Scientists follow brain activity as fish find their dinner
Using a sensitive new imaging molecule, researchers can watch neurons in the larval zebrafish brain spring into action when the fish sees a potential meal, according to a study published 29 January in Current Biology1.
The technique may allow scientists to map which neuronal circuits are involved in particular behaviors.
As they transmit signals, neurons open ion channels along their long projections, which allows an influx of calcium into the cell. Molecules that fluoresce in response to calcium can help trace the path of neuronal activity.
For example, scientists can survey spikes of neuronal activity as transparent zebrafish larvae begin to swim. Most molecules are not sensitive enough to allow real-time monitoring of activity in particular neurons, however.
In the new study, researchers used a modified and highly sensitive version of a calcium indicator that allows them them to restrict its expression to certain neurons. Neurons expressing this molecule in the tectum, a brain region responsible for the visual reflex, light up as they fire.
As a spot of light travels either right to left or top to bottom near the head of a zebrafish, neurons in the tectum spark into action, moving in the corresponding direction. Neurons sensitive to movement and direction probably play a role in the hunt and capture of prey, the researchers say.
Accordingly, these neurons light up as a paramecium — a single-celled organism and a meal for a zebrafish — moves around the head of an immobilized fish. The tectum does not respond if the paramecium is immobile.
If the zebrafish is free to move, neurons towards the back of the tectum light up as the fish goes in for the kill. This suggests that these neurons play a role in prey approach and capture, the researchers say.
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1: Muto A. et al. Curr. Biol. 23, 307-311 (2013) PubMed