Figure 3.

Respiratory rhythm entrainment by the cyclic activation of spinal low-threshold somatic afferent pathways. A, Left, Schematics of isolated brainstem/spinal cord preparations showing electrode placements for extracellular ventral root recordings and DR stimulation in each experimental condition. Right, Cervical (C5) ventral root activity under control conditions and during repetitive electrical stimulation of a cervical (C8), thoracic (T7), or sacral (S2) DR (DR stim., bottom traces). Respiratory rhythm entrainment occurred during cervical or lumbosacral DR stimulation, but not with thoracic DR activation. B, Expanded traces of spontaneous inspiratory (C5) and expiratory (L1) bursts (B1) and of an equivalent respiratory cycle elicited by a single C8 DR train stimulation (B2). C, Histograms of the mean respiratory cycle period (vertical bars) and corresponding SEM (vertical lines) in control condition (unfilled bar) and during cyclic train stimulation of a cervical, thoracic, or lumbosacral DR (filled bars). Data were pooled from seven preparations in each case. ***p < 0.001. D, Top, Horizontal bar plots indicating mean levels of stimulus threshold intensity for respiratory entrainment by individual DRs along the spinal cord. Vertical lines: SEM; *p < 0.05; ***p < 0.001. Bottom, Histograms (expressed as percentage of preparations) indicating the ability of the DR afferents to entrain spontaneous fictive respiration. C, cervical; T, thoracic; L, lumbar; S, sacral.