The effect of complex double-axis rotation model on GABAergic neurons in caudal ventrolateral medulla of rats along the vestibulo-sympathetic reflex pathway.

Motion sickness is a common physiological disorder induced by with unusual movement exposure, characterized by conflicting motion signals that trigger vestibulo-sympathetic reflexes (VSR). These reflexes mediate autonomic responses to motion-induced stress. Previous studies have implicated the vestibular nucleus complex and the caudal ventrolateral medulla (CVLM) in VSR modulation. GABA (γ-aminobutyric acid), the primary inhibitory neurotransmitter in the central nervous system (CNS), plays a key role in both cardiovascular regulation and vestibular function. However, the specific contribution of GABAergic structures to motion sickness-related cardiovascular responses remains unclear. In this study, we combined retrograde tracing and immunofluorescence labeling to investigate GABAergic pathways using complex double-axis rotation model. Fluoro-Gold (FG) was injected into the CVLM, while biotinylated dextran amine (BDA) was delivered to the medial vestibular nuclei (MVe). Our results revealed a bilateral distribution of GABAergic neurons, predominantly within the caudal raphe nuclei. Notably, a subset of these neurons was activated (as indicated by Fos immunoreactivity) and projected to the CVLM (as shown by retrograde labeling with FG) under complex double-axis rotation model. Furthermore, these same neurons also received direct inputs from the MVe, as evidenced by their labeling with BDA. Our findings offer morphological evidence that GABAergic neurons in the caudal raphe nuclei participate in the cardiovascular responses evoked by motion sickness in a complex double-axis rotation model.