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Preferred Name


Date of Award

Summer 2016

Document Type


Degree Name

Master of Science (MS)


Department of Biology


Corey L. Cleland


The nociceptive withdrawal reflex (NWR) is a protective reflex that allows mammals to avoid noxious stimuli by withdrawing the affected area of the body away from the stimulus. Although previous studies on non-human mammals showed that the NWR depends on stimulus location and initial posture, these studies were performed on spinalized or anaesthetized animals, which may yield results differing from intact animals. Therefore, the purpose of this study was to determine whether the kinematics of the NWR of the tail depends on stimulus location and initial posture in intact and unanesthetized animals. The NWR was evoked by heat applied to the lateral aspect of multiple locations along the length of the tail in intact and unanesthetized rats. The tail was either initially straightened or rotated/curved. Movement in the horizontal plane was recorded using high speed video. Movement consisted of only two components: rotation around the base of tail and a local bend near the stimulus location, one location rostral to stimulus location. When the tail was initially rotated, but not curved, the direction of tail base rotation reversed; that is, when the tail was straight the tail base rotated away from the stimulus, but when the tail was initially rotated, the tail base rotated into the stimulus. These results suggest the rat uses a simple strategy to withdraw from localized noxious stimuli. Following stimulation, muscle(s) apply rostral-lateral force directly to the segment being stimulated, which results in an active local bend, passive rotation of the more proximal tail base and passive “whipping” of the distal regions of the tail. When the initial posture of the tail is altered by rotating the tail to the side, the reflex movement around the tail base reverses, thus moving the tail into the stimulus but away from the body. The change in direction may arise passively from the altered posture, further simplifying control. Taken together, although the kinematics of the tail movement is complex, these results suggest that the rat uses a simple active and passive kinetic strategy to effectively withdraw its tail from noxious stimuli under various postural conditions.

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