Preproenkephalin gene expression in the rat cerebral cortex during chronic tracheal stenosis

To evaluate whether the endogenous opioid system is activated in the higher brain centre while a chronic resistance to airflow, we examined changes of mRNAs for preproenkephalin (PPE)-A, which is a precursor of enkephalin, and for 70 kD heat shock protein (HSP70) in the cerebral cortex of rat brain during chronic tracheal stenosis. Northern blot revealed that PPE-A mRNA was induced at 3 days of airway stenosis. In situ hybridization revealed that PPE-A mRNA was gradually induced in frontal cortex. The significant induction of PPE-A mRNA was observed at 3 and 7 days. However, no significant induction of HSP70 gene was observed. These results suggest that the endogenous opioid system may be at work as an important compensatory mechanism to reduce the respiratory sensation during chronic respiratory stress.