C-fos expression in the hypothalamo-pituitary system induced by electroacupuncture or noxious stimulation
IN the anaesthetized rat, low frequency electrical stimulation of the Zusanli acupoint (S36) or noxious thermal stimulation caused by immersing the footpad in water at 52°C caused marked expression of c-fos in the anterior lobe of the pituitary gland, as well as in the arcuate and some nearby hypothalamic nuclei. A similar anterior lobe response was caused by immobilization stress in awake rats but in this case Fos-immunoreactive cells extended into the intermediate lobe and were very abundant in the para-ventricular nucleus. It is suggested that the anterior pituitary cells that respond to stress are also activated by acupuncture or painful stimulation. However, the mechanisms of pituitary cell activation seem distinct from those occurring in stress, since different hypothalamic nuclei are involved.