Neonatal opioid withdrawal syndrome disrupts the ventral swallow pattern generator in germline‐GCaMP6F mouse

Abstract

Opioid exposure during gestation can lead to neonatal opioid withdrawal syndrome (NOWS) at birth. A feature of NOWS is dysphagia. To better understand the contribution of dysregulated central control to dysphagia in NOWs infants, we compared fictive swallow in neonate (P2‐P6) control mice and mice exposed to methadone from E14.5 onwards. Propriobulbar interneuronal and cranial premotoneuronal networks that coordinate orofacial and laryngeal activity during feeding, as well as constituents of the ventral respiratory column were recorded optically in mice expressing the genetically encoded Ca2+ indicator GCaMP6F in the germline. In the sagittally‐sectioned isolated brainstem, swallow can be evoked by electrical stimulation of command neurons along the dorsomedial edge of the preparation. In vitro swallow is defined as a burst at the hypoglossal nerve (XIIn) unaccompanied by phrenic (C4) motor output. In control animals evoked swallow was accompanied by sequential activation of networks dorsal and medial to the facial nucleus (VIIn), a nucleus in the intermediate reticular formation implicated in vibrissal control (vIRT), and (pre‐)motoneurons along the nucleus ambiguus (NA). In opioid‐exposed pups fictive swallow could reliably be evoked, but only networks dorsomedial to VIIn were reliably activated, while vIRT and NA networks were silent. The distribution of ChAT+, phox2b+, and SST+ neurons was the same in control and MTD‐exposed mice, as were the networks active during inspiration. These findings suggest that dysphagia may at least in part be due to network‐level dysregulation of central networks mediating swallow, but not to gross developmental abnormality of these networks. Because neonate feeding behaviors are highly conserved in mammals, these findings suggest that the sagittally‐sectioned mouse hindbrain provides a platform to investigate the contribution of central networks to dysphagia in NOWS infants.