Effect of midthoracic spinal cord constriction on catalytic nitric oxide synthase activity in the white matter columns of rabbit.

The distribution and changes of catalytic nitric oxid synthase (cNOS) activity in the dorsal, lateral and ventral white matter columns at midthoracic level of the rabbit's spinal cord were studied in a model of surgically-induced spinal cord constriction performed at Th7 segment level and compared with the occurrence of nicotinamide adenine dinucleotide phosphate diaphorase expressing and neuronal nitric oxide synthase immunoreactive axons in the white matter of the control thoracic segments. Segmental and white-column dependent differences of cNOS activity were found in the dorsal (141.5 +/- 4.2 dpm/microm protein), lateral (87.3 +/- 11.5 dpm/microm protein) and ventral (117.1 +/- 7.6 dpm/microm protein) white matter columns in the Th5-Th6 segments and in the dorsal (103.3 +/- 15.5 dpm/microm protein), lateral (54.9 +/- 4.9 dpm/microm protein), and ventral (86.1 +/- 6.8 dpm/microm protein) white matter columns in the Th8-Th9 segments. A surgically-induced constriction of Th7 segment caused a disproportionate response of cNOS activity in the rostrally (Th5-Th6) and caudally (Th8-Th9) located segments in both lateral and ventral white matter columns. While a statistically significant decrease of cNOS activity was detected above the constriction site in the ventral columns, a considerable, statistically significant increase of cNOS activity was noted in the white lateral columns below the site of constriction. It is reasoned that the changes of cNOS activity may have adverse effects on nitric oxide (NO) production in the white matter close to the site of constriction injury, thus broadening the scope of the secondary mechanisms that play a role in neuronal trauma.