ABSTRACT
The adducin family of proteins interacts with the actin cytoskeleton and the plasma membrane in a calcium- and cAMP-dependent manner. Thus, adducins may be involved in changes in cytoskeletal organization resulting from synaptic stimulation. beta-Adducin knock-out mice were examined in physiological and behavioral paradigms related to synaptic plasticity to elucidate the role the adducin family plays in processes underlying learning and memory. In situ hybridization for alpha- and beta-adducin demonstrates that these mRNAs are found throughout the brain, with high levels of expression in the hippocampus. Schaffer collateral-CA1 tetanic long-term potentiation decayed rapidly in acute hippocampal slices from beta-adducin knock-out mice, although baseline spine morphology and postsynaptic density were normal. Interestingly, the input-output relationship was significantly increased in hippocampal slices from beta-adducin knock-out mice. Furthermore, beta-adducin knock-out mice were impaired in performance of fear conditioning and the water maze paradigm. The current results indicate that beta-adducin may play an important role in the cellular mechanisms underlying activity-dependent synaptic plasticity associated with learning and memory.
Subject(s)
Actins/metabolism , Calmodulin-Binding Proteins/physiology , Cytoskeleton/metabolism , Learning Disabilities/genetics , Memory Disorders/genetics , Nerve Tissue Proteins/physiology , Neuronal Plasticity/physiology , Animals , Avoidance Learning/physiology , Calmodulin-Binding Proteins/deficiency , Calmodulin-Binding Proteins/genetics , Conditioning, Classical/physiology , Cytoskeleton/ultrastructure , Dendrites/ultrastructure , Electroshock , Fear/physiology , Female , Freezing Reaction, Cataleptic/physiology , Gyrus Cinguli/metabolism , Hippocampus/metabolism , Hippocampus/pathology , Learning Disabilities/physiopathology , Male , Maze Learning/physiology , Memory Disorders/physiopathology , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Neurologic Mutants , Nerve Tissue Proteins/deficiency , Nerve Tissue Proteins/genetics , Neuronal Plasticity/genetics , Nucleus Accumbens/metabolism , RNA, Messenger/biosynthesisABSTRACT
Phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) has an important function in cell regulation both as a precursor of second messenger molecules and by means of its direct interactions with cytosolic and membrane proteins. Biochemical studies have suggested a role for PtdIns(4,5)P2 in clathrin coat dynamics, and defects in its dephosphorylation at the synapse produce an accumulation of coated endocytic intermediates. However, the involvement of PtdIns(4,5)P2 in synaptic vesicle exocytosis remains unclear. Here, we show that decreased levels of PtdIns(4,5)P2 in the brain and an impairment of its depolarization-dependent synthesis in nerve terminals lead to early postnatal lethality and synaptic defects in mice. These include decreased frequency of miniature currents, enhanced synaptic depression, a smaller readily releasable pool of vesicles, delayed endocytosis and slower recycling kinetics. Our results demonstrate a critical role for PtdIns(4,5)P2 synthesis in the regulation of multiple steps of the synaptic vesicle cycle.
Subject(s)
Phosphatidylinositol Phosphates/metabolism , Presynaptic Terminals/metabolism , Synaptic Transmission , Synaptic Vesicles/metabolism , Action Potentials , Animals , Biological Transport , Cells, Cultured , Clathrin/metabolism , Electric Conductivity , Endocytosis , Exocytosis , Gene Deletion , Kinetics , Mice , Mice, Knockout , Neurons/cytology , Neurons/metabolism , Phosphatidylinositol 4,5-Diphosphate , Phosphatidylinositol Phosphates/biosynthesis , Phosphotransferases (Alcohol Group Acceptor)/deficiency , Phosphotransferases (Alcohol Group Acceptor)/genetics , Phosphotransferases (Alcohol Group Acceptor)/metabolismABSTRACT
Regulation of intracellular calcium influences neuronal excitability, synaptic plasticity, gene expression, and neurotoxicity. In this study, we investigated the role of calcium in mechanisms underlying nicotine-mediated neuroprotection from glutamate excitotoxicity. Neuroprotection by nicotine in primary cortical cultures was not seen in knock-out mice lacking the beta2 subunit of the nicotinic acetylcholine receptor (nAChR). Neuroprotection was partially blocked in wild-type cultures by alpha-bungarotoxin, an antagonist of the alpha7 nAChR subtype, suggesting a potential cooperative role for these subtypes. Pretreatment with nicotine decreased glutamate-mediated calcium influx in primary cortical cultures by 41%, an effect that was absent in cultures from knock-out mice lacking the beta2 subunit of the nAChR. This effect was dependent on calcium entry through L-type channels during nicotine pretreatment in wild-type cultures. The ability of nicotine to decrease glutamate-mediated calcium influx was occluded by cotreatment with nifedipine during glutamate application, suggesting that nicotine pretreatment decreased subsequent activity of L-type calcium channels. Treatment with the calcineurin antagonists FK506 and cyclosporine during pretreatment eliminated both nicotine-mediated neuroprotection and the effects of nicotine on L-type channels. We conclude that neuroprotective effects of nicotine in cortical neurons involve both beta2- and alpha7-containing nAChRs, activation of calcineurin, and decreased intracellular calcium via L-type channels.
