RAPID COMMUNICATION Modulation of Motoneuron Excitability by Brain-Derived Neurotrophic Factor

Gonzalez, Michael and William F. Collins, III. Modulation of whereas Type S motoneurons are able to dictate motor unit motoneuron excitability by brain-derived neurotrophic factor. J. contractile speed via an orthodromic mechanism (for review, Neurophysiol. 77: 502–506, 1997. The influence of neurotrophins see Mendell et al. 1994). on motoneuron survival and development has been well docuRecently, it has been hypothesised that two members of the mented in cell cultures and neonates. In the present study, the role nerve growth factor family of neurotrophins, brain-derived neuof brain-derived neurotrophic factor (BDNF) in the maintenance rotrophic factor (BDNF) and neurotrophin-4 (NT-4) act as musof motoneuron electrical properties was investigated. In adult male cle-derived neurotrophic factors for motoneurons (Funakoshi et rats, BDNFor saline-saturated gelfoam was inserted between the al. 1993; Koliatsos et al. 1993). Both are produced by skeletal medial and lateral heads of the gastrocnemius muscles. After 5 muscle (Funakoshi et al. 1993; Koliatsos et al. 1993) and can days survival, in vivo intracellular recordings were obtained, and motoneuron biophysical properties were measured. In BDNFbe retrogradely transported by motoneurons (Koliatsos et al. treated rats, significant decreases in mean rheobase and in total 1993; Yan et al. 1993). Further, BDNF has been shown to cell capacitance of medial gastrocnemius motoneurons were obrescue motoneurons from programmed or injury-induced cell served. In addition, a concommitant increase in input resistance death during development (Oppenheim et al. 1992; Sendtner et and decrease in membrane time constant were noted in BDNFal. 1992; Yan et al. 1993). The present study addresses the treated rats but were not statistically significant. No significant possible role of muscle-derived BDNF in the regulation of mototreatment effect was observed in motoneuron conduction velocity, neuron electrical properties and is prompted by the observations action potential amplitude, equalizing time constant, electrotonic that BDNF mRNA expression is upregulated in medial gastroclength, afterhyperpolarization amplitude and duration, and memnemius muscle following denervation (Funakoshi et al. 1993; brane potential sag during current injection. The observed changes Koliatsos et al. 1993). The results indicate that application of in motoneuron rheobase and total cell capacitance suggest that application of BDNF produces an increase in motoneuron excitabilBDNF to the medial gastrocnemius muscle produces a signifiity coincident with a reduction in size. These data are discussed cant increase in electrical excitability of medial gastrocnemius with respect to the possible role of BDNF as a muscle-derived motoneurons. These data have been previously reported in abtrophic factor for the regulation of motoneuron excitability. stract form (Gonzalez and Collins 1995).