Every nerve cell of a zebrafish’s brain monitored at the same time to identify alertness neurons brian wang | 6 November 2017 Stanford researchers were able to simultaneously monitor activity in every nerve cell of a zebrafish’s brain and determine which types of neurons were tied to alertness.
Extending findings to mice They extended their findings to mice confirming that the evolution left this system similar in mammals whose ancestors split from those of zebrafish hundreds of millions of years ago.
It let them track the activity of nearly every neuron in the zebrafish brain and then identify the cell type of every neuron of interest — the crucial step in determining which neuronal circuits are participating in the induction of a brain state such as alertness.
“We looked at every neuron in the fish’s brain during life, when those cells were actively firing, and learned which cells were most active at moments when we knew that the fish was most alert,” said Deisseroth.
“Then, after the fish’s brain tissue was preserved with a fixative without altering relative positions of cells within the fish’s head, we could target those neurons with molecular probes and determine their cell types.” In particular, the investigators wanted to explore the activity of the brain’s neuromodulatory circuitry.
Different types of neuromodulatory neurons can be distinguished not only by the different kinds of substances they secrete, such as dopamine, acetylcholine and serotonin, but also by various biological markers, such as proteins that appear in or on one but not another neuromodulatory cell type.
They carved the gel away from the fish’s tail, whose movements would be key to their experiments.
The time elapsed between each exposure and the consequent swishing of the fish’s tail — the animal’s reaction time — was measured.
Guided by their findings in zebrafish, the researchers then targeted the equivalent neuronal populations in the much more complex brains of mice.
Other cell types correlated with alertness did not directly influence the behavior; Deisseroth said he thinks these neuromodulatory circuits, rather than directly triggering alertness, report on its status to other brain circuits.

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