SynGAP, a prominent Ras/Rap GTPase-activating protein in the postsynaptic density, regulates the timing of spine formation and trafficking of glutamate receptors in cultured neurons. However, the molecular mechanisms by which it does this are unknown. Here, we show that synGAP is a key regulator of spine morphology in adult mice. Heterozygous deletion of synGAP was sufficient to cause an excess of mushroom spines in adult brains, indicating that synGAP is involved in steady-state regulation of actin in mature spines. Both Ras-and Rac-GTP levels were elevated in forebrains from adult synGAP

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synGAP is a neuron-specific Ras GTPase-activating protein found in high concentration in the postsynaptic density fraction from mammalian forebrain. Proteins in the postsynaptic density, including synGAP, are part of a signaling complex attached to the cytoplasmic tail of the N-methyl-D-aspartate-type glutamate receptor. syn-GAP can be phosphorylated by a second prominent component of the complex, Ca 2؉ /calmodulin-dependent protein kinase II. Here we show that phosphorylation of synGAP by Ca 2؉ /calmodulin-dependent protein kinase II increases its Ras GTPase-activating activity by 70 -95%. We identify four major sites of phosphorylation, serines 1123, 1058, 750/751/756, and 764/765. These sites together with other minor phosphorylation sites in the carboxyl tail of synGAP control stimulation of GTPaseactivating activity. When three of these sites and four other serines in the carboxyl tail are mutated, stimulation of GAP activity after phosphorylation is reduced to 21 ؎ 5% compared with 70 -95% for the wild type protein.We used phosphosite-specific antibodies to show that, as predicted, phosphorylation of serines 765 and 1123 is increased in cultured cortical neurons after exposure of the neurons to the agonist N-methyl-D-aspartate.Storage of information in the brain is mediated in part by changes in the strength of synaptic connections between neurons initiated by specific patterns of electrical activity (1). These changes involve complex regulatory pathways that are controlled by the pattern of influx of Ca 2ϩ ion through Nmethyl-D-aspartate (NMDA) 1 -type glutamate receptors (NMDA receptors) at postsynaptic sites. Much present research concerns the nature of the relevant biochemical pathways and the mechanisms of Ca 2ϩ control. One set of regulatory proteins associates tightly with the cytosolic portion of the NMDA receptor (2, 3). These include Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII) (4, 5), which is activated by Ca 2ϩ flux through the receptor, and several proteins that are held near the receptor by the scaffold protein PSD-95 (6, 7). A complex containing many of these proteins can be isolated from brain homogenates and is called the postsynaptic density (PSD) fraction (8).synGAP was identified as a prominent 140-kDa protein in the PSD fraction (9, 10) and as a protein that interacts with PSD-95 in a yeast two-hybrid screen (11). Its message is detected only in brain (10, 11). It is expressed only in neurons, including most excitatory neurons and a subset of inhibitory neurons (12), where it is highly localized to the postsynaptic density (10). It contains a PH domain, a C2 domain, and a Ras GAP domain that are 23%, 33%, and 47% similar, respectively, to those of the prototype Ras GAP protein p120 Ras GAP (13). In brain homogenates, synGAP is tightly bound to the particulate fraction and full-length synGAP has not yet been purified in soluble form; however, the GAP domain, expressed as a GST fusion protein in Escherichia coli, has been shown to stimulate hydrolysis of bound GTP by Ras (11). ...

Mild traumatic brain injury (mTBI) produces symptoms similar to those typifying posttraumatic stress disorder (PTSD) in humans. We sought to determine whether a rodent model of stress concurrent with mTBI produces characteristics of PTSD such as impaired contextual fear extinction, while also examining concurrent alterations to limbic monoamine activity in brain regions relevant to fear and anxiety states. Male rats were exposed to social stress or control conditions immediately prior to mTBI induction, and 6 days later were tested either for anxiety-like behavior using the elevated plus maze (EPM), or for contextual fear conditioning and extinction. Brains were collected 24 h after EPM testing, and tissue from various limbic regions analyzed for content of monoamines, their precursors and metabolites using HPLC with electrochemical detection. Either social defeat or mTBI alone decreased time spent in open arms of the EPM, indicating greater anxiety-like behavior. However, this effect was enhanced by the combination of treatments. Further, rats exposed to both social defeat and mTBI exhibited greater freezing within extinction sessions compared to all other groups, suggesting impaired contextual fear extinction. Social defeat combined with mTBI also had greater effects on limbic monoamines than either insult alone, particularly with respect to serotonergic effects associated with anxiety and fear learning. The results suggest social stress concurrent with mTBI produces provides a relevant animal model for studying the prevention and treatment of post-concussive psychobiological outcomes.

This review addresses our current understanding of the regulatory mechanisms for classical cadherin expression during development of the vertebrate nervous system. The complexity of the spatial and temporal expression patterns is linked to morphogenic and functional roles in the developing nervous system. While the regulatory networks controlling cadherin expression are not well understood, it is likely that the multiple signaling pathways active in the development of particular domains also regulate the specific cadherins expressed at that time and location. With the growing understanding of the broader roles of cadherins in cell-cell adhesion and non-adhesion processes, it is important to understand both the upstream regulation of cadherin expression and the downstream effects of specific cadherins within their cellular context.