Tract-tracing study of the extrabulbar Olfactory projections in the brain of some teleosts

Abstract

The extrabulbar olfactory projections (EBOP) is a collection of nerve fibers that originate from primary olfactory receptor neurons. These fibers penetrate into the brain, bypassing the olfactory bulbs (OBs). While the presence of an EBOP has been well established in teleosts, here we morphologically characterize the EBOP structure in four species each with a different morphological relationship of OB with the ventral telencephalic area. Tract-tracing methods (carbocyanine DiI/DIA and biocytin) were used. FMRFamide immunoreactive nervus terminalis (NT) components were also visualized to define any neuroanatomical relationship between the NT and EBOP. Unilateral DiI/DiA application to the olfactory chamber stained the entire olfactory epithelium, olfactory nerve fibers, and ipsilateral olfactory bulb. Labeled primary olfactory fibers running ventromedially as extrabulbar primary olfactory projections reached various regions of the secondary prosencephalon. Only in Moenkhausia sanctaefilomenae (no olfactory peduncle) did lipophilic tracer-labeled fibers reach the ipsilateral mesencephalon. The combination of tracing techniques and FMRFamide immunohistochemistry revealed a substantial overlap of the label along the olfactory pathways as well as in the anterior secondary prosencephalon. However, FMRFamide immunoreactivity was never colocalized in the same cellular or fiber component as visualized using tracer molecules. Our results showed a certain uniformity in the neuroanatomy and extension of EBOP in all four species, independent of the pedunculate feature of the OBs. The present study also provided additional evidence to support the view that EBOP and FMRFamide immunoreactive components of the NT are separate anatomical entities.

Cobalt Chloride Treatment Used to Ablate the Lateral Line System Also Impairs the Olfactory System in Three Freshwater Fishes

“…This is in agreement with our data where we observed decreased neural activity in the Dp only at 18-hours post-treatment. Although we only examined cfos staining in the Dp and one other control region, extra-bulbar projections from the olfactory epithelium also project directly to regions of the brain implicated in social behaviors (such as the ventral nucleus of the ventral telencephalon, Vv, and preoptic area) [ 73 , 85 – 87 ] suggesting that they could also be directly affected by CoCl 2 treatment. If this is the case, cobalt chloride treatment could have even more widespread effects on neural circuits and social behaviors at multiple levels within the brain.…”

Neuroanatomical relationships between FMRFamide-immunoreactive components of the nervus terminalis and the topology of olfactory bulbs in teleost fish

“…The position of the NT cells, as visualized by gonadotropin-releasing hormone (GnRH) immunohistochemistry and the type of OBs are reported to follow a particular evolutionary trend, with basal teleost species having pedunculate OBs and more peripherally displaced NT cells, whereas more derived species tend to have sessile OBs and fewer, more centrally located GnRHimmunoreactive (ir) NT cells (Parhar 2002). In addition to GnRH (Schreibman et al 1979;Oka and Ichikawa 1990;Yamamoto et al 1995), the teleost NT cells and fibres also contain FMRFamide-like compounds (Walker and Stell 1986;Ekström et al 1988;Östholm et al 1990;Rama Krishna and Subhedar 1992;Vecino and Ekström 1992;Pinelli et al 2000;Mathieu et al 2002;D'Aniello et al 2015). The presence of FMRFamide-ir NT cells in a pre-bulbar position has been reported in species with pedunculate OBs (Bonn and König 1989a;Fujii and Kobayashi 1992;Biju et al 2003), although in some other species, FMRFamide-ir NT cells have also been observed in postbulbar positions (Rama Krishna and Subhedar 1992).…”

Cranial Pair 0: The Nervus Terminalis

“…The nervus terminalis complex has been described in all major groups of vertebrates (Demski, ) including lampreys and lungfishes (Von Bartheld, ), teleost fishes (D'Aniello et al, ), amphibians (McKibben, ; Muske and Moore, ; Hofmann and Meyer, ; Wirsig‐Wiechmann, ), reptiles (Johnston, ; D'Aniello et al, ), birds (Wirsig‐Wiechmann, ), and different mammalian groups (Huber and Guild, ; Larsell, ) including rodents (Bojsen‐Moller, ; Schwanzel‐Fukuda et al, ), bats (Oelschlager, ), cetaceans (Oelschlager et al, ; Ridgway et al, ), primates (Witkin, ), and humans—embryos (Bossy, ; Muller and O'Rahilly, ) and adults (Fuller and Burger, ).…”