225 — Electron Microscopic Reconstruction of Functionally Identified Cells in a Neural Integrator

The oculomotor integrator, present in many animals, is a neural integrator circuit that controls the motion of the eyes. The integrator (like, the $\int$ kind) receives as input velocity information from the rest of the body (in the example of the zebrafish, from head motion) and uses these data to maintain the direction of the eyes.

The authors first recorded two-photon functional calcium imagery over time to determine which neurons in the sample volume were active when the eyes were moving spontaneously. Then the tissue was imaged again in serial-section electron microscopy in order to identify these cells and their targets. This work yielded three “classifications” of integrator neurons: Ipsilaterally projecting neurons (which tended to be more medial), contralaterally projecting neurons (which tended to be more lateral), and another population in which the authors could not identify clear axons.

When this anatomical information was overlaid with the functional data from the calcium imaging, the researchers noted that the ipsilateral neurons were more commonly glutamatergic, and the contralaterally projecting neurons were more commonly GABAergic.

An (extremely time-consuming) exercise for the reader: I previously read about a full-brain scan of a zebrafish at nanometer resolution. It should be possible for you to go back to the data from that paper and identify this same neural integrator. Let me know when you’re finished!

The data were traced with TrakEM2 and uploaded to NeuroMorpho.org. The data are available here if you feel like playing!