Morphological characterization of photochemical graded spinal cord injury in the rat.

This study characterizes the histological and immunohistochemical changes in the adult rat spinal cord following photochemically induced spinal cord lesions. The spinal cord was exposed by laminectomy (T12-L1 vertebrae) and bathed with 1.5% rose bengal solution for 10 min. The excess dye was removed by saline rinse and the spinal cord was irradiated with "cold" light for 0, 1, 2.5, 5, and 10 min in different groups of rats. After 15 days a graded loss of spinal tissue was observed according to photoinduction times. Animals irradiated for 1 min showed spinal cavities involving the dorsal funiculi. The cavity became progressively larger, involving dorsal horns in animals irradiated for 2.5 min, together with the dorsolateral funiculi in animals irradiated for 5 min and the ventrolateral funiculi in those irradiated for 10 min, with loss of gray matter in these three groups. Changes in GFAP-, CGRP-, proteoglycan- and calbindin-immunoreactivity were observed in all lesioned groups when compared with control spinal cords. Hypertrophied and heavily GFAP- and proteoglycan-stained astrocytes were seen in irradiated spinal cords. Reactive microglial cells were also found. Both astroglial and microglial reactions paralleled the severity of the spinal cord lesion. A significant loss of CGRP-immunoreactive somas was seen in animals irradiated for 10 min, whereas the wider distribution of calbindin-positive neurons was found in lesioned rats. In spinal cord sections from animals illuminated for 5 min and perfused 60 min postillumination, light and electron microscopy showed cytotoxic edema with astrocytic swelling, red blood cell extravasation, and myelin degradation.