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

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.

Unconventional neuroprotection against Ca2+ -dependent insults by metalloporphyrin catalytic antioxidants

We evaluated whether both inert and catalytically active metalloporphyrin antioxidants, meso-substituted with either phenyl-based or N-alkylpyridinium-based groups, suppress Ca(2+)-dependent neurotoxicity in cell culture models of relevance to cerebral ischemia. Representatives from both metalloporphyrin classes, regardless of antioxidant strength, protected cultured cortical neurons or PC-12 cultures against the Ca(2+) ionophores ionomycin or A23187, by suppressing neurotoxic Ca(2+) influx. Some metalloporphyrins suppressed excitotoxic Ca(2+) influx indirectly induced by the Ca(2+) ionophores in cortical neurons. Metalloporphyrins did not quench intracellular fluorescence, suggesting localization to the plasma membrane interface and/or interference with Ca(2+) ionophores. Metalloporphyrins suppressed ionomycin-induced Mn(2+) influx, but did not protect cortical neurons against pyrithione, a Zn(2+) ionophore. In other Ca(2+)-dependent paradigms, Ca(2+) influx via plasma membrane depolarization, but not through reversal of plasmalemmal Na(+)/Ca(2+) exchangers, was modestly suppressed by Mn(III)meso-tetrakis(4-benzoic acid)porphyrin (Mn(III)TBAP) or by an inert analog, Zn(II)TBAP. Mn(III)TBAP and Zn(II)TBAP potently protected cortical neurons against long-duration oxygen-glucose deprivation (OGD), performed in the presence of antagonists of NMDA, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and L-type voltage-gated Ca(2+) channels, raising the possibility of an unconventional mode of blockade of transient receptor protein melastatin 7 channels by a metalloTBAP family of metalloporphyrins. The present study extends the range of Ca(2+)-dependent insults for which metalloporphyrins demonstrate unconventional neuroprotection. MetalloTBAPs appear capable of targeting an OGD temporal continuum.

Induction of GABAergic phenotype in a neural stem cell line for transplantation in an excitotoxic model of Huntington's disease

The implementation of cell replacement therapies for Huntington's disease using multipotent neural stem cells (NSCs) requires the specific differentiation into gamma-aminobutyric acid (GABA) neuronal subtype before transplantation. Here we present an efficient culture procedure that induces stable GABAergic neurons from the immortalized striatal neural stem cell line ST14A. This process requires sequential retinoic acid treatment and KCl depolarization. Initial addition of 10 microM retinoic acid increased cell survival and promoted neuronal differentiation. Subsequent stimulation with 40 mM KCl induced specific differentiation into GABAergic neurons, yielding 74% of total cultured cells. KCl-evoked Ca(2+) influx reduced cell proliferation and nestin expression, and induced neurite outgrowth and GABAergic markers as well as GABA contents, release, and uptake. Characterization of the integration, survival, and phenotype of these predifferentiated GABAergic neurons following transplantation into the adult brain in a model of Huntington's disease revealed long-term survival in quinolinate-lesioned striata. Under these conditions, cells maintained their GABAergic phenotype and elaborated neurite processes with synaptic contacts with endogenous neurons. In conclusion, we have generated a homogeneous population of functional GABAergic neurons from a neural stem cell line, which survive and maintain their acquired fate in vivo. These data may lend support to the possibility of cell replacement therapies for Huntington's disease using neural stem cells.