Leu-enkephalin is a naturally occurring peptide in the body that acts as a neurotransmitter. It belongs to a group of molecules called opioid peptides, which are known for their role in pain relief and mood regulation. Leu-enkephalin specifically binds to opioid receptors in the brain, helping to reduce the perception of pain and promote feelings of well-being. This peptide is produced in various parts of the body, including the brain and spinal cord. It plays a crucial role in the body's response to stress and can influence emotional states. Research on leu-enkephalin contributes to our understanding of pain management and the development of new treatments for conditions like chronic pain and depression.