Brain dopamine receptors in schizophrenia and tardive dyskinesia

Brain dopamine receptors (type D2) mediate the psychomotor effects of dopamine. The D2 dopamine receptor can exist in either a high-affinity state for dopamine (nanomolar dissociation constant) or in a low-affinity state (micromolar dissociation constant). Both states of the receptor, however, have high affinity for neuroleptics (60 pM for spiperone). The postsynaptic receptor probably operates mainly in the D2 slow state. The presynaptic dopamine receptor, and also the dopamine receptors in the pituitary gland and the area postrema, probably function in the D2 high state. The density of brain D2 dopamine receptors is elevated in schizophrenia. The control densities were 10.5 pmol per g tissue. Half of the schizophrenic tissues (putamen, caudate nucleus, and nucleus accumbens) revealed densities of about 11.9 pmol per g, while the other half of the tissues revealed a density mode of 23.8 pmol per g. The bimodal distribution may support the concept of two types of schizophrenia. Future work must decide which group has more tardive dyskinesia.