Figure 7.

A scheme of the proposed DNIC circuitry activated by noxious electrical or formalin stimulations. Both noxious stimuli at the hindlimb can excite projection neurons in the corresponding spinal dorsal horn (DH) to activate descending inhibitory systems (e.g. noradrenergic pathway, NA) in the supraspinal structures to inhibit the noxious excitability in different spinal segments, e.g. the tail. In comparison, noxious formalin and electroacupuncture (EA), which is a low-intense electrical stimulation and may not be DNIC-mediated, produces analgesia through NA- and opioid-dependent actions (left upper panel), whereas the analgesic effect of noxious electrical stimulus may not depend on activation of opioid receptors (opioid-independent, right upper panel). Symbols +: excitation; -: inhibition.