ABSTRACT. We examined the proliferation capacity and neuronal differentiation potency of canine bone marrow stromal cells (BMSCs). In addition, the microstructures of neuron-like cells after neuronal differentiation were observed under a scanning electron microscope. Canine BMSCs grew to confluency at 10.0 ± 2.5 days, and 3.8 ± 2.1 × 10 6 BMSCs were collected in one passage. Approximately 65% of canine BMSCs changed to neuron-like morphology after neuronal differentiation, and nearly all neuron-like cells stained positive against neuron-specific enolase. In addition, microstructures such as the cellular organelles, filaments and growth cones of these cells bore a close resemblance to those of the original mature neurons. These results suggested that canine BMSCs might be capable of differentiating into neurons. KEY WORDS: bone marrow stromal cell, canine, differentiation, microstructure, neuron.doi: 10.1292/jvms.11-0388; J. Vet. Med. Sci. 74 (7): [923][924][925][926][927] 2012 Despite the progress in the treatment of spinal cord injury (SCI) in recent years, it is still difficult to recover from severe paralysis. Recently, spinal cord regenerative therapy using stem cells has been clinically applied as one option for the treatment of severe SCI in human medicine [3,11,15]. Among the stem cells, bone marrow stromal cells (BMSCs) and olfactory ensheathing glia (OEG) have been the focus of research and clinical application for spinal cord regenerative therapy in dogs [5,7,8,12,14,17].BMSCs are adherent cells in the culture of bone marrow aspirates, but are not hematopoietic cells [13]. BMSCs are capable of differentiating into bone [2,6] BMSCs are easy to isolate in dogs and expand without serious technical problems [6]. The most significant practical advantages of using BMSCs are that autologous transplantation is possible, the costs of culturing are lower, and the risk of teratoma formation is very low [13]. Some studies have shown that canine BMSCs can differentiate into neuron-like cells expressing mature neuronal markers [5,7,8]. For these reasons, our laboratory is currently investigating BMSCs for use in spinal cord regenerative therapy in dogs.Recently, the experimental study and clinical trial of regenerative therapy for SCI using autologous BMSCs also been performed in dogs [5,12]. Surprisingly, there have been almost no reports regarding basic research on canine BMSCs, although this is very important for the clinical application of canine BMSCs. Therefore, the purpose of the present study was to investigate the number of days until the canine BMSCs reach confluency and the number of cells collected in one passage. In addition, the percentage of total cells that changed to a neuron-like morphology and the percentage of cells shown to stain positive against a mature neuronal marker after neuronal differentiation were examined. We also observed the microstructures of the neuron-like cells differentiated from canine BMSCs under a scanning electron microscope (SEM).Six male beagle dogs (2.3 ± 1.8 years old...