Respiratory pattern reflects state and trait anxiety in rats

In humans, anxiety states are accompanied by alterations in respiratory patterns. Despite this clear association, the link between respiration and anxiety has never been evaluated in experimental animals. The aim of this study was to describe how anxiety states are reflected in the pattern of respiration using genetically diverse rats that differ in their level of innate anxiety. Respiratory rate was recorded in high-anxiety behavior (HAB, n=10) and low-anxiety behavior (LAB, n=10) adult rats using whole-body plethysmography, with a piezoelectric sensor attached to the chamber to simultaneously monitor physical activity. Rats were introduced in the pletysmograph and recorded for 40 min. Subsequently, they were exposed to acoustic (predator call), olfactory (cat fur odor) and psychophysical (restraint) stressful stimuli, with a 5-min intervals between each stimulus. During the first 20 min in the pletysmograph, HAB rats spent significantly less time ay high respiratory rates (400–600 cpm) compared to LABs, which likely reflected suppression of the exploratory sniffing in the new environment. At the end of 40-min baseline period, respiratory rate was higher in HAB (92±6 cpm) compared to LAB (62±5 cpm, p<0.05) rats. Exposure to the stressful stimuli produced similar tachypnoeic responses in both groups. However, HAB's respiratory response to the second acoustic stimulus failed to habituate. In addition, HAB rats showed higher number of sighs (augmented breaths) both during the first 40 minutes of recording (HAB=19±1 vs. LAB=10±1, p<0.05) and under any stress condition. We conclude that: i) high-anxiety behavior rats show emotion-related respiratory changes (elevated basal respiratory rate, increase in the number of sighs, reduced tachypnoea/sniffing in novel environment and no habituation of the respiratory response to repetitive stimuli) that resemble those observed in patients with anxiety; and ii) changes in respiratory patterns represent new and promising way for assessing anxiety states in preclinical studies.