Examining the role of inhibition in establishing the three respiratory phases in a horizontal slice (712.14)

Breathing is composed of three phases: inspiration (I), post‐inspiration (E1), and active expiration (E2). Essential for the generation of breathing is the preBtzinger complex (preBtC). Isolated in transverse slices (TS) the preBtC generates predominantly inspiratory activity which can be recorded as population activity. Yet, the preBtC is only one part of a wider respiratory network that is distributed along the rostro‐caudal axis of the ventral respiratory column (VRC) in the ventrolateral medulla of the brainstem. The interactions between this extended respiratory network and how it generates different forms of expiration are not entirely understood. We recently developed a novel horizontal slice (HS) preparation (CD1 mice, p5‐8) that preserves the entire VRC bilaterally while maintaining amenability for intracellular manipulation. Inspiratory population bursts from the HS preBtC are broader compared to the TS and appear to consist of two components. Burst durations in the HS decrease in the presence of 1µM strychnine, and we hypothesize that the increased burst durations reflect the glycine‐dependent partial separation of the I and E1 phases. Moreover, we discovered an additional, yet conditional rhythm rostral to the preBtC that is tightly coupled to the inspiratory rhythm. Based on the location, the phase, and the low spontaneous frequency of the rostral rhythm, we hypothesize that it represents the E2 phase. The rostral rhythm can be stimulated with 4uM norepinephrine or hypoxia and can be tightly coupled to fictive sighs in the HS. The addition of 10µM gabazine synchronizes the two rhythms suggesting that the separation of I and E2 is GABA‐dependent. Thus, the horizontal slice offers a novel approach to examining the role of inhibition in generating expiration. Grant Funding Source : Supported by the NIH