Sheng Li Xue Bao. 1996 Apr; 48(2): 125-31.

[Increase of mu opioid receptor density in rat central nervous system following formalin nociception and its enhancement by electroacupuncture]

Gao M, He LF.

Department of Neurobiology, Shanghai Medical University.

Using receptor autoradiography it was found: (1) After formalin injection in the rat hind paw, the mu opioid receptor density was significantly increased in certain central areas related to antinociception, i.e., the caudate nucleus, nucleus accumbens, amygdaloid nucleus, periaqueductal gray, interpeduncular nucleus, nucleus raphe magnus and spinal dorsal horn. (2) In addition to most of above mentioned central areas, in rat whose noxious responses were inhibited by electroacupuncture, there was a significant increase of receptor density in the cingulate cortex, septal area, preoptic area, superior central nucleus, superior colliculus and medial geniculate body. In comparison with the rats with formalin injection alone, the receptor density in the interpeduncular nucleus, the ventrolateral part of the caudal periaqueductal gray and spinal dorsal horn of the lumbar enlargement was further increased in the rats showing electroacupuncture analgesia. The above results provide further evidence supporting the postulation that noxious stimulation is capable of activating endogenous opioid peptidergic system which is further enhanced by electroacupuncture.