INTACT AND REGENERATING SYMPATHETIC NORADRENALINE AXONS IN RAT SCIATIC NERVE

The noradrenaline (NA)-axons of the rat sciatic nerve were studied with the histochemical fluorescence technique of Falck and Hillarp. Using freeze-dried and spreadprepared specimens, it was possible to visualize most of the normally present NA-axons in spite of their low content of noradrenaline. The degenerative and regenerative patterns of these fibres were examined after cutting or compressing the nerve. The superior cervical ganglion was transplanted to the sciatic nerve in order to study the outgrowth of NA-axons from the ganglion into the nerve trunk. The findings were as follows: 1. The normally present NA-axons run singly or in small groups in the nerve trunk and have a lower fluorescence intensity than adrenergic nerve terminals. They are relatively smooth in their most proximal parts, but become more beaded distally. 2. After interruption of the axons by cutting or compression, the fluorescent fibres in the distal stump loose their fluorescence and thus the noradrenaline content within 45 hrs probably in a proximo-distal fashion. 3. It was confirmed that a heavy accumulation of noradrenaline rapidly develops above a compression. The accumulated parts closest to the compression desintegrate into degeneration spheroids. At this level the regeneration then starts. 4. Regenerating fibres show great morphological variability. Thin sprouting fibres as well as larger typical growth cones are described. The thinnest fibres were found to grow initially as fast as 9.2 mm/24 hrs. The minimum mean growth rate for most of the fluorescent fibres in the nerve was 1.4 mm/24 hrs during the first week, and 2.9 mm/24 hrs during the second week. 5. NA-axons from the superior cervical ganglion transplanted to the proximally cut sciatic nerve grow vigorously in both directions into the nerve. The growth rate for these fibres was at least equal to that mentioned above. When transplanted to the intact sciatic nerve, however, the adrenergic neurons of the ganglion seemed to give rise to fluorescent fibres to a much lesser extent. The implications of the above findings were discussed. © 1969 Springer-Verlag.