Morphometric Studies of the Effects of Capsaicin on the Lissauer's tract of the Adult Rats

Until recently the neurotoxic effects of capsaicin to adult animals were thought to be limited to the peripheral nervous system. Several reports suggest the possibility of central nervous system changes after capsaicin administration to the adult rat. To determine the effect of capsaicin to the adult central nervous system, morphologic changes of the Lissauer tract were investigated by electron microscopy. The number of axons and substance P and CGRP immunoreactive axons of the tract of Lissauer were also counted and analyzed by electron microscopic and immunocytochemical techniques. Ultrastructural degenerative changes were observed in the Lissauer tract of the capsaicin treated adult rats. The number of axons in the tract of Lissauer were decreased in most cases of the capsaicin treated rats. The number of substance P and CGRP immunoreactive axons in the tract of Lissauer were decreased in the capsaicin treated rats. The number of substance P and CGRP immunoreactive axons were decreased more than those of the total axons. Numerical changes were more pronounced in unmyelinated axons than in myelinated axons after capsaicin administration. The changes of L2 spinal tract of Lissauer were more pronounced than those of T10 tract of Lissauer. In conclusion, morphologic changes of the adult rat by capsaicin are not limited to the peripheral nervous system, but extend into the central nervous systemrestrictio