The Olfactory System

The brain of the tree pangolin (Manis tricuspis). II. The olfactory system

“…The main olfactory system of the tree pangolin was comprised of the main olfactory bulb, the anterior olfactory nucleus, the rostral olfactory cortex, the olfactory tubercle, the lateral olfactory tract and the olfactory limb of the anterior commissure, the nucleus of the lateral olfactory tract, the piriform cortex and the rostral migratory stream, all of these being standard features of the main olfactory system in mammals. In addition, the anatomy and neurochemistry of these structures were very similar to that observed in other mammalian species and could be readily matched with the same features studied in far more detail in the rat brain (Ennis et al, ; Paxinos & Watson, ; Shipley & Ennis, ). Despite this global similarity there were three minor points of variation that warrant discussion, two regarding the main olfactory bulb and one regarding the nucleus of the lateral olfactory tract (NLOT).…”

“…The components of the accessory olfactory system observed in the tree pangolin include the accessory olfactory bulb and the nucleus of the accessory olfactory tract. Structurally, no major differences in the organization of this system in the tree pangolin, in comparison with other mammalian species, especially the rat (Ennis et al, ; Shipley & Ennis, ), were observed; however, one specific difference was noted, this being related to the subdivision of the accessory olfactory bulb into anterior and posterior divisions, a division often marked by the presence of a linea alba (Larriva‐Sahd, ). This was not observed in the tree pangolins analyzed in this study.…”

“…As the tree pangolin is an anatomically specialized, myrmecophagous, nocturnally active mammal (Doran & Allbrook, ; Ganguly, ; Meyer et al, ; Mohapatra & Panda, ; Swart et al, ), we examined the olfactory system of the tree pangolin to determine whether any specializations were present. The olfactory system of the tree pangolin occupies a proportion of the brain that could be considered quite typical for mammals, has all the major components of this system (both for the main and accessory/vomeronasal portions of this system) as found generally across mammals, and shows no distinct specializations in terms of the loss or addition of nuclei/cortical regions or components of these in relation to other mammals (e.g., compared to the laboratory rat, Ennis et al, ; Paxinos & Watson, ; Shipley & Ennis, ). Nevertheless, a range of small variations in the architecture and neurochemistry were noted, and the findings of the current study are relevant to understanding the relationship of olfactory‐mediated pangolin behavior with their environment.…”

“…human—60 μm, mouse—50–100 μm, honey bee—20–65 μm, Sinakevitch, Bjorklund, Newbern, Gerkin, & Smith, ), but not as large as observed in the African elephant (200–400 μm, Ngwenya, Patzke, Ihunwo, & Manger, ). The second variance was the lack of a distinct internal plexiform layer, the layer that normally houses the axons emerging from the mitral and tufted cells (Ennis et al, ; Shipley & Ennis, ). In the tree pangolin it appears that rather than being clustered into a distinct internal plexiform layer, these axons are found in horizontally oriented, loosely arranged, myelinated fascicles throughout the granular cell layer.…”

“…The sense of smell has been shown to be of strong adaptive value in many vertebrates, being an important sense used in foraging, environmental exploration, conspecific identification, and mate selection, amongst a broad range of olfactory associated behaviors related to survival (Aboitiz & Montiel, ; Jacobs, ; Kunio, Zhonghua, Xiaolan, David, Bradford, & Linda, ; Meister, ). While there is a diverse set of anatomical, neural, and genomic traits related to olfaction in mammals (Grus, Shi, Zhang, & Zhang, ; Hayden, Bekaert, Crider, Mariani, Murphy, & Teeling, ; Moulton, ), variation in the neural architecture of the components of the olfactory system appears to be conservative (Ennis, Puche, Holy, & Shipley, ; Grabe, Baschwitz, Dweck, Lavista‐Llanos, Hansson, & Sachse, ; Imai, ; Kosaka & Kosaka, ; Nagayama, Homma, & Imamura, ). Apart from superficial observations (Weber, ; Imam et al, ), the architecture of the olfactory system within the brain of pangolins is yet to be explored.…”