Beretta and colleagues uncover the importance of cross-communication between brain hemispheres for neural network formation.
Neural network formation requires the precise temporal co-ordination of multiple processes. A failure to establish any of the billions of neural connections can have devastating consequences for the organism. The authors have investigated the formation of the habenular neural circuit in the zebrafish forebrain, which develops within the first 5 days of embryonic development. This evolutionarily conserved neural circuit steers multiple behaviors and has been linked to pathophysiological syndromes such as autism, depression and schizophrenia. The habenular neurons are formed bilaterally and extend long axon bundles to connect the dorsal diencephalon with the ventral midbrain. Unprecedented long-term time-lapse imaging revealed that axonal growth is co-ordinated and occurs synchronously. On their long journey, the habenular axons pass clusters of thalamic neurons (ThEPC), which unlike the habenular neural circuit, establishes commissures, which connect the two halves of the brain. Using a laser to focally ablate these thalamic neurons on one brain hemisphere results in a delay of habenular axon growth on that side and the failure to extend to the midbrain target. Intriguingly, the habenular axons also stop extending on the non-manipulated half of the brain and the neural network fails to develop. This failure is preceded by the disability of thalamic neurons to establish connections to the contralateral side of the brain. Thus, the thalamic neurons are pivotally important for the generation of the habenular neural circuitry across brain hemispheres.
Matthias Carl says: "Carlo Beretta and team did a wonderful job! They really went to explore the limits of state-of-the-art time-lapse imaging and on top of it uncovered an exciting mechanism of neural network formation. I honestly could not believe what I saw. Yet, here it is and this would not have been possible without the dedication of everyone involved."
Curr Biol. 2017 Jan 23;27(2):270-278. doi: 10.1016/j.cub.2016.11.038.
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