Remote automated delivery of mechanical stimuli coupled to brain recordings in behaving mice

The canonical framework for testing pain and mechanical sensitivity in
rodents is manual delivery of stimuli to the paw. However, this approach
is time consuming, produces variability in results, requires significant
training, and is ergonomically unfavorable to the experimenter. To
circumvent limitations in manual delivery of stimuli, we have created a
device called the ARM (Automated Reproducible Mechano-stimulator). Built
using a series of linear stages, cameras, and stimulus holders, the ARM is
more accurate at hitting the desired target, delivers stimuli faster, and
decreases variability in delivery of von Frey hair filaments. We
demonstrate that the ARM can be combined with traditional measurements of
pain behavior and automated machine-learning based pipelines. Importantly,
the ARM enables remote testing of mice with experimenters outside the
testing room. Using remote testing, we found that mice habituated more
quickly when an experimenter was not present and experimenter presence
leads to significant sex-dependent differences in paw withdrawal and pain
associated behaviors. Lastly, to demonstrate the utility of the ARM for
neural circuit dissection of pain mechanisms, we combined the ARM with
cellular-resolved microendoscopy in the amygdala, linking stimulus,
behavior, and brain activity of amygdala neurons that encode negative pain
states. Taken together, the ARM improves speed, accuracy, and robustness
of mechanical pain assays and can be combined with automated pain
detection systems and brain recordings to map central control of pain.