We have recently disrupted Slc12a2, the gene encoding the secretory Na-K-2Cl cotransporter in mice (NKCC1) . Gramicidin perforated-patch and whole-cell recordings were performed to study GABA-induced currents in dorsal root ganglion (DRG) neurons isolated from wild-type and homozygote NKCC1 knock-out mice. In wild-type DRG neurons, strong GABA-evoked inward current was observed at the resting membrane potential, suggesting active accumulation of Cl Ϫ in these cells. This GABA-induced current was blocked by picrotoxin, a GABA A receptor blocker. The strong Cl Ϫ accumulation that gives rise to depolarizing GABA responses is caused by Na-K-2Cl cotransport because reduction of external Cl Ϫ or application of bumetanide induced a decrease in [Cl Ϫ ] i , whereas an increase in external K ϩ caused an apparent [Cl Ϫ ] i accumulation. In contrast to control neurons, little or no net current was observed at the resting membrane potential in homozygote NKCC1 mutant DRG neurons. E GABA was significantly more negative, demonstrating the absence of Cl Ϫ accumulation in these cells. Application of bumetanide induced a positive shift of E GABA , suggesting the presence of an outward Cl Ϫ transport mechanism. In agreement with an absence of GABA depolarization in DRG neurons, behavioral analysis revealed significant alterations in locomotion and pain perception in the knock-out mouse. Our results clearly demonstrate that the Na-K-2Cl cotransporter is responsible for [Cl Ϫ ] i accumulation in DRG neurons and that via regulation of intracellular Cl Ϫ , the Na-K-2Cl cotransporter participates in the modulation of GABA neurotransmission and sensory perception.

Activation of metabotropic glutamate receptors (mGluRs), which are coupled to G proteins, has important roles in certain forms of synaptic plasticity including corticostriatal long-term depression (LTD). In the present study, extracellular field potential and whole cell voltage-clamp recording techniques were used to investigate the effect of mGluR antagonists with different subtype specificity on high-frequency stimulation (HFS)-induced LTD of synaptic transmission in the striatum of brain slices obtained from 15-to 25-day-old rats. Induction of LTD was prevented during exposure to the nonselective mGluR antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (500 microM). The group I mGluR-selective antagonists (S)-4-carboxy-phenylglycine (50 microM) and (RS)-1-aminoindan-1,5-dicarboxylic acid (100 microM) prevented induction of LTD when applied before and during HFS. The mGluR1-selective antagonist 7-(Hydroxyimino) cyclopropa[b]chromen-1a-carboxylate ethyl ester (80 microM) also blocked LTD induction. Unexpectedly, the mGluR5-selective antagonist 2-methyl-6-(phenylethyl)-pyridine (10 microM) also prevented LTD induction. The group II mGluR antagonist LY307452 (10 microM) did not block LTD induction at corticostriatal synapses, but LY307452 was able to block transient synaptic depression induced by the group II agonist LY314593. None of the antagonists had any effect on basal synaptic transmission at the concentrations used, and mGluR antagonists did not reverse LTD when applied beginning 20 min after HFS. These results suggest that both group I mGluR subtypes contribute to the induction of LTD at corticostriatal synapses.

To determine whether the pathophysiological processes after transient forebrain ischemia are mediated via a signal pathway involving gp130 (a signal transducer for the interleukin-6 family), we analyzed changes in the expression of gp130 and its downstream transcription factor, signal transducer and activator of transcription factor 3 (STAT3), in the rat hippocampus of a four-vessel occlusive ischemia model. Expression of gp130 mRNA was restricted to neurons of the pyramidal cell and granule cell layers in control animals. Four hours after ischemic injury, astrocytes expressed gp130 mRNA. Expression of gp130 increased preferentially in the CA1 and dentate hilar regions, and was maintained for at least 2 weeks. Increase in gp130 expression was accompanied by the activation of STAT3 following ischemic injury. Four hours after injury, STAT3 and phosphorylated STAT3 (pSTAT3) were observed in the nuclei of the dentate hilar region, and sequentially in the CA1 region at day 1. By day 3, STAT3 immunoreactivity markedly increased in these areas, where small cells with the morphology of astrocytes showed nuclear and cytoplasmic STAT3 and nuclear pSTAT3 immunoreactivities. These patterns were especially maintained in the CA1 area until 14 days of reperfusion. Double-labeling experiments revealed that the cells expressing STAT3 and pSTAT3 were glial fibrillary acidic protein-expressing reactive astrocytes. These results show a coordinated and long-lasting upregulation of gp130 mRNA and STAT3 activation in reactive astrocytes of the postischemic hippocampus, indicating that they may be involved in the astrocytic response to an ischemic insult.

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