A novel view of opiate tolerance

Opiate substances occur as natural compounds in various invertebrate and vertebrate neural tissues. Recently we have discovered a novel opiate alkaloid-selective and opioid peptide-insensitive receptor, designated mu 3, that provides further evidence of the existence of separate morphine processes. Interestingly morphine biosynthesis appears to be linked to the dopamine pathway. Based on studies documenting the presence of morphine after stress, e.g., trauma, it is noted that this signal substance emerges after a timely delay. From this we speculate that this molecule can serve a specific effect to downregulate physiological processes after stress. We conclude that tolerance represents a natural process that terminates its action. In this regard a morphine hypothesis may be essential to a complete picture of motive circuitry. A speculative view of the psychiatric implications in schizophrenia, depression, and autism are presented with this in mind.