Regulation of heart rate in zebrafish embryos

Abstract

Although zebrafish has emerged as model for studying cardiovascular function, still very little is known about heart rate control in these animals. Here we report that known drugs that modify heart rate in mammals have similar effects in 2 days post fertilization zebrafish embryos. Injection of 0.5mM carbachol or propranolol into the blood stream reduced the heart rate by >25%, while norepinephrine resulted in a ~10% increase. We further discovered that brief exposure of embryos (5 sec) to UV light similarly increased the heart rate, up to 50%. Surprisingly, UV light exposure restored the charbacol‐induced drop in heart rate to normal levels. To determine whether UV light sensitive photoreceptors in the eyes or pineal gland (PG) mediated this effect, we ablated either one or both organs in GFP‐expressing transgenic embryos using a two‐photon laser. Ablation of both eyes and PG reduced the UV light‐mediated heart rate increase by ~30%, whereas ablation of either one led to a partial reduction. Nevertheless, we still observed a small but persistent increase, corresponding to a yet unknown source. Our observations suggest a novel mechanism for the regulation of heart rate by UV light, independent of autonomic function.