Figure 1.

Kainate stimulated Co²⁺ uptake labeling confirms the presence of Ca-perm AMPAr in adult MNs. Acute lumbar spinal cord sections from 55–65 day old rats were subjected to kainate stimulated Co²⁺ uptake labeling as described. Note the distinct Co²⁺ accumulation in ventral horn MNs (A, low magnification; B, detail of ventral horn). Indicating the specificity of the stain, it was substantially prevented by the addition of the non-NMDA (AMPA and kainate) receptor antagonist, NBQX (10 μM) during the kainate + Co²⁺ exposure (C). For comparison, studies of embryonic animals (in the illustrated case, E14 mice) show Co²⁺ labeling in immature ventral horn MNs (D). Note that the immature Co²⁺ labeled MNs are clustered, and are in the process of migrating to their adult positions. Inserts (C, D) show high power view of ventral horn regions marked by squares. Double labeling indicates that many of the putative ventral horn MNs that are identified by kainate stimulated Co²⁺ uptake labeling are also immunoreactive for the SMI-32 antibody in both adult (E; left, SMI-32 IF; right, Co²⁺ labeling) and embryonic animals (F, left, SMI-32 IP; right, Co²⁺ labeling). In F, note the absence of SMI-32 labeling, but the accumulation of Co²⁺ labeling reaction product in the nuclei of identified neurons. Bar = 500 μm (A, C); 100 μm (B, E, insert C); 200 μm (D); 50 μm (F, insert D).