The effect of conduction block on the spinal release of immunoreactive-neuropeptide Y (ir-NPY) in the neuropathic rat

Peripheral nerve injury may result in significant changes in neuropeptide production and the development of neuropathic pain behaviour. Rats with a chronic constriction injury of one sciatic nerve were used to study the spinal release of immunoreactive neuropeptide Y (ir-NPY), using the antibody-coated microprobe technique. Previous work has shown an increase in NPY synthesis by large to medium-sized primary afferent neurones, as well as a new area of ir-NPY release in the deep dorsal horn on the side of nerve injury, when compared to uninjured rats. The stimulus for spontaneous ir-NPY release was unclear, but may have been due to ectopic neuronal discharges developing after nerve injury. This study used local anaesthetic to block all electrical input from the injured nerve. No change was found in the new zone of spontaneous release of ir-NPY in the deep dorsal horn ipsilateral to nerve injury. It appears therefore, that ir-NPY is released from the central termination of primary afferent neurones, without regulation from neuronal activity in the primary afferent neurones themselves.