N-Methyl-D-aspartate receptor blockade during development induces short-term but not long-term changes in c-jun and parvalbumin expression in the rat cervical spinal cord

During postnatal development, N-methyl-D-aspartate receptor (NMDA-R) expression progressively decreases in ventral and deep dorsal horns. This transient expression might play a role in activity-dependent development of segmental circuitry. NMDA-Rs were blocked unilaterally in the lower cervical spinal cord using Elvax implants that released the NMDA-R antagonist MK-801 maximally over a 2-week period from postnatal day 7 (P7) onward. At P14, the ratio of c-Jun immunoreactive motoneurons ipsilateral/contralateral to the implants was significantly increased and the ratio of parvalbumin immunoreactive neurons decreased, compared to control implants. However, at P84, MK-801-treated and control spinal cords appeared the same. Therefore, NMDA-R blockade during development only transiently altered expression of activity-dependent proteins in the spinal cord, unlike lesions to the developing motor cortex, which we have previously shown to have a permanent effect.