A system of atypical catecholamine-containing nerve fibres in the rat iris present after total superior cervical ganglionectomy.

A system of hitherto unknown weakly fluorescent fibres was detected in the rat iris by Falck-Hillarp fluorescence histochemistry after superior cervical ganglionectomy. These long smooth winding (SW)-fibres had a scarce and unusual distribution, forming loops and meandering for long distances with limited branching. Pharmacological tests suggest that they store a catecholamine but differ from adrenergic nerves in lacking an efficient uptake mechanism for amines. SW-fibres reached all parts of the iris and gave rise to few scattered extremely faint green fluorescent, limited plexuses of irregularly bulgy fibres. Suggestions as to the cellular origin of the SW-fibres include the ciliary ganglion and the central nervous system.