Stability of Met-enkephalin content in brain structures of morphine-dependent or foot shock-stressed rats

The discovery of enkephalin has suggested one more theory to explain the mechanisms of opiate tolerance and addiction and by killing the rats with a microwave beam focused to the head and by taking particular precautions in preparing the brain samples, it is shown that Met-enkphalin concentrations are higher than those measured by other authors who failed to take such precautions.

Abstract

THE discovery of enkephalin has suggested one more theory to explain the mechanisms of opiate tolerance and addiction. Kosterlitz and Hughes1 proposed that a reduced enkephalin release might explain tolerance and physical dependence to opiates. Simantov and Snyder2 supported this view by showing that the content of enkephalin was changed in brain of morphine-dependent rats. Others3–5 have reported that Met-enkephalin is rapidly metabolised by brain tissue. Because of this in vivo lability of Met-enkephalin, particular precaution must be taken in the preparation of brain tissue samples for enkephalin assay. In fact, we have shown that by killing the rats with a microwave beam focused to the head and by taking particular precautions in preparing the brain samples we could measure Met-enkephalin concentrations which were higher (by several orders of magnitude) than the concentrations measured by other authors who failed to take such precautions6. Since the changes in the brain enkephalin content reported to occur either after a stress induced by foot shock7 or during morphine dependence2, were measured by a binding assay which lacks specificity for enkephalin, we decided to repeat these experiments with a technique that specifically measures Met-enkephalin6 to decide whether the brain enkephalin content changes during stress7 or opiate dependence2.