Development of a Controlled Electrical Stimulation System for the Study of Behavioral Responses in Zebrafish Larvae

The habenula (Hb) is a brain structure that plays an important role in negative reward processing. We aim to study how social isolation during early development affects habenular function in larval zebrafish. In particular, we want to analyze habenular neuronal responses to mild electric shocks of socially raised and isolated larval zebrafish using in vivo calcium imaging while we record tail motor responses. As a first step towards these aims we developed a stage platform for individual larvae that allowed applying controlled and reproducible electrical stimuli while recording brain activity and tail movements. The project involved designing a recording chamber for use with larvae approximately 4 mm in length and configuring an electrical stimulator capable of delivering current pulses while allowing the experimenter to control their amplitude, duration, frequency, and number of pulses. Our electrical stimulator can deliver a constant current of up to approximately 0.8 mA which is independent of experimental variations of the load resistance. The circuit can also reverse the polarity of the pulses to prevent capacitive effects generated by the aqueous medium in which the larva is immersed. The optimal operating range of the circuit was characterized, and the fish responses were statistically quantified as a function of the variable pulse parameters.