Developmental and stimulus-specific expression of the immediate-early gene zif268 in rat spinal cord

Expression of the cellular immediate-early gene, zif268, was investigated using immunocytochemical methods in cervical spinal cord of neonatal and adult rats. The postnatal expression of zif268 follows a specific temporal and spatial sequence in the spinal dorsal horn. Neurons immunoreactive for Zif268 protein were not present in cervical spinal cord before postnatal day (P) 6. At P6 they were occasionally observed in Rexed's lamina 1. By P11, a few additional, faintly labeled, Zif268-positive neurons appeared in lamina III Around P16, however, many immunoreactive neurons were found in laminae I-III and a few in laminae IV-VII. The number of Zif268-immunoreactive neurons decreased markedly by P21 and was further reduced by P26 to become virtually absent in adult rats. In adults, surgical exposure of peripheral nerves alone enhanced Zif268 expression, but this effect largely disappeared in less than 6 h. Electrical stimulation of the nerves with high-frequency long trains, typical of those known to elicit long-term neural plasticity, induced a marked increase in Zif268 expression in the dorsal horn. Stimulation with single pulses had a much weaker effect, Zif268 may thus play a role in stimulus-induced, long-term neural plasticity in the spinal cord.