Acute effects of methylprednisolone sodium succinate on spinal reflexes

The acute effects of single intravenous doses of methylprednisolone sodium succinate (30, 60, or 90 mg/kg) on segmental spinal cord function were examined by stimulating the triceps surae nerves and recording the monosynaptic (2N) and polysynaptic discharges at ventral root L7. Five to ten seconds after injection, an intense but short-lived, spontaneous discharge concomitant with a dose-related reduction in the stimulus-evoked 2N response occurred. This was rapidly followed by enhancement in the 2N discharge amplitude which peaked by 45 s after administration. The duration of the 2N increase was 10 to 60 min. Polysynaptic discharge was augmented to a lesser extent and for a shorter time. The reflex enhancement was reproducible in preparations in which the distally transected dorsal roots were stimulated. All drug-induced responses were prevented by preadministration of 2.5 to 10.0 mg/kg Na pentobarbital i.v. These results indicate that i.v. glucocorticoid enhances mainly monosynaptic transmission perhaps by an action on the primary afferent terminals which augments their spontaneous and evoked transmitter release. Furthermore, they provide additional support for the view that the beneficial effects of glucocorticoids in central nervous system trauma and stroke may in part reflect an improved synaptic function.