APOPTOSIS IN CELLULAR COMPARTMENTS OF RAT SPINAL-CORD AFTER SEVERE CONTUSION INJURY

Following a controlled, severe contusion lesion to the lower thoracic spinal cord in adult rats, we found that apoptosis occurred in cells l ocated in both gray and white matter. This suggested that both nonneur onal cells, including astrocytes, oligodendroglia and microglia, as we ll as neurons, might participate in programmed cell death (PCD) follow ing spinal cord injury (SCI). Determination of which cell populations participate, and the kinetics and extent of their involvement might re veal new paradigms for approaches to therapy. Consequently, we assesse d the functional deficit, comparing a comprehensive locomotor rating s cale (LRS) with the inclined plane test at various times after injury. Using standard histology, along with cell-specific markers, we assess ed PCD in different spinal cord segments using several parameters of a poptosis. Our results indicate that hind limb motor function was lost at day 1, and then only gradually and ineffectively (about 10-15%) rec overed over the next month. Evidence for increased cell number was pre sent for astrocytes and microglia beginning at day 1 after injury. Ove r the postinjury time period, apoptotic cells appeared (from day 1 to 14), and peaked (in terms of apoptotic index) on day 3. About one-thir d mere microglia, whereas neurons, both large and small, also underwen t apoptosis, again peaking at day 3. However, neurons continued to die and were not replaced by proliferation, so that at day 7, three times as many neurons (as a percentage) underwent PCD compared with the gli al compartment. Oligodendrocytes also underwent apoptosis, with a biph asic curve, both at days 3 and 14 following injury. Thus, in addition to immediate, passive necrosis, delayed and apoptotic PCD also occurre d in all cell populations in severely injured spinal cord.