Browsing by Subject "plasticity"
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Item CHARACTERIZATION OF COCAINE-CONDITIONED LOCOMOTOR RESPONSES BY MODULATION OF ENVIRONMENTAL CONTEXT AND NEURAL PLASTICITY-SIGNALING PATHWAYS(2014-03) Nguyen, Jacques D.; Forster, Michael J.Rodent models are commonly used for the study of substance abuse and addiction. The objective of this study was to characterize the cocaine-conditioned locomotor response, a behavioral phenomenon observed in mice, following an acute injection of cocaine, and to determine its mechanism of action for potential therapeutic targeting. Compounds known to modulate neural plasticity were evaluated for their ability to affect the acquisition and expression of the conditioned behavior. Purpose (a): In rodents, increase in locomotion is a hallmark effect of psychostimulant exposure and conditioning that is associated with activation of mesocorticolimbic dopamine signals mediating reinforcing/rewarding actions. The objective of this study was to characterize the cocaine-conditioned locomotor response following an acute injection of cocaine, specifically the modulating roles of environmental context and plasticity-associated signals. Methods (b): Cocaine (40mg/kg) was administered to different groups of Swiss-Webster, C57Bl/6, or DBA2 mice via intraperitoneal injection (i.p.), in either a locomotor activity testing apparatus or the home cage, 2 hours following an activity test under saline. Mice placed in the testing chambers were given 30 minutes to explore freely and locomotion was monitored using a Digiscan photocell apparatus. A conditioned effect of cocaine was inferred by an increase in horizontal activity counts relative to home cage cocaine controls during a test in the same apparatus on the following day. Compounds known to modulate neural plasticity-associated signaling cascades were evaluated for their ability to affect the acquisition and expression of cocaine-conditioned locomotor response, using a two-day protocol. Mice were administered haloperidol (0.05-1 mg/kg), dizocilpine (0.01-0.25mg/kg), nifedipine (0.1-10 mg/kg), cycloheximide (2.5-10mg/kg), or vehicle, prior to placement into the activity chambers on the test day for expression or prior to acquisition day. Results (c): Haloperidol (0.25-1 mg/kg) inhibited expression of the cocaine-conditioned locomotion, though failed to alter acquisition of the behavioral response. Dizocilpine (0.05-0.25 mg/kg) attenuated acquisition and exacerbated expression. Nifedipine had no effect on the conditioned locomotor response. Cycloheximide (2.5-10 mg/kg) attenuated acquisition of the conditioned response. Conclusions (d): These findings suggest that plasticity-dependent signaling pathways mediate associations of context following acute cocaine exposure and are necessary for the acquisition and expression of the cocaine-conditioned locomotor response.Item The Effect of Dietary Loading on Structural Determinants of Force Production in the Rat Masseter(2020-05) Rossiter, Jeffrey A.; Menegaz, Rachel A.; Maddux, Scott D.; Reeves, Rustin E.Rossiter, Jeffrey A., The Effect of Dietary Loading on Structural Determinants of Force Production in the Rat Masseter. Master of Science in Medical Sciences - Anatomy, May 2020. Biomechanical loading associated with feeding is known to direct cranial bone growth, however less is known about its effects on masticatory muscle growth and performance. Peak muscle contractile forces are determined by a combination of factors including total muscle mass, fiber length, and fiber type. Here, we test two hypotheses: that mechanically challenging diets will (1) increase the physiological cross-sectional area (PCSA), an estimate of maximum contractile force at tetanus, and (2) increase the number and proportion of type II (fast-twitch) muscle fibers in the masseter of the rat. Sprague-Dawley rats were raised on either a hard/tough (overuse) diet or a soft (underuse) diet (n=5/cohort). The superficial masseters were dissected and photographed using a trifocal stereo microscope, and muscle fiber length (6/individual) were measured using ImageJ. Muscle volumes were calculated from in-situ diffusible iodine-based contrast-enhanced μCT scans. Muscles were stained using an IHC protocol for the fast isoform of myosin heavy chain, allowing the number and areas of type II (stained) and type I (unstained) fibers to be quantified in ImageJ. Results from this study do not support our hypotheses, most likely due to the small sample sizes (n=5/treatment group) available for this study. Paradoxical results were found, with rats raised on a soft diet tending to have longer superficial masseter muscle fibers and more type II muscle fibers with larger cross-sectional areas in the posterior masseter. Rats raised on a hard diet tend to have larger masseter muscle volumes. However, these trends were not statistically significant (p > 0.05). Mechanically challenging diets tend to be associated with greater masticatory muscle volumes and thus increased PCSA. The fiber type results from the posterior masseter (with more deep masseter fibers) were the opposite of those previous results from the middle masseter (with more superficial masseter fibers) in the same animals. Future studies with increased sample sizes are needed to better understand the structural determinants of force production in the rat masseter.