MODULATION OF MOTONEURON EXCITABILITY BY BRAIN-DERIVED NEUROTROPHIC FACTOR

The influence of neurotrophins on motoneuron survival and development has been well documented in cell cultures and neonates. In the present study, the role of brain-derived neurotrophic factor (BDNF) in the ma intenance of motoneuron electrical properties was investigated. In adu lt male rats, BDNF- or saline-saturated gelfoam was inserted between t he medial and lateral heads of the gastrocnemius muscles. After 5 days survival, in vivo intracellular recordings were obtained, and motoneu ron biophysical properties were measured. In BDNF-treated rats, signif icant decreases in mean rheobase and in total cell. capacitance of med ial gastrocnemius motoneurons were observed. In addition, a concommita nt increase in input resistance and decrease in membrane time constant were noted in BDNF-treated rats but were not statistically significan t. No significant treatment effect was observed in motoneuron conducti on velocity, action potential amplitude, equalizing time constant, ele ctrotonic length, afterhyperpolarization amplitude and duration, and m embrane potential sag during current injection. The observed changes i n motoneuron rheobase and total cell capacitance suggest that applicat ion of BDNF produces an increase in motoneuron excitability coincident with a reduction in size. These data are discussed with respect to th e possible role of BDNF as a muscle-derived trophic factor for the reg ulation of motoneuron excitability.