THE CAUDAL NEUROSECRETORY-SYSTEM AND ITS AFFERENT SYNAPSES IN THE GOLDFISH, CARASSIUS-AURATUS - MORPHOLOGY, IMMUNOHISTOCHEMISTRY, AND FINE-STRUCTURE

Morphological features of the goldfish caudal neurosecretory system we re investigated by means of immunohistochemical localization of uroten sins I and II (UI and UII) and electron microscopic examination of the caudal neurosecretory neurons, the urophysis, and the synaptic neurop il. The aim of the work is to provide a detailed morphological descrip tion of the afferent synapses to the caudal neurons and to analyze the ir distribution through the rostrocaudal extension of the caudal neuro secretory system. Three morphologically different types of neurosecret ory cells have been identified according to size and shape: large, med ium, and small Dahlgren cells. The three different-sized cells share s imilar patterns of immunoreactivity with the UI (or oCRF) and the UII antisera. Electron microscopic examination of the synaptic neuropil th roughout the caudal system revealed the presence of four types of term inals: dense-cored-vesicle end bulbs (DC), spherical-vesicle end bulbs (S), flattened-vesicle end bulbs (F), and granular-vesicle end bulbs (CT). The present study demonstrates that the small Dahlgren cells rec eive different synaptic inputs from the large and the medium neurosecr etory cells. Indeed, G terminals are only found on the small Dahlgren cells, whereas DC, S, and F terminals are distributed on the large, me dium, and small Dahlgren cell bodies and proximal processes. (C) 1998 Wiley-Liss, Inc.