[Hallucinations: Etiological analysis of children admitted to a pediatric emergency department]

Children's hallucinations pose the dual challenge of diagnosing a possible medical emergency and a possible psychiatric disorder.

PURPOSE

The main objective was to analyze the causes of such hallucinations in children presenting to a pediatric emergency department.

MATERIAL AND METHODS

We conducted a single-center, observational, retrospective study including all children aged less than 15 years experiencing hallucinations and admitted to our tertiary level pediatric emergency department between 1 January 2007 and 31 December 2015. The data collected were demographic; medical: previous medical or psychiatric history, current medications, associated clinical or psychiatric symptoms, type and character of hallucinations, length and recurrence of hallucinatory phenomena; and other biological, radiological and neurological explorations.

RESULTS

Sixty-eight patients were included (29 boys). The mean age was 9.1±3 years (range, 2-14 years and 10 months; median, 9.2 years). Admissions were seasonal with a bimodal distribution (a peak during springtime and another one during fall). Hallucinations were mainly visual (90%), acute (77%) and complex (63%). Visual hallucinations were associated with other types of hallucinations: auditory (n=17), somatosensory (n=7). Fifteen children had a psychiatric history and had already experienced hallucinatory phenomena (93%). Among 47 patients (69%), these hallucinations were associated with other symptoms: agitation (41%), headaches (28%), hyperthermia (21%) and negative symptoms of the schizophrenia spectrum (15%). On admission, 20 patients (29%) had one or more treatments under way (34 drugs, 41% known for hallucinogenic adverse effects). Neurological explorations were undertaken in half of the cases. Toxicological analysis prescribed in 19 children was positive in five cases (26%). Fifty-three percent of patients were hospitalized and 51 children received a specialized follow-up (by a neurologist and/or a psychiatrist). A nonpsychiatric origin of these hallucinations was diagnosed in 29 patients (43%): neurological causes (n=10), infectious diseases (n=10), intoxications (n=5) and a medication side effect (n=4).

CONCLUSION

Hallucinations with a suspected underlying psychiatric cause differed on several factors: chronic duration (p=0.02), an onset after 10 years of age (p=0.004), previous identical episodes (p=0.014) and a parental psychiatric history (p=0.036), auditory hallucinations (p=0.0009), absence of fever (p=0.005), headaches (p=0.036) and the presence of negative symptoms of the schizophrenic spectrum (p=0.02).

In-mold patterning and actionable axo-somatic compartmentalization for on-chip neuron culture

Oriented neuronal networks with controlled connectivity are required for many applications ranging from studies of neurodegeneration to neuronal computation. To build such networks in vitro, an efficient, directed and long lasting guidance of axons toward their target is a pre-requisite. The best guidance achieved so far, however, relies on confining axons in enclosed microchannels, making them poorly accessible for further investigation. Here we describe a method providing accessible and highly regular arrays of axons, emanating from somas positioned in distinct compartments. This method combines the use of a novel removable partition, allowing soma positioning outside of the axon guidance patterns, and in-mold patterning (iMP), a hybrid method combining chemical and mechanical cell positioning clues applied here for the first time to neurons. The axon guidance efficiency of iMP is compared to that of conventional patterning methods, e.g. micro-contact printing (chemical constraints by a poly-l-lysine motif) and micro-grooves (physical constraints by homogeneously coated microstructures), using guiding tracks of different widths and spacing. We show that iMP provides a gain of 10 to 100 in axon confinement efficiency on the tracks, yielding mm-long, highly regular, and fully accessible on-chip axon arrays. iMP also allows well-defined axon guidance from small populations of several neurons confined at predefined positions in μm-sized wells. iMP will thus open new routes for the construction of complex and accurately controlled neuronal networks.

Combining microfluidics, optogenetics and calcium imaging to study neuronal communication in vitro

In this paper we report the combination of microfluidics, optogenetics and calcium imaging as a cheap and convenient platform to study synaptic communication between neuronal populations in vitro. We first show that Calcium Orange indicator is compatible in vitro with a commonly used Channelrhodopsine-2 (ChR2) variant, as standard calcium imaging conditions did not alter significantly the activity of transduced cultures of rodent primary neurons. A fast, robust and scalable process for micro-chip fabrication was developed in parallel to build micro-compartmented cultures. Coupling optical fibers to each micro-compartment allowed for the independent control of ChR2 activation in the different populations without crosstalk. By analyzing the post-stimuli activity across the different populations, we finally show how this platform can be used to evaluate quantitatively the effective connectivity between connected neuronal populations.

A review of microfabrication and hydrogel engineering for micro-organs on chips

This review highlights recent trends towards the development of in vitro multicellular systems with definite architectures, or "organs on chips". First, the chemical composition and mechanical properties of the scaffold have to be consistent with the anatomical environment in vivo. In this perspective, the flourishing interest in hydrogels as cellular substrates has highlighted the main parameters directing cell differentiation that need to be recapitulated in artificial matrix. Another scaffold requirement is to act as a template to guide tissue morphogenesis. Therefore specific microfabrication techniques are required to spatially pattern the environment at microscale. 2D patterning is particularly efficient for organizing planar polarized cell types such as endothelial cells or neurons. However, most organs are characterized by specific sub units organized in three dimensions at the cellular level. The reproduction of such 3D patterns in vitro is necessary for cells to fully differentiate, assemble and coordinate to form a coherent micro-tissue. These physiological microstructures are often integrated in microfluidic devices whose controlled environments provide the cell culture with more life-like conditions than traditional cell culture methods. Such systems have a wide range of applications, for fundamental research, as tools to accelerate drug development and testing, and finally, for regenerative medicine.

Synapto-protective drugs evaluation in reconstructed neuronal network

Chronic neurodegenerative syndromes such as Alzheimer's and Parkinson's diseases, or acute syndromes such as ischemic stroke or traumatic brain injuries are characterized by early synaptic collapse which precedes axonal and neuronal cell body degeneration and promotes early cognitive impairment in patients. Until now, neuroprotective strategies have failed to impede the progression of neurodegenerative syndromes. Drugs preventing the loss of cell body do not prevent the cognitive decline, probably because they lack synapto-protective effects. The absence of physiologically realistic neuronal network models which can be easily handled has hindered the development of synapto-protective drugs suitable for therapies. Here we describe a new microfluidic platform which makes it possible to study the consequences of axonal trauma of reconstructed oriented mouse neuronal networks. Each neuronal population and sub-compartment can be chemically addressed individually. The somatic, mid axon, presynaptic and postsynaptic effects of local pathological stresses or putative protective molecules can thus be evaluated with the help of this versatile "brain on chip" platform. We show that presynaptic loss is the earliest event observed following axotomy of cortical fibers, before any sign of axonal fragmentation or post-synaptic spine alteration. This platform can be used to screen and evaluate the synapto-protective potential of several drugs. For instance, NAD⁺ and the Rho-kinase inhibitor Y27632 can efficiently prevent synaptic disconnection, whereas the broad-spectrum caspase inhibitor zVAD-fmk and the stilbenoid resveratrol do not prevent presynaptic degeneration. Hence, this platform is a promising tool for fundamental research in the field of developmental and neurodegenerative neurosciences, and also offers the opportunity to set up pharmacological screening of axon-protective and synapto-protective drugs.

Axon diodes for the reconstruction of oriented neuronal networks in microfluidic chambers

Various experimental models are used to study brain development and degeneration. They range from whole animal models, which preserve anatomical structures but strongly limit investigations at the cellular level, to dissociated cell culture systems that allow detailed observation of cell phenotypes but lack the highly ordered physiological neuron connection architecture. We describe here a platform comprising independent cell culture chambers separated by an array of "axonal diodes". This array involves asymmetric micro-channels, imposing unidirectional axon connectivity with 97% selectivity. It allows the construction of complex, oriented neuronal networks not feasible with earlier platforms. Different neuronal subtypes could be co-cultivated for weeks, and sequential seeding of different cell populations reproduced physiological network development. To illustrate possible applications, we created and characterized a cortico-striatal oriented network. Functional synaptic connections were established. The activation of striatal differentiation by cortical axons, and the synchronization of neural activity were demonstrated. Each neuronal population and subcompartment could be chemically addressed individually. The directionality of neural pathways being a key feature of the nervous system organization, the axon diode concept brings in a paradigmatic change in neuronal culture platforms, with potential applications for studying neuronal development, synaptic transmission and neurodegenerative disorder such as Alzheimer and Parkinson diseases at the sub-cellular, cellular and network levels.

The dynamics of root meristem distribution in the soil

Plants must develop efficient root architectures to secure access to nutrients and water in soil. This is achieved during plant development through a series of expansion and branching processes, mostly in the proximity of root apical meristems, where the plant senses the environment and explores immediate regions of the soil. We have developed a new approach to study the dynamics of root meristem distribution in soil, using the relationship between the increase in root length density and the root meristem density. Initiated at the seed, the location of root meristems in barley seedlings was shown to propagate, wave-like, through the soil, leaving behind a permanent network of roots for the plant to acquire water and nutrients. Data from observations on barley roots were used to construct mathematical models to describe the density of root meristems in space. These models suggested that the morphology of the waves of meristems was a function of specific root developmental processes. The waves of meristems observed in root systems of barley seedlings exploring the soil might represent a more general and fundamental aspect of plant rooting strategies for securing soil resources.

[Treatment of children with feeding disorders]

The treatment of children presenting a refusal of feeding is multidisciplinary. This is why the point of view of various speakers were approached at the time of this round table. The gastroenterologists -pediatrician stressed the importance of the clinical data to support the diagnosis of a possible organic pathology and to evaluate the nutritional state. When the denutrition is proven, it is sometimes necessary to have recourse to an artificial enteral feeding. If this one must be prolonged a gastrostomy is preferred. The psychiatrics pointed out the oropharyngeal psychopathologies related to the various feeding disorders met during the childhood, including anorexia, the type of treatment being specific to each nosologic entity. The parent-child's observation in interaction is of primary importance for the diagnosis. The speech therapists evoked the importance of the knowledge of the various stages of maturation of the swallowing and the sensory character of this act to understand the bases of rehabilitation. This rehabilitation is long and does not have to neglect relational dynamics.

An endogenous adrenoceptor ligand potentiates excitatory synaptic transmission in cultured hippocampal neurons

Noradrenergic inputs modulate hippocampal function via distinct receptors. In hippocampal neuronal cultures, mRNA expression of adrenoceptor subtypes is maintained from 1 day in vitro (DIV) to 22 DIV. Noradrenaline dose-dependently stimulates phosphoinositide (PI) breakdown in both immature and mature cultures through the activation of alpha1 receptors. At 22 DIV, basal PI breakdown depends on excitatory synaptic activity since it is decreased by tetrodotoxin or glutamate receptor antagonists. At 22 DIV, a similar decrease of basal PI breakdown is also observed with alpha1, alpha2 or beta adrenoceptor antagonists. These effects are not additive with that produced by tetrodotoxin. Adrenergic antagonists also strongly reduce spontaneous excitatory post-synaptic currents (sEPSC) as evidenced by whole cell recording. Therefore, in hippocampal cultures, excitatory transmission is modulated by a tonic activation of adrenoceptors probably produced by an endogenous ligand. Indeed, (i) the depletion of catecholamine pools by reserpine also decreases both basal PI metabolism and sEPSC; (ii) hippocampal neurons possess both tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase mRNAs, encoding enzymes required for catecholamine synthesis; and (iii) some hippocampal neurons show TH-immunoreactivity. TH-positive cells are also detected in E18 hippocampal sections. Thus, cultured hippocampal neurons synthesize and release an adrenergic-like ligand, which tonically potentiates excitatory synaptic transmission in mature cultures.

[Children also die]

Palliative care has recently been developed in adults. However, children die as well and quite a few articles have been published on this special issue. The object of this article is to summarize the available literature in order to call for the development of clinical policies and minimum standards adapted to French pediatrics.

Regulation of spontaneous inhibitory synaptic transmission by endogenous glutamate via non-NMDA receptors in cultured rat hippocampal neurons

The regulation of gamma-aminobutyric acid (GABA)-mediated spontaneous inhibitory synaptic transmission by endogenously released glutamate was studied in cultured rat hippocampal neurons. After 7 days in vitro (DIV), both spontaneous excitatory postsynaptic currents (sEPSCs) and spontaneous inhibitory postsynaptic currents (sIPSCs) could be detected. After 15 DIV, most postsynaptic spontaneous currents occurred as sEPSC/sIPSC sequences when recorded at a holding voltage of -30 mV. In the presence of the glutamate alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subtype antagonist LY303070, both the frequency and amplitude of sIPSC were strongly and reversibly reduced. The N-methyl-D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonopentanoic acid (AP5), had no effect on sIPSC while cyclothiazide strongly increased sIPSC frequency. Under blockade of AMPA receptors, the kainate- and GluR5-selective kainate receptor agonists, (RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl) propanoic acid) (ATPA) and (S)-5-iodowillardiine (5IWill), induced a large enhancement of the frequency of small-amplitude sIPSC which was blocked by the non-NMDA receptor antagonist, 2,3-dihydro-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX). All of these effects were sensitive to tetrodotoxin (TTX). In the presence of LY303070 and TTX, kainate could induce a small inward current while GluR5 agonists had no effect. In the presence of NMDA and AMPA receptor antagonists, the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (t-PDC) could restore sIPSC. When NBQX was used as an AMPA antagonist, the stimulatory effect of t-PDC was blocked while the group I metabotropic glutamate agonist, 3,5-dihydroxyphenylglycine (DHPG), induced a strong enhancement of sIPSC. Therefore, both AMPA and kainate receptors can regulate inhibitory synaptic transmission in cultured hippocampal neurons, the former by tonic activation, the latter when the glutamate concentration is increased by impairing glutonate uptake.

Kainate receptors are involved in synaptic plasticity

The ability of synapses to modify their synaptic strength in response to activity is a fundamental property of the nervous system and may be an essential component of learning and memory. There are three classes of ionotropic glutamate receptor, namely NMDA (N-methyl-D-aspartate), AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionic acid) and kainate receptors; critical roles in synaptic plasticity have been identified for two of these. Thus, at many synapses in the brain, transient activation of NMDA receptors leads to a persistent modification in the strength of synaptic transmission mediated by AMPA receptors. Here, to determine whether kainate receptors are involved in synaptic plasticity, we have used a new antagonist, LY382884 ((3S, 4aR, 6S, 8aR)-6-((4-carboxyphenyl)methyl-1,2,3,4,4a,5,6,7,8,8a-decahydro isoquinoline-3-carboxylic acid), which antagonizes kainate receptors at concentrations that do not affect AMPA or NMDA receptors. We find that LY382884 is a selective antagonist at neuronal kainate receptors containing the GluR5 subunit. It has no effect on long-term potentiation (LTP) that is dependent on NMDA receptors but prevents the induction of mossy fibre LTP, which is independent of NMDA receptors. Thus, kainate receptors can act as the induction trigger for long-term changes in synaptic transmission.

The GluR5 subtype of kainate receptor regulates excitatory synaptic transmission in areas CA1 and CA3 of the rat hippocampus

Activation of kainate receptors depresses excitatory synaptic transmission in the hippocampus. In the present study, we have utilised a GluR5 selective agonist, ATPA [(RS)-2-amino-3-(3-hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid], and a GluR5 selective antagonist, LY294486 [(3SR,4aRS,6SR,8aRS)-6-([[(1H-tetrazol-5-y l)methyl]oxy]methyl)-1,2,3,4,4a,5,6,7,8,8a-decahydroisoquinoline-3 -carboxylic acid], to determine whether GluR5 subunits are involved in this effect. ATPA mimicked the presynaptic depressant effects of kainate in the CA1 region of the hippocampus. It depressed reversibly AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) receptor-mediated field excitatory postsynaptic potentials (field EPSPs) with an IC50 value of approximately 0.60 microM. The dual-component excitatory postsynaptic current (EPSC) and the pharmacologically isolated NMDA (N-methyl-D-aspartate) receptor-mediated EPSC were depressed to a similar extent by 2 microM ATPA (61 +/- 7% and 58 +/- 6%, respectively). Depressions were associated with an increase in the paired-pulse facilitation ratio suggesting a presynaptic locus of action. LY294486 (20 microM) blocked the effects of 2 microM ATPA on NMDA receptor-mediated EPSCs in a reversible manner. In area CA3, 1 microM ATPA depressed reversibly mossy fibre-evoked synaptic transmission (by 82 +/- 10%). The effects of ATPA were not accompanied by any changes in the passive properties of CA1 or CA3 neurones. However, in experiments where K+, rather than Cs+, containing electrodes were used, a small outward current was observed. These results show that GluR5 subunits comprise or contribute to a kainate receptor that regulates excitatory synaptic transmission in both the CA1 and CA3 regions of the hippocampus.

Altered distribution of Galphah/type 2 transglutaminase following catecholamine deprivation is associated with depression of adrenoreceptor signal transduction in cultured ventricular zone germinal cells

Type 2 transglutaminase (Tg), which catalyzes the covalent cross-linking of cytoplasmic proteins during apoptosis, also functions as the alpha subunit of a heterodimeric G-protein (Gh) which can activate phospholipase C-delta1 during the signal transduction pathway linked to alpha1-adrenoreceptors. Continued stimulation of rat forebrain ventricular zone (VZ) germinal cells with the alpha1-agonist phenylephrine during development in vitro suppresses apoptosis and promotes DNA synthesis [Pabbathi et al., Brain Res., 760, 1997, 22-33]. Immunocytochemistry with a monoclonal antibody to Galphah/Tg reveals that alpha1-agonist deprivation during culture of VZ cells in the presence of a protein synthesis inhibitor results after 20 h in a loss of peripheral distribution of the protein and an increase in the reaction product of Tg in the cytoplasm of cells undergoing apoptosis. Using photoaffinity labelling, we observed reduced GTP binding to Galphah/Tg in phenylephrine-deprived cultures. Formation of inositol triphosphate (IP3) and intracellular Ca2+ transients occurred in the presence of phenylephrine. In cultures grown in phenylephrine-deprived conditions in the presence of protein synthesis inhibitor, both the IP3 response and the amplitude and duration of Ca2+ transients were reduced. These results show that loss of signal transduction coincides with the onset of transglutaminase activity in VZ cells during a period when cell survival is reduced following withdrawal of alpha1-agonist, and support the hypothesis that Tg/Galphah could be implicated in both signal transduction and programmed cell death.

The synaptic activation of the GluR5 subtype of kainate receptor in area CA3 of the rat hippocampus

Two new compounds (LY293558 and LY294486), that antagonize homomeric human GluR5 receptors, were examined against responses mediated by kainate receptors in the CA3 region of rat hippocampal slices. Both compounds (applied at a concentration of 10 microM) antagonized reversibly currents induced by 200 nM kainate. They also antagonized reversibly the synaptic activation of kainate receptors, evoked by high-frequency stimulation of mossy fibres, in the presence of NMDA and AMPA receptor antagonists. These results show that GluR5 subunits are likely to contribute to a kainate receptor on CA3 neurones that mediates responses to both kainate and synaptically-released L-glutamate.

The synaptic activation of kainate receptors

L-Glutamate, the principal excitatory neurotransmitter in the vertebrate central nervous system, acts on three classes of ionotropic glutamate receptors, named after the agonists AMPA, NMDA and kainate. AMPA receptors are known to mediate fast synaptic responses and NMDA receptors to mediate slow synaptic responses at most excitatory synapses in the brain. Kainate receptors are formed from a separate set of genes (GluR5-7, KA-1 and KA-2) and are widely distributed throughout the brain. They are implicated in epileptogenesis and cell death. However, the physiological functions of kainate receptors are not known. The development of 2,3-benzodiazepine antagonists that are selective for AMPA receptors enables kainate receptors to be specifically activated by exogenous ligands, such as kainate. Here we demonstrate that high-frequency stimulation of mossy fibres in rat hippocampal slices, in the presence of the highly selective AMPA receptor antagonist GYKI 53655 plus NMDA- and GABA-receptor antagonists, activates an inward current in CA3 neurons that has a pharmacology typical of kainate receptors. The finding that kainate receptors can be activated synaptically adds to the diversity of information transfer at glutamatergic synapses.

Catecholaminergic regulation of proliferation and survival in rat forebrain paraventricular germinal cells

We have investigated the possible role of alpha1-adrenoreceptors in regulating the germination of progenitor cells cultured from embryonic rat neocortex. High binding levels of the alpha1-selective radioligand 3[H]prazosin were detected in the forebrain of the rat embryo at E13, and the greatest density of binding sites was localized to the ventricular and subventricular zones. Catecholamine-containing axon terminals were present in these zones in the same period. Germinal neuroepithelial cells retained specific 3[H]prazosin binding in culture. Approximately 25% of cells in culture displayed complex intracellular Ca2+ transients in response to phenylephrine, many of which were abolished with the alpha1B antagonist, chloroethylclonidine. Cultures exhibited concentration-dependent catecholamine stimulation of DNA synthesis mediated by alpha1 receptors in serum-limited conditions. Neuroepithelial cells were labelled via their ventricular processes by intraventricular injection of Fast blue in E13 embryos prior to transfer of the neocortex to dissociated cell culture. Many of labelled cells were present in culture in germinal foci. Some cells which migrated from these foci underwent apoptosis, as determined by TUNEL in situ hybridization. During a transitory period of up to 48 h in culture, alpha1-adrenoreceptor activation by phenylephrine or noradrenaline increased the number of surviving cells. Apoptosis was observed in vivo in both ventricular and subventricular zones of the neocortex from E13 to E15 in increasing numbers. We propose that both the supply of noradrenaline to forebrain germinal cells, and the expression of alpha1-adrenoreceptors on their surface could act to determine whether they die or continue to proliferate.

Cadmium rapidly and irreversibly blocks presynaptic phospholipase C-linked metabotropic glutamate receptors

Calcium ions (Cd2+) inhibit inositol phosphate (IP) formation elicited by glutamate (GLU) or K+ ions, without affecting carbachol (Carb)-induced IP response in 8-day-old rat forebrain synaptoneurosomes and synaptosomes. On the contrary, Cd2+ was almost ineffective in blocking GLU- and K(+)-responses in hippocampal neurones in culture. The mechanism of Cd2+ inhibition was thus examined in synaptoneurosomes. Extensive washing of synaptoneurosomes pretreated for 1, 5, 15, or 30 min by 100 microM Cd2+ did not modify the inhibitory effect of Cd2+ on GLU-, K(+)- and A23187-evoked IP formation or its lack of effect on Carb response. The later addition of a high affinity Cd2+ chelator (100 microM), N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) also did not reverse the inhibitory effect. TPEN, however, penetrates into synaptoneurosomes and efficiently displaces Cd2+ from the Fura-2-Cd2+ complex as shown by Fura-2 fluorescence recordings. TPEN is not easily removed from the intracellular space, as demonstrated by its ability to still block Cd(2+)-induced Fura-2 fluorescence increase after extensive washing. Pretreatment of synaptoneurosomes by this chelator did not prevent Cd2+ inhibition of GLU-induced IP formation. These data indicate that Cd2+ ions rapidly, irreversibly and extracellularly inhibit GLU-elicited IP formation in synaptoneurosomes or synaptosomes, but not in hippocampal neurones in culture. It is speculated that Cd2+ ions could allow one to distinguish the activity of presynaptic metabotropic glutamate receptors (mGLURs) linked to phosphoinositide metabolism from that of mGLURs located postsynaptically.

Intra- vs extracellular calcium regulation of neurotransmitter-stimulated phosphoinositide breakdown

The dependence on Ca2+ of basal, glutamate- and carbachol-stimulated phosphoinositide (PI) turnover was studied on 8-day old rat brain synaptoneurosomes. For that purpose, intracellular and extracellular Ca2+ concentrations were buffered by bis-(alpha-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, in its tetra(acetoxymethyl)-ester form (BAPTA-AM) and in its free acid form (BAPTA), respectively. The effects of both forms of the calcium chelator intracellular and extracellular Ca2+ buffering on intracellular and extracellular Ca2+ concentration ([Ca2+]i and [Ca2+]e) were determined with fluorimetric assay using fura2, either in its acetoxymethyl ester form (fura2-AM) or in its free acid form. Intracellular chelation of Ca2+ ions with BAPTA-AM induced a dose-dependent reduction of the [Ca2+]i. Basal inositol phosphate (IP) formation was slightly affected by this [Ca2+]i buffering, while glutamate and carbachol stimulations of PI hydrolysis were similarly diminished. Chelation of extracellular Ca2+ ions with BAPTA produced a reduction of both [Ca2+]e and [Ca2+]i. Basal IP accumulation was maximally inhibited by 50%. The carbachol-induced PI hydrolysis was completely inhibited in the presence of 200 microM BAPTA, while a substantial residual glutamate-elicited IP response remained (40% of the control response). It is concluded that [Ca2+]i of synaptoneurosomes is not critical for basal and neurotransmitter-stimulated IP formation, whilst [Ca2+]e is critical. Glutamate may, in part, stimulate PI breakdown in a Ca(2+)-insensitive way.

Regulation of glutamate release by presynaptic kainate receptors in the hippocampus

Most reported actions of kainate are mediated by AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors. Here we report that, unlike AMPA which stimulates, kainate elicits a dose-dependent decrease in L-glutamate release from rat hippocampal synaptosomes and also depresses glutamatergic synaptic transmission. Brief exposure to kainate inhibited Ca(2+)-dependent [3H]L-glutamate release by up to 80%. Inhibition was reversed by kainate antagonists but not by the AMPA-selective non-competitive antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466). A corresponding reversible kainate-evoked depression of NMDA (N-methyl-D-aspartate) receptor-mediated excitatory postsynaptic currents (e.p.s.cs) was observed when AMPA receptors were blocked by GYKI 52466. The synaptic depression was preceded by a brief period of enhanced release and a small inward current was also observed. The effects of kainate were unaffected by metabotropic glutamate (mGlu), GABAA, GABAB, glycine and adenosine receptor antagonists. These results indicate that glutamate release can be modulated directly by kainate autoreceptors.

A modulation of glutamate-induced phosphoinositide breakdown by intracellular pH changes

The influence of intracellular pH (pHi) changes on the formation of inositol phosphate metabolites (IPs) produced by glutamatergic stimulation was studied in 8-day-old rat brain synaptoneurosomes. For this purpose pHi was measured using 2',7'-bis-(2-carboxyl)-5,6-carboxyfluorescein (BCECF) fluorimetric assay in parallel with the basal and receptor-mediated formations of inositol monophosphate (IP1) and inositol bisphosphate (IP2). We found that glutamate (1 mM), which induces a transient acidification (delta pH = -0.05), produces an identical accumulation of IP1 and IP2. K+ (30 mM), which provokes an alkalinization of the internal medium (delta pH = +0.22), mainly leads to the formation of IP1 metabolites. Paired combinations of glutamate with 1, 5 and 10 mM NH4+ finally result in an alkalinization of the intrasynaptoneurosomal medium. These combinations produce a strong decrease of the IP2 level concomitant with an increase of the IP1 formation, compared to the levels of IP1 and IP2 evoked by glutamate alone. The total amount of IPs (IP1 + IP2) produced by these combinations is not different from that obtained with glutamate alone. Paired combinations of carbachol with NH4+ produce an identical alkalinization to that produced by NH4+ alone. These combinations produce an increased IP1 accumulation, while the IP2 formation is slightly decreased. When the internal medium is acidified by diminishing the external concentration of Na+, the ratio IP1/IP2 produced after metabotropic glutamate receptor (mGluR) activation is shifted to lower values, while it is not affected for the muscarinic stimulation. These data suggest that the mGluR-associated pathway in synaptoneurosomes is sensitive to pHi shifts, while the muscarinic receptor-associated pathway is less altered when pHi is manipulated. It may be proposed that pH-sensitive inositol phosphate dephosphorylating systems, i.e. phosphatases, are associated with mGluRs in this preparation.

Pharmacological evidence for an involvement of group II and group III mGluRs in the presynaptic regulation of excitatory synaptic responses in the CA1 region of rat hippocampal slices

The actions of four mGluR antagonists, (+)-MCPG, MAP4, MCCG and (S)-4CPG, were evaluated against agonist-induced depressions of synaptic transmission at the Schaffer collateral-commissural pathway in rat hippocampal slices. (+)-MCPG (1 mM) reversed very effectively depressions of field EPSPs induced by (1S,3R)-ACPD and (1S,3S)-ACPD but had weak and variable effects on depressions induced by L-AP4. It had no effect on depressions induced by either (-)-baclofen or carbachol. In contrast, MAP4 (500 microM) reversed very effectively depressions induced by L-AP4 without affecting depressions induced by (1S,3S)-ACPD. MCCG (1 mM) had the opposite activity; it antagonized depressions induced by (1S,3S)-ACPD but not those induced by L-AP4. Finally, (S)-4CPG (1 mM) reversed small depressions of field EPSPs induced by high concentrations (50-100 microM) of (1S,3R)- and (1S,3S)-ACPD, but not L-AP4, whilst having no effect on large depressions induced by 10 microM (1S,3S)-ACPD in voltage-clamped cells. These results confirm and extend the effectiveness and selectivity of (+)-MCPG as an mGluR antagonist. The divergent effects of the group I antagonist, (S)-4CPG, can be explained by an indirect action on postsynaptic receptors which is manifest when high agonist concentrations are used in non-voltage-clamp experiments. The action of MCCG and MAP4 indicates that two pharmacologically-distinct mGluRs, belonging to classes II and III, can regulate synaptic transmission in the CA1 region via presynaptic mechanisms.

Stimulation of Ca(2+)-activated non-specific cationic channels by phospholipase C-linked glutamate receptors in synaptoneurosomes?

The regulation of intracellular Ca2+ concentration ([Ca2+]i) by glutamate metabotropic receptors (mGluR) was studied in 8-day-old rat forebrain synaptoneurosomes using spectrofluorimetric methods. Here we demonstrate that metabotropic glutamate agonists induce in rat brain synaptoneurosomes a Ca2+ influx largely dependent upon the presence of Ca2+ in the external medium. The pharmacological profile of this influx is strongly correlated with the pharmacological profile of the activation of phosphoinositide hydrolysis, i.e. quisqualic acid >> 1S,3R-amino-1-dicarboxylate-1,3 cyclopentane approximately equal to glutamate. This metabotropic glutamate receptor-induced Ca2+ influx is insensitive to voltage-dependent Ca2+ channel antagonists and occurs through a Mn2+ impermeant pathway. The study of the rapid kinetics shows that this influx is triggered after a 300 ms delay compared with that elicited by depolarizing agents and Ca2+ ionophore A23187. In order to assess further if mGluR stimulate this influx through the recruitment of inositol triphosphate (IP3)-sensitive intracellular Ca2+ stores, we have tested the effect of thapsigargin on membrane potential and intracellular Ca2+ simultaneously. Thapsigargin induces a depolarization of the synaptoneurosomal membrane followed by a massive Ca2+ influx, occurring via a Mn2+ nonpermeant route. This depolarizing effect is sensitive to the presence of the intracellular Ca2+ chelator [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetoxymethyl ester], and partially sensitive to extracellular Na+, but insensitive to the presence of extracellular Ca2+. Taken together, our data suggest that mGluR stimulate self-maintained increases of [Ca2+]i in rat forebrain synaptoneurosomes via the activation of a multistep mechanism, sequenced in the following steps: (i) mGluR-induced IP3 synthesis; (ii) IP3-stimulated intracellular Ca2+ release; (iii) Ca(2+)-activated non-specific cation channel, leading to local depolarization and a Ca2+ influx; and (iv) activation of Ca(2+)-sensitive phospholipase C.

Protein kinase C differently regulates quisqualate- and 1S,3R-trans aminocyclopentane dicarboxylate-induced phosphoinositide hydrolysis during in vitro development of hippocampal neurons

Transient peaks of quisqualate (QA)-, but not 1S,3R-1-amino-3-cyclopentane dicarboxylate (1S,3R-ACPD)- and carbachol-induced inositol phosphate formation occur between 2 and 5 days in vitro (DIV) in hippocampal neurons in culture. In order to elucidate the putative origin of such developmental activity differences, the effect of PKC on metabotropic glutamate receptor (mGluR) and muscarinic receptor responses was investigated at 3 and 10 DIV. (i) Stimulation of PKC by phorbol-12,13-dibutyrate inhibited QA, 1S,3R-ACPD and carbachol responses at 3 DIV. At 10 DIV, only 1S,3R-ACPD response was still inhibited by phorbol esters. (ii) Inhibition of PKC by staurosporine at 3 DIV potentiated 1S,3R-ACPD-induced inositol phosphate formation, but had no effect on QA and carbachol responses. At 10 DIV, all responses were potentiated by staurosporine. These data strongly suggest that PKC differently modulates 1S,3R-ACPD- and QA-induced inositol phosphate accumulations during in vitro development. The specific activity of mGluRs during development, vs that of muscarinic receptor, and the peculiar modes of regulation by PKC of these two mGluR activities further suggest their particular involvement in the maturation of neuronal culture.

Location of profilin at presynaptic sites in the cerebellar cortex; implication for the regulation of the actin-polymerization state during axonal elongation and synaptogenesis

Profilin is a 15 kDa protein that binds actin monomers and inhibits their polymerization in vitro. The actin-profilin complex can be rapidly dissociated in vitro by phosphatidylinositol-4,5-bis-phosphate, providing a mechanism for regulating actin assembly-disassembly cycles during cell motile events. We have used a polyclonal antibody to calf spleen profilin to analyse the developmental expression and cellular distribution of profilin in the rat cerebellum and cultured cortical neurons. Immature neurons contain large amount of profilin both in vivo and in vitro. Immunofluorescence showed it to be present in developing neurites and growth cones but not in the filopodia of cortical neurons in culture. Profilin immunoreactivity was intense in the parallel fibres, the granule cell axons of the cerebellar cortex, at the time when they are elongating. Purkinje cell dendrites were not labelled. Profilin immunostaining was present in presynaptic varicosities, but not in dendritic spines within the molecular layer of juvenile and adult rats. The profilin concentration was higher in synaptosomes than in the total cerebellum during the second and third postnatal weeks, a period of intense synaptogenesis. Thus, profilin may help regulate actin polymerization and depolymerization during axonal elongation and synaptogenesis. Its restriction to the presynaptic site in the adult suggests that it may also be involved in the regulation of the release of synaptic vesicles.

Effect of thiol reagents on phosphoinositide hydrolysis in rat brain synaptoneurosomes

Some divalent ions, such as Cd2+ and Zn2+, are able to stimulate phosphoinositide (PI) breakdown and to inhibit receptor-mediated PI metabolism. These ions are also known to react with the free -SH groups of proteins. This prompted us to investigate the effects of more potent sulphydryl reagents, Hg2+ and p-chloromercuric benzosulphonic acid (PCMBS), on the inositol phosphate (IP) accumulation triggered by the neuroactive substances: glutamate, carbachol and K+, using synaptoneurosomes from 8-day-old rat forebrains. Hg2+ and PCMBS, depending on their concentration, had two distinct effects on IP accumulation: at low doses, Hg2+ (from 1 to 10 microM) and PCMBS (0.1 mM) by themselves stimulated PI breakdown, inhibited glutamate-elicited IP accumulation and had additive effects with respect to carbachol-induced IP stimulation. At higher doses, Hg2+ (from 0.01 to 1 mM) inhibited both basal and neuroactive substance-stimulated IP accumulation. PCMBS (1 mM), provoked only an inhibition of the agonist-stimulated IP formation. Monitoring membrane potential and intracellular Ca2+ with the fluorescent dyes diSC2(5) and fura2, respectively, indicated that these mercurials could strongly depolarize the synaptoneurosomal membrane and produce a Ca2+ influx dependent on extracellular Ca2+. The stimulatory effects of low concentrations of mercurials on PI turnover could be linked to the depolarization they provoke and the subsequent Ca2+ rise, which in turn is known to stimulate some phospholipase C enzymes. The inhibitory effects observed at high concentrations might be due to a loss of activity of proteins involved in PI breakdown, as all receptor-mediated IP accumulations were inhibited.

Dithiotreitol specifically inhibits metabotropic responses of glutamate and depolarizing agents in rat brain synaptoneurosomes

Dithiotreitol (DTT), a sulfhydryl reducing agent inhibits in a dose-dependent manner the inositol phosphates (IPs) accumulation responses evoked by glutamate and potassium without affecting that of carbachol in rat forebrain synaptoneurosomes. Furthermore, DTT neither provokes a depolarization of the membrane, nor increases the internal calcium concentration. Depolarization and internal calcium rise are known to stimulate IPs production. Moreover, DTT does not modify the depolarizing effect and the calcium rise elicited by glutamate and potassium. In addition, the antioxidant compounds 2-aminoethylisothiouronium bromide (AET) and ascorbic acid have no effect on the basal and stimulated IPs accumulation. Thus, it is concluded that: (1) two distinct transduction pathways exist, one stimulated by glutamate and depolarizing agents and the other one by cholinergic agonists; (2) DTT produces its inhibition by reducing disulfide bridges likely at the level of proteins of the phosphoinositide transduction mechanism.

[Alcohol dependence. Financial aspect and socio-occupational consequences]

The financial cost of alcohol dependence was evaluated in 133 alcoholic patients. The main amount of money spent daily on alcoholic beverages was 94 French francs, a figure that was unrelated to the patients' monthly incomes and highest in those living alone and in those drinking exclusively out of home. These results suggest that the economic cost of alcohol dependence plays a key role in the socio-professional degradation of alcoholics.

A specific transduction mechanism for the glutamate action on phosphoinositide metabolism via the quisqualate metabotropic receptor in rat brain synaptoneurosomes: II. Calcium dependency, cadmium inhibition

In this article, we demonstrate that an increase in intracellular Ca2+ concentration may represent a specific common step(s) in the mechanism(s) of action of glutamate (Glu) and depolarizing agents on formation of inositol phosphates (IPs) in 8-day-old rat forebrain synaptoneurosomes. In fact, A23187, a Ca2+ ionophore, induces a dose-dependent accumulation of IPs, which is not additive with that evoked by Glu and K+ but is slightly synergistic with that induced by carbachol. In addition, Glu and K+ augment the intracellular Ca2+ concentration in synaptoneurosome preparations as measured by the fura-2 assay. The absence of external Ca2+ decreases basal and Glu-, and K(+)-stimulated formation of IPs. Cd2+ (100 microM) fully inhibits both Glu- and K(+)-evoked formation of IPs without affecting the carbachol-elicited response of IPs. Zn2+ inhibits Glu- and K(+)-stimulated accumulation of IPs (IC50 approximately 0.4 mM) but with a lower affinity than Cd2+ (IC50 approximately 0.035 mM). The organic Ca2+ channel blockers verapamil (10 microM), nifedipine (10 microM), omega-conotoxin (2 microM), and amiloride (10 microM) as well as the inorganic blockers Co2+ (100 microM) and La3+ (100 microM) block neither Glu- nor K(+)-evoked formation of IPs, a result suggesting that the opening of the L-, T-, N-, or P-type Ca2+ channels does not participate in these responses. All these data suggest that an increase in intracellular Ca2+ concentration resulting from an influx of Ca2+, sensitive to Cd2+ but not to other classical Ca2+ antagonists, may play a key role in the transduction mechanism activated by Glu or depolarizing agents.

A specific transduction mechanism for the glutamate action on phosphoinositide metabolism via the quisqualate metabotropic receptor in rat brain synaptoneurosomes: I. External Na+ requirement

The characteristics of the transduction mechanism(s) activated by glutamate (Glu) via the quisqualate metabotropic receptor, as well as by depolarizing agents, to trigger formation of inositol phosphates (IPs) were investigated in 8-day-old rat forebrain synaptoneurosomes. The replacement of external Na+ by various compounds (Li+, Tris+, N-methyl-D-glucamine+, and sucrose) induces an increase in basal accumulation of IPs and depolarizes synaptoneurosome membranes. Under these conditions, Glu- and K(+)-induced accumulations of IPs are inhibited, whereas the carbachol (Carb)-elicited response of IPs parallels the basal one. Agents increasing Na+ influx, such as veratridine and monensin, depolarize synaptoneurosomes and stimulate formation of IPs. These stimulations are not additive with responses of IPs elicited by Glu or K+. These data suggest that (a) Glu activates phosphoinositide metabolism via a specific mechanism (distinct from that of cholinergic agonists), (b) depolarizing agents and Glu share at least one common intermediate step in their mechanisms of activation of the metabolism of IPs, and (c) the depolarization may correspond to this common step. In addition, Na+ seems to be required for Glu stimulation of metabolism of IPs. The depolarization associated with the action of Glu on formation of IPs results neither from an influx via tetrodotoxin-sensitive voltage-dependent Na+ channels nor from an entry via the classically characterized Na+/Ca2+ or Na+/H+ exchangers. In fact, tetrodotoxin (2 microM) has no effect on the Glu- or K(+)-elicited response of IPs. Amiloride (greater than 50 microM) and some of its derivatives similarly inhibit not only Glu- and K(+)- but also Carb-evoked formation of IPs.

Effects of benzyl alcohol on transferrin and low density lipoprotein receptor mediated endocytosis in leukemic guinea pig B lymphocytes

We demonstrated that benzyl alcohol, a neutral local anesthetic drug, inhibits the uptake and degradation of lowdensity lipoprotein and endocytosis of transferrin receptors of guinea pig leukemic B lymphocytes (L2C). This inhibition is very rapid, concentration dependant and reversible by simple washing. Membrane fluidity of the living cells is also modified.