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| Poster #170 Repeated sodium depletion increases sodium consumption and decreases reward sensitivity as assayed by intracranial self-stimulation |
| Rachel M Donka & Jamie D Roitman University of Illinois Chicago, Chicago, IL, United States |
Physiological need states invigorate goal-directed behaviors to restore homeostatic balance, engaging sensory and motivational pathways. Neural circuits that command motivated behaviors are engaged by the positively reinforcing properties of obtaining the needed stimuli or by the alleviation of need-induced negative affect. Previous work from our lab demonstrated that chronic, but not acute, fluid restriction reduced sensitivity to brain stimulation reward. The maintenance of fluid and sodium balance are linked, with sodium need eliciting strong goal-directed behavior. Multiple depletions drive escalating behavior to seek and consume sodium, modulating the palatability of high concentrations of sodium. Unknown are the mechanisms by which changes in need states modulate reward sensitivity, as well as how sensitivity shifts in response to repeated homeostatic challenges. To address this question, we used intracranial self-stimulation (ICSS) in rats with acute sodium depletion induction (furosemide, 10 mg/kg, sc) once per week for four consecutive weeks. Stimulating electrodes were implanted in the medial forebrain bundle and animals were trained to lever press for stimulation (n = 16). Using a rate-frequency protocol we determined the threshold stimulation frequency (theta) that was reinforcing for each subject and measured how sodium depletion altered theta in a within-subjects design. We found increased ICSS theta values, indicating a decrease in reward sensitivity over four sodium depletions. Sodium intake in the 1-hour post ICSS intake period increased across the four depletion sessions. Sodium intake post sodium depletion also increased across weeks. Collectively, these results suggest that repeated sodium depletion decreases reward sensitivity, while driving increased consumption of sodium. |