Noeud vital for breathing in the brainstem: gasping—yes, eupnoea—doubtful

Abstract

For the past 200 years, various regions of the brainstem have been proposed as a 'noeud vital' for breathing-a critical region which, when destroyed, results in an irreversible cessation of breathing and death. Complicating this search for a noeud vital is the extensive network of neurons that comprises the brainstem respiratory control system of pons and medulla. Does a cessation of breathing following ablation of any region reflect the removal of a critical set of neurons whose activity generates the respiratory rhythm or does it reflect the interruption of one component of the neuronal circuit, such that this circuit cannot function, at least temporarily? An additional complication is that in contemporary neuroscience, a number of in vitro preparations have been introduced for the study of the generation of the respiratory rhythms. However, how are the rhythms that these preparations generate related to normal breathing? Are these rhythms similar to those of gasping, which is recruited when normal, eupnoeic breathing fails, or are these rhythms unique to the in vitro preparation and not related to any breathing pattern in vivo?

Brainstem respiratory networks: building blocks and microcircuits

“…Importantly, similar transformations can also occur when the intact network goes through various physiological and/or metabolic disturbances [7]. For example, apneusis, a two-phase inspiratory–expiratory pattern [32], and gasping, one-phase inspiratory oscillations originating in the pre-BötC [33], are evoked during hypocapnia and severe hypoxia, respectively. These findings are important because researchers have been attempting to explain the neural substrates and mechanisms for these established motor patterns for decades.…”

Computational Models and Emergent Properties of Respiratory Neural Networks

“…These neurons are driven by the pre-BötC excitatory neurons and are inhibited during expiration by the BötC inhibitory neurons (18, 72, 299); both of these inputs along with other modulatory drives shape and control the characteristic ramping pattern of inspiratory rVRG activity. Thus, the rVRG is also a compartment with multiple convergent input drives essential for inspiratory pattern formation but in contrast to the pre-BötC, this neuronal population as a whole does not appear to have intrinsic rhythmogenic capability (310) although neurons with intrinsic rhythmic bursting properties have been identified in this region (322). …”

Brainstem: neural networks vital for life

“…Does the rhythm originate from a discrete group of pacemaker neurons that display inherent rhythmicity of firing (as, for example, in cardiac muscle) (Smith et al 2009;St John 2009). Or does it result from the integrated activity of diffuse networks of inspiratory and expiratory neurons that excite and inhibit each other?…”

“…How prevalent are chemically and electrically mediated synaptic transmission and what transmitters are used (Cifra et al 2009)? Related problems concern whether multiple sites for rhythm generation exist, and if so how many there are and where they are situated in the pons and/or medulla (Nuding et al 2009;Smith et al 2009;St John 2009).…”