No abstract

Understanding the pathophysiological changes triggered by an acute spinal cord injury is a primary goal to prevent and treat chronic disability with a mechanism-based approach. After the primary phase of rapid cell death at the injury site, secondary damage occurs via autodestruction of unscathed tissue through complex cell-death mechanisms that comprise caspase-dependent and caspase-independent pathways. To devise novel neuroprotective strategies to restore locomotion, it is, therefore, necessary to focus on the death mechanisms of neurons and glia within spinal locomotor networks. To this end, the availability of in vitro preparations of the rodent spinal cord capable of expressing locomotor-like oscillatory patterns recorded electrophysiologically from motoneuron pools offers the novel opportunity to correlate locomotor network function with molecular and histological changes long after an acute experimental lesion. Distinct forms of damage to the in vitro spinal cord, namely excitotoxic stimulation or severe metabolic perturbation (with oxidative stress, hypoxia/aglycemia), can be applied with differential outcome in terms of cell types and functional loss. In either case, cell death is a delayed phenomenon developing over several hours. Neurons are more vulnerable to excitotoxicity and more resistant to metabolic perturbation, while the opposite holds true for glia. Neurons mainly die because of hyperactivation of poly(ADP-ribose) polymerase-1 (PARP-1) with subsequent DNA damage and mitochondrial energy collapse. Conversely, glial cells die predominantly by apoptosis. It is likely that early neuroprotection against acute spinal injury may require tailor-made drugs targeted to specific cell-death processes of certain cell types within the locomotor circuitry. Furthermore, comparison of network size and function before and after graded injury provides an estimate of the minimal network membership to express the locomotor program.

No abstract

In vitro preparations of the neonatal rat spinal cord or brainstem are useful to investigate the organization of motor networks and their dysfunction in neurological disease models. Long-term spinal cord organotypic cultures can extend our understanding of such pathophysiological processes over longer times. It is, however, surprising that detailed descriptions of the type (and number) of neurons and glia in such preparations are currently unavailable to evaluate cell-selectivity of experimental damage. The focus of the present immunohistochemical study is the novel characterization of the cell population in the lumbar locomotor region of the rat spinal cord and in the brainstem motor nucleus hypoglossus at 0-4 postnatal days, and its comparison with spinal organotypic cultures at 2-22 days in vitro. In the nucleus hypoglossus, neurons were 40% of all cells and 80% of these were motoneurons. Astrocytes (35% of total cells) were the main glial cells, while microglia was <10%. In the spinal gray matter, the highest neuronal density was in the dorsal horn (>80%) and the lowest in the ventral horn (≤57%) with inverse astroglia numbers and few microglia. The number of neurons (including motoneurons) and astrocytes was stable after birth. Like in the spinal cord, motoneurons in organotypic spinal culture were <10% of ventral horn cells, with neurons <40%, and the rest made up by glia. The present report indicates a comparable degree of neuronal and glial maturation in brainstem and spinal motor nuclei, and that this condition is also observed in 3-week-old organotypic cultures.