Dopamine Receptor Sites and States in Human Brain
Of the several dopamine-sensitive sites in the brain, the one that most correlates with psychomotor behaviour is the D2 receptor. This receptor has two states. The D 2 Hi state is characterized by its nM affinity for dopamine. The D 2 Lo state is typified by its μM affinity for dopamine. Neuroleptics have the same affinity (50 pM for spiperone) for both states. Guanine nucleotides convert most, if not all, of the D 2 Hi sites into D 2 Lo sites. Any D 2 Hi sites which are insensitive to GTP, if such exist, may be separate D4 sites. In addition to the binding of 3H-spiperone being higher in post-mortem schizophrenic brains, the proportions of the D2 receptor in the D 2 Hi state appear to be less in preliminary data on the schizophrenic brain.
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