ABSTRACT
Opioids have analgesic effects by activation of μ (mu), κ (kappa), and/or δ (delta) receptors in the central nervous system (CNS) [1]. Each receptor class has subtypes that have different clinical effects. Analgesia occurs by activation of spinal or supraspinal opioid receptors, leading to decreased neurotransmitter release from nociceptive neurons, inhibiting the ascending neuronal pain pathways and altering the perception and response to pain [2]. Opioid receptors also exist outside the CNS, in the dorsal root ganglia and on primary afferent neurons’ peripheral terminals [3].
