Bötzinger inhibitory neurons and the control of active expiration

Abstract

Neural circuits controlling breathing in mammals are well organized within serially and functionally interacting brainstem compartments (Del Negro et al. 2018). The core circuit components that constitute the neural machinery for generating respiratory rhythm and shaping inspiratory and expiratory motor patterns are distributed within the ventral respiratory column with the following compartments: parafacial respiratory group and retrotrapezoid nucleus (pFRG and RTN), the Bötzinger complex (BötC), pre-Bötzinger complex (pre-BötC) and the premotor neurons in the rostral and caudal ventral respiratory groups (rVRG and cVRG) (Fig. 1). Additional structures essential for normal breathing include the dorsolateral pons (intertrigeminal region, the Kölliker-Fuse nucleus, and the lateral parabrachial complex) and the dorsal respiratory group (nucleus of the solitary tract) (Del Negro et al. 2018) (Fig. 1). The integrity of the connections between all these regions is necessary for the production of the physiological phases of the breathing pattern (inspiration, post inspiration, and late expiration) and for proper control of the airway muscles that are involved in the slow expiratory airflow after inspiration (Del Negro et al. 2018). Therefore, understanding the arrangement and connections of the respiratory circuitries is essential to know how breathing is generated and adjusted to attend to metabolic and behavioural demands. Under resting conditions, mammalian breathing exhibits a two-phase pattern in which the expiratory phase occurs passively