Changes in striatal dopamine D2 receptors in relation to expression of and recovery from experimental parkinsonism

Changes in dopamine D₂ receptor number in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cats during various stages of experimental parkinsonism were examined. In the normal adult cat, D₂ receptors were expressed throughout the striatum. In symptomatic cats (assessed 7 days after the last MPTP administration), there was a slight elevation of D₂ receptors in all striatal regions. At 2 weeks after MPTP (animals still grossly symptomatic), D₂ receptor number was increased 60–75% above normal. At 3 weeks after MPTP (partial functional recovery), D₂ receptor number remained elevated at a level slightly less than that observed at 2 weeks. At 6 weeks after MPTP (full functional recovery), D₂ receptor levels were back to normal. Changes in D₂ receptor mRNA expression in the striatum essentially mirrored the changes in receptor number. Increases in D₂ receptor number and mRNA expression did not coincide with the onset of parkinsonian signs and peaked after the parkinsonism was established. Permanent reduction of parkinsonian signs corresponded to normalization of D₂ receptor number.