Rodríguez-Romaguera, Ung, Stuber and colleagues examined a brain region within the amygdala called the BNST (bed nucleus of the stria terminalis), which has been linked in prior research to fear and anxiety-like behaviors in mice. Increasingly, scientists view this region as a promising target for future psychiatric drugs. In this case, the researchers zeroed in on a set of BNST neurons that express a neurotransmitter gene, Pnoc, known to be linked to pain sensitivity and more recently to motivation.

The team used a relatively new technique called two-photon microscopy to directly image BNST Pnoc neurons in the brains of mice while the mice were presented with noxious or appealing odors – stimuli that reliably induce fear/anxiety and reward behaviors, respectively, along with the appropriate arousal responses. In this way, the scientists found that activity in these neurons tended to be accompanied by the rapid dilation of the pupils of the mice when the animals were presented with either of these odor stimuli.