Morphine dependence in the rat: the appearance in the spinal cord of a dorsal root ganglion cell neurotrophic factor.

An increase in neurotrophic activity for the survival of dissociated sensory neurones has been found in the spinal cord of morphine dependent rats. This activity is not due to morphine itself and is not due to an increase in the nerve growth factor as antibodies to nerve growth factor fail to block the response. A new hypothesis is presented that some of the spinal effects of morphine dependence may be due to an increase in the level of neurotrophic factors as a response to an apparent denervation of the target cells in the spinal cord.