Objectives: Clinical models have outpaced animal models assessing orofacial pain. Orofacial pain animal models are needed to assess new therapies. The objective of this study was to develop an accurate, unbiased operant conditioning device to assess mechanical orofacial pain in rats (adapted from a previously developed device used to detect thermal orofacial pain in rats).
Methods: An aversive stimuli (air puffs) was placed between a reward (sweetened condensed milk) and a rat separated by a wall with a hole giving access to the reward (see picture). Attempts and successes to reach the reward were measured. The number and duration of attempts were measured by a beam-breaker. The number and duration of rewards were measured by the current change when the tongue licked the sipper. Both signals were outputted to a computer not requiring a human in the room and a camera was used to confirm beam-breaks and sipping. Number and duration of beam-breaks and sipping were used to assess the level of aversion elicited by the low pressure (~15psi) and high pressure (~45psi) air puffs. Previous research showed 45psi as the point where air pressure becomes aversive in the rat orofacial area.
Results: The number and duration of beam-breaks and sipping with the high pressure air puff (~45psi) decreased as compared to the low pressure air puff (~15psi). The number and duration of beam-breaks decreased by 15% and 30%, respectively (N=2). The number and duration of sips decreased by 33% and 18%, respectively (N=2).
Conclusions: This novel orofacial behavioral device provides an unbiased, accurate method that can be used in the future to assess orofacial pain and the effect of analgesics.