Activation of anterior lobe corticotrophs by electroacupuncture or noxious stimulation in the anaesthetized rat, as shown by colocalization of Fos protein with ACTH and beta-endorphin and increased hormone release.

A marked expression of the c-fos proto-oncogene has been recently reported in cells of the anterior lobe of the pituitary gland in rats subject to electroacupuncture or noxious thermal stimulation under pentobarbital anaesthesia. The present study was undertaken to identify the activated pituitary cells. Following both kinds of stimulation, most Fos-immunoreactive anterior lobe cells showed colocalization with adrenocorticotropic hormone or beta-endorphin immunoreactivity. No c-fos expression occurred in pituitary cells immunoreactive for growth hormone, prolactin, luteinizing hormone, or thyrotropin-stimulating hormone. A marked rise of adrenocorticotropic hormone and beta-endorphin concentrations occurred in plasma. In the hypothalamus, c-fos expression was increased in the mediobasal nuclei-namely, the arcuate nucleus-and in the paraventricular nucleus, but more in the former. It is suggested that somatosensory noxious input, or the partly noxious input evoked by electroacupuncture, activate the hypothalamo-pituitary-adrenocortical axis as in common forms of stress, but with a specific activation of the mediobasal hypothalamic nuclei and no stimulation of intermediate lobe cells. Opiate release from the pituitary gland may contribute to acupuncture analgesia or the intrinsic antinociceptive reactions triggered by noxious stimulation.