Regulation of dopamine D₃ receptor in the striatal regions and substantia nigra in diffuse Lewy body disease

Abstract

The regulation of D₃ receptor has not been well documented in diffuse Lewy body disease (DLBD). In this study, a novel D₃-preferring radioligand [(3)H]WC-10 and a D₂-preferring radioligand [(3)H]raclopride were used and the absolute densities of the dopamine D₃ and D₂ receptors were determined in the striatal regions and substantia nigra (SN) from postmortem brains from five cases of DLBD, which included dementia with Lewy bodies (DLB, n=4) and Parkinson disease dementia (PDD, n=1). The densities of the dopamine D₁ receptor, vesicular monoamine transporter 2 (VMAT2), and dopamine transporter (DAT) were also measured by quantitative autoradiography using [(3)H]SCH23390, [(3)H]dihydrotetrabenazine, and [(3)H]WIN35428, respectively. The densities of these dopaminergic markers were also measured in the same brain regions in 10 age-matched control cases. Dopamine D₃ receptor density was significantly increased in the striatal regions including caudate, putamen and nucleus accumbens (NAc). There were no significant changes in the dopamine D₁ and D₂ receptor densities in any brain regions measured. VMAT2 and DAT densities were reduced in all the brain regions measured in DLB/PDD, however, the significant reduction was found in the putamen for DAT and in the NAc and SN for VMAT2. The decrease of dopamine pre-synaptic markers implies neuronal loss in the substantia nigra pars compacta (SNpc) in these DLB/PDD cases, while the increase of D₃ receptors in striatal regions could be attributed to dopaminergic medication history and psychiatric states such as hallucinations. Whether it also reflects compensatory regulation upon dopaminergic denervation warrants further confirmations on larger populations.

Keywords: Parkinson disease; diffuse Lewy body disease; dopamine receptors; quantitative autoradiography.

Figure 1. Chemical structures of [³H]WC-10 and [³H]raclopride

K_d values were obtained through saturation binding of [³H]WC-10 and [³H]raclopride to cloned human D₃ and D_2L receptors expressed in HEK cells. a₁ and b₁ represent the fractional receptor occupancy to dopamine D₂ and D₃ receptors in human brain at a ligand concentration of 3.54 nM for [³H]WC-10. a₂ and b₂ represent the same parameters at a ligand concentration of 2.50 nM [³H]raclopride. The receptor occupancy fractions were calculated from the saturation binding isotherm using the K_d values. *Data taken from (Xu et al., 2009)

Figure 2. Quantitative autoradiographic analysis of dopamine D₁ receptor density in the striatal regions and substantia nigra (SN) of subjects with DLB/PDD and age-matched controls

Autoradiograms show total binding of 1.44 nM [³H]SCH23390 (A, B) and nonspecific binding in the presence of 1 μM (+) butaclamol (C,D) in the striatal regions (A, C) and substantia nigra (SN) (B, D) in DLB/PDD and age-matched controls. [³H]Microscale standards (ranging from 0 – 36.3 nCi/mg) were also counted (E). Quantitative analysis of the dopamine D₁ receptor density (fmol/mg) in the striatal regions and SN of DLB/PDD and age-matched control are shown in F and G respectively. The numbers 1 – 4 designate the following regions: Putamen (1); Caudate (2); Nucleus Accumbens (3); Substantia Nigra (4).

Figure 3. Quantitative autoradiographic analysis of dopamine D₂ receptor density in the striatal regions and substantia nigra of subjects with DLB/PDD and age-matched controls

Autoradiograms show total binding of 2.50 nM [³H]raclopride (A, B) and nonspecific binding in the presence of 1 μM S(−)-eticlopride (C, D) in the striatal regions (A, C) and substantia nigra (SN) (B, D) in DLB/PDD and age-matched controls. [³H]Microscale standards (ranging from 0 – 36.3 nCi/mg) were also counted (E). Quantitative analysis of the dopamine D₂ receptor density (fmol/mg) in the striatal regions and SN of DLB/PDD and age-matched controls are shown in F and G respectively. The numbers 1 – 4 designate the following regions: Putamen (1); Caudate (2); Nucleus Accumbens (3); Substantia Nigra (4).

Figure 4. Quantitative autoradiographic analysis of dopamine D₃ receptor density in the striatal regions and substantia nigra of subjects with DLB/PDD and age-matched controls

Autoradiograms show total binding of 3.54 nM [³H]WC-10 (A, B) and nonspecific binding in the presence of 1 μM S(−)-eticlopride (C, D) in striatal regions (A, C) and substantia nigra (SN) (B,D) in DLB/PDD and age-matched controls. [³H]Microscale standards (ranging from 0 – 36.3 nCi/mg) were also counted (E). Quantitative analysis of the dopamine D₃ receptor density (fmol/mg) in the striatal regions and SN of DLB/PDD and age-matched controls are shown in F and G respectively. The numbers 1 – 4 designate the following regions: Putamen (1); Caudate (2); Nucleus Accumbens (3); Substantia Nigra (4). *p<0.05 for DLB/PDD vs. control

Figure 5. L-Dopa effect on dopamine D₃ receptor density in the striatal regions and substantia nigra

Two of DLBD cases had history of L-Dopa treatment and showed as open scale. L-Dopa effect on D₃ receptor density is minimal in all the brain regions, with an exception in nucleus accumbens, where an increased trend of D₃ receptor density in L-Dopa treatment cases was found. DLBD: Diffuse Lewy body disease.

Figure 6. Hallucinations and dopamine D₃ receptor density in the striatal regions and substantia nigra

Three of DLBD cases presented with hallucinations and showed as open scale. DLBD cases with hallucinations didn’t show increased level of dopamine D₃ receptor density in any brain regions. DLBD: Diffuse Lewy body disease; Ha: Hallucinations.

Figure 7. Quantitative autoradiographic analysis of VMAT2 density in the striatal regions and substantia nigra of subjects with DLB/PDD and age-matched controls

Autoradiograms show total binding of 4.53 nM [³H]DTBZ (A, B), and nonspecific binding in the presence of 1 μM S(−)-tetrabenazine (C, D) in the striatal regions (A, C) and substantia nigra (SN) (B, D) in DLB/PDD and age-matched controls. [³H]Microscale standards (ranging from 0 to 36.3 nCi/mg) were also counted (E). Quantitative analysis of the VMAT2 density (fmol/mg) in the striatal regions and SN of DLB/PDD and age-matched controls are shown in F and G respectively. The numbers 1 – 4 designate the following regions: Putamen (1); Caudate (2); Nucleus Accumbens (3); Substantia Nigra (4). *p<0.05 for DLB/PDD vs. control

Figure 8. Quantitative autoradiographic analysis of DAT density in the striatal regions and substantia nigra of subjects with DLB/PDD and age-matched controls

Autoradiograms show total binding of 2.19 nM [³H]WIN35428 (A, B), and nonspecific binding in the presence of 1 μM nomifensine (C, D) in the striatal regions (A, C) and substantia nigra(SN) (B, D) in DLB/PDD and age-matched controls. [³H]Microscale standards (ranging from 0 – 36.3 nCi/mg) were also counted (E). Quantitative analysis of DAT density (fmol/mg) in the striatal regions and SN of DLB/PDD and age-matched controls are shown in F and G respectively. The numbers 1 – 4 designate the following regions: Putamen (1); Caudate (2); Nucleus Accumbens (3); Substantia Nigra (4). # p<0.01 for DLB/PDD vs. control