Received July 30, 1999
Accepted September 21, 1999

Summary
The latest research reveals that nitric oxide as a gas messenger may diffuse into the surrounding extracellular fluid and act locally upon neighboring target cells. However, several observations raise the possibility that nitric oxide may also be released at a greater distance from the neuronal cell body. The catalytic nitric oxide synthase (cNOS) activity was therefore studied in the cervicothoracic and lumbosacral segments of the spinal cord of rabbits, including the white matter of dorsal columns (DC), lateral columns (LC) and ventral columns (VC), as well as the gray matter of dorsal horns (DH), intermediate zone (IZ) and ventral horns (VH). Lower cNOS activity was found in the white matter of both cervicothoracic (47 %) and lumbosacral (30 %) regions, whereas that detected in the gray matter of the lumbosacral part of the spinal cord was considerably higher (70 %). Enzyme activity varied from 43.4 to 77.2 dpm/µg protein in the cervicothoracic segments of the gray matter in the descending order: DH>VH>IZ. Similar cNOS activity was found in the white matter of the cervicothoracic segments (42.1-62.8 dpm/µg protein). When the activity of cNOS was compared in the lumbosacral segments, the highest enzyme activity was found in DH of the gray matter (198.7 dpm/µg protein) and the lowest cNOS in DC (45.8 dpm/µg 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.