Volumetric mapping of the functional neuroanatomy of the respiratory network in the perfused brainstem preparation of rats

Abstract

Key points The functional neuroanatomy of the mammalian respiratory network is far from being understood since experimental tools that measure neural activity across this brainstem‐wide circuit are lacking. Here, we use silicon multi‐electrode arrays to record respiratory local field potentials (rLFPs) from 196–364 electrode sites within 8–10 mm3 of brainstem tissue in single arterially perfused brainstem preparations with respect to the ongoing respiratory motor pattern of inspiration (I), post‐inspiration (PI) and late‐expiration (E2). rLFPs peaked specifically at the three respiratory phase transitions, E2–I, I–PI and PI–E2. We show, for the first time, that only the I–PI transition engages a brainstem‐wide network, and that rLFPs during the PI–E2 transition identify a hitherto unknown role for the dorsal respiratory group. Volumetric mapping of pontomedullary rLFPs in single preparations could become a reliable tool for assessing the functional neuroanatomy of the respiratory network in health and disease. Abstract While it is widely accepted that inspiratory rhythm generation depends on the pre‐Bötzinger complex, the functional neuroanatomy of the neural circuits that generate expiration is debated. We hypothesized that the compartmental organization of the brainstem respiratory network is sufficient to generate macroscopic local field potentials (LFPs), and if so, respiratory (r) LFPs could be used to map the functional neuroanatomy of the respiratory network. We developed an approach using silicon multi‐electrode arrays to record spontaneous LFPs from hundreds of electrode sites in a volume of brainstem tissue while monitoring the respiratory motor pattern on phrenic and vagal nerves in the perfused brainstem preparation. Our results revealed the expression of rLFPs across the pontomedullary brainstem. rLFPs occurred specifically at the three transitions between respiratory phases: (1) from late expiration (E2) to inspiration (I), (2) from I to post‐inspiration (PI), and (3) from PI to E2. Thus, respiratory network activity was maximal at respiratory phase transitions. Spatially, the E2–I, and PI–E2 transitions were anatomically localized to the ventral and dorsal respiratory groups, respectively. In contrast, our data show, for the first time, that the generation of controlled expiration during the post‐inspiratory phase engages a distributed neuronal population within ventral, dorsal and pontine network compartments. A group‐wise independent component analysis demonstrated that all preparations exhibited rLFPs with a similar temporal structure and thus share a similar functional neuroanatomy. Thus, volumetric mapping of rLFPs could allow for the physiological assessment of global respiratory network organization in health and disease.

Keeping the Breath in Mind: Respiration, Neural Oscillations, and the Free Energy Principle

“…Readiness potential amplitudes were also smaller during the expiration phase as compared to inspiration. This interpretation of the results is further supported by a recent study of Dhingra et al (2020) showing that the transitions between inspiration and post-inspiration are especially relevant for synaptic engagement: the I-PI transition exclusively engages a brainstem-wide respiratory network.…”

Fentanyl effects on respiratory neuron activity in the dorsolateral pons

“…In fact, late-inspiratory and postinspiratory dorsolateral pontine neuronal activity always occurred in the three-phase output and never occurred during shallow two-phase respiratory output. This finding suggests pontine neuronal activity is correlated with three-phase breathing (defined by postinspiratory vagal output and augmenting phrenic output), which is highly congruent with the role of the dorsolateral pons in the inspiratory off-switch ( 17 , 19 , 20 , 37 – 40 ), and the loss of decrementing vagal postinspiratory activity and augmenting phrenic inspiratory activity following opioid administration into the dorsolateral pons ( 11 ).…”

The role of glycinergic inhibition in respiratory pattern formation and cardio-respiratory coupling in rats

“…Recently, we have demonstrated that balanced excitation and inhibition within the ventrolateral respiratory column, dorsal respiratory group and pontine respiratory group is necessary for the expression of the three-phase respiratory motor pattern ( Dhingra et al., 2019a ). Further, by mapping the distribution of local field potentials throughout a broad region of the medulla and pons that contain the core elements of the respiratory network, we were able to demonstrate that the transition from inspiration to postinspiration simultaneously engaged an expansive network that includes the ventrolateral respiratory column, dorsal and pontine respiratory groups ( Dhingra et al., 2020 ). Further, the formation of the respiratory motor pattern depends on synaptic interactions between the medullary ventrolateral respiratory column and the pontine respiratory groups ( Jones and Dutschmann, 2016 ).…”