Fine structure of noradrenaline nerve terminals in the dorsomedial portion of the nucleus tractus solitarii as demonstrated by a modified potassium permanganate method.

Fine structure of the noradrenaline (NA) nerve terminals in the dorsomedial portion of the nucleus tractus solitarii (NTS) was investigated by glyoxylic acid-potassium permanganate fixation method. The NA nerve terminals in this area contained a large number of small cored vesicles (SCV) (about 400-600 A in diameter) together with a few large cored vesicles (LCV) (about 1000 A in diameter). The most frequent feature of NA nerve terminals observed in this area was axo-dendritic contact. An axo-axonic contact between NA and non-NA terminals was also occasionally identified, while no axo-somatic contact was found in this area as far as examined. At the contact zone between NA terminals and other neuronal elements, the following profiles suggestive of synapse-like contact were identified: 1) somewhat dense material between contact membranes (intersynaptic filaments); 2) a slight accumulation of dense material adjacent to postcontact membranes; 3) disarrangement of contact membranes and enlargement of the space between these membranes; 4) aggregation of SCV and LCV to contact membranes. Finally it should be emphasized that NA nerve terminals often made a neuronal cluster or rosette with other neuronal elements, suggestive of a complicated role of NA on NTS function.