Functional Neuroimaging Lab School of Psychology University of Newcastle

1. Comparison of methodologies for the assessment of dopamine receptor binding in subregions of the striatum Sharna Jamadar Mentor: Julie Price PET Modality Coordinator: Jonathan Carney Functional Neuroimaging Lab School of Psychology University of Newcastle Schizophrenia Research Institute Darlinghurst, Australia

2. Become familiar with the basics of PET radioligand methods Compartmental models Logan graphical method (arterial input function) Logan graphical method (cerebellum reference tissue) Become familiar with two types of dopamine radioligands Raclopride CFT How do these differ? Project Aims Understand utility of PET radiotracer methods for the study of behaviour

3. VT = free + nonspecific + specific VND = free + nonspecific (non-displaceable reference uptake) PET Methodology 1T • Compartmental models • Model parameters determined by iterative non-linear least-squares fitting, used to obtain receptor binding measures, use arterial blood as model input • Outcome measures: • Distribution volume (VT) the ratio of the concentration of radioligand in a region of tissue to that in plasma (at equilibrium) • Distribution volume ratio (DVR) is related to receptor density x affinity, and equal to VT / VND • Binding potential (BP) proportional to receptor density x affinity 2T

4. PET Methodology Logan Graphical Methods Linear alternative, use arterial blood as input (VT), possible to use reference-tissue (DVR) Transforms multiple time measurements of plasma and tissue uptake into a linear plot, the slope related to receptor binding measures Appropriate for radiotracers for which a constant relationship between blood and brain tissue radioactivity is established during the study (steady-state) Advantages Simpler calculations (non-iterative) Not reliant upon definition of underlying compartments

5. Radiotracers for Dopamine [C-11]Raclopride D2/3receptors Benzamide that shows selective and moderate affinity for D2 receptors and binds reversibly to postsynaptic D2 receptors [C-11]CFT 2-carbomethoxy-3-(4-[18F]-fluorophenyl)tropane Dopamine transporter Cocaine analogue that shows good selectivity for the dopamine transporter over other transporters and shows little non-specific binding in the brain Dopamine transporter is present exclusively in dopamine-synthesising neurons, thus is an index of presynaptic dopaminergic function. (Almost) irreversible binding

6. Project • N=4 • Assess compartmental modeling and graphical methods for [C-11]raclopride & [C-11]CFT • Estimate binding potential: BP  (VT/VND) – 1 • Cerebellum used as reference tissue to estimate VND • Free of dopamine receptors, good estimate of non-displaceable (i.e., free + non-specific) uptake • Which method(s) are acceptable? • 1 tissue compartment model • 2 tissue compartment model • Logan (arterial) • Logan (reference tissue)

7. Project • Dorsal caudate (DCA) • Anteroventral striatum (AVS) • accumbens, ventromedial caudate + anteroventral putamen • Middle caudate (MCA) • Dorsal putamen (DPU) • Ventral putamen (VPU) First defined in Drevets et al. (1999) in baboon, used in humans Drevets et al. (2001)

8. [C-11]RAC Receptor free region = free + unspecific binding 1 Tissue Compartment CER 0.35 µCi/mL 0.1 obs-fit Time (min)

9. [C-11]RAC Receptor free region = free + unspecific binding 1 Tissue Compartment CER 0.35 µCi/mL 0.1 obs-fit Similar VT Slightly lower SS in 2T Better k estimation in 1T Time (min) 2 Tissue Compartment CER 0.35 0.1

10. [C-11]RAC 1 Tissue Compartment Receptor-rich region = free + unspecific + specific binding DPU CER 0.35 0.5 Differences in curve shapes = differences in clearance & specific binding 0.14 0.1 2 Tissue Compartment CER 0.35 0.1

11. [C-11]RAC 1 Tissue Compartment Differences in curve shapes = differences in clearance & specific binding DPU CER 0.35 0.5 0.14 0.1 Similar VT Lower SS in 2T Better k estimation in 1T 2 Tissue Compartment DPU CER 0.35 0.5 0.14 0.1

12. [C-11]RAC 1 Tissue Compartment DPU CER µCi/mL obs-fit Time (min) 2 Tissue Compartment DPU CER

13. [C-11]RAC 1 Tissue Compartment DPU CER Logan Arterial DPU CER µCi/mL ROI/ROI VT = 1.87 VT = 0.459 obs-fit Cp/ROI DVR = 1.87/0.459 = 4.08 Time (min) Logan Cerebellum 2 Tissue Compartment DPU DPU CER VT = 1.81 VT = 0.39 DVR = 4.02 DVR=4.64

14. [C-11]CFT 1 Tissue Compartment CER 0.6 µCi/mL 0.08 obs-fit Time (min)

15. [C-11]CFT 1 Tissue Compartment CER 0.6 µCi/mL 0.08 obs-fit VT 1T < 2T Lower SS in 2T Better k estimation in 1T Time (min) 2 Tissue Compartment CER 0.6 0.14

16. [C-11]CFT Irreversible binding 1 Tissue Compartment DPU CER 1.0 0.6 0.06 0.08 2 Tissue Compartment DPU CER 0.6 1.0 0.14 0.12

17. [C-11]CFT 1 Tissue Compartment DPU CER 1.0 0.6 µCi/mL VT = 68 VT = 8.34 0.06 0.08 obs-fit Time (min) 2 Tissue Compartment DPU CER 0.6 1.0 0.14 0.12

18. [C-11]CFT  1 Tissue Compartment DPU CER Logan Arterial 1.0 0.6 DPU CER VT = 68 VT = 8.34 DVR=8.14 0.06 0.08 ROI/ROI VT = 65 VT = 8.84 Cp/ROI DVR = 65/8.84 = 7.45 Logan Cerebellum 2 Tissue Compartment DPU DPU CER 0.6 1.0 0.14 0.12 DVR = 3.03

19. Interim Summary • [C-11]Raclopride 2Tcomp better fit • [C-11]CFT 1Tcomp better fit • Conclusions consistent with known properties of the radiotracers: • [C-11]Raclopride shows reversible binding during the PET study. Thus k3 and k4 can be determined • [C-11]CFT shows irreversible binding in receptor-rich regions during the PET study. Thus k4 cannot be accurately determined RAC - DPU CFT - DPU

20. Comparison of binding potential between methods Simplified methods are appropriate for raclopride

21. Comparison of binding potential between methods

22. Utility of PET radioligand methods for the study of behaviour • Or, I’m a psychologist, why do I care?

23. Utility of PET radioligand methods for the study of behaviour • Or, I’m a psychologist, why do I care?

24. Utility of PET radioligand methods for the study of behaviour • Sequential motor learning • [C-11]Raclopride BP in dorsal striatum decreases during finger sequence learning task • Both implicit & implicit learning of complex motor sequences increase [C-11]raclopride displacement in the caudate & putamen • Reward-related processes • Decreased striatal [C-11]raclopride BP during an active but not passive reward task • Cognition • Decreases in [C-11]raclopride BP when planning a set shift, during spatial planning and spatial working memory Variability in BP outcomes are related to behaviour

25. Utility of PET radioligand methods for the study of behaviour • Variability in BP outcomes are related to behaviour • Variability in BP outcomesare related to EEG synchrony

26. Acknowledgements • PET Facility • Julie Price • Jonathan (Eoin) Carney • Carl Becker • Amy Wagner • MNTP • Seong-Gi Kim • Bill Eddy • Tomika Cohen • Rebecca Clark • Schizophrenia Research Institute, Australia • University of Newcastle, Australia

27. Comparison of binding potential between methods

28. Comparison of binding potential between methods

29. Comparison of binding potential between methods BP = K3/k4 BP=VTROI/VTCER-1 = K1/k2(1+k3/k4)-1

30. Interim Summary • Logan • Susceptible to bias • Bias is worse in CFT because of slower reference tissue clearance relative to plasma • Bias not so bad in RAC because of similar clearance in reference tissue relative to plasma