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Dendritic NMDA receptors activate axonal calcium channels.

ABSTRACT: NMDA receptor (NMDAR) activation can alter synaptic strength by regulating transmitter release from a variety of neurons in the CNS. As NMDARs are permeable to Ca(2+) and monovalent cations, they could alter release directly by increasing presynaptic Ca(2+) or indirectly by axonal depolarization sufficient to activate voltage-sensitive Ca(2+) channels (VSCCs). Using two-photon microscopy to measure Ca(2+) excursions, we found that somatic depolarization or focal activation of dendritic NMDARs elicited small Ca(2+) transients in axon varicosities of cerebellar stellate cell interneurons. These axonal transients resulted from Ca(2+) entry through VSCCs that were opened by the electrotonic spread of the NMDAR-mediated depolarization elicited in the dendrites. In contrast, we were unable to detect direct activation of NMDARs on axons, indicating an exclusive somatodendritic expression of functional NMDARs. In cerebellar stellate cells, dendritic NMDAR activation masquerades as a presynaptic phenomenon and may influence Ca(2+) -dependent forms of presynaptic plasticity and release.

SUBMITTER: Christie JM

PROVIDER: S-EPMC2644657 | biostudies-literature | 2008 Oct

REPOSITORIES: biostudies-literature

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Dendritic NMDA receptors activate axonal calcium channels.

Christie Jason M JM Jahr Craig E CE

Neuron 20081001 2

NMDA receptor (NMDAR) activation can alter synaptic strength by regulating transmitter release from a variety of neurons in the CNS. As NMDARs are permeable to Ca(2+) and monovalent cations, they could alter release directly by increasing presynaptic Ca(2+) or indirectly by axonal depolarization sufficient to activate voltage-sensitive Ca(2+) channels (VSCCs). Using two-photon microscopy to measure Ca(2+) excursions, we found that somatic depolarization or focal activation of dendritic NMDARs el ...[more]

PMID: 18957221

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Project description:Neurons, represented as a tree structure of morphology, have various distinguished branches of dendrites. Different types of synaptic receptors distributed over dendrites are responsible for receiving inputs from other neurons. NMDA receptors (NMDARs) are expressed as excitatory units, and play a key physiological role in synaptic function. Although NMDARs are widely expressed in most types of neurons, they play a different role in the cerebellar Purkinje cells (PCs). Utilizing a computational PC model with detailed dendritic morphology, we explored the role of NMDARs at different parts of dendritic branches and regions. We found somatic responses can switch from silent, to simple spikes and complex spikes, depending on specific dendritic branches. Detailed examination of the dendrites regarding their diameters and distance to soma revealed diverse response patterns, yet explain two firing modes, simple and complex spike. Taken together, these results suggest that NMDARs play an important role in controlling excitability sensitivity while taking into account the factor of dendritic properties. Given the complexity of neural morphology varying in cell types, our work suggests that the functional role of NMDARs is not stereotyped but highly interwoven with local properties of neuronal structure. Author summary A single neuron receives a large number of inputs from its dendrites. A fundamental principle for neural dynamics is how these inputs are collectively integrated and converged to the neuronal soma to generate diverse patterns of action potentials. Such a principle has been formulated as a question of dendritic integration, which depends on the biophysical properties of neuronal dendrites and their associated synapses. It has been documented that NMDA plays an important role in dendritic integration. However, it remains unclear how dendritic integration is related to the distribution of NMDA receptors on various parts of the dendritic morphology of a neuron. Here we use Purkinje cell as a model system to symmetrically investigate this question, as the Purkinje cell exhibits a mixture of simple and complex spikes. By exploring the role of NMDA at different parts of dendritic branches and regions, we found somatic responses are diverse from simple to complex spikes, depending on specific dendritic branches. Our results suggest that the functional role of NMDA is highly interplayed with the local properties of neuronal dendrites.

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Dendritic NMDA receptors activate axonal calcium channels.

Publications

Dendritic NMDA receptors activate axonal calcium channels.

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