Dopamine

Question 1

Dopamine is metabolised by which of the following?

Answer 1

COMT, MAO-B, MAO-A

Question 2

Synthesis of dopamine

Answer 2

The first step in the synthesis of dopamine is tyrosine, which is an amino acid found in dietary proteins. Tyrosine is taken up from the blood into neurons where it is converted to L-DOPA (dihydroxyphenylalanine) by the enzyme tyrosine hydroxylase. L-DOPA is then converted to dopamine by dopa decarboxylase.

Question 3

Storage of dopamine

Answer 3

Dopaminergic neurons originate in substantia nigra pars compacta, ventral tegmental area (VTA), and hypothalamus. These project axons to large areas of the brain through four major pathways:

The mesolimbic pathway
The mesocortical pathway
The nigrostriatal pathway
The tuberoinfundibular pathway

Question 4

Mesolimbic pathway

Answer 4

The mesolimbic pathway transports dopamine from the (VTA) ventral tegmental area (in the midbrain) to the nucleus accumbens (found at the junction of the caudate and putamen). This is a reward pathway. Blockage of D-2 receptors in this pathway is thought to account for the therapeutic benefit of antipsychotics.

Question 5

Mesocortical pathway

Answer 5

The mesocortical pathway goes from the VTA to the frontal cortex. This pathway is involved with motivation and emotion. Blockage of D-2 receptors in this pathway is thought to lead to the negative symptoms of schizophrenia.

Question 6

Nigroatriatal pathway

Answer 6

The nigrostriatal pathway connects the substantia nigra to the striatum (caudate and putamen). Blockage here produces extra pyramidal side effects (EPSE’s)

Question 7

tuberoinfundibular pathway

Answer 7

The tuberoinfundibular pathway goes from the hypothalamus to the pituitary gland. Blockage of dopamine in this pathway causes the pituitary gland to secrete prolactin.