Auxiliary proteins modify the biophysical function and pharmacological properties of ionotropic glutamate receptors and likely are important components of receptor signaling complexes in vivo. NETO1 and NETO2, two closely related CUB domain-containing integral membrane proteins, were identified recently as auxiliary proteins that slowed GluK2a kainate receptor current kinetics without impacting receptor membrane localization. Here we demonstrate that NETO2 profoundly slows the desensitization rate of GluK1 kainate receptors, promotes plasma membrane localization of transfected receptors in heterologous cells and rat hippocampal neurons, and targets GluK1-containing receptors to synapses. Conversely, the closely related protein NETO1 increases the rate of GluK1 receptor desensitization. Incorporation of NETO proteins into kainate receptor signaling complexes therefore extends the temporal range of receptor gating by over an order of magnitude. The presence of these auxiliary proteins could underlie some of the unusual aspects of kainate receptor function in the mammalian CNS.

General or brain region-specific decreases in spine number or morphology accompany major neuropsychiatric disorders. It is unclear however, whether changes in spine density are specific for an individual mental process or disorder, and if so, which molecules confer such specificity. Here we identify the scaffolding protein IQGAP1 as a key regulator of dendritic spine number with a specific role in cognitive but not emotional or motivational processes. We show that IQGAP1 is an important component of N-methyl-D-aspartate receptor (NMDAR) multiprotein complexes and functionally interacts with the NR2A subunits and the extracellular signal-regulated kinases 1 and 2 (ERK) signaling pathway. Mice lacking the IQGAP1 gene exhibited significantly lower levels of surface NR2A and impaired ERK activity compared to their wild type littermates. Accordingly, primary hippocampal cultures of IQGAP1−/− neurons exhibited reduced surface expression of NR2A and disrupted ERK signaling in response to NR2A-dependent NMDAR stimulation. These molecular changes were accompanied by region-specific reductions of dendritic spine density in key brain areas involved in cognition, emotion and motivation. IQGAP1 knockouts exhibited marked long-term memory deficits accompanied by impaired hippocampal long-term potentiation (LTP) in a weak cellular learning model; in contrast, LTP was unaffected when induced with stronger stimulation paradigms. Anxiety- and depression-like behavior remained intact. On the basis of these findings, we propose that a dysfunctional IQGAP1 gene contributes to the cognitive deficits in brain disorders characterized by fewer dendritic spines.

The dentate gyrus (DG) is a critical entry point regulating function of the hippocampus. Integral to this role are the sparse, selective activation characteristics of the principal cells of the DG, dentate granule cells (DGCs). This sparse activation is important both in cognitive processing, and in regulation of pathological activity in disease states. Using a novel, combined dynamic imaging approach capable of resolving sequentially both synaptic potentials and action potential firing in large populations of DGCs, we characterized the postnatal development of firing properties of DG neurons in response to afferent activation in mouse hippocampal-entorhinal cortical slices. During postnatal development, there was a protracted, progressive sparsification of responses, accompanied by increased temporal precision of activation. Both of these phenomena were primarily mediated by changes in local circuit inhibition, and not by alterations in afferent innervation of DGCs, since GABAA antagonists normalized developmental differences. There was significant theta and gamma frequency-dependent synaptic recruitment of DGC activation in adult, but not developing, animals. Finally, we found that the decision to fire or not fire by individual DGCs was robust and repeatable at all stages of development. The protracted postnatal development of sparse, selective firing properties, increased temporal precision and frequency dependence of activation, and the fidelity with which the decision to fire is made are all fundamental circuit determinants of DGC excitation, critical in both normal and pathological function of the DG.

The microtubule-associated protein tau is highly soluble under physiological conditions. However, in tauopathies, tau protein aggregates into insoluble filaments and neurofibrillary tangles (NFTs). The mechanisms underlying the formation of tau filaments and NFTs in tauopathies remain unclear. Several lines of evidence suggest that transglutaminase may cross-link tau into stable, insoluble aggregates, leading to the formation of NFTs in Alzheimer's disease and progressive supranuclear palsy. To further determine the contribution of transglutaminase in the formation of NFTs, we compared the levels of cross-linked tau protein from P301L tau transgenic mice that develop NFTs to four-repeat wild-type (4RWT) tau transgenic and nontransgenic mice that do not develop NFT pathology. Immunoprecipitation and immunoblotting experiments show that transglutaminase cross-links phosphorylated tau in the hindbrain of P301L tau transgenic mice but not in mice overexpressing 4RWT tau and nontransgenic mice. Cross-linked, phosphorylated tau from P301L tau transgenic mice runs as high-molecular mass aggregates on Western blots, similar to cross-linked tau from paired helical filaments of Alzheimer's disease. We also used double-label immunofluorescence to demonstrate colocalization of PHF-1-immunoreactive tau and the transglutaminase-catalyzed cross-link in the hindbrain, spinal cord, and cortex of P301L tau transgenic mice. In the spinal cord, 87% of PHF-1-labeled cells colocalize with the transglutaminase-catalyzed cross-link. Additionally, transglutaminase enzymatic activity is significantly elevated in the spinal cord of P301L tau transgenic mice. These studies further implicate transglutaminase in the formation and/or stabilization of NFT and paired helical filaments and provide a model system to investigate the therapeutic potential of transglutaminase inhibitors in tauopathies.

The actions of ethanol on brain ligand-gated ion channels have important roles in the pathophysiology of alcohol-related neurodevelopmental disorders and fetal alcohol syndrome. Studies have shown that N-methyl-Daspartate (NMDA) receptors are among the ligand-gated ion channels affected by prenatal ethanol exposure. We exposed pregnant dams to an ethanol-containing liquid diet that results in blood ethanol levels near the legal intoxication limit in most states (0.08%). Primary cultures of hippocampal neurons were prepared from the neonatal offspring of these dams, and NMDA receptor function was assessed by patch clamp electrophysiological techniques after 6 -7 days in culture in ethanol-free media. Unexpectedly, we did not detect any changes in hippocampal NMDA receptor function at either the whole-cell or single-channel levels. However, we determined that fetal alcohol exposure alters the actions of the neurosteroids pregnenolone sulfate and pregnenolone hemisuccinate, which potentiate NMDA receptor function. Western immunoblot analyses demonstrated that this alteration is not due to a change in the expression levels of NMDA receptor subunits. Importantly, in utero ethanol exposure did not affect the actions of neurosteroids that inhibit NMDA receptor function. Moreover, the actions of pregnenolone sulfate on type A ␥-aminobutyric acid and non-NMDA receptor function were unaltered by ethanol exposure in utero, which suggests that the alteration is specific to NMDA receptors. These findings are significant because they provide, at least in part, a plausible mechanistic explanation for the alterations in the behavioral responses to neurosteroids found in neonatal rats prenatally exposed to ethanol and to other forms of maternal stress (Zimmerberg, B., and McDonald, B. C. (1996) Pharmacol. Biochem. Behav. 55, 541-547).Ingestion of ethanol during pregnancy can have profound effects on normal fetal development. These effects range from isolated alcohol-related birth defects to a combination of abnormalities that characterize the fetal alcohol syndrome (1). This syndrome is characterized by alterations in growth, facial and skull development, and central nervous system function. Fetal ethanol exposure produces long-lasting and debilitating neurobehavioral and neurophysiological dysfunctions such as deficits in learning, memory, information processing, and problem solving skills (2-5). Therefore, there is considerable interest in understanding the consequences of the teratogenic actions of ethanol in the central nervous system.Research from a number of laboratories suggests that the actions of ethanol on ligand-gated ion channels have important roles in the pathophysiology of alcohol-related neurodevelopmental disorders (for review, see Ref. 6). Experimental evidence indicates that glutamate receptors of the N-methyl-Daspartate (NMDA)1 subtype are among the ligand-gated ion channels affected by fetal exposure to ethanol. Studies have shown that fetal and/or neonatal ethanol exposure alters ligand binding to NMDA rece...