Functioning and Gene Expression of Adenosine A₁ Receptor During Zebrafish (Danio rerio) Development

The A1 adenosine receptor is the most widely expressed P1 receptor in vertebrates, performing inhibitory tone of the nervous system. Increased levels of adenosine are crucial to promote tissue protection in threatening situations, such as convulsion and hypoxia. Zebrafish is an established model organism for studies on health and disease. In this study, we evaluated the functionality of A₁ adenosine receptor through development of zebrafish (6-7-day-, 3-, 8-, and 24-month-old), assessing: (I) the effects of the agonist N₆-cyclopenthyladenosine (CPA) over locomotor parameters, (II) the anticonvulsant properties of CPA and adenosine per se in the pentylenetetrazol-induced seizure, and (III) the gene expression of adora1b through development. CPA promoted decreased distance traveled in the highest concentrations/doses tested (larvae: 75 to 500 μM; adults: 20 mg.kg^-1), altered mean velocity (larvae: 50-500 μM; adults: 20 mg.kg^-1) and time in the bottom zone of apparatus (adults: decrease in 20 mg.kg^-1). Adenosine increased the latency of the larvae to reach stage II at 5 and 10 μM. CPA anticonvulsant effect against convulsive stage II was reached at 75 μM, although it decreased basal locomotor activity in larvae. For adults, CPA 10 mg.kg^-1 was effective as anticonvulsant without locomotory effects. Adenosine had minor anticonvulsant effects in the concentration tested (larvae: 5 and 10 μM). The level of gene expression of adora1b was stable in brain from adult animals (8- and 24-month-old animals). These results suggest that zebrafish has similar responses to CPA as mammals. To avoid confounding factors, such as locomotor effects, during any brain function investigation using A₁ adenosine receptor as a target, the concentration below 75 μM or below the dose of 20 mg.kg^-1 of CPA is ideal for zebrafish at larval and adult stages, respectively.