Transitional states of central serotonin receptors in Parkinson's disease.

Crude membrane preparations from the frontal cortex of controls and parkinsonian patients were used to demonstrate affinity changes of the specific 3H-5-hydroxytryptamine (5-HT) binding sites. Two such sites were notable in controls, a finding consistent with earlier observations. In Parkinson's disease, both high- and low-affinity sites are significantly decreased. Additional experiments either with prolonged incubation times or pre-incubation with N-ethylmaleimide change the two affinities to a single high-affinity or low-affinity constant. The concept of transitional states of 5-HT receptors is discussed and seems to have important implications in the treatment of parkinsonism.