Neurochemistry

The biochemical pathways in the synthesis and metabolism of dopamine are shown in Fig. 7.2 and their position in the context of the dopamine synapse in Fig. 7.3.

Homovanillic acid

Figure 7.2 Biochemical pathways for the synthesis and metabolism of dopamine. (โ€”) indicates drug inhibition of enzyme activity

Homovanillic acid

Figure 7.2 Biochemical pathways for the synthesis and metabolism of dopamine. (โ€”) indicates drug inhibition of enzyme activity

SYNTHESIS

The synthesis and metabolism of DA are very similar to that of NA, even when it functions as a NT in its own right. Although both phenylalanine and tyrosine are found in the brain it is tyrosine which is the starting point for NA and DA synthesis. It appears to be transported into the brain after synthesis from phenylalanine (phenylalanine hydroxylase) in the liver rather than from phenylalanine found in the brain. Despite the fact that the concentration of tyrosine in the brain is high (5 x 10_5M) very little body tyrosine (1%) is used for the synthesis of DA and NA.

1

MitQctwndriora

9

Receptor(s)

4

Transputer

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Veacle

Monoamine

A

Oxidase

*

CGMT

Figure 7.3 Diagrammatic representation of a dompaminergic synapse. (+) = stimulation, agonists; (โ€”) = antagonism

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