Brain and adrenal monoamines and neuropeptide Y in codeine tolerant rats

1. Monoamine turnover and neuropeptide Y (NPY) levels were investigated in the central and peripheral nervous systems in adult male rats chronically treated with codeine. 2. An increase in the dopaminergic turnover was observed in the striatum and cortex. The norepinephrine levels and the serotoninergic turnover were unchanged in all the brain areas. 3. Epinephrine levels were decreased in the adrenal glands. 4. In addition, we observed a significant decrease of NPY levels in the hypothalamus, the striatum and the adrenal glands. These observed changes were not found when assessing NPY level in plasma fluid. 5. The implication of these modifications in the induction of codeine dependence are discussed in view of previous results obtained with morphine.