Effect of puromycin administration on presynaptic bouton regeneration after hemisection of rat spinal cord.

The effect of puromycin on synaptic renewal on spinal neurons 1 to 1.5 mm rostral to the site of a T1-T2 interface after hemisection was studied. Ninety-five Long-Evans rats were utilized (five animals per group) 10, 20, 30, 45, 60, and 90 days posthemisection. The groups consisted of normal animals, those with spinal cord hemisection alone, those with Gelfoam sponge saturated with 0.9% saline placed in the lesion, or those with a Gelfoam sponge saturated with 1.0 mm puromycin dihydrochloride in 0.9% saline placed in the lesion (at surgery). The spinal cords were processed for the light microscopic impregnation of presynaptic boutons. Counts of boutons (lamina IV and IX motoneurons) were made from coded material and analyzed statistically. After spinal cord hemisection alone, there was a cyclic significant renewal of presynaptic boutons on the somata of lamina IV and IX neurons with decreases (P < 0.05) at 10 to 20 days, increases (P < 0.05) at 30 days, and spontaneous loss (P < 0.05) at 45 days. This small number of boutons was retained at 60 days postoperative (DPO) and remains at this value at 90 days on lamina IV neurons or increases on lamina IX neurons. Saline-puromycin-Gelfoam implantation resulted in a significant bouton decrease (P < 0.05) on lamina IX neurons at only 45 days postoperative and no differences from normal on lamina IV neurons. These data show a “protective” effect that stabilized presynaptic boutons on lamina IV neurons for 90 days and on lamina IX neurons for at least 30 days.