Postsynaptic [Ca2+]i changes in pyramidal neurons in the hippocampus play an important role in the induction of various forms of synaptic plasticity, gene expression, and modulation of membrane conductances. All of these mechanisms can affect the behavior of these neurons in circuits involved in learning and memory. Therefore, a detailed understanding of these processes is important for understanding brain function. Ca2+ entry through NMDA receptors and entry through voltage-dependent Ca2+ channels have been studied intensively but less is known about Ca2+ release from internal stores. We will investigate the properties and functions of Ca2+ release mediated by IP3 mobilized by synaptic activation of metabotropic glutamate receptors in pyramidal cells from the CA1 region. Previous experiments established that Ca2+ release spreads as a wave in restricted regions of pyramidal cell dendrites. We will examine the mechanisms that control the propagation of the waves into different regions including oblique dendrites, the soma and nucleus. We will examine the properties and spatial distribution of very small Ca2+ release events and compare them to the properties of regenerative waves. We will try to determine if they correspond to fundamental signaling events evoked by minimal synaptic stimulation. We will investigate the function of Ca2+ released from stores in several important physiological processes, with particular emphasis on the different consequences of Ca2+ released in different dendritic regions. One set of experiments will examine whether dendritic Ca2+ waves block back propagating action potentials important in synaptic plasticity. A second set of experiments will examine the role of the Ca2+ waves in suppressing synaptic inhibition onto pyramidal neurons mediated by endogenous cannabinoids. A third set of experiments will examine the role of Ca2+ release in the induction of long term potentiation. We will make these experiments in slices from the hippocampus of young Sprague Dawley rats. We will employ whole cell patch recordings from the soma and dendrites, and make high speed measurements of [Ca2+]i changes using cooled CCD cameras and 2- photon confocal microscopy to detect the fluorescence changes of injected Ca2+ indicators. We will use focal uncaging of extracellular glutamate and intracellular IP3 and Ca2+ to achieve precise localization of signaling events in thick or thin dendritic regions. ? ?
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