Febrile (fever-induced) seizures are the most common form of childhood seizures, affecting 3%-5% of infants and young children. Here we show that the activity-dependent, retrograde inhibition of GABA release by endogenous cannabinoids is persistently enhanced in the rat hippocampus following a single episode of experimental prolonged febrile seizures during early postnatal development. The potentiation of endocannabinoid signaling results from an increase in the number of presynaptic cannabinoid type 1 receptors associated with cholecystokinin-containing perisomatic inhibitory inputs, without an effect on the endocannabinoid-mediated inhibition of glutamate release. These results demonstrate a selective, long-term increase in the gain of endocannabinoid-mediated retrograde signaling at GABAergic synapses in a model of a human neurological disease.

Depolarization-induced suppression of inhibition (DSI) is an endocannabinoid-mediated short-term plasticity mechanism that couples postsynaptic Ca 2ϩ rises to decreased presynaptic GABA release. Whether the gain of this retrograde synaptic mechanism is subject to long-term modulation by glutamatergic excitatory inputs is not known. Here, we demonstrate that activity-dependent long-term DSI potentiation takes place in hippocampal slices after tetanic stimulation of Schaffer collateral synapses. This activity-dependent, longterm plasticity of endocannabinoid signaling was specific to GABAergic synapses, as it occurred without increases in the depolarizationinduced suppression of excitation. Induction of tetanus-induced DSI potentiation in vitro required a complex pathway involving AMPA/ kainate and metabotropic glutamate receptor as well as CB1 receptor activation. Because DSI potentiation has been suggested to play a role in persistent limbic hyperexcitability after prolonged seizures in the developing brain, we used these mechanistic insights into activity-dependent DSI potentiation to test whether interference with the induction of DSI potentiation prevents seizure-induced longterm hyperexcitability. The results showed that the in vitro, tetanus-induced DSI potentiation was occluded by previous in vivo feverinduced (febrile) seizures, indicating a common pathway. Accordingly, application of CB1 receptor antagonists during febrile seizures in vivo blocked the seizure-induced persistent DSI potentiation, abolished the seizure-induced upregulation of CB1 receptors, and prevented the emergence of long-term limbic hyperexcitability. These results reveal a new form of activity-dependent, long-term plasticity of endocannabinoid signaling at perisomatic GABAergic synapses, and demonstrate that blocking the induction of this plasticity abolishes the long-term effects of prolonged febrile seizures in the developing brain.

Agrin, through its interaction with the receptor tyrosine kinase MuSK, mediates accumulation of acetylcholine receptors (AChR) at the developing neuromuscular junction. Agrin has also been implicated in several functions in brain. However, the mechanism by which agrin exerts its effects in neural tissue is unknown. Here we present biochemical evidence that agrin binds to the alpha3 subunit of the Na+/K+-ATPase (NKA) in CNS neurons. Colocalization with agrin binding sites at synapses supports the hypothesis that the alpha3NKA is a neuronal agrin receptor. Agrin inhibition of alpha3NKA activity results in membrane depolarization and increased action potential frequency in cortical neurons in culture and acute slice. An agrin fragment that acts as a competitive antagonist depresses action potential frequency, showing that endogenous agrin regulates native alpha3NKA function. These data demonstrate that, through its interaction with the alpha3NKA, agrin regulates activity-dependent processes in neurons, providing a molecular framework for agrin action in the CNS.

This video will guide you through the process for generating cortical neuronal cultures from late embryo and early postnatal mouse brain. These cultures can be used for a variety of applications including immunocytochemistry, biochemistry, electrophysiology, calcium and sodium imaging, protein and/or RNA isolation. These cultures also provide a platform to study the neuronal development of transgenic animals that carry a late embryonic or postnatal lethal gene mutation. The procedure is relatively straight forward, requires some experience in tissue culture technique and should not take longer than two to three hours if you are properly prepared. Careful separation of the cortical rind from the thalamo-cortical fiber tract will reduce the number of unwanted non-neuronal cells. To increase yields of neuronal cells triturate the pieces of the cortical tissue gently after the enzyme incubation step. This is imperative as it prevents unnecessary injury to cells and premature neuronal cell death. Since these cultures are maintained in the absence of glia feeder cells, they also offer an added advantage of growing cultures enriched in neurons.

A dinucleotide deletion in human ubiquitin (Ub) B messenger RNA leads to formation of polyubiquitin (UbB) þ 1, which has been implicated in neuronal cell death in Alzheimer's and other neurodegenerative diseases. Previous studies demonstrate that UbB þ 1 protein causes proteasome dysfunction. However, the molecular mechanism of UbB þ 1-mediated neuronal degeneration remains unknown. We now report that UbB þ 1 causes neuritic beading, impairment of mitochondrial movements, mitochondrial stress and neuronal degeneration in primary neurons. Transfection of UbB þ 1 induced a buildup of mitochondria in neurites and dysregulation of mitochondrial motor proteins, in particular, through detachment of P74, the dynein intermediate chain, from mitochondria and decreased mitochondria-microtubule interactions. Altered distribution of mitochondria was associated with activation of both the mitochondrial stress and p53 cell death pathways. These results support the hypothesis that neuritic clogging of mitochondria by UbB þ 1 triggers a cascade of events characterized by local activation of mitochondrial stress followed by global cell death. Furthermore, UbB þ 1 small interfering RNA efficiently blocked expression of UbB þ 1 protein, attenuated neuritic beading and preserved cellular morphology, suggesting a potential neuroprotective strategy for certain neurodegenerative disorders.

Agrin plays a key role in directing the differentiation of the vertebrate neuromuscular junction. Understanding agrin function at the neuromuscular junction has come via molecular genetic analyses of agrin as well as identification of its receptor and associated signal transduction pathways. Agrin is also expressed by many populations of neurons in brain, but its role remains unknown. Here we show, in cultured cortical neurons, that agrin induces expression of the immediate early gene c-fos in a concentration-dependent and saturable manner, as expected for a signal transduction pathway activated by a cell surface receptor. Agrin is active in cortical neurons at picomolar concentrations, is Ca 2ϩ dependent, and is inhibited by heparin and staurosporine. Despite marked differences in acetylcholine receptor (AChR)-clustering activity, all alternatively spliced forms of agrin are equally potent inducers of c-fos in cortical neurons. A similar, isoform-independent response to agrin was also observed in cultures prepared from the hippocampus and cerebellum. Only agrin with high AChR-clustering activity was effective in cultured muscle, whereas non-neuronal cells were agrin insensitive. Although consistent with a receptor tyrosine kinase model similar to the muscle-specific kinase-myotubeassociated specificity component complex in muscle, our data suggest that CNS neurons express a unique agrin receptor. Evidence that neuronal signal transduction is mediated via an increase in intracellular Ca 2ϩ means that agrin is well situated to influence important Ca 2ϩ -dependent functions in brain, including neuronal growth, differentiation, and adaptive changes in gene expression associated with synaptic remodeling.

70-kDa heat shock protein (Hsp70) molecular chaperones are ATPases that participate in protein folding by regulating protein-protein interactions. ATP binds to the highly conserved amino-terminal domain, whereas polypeptides bind to the less conserved carboxyl-terminal domain. These domains are functionally coupled. Polypeptides were previously shown to dissociate from Hsp70s upon ATP binding and to stimulate ATPase activity. We probed the structure of the yeast cytosolic Hsp70 Ssa1p using limited proteolysis to determine whether the conformations of its nucleotide and polypeptide binding domains are also coupled. Ssa1p adopted three distinct conformations, nucleotide-free, ADP-dependent, and ATP-dependent. Complete conformational changes required K ؉ and Mg 2؉. Using aminoterminal sequencing, ATP-agarose chromatography, and a carboxyl-terminal-specific antibody, we mapped the locations of the major proteolytic fragments. Nucleotides altered the conformations of both the nucleotide and polypeptide binding domains. Similarly, a polypeptide altered the conformations of both domains. These results indicate that the conformations of the nucleotide and polypeptide binding domains are coupled.

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