Home > Conscious > Chapter 3 > 3.2. Neurotransmitters

 

More than fifty neurotransmitters have been identified, the following are the most important:

  • Glutamate (Glu)
  • γ-Aminobutyric acid (GABA)
  • Acetylcholine (ACh)
  • Dopamine (DA)
  • Serotonin (5-HT)

Their chemical structures are shown in Figure 3-3.

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Figure 3-3. The chemical structures of major neurotransmitters. [Source: Wikipedia]

Neurotransmitter receptors can be divided into two categories: one belonging to ligand-gated ion channels (see next section), and the other the members of G protein-coupled receptors (see Chapter 6). Since ion channels can directly affect membrane potentials, the binding between neurotransmitters and ligand-gated ion channels can lead to membrane depolarization or hyperpolarization, thereby regulating neuronal excitability. The activation of G protein-coupled receptors by neurotransmitters may regulate neuronal functions through their effects on ion channels and enzymes. A major player in consciousness, GIRK channel, is a potassium channel that works with the G protein (see Chapter 6).

Major neurotransmitter receptors and their classifications are listed below.

  • Glu receptors: NMDA, AMPA and Kainate receptors belong to ligand-gated ion channels, mGluR (metabotropic glutamate receptor) belongs to G protein-coupled receptors.
  • GABA receptors: GABAA receptor belongs to ligand-gated ion channels, GABAB receptor belongs to G protein-coupled receptors.
  • ACh receptors: nAChR (nicotinic acetylcholine receptor) belongs to ligand-gated ion channels, mAChR (muscarinic acetylcholine receptor) belongs to G protein-coupled receptors.
  • DA receptors: There are five types, designated as D1 - D5. D1 and D5 are similar, while D2, D3 and D4 are alike. They all belong to G protein-coupled receptors.
  • 5-HT receptors: They have seven types, named as 5-HT1 - 5HT7. 5-HT3 belongs to ligand-gated ion channels, and the rest belong to G protein-coupled receptors.