Introduction
According to Yamamoto and Vernier (2011), dopamine is without a doubt one of the oldest neurotransmitters acting on the central nervous system. The researchers suggest that the emergence of dopaminergic systems most likely predates the divergence of chordates during evolution, and the neurotransmitter’s common ancestry is suggested by commonalities among different species that express the same enzymes, vesicle transporters, degradation enzymes, and receptors. Since dopamine is a precursor for both noradrenaline and adrenaline, the evolution of dopaminergic systems would have lead to leaps and bounds in the development of the central nervous system. In mammals, dopamine is used primarily in the visual and olfactory systems, and it also plays a role in motivation, memory, emotion, endocrine regulations, and sensory-motor programming (Yamamoto, 2011). Furthermore, the evolution of a dopaminergic system would have given rise to reward-driven and emotionally driven behavior, a large step in the development of a more limbic system in the brain (Vincent, 1998). …show more content…
Yamamoto (2013) explained that the functions of dopamine are somewhat conserved across other vertebrate animals with similar forebrain and midbrain structures to mammals. However, some differences in function are seen in insects, where it plays a role in cuticle hardening and immunity. In invertebrates, it also acts as a neurotransmitter in the brain to relay valence. It is synthesized in an alternate pathway in invertebrates (Yamamoto, 2011). In other animals, it acts as a precursor to melanin pigments. In order for dopamine to act in the central nervous system, it relies on the expression of tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC), which are enzyme catalysts, as well as vesicle transporters (DAT, vMAT), degradation enzymes (MAO and COMT), and D1 and D2 receptors on target cells (Kapsimali, 2000). The enzymes TH and AADC, as well as the transporter vMAT and D1 and D2 receptors, are present in bilaterian groups, excluding sponges, cnidarians, ctenophores, and placozoans. MAO and COMT are found only in chordates (Yamamoto, 2011). In studying the origination of dopaminergic systems in early chordates, the development of the modern central nervous system, the origination of vesicle transporters, receptors, and degradation enzymes, and the development of synaptic transmission in general can be reviewed. It also allows the origination of reward-motivated behavior to be studied (Vincent, 1998). For brevities sake, not all factors in the dopaminergic system will be elaborated on, but the emergence of TH, AADC, and the D1 and D2 receptors will be explained. Background It is impossible to understand the evolution of dopaminergic systems without first introducing the enzymes that catalyze dopamine from food in present systems. Yamamoto and Vernier (2011) explained that tyrosine is the molecular precursor to dopamine and is found in food; however, it is in short supply, so most of the tyrosine that later becomes dopamine in the body is derived from phenylalanine, which is present in food in greater abundance. They went on to elaborate that phenylalanine is transformed to tyrosine by phenylalanine hydroxylase (PAH), another member of the AAAH enzyme family. Tyrosine hydroxylase, an aromatic amino acid hydroxylase, begins the process of catalyzing dopamine from tyrosine. Then, tyrosine is catalyzed into dopamine by an aromatic amino acid decarboxylase (AADC). Dopamine not only acts as one of the most influential neurotransmitters in the central nervous system, but also acts as a precursor of two other catecholamine groups: noradrenaline and adrenaline. This makes dopamine’s emergence in evolution an important step in the development of the central nervous system (Yamamoto, 2013). Dopamine’s emergence in evolution can be tracked and speculated on by looking at the emergence of specific genes that control the expression of genes that transform the compound from tyrosine to dopamine, vesicle transporters, degradation enzymes, and the D1 and D2 receptors. Synthesizing Enzymes Tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC) are both tetramers that are coordinated by the binding co-factor tetrahydrobiopterin (BH4) and one iron atom (Yamamoto, 2011). They are both synthesized by GTP cyclohydrolase. The TH sequence is split into a catalytic C-terminal domain, which has been highly conserved in metazoans, and also an N-terminal regulatory domain
According to Yamamoto and Vernier (2011), dopamine is without a doubt one of the oldest neurotransmitters acting on the central nervous system. The researchers suggest that the emergence of dopaminergic systems most likely predates the divergence of chordates during evolution, and the neurotransmitter’s common ancestry is suggested by commonalities among different species that express the same enzymes, vesicle transporters, degradation enzymes, and receptors. Since dopamine is a precursor for both noradrenaline and adrenaline, the evolution of dopaminergic systems would have lead to leaps and bounds in the development of the central nervous system. In mammals, dopamine is used primarily in the visual and olfactory systems, and it also plays a role in motivation, memory, emotion, endocrine regulations, and sensory-motor programming (Yamamoto, 2011). Furthermore, the evolution of a dopaminergic system would have given rise to reward-driven and emotionally driven behavior, a large step in the development of a more limbic system in the brain (Vincent, 1998). …show more content…
Yamamoto (2013) explained that the functions of dopamine are somewhat conserved across other vertebrate animals with similar forebrain and midbrain structures to mammals. However, some differences in function are seen in insects, where it plays a role in cuticle hardening and immunity. In invertebrates, it also acts as a neurotransmitter in the brain to relay valence. It is synthesized in an alternate pathway in invertebrates (Yamamoto, 2011). In other animals, it acts as a precursor to melanin pigments. In order for dopamine to act in the central nervous system, it relies on the expression of tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC), which are enzyme catalysts, as well as vesicle transporters (DAT, vMAT), degradation enzymes (MAO and COMT), and D1 and D2 receptors on target cells (Kapsimali, 2000). The enzymes TH and AADC, as well as the transporter vMAT and D1 and D2 receptors, are present in bilaterian groups, excluding sponges, cnidarians, ctenophores, and placozoans. MAO and COMT are found only in chordates (Yamamoto, 2011). In studying the origination of dopaminergic systems in early chordates, the development of the modern central nervous system, the origination of vesicle transporters, receptors, and degradation enzymes, and the development of synaptic transmission in general can be reviewed. It also allows the origination of reward-motivated behavior to be studied (Vincent, 1998). For brevities sake, not all factors in the dopaminergic system will be elaborated on, but the emergence of TH, AADC, and the D1 and D2 receptors will be explained. Background It is impossible to understand the evolution of dopaminergic systems without first introducing the enzymes that catalyze dopamine from food in present systems. Yamamoto and Vernier (2011) explained that tyrosine is the molecular precursor to dopamine and is found in food; however, it is in short supply, so most of the tyrosine that later becomes dopamine in the body is derived from phenylalanine, which is present in food in greater abundance. They went on to elaborate that phenylalanine is transformed to tyrosine by phenylalanine hydroxylase (PAH), another member of the AAAH enzyme family. Tyrosine hydroxylase, an aromatic amino acid hydroxylase, begins the process of catalyzing dopamine from tyrosine. Then, tyrosine is catalyzed into dopamine by an aromatic amino acid decarboxylase (AADC). Dopamine not only acts as one of the most influential neurotransmitters in the central nervous system, but also acts as a precursor of two other catecholamine groups: noradrenaline and adrenaline. This makes dopamine’s emergence in evolution an important step in the development of the central nervous system (Yamamoto, 2013). Dopamine’s emergence in evolution can be tracked and speculated on by looking at the emergence of specific genes that control the expression of genes that transform the compound from tyrosine to dopamine, vesicle transporters, degradation enzymes, and the D1 and D2 receptors. Synthesizing Enzymes Tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC) are both tetramers that are coordinated by the binding co-factor tetrahydrobiopterin (BH4) and one iron atom (Yamamoto, 2011). They are both synthesized by GTP cyclohydrolase. The TH sequence is split into a catalytic C-terminal domain, which has been highly conserved in metazoans, and also an N-terminal regulatory domain