Orofacial operant behavioral outcomes at cooling temperatures in sham and ION-CCI rats. A) Left image shows that a sham rat was drinking milk while its cheeks contacted the thermal module. Middle and right images show that an ION-CCI (chronic constrictive nerve-injury induced by infraorbital nerve ligation) rat was biting the thermal module (middle) or reaching the nipple of the milk bottle with its front paw. The thermal module was set at 17 °C. B&C) Two sample traces show the automatic recordings of drinking behavior in a testing period of 10 min in a sham rat (B) and an ION-CCI rat (C). The thermal module was set at 17 °C in both B and C. Orofacial contacts were indicated by “on” and withdraws indicated by “off”. D&E) Summary of total contact time (D) and total contact number (E) in sham (open bars, n=7) and ION-CCI group (solid bars, n=7). The orofacial operant tests were performed with thermal module set at 24 °C, 17 °C, and 12 °C. Rats were tested during the postoperative period of 2 weeks to 6 weeks. Data represent Mean ± SEM; * p<0.05; ** p<0.01.