Respiration and emotion: how and where are they linked?

The link between respiration and emotions is well documented in humans, but animal studies addressing this issue are limited. The current project aims to systematically examine respiratory responses to stressors and stimuli of various intensity and length in rats, compare and correlate these responses with cardiac responses and behavioural indices of anxiety and lastly to investigate central neuronal pathways that mediate them. In the first chapter we show that respiratory responses to brief changes in arousal are more sensitive than traditionally used cardiac responses. Furthermore, respiration during the novelty stress is highly correlated with behavioural indices of anxiety in rats. The subsequent three chapters investigate involvement of the dorsomedial hypothalamic area, the amygdala and the prelimbic prefrontal cortex in mediating respiratory responses to brief and prolonged stimuli of various intensities. This is achieved by examining the effects of inhibition of the target areas with a microinjection of GABAA agonist muscimol. Inhibition of the dorsomedial hypothalamic area abolished respiratory response to the novelty and restraint stress protocols and also significantly inhibited responses to the brief acoustic stimuli. Blockade of the amygdala significantly inhibited responses to the high-intensity stressors of both brief (70-90dB acoustic stimuli) and prolonged (restraint) duration, but had little effect on responses to the low-intensity stimuli (novelty stress and 40-70dB acoustic stimuli). Lastly, inhibition of the prelimbic prefrontal cortex significantly inhibited the respiratory responses to the prolonged stressors (restraint and novelty stress), but had no effect on responses to brief stimuli (acoustic stimuli). Overall, our findings suggest that (i) assessment of respiratory response can be used as a novel index of anxiety in rats; (ii) respiratory rate is more sensitive to changes in arousal than traditionally used heart rate, which has implications for the definition of an orienting response as it is currently defined only in terms of heart rate. Lastly, (iii) we show that the dorsomedial hypothalamic area and the amygdala have critical roles in mediating stress-induced respiratory changes.