Multiple Clusters of Release Sites Formed by Individual Thalamic Afferents onto Cortical Interneurons Ensure Reliable Transmission

Center for Neural Circuits and Behavior, University of California, San Diego, La Jolla, CA 92093, USA.
Neuron (Impact Factor: 15.05). 07/2011; 71(1):180-94. DOI: 10.1016/j.neuron.2011.05.032
Source: PubMed


Thalamic afferents supply the cortex with sensory information by contacting both excitatory neurons and inhibitory interneurons. Interestingly, thalamic contacts with interneurons constitute such a powerful synapse that even one afferent can fire interneurons, thereby driving feedforward inhibition. However, the spatial representation of this potent synapse on interneuron dendrites is poorly understood. Using Ca imaging and electron microscopy we show that an individual thalamic afferent forms multiple contacts with the interneuronal proximal dendritic arbor, preferentially near branch points. More contacts are correlated with larger amplitude synaptic responses. Each contact, consisting of a single bouton, can release up to seven vesicles simultaneously, resulting in graded and reliable Ca transients. Computational modeling indicates that the release of multiple vesicles at each contact minimally reduces the efficiency of the thalamic afferent in exciting the interneuron. This strategy preserves the spatial representation of thalamocortical inputs across the dendritic arbor over a wide range of release conditions.

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    • "It is possible that larger mEPSCs in FSIs, which are practically absent in PNs, are generated by the release of multiple vesicles. Multiple clusters of release sites formed by individual thalamic afferents onto cortical FSIs were found by the EM study (Bagnall et al., 2011). Multiple vesicle release appears to be due to spontaneous 'sparks' of Ca 2+ from intracellular stores (Emptage et al., 2001; Simkus and Stricker, 2002). "
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