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Examination of the Antinociceptive Profile Associated with MU and Delta Opioid Receptor Linked Systems in the Brainstem Periaqueductal Gray Matter (PAG) and the Medullary Reticular Formation (MRF)

INTRODUCTION: Current studies have indicated that the intracerebral administration of opiates into several anatomically distinguishable brainstem sites will produce an attenuation of the animals response to an otherwise noxious stimulus. Mapping studies have demonstrated that opiate receptor linked systems in the brainstem produce their antinociceptive effects by discriminable mechanisms with a differential action on spinal versus supraspinally organized noxious responses. Opioid binding has been demonstrated for putative mu, delta and kappa ligands in brain and spinal cord. While recent studies have shown that spinal opioid receptors characterized as mu, delta and kappa may be identified in modulation of nociceptive transmission it is unclear whether mu and delta opioid receptor linked systems in the brainstem produce their antinociceptive effects by discriminable mechanisms.