Plasticity of the dopaminergic phenotype and of locomotion in larval zebrafish induced by changes in brain excitability during the embryonic period.
Neuronal communication starts before the establishment of the synapses with forms of neuronal excitability occurring during the embryonic period, we called here Embryonic Neuronal Excitability (ENE). ENE has been shown to modulate the correct unfolding of development transcriptional programs but the global consequences for the developing organisms are not all understood. Here we monitored calcium transients as a proxy for ENE in zebrafish to assess the efficacy of transient pharmacological treatments applied by balneation during the embryonic period to modulate ENE. We also report lasting effects of 24h treatments, performed at the end of the embryonic development, on morphology and behavior of larval zebrafish. The post-mitotic differentiation of the dopaminergic phenotype is modulated by ENE in the forebrain. The plasticity of the dopaminergic specification occurs within a stable population of vMAT2 immuno-reactive cells, hence identifying an unanticipated biological marker for this reserve pool. We also report an effect of ENE on locomotion several days after the end of the treatments. In particular, the increase of ENE from 2 to 3 dpf promoted an hyperlocomotion in 6dpf zebrafish larvae which is an endophenotype for Attention Deficit with Hyperactivity Disorders and schizophrenia in zebrafish. These results provide a convenient framework to identify environmental factors that could regulate ENE and to study further the molecular mechanisms linking ENE to the neurotransmitters specification, with clinical relevance for the pathogenesis of neurodevelopmental disorders.