[Met-enkephalin]: Neuropeptide that competes with and mimic the effects of opiate drugs. They play a role in a number of physiologic functions, including pain perception and responses to stress. ; [Leu-enkephalin]: Neuropeptide that competes with and mimic the effects of opiate drugs. They play a role in a number of physiologic functions, including pain perception and responses to stress. ; [Met-enkephalin-Arg-Phe]: Met-enkephalin-Arg-Phe neuropeptide acts as a strong ligand of Mu-type opioid receptor OPRM1. Met-enkephalin-Arg-Phe-binding to OPRM1 in the nucleus accumbens of the brain increases activation of OPRM1, leading to long-term synaptic depression of glutamate release. ; [PENK(114-133)]: Increases glutamate release in the striatum and decreases GABA concentration in the striatum. ; [PENK(237-258)]: Increases glutamate release in the striatum.
