Definitive Evidence for the Identification and Function of Renin-Expressing Cholinergic Neurons in the Nucleus Ambiguus

Background: The importance of the brain renin-angiotensin system (RAS) incardiovascular function is well accepted. However, not knowing the precise source ofrenin in the brain has been a limitation towards a complete understanding of how the brainRAS operates. Methods: Highly sensitive in situ hybridization techniques and conditionalknockout mice were used to address the location and function of renin in the brainstem.Results: We identified novel renin-expressing cholinergic neurons in the nucleusambiguus (NuAm), a major vagal cardioinhibitory center in the brainstem. The expressionof RAS genes was relatively abundant in the NuAm, implying that angiotensin II mightmediate an important regulatory role in this nucleus and other regions with neuralconnectivity to the NuAm. Then, we generated conditional knockout mice lacking theclassical renin isoform (Ren-aChAT-KO), specifically in cholinergic neurons. Ablation of Ren-a in cholinergic neurons abrogated renin expression in the NuAm. Moreover, studiesusing radiotelemetry, heart rate variability analyses, and pharmacological approachesrevealed that the parasympathetic nervous system is depressed in Ren-aChAT-KO maleswhile augmented in the Ren-aChAT-KO females. Subsequently, transcriptomic approacheswere used to infer putative genes and signaling pathways regulated by renin within theNuAm. Conclusions: This study revealed that renin in cholinergic neurons plays afundamental role in preserving autonomic balance and cardiovascular homeostasis in asex-dependent manner. These findings define the NuAm as an endogenous, local sourceof renin with biological function and serve as conclusive evidence for the presence andfunctionality of the brain RAS.