GENERAL HISTOLOGY

Detailed explanation-1: -L-dopa is converted to dopamine in a reaction catalyzed by aromatic amino acid decarboxylase where pyridoxal 5′-phosphate is the cofactor required for dopamine formation. This enzyme is expressed in the brain and other tissues.

Detailed explanation-2: -L-DOPA is converted to dopamine by the aromatic amino-acid decarboxylase enzyme in the blood. This source of dopamine causes peripheral side effects like nausea and reduces the amount of L-DOPA available to cross into the brain.

Detailed explanation-3: -DOPA is converted to dopamine by aromatic amino acid decarboxylase.

Detailed explanation-4: -Levodopa is the most effective symptomatic oral drug. It is converted to dopamine by dopa decarboxylase (see Fig. 3.4) and acts on dopamine receptors. In order to prevent breakdown of levodopa to dopamine in the periphery, it must be given with a dopa decarboxylase inhibitor, -i.e., either carbidopa or benserazide.

Detailed explanation-5: -L-DOPA is a precursor to dopamine that passes the blood-brain barrier and is mainly taken up by the dopaminergic neurons that convert L-DOPA to dopamine and increase their dopamine production and storage.