Fluorescence histochemical and ultrastructural observations on preterminal noradrenergic axons following ligation or treatment with 6-hydroxydopamine.

This study was designed to compare the effects of 6-hydroxydopamine (6-OHDA) treatment with those of mechanical constriction of noradrenergic preterminal fibres in the rat. Constriction produced a progressive accumulation of glyoxylic acid induced fluorescence, attributable to noradrenaline, in nerve trunks proximal to applied ligatures. The electron microscope showed that this accumulation comprised large numbers of granular vesicles in swollen axons. Degenerative changes were also present and the axonal microtubules were distorted or absent. Preterminal fibres also contained accumulated noradrenaline histofluorescence after 6-ODHA (100 mg/kg) treatment, though this accumulation was not as focal as it was after constriction. The ultrastructural appearance of preterminals from 6-OHDA-treated rats closesely resembled that seen proximal to constrictions. Swollen axons were present. These contained many granular vesicles and exhibited degenerative changes. The microtubules were disrupted or absent. It is suggested that 6-OHDA produces accumulation of noradrenaline storage vesicles and other organelles in preterminal fibres because the primary lesion of the terminals presents a barrier to intra-axonal transport of these organelles.