Ontogeny and innervation patterns of dopaminergic, noradrenergic, and serotonergic neurons in larval zebrafish

Abstract

We report the development of aminergic neurons from 0-10 days postfertilization (dpf) in zebrafish (Danio rerio). This study was prompted by the lack of information regarding patterns of spinal aminergic innervation at early stages, when the fish are accessible to optical, genetic, and electrophysiological approaches toward understanding neural circuit function. Our findings suggest that aminergic populations with descending processes are among the first to appear during development. Descending aminergic fibers, revealed by antibodies to tyrosine hydroxylase (TH) and serotonin (5-hydroxytryptamine; 5-HT), innervate primarily the ventral (TH, 5-HT), but also the dorsal (5-HT) aspects of the spinal cord by 4 dpf, with the extent of innervation not changing markedly up to 10 dpf. By tracking the spatiotemporal expression of TH, 5-HT, and dopamine beta hydroxylase reactivity, we determined that these fibers likely originate from neurons in the posterior tuberculum (dopamine), the raphe region (5-HT) and, possibly, the locus coeruleus (noradrenaline). In addition, spinal neurons positive for 5-HT emerge between 1-2 dpf, with processes that appeared to descend along the ventrolateral cord for only 1-2 muscle segments. Their overall morphology distinguished these cells from previously described "VeMe" (ventromedial) interneurons, which are also located ventromedially, but have long, multisegmental descending processes. We confirmed the distinction between spinal serotonergic and VeMe interneurons using fish genetically labeled with green fluorescent protein. Our results suggest that the major aminergic systems described in adults are in place shortly after hatching, at a time when zebrafish are accessible to a battery of techniques to test neuronal function during behavior.

Dopamine D2Receptor Activity Modulates Akt Signaling and Alters GABAergic Neuron Development and Motor Behavior in Zebrafish Larvae

“…Recent studies demonstrated that DA modulates Akt signaling in the adult rodent and primate striatum, which is associated with regulating motor control (Beaulieu et al, 2004(Beaulieu et al, , 2005. Although our study focused on early larval stages, the larval pattern of DA circuitry in zebrafish is comparable to the adult pattern (McLean and Fetcho, 2004), suggesting that this pattern of DA-dependent Akt modulation is maintained in adulthood. However, future investigations are necessary to confirm this hypothesis.…”

“…Several components of the DA biosynthetic and signaling pathways are expressed in the zebrafish larval brain (Holzschuh et al, 2001;Boehmler et al, 2004Boehmler et al, , 2007McLean and Fetcho, 2004;Anichtchik et al, 2006;Li et al, 2007), but which intracellular pathways are modulated by DA and its role in mediating behavior, as well as how DA signaling regulates zebrafish brain development, is not well characterized. Previous studies have demonstrated that DA is involved in larval motor regulation and that this is mediated, in part, by cAMP signaling (Boehmler et al, 2007;Thirumalai and Cline, 2008).…”

Characterization and Expression of Serotonin Transporter Genes in Zebrafish

“…The expression of tphD1, one of the three tryptophan hydroxylases in zebrafish, was previously reported in the subset of the inner nuclear layer neurons (Bellipanni et al 2002). Serotonin was detected in the medulla oblongata of zebrafish embryo (McLean and Fetcho 2004a). Given that both serta and sertb are functional, the sum of the expression pattern of two genes should reflect the cells harboring the serotonin transporter activity in zebrafish.…”

Embryonically Expressed GABA and Glutamate Drive Electrical Activity Regulating Neurotransmitter Specification

“…These findings raise two questions: first, what drives spike activity in the population of neurons that is not affected by GABA or glutamate receptor antagonists? Amine and peptide neurotransmitters are also expressed at early stages of development (Lauder et al, 1981;Hu et al, 2001;McLean and Fetcho, 2004) and are candidates to evaluate. Second, what is the function of calcium spike activity in these neurons if it does not regulate the expression of GABA, glutamate, glycine or acetylcholine?…”