Implication of DA in such a large range of otherwise unrelated functions, its wide distribution in a number of brain nuclei, and fast-growing knowledge about the differentiation of these DA neuronal groups strongly suggest that there is not a unique DA system, but several, independent anatomo-physiological systems, with DA as the only common denominator. In addition, DA has now been shown to significantly contribute to the pathophysiology of several psychiatric disorders such as schizophrenia, addiction to drugs, or attention deficit with hyperactivity. Dysfunction of DA neurotransmission was initially shown in Parkinson’s disease ( Hornykiewicz, 1962), fostering an enormous interest for this neurotransmitter. Indeed, DA acts to modulate early steps of sensory perception in the olfactory bulb and the retina, motor programming, learning, and memory, affective and motivational processes in the forebrain, control of body temperature, food intake, and several other hypothalamic functions as well as chemosensitivity in the area postrema and solitary tract, to cite only the main of the DA-controlled functions. Since the seminal discovery that it could be a neurotransmitter in the central nervous system (CNS) of vertebrates ( Carlsson et al., 1958), dopamine (DA) has received a lot of attention due to its role in many cerebral functions and its implication in a number of major human diseases. These features were instrumental in the adaptation of brain functions to the very variable way of life of vertebrates. The functional flexibility of the DA systems, and the evolvability provided by duplication of the corresponding genes permitted a large diversification of these systems. In contrast, the midbrain cell populations have probably emerged in the vertebrate lineage following the development of the midbrain–hindbrain boundary. Studies of protochordate DA cells suggest that the diencephalic DA cells were present before the divergence of the chordate lineage. Midbrain DA cells are abundant in amniotes while absent in some groups, e.g., teleosts. All the vertebrates possess DA cells in the olfactory bulb, retina, and in the diencephalon. It is likely that the ancestor of vertebrates possessed TH2 DA-synthesizing cells, and the TH2 gene has been lost secondarily in placental mammals. 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. 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. 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. 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.
Neurobiology and Development (UPR3294), Institute of Neurobiology Alfred Fessard, CNRS, Gif-sur-Yvette, Franceĭopamine (DA) neurotransmission in the central nervous system (CNS) is found throughout chordates, and its emergence predates the divergence of chordates.The PD-based enzyme electrode shows better biosensing performance and higher bioactivity of the immobilized Tyr than those based on similarly biosynthesized poly( L-tyrosine) and polydopamine as well as well-established chitosan and Nafion systems, implying that the biosynthesized PD as a melanin-biomimetic material has promising application potential for biomacromolecular immobilization and biosensing. A PD-glucose oxidase (GOx)-Tyr/Pt electrode prepared by casting an aqueous mixture of L-DOPA, GOx and Tyr on a Pt electrode exhibits a linear anodic amperometric response to glucose concentration from 2 to 5700 μM ( R 2 = 0.998) with a sensitivity of 78.6 μA mM −1 cm −2 and a LOD of 0.1 μM (S/N = 3). A poly( L-DOPA) (PD)-Tyr/glassy carbon electrode (GCE) prepared by casting an aqueous mixture of L-DOPA and Tyr on a GCE exhibits a linear cathodic amperometric response to catechol concentration from 0.4 to 57 μM ( R 2 = 0.997) with a sensitivity of 4.29 mA mM −1 cm −2 and a limit of detection (LOD) of 70 nM (S/N = 3). The enzymatic polymerization is examined by UV-vis spectrophotometry, scanning electron microscopy and electrochemical methods. Here, inspired by melanin formation, we report the tyrosinase (Tyr)-catalyzed polymerization of L-DOPA ( versus L-tyrosine and dopamine) to immobilize enzymes for amperometric biosensing. Learning from nature emerges as one of the most promising ways to develop advanced functional materials and biodevices.
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