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

Uppsala University PET Centre ´ Biosynthesis of dopamine and serotonin Precursor amino acid (tyrosine, tryptophan) Hydroxylase (tetrahydrobiopterin)  L-dopa or 5-hydroxytryptophan Aromatic amino acid decarboxylase (pyridoxine, vitamin B 6 )  Dopamine or serotonin

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

Uppsala University PET Centre 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

Uppsala University PET Centre Clinical studies using OSU6162 Parkinson disease Huntington chorea Schizophrenia (Alcoholism, smoking cessation)

Uppsala University PET Centre Apomorphine effect on dopamine synthesis rate, k 3

Uppsala University PET Centre ”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

Uppsala University PET Centre 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

Uppsala University PET Centre 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.

Uppsala University PET Centre 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

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

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

Uppsala University PET Centre The importance of radiolabelling position, 11 C Dopa vs 18 F-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

Uppsala University PET Centre Multitracer protocol on dopamine function in toxicology Toxic Dopamine Presynaptic Postsynaptic reaction synthesis terminals terminals MPTP   (  ) Manganese    Wilson    disease

Uppsala University PET Centre Regulation of presynaptic dopamine function 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

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

Uppsala University PET Centre Brain serotonin synthesis CH 3

Uppsala University PET Centre Positron emission tomography 11 C-Tryptophan 5-hydroxy- 11 C-tryptophan

Uppsala University PET Centre Brain utilization rate 5-Hydroxi (  - 11 C)tryptophan 11 C-tryptophan SUV Time to peak 15 min 15 min Rate Striatum 7.0 x x Frontal ctx Temp ctx ______________________________________________________________________________ 11 C-TRP give insignificant 11 C-HT during PET, but might show some specific uptake of the tracer

Uppsala University PET Centre Endogenous tracer substrates 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

Uppsala University PET Centre Biosynthesis of dopamine and serotonin Precursor amino acid (tyrosine, tryptophan) Hydroxylase (tetrahydrobiopterin)  L-dopa or 5-hydroxytryptophan Aromatic amino acid decarboxylase (pyridoxine, vitamin B 6 )  Dopamine or serotonin

Uppsala University PET Centre Effect of pyridoxine on the decarboxylation rate of 5-hydroxytryptophan

Uppsala University PET Centre Selectivity of aromatic amino acid decarboxylase Treatment Decarboxylation rate, K 3 of L-DOPA 5-hydroxitryptophan ______________________________________________ Pyridoxine 10 mg bolus 0 + Tetrahydrobiopterin 1 –15 mg/kg/h + 0

Uppsala University PET Centre Effect of bolus doses of amino acid on decarboxylation rate of L-DOPA and 5-HTP

Uppsala University PET Centre Factors regulating uptake of amino acids to the brain and neurotransmitter synthesis 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

Uppsala University PET Centre Effect of glucose infusion on uptake of 5- hydroxytryptophan derived radioactivity

Uppsala University PET Centre Cerebral presynaptic synthesis in depression

Uppsala University PET Centre Decarboxylation rate of 5-HTP in different brain areas Area ControlsDepressed __________________________________________________ Lateral frontal cortex min Medial frontal cortex high low0.0001* Caudate Putamen ________________________________________________

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

Uppsala University PET Centre Presynaptic serotonin 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.

Uppsala University PET Centre Regulation of aromatic amino acid decarboxylase activity for L-DOPA and 5-hydroxytryptophan 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

Uppsala University PET Centre What is measured with 5-HTP and PET ? 11 C-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

Uppsala University PET Centre Calculation of decarboxylation rate 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)

Uppsala University PET Centre 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 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 [ 11 C]tryptophan

Uppsala University PET Centre Theses at UUPC Peter BjurlingRadiosynthesis Lars Reibring-Depression Joakim TedroffL-Dopa in PD Karl Johan Lindner Validation of 5 HTP Anna EkesboDA degeneration, OSU Richard Torstenson Regulation of DA Ina MarteinsdottirSSRI responsive diseases Pinelopi Merachtsaki Regulation of serotonin