Book contents
- Frontmatter
- Contents
- Foreword
- Acknowledgments
- Introduction
- 1 The life history of dopamine
- 2 Enzymology of tyrosine hydroxylase
- 3 The assay of tyrosine hydroxylase
- 4 Enzymology of aromatic amino acid decarboxylase
- 5 PET studies of DOPA utilization
- 6 Conjugation and sulfonation of dopamine and its metabolites
- 7 Dopamine synthesis and metabolism rates
- 8 MAO activity in the brain
- 9 Vesicular storage of dopamine
- 10 Dopamine release: from vesicles to behavior
- 11 The plasma membrane dopamine transporter
- 12 Dopamine receptors
- 13 Imaging dopamine D1 receptors
- 14 Imaging dopamine D2 receptors
- 15 Factors influencing D2 binding in living brain
- 16 The absolute abundance of dopamine receptors in the brain
- 17 Conclusions and perspectives
- References
- Index
- Plate section
16 - The absolute abundance of dopamine receptors in the brain
Published online by Cambridge University Press: 04 December 2009
- Frontmatter
- Contents
- Foreword
- Acknowledgments
- Introduction
- 1 The life history of dopamine
- 2 Enzymology of tyrosine hydroxylase
- 3 The assay of tyrosine hydroxylase
- 4 Enzymology of aromatic amino acid decarboxylase
- 5 PET studies of DOPA utilization
- 6 Conjugation and sulfonation of dopamine and its metabolites
- 7 Dopamine synthesis and metabolism rates
- 8 MAO activity in the brain
- 9 Vesicular storage of dopamine
- 10 Dopamine release: from vesicles to behavior
- 11 The plasma membrane dopamine transporter
- 12 Dopamine receptors
- 13 Imaging dopamine D1 receptors
- 14 Imaging dopamine D2 receptors
- 15 Factors influencing D2 binding in living brain
- 16 The absolute abundance of dopamine receptors in the brain
- 17 Conclusions and perspectives
- References
- Index
- Plate section
Summary
Most molecular imaging studies make use of a single injection of the radioligand at very high specific activity, such that the mass of substance is negligible. Consequently, the index of receptor availability (pB) is formally ambiguous, being a function of the number of receptors (Bmax), divided by the apparent affinity of the ligand in vivo (Kdapp). Separate determination of the saturation binding parameters requires multiple tracer injections, such that a range of receptor occupancies are obtained. This chapter summarizes the relationship between PET estimates of dopamine receptor abundance, and estimates obtained using preparations in vitro. The various findings in the cases of dopamine D1 receptors (Table 13.1) and D2 receptors (Table 14.1) reveal the extent of agreement between the several quantitative methods.
The absolute density of dopamine receptors in the brain can be quantified using a variety of methods in vitro (Seeman 1987). The saturation binding parameters for a radioligand are measured under controlled conditions, using either washed membranes or brain cryostat sections. The experimentalist exposes the tissue samples to a range of radioliogand concentrations, ideally extending at least one order of magnitude to each side of the half-saturation concentration, Kd. The ionic composition of the incubation buffer, the incubation temperature, and the duration of incubation are determined entirely by laboratory procedures; the specific binding is measured relative to the binding in the presence of a non-radioactive competitor for the same site.
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- Imaging Dopamine , pp. 224 - 228Publisher: Cambridge University PressPrint publication year: 2009