Concurrent, dual perturbations of the 5-HT and NA systems reveal dynamic interplay in regulating the neonate autoresuscitation reflex
Authors: Lusk Savannah , Ward Christopher , Hernandez Javi , Ray Russell 
Published: May 2023

Sudden Infant Death Syndrome (SIDS) is a leading cause of infant mortality worldwide. Postmortem studies indicate abnormalities in the serotonergic (5-HT) and noradrenergic (NA) systems of the respiratory network. To better understand the relative and potential combined contributions and interactions of these two neurotransmitter systems to SIDS pathology, we developed a novel series of conditionally expressed inhibitory (hM4De) and excitatory (hM3D) DREADD models that allows for singular excitation or inhibition of either the whole 5-HT or whole NA systems as defined by cre- and FLPo- drivers. These models were then uniquely combined to further enable 1) concurrent stimulation or inhibition of both the NA and 5-HT systems in the same animal or 2) inhibition of one system while exciting the other system in the same animal. In total, after two years of complex breeding combining 3 loci and 6 alleles, we developed 8 distinct sets of conditional genetic mouse models for various singular and combined 5-HT and NA system perturbation paradigms.Failure of the neonate auto-resuscitation reflex is hypothesized to be a common endpoint in many SIDS cases. The autoresuscitation reflex can be readily assayed in neonate mice by repeated bouts of exposure to an anoxic gas to induce bradycardia and apnea followed by restoration of room air to observe successful or failed autoresuscitation. The 8 experimental groups and 2 control groups were repeatedly assayed for the autoresuscitation reflex using a new closed loop robotic neonate cardiorespiratory assessment platform and outcomes were analyzed with our recently developed comprehensive respiratory analysis platform, Breathe Easy, to calculate operant outcomes. In >170 mouse pups (≈17 pups per group) assayed over three months, we found that singular DREADD-mediated activation or inhibition of the NA system results in decreased survival. Interestingly, we found that DREADD-mediated 5-HT activation decreases survival. In contrast to previous studies, we found that DREADD-mediated 5-HT inhibition does not impact survival, particularly when all neonates are challenged to autoresuscitation failure. Furthermore, we show survival is restored to control levels when NA inhibition is combined with 5-HT inhibition; however, failure via NA activation is not rescued by 5-HT inhibition. Controls used for comparison were CNO-injected controls as we also show an effect of CNO on survival that cannot be attributed to time of day, rig, experimenter, weight, background genotype, etc. As the underlying genetic and environmental mechanisms driving SIDS are likely to have pleiotropic effects across multiple neural systems, our first-of-its-kind dual 5-HT and NA system modulations sets the stage to more comprehensively model key aspects of SIDS neuropathology that reveal a previously uncharacterized dynamic functional interplay between the NA and 5-HT systems in protective respiratory reflexes. NIH: 1F32HL160073-01A1, R01HL130249 44617-S4. BCM McNair Scholar Program, March of Dimes Basil O'Connor Research Award, Parker B. Francis Fellowship, CJ Foundation for SIDS. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.