The neuronal system of the saccus vasculosus of trout (

Abstract

The neuronal system of the saccus vasculosus of two species of trout was studied with immunocytochemical methods and carboindocyanine-dye (DiI) tract-tracing. The cerebrospinal-fluid-contacting neurons of the saccus were immunoreactive for gamma-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD), and neuropeptide Y (NPY). Immunostaining of alternate sections of the saccus vasculosus of fry with anti-GAD and anti-NPY indicated that these substances were colocalized. The tractus sacci vasculosi and the neuropil of the nucleus sacci vasculosi were also immunoreactive to these substances. The GABA, GAD, and neuropeptide Y immunoreactivity of the saccus vasculosus system appeared early in trout ontogeny. After applying DiI to various levels of the tractus sacci vasculosi of adult trout, we observed massive bilateral saccular projections to the nucleus sacci vasculosi and could follow the course of the sacco-thalamic tract. This tract extended in the subependymal region of the thalamus rostral to the nucleus sacci vasculosi and split into two small tracts that reached the subhabenular-preoptic region. Sacco-thalamic fibers formed extensive periependymal plexuses along their trajectory. Interestingly, no clear evidence of the existence of a saccopetal system was obtained. On the basis of these results, we postulate that the saccus vasculosus system modulates the function of centers of the posterior tubercle and periventricular thalamus.

The Brain of the Archerfish Toxotes chatareus: A Nissl-Based Neuroanatomical Atlas and Catecholaminergic/Cholinergic Systems

“…Ventral to midline (tuberal) hypothalamus, the lobular structure of the saccus vasculosus (SV) ( Figures 3J–N ) is easily recognizable (whereas the pituitary was lost in our preparations). The SV is a photoperiodic sensor which acts on seasonal gonadal changes in teleosts (Nakane et al, 2013) and is associated with a small nucleus in the posterior tuberculum, the NSV ( Figure 3L ), as previously shown in other species (Gómez-Segade and Anadón, 1988; Yáňez et al, 1997). …”

Distribution of gamma‐aminobutyric acid immunoreactivity in the brain of the Siberian sturgeon (Acipenser baeri): Comparison with other fishes

“…The tSV of the sturgeon was also intensely stained with choline acetyltransferase immunohistochemistry (Adrio et al., 2000). The main target of the tSV in teleosts (Yáñez et al., 1997), and elasmobranchs (Molist et al., 1992) is a conspicuous unpaired region from which, at least in teleosts, fibers of the SV extend to the periventricular thalamus (Yáñez et al., 1997). There are not functional studies on the SV of elasmobranchs and sturgeons, but in salmonids coronet cells of the SV form a photoneuroendocrine organ related to seasonal control of fish growth and reproduction although the functions of the CSF‐c neuronal system of the SV are not known (they probably form a sensory device) (Nakane et al., 2013).…”

“…An interesting difference between sturgeon and teleosts and elasmobranchs was noted in the distribution of GABA in the SV. The SV of sturgeon shows CSF-c GABAergic cells that give rise to a conspicuous tract of the SV (tSV), as those observed in trout and sharks (Sueiro et al, 2007;Yáñez et al, 1997). However, the sturgeon coronet cells (a cell type characteristic of the SV) show glycinergic and GABAergic signatures (Adrio et al, 2011;present results) unlike in teleosts and elasmobranchs.…”

“…Studies using anti‐GAD or anti‐GABA antibodies may be affected by the quick transport of GABA or its synthesizing enzyme toward axon terminals, which often makes it difficult to detect immunoreactivity in perikarya. Anyway, immunohistochemical studies have revealed that GABAergic neurons, fibers, and terminals are widely distributed in the brain and spinal cord of major groups of vertebrates (mammals: Aoki et al., 1986, 1989; Katarova et al., 2000; Mugnaini & Oertel, 1985; Oertel & Mugnaini, 1984; Ottersen & Storm‐Mathisen, 1984; birds: Csillag et al., 1987; Domenici et al., 1988; Granda & Crossland, 1989; Veenman & Reiner, 1994; reptiles: Bennis et al., 1991, Keifer et al., 1992; Rio et al., 1995; amphibians: Franzoni & Morino, 1989; Naujoks‐Manteuffel et al., 1994; A. Roberts et al., 1987; lungfishes: Trabucchi et al., 2000; teleosts: Ekström & Ohlin, 1995; Kim et al., 2004; Maler & Mugnaini, 1994; Martinoli et al., 1990; Médina et al., 1994; Mugnaini & Maler, 1987; Yáñez et al., 1997; elasmobranchs: Carrera et al., 2006, 2008; Sueiro, 2003; Sueiro et al., 2004, 2007; cyclostomes: Batueva et al., 1990; Brodin et al., 1990; Christenson, Alford, et al., 1991; Christenson, Bongianni, et al., 1991; Meléndez‐Ferro et al., 2000, 2001, 2003; Meléndez‐Ferro, Pérez‐Costas, et al., 2002; Meléndez‐Ferro, Villar‐Cheda, et al., 2002; Pombal et al., 1997, 1999; Rio et al., 1996; Robertson et al., 2007; Ruiz et al., 2004; Yáñez et al., 1999).…”