Glycinergic Pacemaker Neurons in PreBötzinger Complex of Neonatal Mouse

Abstract

The preBötzinger complex (preBötC) is essential for normal respiratory rhythm generation in rodents, for which the underlying mechanisms remain unknown. Excitatory preBötC pacemaker neurons are proposed to be necessary for rhythm generation. Here we report the presence of a population of preBötC glycinergic pacemaker neurons. We used rhythmic in vitro transverse slice preparations from transgenic mice where neurons expressing the glycine transporter 2 (GlyT2) gene coexpress enhanced green fluorescent protein (EGFP). We combined epifluorescence and whole-cell patch-clamp recording to study preBötC EGFP-labeled, i.e., glycinergic, inspiratorymodulated neurons with pacemaker properties. We defined glycinergic pacemaker neurons as those preBötC EGFP neurons that exhibited the following: (1) ectopic bursting in rhythmic slices when depolarized during their normally silent period and (2) bursting when depolarized in nonrhythmic slices (following AMPA receptor blockade). Forty-two percent of EGFP-labeled neurons were inspiratory (n ϭ 48 of 115), of which 23% (n ϭ 11 of 48 inspiratory; 10% of the total recorded) were pacemakers. We conclude that there is a population of preBötC inspiratory-modulated glycinergic, presumably inhibitory, pacemaker neurons that constitute a substantial fraction of all preBötC pacemaker neurons. These findings challenge contemporary models for respiratory rhythmogenesis that assume the excitatory nature of preBötC pacemaker neurons. Testable and nontrivial predictions of the functional role of excitatory and inhibitory pacemaker neurons need to be proposed and the necessary experiments performed.

Brainstem respiratory networks: building blocks and microcircuits

“…Pre-BötC glutamatergic neurons have widespread projections [20] and are the primary source of rhythmic inspiratory excitatory drive. The cellular composition is heterogeneous and includes glutamatergic populations expressing neurokinin-1 receptors (NK1R), somatotstatin (SST), and the transcription factor developing brain homeobox 1 protein (Dbx1) [17,18], as well as subpopulations of inspiratory glycinergic [58,59] and GABAergic [60] neurons. The latter two types may provide inhibition of expiratory neurons during inspiration.…”

Regulation of Breathing and Autonomic Outflows by Chemoreceptors

“…RVLM presympathetic neurons with an inspiratory peak could be receiving input from IVLM cells that in turn receive input from inhibitory inspiratory neurons. All the postulated inhibitory inputs to the IVLM neurons (early inspiratory, inspiratory, or postinspiratory) are commonly found in the rVRG and pre-Bötzinger region, that is, in the immediate vicinity of the IVLM neurons (246, 296, 381). The late-expiratory peak observed in some presympathetic neurons when the respiratory drive is very elevated could plausibly originate from excitatory pfRG neurons with late-expiratory activity (246, 296, 381) (Fig.…”

The respiratory control mechanisms in the brainstem and spinal cord: integrative views of the neuroanatomy and neurophysiology

“…2 for other phenotypes). There were no inhibitory bursters [55] (the contradictory study [64] could have shown loss of either periodic synaptic drives [32, 52] or multi-cell synchrony [32]) and the kernel rhythm persisted after the inhibitory transmission blockade [65]. They may shape and/or tune the inspiratory activities in vitro.…”