Somatostatin-like immunoreactivity in neurons, nerve terminals, and fibers of the cat spinal cord.

The distribution of somatostatin-like immunoreactivity (SS) was studied in the spinal cord of untreated cats and of cats that had received colchicine at all levels of the cord. In the dorsal horn small (less than 15 microns in diameter), round neurons were found in Rexed laminae II and III at all levels. At all levels laminae IV-VI contained smaller numbers of immunoreactive neurons that were medium (between 15 and 25 microns in diameter) to large (greater than 25 microns in diameter) in size. In addition, small numbers of medium-sized neurons were observed at the dorsal and dorsomedial borders of the gray and white matter in segments C1-5. In the sacral cord (S1-3), a group of medium-sized bipolar neurons was found in the dorsolateral funiculus. In transverse sections the processes of the neurons in these two latter groups travelled in a direction parallel to the border of the gray and white matter. In the intermediate and central gray matter, in addition to the immunoreactive neurons found in the region of the intermediolateral nucleus and nucleus intercalatus of lamina VII in segments C8 to L4 (Krukoff et al., '85a), lamina VII contained immunoreactive neurons at all levels with the largest number occurring in the thoracic cord. These neurons were medium to large in size and were generally multipolar with processes travelling in all directions. Multipolar small immunoreactive neurons were also found in the central gray region (lamina X) in the thoracic and upper lumbar cord. Finally, small numbers of neurons containing SS were found in the ventral horn of the cervical and upper thoracic cord. These multipolar neurons were medium to large in size. The distribution of nerve terminals and fibers containing SS was similar to that previously described in mice, rats, guinea pigs, and primates. Although the function of somatostatin in the spinal cord is not known, its presence in neurons with short processes suggests that it may act to modify local activity in the regions where it is found, including areas involved in sensory, visceromotor, and motor functions.