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Date of Award
Bachelor of Science (BS)
Department of Biology
Corey L. Cleland
Animals have the ability react to noxious stimuli from the environment via a reflex pathway known as the nociceptive withdrawal reflex (NWR). The NWR is a spinal reflex that protects the body from stimuli that may be tissue damaging. In addition, the NWR is known to be supraspinally modulated, which alters the strength of response. Previous studies on the NWR have shown an influence of both stimulus location and initial posture on the NWR. The studies regarding the influence of initial position on the NWR, however, are more limited. Most of the research has been conducted on humans, and in no case has there been studies using intact, unanesthetized rats. The fundamental question this experiment aims to address is whether the initial posture can affect the NWR in intact, unanesthetized rats. Noxious stimuli were provided in the form of heat delivered by a laser for each of the fifteen trials for each rat studied (n=7). The stimuli were aimed at five specific locations on the surface of the rat paw, and the response was recorded with a high speed videocamera positioned under the paw. The response magnitude and direction of the paw movement were quantified by identifying the initial (before NWR) and final (after NWR) position of the raw paw. Similarly, the change in foot angle was also quantified for each of the trials. The results reveal that, unexpectedly, stimulus location did not significantly affect the magnitudes or direction of movement, or the change in foot angle. However, the initial location of the foot did have a significant effect on the withdrawal movement, as stimulation of the foot while it was positioned laterally from the body resulted in medial movement of the foot or stimuli of the foot while it was positioned medially from the body resulted in lateral movement of the foot. In a similar pattern, stimulating the foot while it was positioned rostrally in relation to the body resulted in movement in the caudal direction and stimulating the foot while it was positioned caudally in relation to the body resulted in movement in the rostral direction. The initial angle of the foot was also shown to influence the final angle of the foot, as the angle of the foot changed very little throughout the withdrawal. The results of this study on intact, unanesthetized rats demonstrate that there is evidence that initial position of the rat paw influences the NWR. However, this study was unable to demonstrate that stimulus location influences the NWR. This finding raises the question why stimulus location is not a factor in the rat paw, but has been shown to be a factor in the rat tail and other mammalian studies.
Chrzan, Christopher Anthony II, "Influence of initial position and stimulus location of the paw on the nociceptive withdrawal reflex in intact rats" (2013). Senior Honors Projects, 2010-current. 401.