Description

Neurotransmitters can be amines, amino acids or neuropeptides (Webster et al. 2001). These neurotransmitters and their interactions are involved in various functions of the nervous system. Some of the important neurotransmitters are shown in Figure 1.1 such as acetylcholine, glutamate, aspartic acid, γ-aminobutyric acid (GABA), glycine, dopamine, epinephrine, noradrenaline (norepinephrine), serotonin, tyrosine, adenosine and histamine (Griffith et al. 1982, Hadjiconstantinou et al. 1983, Schwartz et al. 1980, Bowery et al. 2006).

Neurotransmitters can either be excitatory, inhibitory or modulatory. An excitatory neurotransmitter generates an electrical signal (action potential) in the receiving neuron, whereas an inhibitory neurotransmitter prevents it. The classification of the neurotransmitter as excitatory or inhibitory depends on the receptor to which it binds (Chan et al. 1979, McCormick et al. 1989). Neuromodulators are quite different, as they are not only restricted to synaptic cleft but also affect large number of neurons at once. Neuromodulators are known to regulate the neurons (Noudoost et al. 2011).