Brittin et al. 2021
A multi-scale brain map derived from whole-brain volumetric reconstructions
Brittin, C.A., Cook, S.J., Hall, D.H. et al
Nature 591, 105–110
Published: 24 February 2021
Abstract
- Nerve ring is derived from integrating the volumetric reconstructions from two animals with corresponding synaptic and gap junctional connectomes (Cook et al 2019)
- C.elegans connectome is not invariant, but that a precisely wired core circuit is embedded in a background of variable connectivity, and identify a canditate reference connectome for the core circuit.
- Using this reference, they propose a modular network architecture of C.elegans brain that supports sensory computation and integration, sensorimotor convergence and brain-wide coordination.
- These findings reveal scalable and robust features of brain organisation that may be universal across phyla.
Main
- invariant cell lineage and anatomy of C.elegans might suggest that its connectome is too invariant
- small sample size of available reconstructions has precluded a reliable estimate of the reproducibility and variability of the synaptic connectome
- the synaptic wiring has been exhaustively characterised (ref to be inserted) but the spatial proximity of neurons is only partially described (ref to be inserted).
Data
- https://zenodo.org/records/4383277
- https://zenodo.org/records/4383277
- two complete volumetric reconstructions of the C.elegans nerve ring from previously published EMs (ref.) -adult -larval stage 4 (L4) worm
- two series of EMs span approx the same vol. with a length of 36 micrometres, starting in the anterior and ending in the ventral ganglia
- the reconstructiosn of these two nerve rings provide the first complete, nanoscale-resolution datasets of all neuronal membrane contacts of any neuropil.
- "contactome": the set of membrane contacts of the brain
- they define two neurons as immediate neighbours if the membranes along their neural processes are physically adjacent in at least one EM.
- to characterise synaptic pathways within a spatial contex, they integrated volumetric reconstructions with recent rescoring of synapses on the same L4 and adult worms (Cook et al) -for validation and comparison with other datasets (White et al, Witvliet et al)
Discussion
- Despite the C.elegans connectome being available for over 30 years, the delineation of functions within its main neuropil is still incomplete
- There are no physical boundaries within the nerve ring, but their analysis points to the spatial clustering of neural processes into 5 neighbourhoods.
- the concept of a reference connectome was key to their brain map and the modelling framework they sued to establish thsi reference can be accomodated for future connectomes.
- Connectome consists of a core, conserved circuit that is embedded in a considerably variable background
- Due to technical limitations of synaptic scoring, it is hard to determine the extent of the variability
- requires multiple further connectomes
- conserved synapes- like most variable ones- are constrained by the "contactome"
- If the baseline functionality of the animal is represented by a core circuit, the variable component could support redundancy, individuality and plasticity