Opioid is known to suppress respiratory system in mammals including humans that results in opioid overdose. Opioid-induced respiratory suppression in mammals is caused partly by the binding of opioids to mu-opioid receptors expressed by respiratory neurons in the brainstem that result in hyperpolarization (inhibition). However, we recently discovered that the respiratory system of Xenopus laevis is less susceptible to opioid-induced respiratory suppression compared to mammals. In this project, we seek to understand how the respiratory neurons of frogs differ from those of mammals in their responsiveness to opioids.