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Curr Biol. 2017 Jul 24;27(14):2137-2147.e3. doi: 10.1016/j.cub.2017.06.028. Epub 2017 Jul 14.

Electron Microscopic Reconstruction of Functionally Identified Cells in a Neural Integrator.

Author information

1
Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA. Electronic address: ashwinv@princeton.edu.
2
Institute for Computational Biomedicine and Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY 10021, USA.
3
Department of Molecular and Cellular Biology and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA.
4
Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA; Computer Science Department, Princeton University, Princeton, NJ 08544, USA. Electronic address: sseung@princeton.edu.

Abstract

Neural integrators are involved in a variety of sensorimotor and cognitive behaviors. The oculomotor system contains a simple example, a hindbrain neural circuit that takes velocity signals as inputs and temporally integrates them to control eye position. Here we investigated the structural underpinnings of temporal integration in the larval zebrafish by first identifying integrator neurons using two-photon calcium imaging and then reconstructing the same neurons through serial electron microscopic analysis. Integrator neurons were identified as those neurons with activities highly correlated with eye position during spontaneous eye movements. Three morphological classes of neurons were observed: ipsilaterally projecting neurons located medially, contralaterally projecting neurons located more laterally, and a population at the extreme lateral edge of the hindbrain for which we were not able to identify axons. Based on their somatic locations, we inferred that neurons with only ipsilaterally projecting axons are glutamatergic, whereas neurons with only contralaterally projecting axons are largely GABAergic. Dendritic and synaptic organization of the ipsilaterally projecting neurons suggests a broad sampling from inputs on the ipsilateral side. We also observed the first conclusive evidence of synapses between integrator neurons, which have long been hypothesized by recurrent network models of integration via positive feedback.

KEYWORDS:

connectomics; eye-position; neural integrator; positive feedback; serial section electron microscopy; two-photon microscopy; zebrafish

PMID:
28712570
PMCID:
PMC5569574
DOI:
10.1016/j.cub.2017.06.028
[Indexed for MEDLINE]
Free PMC Article

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