electrochemical detection, were used as an index of MAO inhibition. A single dose of befloxatone produced a significant dose-related reduction in plasma DHPG levels, as shown by the decrease in the 24-hour area under the concentration-time curve (AUC0-24) of DHPG, which peaked 2 hours after administration and persisted over 24 hours. Both dose regimens provided equipotent extent and duration of MAO-A inhibition at steady state, suggesting a once daily dosage should be sufficient for most patients. The pharmacokinetic bioavailability at steady state of both dose regimens was also similar. The concentration-time effect curve after a single dose revealed a hysteresis corresponding to the delay necessary to elicit MAO inhibition and/or elimination of DHPG. The relationship between plasma levels of DHPG and/or elimination of plasma concentrations of DHPG and befloxatone after a single dose can be modeled using the Emax model with a mean EC50 of 4.75 ng/mL, and suggests the presence of a maximal response from the single dose. This model permits prediction of steady-state levels of DHPG.

Electrophysiological characterization of adrenoceptors in the rat dorsal hippocampus. III. Evidence for the physiological role of terminal alpha 2-adrenergic autoreceptors.

The present electrophysiological studies were undertaken to assess the role of terminal alpha 2-adrenergic autoreceptors in regulating noradrenergic synaptic transmission in the rat CNS. The effectiveness of the electrical stimulation of the locus coeruleus (LC) in suppressing the firing activity of pyramidal neurons was determined in the dorsal hippocampus. Intravenous clonidine, an alpha 2-adrenergic agonist, decreased the effectiveness of the LC stimulation, without altering the effect of microiontophoretically applied norepinephrine. The subsequent i.v. administration of low doses of idazoxan, an alpha 2-adrenergic antagonist, reversed this effect of clonidine on the LC stimulation. To ascertain that the effect of clonidine administered i.v. was indeed attributable to its action on noradrenergic terminals, it was applied locally by microiontophoresis; it decreased the effectiveness of the LC stimulation. Another paradigm used to assess the function of terminal alpha 2-adrenoceptors was to increase the frequency of the LC stimulation from 1 to 5 Hz. This resulted in a 5-fold decrease of the effectiveness of the stimulation. That this was attributable to an enhanced activation of terminal alpha 2-adrenoceptors was suggested by the reversal of this effect of increasing the frequency of the LC stimulation by intravenous idazoxan. Furthermore, the degree of enhancement of the effectiveness of the LC stimulation by idazoxan was much greater at 5 than at 1 Hz. These results provide novel electrophysiological evidence for the potent regulatory role of terminal alpha 2-adrenoceptors on noradrenergic neurotransmission.

Electrophysiological characterization of adrenoceptors in the rat dorsal hippocampus. I. Receptors mediating the effect of microiontophoretically applied norepinephrine.

The rat hippocampus receives a dense noradrenergic innervation originating exclusively from the locus coeruleus. The present electrophysiological study was undertaken to characterize the adrenoceptor mediating the suppressant effect of microiontophoretically applied norepinephrine (NE) on CA1 and CA3 dorsal hippocampus pyramidal neurons of the rat. The rank order of potency of microiontophoretically applied agonists, in suppressing the firing rate of hippocampus pyramidal neurons was: oxymetazoline greater than NE greater than phenylephrine greater than isoproterenol greater than clonidine. In the hippocampus, oxymetazoline was more potent than NE, whereas it was ineffective in the lateral geniculate nucleus where the effect of NE is mediated by an alpha 1-adrenoceptor. Low currents of clonidine antagonized the effect of NE suggesting that clonidine may exert a partial agonistic effect. The rank order of potency of i.v. administered adrenergic antagonists in blocking the suppressant effect of microiontophoretically applied NE was: idazoxan much greater than prazosin much greater than propranolol. Idazoxan also blocked the effect of oxymetazoline, phenylephrine, and isoproterenol but did not modify the effect of microiontophoretically applied gamma-aminobutyric acid (GABA). In addition, idazoxan, applied by microiontophoresis, readily blocked the suppressant effect of NE without affecting that of GABA. These results suggest that the suppressant effect of microiontophoretically applied NE on rat dorsal hippocampus pyramidal neurons is primarily mediated by alpha 2-adrenoceptors.

Electrophysiological characterization of adrenoceptors in the rat dorsal hippocampus. II. Receptors mediating the effect of synaptically released norepinephrine.

The present studies were undertaken to determine the nature of the receptors mediating the effects of endogenous norepinephrine (NE) released by stimulation of the locus coeruleus (LC) on the firing activity of dorsal hippocampus pyramidal neurons in the rat. Unitary activity of CA3 pyramidal neurons was recorded extracellularly. In most neurons, the LC stimulation produced a period of suppression, followed by a period of activation. The suppression was selectively blocked by prazosin, an alpha 1-adrenoceptor antagonist, whereas the activation was selectively blocked by propranolol, a beta-adrenoceptor antagonist. Idazoxan, an alpha 2-adrenoceptor antagonist, increased the period of suppression without affecting the period of activation. The effectiveness of microiontophoretic applications of NE on the same neurons was reduced by idazoxan, but was modified neither by propranolol nor prazosin. Lesion of the central noradrenergic system by intracerebroventricular 6-hydroxydopamine markedly decreased the NE content in the hippocampus in all rats but the effectiveness of the LC stimulation was reduced only in rats with a depletion greater than 90%. These results demonstrate that the suppressant effect of endogenous NE released by LC stimulation on hippocampus pyramidal neurons is mediated by an alpha 1-adrenoceptor and suggest that its late excitatory effect might involve beta-adrenoceptors. Since the effect of microiontophoretically applied NE on the same neurons is mediated by alpha 2-adrenoceptors, these data provide evidence that, in the rat hippocampus, postsynaptic alpha 1-adrenoceptors are intrasynaptic, whereas postsynaptic alpha 2-adrenoceptors are extrasynaptic.

The formation of deaminated metabolites of dopamine in the locus coeruleus depends upon noradrenergic neuronal activity.

The effect of manipulations of noradrenergic neuronal activity on the levels of the deaminated metabolites of dopamine in the locus coeruleus has been investigated in the rat. Antidromic stimulation of the locus coeruleus increased the levels of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG) in this area. Conversely, local infusion of tetrodotoxin into the locus coeruleus reduced the levels of these metabolites in this region. After systemic injection, idazoxan increased whereas clonidine diminished DOPAC, HVA and MOPEG levels in the locus coeruleus either in normal animals or in animals bearing a lesion of A9 and A10 dopaminergic cells. These results suggest that the formation of dopamine deaminated metabolites in noradrenergic cell bodies is dependent upon, and may serve as an index of, central noradrenergic neuronal activity.

Increase in dopamine and DOPAC levels in noradrenergic terminals after electrical stimulation of the ascending noradrenergic pathways.

The effect of electrical stimulation of the ascending noradrenergic neurons on the formation of dopamine and its major deaminated metabolite dihydroxyphenylacetic acid (DOPAC) in the hippocampal formation, a predominantly noradrenaline-rich brain area, has been investigated in the rat. Electrical stimulation of the locus coeruleus or ascending noradrenergic pathways caused a pronounced increase in hippocampal dopamine and DOPAC levels which paralleled the increase in free and conjugated dihydroxyphenylethyleneglycol levels. The elevation of hippocampal DOPAC was no longer seen after chemical lesion of the noradrenergic pathways. It is suggested that the enhanced formation of dopamine and DOPAC in hopocampal noradrenergic terminals under conditions of increased noradrenergic impulse flow may be connected to an inefficient beta-hydroxylation of dopamine to noradrenaline with a subsequent oxidative deamination of dopamine into its degradation products.

Effect of desipramine and amphetamine on noradrenergic neurotransmission: electrophysiological studies in the rat brain.

The present electrophysiological experiments were undertaken to investigate the effect of desipramine and d-amphetamine on noradrenergic neurotransmission in the rat central nervous system. The effectiveness of electrical stimulation of the locus coeruleus and of microiontophoretic application of norepinephrine (NE) in suppressing the firing activity of CA3 pyramidal neurons was studied in the dorsal hippocampus. Desipramine (0.5 and 5 mg/kg i.v.) and d-amphetamine (0.25 and 5 mg/kg i.v.) decreased the effectiveness of locus coeruleus stimulation and prolonged the effect of microiontophoretically applied NE on the same pyramidal neurons. Subsequent i.v. administration of idazoxan, an alpha 2-adrenoceptor antagonist, reversed the effects of desipramine and d-amphetamine on the effectiveness of locus coeruleus stimulation and decreased that of microiontophoretically applied NE. In addition, idazoxan prevented the effect of subsequent administration of desipramine (5 mg/kg i.v.) on the effectiveness of locus coeruleus stimulation. High doses of d-amphetamine (5 and 10 mg/kg i.v.) decreased the firing activity of hippocampus pyramidal neurons by 70 and 98%, respectively, whereas low doses of desipramine (0.5 mg/kg i.v.) or of d-amphetamine (0.25 mg/kg i.v.) were without effect. After lesioning of NE projections with 6-hydroxydopamine, the effect of the 5 mg/kg dose of d-amphetamine on the firing activity of hippocampus pyramidal neurons was markedly reduced, whereas the cumulative 10 mg/kg dose of d-amphetamine completely suppressed, as in control rats, the firing activity of these neurons. This effect of d-amphetamine in 6-hydroxydopamine-pretreated rats was reversed by the administration of the 5-HT1A receptor antagonist BMY 7378. These data provide evidence that acute administration of desipramine and d-amphetamine decreases the effectiveness of locus coeruleus stimulation by increasing the activation of terminal alpha 2-adrenoceptor autoreceptors. In addition, acute administration of high doses of d-amphetamine decreases the firing rate of hippocampus pyramidal neurons by increasing NE and serotonin release.

Effect of the reversible monoamine oxidase-A inhibitor befloxatone on the rat 5-hydroxytryptamine neurotransmission.

The aim of the present study was to assess, using in vivo electrophysiological paradigms, the effect of sustained administration of the selective and reversible monoamine oxidase-A inhibitor beflotaxone on serotonin (5-hydroxytryptamine, 5-HT) neurotransmission. In male Sprague-Dawley rats with the osmotic minipumps in place, a treatment with befloxatone (0.75 mg/kg per day, s.c.) for 2 days decreased the spontaneous firing activity of dorsal raphe 5-HT neurons. The combination of befloxatone and the 5-HT1A/1B receptor antagonist (-)-pindolol (15 mg/kg per day, s.c.) for 2 days slightly increased the firing activity of 5-HT neurons, whereas a treatment with (-)-pindolol alone for 2 days did not modify this parameter. The suppressant effects on the firing activity of 5-HT neurons of the 5-HT autoreceptor agonist lysergic acid diethylamide (LSD), injected intravenously, and of both 5-HT and the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), applied by microiontophoresis, were attenuated in rats treated with befloxatone for 2 days, suggesting an early desensitization of the somatodendritic 5-HT1A receptors. The firing activity of 5-HT neurons was back to normal after a treatment for 21 days with befloxatone but the suppressant effects of LSD, 5-HT or 8-OH-DPAT was the same as in controls. In contrast, the suppressant effect of the alpha2-adrenoceptor agonist clonidine on the firing activity of 5-HT neurons was significantly attenuated after the treatment with befloxatone for 21 days. At the postsynaptic level, the administration of the selective 5-HT1A receptor antagonist (N-[2-[4(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohe xanecarboxamide trihydroxychloride (WAY 100635, 100 microg/kg, i.v.) did not modify the firing activity of quisqualate-activated dorsal hippocampus CA3 pyramidal neurons in control rats. In contrast, in rats treated with befloxatone in combination with (-)-pindolol for 2 days as well as with befloxatone alone for 21 days, WAY 100635 significantly increased the firing of CA3 pyramidal neurons. In conclusion, these data suggest that when the firing activity of 5-HT neurons is normal in the presence of befloxatone, either after a two-day treatment together with (-)-pindolol or alone for 21 days, the tonic activation of postsynaptic 5-HT1A receptors is enhanced.

Further evidence for, and nature of, the facilitatory GABAergic influence on central noradrenergic transmission.

In order to explore the nature of the facilitatory GABAergic control of cerebral noradrenergic neurons, we have studied the effect of a variety of GABA mimetics (given systemically or injected locally into brain areas containing noradrenergic cell bodies or terminals) on several indices of noradrenaline turnover in the rat brain. Systemic administration of both direct and indirect acting GABA mimetics enhanced; 1) the pargyline induced accumulation of normetanephrine in the hypothalamus; 2) total DOPEG levels in a number of brain regions innervated by noradrenergic neurons; 3) both DOPAC and MOPEG levels in noradrenergic cell body areas (A1, A2 and A6). These effects are probably mediated by GABAA receptors as specific GABAA or mixed GABAA/GABAB agonists but not the GABAB agonist baclofen enhanced noradrenaline turnover. Interruption of noradrenergic impulse flow (by local injection of tetrodotoxin or by hemitransection) blocked the ability of progabide to increase DOPEG concentrations in the hypothalamus and cerebral cortex. Similarly, the co-administration of clonidine with progabide antagonized the progabide-induced increase in hypothalamic total DOPEG levels. Co-administration of yohimbine with progabide provoked an additive effect on hypothalamic DOPEG levels at moderate but not at high doses of yohimbine. Thus, the acceleration of noradrenaline turnover induced by GABA mimetics appears to depend on ongoing activity in noradrenergic neurons and occurs via an increase in neuronal discharges. Local injection of muscimol into the nucleus accumbens or hypothalamus failed to affect DOPEG levels in these structures; similarly, local injection of muscimol into the locus coeruleus failed to modify DOPEG levels in corresponding noradrenergic projection areas. These data indicate that the GABAergic influence is not exerted via GABA receptors located on noradrenergic cell bodies or nerve endings. Furthermore, since systemically administered progabide still increased hypothalamic DOPEG levels after ibotenate-induced destruction of the hypothalamic neuronal cell bodies, a presynaptic modulation of noradrenergic neurons by local GABAergic interneurons is excluded. Chemical destruction of serotoninergic pathways or enhancement of 5-HT transmission by quipazine failed to alter the ability of progabide to increase cerebral DOPEG levels. Moreover, scopolamine or naloxone also failed to affect the progabide-induced increase in cerebral DOPEG levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical pharmacology of befloxatone (MD370503), a new potent reversible MAO-A inhibitor.

In vitro and ex-vivo studies show that befloxatone, a new oxazolidinone derivative, is a potent, reversible, competitive and specific MAO-A inhibitor (KiA from 1.9 to 3.6 nM and KiB/KiA ratio between 100 and 400, in the Rat and in Man, depending on the tissue). Befloxatone possesses a marked activity in antidepressant-sensitive behavioral models in rats (from 0.03 to 0.15 mg/kg po) and mice (from 0.21 to 0.29 mg/kg po). At these doses, befloxatone does not induce a significant potentiation of oral tyramine. Befloxatone is devoid of sedative, anticholinergic and cardiovascular effects. Befloxatone is rapidly and extensively distributed in rat brain, the pharmacokinetics are linear in the rat and in man in a large range of doses. Befloxatone is well tolerated in healthy volunteers and is developed as an antidepressant.

Effects of befloxatone, a new potent reversible MAO-A inhibitor, on cortex and striatum monoamines in freely moving rats.

Single administration of befloxatone (0.75 mg/kg, i.p.) in the rat increased extracellular levels of DA (+300%) in striatum. In frontal cortex, befloxatone (0.75 mg/kg, i.p.) and nialamide (100 mg/kg, i.p.) increased NA by +100% but did not modify 5HT, whereas pargyline (100 mg/kg i.p.) increased extracellular NA and 5HT by 400 and 600%, respectively. At these doses, befloxatone inhibited totally and selectively MAO-A, pargyline inhibited totally MAO-A and MAO-B. Increases of tissue and extracellular concentrations of NA and 5HT were highest after Pargyline suggesting that both monoamines may be metabolized by MAO-A and MAO-B. Befloxatone and nialamide potentiated the effects of idazoxan (20 mg/kg, i.p.) on extracellular NA in frontal cortex, which increased from 350% to 2,000 and 1,500% respectively. These results suggest that alpha 2-adrenoceptors play a major role in the regulation of extracellular NA in frontal cortex.

Clinical pharmacology of befloxatone: a brief review.

Clinical pharmacology studies of befloxatone, a new selective reversible inhibitor of monoamine oxidase-A (MAO-A), have addressed safety, with special emphasis on tyramine interactions, and have also investigated pharmacokinetics (PK) and pharmacodynamics in terms of both MAO-A inhibition (using 3,4-dihydroxyphenylglycol, DHPG, as a pharmacological activity marker) and effects on psychomotor and cognitive function, in young and elderly healthy volunteers. Clinical and laboratory safety data were satisfactory in healthy volunteers given single doses of up to 160 mg or repeated doses of up to 80 mg/day for 7 days. Tyramine interaction studies showed that the expected potentiation of the tyramine pressor effect occurred with a safety margin that was so wide as to make dietary restrictions unnecessary with dosages of up to 20 mg once daily in clinical settings. Absorption was rapid (tmax = 2 h), terminal halflife was about 11 h, and PK parameters increased linearly with the dose. Befloxatone induced a dose-dependent decrease in plasma DHPG levels from 2.5 mg upwards, and a 10-mg dose provided sub-maximal activity (80% DHPG decrease) of 24 h duration. No sedative or stimulant effects were detected using several batteries of psychometric tests. Befloxatone was devoid of deleterious effects on memory in young volunteers, and exhibited the EEG profile of a non-sedative antidepressant. In summary, available clinical pharmacology studies confirm that befloxatone is a safe and potent RIMA with no potential for inducing deleterious CNS effects.

Preclinical profile of befloxatone, a new reversible MAO-A inhibitor.

Befloxatone, a novel oxazolidinone derivative, is a potent, selective and reversible monoamine oxidase A (MAO-A) inhibitor in vitro (K1A = 1.9-3.6 nM) and ex vivo (ED50 MAO-A = 0.02 mg/kg, p.o.). It does not interact with a large number of receptors, monoamine transporters or other amine oxidases. Binding studies with [3H]-befloxatone in rat brain sections show that it labels with high affinity (Kd = 1.3 nM) a single population of sites with the pharmacological characteristics and regional distribution of MAO-A. In the rat brain, befloxatone (0.75 mg/kg, i.p.) increases tissue levels of monoamines and decreases levels of their deaminated metabolites. Acute administration of befloxatone (0.75 mg/kg, i.p.) induces an increase in extracellular striatal dopamine and cortical norepinephrine but not cortical serotonin levels in the rat. Befloxatone (1 mg/kg, i.p.) potently inhibits the firing rate of serotonergic neurons, partially decreases the firing of noradrenergic neurons and has no effect on the firing of dopaminergic neurons (a mirror image of its effects on monoamine release in terminal regions), suggesting that the relative effects of befloxatone on monoamine release may be governed by autoreceptor-mediated control of monoaminergic neurons at the cell body level. Befloxatone (0.03-0.3 mg/kg, p.o.) exhibits potent activity in behavioural models predictive of antidepressant activity. Befloxatone (up to 1.5 mg/kg, p.o.) does not potentiate the pressor effects of orally administered tyramine at centrally active doses and duodenal [3H]-befloxatone binding is displaced by increasing doses of orally administered tyramine (0.1-40 mg/kg, i.p.). These results suggest that befloxatone is a potent reversible MAO-A inhibitor with antidepressant potential and a wide safety margin with regard to the potentiation of the pressor effect of tyramine.

Reduction of oral ethanol self-administration in rats by monoamine oxidase inhibitors.

Evidence for a role of dopamine and serotonin in the control of ethanol intake in animals suggests that monoamine oxidase (MAO) inhibitors, which increase the synaptic availability of serotonin and dopamine by blocking their metabolism, might have efficacy in the treatment of alcohol dependence. The aim of the present study was, therefore, to evaluate several MAO inhibitors for their capacity to affect ethanol self-administration in rats trained to self-administer ethanol (10% v/v) orally in a free-choice two-lever operant task. The nonselective and irreversible MAO inhibitors, phenelzine (3-10 mg/kg), tranylcypromine (1-3 mg/kg), and nialamide (30 mg/kg), decreased rates of responding maintained by ethanol reinforcement. The reversible MAO-A inhibitor, befloxatone (0.3-3 mg/kg), and the irreversible MAO-A inhibitor, clorgyline (10-30 mg/kg), also reduced ethanol self-administration. However, befloxatone-induced effects leveled off at a 50% decrease. The irreversible MAO-B inhibitors, pargyline (30 mg/kg) and l-deprenyl (3-10 mg/kg) also decreased responding maintained by ethanol reinforcement; these results are consistent with previous findings that both drugs decreased ethanol intake in mice. In conclusion, the present results showing that several MAO inhibitors decreased ethanol self-administration in rats are consistent with previous findings that synaptic levels of serotonin and dopamine play a critical role in the control of ethanol self-administration.

Beneficial effects of lysine acetylsalicylate, a soluble salt of aspirin, on motor performance in a transgenic model of amyotrophic lateral sclerosis.

We have studied the effect of lysine acetylsalicylate (LAS; Aspegic), a soluble salt of aspirin, on motor deficits in transgenic mice expressing a human superoxide dismutase SOD1 mutation (Gly-93 --> Ala), an animal model of familial amyotrophic lateral sclerosis (FALS). In nontreated FALS mice, motor impairments appear at 12-14 weeks of age, whereas paralysis is not observed before 20 weeks of age. Life expectancy is 140-170 days. Early treatment with LAS from 5 weeks of age delayed the appearance of motor deficits in FALS mice as measured by extension reflex, loaded grid, and rotarod tests. This beneficial effect of treatment was maintained up to 18 weeks of age, until just before onset of end-stage disease. When treatment was started at 13 weeks, no significant beneficial effect was observed. These results demonstrate that chronic LAS treatment is able to delay the appearance of reflex, coordination, and muscle strength deficits in this animal model of ALS if the treatment is started early enough. However, neither the onset of paralysis nor end-stage disease were improved by the LAS treatment. In the absence of an effect on survival, the functional improvement demonstrated here is probably the maximum that this demanding model could allow. Although other properties of LAS may have contributed to its beneficial effect, we suggest that the antioxidant properties of aspirin are responsible for the positive effects in this model and support the use of antioxidants as effective therapy for ALS.