Neural Mechanisms of Breathing
My collaboration with Christopher A. Del Negro at William & Mary brings mathematical biology and cellular biophysics together with experimental neuroscience to understand the neural control of breathing. We focus on the preBötzinger complex (preBötC), a brainstem network with a central role in inspiratory rhythm generation. Our work asks how this network produces ordinary breaths and sighs, and how opioid signalling alters the neurons that sustain respiratory activity.
Two rhythms in one network
Normal breathing and sighing operate on markedly different timescales. Both rhythms can be studied in neonatal-mouse brainstem slices that retain the preBötC and inspiratory motor output. These reduced preparations allow us to investigate cellular and synaptic mechanisms alongside mathematical models.
Our 2020 study showed that sigh timing is more variable than commonly assumed: a sigh need not follow an ordinary inspiratory event. Blocking glycinergic and GABAergic inhibition did not abolish coupling between the rhythms or the pause after a sigh. The findings supported excitatory coupling and a refractory origin for the post-sigh pause. [1]
In 2024, we combined modelling with experiments to explain how a shared neuronal population can generate both rhythms. In the model, recurrent excitation, synaptic depression and adaptation produce the faster inspiratory rhythm, while slower intracellular calcium dynamics generate sighs. Experiments in neonatal-mouse slices supported key predictions: partially reducing calcium uptake into the endoplasmic reticulum accelerated sighs, whereas reducing calcium release slowed or stopped them. The model provides a mechanistic account of how sigh frequency can change separately from ordinary inspiration without requiring separate dedicated neuronal populations. Del Negro and I contributed equally to this study. [2]
Opioid signalling and respiratory neurons
Our 2026 study with Eva Kalajian and Marco Stettler examined how μ-opioid receptor activation changes preBötC excitability. The receptor gene, Oprm1, was expressed in substantial fractions of both excitatory and inhibitory neurons, but the agonist DAMGO reduced excitability selectively in the glutamatergic neurons studied. Whole-cell and single-channel recordings showed enhanced Kir3, or GIRK, potassium-channel activity through a membrane-delimited signalling mechanism consistent with Gβγ action. [3]
This identifies a postsynaptic route by which opioids can weaken excitatory respiratory drive. It also suggests downstream signalling targets for future investigations of opioid-induced respiratory depression. Whether such targets can support effective interventions remains an open research question.
Molecular context
Related transcriptomic collaborations characterize the molecular identities of preBötC neurons, including electrophysiologically recorded Dbx1-derived cells and single-cell profiles of inspiratory neurons. These datasets complement physiological experiments by documenting the genes expressed in the populations being studied. [4, 5]
Selected joint publications
[1] Borrus DS, Grover CJ, Conradi Smith GD, Del Negro CA (2020). Role of synaptic inhibition in the coupling of the respiratory rhythms that underlie eupnea and sigh behaviors. eNeuro 7(3):ENEURO.0302-19.2020. doi:10.1523/ENEURO.0302-19.2020.
[2] Borrus DS, Stettler MK, Grover CJ, Kalajian EJ, Gu J, Conradi Smith GD, Del Negro CA (2024). Inspiratory and sigh breathing rhythms depend on distinct cellular signalling mechanisms in the preBötzinger complex. The Journal of Physiology 602:809–834. doi:10.1113/JP285582. Conradi Smith and Del Negro contributed equally.
[3] Kalajian EJ, Stettler MK, Conradi Smith GD, Del Negro CA (2026). μ-Opioid receptor signalling enhances Kir3 currents in glutamatergic preBötzinger complex neurons in mice. The Journal of Physiology 604:7351–7374. doi:10.1113/JP291442.
[4] Kallurkar PS, Picardo MCD, Sugimura YK, Saha MS, Conradi Smith GD, Del Negro CA (2022). Transcriptomes of electrophysiologically recorded Dbx1-derived respiratory neurons of the preBötzinger complex in neonatal mice. Scientific Reports 12:2923. doi:10.1038/s41598-022-06834-z.
[5] David CK, Sugimura YK, Kallurkar PS, Picardo MCD, Saha MS, Conradi Smith GD, Del Negro CA (2022). Single cell transcriptome sequencing of inspiratory neurons of the preBötzinger complex in neonatal mice. Scientific Data 9:457. doi:10.1038/s41597-022-01569-y.
Project support
The eupnea and sigh project received support from the National Center for Complementary and Integrative Health through the joint NSF–NIH Collaborative Research in Computational Neuroscience programme: Discovering the neural mechanisms of breathing rhythms — eupnea and sigh. Principal investigators: Greg Conradi Smith and Christopher Del Negro. NIH R01AT010816, August 2019–January 2023.