Non-opioid analgesia of the neuropeptide, neo-kyotorphin and possible mediation by inhibition of GABA release in the mouse brain.

The novel neuropeptide, neo-kyotorphin, produced a naloxone-resistant analgesia in the tail pinch test when given (IC) to mice. Pretreatments with implantation of a morphine pellet or with phentolamine (10 micrograms IT) or with reserpine (10 mg/kg SC) did not attenuate this analgesia, yet the analgesia was antagonized by GABA mimetics, such as muscimol (0.1 microgram IC), nipecotic acid (100 mg/kg IP). Neo-kyotorphin inhibited the Ca2+-dependent and depolarization-evoked release of 3H-GABA, from crude synaptosomes of the lower brain stem of rats. These findings suggest that inhibition of GABA in the brain may in part be involved in neo-kyotorphin-induced analgesia.