SPONTANEOUS ACTIVITY IN THE INTRACARDIAC NERVOUS SYSTEM IN ZEBRAFISH (DANIO RERIO)

Abstract

The final common pathway for neural control of the vertebrate heart consists of autonomic neurons embedded in the cardiac wall, forming the intracardiac nervous system (ICNS). Parasympathetic and sympathetic efferent neurons in the ICNS project to the pacemaker, acting to reduce or increase heart rate (HR), respectively, when activated. Conventionally, ICNS neurons are considered simple relays transferring signals to the pacemaker from cardiac control centres in the brain, so should not be active without central inputs. In the isolated, spontaneously beating zebrafish heart I have shown that the muscarinic antagonist atropine, which blocks parasympathetic output, accelerates HR while the β- adrenergic antagonist timolol, blocking sympathetic output, evokes cardioinhibition. My results show that both parasympathetic and sympathetic neurons are active in the isolated heart without inputs from the brain, supporting the concept that the ICNS can operate as a local “stand-alone” system with potential for controlling HR.