Search

Maintaining constant CO2 and H(+) concentrations in the arterial blood is critical for life. The principal mechanism through which this is achieved in mammals is the respiratory chemoreflex whose circuitry is still elusive. A candidate element of this circuitry is the retrotrapezoid nucleus (RTN), a collection of neurons at the ventral medullary surface that are activated by increased CO2 or low pH and project to the respiratory rhythm generator. Here, we use intersectional genetic strategies to lesion the RTN neurons defined by Atoh1 and Phox2b expression and to block or activate their synaptic output. Photostimulation of these neurons entrains the respiratory rhythm. Conversely, abrogating expression of Atoh1 or Phox2b or glutamatergic transmission in these cells curtails the phrenic nerve response to low pH in embryonic preparations and abolishes the respiratory chemoreflex in behaving animals. Thus, the RTN neurons expressing Atoh1 and Phox2b are a necessary component of the chemoreflex circuitry.

The article talks about the CO2 and H+ concentrations in the arterial blood. The key element of this circuitry is the retrotrapezoid nucleus (RTN) that is activated by increased CO2 or low pH and project to the respiratory rhythm generator. Here, intersectional genetic strategies to lesion the RTN neurons defined by Atoh1 and Phox2b expression. Glutamatergic transmission in cells curtails the phrenic nerve response to low pH.

Key points The respiratory oscillator of the pre-Bötzinger complex (preBötC) can generate distinct inspiratory motor patterns underlying eupnoeic and sigh-related rhythmic activities., The preBötC can generate 'fictive' eupnoea at embryonic stages, but its ability to also generate sigh-like activity remains unexplored at prenatal stages., Here, using mouse brainstem slice preparations, we show that sigh-like activity emerges during embryonic development but later than eupnoeic rhythmogenesis. Inspiratory cells active during the latter are also active during fictive sighing, although a small subset of neurons was found to fire exclusively during sighs. Effective glycinergic inhibitory signalling is also required for sigh generation., We conclude that the developmental emergence of a sigh-generating capability occurs after the onset of eupnoeic rhythmogenesis and requires an appropriate maturational state of chloride-mediated glycinergic synaptic transmission., Abstract In mammals, eupnoeic breathing is periodically interrupted by spontaneous augmented breaths (sighs) that include a larger-amplitude inspiratory effort, typically followed by a post-sigh apnoea. Previous in vitro studies in newborn rodents have demonstrated that the respiratory oscillator of the pre-Bötzinger complex (preBötC) can generate the distinct inspiratory motor patterns for both eupnoea- and sigh-related behaviour. During mouse embryonic development, the preBötC begins to generate eupnoeic rhythmicity at embryonic day (E) 15.5, but the network's ability to also generate sigh-like activity remains unexplored at prenatal stages. Using transverse brainstem slice preparations we monitored the neuronal population activity of the preBötC at different embryonic ages. Spontaneous sigh-like rhythmicity was found to emerge progressively, being expressed in 0/32 slices at E15.5, 7/30 at E16.5, 9/22 at E17.5 and 23/26 at E18.5. Calcium imaging showed that the preBötC cell population that participates in eupnoeic-like discharge was also active during fictive sighs. However, patch-clamp recordings revealed the existence of an additional small subset of neurons that fired exclusively during sigh activity. Changes in glycinergic inhibitory synaptic signalling, either by pharmacological blockade, functional perturbation or natural maturation of the chloride co-transporters KCC2 or NKCC1 selectively, and in an age-dependent manner, altered the bi-phasic nature of sigh bursts and their coordination with eupnoeic bursting, leading to the generation of an atypical monophasic sigh-related event. Together our results demonstrate that the developmental emergence of a sigh-generating capability occurs after the onset of eupnoeic rhythmogenesis and requires the proper maturation of chloride-mediated glycinergic synaptic transmission. [ABSTRACT FROM AUTHOR]

The article talks about the CO2 and H+ concentrations in the arterial blood. The key element of this circuitry is the retrotrapezoid nucleus (RTN) that is activated by increased CO2 or low pH and project to the respiratory rhythm generator. Here, intersectional genetic strategies to lesion the RTN neurons defined by Atoh1 and Phox2b expression. Glutamatergic transmission in cells curtails the phrenic nerve response to low pH.