Drug Administration

To observe the effect of neutralizing spinal NPY, rabbit isotype control IgG (5 μg in 5 μl sterile saline; Cell Signaling Technology) and rabbit anti-NPY IgG (5 μg in 5 μl sterile saline; Cell Signaling Technology) were intrathecally administrated 1 h prior to each behavioral test. NPY (Tocris) and [Leu31, Pro34]-NPY (LP-NPY, a selective agonist for NPY1R; Tocris) were dissolved in 0.9% sterile saline (vehicle) (Fuhlendorff et al., 1990). Both NPY (0.5 μg in 5 μl sterile saline) and LP-NPY (10 μg in 5 μl sterile saline) were intrathecally injected 15 min before each behavioral test (Hua et al., 1991; Acton et al., 2019). Both histamine and chloroquine were dissolved in sterile saline. Each drug injected was previously prepared and then coded by a laboratory assistant and not the experimenter. One experimenter who operated the drug injection was blinded to the code, and thus the chemical injected, as was another observer who carried out the behavioral tests.