Changes in striatal dopamine D(2) receptors in relation to expression of and recovery from experimental parkinsonism

Changes in dopamine D(2) 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, D(2) receptors were expressed throughout the striatum. In symptomatic cats (assessed 7 days after the last MPTP administration), there was a slight elevation of D(2) receptors in all striatal regions. At 2 weeks after MPTP (animals still grossly symptomatic), D(2) receptor number was increased 60-75% above normal. At 3 weeks after MPTP (partial functional recovery), D(2) receptor number remained elevated at a level slightly less than that observed at 2 weeks. At 6 weeks after MPTP (full functional recovery), D(2) receptor levels were back to normal. Changes in D(2) receptor mRNA expression in the striatum essentially mirrored the changes in receptor number. Increases in D(2) 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 D(2) receptor number.