GLIAL CHANGES IN THE PHRENIC NUCLEUS FOLLOWING SUPERIMPOSED CERVICAL SPINAL-CORD HEMISECTION AND PERIPHERAL CHRONIC PHRENICOTOMY INJURIES IN ADULT

The objective of the present study was to characterize the microglial and astroglial reaction in the phrenic nucleus following either an ips ilateral C2 spinal cord hemisection, a peripheral phrenicotomy, or a c ombination of the two injuries in the same adult rat. The present stud y used three different fluorescent markers and a confocal laser image analysis system to study glial cells and phrenic motoneurons at the Li ght microscopic level. Young adult female rats were divided into one c ombined injury group (left phrenicotomy and left Ca spinal hemisection with periods of 1 to 4 weeks between injuries, N = 12) and three othe r groups consisting of noninjured animals (N = 3), animals that receiv ed C2 hemisection only (N = 3), and animals with phrenicotomy only (su rvival periods of 2 (N = 3) and 4 (N = 3) weeks after phrenicotomy). F luorogold was injected into the diaphragm to label phrenic motoneurons in all animals. Microglia and astrocytes were labeled with Texas red and fluorescein, respectively, and were visualized simultaneously alon g with phrenic motoneurons. The results suggest that the microglial an d astrocytic response in the superimposed injury model are similar to the glial reactions characteristically seen in a peripheral axotomy al one model. These reactions include proliferation and migration of micr oglial cells along the perineuronal surface (peaking at 2 weeks) and t he hypertrophy of astrocytes (peaking at 4 weeks). In addition, the in crease in astrocytic tissue, which is characteristically seen in respo nse to axotomy alone, is significantly enhanced in the superimposed in jury model. Also, there is a large and rapid increase in GFAP-positive astrocytes within 24 hours after hemisection alone. The information g ained from the present study will aid in determining, predicting, and eventually manipulating central nervous system responses to multiple i njuries with the objective of reestablishing function in the damaged C NS. (C) 1997 Academic Press.