Dorsal Horn Neurons Firing at High Frequency, But Not Primary Afferents, Release Opioid Peptides that Produce μ-Opioid Receptor Internalization in the Rat Spinal Cord

摘要: To determine what neural pathways trigger opioid release in the dorsal horn, we stimulated root, or dorsolateral funiculus (DLF) spinal cord slices while superfusing them with peptidase inhibitors to prevent degradation. Internalization of μ-opioid receptors (MOR) and neurokinin 1 (NK1R) was measured assess release, respectively. Dorsal root stimulation at low, high, mixed frequencies produced abundant NK1R internalization but no MOR internalization, indicating that primary afferents do not opioids. Moreover, capsaicin NMDA also failed produce internalization. In contrast, horn elicited increased frequency, being negligible