The Involvement of Agmatine in Individual Pain Sensitivity

Abstract

Distribution of agmatinase (AGM), an enzyme of agmatine metabolism, was studied in the spinal cord and dorsal root ganglia of rats with different levels of initial thermal pain sensitivity under normal conditions and during the development of inflammatory pain using immunohistochemistry. The initial type of pain threshold affects the specific pain response of an animal to pain so that the rats with a higher threshold exhibit a less-expressed behavioral pain response. We found a specific distribution and time course of activity of AGM in the brain regions of animals with different nociceptive thresholds. The animals with a lower threshold had a higher number of AGM-immunoreactive neurons in the ganglia and a lower density of fibers and neurons in the dorsal roots of the spinal cord compared to the animals with a higher threshold. The development of tonic pain was associated with differently directed changes of AGM activity in the studied structures and depended on the threshold of nociception. Our data suggest that the endogenous system of agmatine metabolism may be involved in the initial threshold of nociception, as well as in organization of the behavioral response to pain.