Differential olfactory discrimination and performance following stroke induction procedures

Taitum Cothren

Abstract

Stroke is a leading cause of disability in the United States. A stroke can cause both physical and cognitive deficits. Levels of impairment on physical and cognitive functioning depend on the brain structures affected by the stroke. The current study compared the behavioral effects produced by two different stroke induction procedures on an automated Odor Discrimination Task (ODT). Twelve C57BL/6J mice were trained to stability on the ODT, which consists of five odors assigned as target stimuli and one odor assigned as a non-target. Across a series of trials, mice are required to lick in response to target-odors to receive a sucrose reward, and to inhibit licking in response to the non-target odor. Measures derived from the ODT allow for the evaluation of both sensorimotor and cognitive effects. Following training, subjects were counterbalanced into groups based upon performance. Each subject received either a sham operation (n = 4), a photothrombotic stroke (P stroke; n = 4), or a distal middle cerebral artery occlusion (dMCAO; n = 4). The dMCAO models the most common type of ischemic stroke observed in humans. The photothrombotic stroke surgery utilized administration of a light-sensitive dye (Rose Bengal) and a high intensity light stereotactically placed above the primary motor cortex to create microcoagulation. Measures derived from the ODT include sensitivity index, responsivity index, trials completed, short samples (trials terminated prematurely), lick density, hit rate, and correct rejection rate. A 2-way ANOVA of time by condition was used to analyze data for each response parameter. There was a significant time X condition interaction for trials completed (p = 0.008), hit rate (p = 0.007), and lick density during the initial odor exposure period (p < 0.001). Only P stroke led to significantly greater lick density (during the odor release period) compared with baseline; observable on post-surgery day 1 and points up to 2-weeks following surgery. All groups exhibited significant decreases from baseline in trials completed at various points within the post-surgery period. No group evidenced significant differences from baseline with regard to hit rate. Though photothrombotic stroke procedures induced a transitory impact on lick density, performance was similar across conditions by the conclusion of the study (28 days). The lick monitoring procedures of the ODT can be used to detect differential motoric effects of stroke induction procedures.

Faculty Advisor: David MacQueen

Acknowledgment: Holsten, John. Van Leuven, Eric. Murphy, Skylar. Mienzes, Pierson. Prescott, Kimberly. Zeitouni, Megan

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