Neuropeptide NLP-40 and Cognate G- Protein Coupled Receptor AEX-2 Regulate Behavioral Responses During Anoxia in Caenorhabditis elegans

Background: Insufficient oxygen (hypoxia) or complete lack of oxygen (anoxia) causes cellular dysfunction and death in terrestrial animals. As a result, animals have developed homeostatic strategies, including changes in movement strategies to escape and survive stressful environments. Caenorhabditis elegans respond to changes in oxygen by increasing the frequency of reversals (backward movement) and increasing locomotor speed; these behaviors enable them to escape unfavorable environments and move to more suitable ones. The molecular and neural mechanisms underlying behavioral responses to low-oxygen environments are incomplete. Neuropeptides regulate C. elegans behaviors by modifying neural circuit function in response to hypoxia. Loss of function in C. elegans neuropeptide nlp-40 and its receptor aex-2 increased survival to anoxia [1]. However, the cells in which NLP-40 and AEX-2 function for anoxia, as well as the mechanisms underlying responses to anoxia, remain elusive. We hypothesized that NLP-40 and AEX-2 regulate anoxia by altering escape behaviors. Results: We found that neuropeptide NLP-40 functions in cholinergic neurons and AEX-2 functions in cholinergic or GLR-1 interneurons or motor neurons to regulate susceptibility to anoxia. We found that loss of either nlp-40 or aex-2 decreased locomotor activity and reversal frequency early during 48 hours of anoxia, suggesting that nlp-40 and aex-2 are required for the proper execution of these behaviors. We found that neuronal knockdown of nlp-40 recapitulated the behaviors observed in nlp-40 mutant animals and increased survival; however, restoring aex-2 function in glr-1 interneurons or motor neurons was sufficient to rescue behaviors to wild-type and restore vulnerability to anoxia. Conclusions: Overall, our results suggest that NLP-40 and AEX-2 likely function in cholinergic or glr-1 interneurons or motor neurons to regulate escape behaviors during anoxia. Escape behaviors are part of the homeostatic response and are typically protective in the wild; however, in our paradigm, we show that loss of either nlp-40 or aex-2 reduces escape responses and confers protection against 48 hours of anoxia. Collectively, these results highlight a new role for NLP-40 and AEX-2 in anoxia and shed light on mechanisms underlying the adaptive responses to anoxia.