Motor neurons have been known to require a wide variety of neurotrophic factors for their survival. As one of the target-derived trophic factors, glial cell line-derived neurotrophic factor (GDNF) has been shown to exert its effects on motor neurons via a receptor complex including GDNF receptor alpha 1 (GFR alpha-1). Immunoreactivity of GFR alpha-1 was observed at myelinated peripheral nerves and neuromuscular junction (NMJ) of human skeletal muscles. Reverse transcriptase polymerase chain reaction (RT-PCR) analyses showed that mRNA of GFR alpha-1 existed in the ventral horn of hu man spinal cord, but not in the skeletal muscles. The results suggested that GFRa-1 mig ht play a key role for uptake and internalization of GDNF at the human NMJ. (C) 1999 Elsevier Science ireland Ltd. All rights reserved.