Organization of the core respiratory network: Insights from optogenetic and modeling studies
Fig 4
Perturbations of the respiratory rhythm by bilateral photostimulation of VGAT-expressing inhibitory neurons within the pre-Bötzinger complex in situ.
(A-F) Representative examples of the effects of short light pulses of different intensity applied at different phases of the respiratory cycle. In each diagram, the upper traces show extracellular recordings from the pre-BötC (pBC) inspiratory activity, the middle traces show integrated pre-BötC activity (∫pBC), and the bottom traces show the laser stimulus application with the laser intensity given below the stimulus. The timing of the photostimulation is indicated in all three traces by blue shading and dashed red lines. (A) Low-intensity (1.0 mW) photostimulation (300 ms) applied during the inspiratory phase did not perturb the ongoing respiratory rhythm. (B) Same low-intensity laser stimulation (as in A) but with longer duration (1 s) to outlast the inspiratory phase did not terminate inspiration, but caused rebound excitation after ending the stimulus which led to an advanced onset of the next inspiratory phase. (C) Low-intensity (1.0 mW) photostimulation (300 ms) applied during the expiratory phase caused rebound excitation after the end of the stimulus leading to an advanced onset of the next inspiratory phase. (D) When the 300 ms, 1.0 mW laser pulse was applied at the end of the expiratory phase, inspiration was delayed for the duration of the stimulus and after the light stimulation was turned off. (E) High-intensity (2.0 mW) photostimulation (300 ms) applied during the inspiratory phase terminated inspiration and elicited delayed rebound excitation of inspiration after the stimulus ended. (F) The same 2.0 mW stimulation applied during the expiratory phase caused rebound excitation after the end of the stimulus leading to an advanced onset of the next inspiratory phase, similar to the examples shown in panels B, C and E. (G) Population data (n = 9, mean ± SEM, ***p ≤ 0.001) showing that the 2.0 mW stimulations reliably terminated inspiration while 1.0 mW stimulations did not. The open circles indicate the average number of terminated inspiratory bursts normalized to the total number of bursts for each animal. (H) The latency between the end of the light stimulus and the onset of the next inspiration was independent of photostimulation intensity (n = 6, mean ± SEM).