Neurons in the nucleus tractus solitarius mediate the acupuncture analgesia in visceral pain rats

• Somato-visceral convergent neurons in the NTS respond to both CRD and acupuncture stimulations.
• CRD related NTS neurons show multiple firing patterns.
• Acupuncture may reverse responses of some CRD related neurons in the NTS.
• The effect of acupuncture has no somatic locational discrepancy.
• The acupuncture analgesia of CRD relays on polysynaptic connections in the NTS.

The study investigated the role of nucleus tractus solitarius (NTS) neurons in electroacupuncture (EA) analgesia in colorectal distension (CRD) rats. NTS neurons responding to both CRD test and EA conditioning stimulations were considered somato-visceral convergent neurons. The neuronal activities evoked by graded CRD showed multiple firing patterns indicating multisynaptic connections. Some of the CRD excitatory neurons were inhibited by EA and vice versa. There was no discrepancy among different acupoints in inducing the changes of unit discharges. Conclusively, EA could regulate CRD related neurons in the NTS through polysynaptic cross-talk mechnism, which mediates EA analgesia on visceral pain in anesthetized rats.