A neuroanatomical basis for electroacupuncture to drive the vagal-adrenal axis

Somatosensory autonomic reflexes allow electroacupuncture stimulation (ES) to modulate body physiology at distant sites(1-6) (for example, suppressing severe systemic inflammation(6-9)). Since the 1970s, an emerging organizational rule about these reflexes has been the presence of body-region specificity(1-6). For example, ES at the hindlimb ST36 acupoint but not the abdominal ST25 acupoint can drive the vagal-adrenal anti-inflammatory axis in mice(10,11). The neuroanatomical basis of this somatotopic organization is, however, unknown. Here we show that PROKR2(Cre)-marked sensory neurons, which innervate the deep hindlimb fascia (for example, the periosteum) but not abdominal fascia (for example, the peritoneum), are crucial for driving the vagal-adrenal axis. Low-intensity ES at the ST36 site in mice with ablated PROKR2(Cre)-marked sensory neurons failed to activate hindbrain vagal efferent neurons or to drive catecholamine release from adrenal glands. As a result, ES no longer suppressed systemic inflammation induced by bacterial endotoxins. By contrast, spinal sympathetic reflexes evoked by high-intensity ES at both ST25 and ST36 sites were unaffected. We also show that optogenetic stimulation of PROKR2(Cre)-marked nerve terminals through the ST36 site is sufficient to drive the vagal-adrenal axis but not sympathetic reflexes. Furthermore, the distribution patterns of PROKR2(Cre) nerve fibres can retrospectively predict body regions at which low-intensity ES will or will not effectively produce anti-inflammatory effects. Our studies provide a neuroanatomical basis for the selectivity and specificity of acupoints in driving specific autonomic pathways.