The hypothalamo-hypophysial system of the wild carp, Cyprinus carpio L.

Summary

The anterior neurohypophysis (ANH)-pars distalis complex of the carp, Cyprinus carpio L., has been analysed by combined light, fluorescence and electron microscopy. Only few “Gomori-positive” fibres are seen in the caudal and especially in the rostral part of the ANH, where the false “Gomori-positive” fibres predominate. Monoamine fluorescence shows the same distribution although it is extremely weak and only slightly increases after nialamide treatment. Four types of neurosecretory fibres and their terminals have been recognized in each part of the ANH. The sizes of neurosecretory granules contained in peptidergic A₁- and A₂-type fibres terminating in the rostral (120–220 nm and 60–140 nm) and caudal (120–160 nm and 90–120 nm) parts of the ANH differ. Monoaminergic B and B₁-type fibres have rounded (60–100 nm) or elongated (40×80 nm) granules, respectively. Some neurosecretory terminals (NST) of different types make contact with the capillaries located within the ANH roots as well as at the border between the latter and the pars distalis. Direct synaptoid axo-glandular contacts are very limited, and most neurosecretory fibres end close to continuous connective tissue septa separating the nervous tissue from the glandular cells of the rostral and caudal pars distalis. The question of the mode of the neuro-glandular relations in the complex ANH-pars distalis of teleosts is discussed.