The life span of ganglionic glia in murine sensory ganglia estimated by uptake of bromodeoxyuridine

Abstract

Studies of ganglionic glia turnover in the sensory nervous system have implications for understanding nervous system maintenance and repair. These glial cells of the sensory ganglia in the peripheral nervous system (PNS) comprise satellite cells (SCs) and, to a lesser extent, Schwann cells. SCs proliferate in response to trauma such as axotomy; however, the half-life of these glial cells under normal circumstances has not been estimated. To estimate the half-life of sensory ganglionic glial cells, we employed the DNA precursor analog 5-bromo-2′-deoxyuridine (BrdU) to measure the rate of turnover of these cells. BrdU was administered to inbred C57BL6 and outbred Swiss white mice via their drinking water. BrdU incorporation into ganglionic glia in the PNS was estimated by immunofluorescent staining of nervous tissue sections, and the fraction of ganglionic glial cells that acquired BrdU label was measured as a function of time. Mathematical modeling of the rate of uptake of BrdU into murine ganglionic glia enables calculation of the half-life of these cells. The kinetics of BrdU uptake is linear, consistent with ganglionic glia being a homogenous population. The value of the proliferation rate (p) plus death rate (d) derived from the slope of BrdU uptake as a function of time is approximately 2.4 × 10−3 cells per day. Assuming that p = d (because ganglionic glial numbers are in equilibrium and they are assumed to neither emigrate from, or immigrate into, sensory ganglia), then the daily death rate is d = 1.2 × 10−3 cells/day, which implies a half-life for ganglionic glia of about 600 days. Thus murine ganglionic glia in the untraumatized state appear to behave as a homogenous, slowly replicating population.