Multimodal Imaging and Analysis of the Neuroanatomical Organization of the Primary Olfactory Inputs in the Brownbanded Bamboo Shark, Chiloscyllium punctatum

Abstract

There is currently a limited understanding of the morphological and functional organization of the olfactory system in cartilaginous fishes, particularly when compared to bony fishes and terrestrial vertebrates. In this fish group, there is a clear paucity of information on the characterization, density, and distribution of olfactory receptor neurons (ORNs) within the sensory olfactory epithelium lining the paired olfactory rosettes, and their functional implications with respect to the hydrodynamics of incurrent water flow into the nares. This imaging study examines the brownbanded bamboo shark Chiloscyllium punctatum (Elasmobranchii) and combines immunohistochemical labeling using antisera raised against five G-protein α-subunits (Gαs/olf, Gαq/11/14, Gαi–1/2/3, Gαi–3, Gαo) with light and electron microscopy, to characterize the morphological ORN types present. Three main ORNs (“long”, “microvillous” and “crypt-like”) are confirmed and up to three additional microvilli-bearing types are also described; “Kappe-like” (potential or homologous “Kappe” as in teleosts), “pear-shaped” and “teardrop-shaped” cells. These morphotypes will need to be confirmed molecularly in the future. Using X-ray diffusible iodine-based contrast-enhanced computed tomography (diceCT), high-resolution scans of the olfactory rosettes, olfactory bulbs (OBs), peduncles, and telencephalon reveal a lateral segregation of primary olfactory inputs within the OBs, with distinct medial and lateral clusters of glomeruli, suggesting a potential somatotopic organization. However, most ORN morphotypes are found to be ubiquitously distributed within the medial and lateral regions of the olfactory rosette, with at least three microvilli-bearing ORNs labeled with anti-Gαo found in significantly higher densities in lateral lamellae [in lateral lamellae] and on the anterior portion of lamellae (facing the olfactory cavity). These microvilli-bearing ORN morphotypes (microvillous, “Kappe-like,” “pear-shaped,” and “teardrop-shaped”) are the most abundant across the olfactory rosette of this species, while ciliated ORNs are less common and crypt cells are rare. Spatial simulations of the fluid dynamics of the incurrent water flow into the nares and within the olfactory cavities indicate that the high densities of microvilli-bearing ORNs located within the lateral region of the rosette are important for sampling incoming odorants during swimming and may determine subsequent tracking behavior.

Ultramicroscopic organization of the exterior olfactory organ in Anguilla vulgaris in relation to its spawning migration

“…By SEM, the olfactory epithelial surface of the eel under study displayed noticeable longitudinal folds with lengthy furrows between, which symbolized the apical surface of labyrinth cells, as those declared by Chakrabarti and Ghosh (2011a ) in freshwater catfish and tigerperch, respectively. They are easily recognizable as rather large columnar cells crossing the entire olfactory epithelium thickness with clear cytoplasm and apical cup morphology ( Camilieri-Asch et al ., 2020 ). It is plausible that fish can develop the ion balance required for optimal olfactory functions by having their labyrinth cells excrete electrolytes during the sea phase and absorb them during the freshwater phase.…”

“…The post-fixed lamella’s pieces were then dehydrated in a graded series of ethanol and embedded in an Epon-Araldite mixture, which, by using a Reichert ultra-microtome, produced semithin sections of 1.5 mm. These semithin sections were stained with toluidine blue and contrasted in a 50% alcohol-uranyl acetate solution and lead citrate, as recommended by ( Camilieri-Asch et al ., 2020 ). With a transmission Philips EM 400 electron microscope at Alexandria University, Egypt, the olfactory lamellae were examined and photographed.…”

Head anatomy of a lantern shark wet‐collection specimen (Chondrichthyes: Etmopteridae)

“…This study describes the cranial morphology of an etmopterid shark species in detail using (dice)micro‐CT data for the first time. Camilieri‐Asch, Caddy, et al ( 2020 ) and Camilieri‐Asch, Shaw, et al ( 2020 ) have also performed diceCT scans, but of galeomorph sharks, among others, and published the results in two very recent studies. Kamminga et al ( 2017 ) performed CT scans of a wide variety of species but included in their database only hard tissues.…”

“…Camilieri-Asch, Caddy, et al (2020) and have also performed diceCT scans, but of galeomorph sharks, among others, and published the results in two very recent studies Kamminga et al (2017). performed CT scans of a wide variety of species but included in their database only hard tissues.…”

Microstructure of the Bonnethead Shark (Sphyrna tiburo) Olfactory Rosette

“…While a patchy, irregular distribution of epithelium has been described for one shark species, Port Jackson sharks ( Heterodontus portusjacksoni ), other described species have nonsensory epithelium concentrated at the inner margins of lamellae and sensory epithelium extending almost to the outer margin ( Schluessel et al. 2008 ; Camilieri-Asch et al. 2020a ).…”