Characterization of the γ-aminobutyric acid signaling system in the zebrafish (Danio rerio Hamilton) central nervous system by reverse transcription-quantitative polymerase chain reaction.

In the vertebrate brain, inhibition is largely mediated by γ-aminobutyric acid (GABA). This neurotransmitter comprises a signaling machinery of GABA, GABA receptors, transporters, glutamate decarboxylases (gads) and 4-aminobutyrate aminotransferase (abat), and associated proteins. Chloride is intimately related to GABA receptor conductance, GABA uptake, and GADs activity. The response of target neurons to GABA stimuli is shaped by chloride-cation co-transporters (CCCs), which strictly control Cl gradient across plasma membranes. This research profiled the expression of forty genes involved in GABA signaling in the zebrafish (Danio rerio) brain, grouped brain regions and retinas. Primer pairs were developed for reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The mRNA levels of the zebrafish GABA system share similarities with that of mammals, and confirm previous studies in non-mammalian species. Proposed GABA receptors are αβγ, αβδ, αβγ, αβδ, αβγ, αβδ, αβγ and αβδ. Regional brain differences were documented. Retinal hetero- or homomeric ρ-composed GABA receptors could exist, accompanying αβγ, αβδ, αβγ, αβδ. Expression patterns of α and α were opposite, with the former being more abundant in retinas, the latter in brains. Given the stoichiometry αβγ, α- or α-containing receptors likely have different regulatory mechanisms. Different gene isoforms could originate after the rounds of genome duplication during teleost evolution. This research depicts that one isoform is generally more abundantly expressed than the other. Such observations also apply to GABA receptors, GABA transporters, GABA-related enzymes, CCCs and GABA receptor-associated proteins, whose presence further strengthens the proof of a GABA system in zebrafish.