Neuronal network mediating respiratory activation in response to alerting stimuli and stress

Neuronal structures that mediate cardiovascular activation in response to alerting and stressful stimuli have received a lot of attention in the previous research; yet neuronal networks that mediate autonomic respiratory activation in response to such stimuli have never been properly investigated. In the current study 3 groups of Wistar rats (n = 8 each) received microinjections of GABA_A agonist Muscimol or saline via bilateral guide cannulas targeting the dorsomedial hypothalamus (DMH), the medial prefrontal cortex (mPFC) or the central amygdala (CAm) and then were subjected to respiratory assessment using whole-body plethysmography with presentation of 6 alerting acoustic stimuli (white noise, 0.5 msec, 40-90 dB) and restraint stress. Acoustic stimuli produced brief transient increases in respiratory rate, proportional to the stimulus intensity, ranging from 12 ± 9 cpm increase over baseline in response to a 40 dB stimulus to 276 ± 67 cpm increase in response to a 90 dB stimulus. Inhibition of the DMH by Muscimol almost entirely abolished respiratory responses to the alerting stimuli. Inhibition of the mPFC did not affect amplitudes of the responses, but increased latency of responses to 70 and 80 dB stimuli (p = .014 & .024, respectively), while inhibition of the CAm did not affect latency of responses, but reduced amplitude of responses to 70, 80 and 90 dB stimuli (p = .009, .021 & .043, respectively). Restraint stress significantly elevated respiratory rate in all groups from 98 ± 12 to 155 ± 7 cpm (p < .001). Inhibition of the CAm reduced this stress-provoked increase in respiratory rate during the first 5-minute interval of restraint from 57 ± 12 to 12 ± 15 cpm (p = .024), while inhibition of the mPFC reduced it during the last 5-minute interval of restraint from 40 ± 10 to 11 ± 4 cpm (p = .02). In line with previous studies, we conclude that integrity of the DMH is essential for autonomic responses to alerting stimuli, while the CAm contributes to the magnitude of responses and the mPFC facilitates rapid responding.