N-methyl-D-aspartate receptor blockade during development induces short-term but not long-term changes in c-Jun and parvalbumin expression in the ratcervical spinal cord

During postnatal development, N-methyl-D-aspartate receptor (NMDA-R) expres sion progressively decreases in ventral and deep dorsal horns. This transie nt expression might play a role in activity-dependent development of segmen tal circuitry. NWMA-Rs were blocked unilaterally in the lower cervical spin al cord using Elvax implants that released the NMDA-R antagonist MK-801 max imally over a 2-week period from postnatal day 7 (P7) onward. At P14, the r atio of c-Jun immunoreactive motoneurons ipsilateral/contralateral to the i mplants was significantly increased and the ratio of parvalbumin immunoreac tive neurons decreased, compared to control implants. However, at P84, MK-8 01-treated and control spinal cords appeared the same. Therefore, NMDA-R bl ockade during development only transiently altered expression of activity-d ependent proteins in the spinal cord, unlike lesions to the developing moto r cortex, which we have previously shown to have a permanent effect. (C) 20 01 Academic Press.