No neuronal regulation of murine bone marrow function

Bone marrow is innervated by efferent (sympathetic) and afferent nerves, but it is not clear whether these nerves affect cell formation or release in any significant way. To elucidate this problem, we studied mice neonatally sympathectomized with 6-hydroxydopamine and adult mice in which one hind limb was surgically denervated. Progenitor and transit cell numbers and proliferative activity were estimated in bone marrow, blood, and spleen. In addition, we performed unilateral electrical stimulation of nerve fibers to tibial marrow and applied a cell mobilizing stimulus (bleeding, granulocyte colony-stimulating factor injection, or intraperitoneal injection of a chemotactic substance) to investigate cell egress from the marrow. Blood flow to hindleg bone marrow was assessed with the radioactive microsphere technique. Except for a smaller bone marrow cell population and lower body weight in neonatally sympathectomized mice, we found no clear indications that bone marrow innervation influenced cell production. Also, the innervation did not detectably affect cell release from the marrow. Electrical stimulation of hind limb nerves did not change the blood flow to the marrow, whereas it markedly decreased blood flow to the overlying muscle. We therefore conclude that no obvious function can be ascribed to tibial marrow innervation in the mouse.