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) activ ity 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-ind uced spinal cord constriction performed at Th7 segment level and compared w ith the occurrence of nicotinamide adenine dinucleotide phosphate diaphoras e 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/mum protein), lateral (87.3 +/- 11.5 dpm/mum protein) and ventral ( 117.1 +/- 7.6 dpm/mum protein) white matter columns in the Th5-Th6 segments and in the dorsal (103.3 +/- 15.5 dpm/mum protein), lateral (54.9 +/- 4.9 dpm/mum protein), and ventral (86.1 +/- 6.8 dpm/mum protein) white matter c olumns in the Th8-Th9 segments. A surgically-induced constriction of Th7 se gment caused a disproportionate response of cNOS activity in the rostrally (Th5-Th6) and caudally (Th8-Th9) located segments in both lateral and ventr al 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 not ed in the white lateral columns below the site of constriction. It is reaso ned that the changes of cNOS activity may have adverse effects on nitric ox ide (NO) production in the white matter close to the site of constriction i njury, thus broadening the scope of the secondary mechanisms that play a ro le in neuronal trauma.