Generation of Eupnea and Sighs by a Spatiochemically Organized Inspiratory Network

Abstract

The discovery of the rhythmogenic pre-Bötzinger complex (preBötC) inspiratory network, which remains active in a transverse brainstem slice, greatly increased the understanding of neural respiratory control. However, basic questions remain unanswered such as (1) What are the necessary and sufficient slice boundaries for a functional preBötC? (2) Is the minimal preBötC capable of reconfiguring between inspiratory-related patterns (e.g., fictive eupnea and sighs)? (3) How is preBötC activity affected by surrounding structures? Using newborn rat slices with systematically varied dimensions in physiological [K ϩ ] (3 mM), we found that a 175 m thickness is sufficient for generating inspiratory-related rhythms. In 700-m-thick slices with unilaterally exposed preBötC, a kernel Ͻ100 m thick, centered 0.5 mm caudal to the facial nucleus, is necessary for rhythm generation. Slices containing this kernel plus caudal structures produced eupneic bursts of regular amplitude, whereas this kernel plus rostral tissue generated sighs, intermingled with eupneic bursts of variable amplitude ("eupnea-sigh pattern"). After spontaneous arrest of rhythm, substance-P or neurokinin-1 (NK1) receptor agonist induced the eupnea-sigh burst pattern in Ն250-m-thick slices, whereas thyrotropin-releasing hormone or phosphodiesterase-4 blockers evoked the eupnea burst pattern. Endogenous rhythm was depressed by NK1 receptor antagonism. Multineuronal Ca 2ϩ imaging revealed that preBötC neurons reconfigure between eupnea and eupnea-sigh burst patterns. We hypothesize a (gradient-like) spatiochemical organization of regions adjacent to the preBötC, such that a small preBötC inspiratory-related oscillator generates eupnea under the dominant influence of caudal structures or thyrotropin-releasing hormone-like transmitters but eupnea-sigh activity when the influence of rostral structures or substance-P-like transmitters predominates.

Glia Contribute to the Purinergic Modulation of Inspiratory Rhythm-Generating Networks

“…Fluo-4-AM (0.5 mM, Sigma-Aldrich) was pressure injected (0.7-1 psi) into the preBötC for 10 min using a single barrel pipette (5-10 m) Ruangkittisakul et al, , 2008. Fluorescence signals evoked by bath-applied agonists/antagonists were monitored through a multiphoton confocal microscope (Olympus FV300, Fluoview software; Carsen Group) connected to a Ti:Sa laser (Coherent) using a 20ϫ objective and 3ϫ digital zoom with scan rates of 1.08 s/frame.…”

“…Dye injection into the preBötC labeled morphologically diverse cells over an area that was 200 -300 m in diameter and within which cells could be visualized to a depth of 80 m (Ruangkittisakul et al, 2008). Our objective was to assess whether glia in respiratory regions in the brainstem are sensitive to ATP.…”

Opioids prolong and anoxia shortens delay between onset of preinspiratory (pFRG) and inspiratory (preBötC) network bursting in newborn rat brainstems

“…The newborn rat preBötC presumably extends rostrocaudally by <200µm, centered 0.5 mm caudal to the caudal margin of facial (VII) motor nucleus, VII c [49]. Contrary, Pre-I cells are widely distributed in the ventrolateral medulla [2,5,39,40,53], and the pFRG is thus illdefined anatomically.…”

Astrocytic calcium signals induced by neuromodulators via functional metabotropic receptors in the ventral respiratory group of neonatal mice

“…Other neuromodulators augment respiratory rhythm, including Substance P (SP; Pena and Ramirez, 2002) and thyrotropin-releasing hormone (TRH; Mutolo et al, 1999). Regulation of neuronal activity by these neuromodulators appears to be extremely important during early postnatal development (Ruangkittisakul et al, 2008). Moreover, 5-HT and TRH have the potential to overcome hypoxic respiratory depression in neonatal respiratory network, which might be involved in sudden infant death syndrome (Ballanyi, 2004;Guntheroth and Spiers, 2002).…”