Purinergic signaling mediates neuroglial interactions to modulate sighs

Isoproterenol modulates expiratory activities in the brainstem spinal cord preparation in neonatal mice in vitro

Motor behaviors such as breathing required temporal coordination of different muscle groups to insured efficient ventilation and provide oxygen to the body. This action is the result of interactions between neural networks located within the brainstem. Inspiration and expiration depend at least in part on interactions between two separate oscillators: inspiration is driven by a neural network located in the preBötzinger complex (PreBötC) and active expiration is driven by a network in the parafacial respiratory group (pFRG). Neurons of the pFRG are silent at rest and become active when the respiratory drive increased. This study investigated the temporal coordination between the brainstem respiratory network and the lumbar spinal network that generates spontaneous activities that is different of the induced fictive locomotion. The remaining question is how these activities coordinate early during the development. Results of this study show that brainstem networks contribute to the temporal coordination of the lumbar spontaneous activity during inspiration since lumbar motor activity occurs exclusively during the expiratory time. This study also investigated the role of the β-noradrenergic modulation on the respiratory activities. β-noradrenergic receptors activation increased the frequency of the double bursts and increased expiratory activity at the lumbar level. These results suggest interactions between brainstem and spinal networks and reveal a descending drive that may contribute to the coordination of the respiratory and lumbar spontaneous activities.

Brainstem astrocytes regulate breathing and may affect arousal state in rats

Variations in arousal levels can impact respiratory patterns. The mechanisms by which breathing behaviors can influence arousal state is not fully understood. In this study, we investigated the role of astrocytes in the preBötzinger complex (preBötC) in modulating arousal states via breathing in adult conscious rats. Using viral vector tools, we selectively interfered with astrocytic signaling in the preBötC. Rats with inhibited astrocytic signaling exhibited slower breathing rates and behaviors indicative of a calmer state, whereas enhanced purinergic signaling in preBötC astrocytes led to faster breathing and heightened arousal. Our findings reveal a key role for an astrocyte-mediated mechanism in the preBötC that influences both respiratory behaviors and higher-order brain functions like arousal, suggesting a bidirectional link between breathing behaviors and mental states.

Inspiratory and sigh breathing rhythms depend on distinct cellular signalling mechanisms in the preBötzinger complex

Breathing behaviour involves the generation of normal breaths (eupnoea) on a timescale of seconds and sigh breaths on the order of minutes. Both rhythms emerge in tandem from a single brainstem site, but whether and how a single cell population can generate two disparate rhythms remains unclear. We posit that recurrent synaptic excitation in concert with synaptic depression and cellular refractoriness gives rise to the eupnoea rhythm, whereas an intracellular calcium oscillation that is slower by orders of magnitude gives rise to the sigh rhythm. A mathematical model capturing these dynamics simultaneously generates eupnoea and sigh rhythms with disparate frequencies, which can be separately regulated by physiological parameters. We experimentally validated key model predictions regarding intracellular calcium signalling. All vertebrate brains feature a network oscillator that drives the breathing pump for regular respiration. However, in air-breathing mammals with compliant lungs susceptible to collapse, the breathing rhythmogenic network may have refashioned ubiquitous intracellular signalling systems to produce a second slower rhythm (for sighs) that prevents atelectasis without impeding eupnoea. KEY POINTS: A simplified activity-based model of the preBötC generates inspiratory and sigh rhythms from a single neuron population. Inspiration is attributable to a canonical excitatory network oscillator mechanism. Sigh emerges from intracellular calcium signalling. The model predicts that perturbations of calcium uptake and release across the endoplasmic reticulum counterintuitively accelerate and decelerate sigh rhythmicity, respectively, which was experimentally validated. Vertebrate evolution may have adapted existing intracellular signalling mechanisms to produce slow oscillations needed to optimize pulmonary function in mammals.