Functional Imaging Reveals Respiratory Network Activity During Hypoxic and Opioid Challenge in the Neonate Rat Tilted Sagittal Slab Preparation

Abstract

In mammals, respiration-modulated networks are distributed rostrocaudally in the ventrolateral quadrant of the medulla. Recent studies have established that in neonate rodents, two spatially separate networks along this column-the parafacial respiratory group (pFRG) and the pre-Bötzinger complex (preBötC)-are hypothesized to be sufficient for respiratory rhythm generation, but little is known about the connectivity within or between these networks. To be able to observe how these networks interact, we have developed a neonate rat medullary tilted sagittal slab, which exposes one column of respiration-modulated neurons on its surface, permitting functional imaging with cellular resolution. Here we examined how respiratory networks responded to hypoxic challenge and opioid-induced depression. At the systems level, the sagittal slab was congruent with more intact preparations: hypoxic challenge led to a significant increase in respiratory period and inspiratory burst amplitude, consistent with gasping. At opioid concentrations sufficient to slow respiration, we observed periods at integer multiples of control, matching quantal slowing. Consistent with single-unit recordings in more intact preparations, respiratory networks were distributed bimodally along the rostrocaudal axis, with respiratory neurons concentrated at the caudal pole of the facial nucleus, and 350 microns caudally, at the level of the pFRG and the preBötC, respectively. Within these regions neurons active during hypoxia- and/or opioid-induced depression were ubiquitous and interdigitated. In particular, contrary to earlier reports, opiate-insensitive neurons were found at the level of the preBötC.

Spinal and Pontine Relay Pathways Mediating Respiratory Rhythm Entrainment by Limb Proprioceptive Inputs in the Neonatal Rat

“…The reciprocal synaptic connectivity of the PB/KF with the ventrolateral medulla (Herbert and Saper, 1990;Ezure, 2004;Ezure and Tanaka, 2006) where the respiratory centers are located (Smith et al, 1991;Mellen et al, 2003;Onimaru and Homma, 2003;Barnes et al, 2007), further implicates these pontine nuclei in the organization of breathing. Therefore, in a manner equivalent to its role in the interactions between respiration and other functions such as nociception (Jiang et al, 2004) and vocalization (Smotherman et al, 2006), the PB/KF complex could additionally serve as an important integrating locus for coordinating mammalian breathing with locomotion.…”

Cumulative lesioning of respiratory interneurons disrupts and precludes motor rhythms in vitro

“…However, these two cutting strategies expose different respiratory circuits at the rostral face of the slice. VRC-surface slices expose respiratory neurons rostral to the preBötC, in a region that includes the Bötzinger complex (BötC) (16,17), which is not associated with inspiratory rhythmogenesis. We hypothesized that cumulative ablation of VRC inspiratory neurons would not affect cycle period or stop rhythmogenesis.…”

Reconfiguration of respiratory-related population activity in a rostrally tilted transversal slice preparation following blockade of inhibitory neurotransmission in neonatal rats

“…Compared to the tilted sagittal slice preparation which was previously used to study rhythmogenesis [20,33], the novel slice preparation introduced in the present study preserves the bilaterally distributed respiratory network in both hemispheres and its interconnectivity. Recent advances in technology made it possible to image population activity at single-cell resolution while simultaneously recording rhythmic mass activity [33,34]. In this study, we show that distinct rhythms are recordable in the rostrally tilted slice preparation.…”