[Intraepidermal free nerve fiber endings and their importance for cutaneous pain].
BACKGROUND
Former studies performed by means of supravital methylene blue (MB) staining could demonstrate intraepidermal free nerve fiber endings (FNE). Unfortunately, these publications were only illustrated by drawings. Furthermore, the practical details of the method were only insufficiently handed down to posterity. Therefore, a modification of the staining procedure should be worked out for this purpose. Subsequently, the possible advantages of the method compared with common histochemical techniques should be clarified. Regarding the possible nociceptive functions of the FNE, the corresponding conclusions should be drawn from the results.


METHODS
The dye was injected subepidermally into the hairless skin of the palmar- and plantar sites of rat paws followed by light microscopy.


RESULTS
2 different morphological types of FNE could be detected within the epidermis. The thick FNE, which occurred less frequently than the thin ones (approximately 20/mm(2) in relation to 1000/mm(2)), represented nerve fiber branches ascending up to the granular layer where they formed superficial plexus (Figs. 1 and 3b). In contrast to the thick FNE, the thin ones were varicose and unbranched (Figs. 2 and 3a).


CONCLUSIONS
Regarding the demonstration of morphological details, especially the branching pattern and the thickness of FNE, MB-staining achieves interesting results. The visualization of 2 different types of FNE within the epidermis extends the validity of the concept of punctate sensibility into this skin layer. Both types of FNE have to be functionally connected with different sensoric tasks. Possibly, a subpopulation of the thin FNE might be identical to the substance P-immunoreactive one which is wellknown to possess primarily a nociceptive function.
Müller
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Anatomisches Institut, Johannes-Gutenberg-Universität Mainz.