Catalytic nitric oxide synthase activity in the white and gray matter regions of the spinal cord of rabbits

The latest research reveals that nitric oxide as a gas messenger may diffus e into the surrounding extracellular fluid and act locally upon neighboring target cells. However, several observations raise the possibility that nit ric oxide may also be released at a greater distance from the neuronal cell body. The catalytic nitric oxide synthase (cNOS) activity was therefore st udied in the cervicothoracic and lumbosacral segments of the spinal cord of rabbits, including the white matter of dorsal columns (DC), lateral column s (LC) and ventral columns (VC), as well as the gray matter of dorsal horns (DH), intermediate zone (12) and ventral horns (VH). Lower cNOS activity w as found in the white matter of both cervicothoracic (47 %) and lumbosacral (30 %) regions, whereas that detected in the gray matter of the lumbosacra l part of the spinal cord was considerably higher (70 %). Enzyme activity v aried from 43.4 to 77.2 dpm/mu g protein in the cervicothoracic segments of the gray matter in the descending order: DH>VH>IZ. Similar cNOS activity w as found in the white matter of the cervicothoracic segments (42.1-62.8 dpm /mu g protein). When the activity of cNOS was compared in the lumbosacral s egments, the highest enzyme activity was found in DH of the gray matter (19 8.7 dpm/mu g protein) and the lowest cNOS in DC (45.8 dpm/mu g protein) of the white matter. It was concluded that the white matter of the spinal cord contains similar cNOS activity in comparison to the gray matter.