Sympathetic preganglionic neurons in frog spinal cord.

Sympathetic preganglionic neurons innervating the first sympathetic ganglion were identified in a frog (Rana pipiens). After wheat germ agglutinin conjugated horseradish peroxidase was implanted into this ganglion a homogeneous population of labeled sympathetic preganglionic neurones were identified ipsilaterally within the lateral field of the spinal gray at the level of the third spinal nerve. The total population of labeled cells (n = 324 +/- 62) extended in a rostrocaudal field for about 1800 micron as two distinct columns consisting of about equal numbers of cells. One group, at the lateral border of the intermediate zone, corresponds to the intermediolateral column, as also found in mammals, while the second group extends within the intercalated region, as the intercalated nucleus, lateral and slightly dorsal to the central canal. Transection of spinal nerves reveals that 65% of preganglionic axons leave the cord from the third spinal nerve with the remainder coursing through the first and second spinal nerves.