Endogenous morphine modulates acute thermonociception in mice.

The endogenous synthesis of morphine has been clearlydemonstrated throughout the phylogenesis of the nervoussystem of mammals and lower ani maIs. Endogenous mor-phine, serving as either a neurotransmitter or neurohormone,has been demonstrated in the nervous system of both verteb-rates and invertebrates. As one of the effects of exogenousmorphine is the modulation of pain perception, we investi-gated the effects that the depletion of endogenous morphinehad on nociceptive transmission. The immunoneutralization ofendogenous morphine tram brain extracellular spaces wasAbstractThe endogenous synthesis of morphine has been clearlydemonstrated throughout the phylogenesis of the nervoussystem of mammals and lower ani mais. Endogenous mor-phine, serving as either a neurotransmitter or neurohormone,has been demonstrated in the nervous system of both verteb-rates and invertebrates. As one of the effects of exogenousmorphine is the modulation of pain perception, we investi-gated the effects that the depletion of endogenous morphinehad on nociceptive transmission. The immunoneutralization ofendogenous morphine tram brain extracellular spaces was obtained through the intracerebroventricular administration ofaffinity purified anti-morphine IgG to mice, which then under-went the hot plate test. Endogenous morphine immunoneut-ralization decreased thermal response latency and attenuatedthe anti-nociceptive effect of the mu selective agonist DAMGOin hot plate test suggesting that endogenous morphine isinvolved in pain modulation.