Taurine deficiency in dissociated mouse cerebellar cultures affects neuronal migration

Developmental basis of SHH medulloblastoma heterogeneity

Many genes that drive normal cellular development also contribute to oncogenesis. Medulloblastoma (MB) tumors likely arise from neuronal progenitors in the cerebellum, and we hypothesized that the heterogeneity observed in MBs with sonic hedgehog (SHH) activation could be due to differences in developmental pathways. To investigate this question, here we perform single-nucleus RNA sequencing on highly differentiated SHH MBs with extensively nodular histology and observed malignant cells resembling each stage of canonical granule neuron development. Through innovative computational approaches, we connect these results to published datasets and find that some established molecular subtypes of SHH MB appear arrested at different developmental stages. Additionally, using multiplexed proteomic imaging and MALDI imaging mass spectrometry, we identify distinct histological and metabolic profiles for highly differentiated tumors. Our approaches are applicable to understanding the interplay between heterogeneity and differentiation in other cancers and can provide important insights for the design of targeted therapies.

Gut Microbiota and Relevant Metabolites Analysis in Alcohol Dependent Mice

Alcohol abuse is a major public health crisis. Relative evidences supported that the gut microbiota (GM) played an important role in central nervous system (CNS) function, and the composition of them had changed after alcohol drinking. We sought to explore the changes of GM in alcohol dependence. In our study, the GM of mice with alcohol administration was detected through analyzed 16S rRNA gene sequencing and the fecal metabolites were analyzed by LC-MS. The microbial diversity was significantly higher in the alcohol administration group, the abundance of phylum Firmicutes and its class Clostridiales were elevated, meanwhile the abundance of Lachnospiraceae, Alistipes, and Odoribacter showed significant differences among the three groups. Based on LC-MS results, bile acid, secondary bile acid, serotonin and taurine level had varying degrees of changes in alcohol model. From paraffin sections, tissue damage was observed in liver and colon. These findings provide direct evidence that alcohol intake affects the composition of GM, enable a better understanding of the function of GM in the microbiota-gut-brain (MGB) axis, and give a new thought for alcohol addiction treatment.

Taurine as an Essential Neuromodulator during Perinatal Cortical Development

A variety of experimental studies demonstrated that neurotransmitters are an important factor for the development of the central nervous system, affecting neurodevelopmental events like neurogenesis, neuronal migration, programmed cell death, and differentiation. While the role of the classical neurotransmitters glutamate and gamma-aminobutyric acid (GABA) on neuronal development is well established, the aminosulfonic acid taurine has also been considered as possible neuromodulator during early neuronal development. The purpose of the present review article is to summarize the properties of taurine as neuromodulator in detail, focusing on the direct involvement of taurine on various neurodevelopmental events and the regulation of neuronal activity during early developmental epochs. The current knowledge is that taurine lacks a synaptic release mechanism but is released by volume-sensitive organic anion channels and/or a reversal of the taurine transporter. Extracellular taurine affects neurons and neuronal progenitor cells mainly via glycine, GABA(A), and GABA(B) receptors with considerable receptor and subtype-specific affinities. Taurine has been shown to directly influence neurogenesis in vitro as well as neuronal migration in vitro and in vivo. It provides a depolarizing signal for a variety of neuronal population in the immature central nervous system, thereby directly influencing neuronal activity. While in the neocortex, taurine probably enhance neuronal activity, in the immature hippocampus, a tonic taurinergic tone might be necessary to attenuate activity. In summary, taurine must be considered as an essential modulator of neurodevelopmental events, and possible adverse consequences on fetal and/or early postnatal development should be evaluated for pharmacological therapies affecting taurinergic functions.

Taurine activates GABAergic networks in the neocortex of immature mice

Although it has been suggested that taurine is the main endogenous neurotransmitter acting on glycine receptors, the implications of glycine receptor-mediated taurine actions on immature neocortical networks have not been addressed yet. To investigate the influence of taurine on the excitability of neuronal networks in the immature neocortex, we performed whole-cell patch-clamp recordings from visually identified pyramidal neurons and interneurons in coronal slices from C57Bl/6 and GAD67-green fluorescent protein (GFP) transgenic mice (postnatal days 2–4). In 46% of the pyramidal neurons bath-application of taurine at concentrations ≥ 300 μM significantly enhanced the frequency of postsynaptic currents (PSCs) by 744.3 ± 93.8% (n = 120 cells). This taurine-induced increase of PSC frequency was abolished by 0.2 μM tetrodotoxin (TTX), 1 μM strychnine or 3 μM gabazine, but was unaffected by the glutamatergic antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and (±) R(-)-3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonic acid (CPP), suggesting that taurine specifically activates GABAergic network activity projecting to pyramidal neurons. Cell-attached recordings revealed that taurine enhanced the frequency of action potentials (APs) in pyramidal neurons, indicating an excitatory action of the GABAergic PSCs. In order to identify the presynaptic targets of taurine we demonstrate that bath application of taurine induced in GAD67-GFP labeled interneurons an inward current that is mainly mediated by glycine receptors and can generate APs in these cells. We conclude from these results that taurine can enhance network excitability in the immature neocortex by selectively activating GABAergic interneurons via interactions with glycine receptors.

Taurine stimulates proliferation and promotes neurogenesis of mouse adult cultured neural stem/progenitor cells

This study reports an effect of taurine (1-10 mM) increasing markedly (120%) the number of neural precursor cells (NPCs) from adult mouse subventricular zone, cultured as neurospheres. This effect is one of the highest reported for adult neural precursor cells. Taurine-containing cultures showed 73-120% more cells than controls, after 24 and 96 h in culture, respectively. Taurine effect is due to enhanced proliferation as assessed by BrdU incorporation assays. In taurine cultures BrdU incorporation was markedly higher than controls from 1.5 to 48 h, with the maximal difference found at 1.5 h. This effect of taurine reproduced at every passage with the same window time. Taurine effects are not mimicked by glycine, alanine or GABA. Clonal efficiency values of 3.6% for taurine cultures and 1.3% for control cultures suggest a taurine influence on both, progenitor and stem cells. Upon differentiation, the proportion of neurons in control and taurine cultures was 3.1% (±0.5) and 10.2% (±0.8), respectively. These results are relevant for taurine implication in brain development as well as in adult neurogenesis. Possible mechanisms underlying taurine effects on cell proliferation are discussed.

GABA(A) receptor and glycine receptor activation by paracrine/autocrine release of endogenous agonists: more than a simple communication pathway

It is a common and widely accepted assumption that glycine and GABA are the main inhibitory transmitters in the central nervous system (CNS). But, in the past 20 years, several studies have clearly demonstrated that these amino acids can also be excitatory in the immature central nervous system. In addition, it is now established that both GABA receptors (GABARs) and glycine receptors (GlyRs) can be located extrasynaptically and can be activated by paracrine release of endogenous agonists, such as GABA, glycine, and taurine. Recently, non-synaptic release of GABA, glycine, and taurine gained further attention with increasing evidence suggesting a developmental role of these neurotransmitters in neuronal network formation before and during synaptogenesis. This review summarizes recent knowledge about the non-synaptic activation of GABA(A)Rs and GlyRs, both in developing and adult CNS. We first present studies that reveal the functional specialization of both non-synaptic GABA(A)Rs and GlyRs and we discuss the neuronal versus non-neuronal origin of the paracrine release of GABA(A)R and GlyR agonists. We then discuss the proposed non-synaptic release mechanisms and/or pathways for GABA, glycine, and taurine. Finally, we summarize recent data about the various roles of non-synaptic GABAergic and glycinergic systems during the development of neuronal networks and in the adult.

Taurine stimulates proliferation of mice embryonic cultured neural progenitor cells

Taurine is present in high levels in fetal brain which decrease in the adult, suggesting its role in brain development. In some regions of taurine deficient animals cells show defective migration and the presence of numerous mitotic figures, suggesting a delay in cell proliferation. To know more about the role of taurine in the developing brain cells, the present study investigated whether taurine is a factor involved in proliferation or/and viability of neural progenitor cells (NPC). NPC were obtained from 13.5-days mice embryos mesencephalon, and cultured during 4-5 days to form neurospheres in the presence of EGF plus FGFb (EGF/FGF) or EGF alone. Mesencephalon taurine content (349 mmoles/kg protein) was lost in NPC and recovered after addition of 10 mM taurine to the culture. Neurospheres-forming NPC were over 94% nestin-positive. Taurine increased 38.6% and 43.2% the number of NPC formed in EGF/FGF or EGF conditions, respectively. In secondary neurospheres this increase was 24.6% and 62.1%, in EGF/FGF or EGF cultures respectively. Correspondingly neurospheres size was increased by taurine but neurospheres number was not enhanced. Taurine significantly increased the number of BrdU-positive cells, without affecting cell viability, suggesting proliferation as the mechanism responsible for taurine action increasing NPC. Taurine seems unable to increase the number of beta-III-tubulin-positive cells differentiated from neurospheres after serum addition, and rather an increase in astrocytes was observed. These results point to taurine as a trophic factor contributing to optimize NPC proliferation.

Taurine and guanidinoethanesulfonic acid (GES) differentially affects the expression and phosphorylation of cellular proteins in C6 glial cells

Effects of taurine and guanidinoethanesulfonic acid (GES), a taurine transport inhibitor, on the expression and phosphorylation of cellular proteins in C6 glial cells were examined using two-dimensional (2-D) gel electrophoresis and 2-D immunoblots. 2-D gels stained with Coomassie Blue or SYPRO Ruby showed differential distribution patterns of cellular proteins in the control, taurine-supplemented and GES-supplemented cells. 2-D immunoblot analysis using the anti-phosphotyrosine antibody recognized only few immuno-reactive proteins in all three samples, and their distribution patterns were different. On the other hand, 2-D immunoblot analysis using the anti-phosphothreonine antibody recognized many immuno-reactive proteins with distinctly different distribution patterns in the control, taurine-supplemented and GES-supplemented cells. In GES-supplemented cells, the relative number of the anti-phosphotyrosine immuno-reactive protein spots increased modestly, whereas the relative number of the anti-phosphothreonine immuno-reactive protein spots decreased markedly than those in the control and taurine-supplemented cells.

Glycine receptors mediate excitation of subplate neurons in neonatal rat cerebral cortex

The development of the cerebral cortex depends on genetic factors and early electrical activity patterns that form immature neuronal networks. Subplate neurons (SPn) are involved in the construction of thalamocortical innervation, generation of oscillatory network activity, and in the proper formation of the cortical columnar architecture. Because glycine receptors play an important role during early corticogenesis, we analyzed the functional consequences of glycine receptor activation in visually identified SPn in neocortical slices from postnatal day 0 (P0) to P4 rats using whole cell and perforated patch-clamp recordings. In all SPn the glycinergic agonists glycine, beta-alanine, and taurine induced dose-dependent inward currents with the affinity for glycine being higher than that for beta-alanine and taurine. Glycine-induced responses were blocked by the glycinergic antagonist strychnine, but were unaffected by either the GABAergic antagonist gabazine, the N-methyl-d-aspartate-receptor antagonist d-2-amino-5-phosphonopentanoic acid, or picrotoxin and cyanotriphenylborate, antagonists of alpha-homomeric and alpha1-subunit-containing glycine receptors, respectively. Under perforated-patch conditions, glycine induced membrane depolarizations that were sufficient to trigger action potentials (APs) in most cells. Furthermore, glycine and taurine decreased the injection currents as well as the synaptic stimulation strength required to elicit APs, indicating that glycine receptors have a consistent excitatory effect on SPn. Inhibition of taurine transport and application of hypoosmolar solutions induced strychnine-sensitive inward currents, suggesting that taurine can act as a possible endogenous agonist on SPn. In summary, these results demonstrate that SPn express glycine receptors that mediate robust excitatory membrane responses during early postnatal development.

Taurine deficiency and apoptosis: findings from the taurine transporter knockout mouse

Apoptosis is characterized by cell shrinkage, nuclear condensation, DNA-fragmentation and apoptotic body formation. Compatible organic osmolytes, e.g. taurine, modulate the cellular response to anisotonicity and may protect from apoptosis. Taurine transporter knockout mice (taut-/- mice) show strongly decreased taurine levels in a variety of tissues. They develop clinically important age-dependent diseases and some of them are characterized by apoptosis. Increased photoreceptor apoptosis leads to blindness of taut-/- mice at an early age. The taurine transporter may not be essential for the differentiation of photoreceptor cells, but many mature cells do not survive without an intact taurine transporter. The olfactory epithelium of taut-/- mice also exhibits structural and functional abnormalities. When compared with wild-types, taut-/- mice have a significantly higher proliferative activity of immature olfactory receptor neurons and an increased number of apoptotic cells. This is accompanied by electrophysiological findings indicating a reduced olfactory sensitivity. Furthermore, taut-/- and taut+/- mice develop moderate unspecific hepatitis and liver fibrosis beyond 1 year of age where hepatocyte apoptosis and activation of the CD95 system are pronounced.

Amyloid Fibrils of Mammalian Prion Protein Are Highly Toxic to Cultured Cells and Primary Neurons

A growing body of evidence indicates that small, soluble oligomeric species generated from a variety of proteins and peptides rather than mature amyloid fibrils are inherently highly cytotoxic. Here, we show for the first time that mature amyloid fibrils produced from full-length recombinant mammalian prion protein (rPrP) were highly toxic to cultured cells and primary hippocampal and cerebella neurons. Fibrils induced apoptotic cell death in a time- and dose-dependent manner. The toxic effect of fibrils was comparable with that exhibited by soluble small beta-oligomers generated from the same protein. Fibrils prepared from insulin were not toxic, suggesting that the toxic effect was not solely due to the highly polymeric nature of the fibrillar form. The cell death caused by rPrP fibrils or beta-oligomers was substantially reduced when expression of endogenous PrP(C) was down-regulated by small interfering RNAs. In opposition to the beta-oligomer and amyloid fibrils of rPrP, the monomeric alpha-helical form of rPrP stimulated neurite out-growth and survival of neurons. These studies illustrated that both soluble beta-oligomer and amyloid fibrils of the prion protein are intrinsically toxic and confirmed that endogenously expressed PrP(C) is required for mediating the toxicity of abnormally folded external PrP aggregates.

Taurine effect on neuritic outgrowth from goldfish retinal explants in the absence and presence of fetal calf serum

Post-crush goldfish retinal explants were cultured in the absence of fetal calf serum and in the presence of calcium, albumin, glucose or taurine. There was an increase in length and density of the neurites in a dose-dependent manner when fetal calf serum was added to the medium. The addition of calcium to the basic medium, Leibovitz, produced a small increase in neuritic outgrowth at low concentrations, but inhibited outgrowth at higher levels. Albumin did not significantly modify neuritic outgrowth. Glucose, at variable concentrations, produced a bell-shaped increase in length and density of the neurites. Taurine, in the absence of fetal calf serum, produced a small increase in neuritic outgrowth at 10 mM. In the presence of glucose, taurine stimulated outgrowth was less efficient than in the presence of fetal calf serum. In order to investigate the mechanisms of action of taurine as a trophic agent, the culture medium in the absence of fetal calf serum will be supplemented with glucose.

Selective neuroinhibitory effects of taurine in slices of rat main olfactory bulb

Taurine is abundant in the main olfactory bulb, exceeding glutamate and GABA in concentration. In whole-cell patch-clamp recordings in rat olfactory bulb slices, taurine inhibited principal neurons, mitral and tufted cells. In these cells, taurine decreased the input resistance and caused a shift of the membrane potential toward the chloride equilibrium potential. The taurine actions were sustained under the blockade of transmitter release and were reversible and dose-dependent. At a concentration of 5 mM, typically used in this study, taurine showed 90% of its maximal effect. GABA(A) antagonists, bicuculline and picrotoxin, blocked the taurine actions, whereas the glycine receptor antagonist strychnine and GABA(B) antagonists, CGP 55845A and CGP 35348, were ineffective. These findings are consistent with taurine directly activating GABA(A) receptors and inducing chloride conductance. Taurine had no effect on periglomerular and granule interneurons. The subunit composition of GABA(A) receptors in these cells, differing from those in mitral and tufted cells, may account for taurine insensitivity of the interneurons. Taurine suppressed olfactory nerve-evoked monosynaptic responses of mitral and tufted cells while chloride conductance was blocked. This action was mimicked by the GABA(B) agonist baclofen and abolished by CGP 55845A; CGP 35348, which primarily blocks postsynaptic GABA(B) receptors, was ineffective. The taurine effect most likely was due to GABA(B) receptor-mediated inhibition of presynaptic glutamate release. Neither taurine nor baclofen affected responses of periglomerular cells. The lack of a baclofen effect implies that functional GABA(B) receptors are absent from olfactory nerve terminals that contact periglomerular cells. These results indicate that taurine decreases the excitability of mitral and tufted cells and their responses to olfactory nerve stimulation without influencing periglomerular and granule cells. Selective effects of taurine in the olfactory bulb may represent a physiologic mechanism that is involved in the inhibitory shaping of the activation pattern of principal neurons.

Homogenous glycine receptor expression in cortical plate neurons and cajal-retzius cells of neonatal rat cerebral cortex

Glycinergic membrane responses have been described in cortical plate neurons (CPn) and Cajal-Retzius cells (CRc) during early neocortical development. In order to elucidate the functional properties and molecular identity of glycine receptors in these two neuronal cell types, we performed whole-cell patch-clamp recordings and subsequent single-cell multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) analyses on visually identified neurons in tangential and coronal slices as well as in situ hybridizations of coronal slices from neonatal rat cerebral cortex (postnatal days 0-4). In both CPn and CRc the glycinergic agonists glycine, beta-alanine and taurine induced inward currents with larger current densities in CRc. The functional properties of these currents were similar between CPn and CRc. In both cell types the glycine receptor showed a higher affinity for glycine than for the glycinergic agonists beta-alanine and taurine. The glycinergic responses of both cells were blocked by the glycinergic antagonist strychnine and were unaffected by the GABAergic antagonist bicuculline (100 microM), the N-methyl-D-aspartic acid receptor antagonist (+/-)-2-amino-5-phosphonopentatonic acid (60 microM) and by picrotoxin (30 microM), an antagonist of alpha homomeric glycine receptors. Single-cell multiplex RT-PCR revealed the expression of glycine receptor alpha(2) and beta subunits in CPn and CRc, while no alpha(1) and alpha(3) subunits were observed. In situ hybridization histochemistry showed the expression of mRNAs for alpha(2) and beta subunits within the cortical plate and in large neurons of the marginal zone, while there were no signals for alpha(1) and alpha(3) subunits. In summary, these results suggest that CPn and CRc express glycine receptors with similar functional and pharmacological properties. The correlation of pharmacological properties and mRNA expression suggests that the glycine receptors in both cell types may consist of alpha(2)/beta heteromeric receptors.

Exogenous glutamate and taurine exert differential actions on light-induced release of two endogenous amino acids in isolated rat retina

A dark-adapted isolated rat retina, preloaded with [(14)C]glutamate ([(14)C]Glu) and [(3)H]taurine ([(3)H]Tau), was superfused with artificial cerebrospinal fluid (ACSF) in the absence and presence of Glu (1 mM) or Tau (1 mM), as well as the Glu uptake inhibitors dihydrokainic acid (DHK, 0.04 mM) and trans-L-pyrrolidine-2,4-dicarboxylate (t-PDC, 0.004 mM). After 10 min of light stimulation, the extracellular level of [(14)C]Glu and [(3)H]Tau was reduced to 82 +/- 2% and 65 +/- 4% of the control, respectively. Basal release was enhanced when Tau and t-PDC were applied together, although none of the compounds had any effect when applied individually. Glu and DHK had no effect. The decrease of [(14)C]Glu efflux evoked by light stimuli was enhanced by t-PDC and Tau, either added separately or together, whereas Glu and DHK were without effect. In contrast, [(3)H]Tau efflux variations induced by light stimuli were reduced markedly by both Tau and Glu. These findings suggest distinctly different roles of Tau and Glu in light-induced responses in mammalian retina, including a possible role for Tau in light adaptation processes.

Medium requirements for neuritic outgrowth from goldfish retinal explants and the trophic effect of taurine

The use of culture media of known composition are necessary for studying the role of trophic molecules. Since most of the in vitro research on regeneration of the optic nerve has been performed in the presence of fetal calf serum, the aim of this study was to obtain a medium in which the neuritic outgrowth from post-crush goldfish retinal explants could take place without adding fetal calf serum. After the lesion of the optic nerve (10 days), the retina of goldfish was dissected and explants were cultured for 5 and 10 days in the absence or in the presence of fetal calf serum, at which time the neuritic outgrowth was determined. Various concentrations and combinations of glucose, albumin, calcium, HEPES and taurine were used. The highest neuritic outgrowth was observed in the presence of fetal calf serum, in which condition the amino acid taurine increased length and density of neurites. Media supplemented with albumin, calcium or HEPES did not modify the outgrowth of neurites from the explants. However, glucose favored the neuritic outgrowth in a bell-shaped manner, although fibers were thinner than those observed in the presence of fetal calf serum. Taurine did not stimulate outgrowth of neurites from explants growing in a medium with optimal concentrations of glucose, indicating that elements of the fetal calf serum are determinant for the trophic effect of taurine. The present results contribute to further studies, such as those related to the effect of taurine and of trophic factors derived from the optic tectum, which would be performed in the presence of a medium free of fetal calf serum.

Depolarizing glycine responses in Cajal-Retzius cells of neonatal rat cerebral cortex

We investigated the properties of glycine-induced responses in Cajal-Retzius cells, a neuronal cell type essential for the establishment of neocortical lamination. Whole-cell and gramicidin-perforated patch-clamp recordings were performed on visually identified Cajal-Retzius cells in tangential slices from neonatal rat cortex (postnatal days 0-3). With a pipette Cl(-) concentration of 50 mM, bath application of 1 mM glycine induced a membrane depolarization of 32.8+/-7.4 mV and a massive decrease in membrane resistance by 88+/-1.4%. The membrane depolarization was abolished in the presence of the glycinergic antagonists strychnine (30 microM) and phenylbenzene-omega-phosphono-alpha-amino acid (100 microM), while the GABA(A) receptor antagonist bicuculline (100 microM) and the glutamatergic antagonist (+/-)-2-amino-5-phosphonopentatonic acid (60 microM) were without effect, suggesting that the glycine-induced membrane responses were mediated exclusively by the strychnine-sensitive glycine receptor. The EC(50) for activation of glycine receptors was 0.54 mM, 1.62 mM and 2.41 mM, for the glycinergic agonists glycine, beta-alanine and taurine, respectively. Since the reversal potential of the glycine-induced currents showed a strong dependency on the intracellular chloride concentration and was virtually unaffected under HCO(3)(-)-free conditions, the activation of glycine receptors was probably linked to Cl(-) fluxes with little contribution of HCO(3)(-) ions. Perforated patch recordings from Cajal-Retzius cells demonstrated that glycine elicited depolarizing responses mediated by Cl(-) currents which reversed at -41+/-3.7 mV. In summary, from these results we suggest that Cajal-Retzius cells of the neonatal rat cerebral cortex express functional strychnine-sensitive glycine receptors that mediate depolarizing membrane responses via Cl(-) efflux.

Induction of neuronal differentiation by a peptide corresponding to the homophilic binding site of the second Ig module of the neural cell adhesion molecule

NCAM plays a key role in neural development and plasticity-mediating cell adhesion and differentiation mainly through homophilic binding. Until recently, attempts to modulate neuronal differentiation and plasticity through NCAM have been impeded by the absence of small synthetic agonists mimicking homophilic interactions of NCAM. We show here that a peptide, P2, corresponding to a 12-amino acid sequence localized in the FG loop of the second Ig module of NCAM, binds to the first Ig module, which is the natural binding partner of the second Ig module, with an apparent K(d) of 4.7 +/- 0.9 x 10(-6) m. P2 inhibits cell aggregation and induces neurite outgrowth from hippocampal neurons, maximal neuritogenic effect being obtained at a concentration of 0.8 microm. The neuritogenic effect was inhibited by preincubation of P2 with the recombinant NCAM-IgI. Both the length of P2 and the basic amino acid residues at the N and C termini are important for its neuritogenic activity. Treatment of hippocampal cultures with P2 results in induction of phosphorylation of the mitogen-activated protein kinases ERK1 and ERK2. Thus, P2 is a potent mimetic of NCAM, and therefore, an attractive compound for the development of drugs for the treatment of neurodegenerative diseases.

The taurine uptake inhibitor guanidinoethyl sulphonate is an agonist at gamma-aminobutyric acid(A) receptors in cultured murine cerebellar granule cells

In patch clamp experiments the beta-amino acid uptake inhibitor guanidinoethyl sulphonate (GES) activated currents in intact cultured murine cerebellar granule neurones. These responses could be attenuated by the gamma-aminobutyric acid(A) (GABA(A)) receptor antagonists bicuculline and picrotoxin. With intracellular chloride concentrations of either 20 or 130 mM, GES-induced current responses reversed polarity near the chloride equilibrium potential. When fast applications of agonist were made to excised granule cell macropatches GES responses were dose-dependent and exhibited significant outward rectification. Like taurine (but unlike GABA and beta-alanine) responses, macroscopic desensitisation of GES-induced currents was slow. Our data indicate that care should be exercised when using GES as a taurine uptake inhibitor in systems that also contain GABA(A) receptors.

Effects of taurine depletion on cell migration and NCAM expression in cultures of dissociated mouse cerebellum and N2A cells

Cultures of dissociated cerebellum from 5- to 6-day-old mice as well as of the N2A neuronal cell line were exposed to guanidino ethane sulfonate (GES, 2-5 mM) to reduce the cellular taurine content. Control cultures were kept in culture medium or medium containing 2-5 mM GES plus 2-5 mM taurine to restore the intracellular taurine content. Taurine depletion led to changes in the expression of certain splice variants of NCAM mRNA such as the AAG and the VASE containing forms, while no differences were seen in the expression of the three forms of NCAM protein. In the N2A cells taurine depletion led to a decreased migration rate of the cells. The results suggest that the reduced migration rate of neurons caused by taurine depletion may be correlated to changes in expression of certain adhesion molecules such as NCAM. Moreover, taurine appears to be involved in regulation of transcription processes.

Potassium-stimulated taurine release and nitric oxide synthase activity during quinolinic acid lesion of the rat striatum

The microdialysis technique was used to study the effect of nitric oxide synthase (NOS) activity on taurine release. Taurine release was characterized in rat striatum that was excitotoxically lesioned compared to normal conditions. The basal taurine level of the dialysate decreased during quinolinate (QUIN) lesion in parallel to the cell degeneration process. The K+-stimulated taurine concentration also decreased during QUIN-lesion, but to an extent that was different from that of basal values. K+-stimulated taurine levels were further markedly lowered by coapplication of the NOS inhibitor L-NAME in control and in lesioned animals up to 30 days after QUIN-injection. Postdegenerative tissue did not show any NOS-dependency in K+-induced taurine release. We conclude that a substantial part of K+-induced taurine release depends on NOS-activity both in normal brain tissue and in excitotoxically induced neurodegeneration. The main source of K+-induced taurine release in control rats are neurons but in lesioned animals are activated astroglial cells.

Prediction of teratogenic potency of valproate analogues using cerebellar aggregation cultures

The aim of this study was to develop a novel in vitro system suitable for preclinical testing for developmental toxicity of drugs. An assay system consisting of primary cultures of dissociated cerebella from 6-day-old mice was chosen, since it allowed quantification of neuronal aggregation and fasciculated neurites. A human teratogen, the antiepileptic drug valproic acid (VPA), as well as its structural analogues, ( +/- )-4-en-VPA and E-2-en-VPA, with varying teratogenic activities, were tested and found to affect aggregation and fiber formation of cerebellar neurons. Based on a dose-response study, the concentrations of compounds causing 50%, inhibition (IC50) of formation of thick and thin fibers were determined. The lowest IC50 values were found for VPA (52 +/- 7 and 86 +/- 11 microM for thick and thin fibers, respectively), which in vivo caused the highest rate of exencephaly among the three compounds tested, ( +/- )-4-en-VPA exhibited intermediate values (150 +/- 30 and 300 +/- 40 microM), whereas the highest IC50 values were found for E-2-en-VPA (260 +/- 42 and 430 +/- 40 microM). The latter compound does not induce neural tube defects, but has been shown to have neurobehavioral effects in prenatally exposed animals. Subsequently, the purified S- and R-enantiomers of 4-yn-VPA (teratogenic and non-teratogenic, respectively) were tested for their effects on aggregation and fiber formation of the cerebellar neurons. Treatment with S-4-yn-VPA resulted in pronounced changes in numbers of aggregates and fasciculated processes compared to the cultures treated with R-4-yn-VPA, indicating that the intrinsic stereoselective potency of the enantiomers may be correlated to the difference in their effects on cerebellar neurons in vitro. Thus, the teratogenic potency of VPA and its analogues correlated with their effects on aggregation of neural cells and formation of fasciculated neurites in primary cultures of dissociated cerebella, indicating that the in vitro assay system employed may be used as a pre-screening test for prediction of teratogenic potency of drugs.

Effect of K+- and kainate-mediated depolarization on survival and functional maturation of GABAergic and glutamatergic neurons in cultures of dissociated mouse cerebellum

The effect of the depolarizing agents, an elevated potassium concentration (25 mM) or kainic acid (50 microM) on neuronal survival and differentiation was investigated in cultures of dissociated neurons from cerebella of 7-day-old mice. When maintained in the presence of an antimitotic agent such cultures consist primarily of glutamatergic and GABAergic neurons. Cell survival was monitored by measurement of DNA, and differentiation by determining uptake and depolarization coupled release of glutamate (D-aspartate as label) and GABA. The depolarizing agents were added separately or together either from the start of the culture period (7-8 days) or at day 5 in culture. The main findings are that K+ depolarization is important for differentiation of glutamatergic neurons but not for GABAergic neurons. This depolarizing signal is important during the early phase of development in culture. For glutamatergic neurons, kainate may replace K+ as a depolarizing signal whereas in case of the GABAergic neurons, kainate was toxic particularly during the late phase of development. It was further observed that the glutamatergic neurons when maintained in a medium with 5 mM K+ during the first 5 days in culture became sensitive to kainate toxicity when this amino acid was added at day 5. This was not the case when the medium contained 25 mM K+ from the start of the culture period.