<p> Recent research has associated obesity with cognitive impairments and alterations in brain-derived neurotrophic factor (BDNF), with the majority of studies examining this in older adult or aging animals. To expand upon these efforts, two experiments were performed to examine the effects of diet-induced obesity (DIO) on spatial performance and hippocampal BDNF expression in young adult female and male rats. To expand upon these efforts, we examined these effects over dietary interventions of differing durations. To investigate these issues rats (female rats in Experiment 1 and male rats in Experiment 2) were assigned to either a standard chow condition or a DIO condition and remained on these diets for 4-, 8- or 12-weeks. Compared to their chow-fed counterparts, female DIO rats consumed significantly more average weekly calories, weighed significantly more, and exhibited significant alterations in glucose metabolism. However, these obesity-related physiological changes were not associated with concurrent impairments in spatial ability as measured using the Morris water maze, and only the 4-week DIO dietary intervention demonstrated a difference in hippocampal BDNF mRNA expression. Compared to their chow-fed counterparts, male DIO rats consumed significantly more average weekly calories than their chow-fed counterparts, weighed significantly more, and exhibited significant alterations in glucose metabolism. However, obesity-related physiological alterations were not associated with concurrent impairments in spatial ability or differences in BDNF mRNA expression, with the exception of the 12-week DIO animals performing significantly better than their chow-fed counterparts during the reversal probe trial on the final day of training. These findings were unexpected and will be discussed further later in the thesis. </p><p>