Development of taurine biosynthesizing system in cerebral cortical neurons in primary culture

Mammalian CSAD and GADL1 have distinct biochemical properties and patterns of brain expression

Variants in the gene encoding the enzyme glutamic acid decarboxylase like 1 (GADL1) have been associated with response to lithium therapy. Both GADL1 and the related enzyme cysteine sulfinic acid decarboxylase (CSAD) have been proposed to be involved in the pyridoxal-5'-phosphate (PLP)-dependent biosynthesis of taurine. In the present study, we compared the catalytic properties, inhibitor sensitivity and expression profiles of GADL1 and CSAD in brain tissue. In mouse and human brain we observed distinct patterns of expression of the PLP-dependent decarboxylases CSAD, GADL1 and glutamic acid decarboxylase 67 (GAD67). CSAD levels were highest during prenatal and early postnatal development; GADL1 peaked early in prenatal development, while GAD67 increased rapidly after birth. Both CSAD and GADL1 are being expressed in neurons, whereas only CSAD mRNA was detected in astrocytes. Cysteine sulfinic acid was the preferred substrate for both mouse CSAD and GADL1, although both enzymes also decarboxylated cysteic acid and aspartate. In silico screening and molecular docking using the crystal structure of CSAD and in vitro assays led to the discovery of eight new enzyme inhibitors with partial selectivity for either CSAD or GADL1. Lithium had minimal effect on their enzyme activities. In conclusion, taurine biosynthesis in vertebrates involves two structurally related PLP-dependent decarboxylases (CSAD and GADL1) that have partially overlapping catalytic properties but different tissue distribution, indicating divergent physiological roles. Development of selective enzyme inhibitors targeting these enzymes is important to further dissect their (patho)physiological roles.

Nicotinic acetylcholine receptors regulate type 1 inositol 1,4,5-trisphosphate receptor expression via calmodulin kinase IV activation

Type 1 inositol 1,4,5-trisphosphate receptors (IP3 R-1) are among the important calcium channels regulating intracellular Ca(2+) concentration in the central nervous system. In a previous study, we showed that drugs of abuse, such as cocaine, methamphetamine, and ethanol, induced IP3 R-1 upregulation via the calcium signal transduction pathway in psychological dependence. Although nicotine, a major component in tobacco smoke, participates in psychological and/or physical dependence, it has not yet been clarified how nicotine alters IP3 R-1 expression. The present study, therefore, seeks to clarify the mechanism bgy which nicotine modifies IP3 R-1 expression by using mouse cerebral cortical neurons in primary culture. Nicotine induced dose- and time-dependent upregulation of IP3 R-1 protein following its mRNA increase, and the latter was significantly suppressed by a nonselective nicotinic acetylcholine receptors (nAChR) antagonist, mecamylamine. Both cFos and phosphorylated-cJun (p-cJun) were immediately increased in the nucleus, together with an increase of calmodulin kinase (CaMK) IV but not CaMKII expression after nicotine exposure. A nonselective inhibitor of CaMKs, KN-93, and a calcium chelating regent, BAPTA-AM, completely suppressed the expression of cFos and p-cJun in the nucleus as well as the nicotine-induced IP3 R-1 upregulation. These results indicate that nAChR activation by nicotine upregulates IP3 R-1 via increase of activator protein-1, which is a cFos and cJun dimmer, in the nucleus, with activation of Ca(2+) signaling transduction processes.

Cytotoxicity of synthetic cannabinoids on primary neuronal cells of the forebrain: the involvement of cannabinoid CB1 receptors and apoptotic cell death

The abuse of herbal products containing synthetic cannabinoids has become an issue of public concern. The purpose of this paper was to evaluate the acute cytotoxicity of synthetic cannabinoids on mouse brain neuronal cells. Cytotoxicity induced by synthetic cannabinoid (CP-55,940, CP-47,497, CP-47,497-C8, HU-210, JWH-018, JWH-210, AM-2201, and MAM-2201) was examined using forebrain neuronal cultures. These synthetic cannabinoids induced cytotoxicity in the forebrain cultures in a concentration-dependent manner. The cytotoxicity was suppressed by preincubation with the selective CB1 receptor antagonist AM251, but not with the selective CB2 receptor antagonist AM630. Furthermore, annexin-V-positive cells were found among the treated forebrain cells. Synthetic cannabinoid treatment induced the activation of caspase-3, and preincubation with a caspase-3 inhibitor significantly suppressed the cytotoxicity. These synthetic cannabinoids induced apoptosis through a caspase-3-dependent mechanism in the forebrain cultures. Our results indicate that the cytotoxicity of synthetic cannabinoids towards primary neuronal cells is mediated by the CB1 receptor, but not by the CB2 receptor, and further suggest that caspase cascades may play an important role in the apoptosis induced by these synthetic cannabinoids. In conclusion, excessive synthetic cannabinoid abuse may present a serious acute health concern due to neuronal damage or deficits in the brain.

Dopamine D1 receptors regulate type 1 inositol 1,4,5-trisphosphate receptor expression via both AP-1- and NFATc4-mediated transcriptional processes

Although our recent report demonstrates the essential involvement of up-regulation of a regulator of intracellular Ca(2+) concentration, type 1 inositol 1,4,5-trisphosphate receptors (IP(3) Rs-1), mediated via dopamine D1-like receptor (D1DR) stimulation in the cocaine-induced psychological dependence, the exact mechanisms of regulation of IP(3) R-1 expression by D1DRs have not yet been clarified. This study attempted to clarify these mechanisms using mouse cerebral cortical neurons. An agonist for phosphatidylinositide-linked D1DRs, SKF83959, induced dose- and time-dependently IP(3) R-1 protein up-regulation following its mRNA increase without cAMP production. U73122 (a phospholipase C inhibitor), BAPTA-AM (an intracellular calcium chelating reagent), W7 (a calmodulin inhibitor), KN-93 (a calmodulin-dependent protein kinases inhibitor), and FK506 (a calcineurin inhibitor), significantly inhibited the SKF83959-induced IP(3) R-1 up-regulation. Furthermore, immunohistochemical examinations showed that SKF83959 increased expression of both cFos and cJun in nucleus as well as enhanced translocation of both calcineurin and NFATc4 complex to nucleus from cytoplasm. In addition, SKF83959 directly recruited binding of both AP-1 and NFATc4 to IP(3) R-1 promoter region. These results indicate that D1DR activation induces IP(3) R-1 up-regulation via increased translocation of AP-1 as well as NFATc4 in Gαq protein-coupled calcium signaling transduction pathway.

Increase of ryanodine receptors by dopamine D1 receptors is negatively regulated by γ-aminobutyric acid type B receptors in primary cultures of mouse cerebral cortical neurons

Although upregulation of ryanodine receptor (RyR)-1 and -2 is mediated through the activation of dopamine D1 receptors (D1DRs) in the development of psychostimulant-induced place preference, little is known about how such increased expressions of RyRs are negatively regulated. This study investigated negative regulatory mechanisms of increase of RyR-1 and -2 expression by D1DR stimulation with its full agonist, SKF82958 or A 68930, using cultures of mouse cerebral cortical neurons. Sustained exposure to SKF82958 or A 68930 of the neurons increased RyR-1 and -2 proteins in a dose- and time-dependent-manner. The SKF82958-induced increases of RyR-1 and -2 proteins were significantly suppressed by SCH23390 (a selective D1DR antagonist). In addition, the SKF82958- or A 68930-induced increases of RyR-1 and -2 proteins were completely abolished by baclofen (a selective γ-aminobutyric acid type B [GABA(B)] receptor agonist), whereas muscimol (an agonist specific to GABA(A) receptors) had no effect. SKF82958 or A 68930 significantly increased intracellular cAMP level, which was completely suppressed by baclofen. Furthermore, sustained exposure to phorbol 12,13-dibutyrate, a protein kinase C activator, did not change the expression of RyR-1 or -2 proteins. Immunohistochemical study showed colocalizaton of immunoreactivities for three types of proteins, D1DRs and GABA(B) receptor R1 and R2 subunits in the same neuronal bodies, suggesting that the neurochemical changes induced by the activation of D1DRs and GABA(B) receptors occur in the same neurons. These results indicate that RyR-1 and -2 expression facilitated by D1DR stimulation are negatively regulated by GABA(B) receptor via suppression of cAMP production.

β₁-adrenergic receptor up-regulation induced by nadolol is mediated via signal transduction pathway coupled to α₁-adrenergic receptors

Although up-regulation of β-adrenergic receptors (β-ARs) occurs after long-term use of their antagonists in various tissues, the available data are little on mechanisms of β-AR up-regulation induced by their continuous blockade. The present study attempted to clarify mechanisms of β-AR up-regulation using mouse cerebral cortical neurons continuously exposed to nadolol (10 nM), a non-selective β-AR antagonist, for 24 h. Nadolol dose-dependently induced both subtypes of β-ARs, β₁- and β₂-ARs, which were not suppressed by protein A kinase inhibition with KT5720. On the other hand, blockade of α₁-ARs, which are immunohistochemically confirmed to be co-localized with β-ARs in the same neurons, significantly inhibited only β₁-AR up-regulation and the expression of β₂-ARs did not alter. In addition, phenylephrine, an agonist specific to α₁-ARs up-regulated β₁-ARs, but not β₂-ARs. Under the conditions with β-AR up-regulation, the level of phosphorylated protein kinase Cα (pPKCα) increased, which is significantly suppressed by prazosin, an α1-AR antagonist. Furthermore, nadolol decreased the degradation of mRNA of β₁-ARs, but not β₂-ARs. These results indicate that the nadolol-induced β₁-AR up-regulation is mediated via PKC-relating pathway via α₁-AR activation with stabilizing β₁-AR mRNA and that the increased expression of β₂-ARs is regulated by pathways different from those for β₁-AR expression.

Direct evidence for the up-regulation of Vps34 regulated by PKCgamma during short-term treatment with morphine

In this study, we investigated whether PKCgamma could be associated with functional changes of vacuolar protein sorting 34 (Vps34) during morphine treatment using primary cultures of cerebral cortical neurons from mice. The immunoprecipitation analysis showed that p-PKCgamma and Vps34 are present together in molecular complexes. The treatment with morphine increases PKCgamma and Vps34 levels. Phosphorylation of PKCgamma increased Vps34 level. The inhibition of morphine-induced increase in PKCgamma phosphorylation reduced Vps34 level. These results indicates that opioid receptor activation increases PKCgamma phosphorylation in the neurons and, in turn, upregulates Vps34 during short-term treatment with neurons.

Up-regulation of L-type high voltage-gated calcium channel subunits by sustained exposure to 1,4- and 1,5-benzodiazepines in cerebrocortical neurons

The aim of this study is to examine how sustained exposure to two 1,4-benzodiazepines (BZDs) with different action period, diazepam and brotizolam, and a 1,5-BZD, clobazam, affects L-type high voltage-gated calcium channel (HVCC) functions and its mechanisms using primary cultures of mouse cerebral cortical neurons. The sustained exposure to these three BZDs increased [(45)Ca2+] influx, which was due to the enhanced [(45)Ca2+] entry through L-type HVCCs but not through of Cav2.1 and Cav2.2. Increase in [(3)H]diltiazem binding after the exposure to these three BZDs was due to the increase in the binding sites of [(3)H]diltiazem. Western blot analysis showed increase of Cav1.2 and Cav1.3 in association with the increased expression of alpha2/delta1 subunit. Similar changes in [(3)H]diltiazem binding and L-type HVCC subunit expression were found in the cerebral cortex from mouse with BZD physical dependence. These results indicate that BZDs examined here have the potential to increase L-type HVCC functions mediated via the enhanced expression of not only Cav1.2 and Cav1.3 but also alpha2/delta1 subunit after their sustained exposure, which may participate in the development of physical dependence by these BZDs.

Increase in diazepam binding inhibitor expression by sustained morphine exposure is mediated via μ-opioid receptors in primary cultures of mouse cerebral cortical neurons

Our previous in vivo experiment demonstrates that chronic morphine treatment up-regulates diazepam binding inhibitor (DBI) transcripts in mouse cerebral cortex, although detailed mechanisms were unclear (Katsura et al. [1998] J. Neurochem. 71:2638-2641). This study sought to elucidate the precise mechanisms of DBI mRNA up-regulation by long-term treatment with morphine using primary cultures of mouse cerebral cortical neurons. A significant increase in DBI mRNA was observed after sustained exposure to 0.3 microM morphine for 2 days, and the maximal expression occurred after 2 days of exposure, whereas transient exposure to 0.3 microM morphine for 15 min, 1 hr, and 3 hr produced no changes in the expression. Continuous exposure to DAMGO also significantly increased DBI mRNA expression, which was completely abolished by a selective antagonist of mu-opioid receptors, beta-funaltrexamine (beta-FNA). The morphine-induced increase in DBI mRNA expression and its content were completely inhibited by naloxone and beta-FNA, and the inhibitory potential of naloxonazine was about half that of beta-FNA. On the other hand, kappa- and delta-opioid receptor antagonists showed no effects on the morphine-induced increase in DBI mRNA. In addition, both a calmodulin antagonist and a CaM II kinase inhibitor significantly suppressed the morphine-induced increase in DBI mRNA. These results indicate that the increase in DBI expression is induced by continuous activation of mu-opioid receptors but not of kappa- and delta-opioid receptors and is regulated by the calcium/calmodulin-related phosphorylation system.

Up-regulated l-type high voltage-gated calcium channels cause increase in diazepam binding inhibitor induced by sustained morphine exposure in mouse cerebrocortical neurons

Mechanisms of increase in diazepam binding inhibitor (DBI) mRNA expression in mouse cerebrocortical neurons after sustained morphine exposure were investigated. Increases in DBI and its mRNA expressions induced by sustained morphine (0.3 microM) exposure for 3 days were completely abolished by naloxone and nifedipine, but not by omega-agatoxin VIA and omega-conotoxin GIVA. Increase in [(3)H]diltiazem binding to the particulate fractions from the morphine-treated neurons was due to increased B(max) value with no changes in K(d) value. Western blot analysis on L-type high voltage-gated calcium channel (HVCC) subunits revealed the increased expressions of alpha1C, alpha1D, and alpha2/delta1 subunits and decreased of beta4 subunit expression, whereas expression of N- and P/Q-type HVCC subunits was not changed. These results indicate that morphine-induced increase in DBI mRNA expression is mediated via increased Ca(2+) entry through up-regulated L-type HVCCs.

Increase in Expression of α1 and α2/δ1 Subunits of L-Type High Voltage-Gated Calcium Channels After Sustained Ethanol Exposure in Cerebral Cortical Neurons

Previous reports revealed up-regulation of L-type high voltage-gated calcium channels (HVCCs) in mouse brains with ethanol physical dependence. We investigated mechanisms of enhancement of L-type HVCC function using mouse cerebrocortical neurons exposed to 50 mM ethanol for 3 days and the brains of mouse physically dependent on ethanol. Ethanol facilitated 30 mM KCl-stimulated (45)Ca(2+) influx in dose- and duration-dependent manners, which was abolished by nifedipine, an inhibitor specific to L-type HVCCs, but not by inhibitors for other types of HVCCs. Increase in [(3)H]PN200-110 binding to the particulate fractions from the ethanol-treated neurons was due to increased B(max) value with no changes in K(d) value. Western blot analysis showed the increased expression of alpha1C, alpha1D, and alpha2/delta1 subunits with decreased beta4 subunit expression and no changes in expressions of alpha1A, alpha1B, alpha1F, and alpha2 subunits. A similar pattern of the changes in the expression of these subunits of L-type HVCCs were observed in the cerebral cortex from mouse with ethanol physical dependence. These results indicate that sustained ethanol exposure to the neurons induces up-regulation of L-type HVCCs, which is due to increased expressions of alpha1C, alpha1D, and alpha2/delta1 subunits, and produces no alterations in P/Q- and N-type HVCC functions.

Continuous exposure to nitric oxide enhances diazepam binding inhibitor mRNA expression in mouse cerebral cortical neurons

Effects of sustained exposure to nitric oxide (NO) formed by long-term activation of N-methyl-D-aspartate (NMDA) receptors and liberated from a long-lasting NO generator, DETA NONOate, on diazepam binding inhibitor (DBI) and its mRNA expressions were examined using mouse cerebral cortical neurons. Long-term exposure to NMDA increased DBI mRNA expression, and NO synthase inhibitors dose-dependently inhibited this increase. DETA NONOate dose-dependently increased DBI mRNA expression when exposing the neurons to this agent for 3 days and a maximal enhancement of the expression was found at 100 microM of the NO generator. In addition, a significant increase in DBI mRNA expression was observed 1 day after the exposure to 100 microM DETA NONOate, and the maximal expression was observed 2 days after the exposure, whereas transient exposure for less than 3 h to 100 microM DETA NONOate produced no changes in the expression. DETA NONOate (100 microM)-induced increase in DBI mRNA expression was completely abolished by concomitant exposure to hemoglobin. DBI content was also dose-dependently increased by DETA NONOate after the exposure for 3 days. The inhibition of cGMP formation by 1H-[1,2,4] oxadiazolo [4,3-alpha]quinoxalin-1-one (ODQ) showed no affects on the DETA NONOate-induced expression, suggesting that the increased expression of DBI mRNA is mediated via processes independent of cGMP. These results indicate that continuous exposure of the neurons to NO is an essential factor for increasing DBI mRNA expression in the neurons.

L-type high voltage-gated calcium channels cause an increase in diazepam binding inhibitor mRNA expression after sustained exposure to ethanol in mouse cerebral cortical neurons

Mechanisms for increase in diazepam binding inhibitor (DBI) mRNA expression after sustained exposure to ethanol (EtOH) were investigated. Increases in 30 mM KCl-induced [45Ca(2+)] influx and DBI mRNA expression after EtOH (50 mM) exposure for 3 days were completely abolished by nifedipine, but not by omega-agatoxin VIA and omega-conotoxin GIVA. These results indicate that EtOH-induced increase in DBI mRNA expression is mediated via increased Ca(2+) entry through up-regulated L-type high voltage-gated calcium channels.

Functional significance of nitric oxide in ionomycin-evoked [3H]GABA release from mouse cerebral cortical neurons

We investigated a role of nitric oxide (NO) on ionomycin-evoked [3H]GABA release using mouse cerebral cortical neurons. lonomycin dose-dependently released [3H]GABA up to 1 microM. The extent of the release by 0.1 microM ionomycin was in a range similar to that by 30 mM KCl. The ionomycin (0.1 microM)-evoked [3H]GABA release was dose-dependently inhibited by NO synthase inhibitors and hemoglobin, indicating that the ionomycin-evoked [3H]GABA release is mediated through NO formation. The inhibition of cGMP formation by 1H-[1,2,4] oxodizao [4,3-a] quinoxalin-1-one (ODQ), a selective inhibitor for NO-sensitive guanylate cyclase, showed no affects on the ionomycin-evoked [3H]GABA release. Tetrodotoxin and dibucaine significantly suppressed the ionomycin-evoked [3H]GABA release and ionomycin increased fluorescence intensity of bis-oxonol, suggesting the involvement of membrane depolarization in this release. The ionomycin-evoked [3H]GABA release was maximally reduced by about 50% by GABA uptake inhibitors. The concomitant presence of nifedipine and omega-agatoxin VIA (omega-ATX), inhibitors for L- and P/Q-type voltage-dependent calcium channels, respectively, caused the reduction in the ionomycin-evoked release by about 50%. The simultaneous addition of nifedipine, omega-ATX and nipecotic acid completely abolished the release. Although ionomycin released glutamate, (+)-5-methyl-1-,11-dihydro-5H-dibenzo-[a,d]cycloheptan-5,10-imine (MK-801) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) showed no effects on the ionomycin-induced [3H]GABA release. Based on these results, it is concluded that NO formed by ionomycin plays a critical role in ionomycin-evoked [3H]GABA release from the neurons.

Up-regulation of L-type voltage-dependent calcium channels after long term exposure to nicotine in cerebral cortical neurons

Effects of long term (72-h) exposure to low concentration (0.1 mum) of nicotine on various types of voltage-dependent Ca(2+) channels (VDCCs) and neuronal nicotinic acetylcholine receptors (nnAChRs) were examined using primary cultures of mouse cerebral cortical neurons. High potassium (30 mm KCl)-stimulated (45)Ca(2+) influx into the neurons increased with increasing the duration of nicotine exposure and its concentrations. The maximal increase of the KCl-stimulated (45)Ca(2+) influx was found 24 h after the initiation of exposure and thereafter maintained up to 72 h. This enhancement of KCl-induced (45)Ca(2+) influx after 72-h exposure to 0.1 mum nicotine was completely abolished by concomitant exposure with mecamylamine, an inhibitor for nnAChRs. Only the component of the KCl-induced (45)Ca(2+) influx observed after long term exposure to nicotine, which was sensitive to nifedipine, an inhibitor of L-type VDCCs, was facilitated, while the (45)Ca(2+) influx through P/Q- and N-type VDCCs showed no changes. Moreover, enhanced immunoreactivity against antibody for the alpha(1C) subunit of L-type VDCCs was recognized, whereas no changes in immunoreactivities against antibodies for alpha(1A) and alpha(1B) subunits of other types of VDCCs were noted. In addition, a Western blot analysis showed an increase of immunoreactivities against antibodies for alpha(1D) and alpha(2)/delta(1), and expression of mRNA for L-type VDCC subunit, alpha(1F), was also enhanced, although beta(4) mRNA expression was not changed. Whole cell patch clamp analysis revealed that the increase of the amplitude of Ba(2+) currents was also recognized in the neurons exposed to nicotine, and nicardipine reduced this increased amplitude to the level of the amplitude detected in nontreated neurons with nicardipine. The up-regulation of alpha(4) and beta(2) subunits, but not the alpha(3) subunit of nnAChRs, was also noted after the nicotine exposure when examining by the Western blot analysis. Taken together, these results indicate that the long term exposure of the neurons to a low concentration of nicotine induces both increased (45)Ca(2+) influx through up-regulated L-type VDCCs and nnAChR up-regulation.

Withdrawal from nicotine facilitates diazepam binding inhibitor mRNA expression in mouse cerebral cortex

Changes in diazepam binding inhibitor (DBI) mRNA expression after withdrawal from nicotine were examined. Withdrawal from nicotine Increased DBI mRNA expression in cerebral cortices derived from nicotine-dependent mice and in the neurons continuously exposed to nicotine (0.1 microM). These results indicate that withdrawal from nicotine after its long-term exposure induces steep increase of DBI mRNA expression as reported previously in ethanol- and morphine-dependent animals.

NMDA receptor activation enhances diazepam binding inhibitor and its mRNA expressions in mouse cerebral cortical neurons

Effects of N-methyl-D-aspartate (NMDA) on diazepam binding inhibitor (DBI) and its mRNA expression in mouse cerebral cortical neurons were examined. A significant increase in DBI mRNA expression was observed 1 day after the exposure to 0.1 microM NMDA and the maximal expression occurred 2 days after the exposure, whereas transient exposure to 0.1 microM NMDA for 15 min, 1 and 3 h produced no changes in the expression. Similarly, no changes in the expression were found by the concomitant exposure to NMDA and MK-801, a NMDA receptor antagonist, for 72 h subsequent to the incubation with NMDA alone for 3 h. Such NMDA-induced increases in DBI mRNA expression were dose-dependently inhibited by MK-801. Moreover, neuronal DBI content significantly increased by treatment with NMDA, which was completely abolished by MK-801. These results indicate that continuous activation of NMDA receptors is an essential factor for increasing DBI expression in the neurons.

Mechanism for increase in expression of cerebral diazepam binding inhibitor mRNA by nicotine: involvement of L-type voltage-dependent calcium channels

We investigated the mechanisms underlying the increase in diazepam binding inhibitor (DBI) and its mRNA expression induced by nicotine (0.1 microM) exposure for 24 h using mouse cerebral cortical neurons in primary culture. Nicotine-induced (0.1 microM) increases in DBI mRNA expression were abolished by hexamethonium, a nicotinic acetylcholine (nACh) receptor antagonist. Agents that stabilize the neuronal membrane, including tetrodotoxin (TTX), procainamide (a Na(+) channel inhibitor), and local anesthetics (dibucaine and lidocaine), dose-dependently inhibited the increased expression of DBI mRNA by nicotine. The nicotine-induced increase in DBI mRNA expression was inhibited by L-type voltage-dependent Ca(2+) channel (VDCC) inhibitors such as verapamil, calmodulin antagonist (W-7), and Ca(2+)/calmodulin-dependent protein kinase II (CAM II kinase) inhibitor (KN-62), whereas P/Q- and N-type VDCC inhibitors showed no effects. In addition, nicotine exposure for 24 h induced [3H]nicotine binding to the particulate fractions of the neurons with an increased B(max) value and no changes in K(d). Under these conditions, the 30 mM KCl- and nicotine-induced 45Ca(2+) influx into the nicotine-treated neurons was significantly higher than those into non-treated neurons. These results suggest that the nicotine-stimulated increase in DBI mRNA expression is mediated by CAM II kinase activation resulting from the increase in intracellular Ca(2+) through L-type VDCCs subsequent to the neuronal membrane depolarization associated with nACh receptor activation.

Role of metabotropic glutamate receptor subclasses in modulation of adenylyl cyclase activity by a nootropic NS-105

The involvement of metabotropic glutamate (mGlu) receptors in the modulatory actions of a novel cognition enhancer, (+)-5-oxo-D-prolinepiperidinamide monohydrate (NS-105), on adenylyl cyclase activity in rat cerebrocortical membranes and primary neuronal cultures was investigated using selective antagonists and antisense oligodeoxynucleotides for mGlu receptor subclasses. In rat cerebrocortical membranes, the inhibitory action of NS-105 (0.1 microM) on forskolin-stimulated cAMP formation was blocked by a group II mGlu receptor antagonist, (+/-)-alpha-ethylglutamic acid, and by a group III antagonist, (+)-2-amino-2-methyl-4-phosphonobutanoic acid (MAP-4), but not by a group I antagonist, (+/-)-1-aminoindan-1,5-dicarboxylic acid (AIDA), whereas the facilitation of cAMP formation by NS-105 (1 microM) in pertussis toxin-pretreated membranes was abolished by AIDA but not by (+/-)-alpha-ethylglutamic acid or MAP-4. In primary cultured neurons of mouse cerebral cortex, the inhibitory action of NS-105 on adenylyl cyclase activity disappeared after treatment with antisense oligodeoxynucleotides for group II (mGlu(2) and mGlu(3) receptors) and group III (mGlu(4) and mGlu(7) receptors) but not group I (mGlu(5) receptor) mGlu receptor subclasses. These findings suggest that the inhibitory action of NS-105 on adenylyl cyclase activity is mediated through group II and group III mGlu receptor subclasses while the facilitatory action is dependent on the group I mGlu receptor subclass.

Blockade by NS-7, a neuroprotective compound, of both L-type and P/Q-type Ca2+ channels involving depolarization-stimulated nitric oxide synthase activity in primary neuronal culture

The effect of 4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride (NS-7), a neuroprotective compound, on Ca2+ channels involving the activation of nitric oxide synthase (NOS) was investigated in primary neuronal culture. The NOS activity was estimated from the cyclic GMP formation. The KCl (25 mM)-stimulated cyclic GMP formation was totally abolished by a combined treatment with nifedipine and omega-agatoxin IVA (omega-Aga), whereas spontaneous cyclic GMP formation was partially but significantly reduced by nifedipine. In contrast to nifedipine, NS-7 blocked KCl-stimulated cyclic GMP formation without affecting spontaneous cyclic GMP formation. Subsequently, the effects of nifedipine and NS-7 on L-type Ca2+ channels were compared. Nifedipine blocked equally the cyclic GMP formation stimulated by various concentrations of (+/-)-Bay K 8644, whereas NS-7 inhibited the maximal response without affecting the responses induced by low concentrations of (+/-)-Bay K 8644. The effects of NS-7 on L-type and P/Q-type Ca2+ channels involving KCl-stimulated cyclic GMP formation were subsequently examined. NS-7 suppressed the KCl-stimulated cyclic GMP formation measured in the presence of omega-Aga to almost the same extent as that determined in the presence of nifedipine. In contrast, NS-7 had no influence on ionomycin-induced enhancement of cyclic GMP formation. Finally, NS-7 reversed KCl-induced elevation of the intracellular free Ca2+ concentration. These findings suggest that NS-7 inhibits NOS activation in primary neuronal culture by reducing Ca2+ entry through L-type and P/Q-type Ca2+ channels, in which the inhibition is largely dependent on Ca2+ channel activity.

Functional involvement of benzodiazepine receptors in ethanol-induced increases of diazepam binding inhibitor (DBI) and its mRNA in the mouse brain

We have attempted to clarify the mechanisms for alcohol (EtOH)-induced elevation of diazepam binding inhibitor (DBI) mRNA and to investigate whether the increase in DBI mRNA is paralleled with that in DBI using EtOH-treated mice and primary cultured neurons. Both the DBI content and the expression of DBI mRNA were elevated in the cerebral cortex of EtOH-inhaled and -withdrawn mice. Simultaneous administration of flunitrazepam (FLN) and Ro15-1788 with EtOH vapor completely abolished the EtOH-induced elevation of DBI mRNA. In addition, the exposure of the neurons for 3 days significantly elevated the expression of DBI mRNA, which was completely inhibited by concomitant exposure of FLN, Ro15-4513 and Ro-15-1788 with EtOH, while muscimol and bicuculline showed no effects on the EtOH-induced increase of DBI mRNA expression. These results indicate that functional interaction between EtOH and benzodiazepine (BDZ) receptors is a critical role in the increased expression of DBI mRNA.

Multiple actions of nitric oxide on voltage-dependent Ca2+ channels in mouse cerebral cortical neurons

We investigated the effects of nitric oxide (NO) on voltage-dependent Ca2+ channels (VDCCs) by examining [45Ca2+]influx into mouse cerebral cortical neurons. S-nitroso-N-acetylpenicillamine (SNAP) induced a dose-dependent increase in [45Ca2+]influx, which was completely abolished by hemoglobin, tetrodotoxin and dibucaine. The NO-induced [45Ca2+influx was significantly inhibited by verapamil and omega-agatoxin VIA (omega-AGX), whereas omega-conotoxin GVIA (omega-CTX) had no effects on the NO-induced [45Ca2+]influx. KCl (30 mM) stimulated [45Ca2+]influx, and verapamil, omega-CTX and omega-AGX reduced the KCl-induced [45Ca2+]influx by about 40, 26 and 34%, respectively, indicating that the neurons used here possess L-, N- and P-typed VDCCs. SNAP itself reduced KCl-induced [45Ca2+]influx by about 28.5%. In the presence of both KCl and SNAP, omega-CTX showed no effects on the influx, while verapamil and omega-AGX significantly inhibited the influx and the concomitant presence of verapamil and omega-AGX completely abolished the influx. These results indicate that NO induces [45Ca2+] influx via the opening of L- and P-typed VDCCs subsequent to neuronal membrane depolarization and that NO itself inhibited the function of N-typed VDCC in the cerebral cortical neurons.

Nonsynaptic glycine receptor activation during early neocortical development

Glycine receptors (GlyRs) contribute to fast inhibitory synaptic transmission in the brain stem and spinal cord. GlyR subunits are expressed in the developing neocortex, but a neurotransmitter system involving cortical GlyRs has yet to be demonstrated. Here, we show that GlyRs in immature neocortex are excitatory and activated by a nonsynaptically released endogenous ligand. Of the potential ligands for cortical GlyRs, taurine is by far the most abundant in the developing neocortex. We found that taurine is stored in immature cortical neurons and that manipulations known to elevate extracellular taurine cause GlyR activation. These data indicate that nonsynaptically released taurine activates GlyRs during neocortical development. As fetal taurine deprivation can cause cortical dysgenesis, it is possible that taurine influences neocortical development by activating GlyRs.

Characteristics of nitric oxide-evoked [3H]taurine release from cerebral cortical neurons

Pharmacological characteristics of [3H]taurine release evoked by nitric oxide (NO) were investigated using mouse cerebral cortical neurons in primary culture. NO generators such as S-nitroso-N-acetylpenicillamine (SNAP) and sodium nitroprusside (SNP) dose-dependently increased [3H]taurine release from neurons. Such stimulatory effects of NO generators were completely abolished by hemoglobin, a NO radical scavenger, indicating that these [3H]taurine releases might be due to NO liberated from SNAP and SNP. Sodium withdrawal from incubation buffer significantly inhibited the SNAP- and SNP-induced [3H]taurine releases, whereas the removal of calcium showed no alterations in the [3H]taurine release evoked by NO generators. Beta-Alanine and guanidinoethane sulfonate, inhibitors of carrier-mediated taurine transport system, inhibited the SNAP- and SNP-evoked releases of [3H]taurine in a dose-dependent manner. These results indicate that the NO-evoked [3H]taurine release from cerebral cortical neurons is mediated by the reverse process of sodium-dependent carrier-mediated taurine transport system.

Role of peroxynitrite in [3H] gamma-aminobutyric acid release evoked by nitric oxide and its mechanism

Role of peroxynitrite in [3H] gamma-aminobutyric acid (GABA) release evoked by N-methyl-D-aspartate (NMDA) and S-nitroso-N-acetyl-penicillamine (SNAP) and mechanisms of [3H]GABA release induced by peroxynitrite in comparison with those induced by NMDA and SNAP were investigated using cerebrocortical neurons. NMDA dose dependently increased [3H]GABA release, which was significantly inhibited by hemoglobin and superoxide scavengers, Cu2+, Zn(2+)-superoxide dismutase and ceruloplasmin. The NMDA-evoked [3H]GABA release was significantly suppressed by GABA transport inhibitors and inhibitors of voltage-dependent L-typed Ca2+ channel. The SNAP-evoked [3H]GABA release was significantly reduced by Ca2+ withdrawal and by GABA transport inhibitors either in the presence or absence of Ca2+. Similar patterns of [3H]GABA release induced by peroxynitrite were observed. These results indicate that peroxynitrite formed by the reaction of NO with superoxide participates, in part, in the release of [3H]GABA induced by NMDA and SNAP.

Nitric oxide-evoked [3H] gamma-aminobutyric acid release is mediated by two distinct release mechanisms

Mechanisms underlying the release of [3H] gamma-aminobutyric acid (GABA) evoked by nitric oxide (NO) were investigated by use of primary cultured neurons prepared from the mouse cerebral cortex. NO generators such as sodium nitroprusside (SNP) and S-nitroso-N-a etylpenicillamine (SNAP) increased both [3H]GABA release from the neurons and [45Ca2+] influx into the neurons in a dose-dependent manner, which was significantly diminished by hemoglobin. The removal of Ca2+ significantly reduced the NO-induced [3H]GABA release by about 50%. Nipecotic acid and 1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1, 2, 5, 6-tetrahydro-3- pyridinecarboxylic acid (NO-711), GABA uptake inhibitors dose-dependently inhibited the NO-evoked [3H]GABA release in either the presence or absence of Ca2+. The concentration of these GABA uptake inhibitors to suppress the NO-induced release of [3H]GABA was sufficiently lower than that to exhibit the inhibition of [3H]GABA transport into the neurons. In addition, the NO-evoked [3H]GABA release was reduced by approximately 50% when total Na+ in incubation buffer was replaced with equimolar choline, and was also completely abolished by the removal of both Ca2+ and Na+. These results indicate that the release of [3H]GABA evoked by NO is mediated by two release mechanisms, a Ca2+ -dependent release system and the reverse process of the Ca2+ -independent and Na+ -dependent carrier-mediated GABA uptake system.

Nitric oxide-evoked [3H]taurine release is mediated by reversal of the Na(+)-dependent carrier-mediated taurine transport system

The pharmacological characteristics of [3H]taurine release evoked by nitric oxide (NO) were investigated using mouse cerebral cortical neurons in primary culture. N-Methyl-D-aspartate (NMDA) and S-nitroso-N-acetylpenicillamine (SNAP) dose-dependently increased [3H]taurine release from neurons. The NMDA-evoked release of [3H]taurine was reduced to the basal level by N omega-nitro-L-arginine, a NO synthase inhibitor, and MK-801, a noncompetitive antagonist for NMDA receptors. The NMDA- and SNAP-evoked releases of [3H]taurine were completely abolished by hemoglobin, indicating that these [3H]taurine releases were evoked by NO produced by NMDA receptor activation and liberated from SNAP. Withdrawal of Na+ from incubation buffer significantly inhibited the NMDA- and SNAP-induced [3H]taurine releases, whereas removal of Ca2+ produced no alteration in the SNAP-evoked [3H]taurine release. In addition, beta-alanine and guanidinoethane sulfonate, antitransporters of the carrier-mediated taurine transport system, reduced the NMDA- and SNAP-evoked releases of [3H]taurine in a dose-dependent manner. These results indicate that the NO-evoked [3H]taurine release from cerebral cortical neurons is mediated by a reversal of the Na(+)-dependent carrier-mediated taurine transport system.

Ethanol stimulates diazepam binding inhibitor (DBI) mRNA expression in primary cultured neurons

Changes in expression of diazepam binding inhibitor (DBI) mRNA in cerebral cortical neurons following long-term ethanol (EtOH) exposure were examined. A significant increase in DBI mRNA expression was observed by the exposure of neurons to 50 mM EtOH for up to 5 days and to EtOH (1-100 mM) for 3 days. These EtOH-induced increases in DBI mRNA expression were further elevated after the additional cultivation of neurons under EtOH-free condition. beta-Actin mRNA expression was not altered by similar EtOH treatments. These results indicate that EtOH possesses the activity to increase the expression of DBI mRNA in cerebral cortical neurons.

Involvement of peroxynitrite in N-methyl-D-aspartate- and sodium nitroprusside-induced release of acetylcholine from mouse cerebral cortical neurons

Functional roles of peroxynitrite in N-methyl-D-aspartate (NMDA)- and sodium nitroprusside (SNP)-evoked releases of acetylcholine (ACh) from cerebral cortical neurons in primary culture have been investigated. NMDA increased the release of ACh in a dose-dependent manner, which was significantly suppressed by (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cycloheptan-5,10-imine (MK-801), a non-competitive antagonist specific for the NMDA receptor complex, and NO synthase inhibitors. SNP also showed a concentration-dependent increase in ACh release. Hemoglobin significantly abolished the stimulatory effects of both NMDA and SNP on ACh release. In addition, superoxide anion scavengers such as superoxide dismutase and ceruloplasmin significantly reduced the increased ACh release evoked by NMDA and SNP. Synthesized peroxynitrite dose-dependently elevated the release of ACh. These results indicate that the increased release of ACh by NMDA and SNP is mediated through peroxynitrite formed in the reaction of superoxide anion with nitric oxide produced by NMDA receptor activation and liberated from SNP rather than nitric oxide itself.

GABAA receptor stimulation enhances NMDA-induced Ca2+ influx in mouse cerebral cortical neurons in primary culture

The effect of GABAA receptor stimulation on N-methyl-D-aspartate(NMDA)-induced [45Ca2+]influx has been examined using primary cultured cerebral cortical neurons. NMDA induced a dose-dependent increase in [45Ca2+]influx, which was blocked by MK-801 in a dose-dependent manner. GABAA receptor agonists significantly enhanced the NMDA-induced [45Ca2+]influx, and this enhancement was dose-dependently inhibited by bicuculline, although picrotoxin and tert-butyl-bicyclo[2.2.2]phosphoro-thionate (TBPS) exhibited no alterations in this stimulatory action of GABAA receptor agonists. Blockers of L-type voltage-dependent calcium channels significantly reduced the NMDA-induced [45Ca2+]influx. The increased [45Ca2+]influx by both NMDA and GABAA receptor agonists was also reduced by verapamil and nifedipine. These results suggest that the enhancement of NMDA-induced [45Ca2+]influx by GABAA receptor stimulation in immature cerebral cortical neurons may be due to the increased opening of voltage-dependent calcium channel by synergestic actions between NMDA and GABAA receptors.

Nicotine increases diazepam binding inhibitor (DBI) mRNA in primary cultured neurons

The effect of nicotine on the expression of diazepam binding inhibitor (DBI) mRNA in primary cultured cerebral cortical neurons was examined using Northern blot analysis. Nicotine exposure (0.001-10 microM) for 24 h increased the DBI mRNA level in a dose-dependent manner, whereas the beta-actin mRNA level showed no change. This effect of nicotine was faded out over 48 h of its exposure. Hexamethonium (100 microM) completely abolished the nicotine-induced increase in DBI mRNA expression. These results indicate that nicotine increases the expression of DBI mRNA in cerebral cortical neurons via the activation of nicotinic acetylcholine receptor.

Muscimol prevents neuronal injury induced by NMDA

The effect of muscimol on N-methyl-D-aspartate (NMDA)-induced injury of primary cultured cerebral cortical neurons was examined. NMDA induced a dose-dependent leakage of LDH activity, which was significantly inhibited by (+-)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclopentan-5,10-imine (MK-801). Muscimol significantly reduced the NMDA-induced increase of lactic dehydrogenase (LDH) leakage, and bicuculline abolished this protective effect of muscimol. Similarly, muscimol reduced the NMDA-induced increase in trypan blue staining of the cells, and bicuculline suppressed this inhibitory action of muscimol. These results suggest that GABAA-receptor stimulation exerts a protective action against the neuronal injury induced by NMDA-receptor activation.

A colorimetric assay method for the evaluation of neurotrophic activity in vitro

A colorimetric assay was established to detect neurotrophic activity by measuring the lysosomal enzyme, acid phosphatase (AP) activity of cultured neuronal cells. Neurons from the cerebral cortex of 14- or 15-day mouse embryo were cultured in serum-free medium for 3 days in 96-well culture plates. A linear relationship was obtained between the AP activity and the number of viable neurons counted under a microscope. The AP assay was used to evaluate the neurotrophic activity of basic fibroblast growth factor. This assay is shown to be simple, sensitive and convenient to detect neurotrophic activity.

Muscimol-induced reduction of GABAA receptor alpha 1-subunit mRNA in primary cultured cerebral cortical neurons

The expression of mRNA for GABAA receptor alpha 1-subunit in mouse cerebral cortical neurons in primary culture was examined using RNA blot analysis and ribonuclease protection assay following the treatment of neurons with muscimol, a selective agonist of GABAA receptor. The level of mRNA for GABAA receptor alpha 1-subunit showed a decrease in comparison with that in non-treated cells, whereas no changes in the level of beta-actin mRNA were noted under the same experimental conditions. This muscimol-induced reduction in GABAA receptor alpha 1-subunit mRNA was counteracted by the simultaneous exposure of neurons to both bicuculline, an antagonist of GABAA receptor, and muscimol. The expression of mRNA for GABAA receptor alpha 1-subunit also showed a decline by the treatment of cells with flunitrazepam alone, an agonist of benzodiazepine receptor, and this change was also abolished by the simultaneous exposure of cells to flunitrazepam and Ro15-1788, an antagonist for central benzodiazepine receptor. These results suggest that the continuous stimulation of cerebral GABAA receptor complex may induce the reduced expression of mRNA for the receptor complex.

Association of functional alteration in intracellular signal transduction systems with the occurrence of up-regulation of muscarinic receptors in primary cultured neurons

1. Alterations in intracellular biosignaling systems associated with the up-regulated muscarinic receptor were investigated using primary cultured neurons exposured to 10 nM atropine for 5 days. 2. In neurons treated with atropine, the response of PI turnover to muscarinic stimulation decreased in comparison with that in non-treated neurons. 3. The GTP gamma S-stimulated PI turnover also reduced in neurons possessing up-regulated muscarinic receptor, although phospholipase C activity was not different in these two types of neurons. 4. In addition, the long-term exposure (5 days) to atropine induced the increase in GTPase activity and [3H]GppNHp binding. 5. These results suggest that the decreased response of PI turnover to muscarinic stimulation may be attributed to the functional deterioration of G-protein itself and/or coupling between G-protein and phospholipase C. 6. The present results also strongly suggest that the accentuation of the function of G protein may occur in association with the up-regulation of muscarinic receptor.

Neuronal survival and neurite extension supported by astrocytes co-cultured in transwells

The influence of astrocytes on the development of cerebral cortical neurons was studied in a co-culture system using transwells with chemically defined medium. Cerebral cortical neurons from 15- or 16-day-old mouse embryo were cultured in the lower wells which were separated by a porous membrane from the upper transwells where cerebral cortical astrocytes from newborn mouse were cultured. Neurons co-cultured with astrocytes for 7 days formed a network-like web and maintained a slightly better survival from 4 to 7 days. However, neurons cultured in conditioned medium obtained from astrocytes did not form any network after 7 days even though they maintained a better cell survival at 4 days.

Ontogeny of beta-adrenergic receptor-mediated cyclic AMP generating system in primary cultured neurons

The developmental changes in the beta-adrenergic receptor/cyclic AMP generating system were examined using mouse cerebral cortical neurons in primary culture. During neuronal growth in vitro, the number of binding sites for [3H]dihydroalprenolol (DHA) showed a tendency to increase (Bmax), while the affinity (Kd) for [3H]DHA did not show any noticeable changes. Basal and isoproterenol-stimulated adenylate cyclase activities as well as the activation of adenylate cyclase by 5'-guanylylimidodiphosphate (GppNHp), NaF and forskolin showed progressive and parallel increases during neuronal growth on a polylysine-coated surface. The treatment of primary cultured neurons with islet-activating protein (IAP), one of the pertussis toxins, attenuated the inhibitory effect of carbachol, a muscarinic agonist, on isoproterenol-induced activation of adenylate cyclase activity. These results indicate that primary cultured neurons possess a cyclic AMP generating system coupled with beta-adrenergic and muscarinic receptors, which is regulated via stimulatory and inhibitory GTP-binding proteins, respectively. The results described above also suggest that the beta-adrenergic receptor, stimulatory and inhibitory types of GTP-binding proteins and adenylate cyclase may develop in a parallel fashion during neuronal growth on a polylysine-coated surface.

Alterations in receptor-coupled second messenger systems at up-regulated muscarinic receptors: analysis using primary cultured neurons

The effect of a long-term exposure (5 days) to atropine on muscarinic acetylcholine receptors and receptor-coupled second messenger systems was investigated using mouse cerebral cortical neurons in primary culture. The long-term exposure of neurons to atropine (10 nM) induced increases in both the Bmax and Kd values of [3H]quinuclidinyl benzilate (QNB) binding to muscarinic acetylcholine receptors. Alterations in muscarinic receptor-coupled second messenger systems, such as phosphoinositide (PI) hydrolysis and cyclic GMP (cGMP) formation following a long-term exposure to atropine, were also examined. Carbachol-stimulated PI hydrolysis was found to be decreased by the exposure to atropine in spite of the increase of muscarinic receptors. In addition, a long-term exposure to atropine had no effect on carbachol-stimulated cGMP formation as well as on the rightward shift of the carbachol competition curve of [3H]QNB binding in the presence of GTP. These results suggest that the up-regulation in muscarinic cholinergic receptors induced by long-term exposure to atropine may involve not only the increase in number of muscarinic receptors but also the decreased responsiveness in muscarinic receptor-coupled second messenger systems.

Potassium-stimulated release of [3H]taurine from cultured GABAergic and glutamatergic neurons

The effect of depolarizing concentrations of potassium (56 mM) on the release of [3H]taurine was examined in two types of cultured neurons from mouse brain: cerebral cortex neurons, which are largely GABAergic, and cerebellar neurons, which after treatment with kainate consist almost entirely of glutamatergic granule cells. The release of [3H]taurine was compared to that of gamma-[3H]aminobutyric acid [( 3H]GABA) in cortical neurons and to that of D-[3H]aspartate in granule cells. Cortical neurons responded to potassium stimulation (1 min or continuously) by an immediate increase in [3H]GABA efflux of more than six times over the basal efflux, followed by a sharp decline despite the persistence of the stimulatory agent. The potassium-induced release of [3H]GABA was largely calcium-dependent. The release of [3H]taurine was considerably less in magnitude, only doubling after the stimulus, with a time course delayed in both onset and decline. The release of [3H]taurine was partially calcium-dependent and was also decreased in low-chloride solutions. In cerebellar granule cells, exposure to potassium resulted in a large (sixfold) and prompt release of D-[3H]aspartate, largely calcium-dependent. A totally different pattern was observed for the release of [3H]taurine. A stimulatory effect occurred only when cells were exposed continuously to potassium. Taurine efflux was very delayed, with a broad stimulus plateau reached after 15-20 min of stimulation. Taurine release was unaffected by omission of calcium, but it was abolished in a low-chloride medium. These results suggest that taurine is released from cells handling other neuroactive amino acids as neurotransmitters.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of endogenous taurine and gamma-aminobutyric acid from brain slices from the adult and developing mouse

The spontaneous and potassium-stimulated release of endogenous taurine and gamma-aminobutyric acid (GABA) from cerebral cortex and cerebellum slices from adult and developing mice was studied in a superfusion system. The spontaneous release of GABA was of the same magnitude in slices from adult and developing mice, but the spontaneous release of taurine was considerably greater in the adults. The potassium-stimulated release of GABA from cerebral cortex slices was about five times greater in adult than in 3-day-old mice, but the potassium-stimulated release of taurine was more than six times greater in 3-day-old than in adult mice. In cerebellar slices from 7-day-old mice, potassium stimulation also evoked a massive release of taurine, whereas the evoked release from slices from adult mice was rather negligible. Also in cerebellar slices the potassium-stimulated release of GABA exhibited the opposite quantitative pattern. The stimulated release of both GABA and taurine was partially calcium dependent. The results suggest that taurine may be an important regulator of excitability in the developing brain.