CHEMICAL SENSORY DEAFFERENTATION ABOLISHES HYPOTHALAMIC-PITUITARY ACTIVATION-INDUCED BY NOXIOUS-STIMULATION OR ELECTROACUPUNCTURE BUT ONLY DECREASES THAT CAUSED BY IMMOBILIZATION STRESS - A C-FOS STUDY

We have shown in previous c-fos studies that noxious stimulation or el ectroacupuncture in deeply anaesthetized rats activate the hypothalami c-pituitary corticotrope axis in a specific way. C-Sos expression was more pronounced in the arcuate than the paraventricular hypothalamic n uclei, and none occurred in the pituitary intermediate lobe. The absen ce of the usual autonomic responses to psychological stress, such as t achycardia or blood pressure elevation, suggested a specific action of the somatosensory input on the hypothalamic-pituitary axis. To prove this hypothesis, c-fos expression was examined in the paraventricular, arcuate and other hypothalamic nuclei, the pituitary gland, and the A l and A2 medullary catecholaminergic cell groups of animals deprived o f nociceptive primary afferent input by neonatal capsaicin. After noxi ous stimulation or electroacupuncture, no c-fos enhancement occurred i n any of those sites in capsaicin-treated animals, and there was no in creased plasma release of adrenocorticotropic hormone. In contrast, th e hypothalamic-pituitary c-fos activation provoked by immobilization s tress though markedly decreased, was not abolished by capsaicin, where as plasma release of adrenocorticotropic hormone remained undiminished . These findings suggest that noxious stimulation or electroacupunctur e act on the hypothalamic-pituitary corticotrope axis through an exclu sively physical effect depending on the noxious signal elicited in the somatosensory pathway. They also demonstrate the occurrence of a mino r somatosensory physical component after forced immobilization, acting on the hypothalamic-pituitary axis probably together with the prevale nt component of emotional arousal elicited by this form of stress. (C) 1997 IBRO. Published by Elsevier Science Ltd.