Objective(s):The relationship between tramadol, as an antinociceptive drug, and locus coeruleus (LC), the main noradrenergic nucleus of the brain that affects regulation and modulation of pain through descending noradrenergic pathways was investigated. Materials and Methods: Male Sprague-Dawley rats were divided into four groups of 10 rats. The rats were fixed in stereotaxic instrument and then...