The cloned dopamine D2 receptor reveals different densities for dopamine receptor antagonist ligands. Implications for human brain positron emission tomography

doi:10.1016/0922-4106(92)90121-B

European Journal of Pharmacology: Molecular Pharmacology

Volume 227, Issue 2, 1 October 1992, Pages 139-146

https://doi.org/10.1016/0922-4106(92)90121-B Get rights and content

Abstract

Since [³H]cmonapride ([³H]YM-0915-2), a benzamide neuroleptic, consistently detects more dopamine D₂ receptors than [³H]spiperone in the same tissue, we tested whether this property was inherent in the cloned dopamine D₂ receptor. We found that the density of dopamine D₂ receptors labelled by [³H]cmonapride was 15-fold to 2-fold (mean of 1.8-fold) higher than the density of dopamine D₂ receptors labelled by [³H]spiperone in cells expressing cloned dopamine D₂ receptors (either the short form (from rat) or the long form (from human)), matching similar findings in anterior pituitary tissue (rat or pig) or in post-mortem human caudate nucleus tissue. The situation was similar for another benzamide, [³H]raclopride, which revealed 1.3-fold to 1.8-fold (mean of 1.5-fold) more binding sites than that for [³H]spiperone in cell membranes containing cloned dopamine D₂ receptors. The apparently different dopamine D₂ receptor densities revealed by these two types of ³H-ligands (i.e. [³H]spiperone and the [³H]benzamides), therefore, arise from an inherent property of the dopamine D₂ receptor protein. These findings for the cloned dopamine D₂ receptor, therefore, partly explain the higher dopamine D₂ receptor density measured in human brain (by positron emission tomography) when using radioactive raclopride compared to results using radioactive methylspiperone. Hence, the apparent density of dopamine D₂ receptors measured by radioactive raclopride may be lower or higher than that revealed by radioactive spiperone or methylspiperone, depending on the magnitude of endogenous dopamine (which inhibits the binding of radioactive raclopride) and the inherent property of dopamine D₂ receptor proteins to exhibit more binding sites (D₂ monomers, possibly) for radioactive benzamides than for radioactive spiperone or methylspiperone (D₂ dimers, possibly).

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A third possible explanation is that the spiperone ligands and the benzamide ligands bind to different aspects of the D2 receptors. For example, the spiperone ligands bind to monomers of D2, while the benzamides bind to dimers or multimers of D2 receptors (Seeman et al., 1992; Zawarynski et al., 1998). For example, nemonapride (also known as emonapride), as well as raclopride, are benzamide antipsychotic drugs that consistently detect 50% more dopamine D2 receptors than spiperone in the same tissue, including the cloned D2 receptor (Seeman et al., 1992).
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Dopamine D₁-like receptors consisting of D₁ and D₅ subtypes are intimately implicated in dopaminergic regulation of fundamental neurophysiologic processes such as mood, motivation, cognitive function, and motor activity. Upon stimulation, D₁-like receptors initiate signal transduction cascades that are mediated through adenylyl cyclase or phosphoinositide metabolism, with subsequent enhancement of multiple downstream kinase cascades. The latter actions propagate and further amplify the receptor signals, thus predisposing D₁-like receptors to multifaceted interactions with various other mediators and receptor systems. The adenylyl cyclase response to dopamine or selective D₁-like receptor agonists is reliably associated with the D₁ subtype, while emerging evidence indicates that the phosphoinositide responses in native brain tissues may be preferentially mediated through stimulation of the D₅ receptor. Besides classic coupling of each receptor subtype to specific G proteins, additional biophysical models are advanced in attempts to account for differential subcellular distribution, heteromolecular oligomerization, and activity-dependent selectivity of the receptors. It is expected that significant advances in understanding of dopamine neurobiology will emerge from current and anticipated studies directed at uncovering the molecular mechanisms of D₅ coupling to phosphoinositide signaling, the structural features that might enhance pharmacological selectivity for D₅ versus D₁ subtypes, the mechanism by which dopamine may modulate phosphoinositide synthesis, the contributions of the various responsive signal mediators to D₁ or D₅ interactions with D₂-like receptors, and the spectrum of dopaminergic functions that may be attributed to each receptor subtype and signaling pathway.
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Additionally, benzamides and butyrophenones do not necessarily bind to the same state of the D2-receptor. To explain the higher binding capacity of [3H]-spiperone in membranes from several tissues (despite the presence of sodium chloride), butyrophenone binding was proposed to be restricted to the monomeric form of the receptor while benzamides were thought to bind to both the mono- and dimeric forms [24]. This suggests that the binding capacity of both types of ligands reflects the equilibrium between mono- and dimeric forms of the receptor in each preparation.
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Dose determination of haloperidol, risperidone and olanzapine using an in vivo dopamine D<inf>2</inf>-receptor occupancy method in the rat
2006, European Journal of Pharmacology
The purpose of the present study was to determine antipsychotic doses that achieve 80% striatal dopamine D₂-receptor occupancy for haloperidol, risperidone and olanzapine in rats. Wistar rats were treated with normal saline vehicle (controls), haloperidol (0.25 and 0.5 mg/kg/day), risperidone (3, 5 and 6 mg/kg/day) and olanzapine (5 and 10 mg/kg/day) for 7 days via osmotic minipumps. Striatal and cerebellar tissue were collected and in vivo dopamine D₂-receptor occupancies were determined using ³H-raclopride. The doses required to achieve dopamine D₂-receptor occupancy of 80% in 11- and 24-week old rats were: haloperidol 0.25 mg/kg/day, risperidone 5 mg/kg/day and olanzapine 10 mg/kg/day.
(-)S amisulpride binds with high affinity to cloned dopamine D<inf>3</inf> and D<inf>2</inf> receptors
2001, European Journal of Pharmacology
Amisulpride is a substituted benzamide antipsychotic with nanomolar affinity and high selectivity for dopamine D₂ and dopamine D₃ receptors. The interaction of racemic (+/−)RS amisulpride and its two enantiomers (+)R and (−)S with dopamine D₂ and dopamine D₃ receptors subtypes were compared with that of haloperidol. Binding studies were performed using either [³H]spiperone or [³H]nemonapride in baculovirus/Spodoptera frugiperda insect (Sf-9) cell system expressing either the human dopamine recombinant D₂long (hD_2L) or the rat dopamine recombinant D₃ (rD₃) receptors. K_i values at dopamine rD₃ receptors were similar regardless of the radioligand used, whereas at hD_2L receptors values were higher using [³H]spiperone than [³H]nemonapride. However, the rank order of compound potency against radiolabeled spiperone or nemonapride both at dopamine hD_2L and at dopamine rD₃ receptors was similar. (−)S amisulpride displaced [³H]spiperone or [³H]nemonapride binding from both dopamine hD_2L or dopamine rD₃ receptors, being twofold more potent than the racemic form and 38–19-fold more potent than (+)R enantiomer. Both racemic and the (−)S enantiomer exhibited 2–4 ([³H]spiperone)- and 3–4 ([³H]nemonapride)-fold higher affinity than haloperidol for dopamine rD₃ receptor, respectively. The (+)R enantiomer has weaker affinity with respect to haloperidol for both dopamine hD_2L and dopamine rD₃ receptors. Our results show that (−)S amisulpride is the active enantiomer of amisulpride, showing high affinity for dopamine D₃ and dopamine D₂ receptors.
Dopamine D<inf>2</inf> receptor dimer formation. Evidence from ligand binding
2001, Journal of Biological Chemistry
Citation Excerpt :
Previous reports would suggest that the binding of both [3H]spiperone andN-[3H]-methylspiperone are largely insensitive to sodium ions (19, 24, 25, 35). Discrepancies between the number of D2 receptors labeled by different radioligands in vitro have been reported extensively and for several ligands,e.g. [3H]spiperone (orN-[3H]methylspiperone) compared with either [3H]raclopride (21, 24), [3H]sulpiride (42), or [3H]nemonapride (3, 19, 21), although this was not seen in all reports (22, 23). In the present study, therefore, in the presence of sodium ions, [3H]raclopride and [3H]spiperone label similar numbers of sites, whereas in the absence of sodium ions [3H]raclopride labels fewer sites than are labeled by [3H]spiperone (69% under control conditions and 55% in the presence of NMDG).
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The cloned dopamine D2 receptor reveals different densities for dopamine receptor antagonist ligands. Implications for human brain positron emission tomography

Abstract

Eur. J. Pharmacol.

Eur. J. Pharmacol.

Neurosci. Lett.

Appl. Radiat. Isot.

Anal. Biochem.

FEBS Lett.

J. Pharmacol. Methods

Jpn. J. Pharmacol.

Eur. J. Pharmacol.

Cloning and expression of a rat D2 dopamine receptor cDNA

Nature

Dimerization of the extracellular domain of the human growth hormone receptor by a single hormone molecule

Science

Molecular dynamics of dopamine at the D2 receptor

D2 dopamine receptors in neuroleptic-naive schizophrenic patients: a positron emission tomography study with [11C]raclopride

Arch. Gen. Psychiatry

Cloning of the cDNA and gene for a human D2 dopamine receptor

D2-Dopamine receptor specific brain uptake of carbon-11-labeled YM-09151-2

J. Nucl. Med.

Measurement of D2 dopamine receptor-specific carbon-11-YM-09151-2 binding in the canine brain by PET: importance of partial volume correction

J. Nucl. Med.

Three-dimensional models of neurotransmitter G-binding protein-coupled receptors

Mol. Pharmacol.

Comparative pharmacokinetics of a new benzamide neuroleptic drug in rats, dogs and monkeys using a stable isotope technique

Xenobiotica

Difference in in vivo receptor binding between [3H]N-methylspiperone and [3H]raclopride in reserpine-treated mouse brain

J. Neural Trans.

The cloned dopamine D₂ receptor reveals different densities for dopamine receptor antagonist ligands. Implications for human brain positron emission tomography

Cloning and expression of a rat D₂ dopamine receptor cDNA

D₂ dopamine receptors in neuroleptic-naive schizophrenic patients: a positron emission tomography study with [¹¹C]raclopride

D₂-Dopamine receptor specific brain uptake of carbon-11-labeled YM-09151-2

Difference in in vivo receptor binding between [³H]N-methylspiperone and [³H]raclopride in reserpine-treated mouse brain