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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.

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.

The effect of hydroxyl radical scavengers on acetylcholine (ACh) release evoked by nitric oxide (NO) generators and N-methyl-D-aspartate (NMDA) was investigated. Dimethylthiourea enhanced dose-dependently NO generators-evoked ACh release. Similarly, uric acid and mannitol significantly facilitated ACh release evoked by NO generators. The NMDA-induced ACh release was also significantly facilitated by hydroxyl radical scavengers. These scavengers themselves showed no effects on ACh release. These results suggest that hydroxyl radicals may modify the mechanism for NO-evoked ACh release.

Effects of hydroxyl radical scavengers such as dimethylthiourea (DMTU), uric acid and mannitol on acetylcholine (ACh) release evoked by N-methyl-D-aspartate (NMDA) were examined in cerebral cortical neurones. NMDA increased dose-dependently ACh release. This increase in the release was significantly suppressed by MK-801, N omega-nitro-L-arginine and haemoglobin, indicating that NMDA evokes ACh release via the formation of NO subsequent to NMDA receptor activation. DMTU dose-dependently enhanced the NMDA-induced ACh release. Uric acid (100 microM) and mannitol (1 mM) facilitated significantly the NMDA-induced ACh release, although these scavengers themselves showed no effects on ACh release in the absence of NMDA. These results indicate that the removal of hydroxyl radical facilitates the NO-induced ACh release.

We investigated the effect of removal of hydroxyl radical on nitric oxide (NO)-induced [3H]GABA release from cerebral cortical neurons. NO generators, S-nitroso-N-acetylpenicillamine and sodium nitroprusside, significantly increased [3H]GABA release, which was completely abolished by hemoglobin. These results indicate that the release of [3H]GABA evoked by these NO generators is mediated by NO formation. N,N'-Dimethylthiourea (DMTU), a hydroxyl radical scavenger, dose-dependently stimulated the increase of NO-induced [3H]GABA release. Similarly, other hydroxyl radical scavengers such as uric acid and mannitol, significantly enhanced the NO-induced [3H]GABA release. On the other hand, each hydroxyl radical scavenger alone showed no effect on [3H]GABA release in the absence of NO generators. These results indicate that the removal of hydroxyl radical enhances NO-evoked [3H]GABA release from cerebral cortical neurons.

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.