Synthesis And Removal Of Catecholamines And Indolamines

Question 1

Describe the synthesis and removal of dopamine

Answer 1

1. Tyrosine actively transported into catecholaminergic neurons
2. Tyrosine hydroxylase converts tyrosine to dopa
3. Dopa decarboxylase converts dopa to DA
4. DA loaded into vesicles for release
5. Reuptake-1 actively transports DA into presynaptic neuron

a. Some DA reloaded into vesicles
b. Remainder metabolized by MOA
6. Reuptake-2 actively transports DA into postsynaptic cell for metabolism by COMT
7. Remaining synaptic DA diffuses and is absorbed by blood for peripheral metabolism

Question 2

Describe the synthesis and removal of Norepinephrine

Answer 2

1. DA enters vesicles (as above) with dopamine-β-hydroxylase, which converts DA to NE
2. Reuptake-1 actively transports NE into presynaptic neuron
   
   1. Some NE reloaded into vesicles
   2. Remainder metabolized by MOA
3. Reuptake-2 actively transports NE into postsynaptic cell for metabolism by COMT
4. Remaining synaptic NE diffuses and is absorbed by blood for peripheral metabolism

Question 3

Describe the synthesis and re,oval 9f Epinephrine

Answer 3

1. NE in vesicles leaks into the cytoplasm where it is converted to epinephrine by phenylethanolamine N transferase (PMT)
2. Reuptake-1 actively transports epinephrine into presynaptic neuron
   
   1. Some E reloaded into vesicles
   2. Remainder metabolized by MOA
3. Reuptake-2 actively transports epinephrine into postsynaptic cell for metabolism by COMT
4. Remaining synaptic epinephrine diffuses and is absorbed by blood for peripheral metabolism

Question 4

Describe the synthesis and removal of Serotonin

Answer 4

Tryptophanhydroxylaseconvertscytoplasmic
tryptophan to 5-hydroxytryptophan

• Aromaticaminoaciddecarboxylaseconverts 5-hydroxy-tryptophan to serotonin (5-hydrox- tryptamine or 5-HT)
• Serotoninactivelytransportedintovesicles for storage and then release
• Synaptic serotonin can undergo reuptake or metabolism by monoamine oxidase to 5- hydroxy-indoleacetyldehyde
• Aldehydedehydrogenasethenconverts5- hydroxy-indoleacetyldehyde to 5-hydroxy- indoleacetic acid for urinary excretion