title: The conserved dopaminergic diencephalospinal tract mediates vertebrate locomotor development in zebrafish larvae.
abstract: The most conserved part of the vertebrate dopaminergic system is the orthopedia (otp)-expressing diencephalic neuronal population that constitutes the dopaminergic diencephalospinal tract (DDT). Although studies in the neonatal murine spinal cord in vitro suggest an early locomotor role of the DDT, the function of the DDT in developing vertebrates in vivo remains unknown. Here, we investigated the role of the DDT in the locomotor development of zebrafish larvae. To assess the development of the behavioral and neural locomotor pattern, we used high-throughput video tracking in combination with peripheral nerve recordings. We found a behavioral and neural correspondence in the developmental switch from an immature to mature locomotor pattern. Blocking endogenous dopamine receptor 4 (D(4)R) signaling in vivo either before or after the developmental switch prevented or reversed the switch, respectively. Spinal transections of post-switch larvae reestablished the immature locomotor pattern, which was rescued to a mature-like pattern via spinal D(4)R agonism. Selective chemogenetic ablation of otp b (otpb) neurons that contribute to the DDT perpetuated the immature locomotor pattern in vivo. This phenotype was recapitulated by diencephalic transections that removed the dopaminergic otpb population and was rescued to a mature-like locomotor pattern by D(4)R agonism. We conclude that the dopaminergic otpb population, via the DDT, is responsible for spinal D(4)R signaling to mediate the developmental switch to the mature locomotor pattern of zebrafish. These results, integrated with the mammalian literature, suggest that the DDT represents an evolutionarily conserved neuromodulatory system that is necessary for normal vertebrate locomotor development.
authors.affiliation: Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Lambert
authors.forename: Joshua L
authors.initials: JL
authors.lastname: Bonkowsky
authors.forename: Mark A
authors.initials: MA
authors.lastname: Masino
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D030801:Animals, Genetically Modified; D004027:Diencephalon / Q000166:cytology / Q000254:growth & development*; D004298:Dopamine / Q000378:metabolism*; D015259:Dopamine Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D020287:In Situ Nick-End Labeling; D007814:Larva; D008124:Locomotion / Q000187:drug effects / Q000502:physiology*; D008795:Metronidazole / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009434:Neural Pathways / Q000254:growth & development / Q000293:injuries; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D009601:Nitroreductases / Q000235:genetics; D010525:Peripheral Nerves / Q000502:physiology; D010523:Peripheral Nervous System Diseases / Q000503:physiopathology; D050638:Receptors, Dopamine D4 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D013116:Spinal Cord / Q000254:growth & development*; D014157:Transcription Factors / Q000235:genetics; D014741:Video Recording; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics
chemical_list: D015259:Dopamine Agents; D018690:Excitatory Amino Acid Agonists; D014157:Transcription Factors; D029961:Zebrafish Proteins; C485184:enhanced green fluorescent protein; C515950:orthopedia protein, zebrafish; D050638:Receptors, Dopamine D4; D008795:Metronidazole; D049452:Green Fluorescent Proteins; D016202:N-Methylaspartate; D009601:Nitroreductases; D004298:Dopamine