In the present research, we have employed a variety of anatomical techniques to study the neural circuitry of the spinal cord as it relates to pain and hyperalgesia. Lamina 1 neurons were retrogradely labeled after injections into the caudal midbrain of animals with inflamed hindpaws. Spinal cord sections from these animals were processed for dynorphin immunoreactivity. It was found that the number of lamina I projection neurons immunoreactive for dynorphin was substantially greater in spinal cord sections ipsilateral to the inflamed hindpaw. Spinal cord section of normal animals were processed for GABA immunoreactivity and either Calcitonin Gene Related Peptide (CGRP) or Enkephalin (ENK) immunoreactivity. It was found that a small number of GABAergic neurons were contacted by either GGRP or ENK varicosities. On the other hand, large numbers of GABA varicosities were in apposition to ENK-containing neurons.
