Effects of Activation of [kappa]-Opioid Receptors on Behavior during Postnatal Formation of the Stress Reactivity Systems

Stress at any age, including at the early stages of postnatal development, leads to changes in the state and reactivity of the stress-related humoral systems, particularly the hypothalamo-hypophyseal-adrenal system (HHAS) and the dynorphin- [kappa]-opioid system (DKOS). These changes are suggested to underlie a number of diseases. Stress-induced changes in the HHAS have been well studied. However, the role of the DKOS is unclear. Further studies of this system require generalization of existing published data on the physiological mechanisms and ethological characteristics of DKOS activation seen at different stages of the body's development. The generalization provided here leads to the conclusion that the mode of the animal's response to stimulation of the DKOS during early ontogeny differs from that in adults and changes depending on the stage of development of the stress reactivity system, at any particular period depending on whether the stress system had previously been activated.