LEVELS OF IMMUNOREACTIVE DYNORPHIN A(1-13) DURING DEVELOPMENT OF MORPHINE-DEPENDENCE IN RATS

AIM: To study the; relationship between the levels of immunoreactive d ynorphin A(1-13) (ir-dynorphin A(1-13)) and the degree of-morphine dep endence. METHODS: The levels of ir-dynorphin A(1-13) in discrete brain regions, spinal cord, and plasma in rats were determined by radioimmu noassay, and the degree of morphine dependence was assessed by scoring withdrawal signs on d 3, d 6, and d 12. RESULTS: Morphine injection s c decreased the levels of ir-dynorphin A(1-13) in spinal cord, pituita ry, and plasma. The levels of ir-dynorphin A(1-13) in hippocampus and hypothalamus were increased. No changes in cortex, midbrain, cerebellu m, pens, and medulla were observed. With continuous injection of morph ine, withdrawal signs scores were increased on d 6, but there was no d ifference between the scores of d 6 and d 12. CONCLUSION: The changes of the levels of endogenous ir-dynorphin A(1-13) in pituitary, spinal cord, and plasma were compatible with the degree of morphine dependenc e.