Neurotransmitter Chemistry

Introduction to Neurotransmitters

Neurotransmitters are a class of chemical molecules that are used to deliver messages among neurons, tissues, or cells. The signal transmission in different neurons often occurs at the synaptic cleft. Normally, electrical signals can be translated into chemical signals by releasing various kinds of neurotransmitters to trigger certain responses in the nervous system. Up to date, three main types of neurotransmitters, including excitatory transmitters, inhibitory transmitters, and neuromodulators, have been identified according to the different ways in which they affect neurons. An excitatory transmitter can promote action potential reception, and an inhibitory transmitter can prevent action potential production in neurons. Moreover, previous studies have demonstrated that neurotransmitter receptors play a significant role in determining the ultimate nature of the neurotransmitters. Neuromodulators can affect multiple neurons but require a longer time and process.

Fig.1 Structures and common abbreviations of selected amino acid, amine or peptide neurotransmitters. (Angelovski, 2017)

Key Neurotransmitters

In chemistry, most neurotransmitters belong to small molecules, peptides, or amino acids. Till now, seven neurotransmitters, acetylcholine, glutamate, dopamine, noradrenaline, gamma-aminobutyric acid (GABA), serotonin, as well as norepinephrine, have been discovered and widely studied. The data have suggested that neurotransmitters can transmit specific chemical signals from neurons to target cells, like glands. Furthermore, recent reports have revealed that several neurotransmitters may regulate the brain functions, such as concentration, digestion, and muscle movement. The following sections describe some popular neurotransmitters.

• Acetylcholine

Acetylcholine is a type of acetic acid and choline ester. Numerous data have indicated that it is a small molecule neurotransmitter that is important to regulate muscle contractions, stimulate hormone production, as well as control the heartbeat. It is also essential for maintaining cognitive function in the human body.

• Glutamate

Glutamate is a kind of amino acid anion. It is a conjugate base of glutamic acid. It has an anion carboxyl group and cation amino group. It has become one of the main excitatory neurotransmitters in the nervous system. However, its derivative (GABA) has been regarded as a key inhibitory neurotransmitter in synaptic transmission.

• Dopamine

Dopamine is a major neuromodulator involved in pleasure or reward. In general, it consists of a catechol structure and is responsible for regulating muscle movement, learning, and behavior. Many studies have shown that the deficiency of dopamine in the human body is one of the main causes of Parkinson's disease.

• Noradrenaline

Noradrenaline is a catecholamine neurotransmitter that can mediate physiological responses of stress and acute anxiety in humans. Besides, recent researchers have illustrated that it can promote alertness, enhance memory formation, and help focus attention in the brain.

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Reference

1. Angelovski, G.; et al. Strategies for sensing neurotransmitters with responsive MRI contrast agents. Chemical Society Reviews. 2017, 46(2): 324-336.