c-Fos expression in the periaqueductal gray is induced by electroacupuncture in the rat, with possible reference to GABAergic neurons.

Electroacupuncture (EA) delivered to the acupoint (AP) called Zusanli (ST36) was administered on the bilateral hindlimb. This experiment resulted in strong expression of c-Fos immunoreactivity in the ventrolateral to lateral subdivision throughout the periaqueductal gray (PAG) compared to the non-AP and sham cases. On the other hand, it was of particular interest in the experiment of the AP that strong expression of gamma aminobutylic acid (GABA) frequently showed similar pattern of distribution to that of c-Fos in the PAG. This overlapped pattern of distribution, demonstrated in the present study, suggests that the PAG neurons activated by EA at the AP might play an important role in the descending pain control system involving the GABA since the PAG has special reference to the dorsal horn of the spinal cord and function of pain control.