Harvesting of olfactory ensheathing cells for autologous transplantation into the spinal cord injury. Its complexity in dogs

(2015) Harvesting of olfactory ensheathing cells for autologous transplantation into the spinal cord injury. Its complexity in dogs. The mucosa lining the nasal cavity and its content contains olfactory sensory neurons (OSNs). The OSNs are organized into different territories (four in mammals with a more sophisticated model) and, with the exception of the OSNs enclosed in the vomeronasal organ, they are directly exposed to the external environment and are hence vulnerable to physical, chemical or traumatic injuries. This permanent exposure to toxic substances is probably the reason why the olfactory epithelium has developed the ability to continually replace neurons (Graziadei and Graziadei, 1979). Due to neurogenesis, which persists even through adulthood, there are neurons in the OE with different degrees of development. The apical end of the mature neurons detects odorants trough the cilia of the corresponding dendrites, and from the basal side of such neurons an axon projects outside the OE into the lamina propria (LP). Axons from different adult neurons form bundles and later nerves, olfactory nerves, which cross the cribriform plate of the ethmoid bone and meninges reaching the olfactory nerve and glomerular layers of the olfactory bulb. From the LP to their target, only the olfactory ensheathing cells (OECs) enwrap these unmyelinated olfactory axons preventing them from having contact with any other kind of glial cells (Ramón-Cueto and Avila, 1998). OECs have emerged as one of the most promising candidates to repair nervous system lesions, specifically spinal cord injuries (SCIs) (Raisman et al., 2012), although this is a matter of not little controversy, due to methodological concerns and deficits in experimental designs (Granger et al., 2014). Methodologically, autologous transplantation implies serious difficulties, and the adequate taking of tissue samples is an important prerequisite to define. To date, different species have been used to evaluate the transplantation of OECs and the dog is thought to be an interesting model, among other reasons, because (i) SCI occurs naturally (Bergknut et al., 2013), (ii) some true trial has been successfully done (Granger et al., 2012), (iii) the size and peculiarities of their olfactory tissue (Ziege et al., 2013), and (iv) the morphological proximity of their vertebral column and spinal cord to humans'. In dogs the LP is especially well developed in the olfactory mucosa (OM) of the posterior part of the nasal septum, near the cribriform plate of the ethmoid bone, and that is therefore the most favorable area …