Predicting human neurotoxicity of propylene glycol methyl ether (PGME) by implementing in vitro neurotoxicity results into toxicokinetic modelling.

Although organic solvents have been associated with CNS toxicity, neurotoxicity testing is rarely a regulatory requirement. We propose a strategy to assess the potential neurotoxicity of organic solvents and predict solvent air concentrations that will not likely produce neurotoxicity in exposed individuals. The strategy integrated an in vitro neurotoxicity, an in vitro blood-brain barrier (BBB), and an in silico toxicokinetic (TK) model. We illustrated the concept with propylene glycol methyl ether (PGME), widely used in industrial and consumer products. The positive control was ethylene glycol methyl ether (EGME) and negative control propylene glycol butyl ether (PGBE), a supposedly non-neurotoxic glycol ether. PGME, PGBE, and EGME had high passive permeation across the BBB (permeability coefficients (Pe) 11.0 × 10-3, 9.0 × 10-3, and 6.0 × 10-3 cm/min, respectively). PGBE was the most potent in in vitro repeated neurotoxicity assays. EGME's main metabolite, methoxyacetic acid (MAA) may be responsible for the neurotoxic effects reported in humans. No-observed adverse effect concentrations (NOAECs) for the neuronal biomarker were for PGME, PGBE, and EGME 10.2, 0.07, and 79.2 mM, respectively. All tested substances elicited a concentration-dependent increase in pro-inflammatory cytokine expressions. The TK model was used for in vitro-to-in vivo extrapolation from PGME NOAEC to corresponding air concentrations (684 ppm). In conclusion, we were able to predict air concentrations that would not likely result in neurotoxicity using our strategy. We confirmed that the Swiss PGME occupational exposure limit (100 ppm) will not likely produce immediate adverse effects on brain cells. However, we cannot exclude possible long-term neurodegenerative effects because inflammation was observed in vitro. Our simple TK model can be parameterized for other glycol ethers and used in parallel with in vitro data for systematically screening for neurotoxicity. If further developed, this approach could be adapted to predict brain neurotoxicity from exposure to organic solvents.

[Metabolites of ecstasy and cytotoxicity effects]. / Métabolites de l'ecstasy et phénomènes de cytotoxicité

Intracerebroventricular injection of methylenedioxymethamphetamine (MDMA, ecstasy) in rats fails to reproduce long-term toxic effects observed after peripheral administration. Therefore, systemic metabolites would play an essential role in the development of cytotoxicity. In humans, the major metabolite is the 3,4-dihydroxymethamphetamine derivative (HHMA), which is easily oxidizable to the orthoquinone species. This can either participate to redox cycling generating semiquinone radicals and reactive oxygen species (ROS), or react with endogenous thiol derivatives yielding catechol-thioether conjugates whose the toxicity is not well established. A one pot electrochemical procedure has been developed allowing the synthesis of several catechol-thioether metabolites. Two in vitro assays have been used for evaluating their specific cytotoxicity. The first one is a bacterial assay, which shows that HHMA and some catechol-thioether conjugates can induce toxic phenomena leading to the formation of ROS, through redox cycling processes involving o-quinonoid species. The second one is an assay of cellular viability, performed on rat hippocampal pyramidal neurons. It confirms that some of these metabolites exhibit a noticeable cytotoxicity by markedly eliciting both necrosis and apoptosis markers.

Comparative study of responses in four Datura species to a zinc stress.

The effects of zinc toxicity on the growth and the photosynthetic activities of four Datura species (Datura metel, Datura innoxia, Datura sanguinea, Datura tatula) were studied using various ZnSO4 concentrations (0, 1, 2.5 and 5 mM) added in the Coic Lessaint solution. Growth, photosynthesis, chlorophyll fluorescence and chlorophyll concentration were measured after 20 days of zinc stress. These parameters were severely reduced by this heavy metal. The zinc excess involves the stomate closing, the increase of CO2 concentration in the leaves, the inhibition of certain enzyme of the Calvin cycle, a degradation of photosystem and the chlorophyll decomposition. These phenomena allow the decrease of the net photosynthesis to be partially explained. These key parameters to assess photosynthetic performance allow the plants to be classified according to their resistance to zinc. Compared with the three other species, D. innoxia showed a very strong capacity to protect itself against toxic zinc concentrations; a large amount of ZnSO4 (5 mM) was required to inhibit 43% of the photosynthesis.

Binding of antipsychotic drugs to cortical 5-HT2A receptors: a PET study of chlorpromazine, clozapine, and amisulpride in schizophrenic patients.

OBJECTIVE: This study examined the binding to cortical serotonin 5-HT2A receptors of conventional doses of the typical neuroleptic chlorpromazine in comparison with clozapine, the prototype atypical antipsychotic, and amisulpride, a specific dopamine D2-D3 blocker. METHOD: Seventeen schizophrenic patients treated with chlorpromazine (75-700 mg/day), four treated with clozapine (200-600 mg/day), and five treated with amisulpride (200-1200 mg/day) were studied. Cortical 5-HT2A binding was estimated by reference to the values for 14 antipsychotic-free schizophrenic subjects with the use of positron emission tomography and [18F]setoperone, a high-affinity radioligand for cortical 5-HT2A receptors. RESULTS: A dose-dependent decrease in the number of available cortical binding sites for [18F] setoperone was demonstrated in the chlorpromazine group; for the highest dose, there was a virtual lack of sites available for binding. A very low percentage of available binding sites was also observed in the clozapine-treated patients at all doses. This suggests a high level of 5-HT2A blockade with both clozapine and high doses of chlorpromazine. No significant binding of amisulpride to 5-HT2A receptors was detected. CONCLUSIONS: A high level of 5-HT2A receptor blockade does not appear specific to clozapine in comparison with high doses of chlorpromazine, suggesting that the distinct clinical profiles of both drugs are unrelated to 5-HT2A blockade itself.

Differential effects of sigma ligands on the N-methyl-D-aspartate response in the CA1 and CA3 regions of the dorsal hippocampus: effect of mossy fiber lesioning.

In the CA3 region of rat dorsal hippocampus, several sigma ligands, such as 1,3-di(2-tolyl)guanidine (DTG), (+)-pentazocine and (+)-N-cyclopropylmethyl-N-methyl-1, 4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride (JO-1784), administered intravenously at low doses, potentiate selectively the pyramidal neuron firing activity induced by microiontophoretic applications of N-methyl-D-aspartate, without affecting those induced by quisqualate, kainate or acetylcholine. A similar potentiation of the N-methyl-D-aspartate response has also been found with microiontophoretic applications of neuropeptide Y, an effect exerted via delta receptors. The present experiments were carried out to determine the effects of these sigma ligands and of neuropeptide Y; in the CA1 and CA3 regions following unilateral destruction by a local injection of colchicine of the mossy fiber system, which is a major afference to CA3 pyramidal neurons. In the CA1 region, DTG, JO-1784 and neuropeptide Y did not potentiate the activation induced by microiontophoretic applications of N-methyl-D-aspartate. However, (+)-pentazocine potentiated the N-methyl-D-aspartate response, similarly to its effect in the CA3 region on the intact side. In the CA3 region, on the intact side, (+)-pentazocine, DTG, JO-1784 and neuropeptide Y induced a selective potentiation of N-methyl-D-aspartate-induced activation, in keeping with previous reports. On the lesioned side, the effect of (+)-pentazocine on the N-methyl-D-aspartate response was still present, but those of DTG, JO-1784 and neuropeptide Y were abolished. These results suggest that (+)-pentazocine, on the one hand, and DTG, JO-1784 and neuropeptide Y, on the other, are not acting on the same subtype of sigma receptors. Since (+)-pentazocine, JO-1784 and neuropeptide Y have been suggested to act on the sigma 1 subtype of receptors, these data suggest the existence of two subtypes of sigma 1 receptors. They also suggest that the receptors on which DTG, JO-1784 and neuropeptide Y are acting are located on the mossy fiber terminals in the CA3 region and are absent in the CA1 region.

Differentiation of sigma ligand-activated receptor subtypes that modulate NMDA-evoked [3H]-noradrenaline release in rat hippocampal slices.

1. It is now widely accepted that there are two classes of sigma (sigma) binding sites, denoted sigma(1) and sigma(2), and recently sigma(3) subtype has been proposed. Selective sigma(1) and sigma(2) receptor agonists are known to modulate the neuronal response to N-methyl-D-aspartate (NMDA) in vivo and in vitro. To identify the site of action of a series of recently synthesised high affinity sigma ligands, the present in vitro series of experiments was carried out on NMDA-evoked [3H]-noradrenaline ([3H]-NA) overflow from preloaded hippocampal slices of the rat. 2. The ligands (+)-cis-N-methyl-N-[2,(3,4-dichlorophenyl) ethyl]-2-(1-pyrrolidinyl) cyclohexylamine (BD-737) and (+)-pentazocine, considered as the prototypic sigma(1) agonists, potentiated the NMDA response from 10 nM to 100 nM. This potentiation faded between 100 nM and 1 microM ligand concentrations. On the other hand, 1,3-di(2-tolyl)guanidine (DTG), a mixed sigma(1)/sigma(2) agonist, at concentrations greater than 100 nM inhibited the NMDA-evoked [3H]-NA release. Spiperone, considered as active on putative sigma(3) receptors, was without effect on the NMDA response, or on the potentiating effect of BD-737. 3. The high affinity sigma antagonists haloperidol and 1[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine (BD-1063), inactive by themselves on the NMDA-induced response, at concentrations above 30 nM totally prevented the potentiating effect of (+)-pentazocine (100 nM) as well as the inhibitory effect of DTG (300 nM) on NMDA-evoked [3H]-NA release. Whereas haloperidol and BD-1063, at concentrations < 1 microM, were inactive on the potentiating effect of BD-737 (100 nM). 4. 4-(4-Chlorophenyl)-alpha-4-fluorophenyl-4-hydroxy-1-piperidinebutanol (reduced haloperidol), N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (BD-1008), inactive by themselves on the NMDA-evoked [3H]-NA release, failed to reverse the effects of (+)-pentazocine and DTG, but at concentrations of 30 nM to 1 microM antagonised the BD-737-induced potentiation of the NMDA response. Conversely, N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) blocked the effects of (+)-pentazocine as well as those of BD-737, but not those of DTG. 5. The present results provide in vitro functional evidence for a sigma receptor type preferentially sensitive to BD-737, reduced haloperidol, BD-1008 and also to NE-100, that differs from the already identified sigma(1), sigma(2) and sigma(3) sites.

The effects of sigma ligands and of neuropeptide Y on N-methyl-D-aspartate-induced neuronal activation of CA3 dorsal hippocampus neurones are differentially affected by pertussin toxin.

1. The in vivo effects of the high affinity sigma ligands 1,3-di(2-tolyl)guanidine (DTG), (+)-N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1- ethyl-but-3-en-1-ylamine hydrochloride (JO-1784), (+)-pentazocine and haloperidol, as well as of those of neuropeptide Y (NPY), on N-methyl-D-aspartate (NMDA)- and quisqualate (Quis)-induced neuronal activations of CA3 pyramidal neurones were assessed, using extracellular unitary recording, in control rats and in rats pretreated with a local injection of pertussis toxin (PTX), to evaluate the possible involvement of Gi/o proteins in mediating the potentiation of the neuronal response to NMDA by the activation of sigma receptors in the dorsal hippocampus. 2. Microiontophoretic applications as well as intravenous injections of (+)-pentazocine potentiated selectively the NMDA response in control rats as well as in PTX-pretreated animals. In contrast, the PTX pretreatment abolished the potentiation of the NMDA response by DTG, JO-1784 and NPY. Moreover, microiontophoretic applications of DTG induced a reduction of NMDA-induced neuronal activation. Neither in control nor in PTX-treated rats, did the sigma ligands and NPY have any effect on Quis-induced neuronal response. 3. In PTX-treated rats, the potentiation of the NMDA response induced by (+)-pentazocine was suppressed by haloperidol, whereas the reduction of the NMDA response by DTG was not affected by haloperidol. 4. This study provides the first in vivo functional evidence that sigma ligands and NPY modulate the NMDA response by acting on distinct receptors, differentiated by their PTX sensitivity.

Functional cooperation between neurosteroids and D2 dopamine antagonists on KCl-evoked [3H]noradrenaline release: modulation by calcium channel blockers.

It has recently been proposed that neurosteroids, such as dehydroepiandrosterone sulphate and pregnenolone sulphate, interfere with the dopamine system in the central nervous system. According to our previous report showing that the butyrophenone, spiperone, slightly enhances the evoked release of [3H]-noradrenaline ([3H]NA) in the presence of these sulphated steroids, the present study was carried out to document the putative interplay between steroids and spiperone, which is known to be a prototypic D2 dopamine antagonist and also a 5-HT2 serotonin antagonist. For this purpose, the paradigm of KCl-evoked [3H]NA release from preloaded rat hippocampal slices was used to investigate the interactions between neurosteroids, spiperone and the voltage-sensitive calcium channels (VSCCs). The selective 5-HT2 serotonin antagonist ritanserine was ineffective, whereas sulpiride, a selective D2 dopamine antagonist mimicked the action of spiperone, thus suggesting that the blockade of D2 dopamine receptors accounted for the modulatory effect of spiperone on neurosteroid-induced modulation of evoked [3H]NA release. In addition, this facilitation of KCl-evoked [3H]NA release by the combination of a steroid and a D2 dopamine antagonist was partially inhibited by the L- and N-type VSCC blockers nifedipine and omega-conotoxin GVIA, respectively. The present results provide in-vitro functional evidence for the putative role of VSCCs in the interplay between steroids and D2 dopamine receptors.

Melatonin modulates [3h]serotonin release in the rat hippocampus: effects of circadian rhythm.

Serotonin (5-HT) participates as a neurotransmitter in the control of the circadian sleep/wake rhythm, feeding and sexual behaviours, and emotional and affective states. The present study investigated whether melatonin affects the circadian rhythm of 5-HT neurotransmission in the hippocampus, a major target for serotoninergic antidepressants. The present results show a daytime dependency of [3H]5-HT uptake insensitive to melatonin, with a peak from 14.00 h to 22.00 h and a trough from 02.00 h to 06.00 h. They also indicate that melatonin reduced the spontaneous efflux of [3H]5-HT as well as KCl-evoked release of [3H]5-HT during the dark phase, while it increased the evoked release during the light phase. Both effects were concentration-dependent; the facilitatory effect was maximum at high nanomolar concentrations of melatonin, whereas the inhibition preferentially occurred at low concentrations. Finally, nifedipine, an effective antagonist of L-type voltage-sensitive calcium channels, prevented the effects of melatonin on KCl-evoked [3H]5-HT release during the light but not the dark phase. Together, these data suggest the involvement of two distinct mechanisms by which melatonin might regulate both spontaneous efflux and evoked release of 5-HT in the hippocampus.

Time of injection determines the effect of alpha-MSH antiserum on DA neurons in psychological stress.

Male rats were subjected to "psychological stress" which consisted in 10 sec footshock on the first day followed 24 hr later by a 10 sec stay in the experimental chamber without shock. Intravenous antiserum against alpha-MSH markedly changed the functional state of mesencephalic and hypothalamic DA neurons (assessed by histochemical microfluorimetry) when administered before the second session but not when given before the first session. These observations reveal an interesting parallelism in the temporal characteristics of the effects of alpha-MSH on avoidance behavior and central DA systems.

N-methyl-D-aspartate-induced neuronal activation is selectively modulated by sigma receptors.

The effects of two high-affinity sigma ligands, DTG (1,3-di(2-tolyl)guanidine) and haloperidol, on the activation of dorsal hippocampus pyramidal neurons induced by microiontophoretic application of N-methyl-D-aspartate (NMDA) were assessed electrophysiologically. Low doses of DTG (0.5-3 micrograms/kg i.v.) potentiated the NMDA response. This effect of DTG was blocked by haloperidol (10 micrograms/kg i.v.), but not by spiperone, a potent dopamine antagonist with low affinity for sigma receptors. These results suggest that sigma receptors modulate the NMDA-induced neuronal activation.

Modulation by sigma ligands of N-methyl-D-aspartate-induced [3H]noradrenaline release in the rat hippocampus: G-protein dependency.

The effects of the high affinity sigma (sigma) ligands 1,3-di(2-tolyl)guanidine (DTG), (+)N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1- ethyl-but-3-en-1-yl-amine hydrochloride (JO-1784), (+)3-[3-hydroxyphenyl]-N-(1-propyl)piperidine hydrochloride [(+)3-PPP] and haloperidol were studied on N-methyl-D-aspartate (NMDA)-evoked release of [3H]noradrenaline (NA) from preloaded hippocampal slices made from Sprague-Dawley rats. The [3H]NA release was evoked once by a 4 min exposure to NMDA, 40 min after the beginning of superfusion with a Mg+(+)-free Krebs' solution. In the absence of any drug, NMDA evoked a concentration-dependent [3H]NA release. Mg++ and EGTA abolished the [3H]NA release induced by NMDA. JO-1784 and (+)3-PPP potentiated in a concentration-dependent manner NMDA-induced [3H]NA release, without affecting the basal outflow. DTG concentration-dependently inhibited the overflow of [3H]NA evoked by NMDA, without affecting the basal efflux. Haloperidol, which did not modify NMDA-evoked [3H]NA release by itself, completely prevented the effects of JO-1784, (+)3-PPP and DTG. In contrast, spiperone, also a potent dopamine receptor antagonist but with low affinity for sigma binding sites, failed to prevent the potentiation of NMDA-evoked release of [3H]NA by JO-1784 and (+)3-PPP. The possible involvement of Gi/o proteins in the modulation by sigma ligands of NMDA-evoked [3H]NA release in the rat hippocampus was also investigated. To this end, Gi/o proteins were inactivated with pertussis toxin (PTX), injected locally 3 to 11 days prior to the experiment or with in vitro preincubation with N-ethylmaleimide (NEM) for 30 min prior the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

[Involvement of sigma receptors in schizophrenic syndromes. Pathophysiological approach]. / Implication des récepteurs sigma dans les syndromes schizophréniques. Approche physiopathologique.

Sigma ligands have been identified as psychotomimetic agents unrelated to opioids. A number of neuroleptics possess moderate to high affinity for sigma binding sites, raising the possibility that sigma receptors mediate some of the antipsychotic effects of neuroleptics. In addition, sigma binding sites have been reported to be reduced in the temporal cortex and in the hippocampus of schizophrenic patients. This hypothesis is further supported by the use of the sigma ligands rimcazole, BMY-14802 and remoxipride as effective antipsychotic agents. The present report, reviewing briefly the physiological effects of sigma ligands, suggests that their antipsychotic properties are related to modulation of NMDA receptors. Thus, the use of sigma ligands may provide further understanding of the pathophysiology of psychoses and open new avenues for their treatment.

[Spinal anesthesia and multiple sclerosis]. / Rachianesthésie et sclérose en plaque.

Spinal anaesthesia was performed in 9 patients with multiple sclerosis for 14 surgical procedures: urological surgery 13 times and plastic surgery once. No complication was observed. except for a transient exacerbation in one case. Spinal anaesthesia appeared to be an innocuous procedure in multiple sclerosis as no neurotoxicity was observed. Exacerbation of multiple sclerosis was similar to that seen with general anaesthesia. Moreover, spinal anaesthesia improved the operating conditions by relieving bladder spasticity; it was also often asked for by patients who feared the loss of consciousness of general anaesthesia.

Investigation of the role of sigma1-receptors in inositol 1,4,5-trisphosphate dependent calcium signaling in hepatocytes.

In hepatocytes, as in other cell types, Ca(2+) signaling is subject to complex regulations, which result largely from the intrinsic characteristics of the different inositol 1,4,5-trisphosphate receptor (InsP(3)R) isoforms and from their interactions with other proteins. Although sigma1 receptors (Sig-1Rs) are widely expressed in the liver, their involvement in hepatic Ca(2+) signaling remains unknown. We here report that in this cell type Sig-1R interact with type 1 isoforms of the InsP(3) receptors (InsP(3)R-1). These results obtained by immunoprecipitation experiments are confirmed by the observation that Sig-1R proteins and InsP(3)R-1 colocalize in hepatocytes. However, Sig-1R ligands have no effect on InsP(3)-induced Ca(2+) release in hepatocytes. This can be explained by the rather low expression level expression of InsP(3)R-1. In contrast, we find that Sig-1R ligands can inhibit agonist-induced Ca(2+) signaling via an inhibitory effect on InsP(3) synthesis. We show that this inhibition is due to the stimulation of PKC activity by Sig-1R, resulting in the well-known down-regulation of the signaling pathway responsible for the transduction of the extracellular stimulus into InsP(3) synthesis. The PKC sensitive to Sig-1R activity belongs to the family of conventional PKC, but the precise molecular mechanism of this regulation remains to be elucidated.

Neuroendocrine regulation and central dopamine (DA) systems in physical and psychological stress.

Physical and psychological stress cause different patterns of changes in the fluorescence intensity of nigral and tuberoinfundibular DA neurons which point to changes in neuronal activity. In order to investigate possible interactions between alpha-MSH (alpha-melanotropin) and DA systems in stress, systemic and intraventricular injections of antiserum against alpha-MSH were made. The functional state of DA neurons was assessed by histochemical microfluorimetry and hormone levels were measured by radioimmunossay. Antiserum against alpha-MSH was found to affect the functional state of DA neurons, but only thorugh the intravenous route. Under physical stress i.v. injection of antiserum against alpha-MSH was accompanied by elevated levels of activity of the DA neurons of the substantia nigra. An intraventricular injection of the same antiserum was ineffective. In psychological stress, an effect was again seen only after intravenous injection of antiserum against alpha-MSH. In this situation, the activity in DA cell groups of the substantia nigra, ventral tegmental area and tubero-infundibular system was increased after antiserum injection. Possible influences from manipulations were checked; certain effects which depended upon experimental situation were noted. Our data suggest a modulatory influence of circulating alpha-MSH on the functional state of central DA systems.