Per Hartvig, Uppsala University PET Centre

1. Per Hartvig, Uppsala University PET Centre Central dopaminergic and serotonergic function studied with positron emission tomography

2. Precursor amino acid (tyrosine, tryptophan) Hydroxylase (tetrahydrobiopterin)  L-dopa or 5-hydroxytryptophan Aromatic amino acid decarboxylase (pyridoxine, vitamin B6)  Dopamine or serotonin ´Biosynthesis of dopamine and serotonin

3. Effect of the the dopamine D2 antagonist OSU6162 Dopamine synthesis rate, k3, min-1 in Rhesus monkeys before and after 3 mg/kg of OSU 6162.

4. Effect of tyrosine and R-tetrahydrobiopterin on dopamine synthesis rate and stabilization with OSU 6162 Tyrosine and biopterin increases dopamine synthesis rate The increased rate is stabilized to baseline by OSU6162

5. Parkinson disease Huntington chorea Schizophrenia (Alcoholism, smoking cessation) Clinical studies using OSU6162

6. Apomorphine effect on dopamine synthesis rate, k3

7. ”Tune” dependent change of dopamine synthesis rate Apomorphine 0.1 mg/kg induced decrease of dopa- mine change is dependent on baseline dopamine tuning in the Rhesus monkey

8. Effect of L-DOPA in early and advanced Parkinsons disease L-DOPA infusion saturates dopamine synthesis in early Parkinson´s disease In advanced disease a loss of presynaptic dopamine receptors explains the induction of rate

9. Is L-DOPA an endogenous neurotransmitter ? (Miwa, Goishima 1993) L-DOPA infusion 3 or 15 mg/kg/h induces an increase in dopamine synthesis rate.

10. Effect of 5R-erythro-tetrahydro-biopterin on dopamine synthesis 6R-erythro-5,5,7,8 tetra- hydrobiopterin, the endo- genous cofactor for the hydroxylases induces an increased dopamine synthesis rate

11. Pharmacological effects Release of monoamines and serotonin Receptor effects Enhances synthesis of monoamines Hydroxylase AADC Tyrosine  L-DOPA  Dopamine Biopterin,BH4 Pyridoxin 6R-erythro-5,6,7,8-tetrahydrobiopterin

12. Clinical studies Infantil autistic disorder (Double blind 3 mg/kg cross over, randomized study in children 4-8 y with PET, neurochemistry, immunology and clinicalevaluation) Parkinson´s disease Alzheimer´s disease 6R-erythro-5,6,7,8-tetrahydrobiopterin

13. The importance of radiolabelling position, 11C Dopa vs 18F-fluoro-dopa No effect of tetrahydrobiopterin due to increased synthesis of 3-O-methyl dopa which is Passing to the brain giving increased background radioactivity in the reference

14. Toxic Dopamine Presynaptic Postsynaptic reaction synthesis terminals terminals MPTP   () Manganese   Wilson    disease Multitracer protocol on dopamine function in toxicology

15. Supply of tyrosine and L-DOPA L-DOPA catalysing effect on synthesis Tetrahydrobiopterin effects on synthesis and release Presynaptic control in Parkinson disease Tune dependent control Dopamine stabilisers Regulation of presynaptic dopamine function

16. [-11C]L-tryptophan Carboxy - [11C]L-tryptophan 5-hydroxy- [-11C]L-tryptophan [11C] --methyl-L-tryptophan Radiotracers used with PET for studies on presynaptic serotonin

17. Brain serotonin synthesis CH3

18. 11C-Tryptophan 5-hydroxy-11C-tryptophan Positron emission tomography

19. 5-Hydroxi (-11C)tryptophan11C-tryptophan SUV 0.90 1.1 Time to peak 15 min 15 min Rate Striatum 7.0 x 10-3 - 2.0 x 10-3 Frontal ctx 3.3 - 1.5 Temp ctx 1.2 - 0.7 ______________________________________________________________________________ 11C-TRP give insignificant 11C-HT during PET, but might show some specific uptake of the tracer Brain utilization rate

20. Uptake into the target tissue, passing over the BBB Regional tissue accumulation of tracer Uptake into target cells Complex with enzymes in target cells Formation of active transmitter Uptake of active transmitter Release of transmitter to the synapse Binding to target receptors Metabolism of transmitter with cumulation Endogenous tracer substrates

21. Biosynthesis of dopamine and serotonin Precursor amino acid (tyrosine, tryptophan) Hydroxylase (tetrahydrobiopterin)  L-dopa or 5-hydroxytryptophan Aromatic amino acid decarboxylase (pyridoxine, vitamin B6)  Dopamine or serotonin

22. Effect ofpyridoxine on the decarboxylation rate of 5-hydroxytryptophan

23. Selectivity of aromatic amino acid decarboxylase Treatment Decarboxylation rate, K3 of L-DOPA 5-hydroxitryptophan______________________________________________Pyridoxine10 mg bolus 0 +Tetrahydrobiopterin 1 –15 mg/kg/h + 0

24. Effect of bolus doses of amino acid on decarboxylation rate of L-DOPA and 5-HTP

25. Plasma amino acids Diurnal rythm Age Gender Food and drinking Proteins, carbohydrates and fat Caffeine, ethanol Co-factors and vitamins (Pyridoxin B6, biopterin) Drugs, SSRI Factors regulating uptake of amino acids to the brain and neurotransmitter synthesis

26. Effect of glucose infusion on uptake of 5-hydroxytryptophan derived radioactivity

27. Cerebral presynaptic synthesis in depression

28. Decarboxylation rate of 5-HTP in different brain areas Area Controls Depressed __________________________________________________ Lateral frontal cortex 0.0011 min-1 0.0022 Medial frontal cortex high 0.0029 0.0060 low 0.0001* 0.0042 Caudate 0.0098 0.0098 Putamen 0.0072 0.0081 ________________________________________________

29. Disease SUV Synthesis rate Sex F > M Depression  Med pre frt ctx Schizophrenia  Do, ganglia  Tourette  ganglia  OCD  ganglia  ECT  Brain disposition of precursor amino acids

30. Presynapticserotonin function in social phobia(Ina Marteinsdottir et al 2001) Method: Statistical evaluation of PET with 5-hydroxy- tryptophan by a pixel wise blocked analysis of variance contrasting differences between patients and controls. Results: A a focal hyposerotonergic tonus in social phobics as compared to controls was evident in temporal cortex (periamygdala/rhinal, temporal pole and gyrus); frontal cortex, anterior cingulatae, right insula and left basal ganglia.

31. Several mechanisms regulate amino acid transport to the brain and presynaptic synthesis serotonin Synthesis of serotonin may be regulated by a similar decarboxylase enzyme but with different selectivity Modulating effect of enzyme co-factors e.g. tetrahydrobiopte-rin and vitamin B6 varied for the two transmitters Capacity limitation in transport and enzyme activity for 5HTP Limited capacity of amino acid transport may influence serotonin function with special impact in affective disorders Regulation of aromatic amino acid decarboxylase activity for L-DOPA and 5-hydroxytryptophan

32. 11C-labelling in carboxy and -position of 5-HTP Blockade of central decarboxylase with NSD1015 Bioanalysis of brain radioactivity using rat brain homogenate by HPLC shows radiolabelled 5-HTP, serotonin and metabolites Calculated rates analysed of brain radioactivity in rat brain are similar to rates measured in monkey and man with 5-HTP and PET What is measured with 5-HTP and PET ?

33. Brain reference region after validation of accumulation (Patlack plot, Hartvig et al 1992) Simulation of a brain refrence region with negligable 5HT synthesis gives rates close to measured (Blomquist et al 2001) Plasma as reference with metabolite correction shows regional 5HT rates in accordance with AADC activity (Hagberg et al JBFM, 2002) Calculation of decarboxylation rate

34. Rapid in vivo metabolism to radiolabelled products Low plasma concentration of radioactivity Serotonergic activity in most brain areas - no obvious reference area in the brain Steady state in the brain not established in 15-20 min Limited capacity for transport over BBB and for synthesis Use of tracer may occur in non-serotonergic neurons Limitations in studies with 5-hydroxy [11C]tryptophan

35. Peter Bjurling Radiosynthesis Lars Reibring- Depression Joakim Tedroff L-Dopa in PD Karl Johan Lindner Validation of 5 HTP Anna Ekesbo DA degeneration, OSU Richard Torstenson Regulation of DA Ina Marteinsdottir SSRI responsive diseases Pinelopi Merachtsaki Regulation of serotonin Theses at UUPC