The caudal neurosecretory system and its afferent synapses in the goldfish, Carassius auratus: Morphology, immunohistochemistry, and fine structure

Abstract

Morphological features of the goldfish caudal neurosecretory system were investigated by means of immunohistochemical localization of urotensins I and II (UI and UII) and electron microscopic examination of the caudal neurosecretory neurons, the urophysis, and the synaptic neuropil. The aim of the work is to provide a detailed morphological description of the afferent synapses to the caudal neurons and to analyze their distribution through the rostrocaudal extension of the caudal neurosecretory system. Three morphologically different types of neurosecretory cells have been identified according to size and shape: large, medium, and small Dahlgren cells. The three different-sized cells share similar patterns of immunoreactivity with the UI (or oCRF) and the UII antisera. Electron microscopic examination of the synaptic neuropil throughout the caudal system revealed the presence of four types of terminals: dense-cored-vesicle end bulbs (DC), spherical-vesicle end bulbs (S), flattened-vesicle end bulbs (F), and granular-vesicle end bulbs (G). The present study demonstrates that the small Dahlgren cells receive different synaptic inputs from the large and the medium neurosecretory cells. Indeed, G terminals are only found on the small Dahlgren cells, whereas DC, S, and F terminals are distributed on the large, medium, and small Dahlgren cell bodies and proximal processes.

Development of the caudal neurosecretory system of the Nile tilapia Oreochromis niloticus: An immunohistochemical and electron microscopic study

“…These might represent sites where the content of small vesicles is discharged into the extracellular space by exocytosis, as the vesicles appear to fuse with the axolemma in these sites. The contemporaneous presence of small clear vesicles and large neurosecretory vesicles has been repeatedly described in the urophysis of different species (Cioni et al, 1996(Cioni et al, , 1998. Therefore, it is probably correlated with the functional activity of the neurosecretory terminals (i.e., the release of urotensins).…”

“…Sections were mounted on microscope slides coated with chrom-alum gelatin and incubated with antisera. Polyclonal rabbit antiserum to synthetic ovine CRF (Peninsula Laboratories, Belmont, CA) (dilution 1:800) was used to localize UI-like immunoreactivity (see also Cioni et al, 1998). The antiserum to oCRF cross-reacts with UI (Onstott and Elde, 1984).…”

Ontogenetic Development of the Caudal Neurosecretory System in the Chum Salmon, Oncorhynchus keta, with Regard to Its Ultrastructural Changes and with Relation to Neuropeptide Y-immunoreactive Fibers

“…Concerning the afferent peptidergic innervation of the caudal neurosecretory system, Miller and Kriebel (1986a, b) reported that descending peptidergic innervation in the caudal neurosecretory system of the molly may arise from the dorsal tegmental magnocellular nucleus, which includes GnRH immunoreactive neurons. More recently, four types of synaptic inputs to the Dahlgren cells have been identified, and at least two subpopulations of the Dahlgren cells were differentiated in the goldfish based on the ultrastructural features (Cioni et al, 1998). Further studies are needed to confirm the differentiation and development of the Dahlgren cells and their innervation in the chum salmon.…”