Mechanisms of Calcium Influx into Hippocampal Spines: Heterogeneity among Spines, Coincidence Detection by NMDA Receptors, and Optical Quantal Analysis

Abstract

Dendritic spines receive most excitatory inputs in the vertebrate brain, but their function is still poorly understood. Using two-photon calcium imaging of CA1 pyramidal neurons in rat hippocampal slices, we investigated the mechanisms by which calcium enters into individual spines in the stratum radiatum. We find three different pathways for calcium influx: high-threshold voltage-sensitive calcium channels, NMDA receptors, and an APV-resistant influx consistent with calcium-permeable AMPA or kainate receptors. These pathways vary among different populations of spines and are engaged under different stimulation conditions, with peak calcium concentrations reaching >10 microM. Furthermore, as a result of the biophysical properties of the NMDA receptor, the calcium dynamics of spines are exquisitely sensitive to the temporal coincidence of the input and output of the neuron. Our results confirm that individual spines are chemical compartments that can perform coincidence detection. Finally, we demonstrate that functional studies and optical quantal analysis of single, identified synapses is feasible in mammalian CNS neurons in brain slices.

Attenuation of Ketamine Effects by Nimodipine Pretreatment in Recovering Ethanol Dependent Men Psychopharmacologic Implications of the Interaction of NMDA and L-Type Calcium Channel Antagonists

“…Ketamine appears to disinhibit cortical glutamatergic activity (Grunze et al 1996;Moghaddam et al 1997). It is possible that nimodipine attenuated glutamate release or its postsynaptic consequences (Schiller et al 1998;Segal 1995;Yuste et al 1999). From this perspective, one would have predicted that nimodipine would reduced only those behavioral effects of ketamine dependent on its capacity to stimulate glutamate release, but not behavioral effects arising directly from reduction of NMDA receptor function.…”

Three-dimensional random access multiphoton microscopy for functional imaging of neuronal activity

“…Indeed, several studies have met the first two challenges listed above by using the diffractionlimited spatial resolution and optical sectioning capabilities provided by confocal and multiphoton microscopy to study physiological dynamics in thin oblique dendrites [3][4][5][6] , as well as dendritic spines [7][8][9][10][11][12][13] . Recent studies have further extended the temporal resolution of these techniques by replacing galvanometer-driven beam steering mirrors with inertia-free acoustooptic deflectors (AODs) [14][15][16][17][18] .…”

Reporting neural activity with genetically encoded calcium indicators

“…The spatiotemporal pattern of intracellular [Ca 2+ ] is tightly coupled to neural activity (Denk et al, 1996). Therefore, the timing of spikes and patterns of synaptic input can be monitored by observing intracellular [Ca 2+ ] Denk et al, 1996;Yuste and Denk, 1995;Yuste et al, 1999).…”