Identifying deficits in brainstem respiratory circuits during viral encephalitis

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 DESCRIPTION (provided by applicant): The overall goal is to identify respiratory neuro-circuits within the brainstem damaged by arbovirus encephalitis that eventually lead to respiratory distress and failure. Respiratory insufficiency is a serious outcome of arbovirus encephalitis and can result in a poor prognosis. Rodent models have been used to establish that neurological deficits cause the respiratory distress, which is the primary patho- physiological mechanism of death for West Nile virus (WNV) and other viral encephalitis. However, the respiratory neuro-circuits damaged by the virus are unknown, which is subject of this application. The hypothesis to be tested is that WNV damages the retrotrapazoid nucleus/parafacial respiratory group (RTN/pFRG) controlling response to hypercapnia and the pre-Bötzinger complex (preBötC) controlling generation of breathing rhythm. The specific aims are: Aim 1. Identify deficits in spontaneous rhythmic activity in the medullary core rhythm generator (preBötC) from WNV-infected neonatal mice. Suction electrode measurements will be obtained from cranial nerve XII rootlets in the preBötC slice from pups with respiratory deficits. Aim 2. Identify deficits in respiratory circuitry using brainstem-spinal cord preparations (en bloc preparations) in neonatal WNV-infected mice. Nerve root discharges of the XII and phrenic nerves will be simultaneously measured using suction electrodes. The ventral surface of the medulla will be imaged for calcium to pin point chemoreceptor deficits to the RTN/pFRG. Aim 3. Deficits identified in Aims 1 and 2 will be corroborated in adult WNV-infected mice. Chemosensory, rhythmogenesis, and phrenic motor neurons functions will be ascertained by measuring nerve discharges in XII and phrenic nerves. Procedures will be performed within a single mouse so that we can better understand the contributions of each type of deficit to the total WNV-induced respiratory failure. Upon completion of these in vivo measurements, the brainstem and spinal cord containing regions of respiratory function will be analyzed histologically to determine if functional deficits correlate with anatomical pathology. If WNV infection adversely affects central breathing function, it would represent a paradigm shift for the neurological mechanism of pathogenesis for viral encephalitis. Importantly, results of this project will provide supporting data for an IRB application to measure respiratory function in WNV-infected human subjects in a forthcoming project