Changes in cyclic AMP levels in the developing opossum spinal cord at the time when regeneration stops being possible.

Cyclic AMP (cAMP) is an important second messenger in signaling pathways that regulate cellular processes involved in development and regeneration. The changes in cAMP content of opossum spinal cords have been studied during the critical period of development, when the ability to regenerate axons after injury is lost. Endogenous cAMP levels were measured in tissue homogenates, and cAMP immunoreactivity was displayed in sections of lesioned and non-lesioned opossum P6 (can regenerate) and P13 (cannot regenerate) spinal cords. There was a significant decrease of the cAMP levels during the period critical for regeneration, while the level of cAMP was increased in P6 spinal cords after injury. Moreover, 5 mM db-cAMP induced growth in vitro of the injured axons in the spinal cord that has lost the capacity to regenerate.