The Carotid Body Detects Circulating Tumor Necrosis Factor-Alpha to Activate a Sympathetic Anti-Inflammatory Reflex
Recent evidence has suggested that the carotid bodies might act as immunological sensors, detecting pro-inflammatory mediators and signalling to the central nervous system, which, in turn, orchestrates autonomic responses. Here, we demonstrated that the TNF- receptor type I is expressed in the carotid bodies of rats. The systemic administration of TNF- increased carotid body afferent discharge and activated glutamatergic neurons in the nucleus tractus solitarius (NTS) that project to the rostral ventrolateral medulla (RVLM), where the majority of pre-sympathetic neurons reside. The activation of these neurons was accompanied by generalized activation of the sympathetic nervous system. Carotid body ablation blunted the TNF--induced activation of RVLM-projecting NTS neurons and the increase in splanchnic sympathetic nerve activity. Finally, plasma and spleen levels of cytokines after TNF- administration were higher in rats subjected to either carotid body ablation or splanchnic sympathetic denervation. Collectively, our findings indicate that the carotid body detects circulating TNF- to activate a counteracting sympathetic anti-inflammatory mechanism.