Sympathetic and afferent neurones projecting into forelimb and trunk nerves and the anatomical organization of the thoracic sympathetic outflow of the rat.

The anatomy of the cervicothoracic sympathetic nerves was studied in the rat. Details of the arrangements of white and grey rami communicantes and superior cervical, middle cervical and stellate ganglia are given. Dorsal root and sympathetic ganglion neurones projecting to skin and muscle of the forelimb and trunk were labelled retrogradely with horseradish peroxidase (HRP) in order to study their number, segmental distribution and location. HRP was applied to forelimb nerves supplying skeletal muscles (Ramus profundus of radial nerve, RP) or hairy skin (N. cutaneus brachii lateralis superior of axillary nerve, CB), to mixed nerves (median nerve, ME; ulnar nerve, UL; radial nerve, RA) and to segmental thoracic nerves supplying hairy skin of the back (dorsal cutaneous nerve, CD) and to mixed internal intercostal nerves (IC). All sensory and sympathetic neurones were located ipsilaterally. In the forelimb nerves sensory somata were commonly restricted to two or three adjacent dorsal root ganglia (usually C6-7 for CB; C7-8 for ME; C7-Th1 for RA and RP; C8-Th1 for UL). Nearly all of the sympathetic somata were located in the middle cervical and stellate ganglia (fusion of C6-Th3). Some 0-0.4% lay in Th4 and Th5, none in the superior cervical ganglia. In the trunk nerves sensory somata were strictly segmentally organized. Sympathetic somata were distributed more widely over 4-5 segments with 50-55% in the segmental ganglion and up to 41% in the next caudal segment. From the data, it is estimated that 400 sympathetic (28%) and 1050 afferent neurones project into CB, 1660 (29%) and 4050 into RA, 540 (42%) and 760 into RP, 1010 (22%) and 3670 into ME, 880 (22%) and 3040 into UL, 350 (25%) and 1040 into IC and 500 (27%) and 1370 into CD.