Chance disfavors the unprepared mind, which may explain why the brains of animals as evolutionarily divergent as zebrafish and mice share neuronal circuits associated with vigilance. Animals lacking these circuits—the neuronal basis of alertness—would likely respond more slowly to threatening stimuli, or propitious stimuli, for that matter, limiting their prospects for survival.
The neural basis of alertness found in zebrafish and mice may also occur in humans, suggested the director of the NIH’s National Institute of Mental Health, Joshua Gordon, M.D., Ph.D. He was commenting on NIH-supported research that used two novel technologies—optogenetics and neural activity screening—to study how brains states are correlated with the activity of neuromodulatory cells. Of primary interest were brain states associated with vigilance.
“Vigilance gone awry marks states such as mania and those seen in posttraumatic stress disorder and depression,” explained Dr. Gordon. “Gaining familiarity with the molecular players in a behavior—as this new tool promises—may someday lead to clinical interventions targeting dysfunctional brain states.”
In this statement, Dr. Gordon was referring to the neural activity screening tool called MultiMAP, or Multiplexed-alignment of Molecular and Activity Phenotypes. MultiMAP was developed by Stanford University researchers, who recently described, in a November 2 article in the journal Cell, how they put it to use.
The article (“Ancestral Circuits for the Coordinated Modulation of Brain State”) detailed how cell types involved in behavior were screened by integrating brain-wide activity imaging with high-content molecular phenotyping and volume registration at cellular resolution. Essentially, the MultiMAP tool was used to record from 22 neuromodulatory cell types in behaving zebrafish during a reaction-time task that reports alertness.
“We identified multiple monoaminergic, cholinergic, and peptidergic cell types linked to alertness and found that activity in these cell types was mutually correlated during heightened alertness,” wrote the article’s authors. “We next recorded from and controlled homologous neuromodulatory cells in mice; alertness-related cell-type dynamics exhibited striking evolutionary conservation and modulated behavior similarly.”
For the first time, MultiMAP makes it possible to see which neurons are activated in a behaving animal during a particular brain state—and subsequently molecularly analyze just those neurons to identify the subtypes and circuits involved.
In this case, the researchers—Karl Deisseroth, M.D., Ph.D., Matthew Lovett-Barron, Ph.D., and colleagues—used the technique to screen activity of neurons visible through the transparent heads of genetically engineered larval zebrafish. They gauged vigilance by measuring how long it took the animals to swish their tails in response to a threatening stimulus.
A molecular analysis revealing subtypes led to identification of six suspect circuits composed of distinct populations of neurons that modulate neuronal activity, only one of which had previously been linked to vigilance. Virtually the same players were operative in follow-up experiments examining such reaction time-related circuitry in the mouse brain. Using optogenetics—another breakthrough exploratory tool developed by Deisseroth and colleagues—the researchers narrowed the field to three circuits that definitively boost alertness in mice, including the one previously known. The other three are thought to play a reportorial rather than regulatory role.