Centrally applied NPY mimics immunoactivation induced by non-analgesic doses of met-enkephalin

NEUROPEPTIDE Y (NPY) and endogenous opioids (EOPs) such as methionine-enkep halin (Met-enk) regulate similar physiological responses, but it is not kno wn whether nociceptive and immune responses also show analogy after intrace rebroventricular (i.c.v.) application. Dose-response studies show that Met- enk stimulates the blood granulocyte and splenic natural killer (NK) cell f unction of Lewis rats at a low dose (10(2) ng/kg, i.c.v.), whereas a high d ose (10(5) ng/kg) causes suppression of innate immune functions associated with analgesia in the hot-plate test. At 15 min, 1 h and 24 h after i.c.v. application, both Met-enk (102 ng/kg) and NPY (1 ng/kg) produced similar ef fects: An initial suppression of innate immune function Nas followed by a l ong lasting stimulatory action on cell functions and serum interleukin-6 (s IL-6) levels. Thus, central NPY application resembles Met-enk-induced immun ostimulation at doses not affecting nociception, suggesting an involvement of both peptides in shaping stress-induced immunomodulation of the non-anal getic form, possibly via activation of a common immunomodulatory effector m echanism. NeuroReport 9: 3881-3885 (C) 1998 Lippincott Williams & Wilkins.