Demonstration of calcitonin gene-related peptide immunoreactive axons contacting dynorphin A(1-8) immunoreactive spinal neurons in a rat model of peripheral inflammation and hyperalgesia.

In a rat model of peripheral inflammation and hyperalgesia, dynorphin A(1-8)-like immunoreactive (DYN-LIr) spinal neurons were examined for contacts from calcitonin gene-related peptide-like immunoreactive (CGRP-LIr) varicosities using a double-label PAP method. Ipsilateral to the inflammation, CGRP-LIr varicosities contacted both dendrites and somata of DYN-LIr neurons in lumbar laminae I, II and V. Few such contacts were found on the contralateral side. The results suggest that opioid neurons which exhibit a dynamic change in dynorphin associated with inflammation, represent a subpopulation of neurons that receive contacts from presumptive nociceptive primary afferents.