Try the Textbook of Pain- Melzak and Wall
Gavril (W) Pasternak (New York-Sloan) routinely writes reviews of
mechanisms of opiate-mediated pain. For example:
Pharmacological Mechanisms of Opioid Analgesics
Clinical Neuropharmacology 16, 1-18, 1993.
Standards: Besson and Chaouch, 1987, Peripheral and spinal
mechanisms of nociception, Physiological Reviews, 67, p. 67.
Basbaum and Fields, 1984, Endogenous Pain Control Systems, Ann. Rev.
Neuroscience 7, p. 309.
Any textbook of Neuroscience or Neuroanatomy will give a fairly
detailed anatomical perspective. Kandel, Shwartz and Jessell
(Principles of Neural Science; Elsevier) does a particularly good job
of integrating several different aspects of pain management and
research.
Also try the journals Trends in Neuroscience (TINS) or
Pharmacological Sciences (TIPS). They write excellent reviews.
Kerry Gergen, Tulane Neuroscience