Laser ablation of Dbx1 neurons in the pre-Bötzinger complex stops inspiratory rhythm and impairs output in neonatal mice.

Xueying Wang,John A Hayes,Hanbing Song,Gregory D Funk,Christopher A Del Negro,M Drew Lamar,Andrew Kottick,Nikolas C Vann,Maria Cristina D Picardo,Victoria T Akins,Ann L Revill

doi:10.7554/elife.03427

Xueying Wang, John A Hayes + Show 9 more

Open Access

https://doi.org/10.7554/elife.03427

Copy DOI

Abstract

To understand the neural origins of rhythmic behavior one must characterize the central pattern generator circuit and quantify the population size needed to sustain functionality. Breathing-related interneurons of the brainstem pre-Bötzinger complex (preBötC) that putatively comprise the core respiratory rhythm generator in mammals are derived from Dbx1-expressing precursors. Here, we show that selective photonic destruction of Dbx1 preBötC neurons in neonatal mouse slices impairs respiratory rhythm but surprisingly also the magnitude of motor output; respiratory hypoglossal nerve discharge decreased and its frequency steadily diminished until rhythm stopped irreversibly after 85±20 (mean ± SEM) cellular ablations, which corresponds to ∼15% of the estimated population. These results demonstrate that a single canonical interneuron class generates respiratory rhythm and contributes in a premotor capacity, whereas these functions are normally attributed to discrete populations. We also establish quantitative cellular parameters that govern network viability, which may have ramifications for respiratory pathology in disease states.

Highlights

Central pattern generator (CPG) circuits give rise to common behaviors such as swimming, walking, and breathing (Grillner, 2006; Grillner and Jessell, 2009; Kiehn, 2011)
The pre-Bötzinger complex (preBötC) adjoins the semi-compact division of the nucleus ambiguus; the ventral border of the preBötC is orthogonal to the dorsal boundary of the principal sub-nucleus of the inferior olive (IOPloop) (Ruangkittisakul et al, 2011, 2014)
Central pattern generators give rise to motor behaviors that are measurable in living animals as well as in reduced preparations that facilitate cellular-level investigations

Summary

Introduction

Central pattern generator (CPG) circuits give rise to common behaviors such as swimming, walking, and breathing (Grillner, 2006; Grillner and Jessell, 2009; Kiehn, 2011). To understand the cellular origins of these behaviors, key problems are to identify the rhythmogenic and premotor populations, and quantify the requisite number of neurons to sustain functionality. We address these issues in the mammalian breathing CPG by cumulatively ablating a genetically identified interneuron population hypothesized to form the rhythmogenic core while monitoring effects on network output in real time. The brainstem pre-Bötzinger complex (preBötC) putatively drives inspiratory breathing rhythms (Smith et al, 1991; Feldman et al, 2013; Moore et al, 2013) These rhythms persist in reduced slice preparations that retain the preBötC and can be monitored via respiratory hypoglossal (XII) nerve discharge, providing a powerful in vitro model of breathing behavior (Lieske et al, 2000; Koizumi et al, 2008; Funk and Greer, 2013).

Methods

Results

Conclusion