Three levels of enhanced inspired CO2 or fasted-state on stress response activation in behaviorally inhibited humans and rats

Abstract

Behavioral inhibition (BI) is believed to be a genetically determined trait that affects roughly 33% of the human population. These individuals tend to respond to stressful situations differently than their non-behaviorally inhibited (NBI) counterparts. In the rodent population, a similar behavioral/stress model exists. The Sprague-Dawley (SD) strain often acts as a “control” among rat strains and can be considered to be the rat equivalent to NBI individuals, and the Wistar-Kyoto (WKY) strain is the rodent equivalent to BI individuals. The differences in the activation of the sympathetic nervous system between chronically stressed and non-stressed populations remain unknown. Our current study tested the hypothesis BI individuals and WKY rats will have increased stress responses. In humans, we tested physiological responses to increasing levels of carbon dioxide (CO2) through analyses of breathing, heart rate, and blood pressure. The Adult Measure of Behavioral Inhibition (AMBI) survey was used to determine the presence of BI. A 15-minute control period baseline was completed followed by an acquisition period of five minutes of each 3%, 5%, and 7% CO2, respectively. Preliminary results were analyzed through a CO2 sensitivity slope (inspired minute ventilation ((L/min) / end-tidal CO2) and show that BI individuals had increased, exaggerated responses to the respiratory stressors across the three levels of enhanced CO2. In the rodent model, signaled lever-press avoidance was used to examine the activation of stress responses. Rats were trained to avoid mild foot shock using a tone warning signal. As demonstrated previously, WKY rats acquired a higher level of avoidance responses. Rats were then food-deprived overnight and subsequently retested on signal lever-press avoidance. Food deprivation did not affect the high rate of avoidance seen in WKY rats; however, food deprivation increased the SD rate of avoidance to nearly the level of WKY rats. Our data suggest that WKY rats do not respond to food deprivation when paired with lever-press avoidance; however, SD rats do. Simply, the addition of a stressor causes SD rats to behave more similarly to their WKY counterparts. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.