The Evolution of Dopamine Systems in Chordates

Abstract

Dopamine (DA) neurotransmission in the central nervous system (CNS) is found throughout chordates, and its emergence predates the divergence of chordates. Many of the molecular components of DA systems, such as biosynthetic enzymes, transporters, and receptors, are shared with those of other monoamine systems, suggesting the common origin of these systems. In the mammalian CNS, the DA neurotransmitter systems are diversified and serve for visual and olfactory perception, sensory–motor programming, motivation, memory, emotion, and endocrine regulations. Some of the functions are conserved among different vertebrate groups, while others are not, and this is reflected in the anatomical aspects of DA systems in the forebrain and midbrain. Recent findings concerning a second tyrosine hydroxylase gene (TH2) revealed new populations of DA-synthesizing cells, as evidenced in the periventricular hypothalamic zones of teleost fish. It is likely that the ancestor of vertebrates possessed TH2 DA-synthesizing cells, and the TH2 gene has been lost secondarily in placental mammals. All the vertebrates possess DA cells in the olfactory bulb, retina, and in the diencephalon. Midbrain DA cells are abundant in amniotes while absent in some groups, e.g., teleosts. Studies of protochordate DA cells suggest that the diencephalic DA cells were present before the divergence of the chordate lineage. In contrast, the midbrain cell populations have probably emerged in the vertebrate lineage following the development of the midbrain–hindbrain boundary. The functional flexibility of the DA systems, and the evolvability provided by duplication of the corresponding genes permitted a large diversification of these systems. These features were instrumental in the adaptation of brain functions to the very variable way of life of vertebrates.

A descending dopamine pathway conserved from basal vertebrates to mammals

“…In contrast, in rats, one remarkable aspect of our findings is that the vast majority of the DA neurons that project to the striatum also project to the MLR, implying a simultaneous ascending and descending modulation of the entire locomotor command circuitry from cortex to brainstem. These DA neurons are mostly located in the SNc with a few in the RRF, two structures that are classically considered as mesencephalic but that also span in the diencephalon (16,19,20). In lampreys, the terminology "mesodiencephalic DA neurons" does not apply, given that the DA neurons are all located in the diencephalon (40).…”

“…An increasing number of authors seem to agree with the hypothesis that at least some of the mesodiencephalic DA neurons located in the diencephalon are homologous in all vertebrates, and thus, homologous to at least a portion of the mammalian substantia nigra pars compacta (SNc)/ ventral tegmental area (VTA) (13,(15)(16)(17)(18)(19); for review, see ref. 20). Alternatively, it was suggested that the posterior tuberculum DA neurons projecting to the striatum in zebrafish are homologs of the mammalian DA neurons of the A11 group (21).…”

The Integration of Sociality, Monoamines, and Stress Neuroendocrinology in Fish Models: Applications in the Neurosciences

“…As described above, important neuroanatomical (absence of the A9/mesolimbic projection) and genomic (duplication of tyrosine hydroxilase and of some receptors) differences exist between teleosts and mammals, and many of these differences are plesiomorphic in Gnathostomata (Yamamoto & Vernier, 2011). Some roles for dopamine receptors have been described in zebrafish defensive behaviour.…”

Dopamine is a key regulator in the signalling pathway underlying predator-induced defences inDaphnia

“…Dopamine is a key neurotransmitter involved in many different metabolic pathways and, more importantly, it serves as a neurohormone in arthropods [20]. It is known to be an important signalling molecule in various metabolic pathways in invertebrates (reviewed in [20]).…”

“…Dopamine is a key neurotransmitter involved in many different metabolic pathways and, more importantly, it serves as a neurohormone in arthropods [20]. It is known to be an important signalling molecule in various metabolic pathways in invertebrates (reviewed in [20]). In fact, dopamine can regulate the synthesis and degradation of juvenile hormones [21,22], and thereby we hypothesized that it has the potential to control predatorinduced polyphenism.…”