Adult and neonatal rat brains contain functional LH/hCG receptors. These findings have led us to hypothesize that the fetal rat brain may also contain these receptors. To test this hypothesis, we isolated neurons from 19-day-old fetal rat brains and cultured them in chemically defined serum-free medium. The reverse transcription polymerase chain reaction amplified an expected 256-base pair size LH/hCG receptor fragment that could hybridize with a full-length LH/hCG receptor cDNA in Southern blotting. Northern blotting demonstrated that neurons contained a major 2.6 kilobase (kb) and a minor 4.3 kb transcript. Immunocytochemistry demonstrated that the neurons contained LH/hCG receptor immunostaining. Western immunoblotting showed that neurons contained an 80-kDa receptor protein that increased to a maximal level on Day 3 of culture and then gradually decreased until the 9th day of culture. Culturing neurons for 3 days in the presence of highly purified hCG resulted in a dose-dependent increase in the outgrowth of neurite processes and total cellular protein and a decrease in DNA fragmentation as compared to values in the corresponding controls. At the maximally effective hCG concentration, the number of neuritebearing cells was increased by 53% and the total cellular protein by 60%, and DNA fragmentation decreased by 31%. In summary, this is the first study to demonstrate the presence of LH/hCG receptors and neurotrophic effects of hCG in fetal rat brain neurons. These findings imply that locally produced gonadotropins may possibly play a role in the growth and development of the fetal brain.