Senior Honors Projects, 2010-current

Preferred Name - First Author

Giavanna Verdi

Date of Award

Spring 2017

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Biology

Advisor(s)

Dr. Corey L. Cleland

Abstract

Mammals rapidly withdraw their hind limb in response to noxious stimulation, which is a protective movement known as the nociceptive withdrawal response (NWR). The NWR has been previously studied in spinalized, decerebrated and anesthetized non-human and human mammals; however, there is minimal information on the NWR in intact, unanesthetized non-human mammals.

The first specific aim was to identify the factors that determine the direction and magnitude of the NWR in intact, unanesthetized rats. Based on previous studies, we hypothesized that the location of stimulation and the initial position of the paw preceding the NWR will influence the direction and magnitude of the NWR. Rats were mechanically stimulated (“Von Frey” monofilament or 30-gauge needle) at five spots widely distributed over the plantar surface of the hind, left paw. In response to heat or mechanical stimulation to the plantar surface of the paw, rats withdraw and then replace the stimulated paw on the surface. The NWR was quantified as the vector between the initial and final positions of the stimulated paw. Unexpectedly, stimulus location did not significantly influence the direction of the response, falsifying our hypothesis. However, the initial position of paw was variable, suggesting an influence on the direction of response. Correlation between the initial position and the change in position rostral/caudally and lateral/medially revealed a significant and inverse effect on response direction. Thus, if the paw was initially rostral, it would move caudal after stimulation; if the paw was initially caudal, it would move rostral.

Second, after determining that the direction of the NWR depended on the initial position of the paw, we tested whether the rat used proprioceptive sensory feedback or corollary discharge to identify the position of the paw prior to stimulation. Based on previous studies, we hypothesized that proprioceptive sensory feedback, rather than corollary discharge, would underlie the dependence on initial paw position. Rats were stimulated by heat with an infrared laser to a single region of the paw, which was placed on an independently movable glass plate. The plate was repositioned rostral-caudally (forward-backward) just before evoking the NWR to dissociate proprioceptive sensory feedback from corollary discharge. The NWR was unaffected by repositioning the paw prior to the evoking the NWR, consistent with proprioceptive sensory feedback being used by the rat to determine the direction and magnitude of the NWR.

Taken together, our results suggest the central nervous system in intact rats primarily uses proprioceptive information about limb posture, but not stimulus location, to determine the direction of the NWR movement. Thus, the NWR appears designed to both maintain posture, as well as protect the paw from injury. Since the NWR is the most widely used clinical test of reflexes, our results may enable improved understanding, diagnosis and treatment of neurological diseases and trauma.

 
 

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