The mRNA levels of NKCC1, an inwardly directed Na + , K + -2Cl − cotransporter that facilitates the accumulation of intracellular Cl − , and of KCC2, an outwardly directed K + -Cl − cotransporter that extrudes Cl − , were studied in surgically resected brain specimens from drug-resistant temporal lobe (TL) epilepsy (TLE) patients. Quantitative RT-PCR analyses of the mRNAs extracted from the human TLE-associated brain regions revealed an up-regulation of NKCC1 mRNA and a down-regulation of KCC2 mRNA in the hippocampal subiculum, compared with the hippocampus proper or the TL neocortex, suggesting an abnormal transcription of Cl − transporters in the TLE subiculum. In parallel experiments, cell membranes isolated from the same TLE-associated brain regions were injected into Xenopus oocytes that rapidly incorporated human GABA A receptors into their surface membrane. The GABA currents elicited in oocytes injected with membranes from the subiculum had a more depolarized reversal potential ( E GABA ) compared with the hippocampus proper or the neocortex. The NKCC1 blocker bumetanide or a temperature decrease of 10°C shifted the GABA-current E GABA more negative in oocytes injected with membranes from TLE hippocampal subiculum, matching the E GABA of TL neocortex-injected oocytes. We conclude that the anomalous expression of both Cl − transporters, KCC1 and NKCC2, in TLE hippocampal subiculum probably causes altered Cl − transport in the “epileptic” neurons, as revealed in the microtransplanted Xenopus oocytes, and renders GABA aberrantly “exciting,” a feature that may contribute to the precipitation of epileptic seizures.

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SummaryThe Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is involved in many cellular processes, including cell growth and differentiation, immune functions and cancer. It is activated by various cytokines, growth factors, and protein tyrosine kinases (PTKs) and regulates the transcription of many genes. Of the four JAK isoforms and seven STAT isoforms known, JAK2 and STAT3 are highly expressed in the brain where they are present in the postsynaptic density (PSD). Here, we demonstrate a new neuronal function for the JAK/STAT pathway. Using a variety of complementary approaches, we show that the JAK/STAT pathway plays an essential role in the induction of NMDA-receptor dependent long-term depression (NMDAR-LTD) in the hippocampus. Therefore, in addition to established roles in cytokine signaling, the JAK/STAT pathway is involved in synaptic plasticity in the brain.

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Pharmacotherapeutic strategies have been difficult to develop for several forms of temporal lobe epilepsy, which are consequently treated by surgical resection. To examine this problem, we have studied the properties of transmitter receptors of tissues removed during surgical treatment. We find that when cell membranes, isolated from the temporal neocortex of patients afflicted with drug-resistant mesial temporal lobe epilepsy (TLE), are injected into frog oocytes they acquire GABA type A receptors (GABA A-receptors) that display a marked rundown during repetitive applications of GABA. In contrast, GABA A-receptor function is stable in oocytes injected with cell membranes isolated from the temporal lobe of TLE patients afflicted with neoplastic, dysgenetic, traumatic, or ischemic temporal lesions (lesional TLE, LTLE). Use-dependent GABA A-receptor rundown is also found in the pyramidal neurons of TLE neocortical slices and is antagonized by BDNF. Pyramidal neurons in cortical slices of a traumatic LTLE patient did not show GABA A-receptor rundown. However, the apparent affinity of GABA A-receptor in oocytes microtransplanted with membranes from all of the epileptic patients studied was smaller than the affinity of receptors transplanted from the nonepileptic brain. We conclude that the use-dependent rundown of neocortical GABA Areceptor represents a TLE-specific dysfunction, whereas the reduced affinity may be a general feature of brains of both TLE and LTLE patients, and we speculate that our findings may help to develop new treatments for TLE and LTLE.human slices ͉ Xenopus oocytes

SummaryInhibition of Arp2/3-mediated actin polymerization by PICK1 is a central mechanism to AMPA receptor (AMPAR) internalization and long-term depression (LTD), although the signaling pathways that modulate this process in response to NMDA receptor (NMDAR) activation are unknown. Here, we define a function for the GTPase Arf1 in this process. We show that Arf1-GTP binds PICK1 to limit PICK1-mediated inhibition of Arp2/3 activity. Expression of mutant Arf1 that does not bind PICK1 leads to reduced surface levels of GluA2-containing AMPARs and smaller spines in hippocampal neurons, which occludes subsequent NMDA-induced AMPAR internalization and spine shrinkage. In organotypic slices, NMDAR-dependent LTD of AMPAR excitatory postsynaptic currents is abolished in neurons expressing mutant Arf1. Furthermore, NMDAR stimulation downregulates Arf1 activation and binding to PICK1 via the Arf-GAP GIT1. This study defines Arf1 as a critical regulator of actin dynamics and synaptic function via modulation of PICK1.

The beta-amyloid(1-42) peptide (Abeta(1-42)), a major constituent of the Alzheimer's disease amyloid plaque, specifically binds to the neuronal alpha-bungarotoxin (alpha-BuTx)-sensitive alpha7 nicotinic acetylcholine receptor (alpha7 nAChR). Accordingly, Abeta1-42 interferes with the function of alpha7 nAChRs in chick and rodent neurons. To gain insights into the human disease, we studied the action of Abeta(1-42) on human alpha7 nAChRs expressed in Xenopus oocytes. In voltage-clamped oocytes expressing the wild-type receptor, Abeta(1-42) blocked ACh-evoked currents. The block was non-competitive, required over 100 s to develop and was partially reversible. In oocytes expressing the mutant L248T receptor, Abeta(1-42) activated methyllycaconitine-sensitive currents in a dose-dependent manner. Peptide-evoked unitary events, recorded in outside-out patches, showed single-channel conductances and open duration comparable to ACh-evoked events. Abeta(1-42) had no effect on the currents evoked by glutamate, GABA or glycine in oocytes expressing human or mouse receptors for these transmitters. Muscle nAChRs are also alpha-BuTx-sensitive and we therefore investigated whether they respond to Abeta(1-42). In human kidney BOSC 23 cells expressing the fetal or adult mouse muscle nAChRs, Abeta(1-42) blocked ACh-evoked whole-cell currents, accelerating their decay. Outside-out single-channel recordings showed that the block was due to a reduced channel open probability and enhanced block upon ACh application. We also report that the inverse peptide Abeta(42-1), but not Abeta(40-1), partially mimicked the effects of the physiological Abeta(1-42) peptide. Possible implications for degenerative neuronal and muscular diseases are discussed.