The effect of niaprazine on the turnover of 5-hydroxytryptamine in the rat brain.

Niaprazine (60 mg/kg i.p.) increased rat brain 5-hydroxyindole acetic acid (5-HIAA) concentrations 30 min after treatment, and reduced them at 3-8 hr after treatment. Rat brain 5-hydroxytryptamine (5-HT) levels were unchanged. Niaprazine also produced a short-lasting depletion of rat brain noradrenaline (NA) and dopamine (DA). Pretreatment with alpha-phenyl-alpha-propyl-benzeneacetic acid, 2-(diethylamino) ethyl ester hydrochloride (SKF 525A) (75 mg/kg i.p.) potentiated the increase in 5-HIAA and depletion of catecholamines produced 1 hr after niaprazine, but abolished the reduction in 5-HIAA produced 8 hr after the drug. This suggested that a metabolite might be responsible for the delayed reduction in 5-HIAA levels. A potential metabolite, p-fluoro-phenylpiperazine (FPP) (5-40 mg/kg i.p.) reduced rat brain 5-HIAA and 3,4-dihydroxyphenyl acetic acid (DOPAC), and inhibited 5-HT and NA uptake in vitro. Unlike niaprazine, FPP produced no behavioural sedation, but in large doses produced a behavioural syndrome indicative of serotonergic stimulation. Studies of the metabolism of 14C-niaprazine in rats indicated the presence of a urinary metabolite with the same chromatographic characteristics as FPP. These results suggest that niaprazine itself depletes brain catecholamines and increases 5-HT turnover, while a metabolite, FPP, subsequently reduces the turnover of 5-HT and DA.

The effects of analogues of valproic acid on seizures induced by pentylenetetrazol and GABA content in brain of mice.

The effect of valproic acid and 10 close analogues (7 branched and 3 non-branched) were studied on the content of gamma-aminobutyric acid (GABA) in brain and on seizures induced by pentylenetetrazol (PTZ) in mice. All 8 branched fatty acids protected against seizures induced by pentylenetetrazol, but the 3 non-branched acids were inactive. A significant correlation was observed between side-chain length and anticonvulsant potency. However, sedative and toxic phenomena became apparent with longer chain lengths. The 3 non-branched fatty acids did not alter levels of GABA in brain, but there was a significant correlation between anticonvulsant activity and increased brain GABA levels, for the 8 branched fatty acids. Despite this correlation, one branched analogue, 2-ethylbutyric acid, possessed anticonvulsant activity but did not increase the content of GABA in brain.

Protective effects of SR 57746A in central and peripheral models of neurodegenerative disorders in rodents and primates.

Compounds possessing neurotrophic properties may represent a possible treatment for neurodegenerative disorders such as Alzheimer's disease. SR 57746A, 1-[2-(naphth-2-yl)ethyl]-4-(3-trifluoromethylphenyl)-1,2,5,6- tetrahydropyridine hydrochloride, is a new compound with neurotrophic activity in a number of in vitro preparations. The neurotrophic effects of this compound have been evaluated in vivo using four distinct rat models of neurodegeneration: transient global ischaemia produced by a four-vessel occlusion; septohippocampal lesion produced by injection of vincristine sulphate into the medial septum; sciatic nerve crushing; and acrylamide-induced peripheral neuropathy. Rats were administered vehicle or 2.5-10 mg/kg p.o. SR 57746A, after initiation of the degenerative process, then once daily for 10 days in the first two models, 16 days in the third and 26 days in the fourth model. Median scores for ischaemia-induced neuronal damage were reduced by 30-40% by SR 57746A treatment in hippocampal CA1, CA2, and CA3 regions, and in the dorsal striatum. Twelve days after intraseptal vincristine administration, there was a marked loss of septohippocampal cholinergic neurons, as indicated by reduced choline acetyltransferase activity in both the septum and hippocampus. SR 57746A dose-dependently reversed this reduction in both areas. These results were confirmed by histoenzymological evaluation of hippocampal acetylcholinesterase content. SR 57746A also reversed the loss of hippocampal choline acetyltransferase induced by intraseptal vincristine in marmosets. Behavioral deficits in these models (exploratory behaviour in the former and short-term social memory in the latter) were also significantly reduced by SR 57746A treatment. In the sciatic crush model, sensorimotor function improved more rapidly in rats treated with 10 mg/kg SR 57746A. In this same model, SR 57746A (10 mg/kg/day) also significantly increased the length of regenerated nerve eight days after the crush, as measured using the pinch test. Finally, SR 57746A retarded the onset, reduced the amplitude and accelerated the recovery of acrylamide-induced peripheral neuropathy. Thus, SR 57746A possesses notable neurotrophic activity in a variety of neurodegenerative models in vivo, suggesting that the compound may possess therapeutic potential for the treatment of neurodegenerative diseases.

Anaesthesia abolishes the effect of valproate on extracellular 5-HIAA, DOPAC and ascorbate as measured in rat striatum by differential pulse voltammetry.

The effect of sodium valproate (VPA, 400 mg kg-1, i.p.) on extracellular ascorbate, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) in the striatum was examined by differential pulse voltammetry in anaesthetized and freely-moving rats. In rats anaesthetized with chloral hydrate (400 mg kg-1, i.p.) pentobarbitone (50 mg kg-1, i.p.) or phenobarbitone (60 mg kg-1, i.p.), VPA produced no significant changes in peak 1 (extracellular ascorbate) or peak 2 (extracellular DOPAC), but produced a slight but statistically significant reduction in the height of peak 3 (extracellular 5-HIAA). In contrast, in freely-moving rats the same dose of VPA greatly reduced extracellular ascorbate and DOPAC concentrations, and increased that of 5-HIAA. These results suggest that VPA may reduce the release or turnover of dopamine, and increase that of 5-hydroxytryptamine in conscious rats. Our data also suggest that caution may be required in the interpretation of the effects of VPA in anaesthetized animals, as the results obtained may not always reflect the situation in the absence of anaesthesia.

The effect of the nonpeptide neurotrophic compound SR 57746A on the progression of the disease state of the pmn mouse.

1. The progressive motor neuronopathy (pmn) mouse is an autosomal recessive mutant, in which the homozygotes suffer caudio-cranial degeneration of motor axons and die several weeks after birth. This strain provides the opportunity of testing potential therapeutic strategies for the treatment of motor neurone diseases such as amyotrophic lateral sclerosis. We have performed a study of the effects on the pmn mouse of SR 57746A, an orally-active, non-peptide compound which has been found to exhibit neurotrophic effects in vitro and in vivo. In order to treat the affected mice from birth, the mothers were administered 2.5 mg kg(-1). p.o., SR 57746A every two days until the weaning of the offspring (at day 20); then the offspring were given every two days a dose of 30 microg kg(-1), p.o., until their death. 2. Affected mice treated with SR 57746A had a lifespan 50% longer than that of the vehicle-treated mice (P=0.01). Compared to vehicle-treated pmn mice, SR 57746A improved the performance of the pmn mice in three different behavioural tasks. SR 57746A also maintained the amplitude of the motor evoked response of the gastrocnemius muscle, reduced the distal motor latency, and delayed the occurrence of the spontaneous denervation activity in this muscle. Histological studies indicated that at 20 days of age the mean surface areas of the fibres of the sciatic nerve were higher in SR 57746A-treated than in vehicle-treated mice. 3. At present, SR 57746A is the only orally active, nonpeptide compound known to be capable of delaying the progression of the motor neurone degeneration in pmn mice.

Effect of the neuroprotective compound SR57746A on nerve growth factor synthesis in cultured astrocytes from neonatal rat cortex.

The neurotrophic factor promoting activity of the neuroprotective compound SR57746A was evaluated in primary cultures of neonatal rat cortical astrocytes by studying the synthesis of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). A concentration- and time-dependent increase of nerve growth factor mRNA was induced by SR57746A (10 nM-1 microM). In these astrocytes, BDNF mRNA contents were increased to a significant but smaller extent, and beta-actin mRNA showed no variation. SR57746A (1 microM) induced increases of both de novo protein translation after 6 h of incubation and NGF release into the extracellular medium after 6-24 h. These effects were preceded by a transient augmentation of junB, c-fos and c-jun mRNA contents. These increases of AP-1 family mRNA were associated with increased nuclear AP-1 binding activity. The results show that SR57746A can increase the synthesis and release of NGF in rat cortical astrocytes. Such effects may contribute to the drug's previously described neuroprotective effects.

The staircase test in mice: a simple and efficient procedure for primary screening of anxiolytic agents.

The staircase test consists of placing a naive mouse in an enclosed staircase with five steps and observing the number of steps climbed and rearings made in a 3-min period. All the clinically active anxiolytics tested (chlordiazepoxide, clorazepate, diazepam, lorazepam, meprobamate, phenobarbital) reduce rearing at doses which did not reduce the number of steps climbed. The majority of non-anxiolytic substances tested (haloperidol, chlorpromazine, imipramine, amitriptyline, amphetamine, morphine and carbamazepine) produced a parallel reduction of both behavioural variables. Ethosuximide had no effect on behaviour. The anticonvulsant sodium valproate produced an anxiolytic profile in this test, since it reduced rearing, while increasing step climbing. This result confirms the anxiolytic properties of valproate observed in other behavioural models. Our results indicate that the staircase test in mice is simple, rapid and selective for anxiolytics. The test is well suited for use as a primary screening method.

The effect of diazepam and Ro 15-1788 on extracellular ascorbic acid, DOPAC and 5-HIAA in the striatum of anaesthetized and conscious freely moving rats, as measured by differential pulse voltammetry.

The effects of diazepam (10 mg/kg i.p.) and the central benzodiazepine receptor antagonist, Ro 15-1788 (30 mg/kg i.p.), on extracellular ascorbate, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) were examined using differential pulse voltammetry in anaesthetized and freely moving rats. In anaesthetized animals, diazepam did not significantly alter the heights of peak 1 (ascorbate) or peak 3 (5-HIAA), but significantly reduced that of peak 2 (DOPAC). In freely moving rats, diazepam greatly reduced the heights of all 3 peaks. Ro 15-1788, injected 2 h after diazepam, reversed the effect of diazepam on peak 3, but not on peaks 1 and 2.

Growth hormone-releasing factor modifies dopaminergic but not serotonergic activity in the arcuate nucleus of hypothalamus in the rat, as recorded in vivo by differential pulse voltammetry.

Parenteral (i.v.) injection of growth hormone-releasing factor (GRF) increases the height of the 3,4-dihydroxyphenylacetic acid oxidation peak (peak 2) but does not change 5-hydroxyindole extracellular content (peak 3) in the arcuate nucleus of the hypothalamus, both peaks being recorded by the differential pulse voltammetry technique using a single specifically pretreated monopyrolytic carbon fibre electrode. Conversely, no significant changes are observed in the peak 2 and peak 3 heights recorded in the medial or in the lateral nucleus of the hypothalamus. These data suggest a specific interaction between GRF and the dopaminergic system.

The sigma receptor ligand SR 31742A increases neurotensin in the nucleus accumbens but not in the caudate-putamen of the rat.

The effects of SR 31742A, a specific sigma site ligand, were investigated on regional neurotensin concentrations in rat brain. Both acute and chronic (21-day) treatment with either SR 31742A (20 mg/kg i.p.) or haloperidol (1 mg/kg i.p.) increased the neurotensin-like immunoreactivity in the nucleus accumbens. In contrast to haloperidol, the administration of SR 31742A failed to increase the concentration of neurotensin-like immunoreactivity in the caudate-putamen. Thus, the effects of SR 31742A appear to be selective for the limbic system.

Antidepressant profile in rodents of SR 58611A, a new selective agonist for atypical beta-adrenoceptors.

beta 2-Adrenoceptor agonists possess antidepressant-like activity in animals and man, but their peripheral side-effects prevent their therapeutic use. Atypical beta-adrenoceptors have not been demonstrated in the central nervous system, but are known to exist in peripheral tissues such as the rat colon. We have now studied the antidepressant-like effects in rodents of a new selective atypical beta-adrenoceptor agonist, SR 58611A. SR 58611A was active with minimal effective doses of 0.1-0.3 mg kg-1 i.p. in several models (antagonism of the hypothermia induced by apomorphine and reserpine; potentiation of the toxicity produced by yohimbine; reversal of learned helplessness), but was inactive in the tests of reserpine-induced ptosis and behavioural despair. The antidepressant-like effect of SR 58611A was not antagonised by selective beta 1- or beta 2-adrenoceptor antagonists, but was blocked by high doses of the non-selective beta-adrenoceptor antagonists, propranolol and alprenolol. Unlike beta 2-adrenoceptor agonists, SR 58611A did not reduce locomotor activity or increase water intake at doses up to 10 mg kg-1. Therefore, SR 58611A may represent the prototype of a new class of antidepressant compounds.

Effects of peripheral benzodiazepines upon the O2 consumption of neuroblastoma cells.

The effects of peripheral benzodiazepines on the respiration of a neuronal cell, the mouse C 1300 neuroblastoma, were analyzed. The presence of 'peripheral receptors' to the [3H]PK 11195 ligand was checked in these cells. A dose-dependent decrease of the O2 consumption in the presence of Ro 5-4864 and PK 11195 was observed at concentrations consistent with a receptor-mediated action. Diazepam, clonazepam and Ro 15-1788 were inactive. Previous studies have localized the peripheral benzodiazepine receptors on the mitochondrial outer membrane. We report here an effect of the peripheral ligand on mitochondrial metabolism.

Characterisation of the effects of SR146131, a novel non-peptide CCK(1) receptor agonist, on IMR-32 human neuroblastoma cells.

The effect of ¿2-[4-(4-chloro-2, 5-dimethoxy-phenyl)-5-[2-cyclohexyl-ethyl)-thiazol-2-ylcarbamoy l]-5, 7-dimethyl-indol-1-yl¿-acetic acid (SR146131), a novel non-peptide agonist of cholecystokinin (CCK) CCK(1) receptors, was compared to the effect of sulphated cholecystokinin octapeptide (CCK-8-S) on CCK(1) receptors of the human neuroblastoma cell line IMR-32. SR146131 inhibited [125I]CCK-8-S binding to IMR-32 cells at nanomolar concentrations. SR146131 and CCK-8-S increased intracellular free Ca(2+) levels ([Ca(2+)](i)) in the same concentration range (EC(50)=6+/-2.3 and 1.3+/-0.14 nM, respectively). Although the shape of the [Ca(2+)](i) increase induced by CCK-8-S and SR146131 was slightly different, extracellular Ca(2+) removal affected the response of both compounds to a similar degree, and the response of both compounds was essentially due to Ca(2+) release from intracellular stores. This was also confirmed by measuring the [Ca(2+)](i) response of single cells: both compounds induced [Ca(2+)](i) oscillations at subnanomolar concentrations and elicited a large peak increase in [Ca(2+)](i) at higher concentrations (EC(50)=0.5+/-0.04 and 5.7+/-1.9 nM for CCK-8-S and SR146131, respectively). Both CCK-8-S and SR146131 induced a sustained increase of phosphoinositide turnover in these cells, and acted at similar concentrations (EC(50)=2.7+/-0.7 and 6+/-3.1 nM, respectively), although the maximal effect of SR146131 was somewhat lower than the effect of CCK-8-S. These data show that SR146131 activates human CCK(1) receptors on IMR-32 cells in a manner and with a potency similar to that of CCK-8-S.

The quinolines PK 8165 and PK 9084 possess benzodiazepine-like activity in vitro but not in vivo.

The quinolines PK 8165 and PK 9084 bind to brain benzodiazepine receptors in vitro. However, unlike diazepam, these molecules do not reduce GABA turnover, possess anxiolytic properties, or displace [3H]flunitrazepam from benzodiazepine receptors in vivo. The pharmacological properties of PK 8165 and PK 9084 in vivo are thus unrelated to the benzodiazepine receptor.

An improved differential pulse voltammetry technique allows the simultaneous analysis of dopaminergic and serotonergic activities in vivo with a single carbon-fibre electrode.

Differential pulse voltammetry has successfully been employed to study either 5-hydroxyindoles, or ascorbic acid and catechols in the brain of anaesthetised or freely moving rats. A new electrochemical pretreatment of pyrolytic carbon-fibre electrodes has been developed, enabling the simultaneous recording of all three compounds in the striatum of anaesthetised rats, using a Tacussel polarography. Furthermore, a fourth peak was recorded at +450 mV. Pharmacological treatments performed to define the nature of the four peaks recorded in the striatum confirmed that peak 1 corresponds to ascorbic acid, peak 2 to dihydroxyphenylacetic acid, peak 3 to 5-hydroxyindoleacetic acid and peak 4 to homovanillic acid.

Effect of SR 59026A, a new 5-HT(1A) receptor agonist, on sexual activity in male rats.

The effect of SR 59026A, a new selective 5-HT(1A) receptor agonist, was evaluated on sexual behaviour of male rats in different experimental conditions. SR 59026A (1-10mg/kg p.o.) stimulated the copulatory behaviour of sexually experienced rats, as evidenced by a decrease in the number of pre-ejaculatory mounts and intromissions and a shortening of the ejaculation latency. SR 59026A also facilitated the sexual behaviour of naive male rats characterized by a low level of sexual performance: over the same dose range, the percentage of naive males that copulated was significantly increased and the ejaculation latency reduced. In experiments designed to evaluate the onset of sexual satiation, SR 59026A (1 and 3mg/kg) increased significantly the number of ejaculations and delayed the time of sexual satiation. Finally, in agreement with studies on other 5-HT(1A) receptor agonists, SR 59026A did not modify the occurrence of spontaneous erections in isolated male rats. Therefore, the present study shows that SR 59026A improves the sexual performance of male rats in a number of different experimental models, and the compound may prove to be of interest for the treatment of certain states of human male sexual dysfunction.

Neuropsychopharmacological profile in rodents of SR 57746A, a new, potent 5-HT1A receptor agonist.

The effect of the 5-HT1A agonist SR 57746A (1-[2-(naphth-2-yl) ethyl]-4-(3-trifluoromethylphenyl))-1,2,5,6 tetrahydropyridine hydrochloride), was evaluated in a variety of psychopharmacological tests in rodents. In the approach-avoidance conflict test in rats, orally administered SR 57746A significantly increased punished responding at doses as low as 3 mg/kg, while unpunished responding was only reduced at 30 mg/kg. SR 57746A was active for at least 4 hours in this test. SR 57746A significantly antagonised the lithium-induced taste aversion in rats at doses of 3 and 10 mg/kg po. In staircase test in mice, SR 57746A reduced rearing at doses which did not reduce the number of steps climbed. In the two-compartment exploratory model in mice, SR 57746A increased the latency to the first entry into the dark compartment (at 2 to 8 mg/kg po), and reduced the time spent in the dark compartment (at 8 mg/kg po), but had no effect on the total number of transitions. SR 57746A potently reduced aggressive behaviour in isolated mice, the dose of 1 mg/kg po produced over 80% inhibition of fighting in this test. SR 57746A was also active in the behavioural despair test of depression in mice and rats, and reversed learned helpless behaviour in rats. SR 57746A was also active in the behavioural despair test of depression in mice and rats, and reversed learned helpless behaviour in rats. SR 57746A dose-dependently generalised to the cue produced by 8-OH-DPAT in rats, but produced only a very weak serotonergic syndrome. Like 8-OH-DPAT and ipsapirone, SR 57746A reduced body temperature in mice, but only at a high dose (10 mg/kg po). SR 57746A reversed haloperidol-induced catalepsy in rats with an ED50 of 3.85 mg/kg po, but was unable to antagonise the stereotypy induced by apomorphine in this species. SR 57746A was inactive or only very weakly active in a series of tests typical of benzodiazepine-like activity, including antagonism of pentetrazol-induced seizures, reduction of muscle tone and locomotor activity, impairment of motor co-ordination, and potentiation of the effects of centrally-acting sedative-hypnotics. SR 57746A was also inactive as an analgesic in the PBQ writhing test. Thus, SR 57746A is active in a number of tests indicative of 5-HT1A receptor stimulation in vivo, and, more particularly, in a number of tests predictive of anxiolytic, anti-aggressive and antidepressant activities. SR 57746A is as potent as diazepam in anxiolytic tests, and more potent than imipramine in antidepressant tests, whereas it is devoid of neuroleptic potential. In view of this profile of activity, SR 57746A merits evaluation as a potential anxiolytic and antidepressant in humans.

Biochemical and electrophysiological properties of SR 57746A, a new, potent 5-HT1A receptor agonist.

SR 57746A (1-[2-(naphth-2-yl) ethyl]-4-(3-trifluoromethylphenyl)-1, 2, 5, 6 tetra-hydropyridine hydrochloride) binds competitively, and with high affinity (Ki = 2.0 +/- 0.7 nM) to 5-HT1A receptors from rat hippocampus in vitro, but has much less affinity for other 5-HT receptor subtypes (IC50 > 650 nM). SR 57746A produces a concentration-dependent inhibition of forskolin-stimulated adenylate cyclase activity in rat hippocampal homogenates, with a maximal effect identical to that of 8-OH-DPAT, suggesting that SR 57746A behaves as a full agonist in this experimental model. SR 57746A potently displaces [3H]8-OH-DPAT binding to rat hippocampal membranes ex vivo, with an ID50 of 11.1 mg/kg po, 30 min after administration, and 2.8 mg/kg po, 2 h after administration. This effect of SR 57746A is long-lasting (at least 24 hours at 10 mg/kg po). SR 57746A does not modify the levels of 5-HT or DA in various brain areas, but decreases the concentrations of 5-HIAA, and increases those of DOPAC, HVA and 3-MT. Following i.v. administration, SR 57746A (0.095 to 0.25 mg/kg) inhibits the spontaneous firing of dorsal raphe neurones, but does not modify the activity of DA neurones in the substantia nigra or ventral tegmental area. Thus, SR 57746A is a potent, selective and full agonist at 5-HT1A receptors in vitro and vivo.

Monoamine oxidase inhibition and brain amine metabolism after oral treatment with toloxatone in the rat.

Rats were administered toloxatone 100 mg kg-1 p.o., and killed 0.5 to 8 hours later. Toloxatone reversibly inhibited type A MAO, but did not affect the activity of type B MAO in whole brain. Cerebral concentrations of noradrenaline, dopamine and 5-hydroxytryptamine were increased after toloxatone, while their metabolite concentrations were reduced. Synaptosomal uptake processes of these amines were not altered by tolaxatone.

The non-peptide neuroprotective agents SR 57746A interacts with neurotrophin 3 to induce differentiation in the PC12 cell-line.

SR 57746A (1-(2beta-naphthylethyl)-4-(3-trifluoromethylphenyl)-1,2,5,6 -tetrahydropyridine hydrochloride) is a neuroprotective compound which potentiates nerve-growth factor (NGF)-induced differentiation in PC12 cells. We have evaluated the interaction of SR 57746A with the other members of the neurotrophin family in this cell-line. In contrast with NGF, neurotrophin-3 did not increase the differentiation of PC12 cells. However, the association of SR 57746A with neurotrophin-3 significantly increased neurite outgrowth. No significant activity on neurite outgrowth was observed with brain-derived neurotrophic factor or neurotrophin-4, either alone or combined with SR 57746A. These results indicate that as well as potentiating the effect of NGF SR 57746A enables neurotrophin-3, which alone is inactive, to increase the differentiation of these cells.