Delineating impacts of gestational opioid exposure on central swallow networks.

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The ability coordinate breathing, suckling, and swallow is required for survival at birth. Infants with prenatal exposure to opioids can have abnormalities in swallow efficiency and swallow-breathing coordination, sensory- motor responses to pharyngeal stimulus, and esophageal motility reflexes, which often results in persistent feeding difficulties. The swallow pattern generator is located within the brainstem, but it has been difficult to study due to its location and widely dispersed neural circuits. Our preliminary studies describe a novel method that allows for the visualization and recording of a vast number of neurons along the intermediate zone of the medial reticular formation and Nucleus Ambiguus (NA), while preserving the Nucleus Tractus Solitarius. We demonstrate reliable central stimulation of swallow with simultaneous optical recording of neurons in the semicompact and compact regions of the NA, along with nerve root recordings. Activation of NA neurons during swallow is affected by prenatal opioid exposure. Our methods also allow superimposition of optical recordings onto subsequent immunohistochemical images to identify regional cellular phenotypes and to confirm recording locations. Our working hypothesis is that the brainstem swallow network spans the medulla and is vulnerable to opioids. The current application has evolved from collaborative work from two established investigators, bringing together expertise in central neural circuitry, optical/ histological techniques, and regulation of swallow. The proposed studies are designed to describe location and type of neurons active during swallow, alterations when swallow is stimulated across the respiratory cycle, and the impact of neonatal opioid withdrawal syndrome. The combined state-of-the-art techniques will provide much-needed mechanistic insight into swallow and clinical observation of infants with neonatal opioid withdrawal syndrome (NOWS).