Effects of centrally acting drugs on the activity of tyrosine hydroxylase in the rat midbrain
The word ‘catecholamines’ applies to any compound which has a catechol nucleus (a benzene ring with two adjacent hydroxyl groups) and an amine-containing side chain. There are three naturally occurring catecholamines: dopamine (DA), noradrenaline (NA) and adrenaline. Dopamine has two functions: it acts as a precursor to NA and also functions as a neurotransmitter in certain areas of the brain. Histochemical and biochemical studies have revealed the presence of separate neuronal cells in the central nervous system (CNS) in which DA is predominant rather than NA. Dopamine is particularly abundant in the striatum. Noradrenaline is a neurotransmitter and is present primarily in the sympathetic neurones of the peripheral nervous system (PNS) and of the CNS. When released, it acts locally on the effector cells of certain smooth muscle, adipose tissue, heart and brain. Adrenaline is found mostly in the chromaffin cells of the adrenal medulla. It is also found in small amounts in certain areas of the brain. It is released as a hormone and acts on many distant effector cells via the blood stream.
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