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Coincident development and synchronization of sleep-dependent delta in the cortex and medulla
Journal article   Peer reviewed

Coincident development and synchronization of sleep-dependent delta in the cortex and medulla

Midha Ahmad, Jangjin Kim, Brett Dwyer, Greta Sokoloff and Mark S. Blumberg
Current biology, Vol.34(12), pp.2570-2579.e5
05/16/2024
DOI: 10.1016/j.cub.2024.04.064
PMCID: PMC11187663
PMID: 38772363

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Abstract

In early development, active sleep is the predominant sleep state before it is supplanted by quiet sleep. In rats, the developmental increase in quiet sleep is accompanied by the sudden emergence of the cortical delta rhythm (0.5–4 Hz) around postnatal day 12 (P12). We sought to explain the emergence of the cortical delta by assessing developmental changes in the activity of the parafacial zone (PZ), a medullary structure thought to regulate quiet sleep in adults. We recorded from the PZ in P10 and P12 rats and predicted an age-related increase in neural activity during increasing periods of delta-rich cortical activity. Instead, during quiet sleep, we discovered sleep-dependent rhythmic spiking activity—with intervening periods of total silence—phase locked to a local delta rhythm. Moreover, PZ and cortical delta were coherent at P12 but not at P10. PZ delta was also phase locked to respiration, suggesting sleep-dependent modulation of PZ activity by respiratory pacemakers in the ventral medulla. Disconnecting the main olfactory bulbs from the cortex did not diminish cortical delta, indicating that the influence of respiration on delta at this age is not mediated indirectly through nasal breathing. Finally, we observed an increase in parvalbumin-expressing terminals in the PZ across these ages, supporting a role for local GABAergic inhibition in the PZ’s rhythmicity. The unexpected discovery of delta-rhythmic neural activity in the medulla—when cortical delta is also emerging—provides a new perspective on the brainstem’s role in regulating sleep and promoting long-range functional connectivity in early development. [Display omitted] •Neurons in the medullary parafacial zone (PZ) fire rhythmically during quiet sleep•Rhythmic PZ spiking activity is phase locked with a local delta rhythm (0.5–4 Hz)•PZ delta develops alongside cortical delta, and the two rhythms are coherent•Rhythmic spiking in the PZ is also phase locked with respiration Researchers have long sought evidence that the brainstem helps synchronize cortical rhythms. Ahmad et al. use infant rats spanning various ages to study the initial emergence of cortical delta during quiet sleep. Their findings demonstrate the expression of delta-rhythmic and breathing-related neural activity in the medulla that is coherent with cortical delta.
 Electrophysiology brainstem functional connectivity local field potential parafacial zone rat respiration rhythms Sleep systems neuroscience

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