Some observations on the catecholaminergic innervation of the intermediate zone of the thoracolumbar spinal cord of the cat.

The anatomical arrangement of catecholaminergic nerve terminals in the intermediate zone of the thoracolumbar spinal cord was examined with the fluorescence microscope in serial sections of spinal cord from adult cats perfused with a formaldehyde-glutaraldehyde mixture. Specific fluorescence in this material was assumed to represent noradrenaline. The distribution of fluorescent varicose nerve terminals was compared with that of neuron cell bodies in the same sections after Nissl counterstaining, and with the known topographic distribution of sympathetic preganglionic neurons. Dense accumulations of noradrenergic fibers were found in the intermediate zone in all segments between the caudal part of C8 and the rostral part of L4. These were not only associated with preganglionic neurons in the intermediolateral columns (ILN), but below T5 also extended in bands (1-3 per mmm of spinal cord) toward, and in some segments across, the midline. Noradrenergic terminals were associated with cell bodies in most parts of the ILN from T1 to T8 and in L2-3. Between T9 and L2, the innervation of the ILN was patchy, and the majority of the noradrenergic fibers projected to regions medial to the ILN. These corresponded to sites at which preganglionic neurons and also possible interneurons of the intermediomedial nucleus occur. Although preganglionic neurons and clusters of noradrenergic terminals are located in similar regions across the intermediate zone, their densities and patterns of distribution differ. This observation applies to comparisons both between anatomical subnuclei and between segments in a characteristic way along the length of the thoracolumbar cord.