VIP and PACAP: very important in pain?

Neuropathic pain arising from direct trauma to, or compression injury of, peripheral nerves is a common clinical problem. It is characterized by the development of abnormal pain states (spontaneous pain, hyperalgesia, allodynia), which can persist long after the initial injury has resolved. The underlying mechanisms are poorly understood and, as a consequence, treatment is often unsatisfactory. Some of the main contributing factors are thought to be the morphological and phenotypic changes that occur centrally, including alterations in the expression of neurotransmitters and their associated receptors, both in the dorsal root ganglia and in the spinal dorsal horn. This article focuses on the functional role of the two structurally related peptides VIP and PACAP within the spinal cord, and their possible contribution to the altered transmission of sensory information in neuropathic conditions.