Age-related decrease in responsiveness to L-DOPA is not due to changes in dopamine receptor mRNAs or G protein mRNAs.

To clarify the cause of the age-related decrease in the responsiveness to L-DOPA seen in parkinsonian patients, we studied age-related changes in the mRNA levels of dopamine receptors (D1, D2) and of G proteins (Gs, Gi, Go) in 22 control human brains aged 50-105 years. Neither the mRNA levels of dopamine receptors or of the G proteins changed with age. Another factor in the receptor-G protein cascade, such as guanine nucleotide binding, may cause the age-related decrease in responsiveness.