The organum vascolosum laminae terminalis of the domestic fowl: a Golgi and ultrastructural study.

The organum vascolosum laminae terminalis (OVLT) of the fowl was studied both with the aid of the rapid Golgi method and at ultrastructural level. Small and medium-sized isodendritic neurons were observed after silver impregnation of the OVLT. Their processes often run towards the great number of blood capillaries of the organ. Small bipolar neurons were intermingled between isodendritic elements. A peculiar ultrastructural finding of the OVLT neurons was the presence of a variable amount of dense-core vesicles 90-150 nm in diameter in their cytoplasm. Numerous nerve fibers and terminals surrounded neurons, glial cells and capillaries of the OVLT. These terminals were classified into 3 main types according to the diameter of dense core vesicles observed in them. Statistical evaluations of the populations of dense core vesicles confirmed this subdivision. Type 3 terminals had ultrastructural features of monoaminergic endings, whereas type 1 and 2 terminals were probably peptidergic fibers. Neurohaemal contacts were observed. between terminals with large dense core vesicles (type 2) and blood capillaries of the OVLT.