d-Amphetamine and Feeding States Cohesively Affect Locomotion and Motor Neuron Response in Zebrafish Larvae

Purpose: Amphetamine (AMPH) increases locomotor activities in animals, and the locomotor response to AMPH is further modulated by caloric deficits such as food deprivation and restriction. The increment in locomotor activity regulated by AMPH-caloric deficit concomitance can be further modulated by varying feeding schedules (e.g., acute and chronic food deprivation and acute feeding after chronic food deprivation). However, the effects of different feeding schedules on AMPH-induced locomotor activity are yet to be explicated. Here, we have explored the stimulatory responses of acutely administered D-amphetamine in locomotion under systematically varying feeding states (fed/sated and food deprivation) and schedules (chronic and acute) in zebrafish larvae.

Method: We exposed wild-type and transgenic [Tg(mnx1:GCaMP5)] zebrafish larvae to 0.7 µM concentration of AMPH and measured swimming activity and spinal motor neuron activity in vivo in real time. The analysis involved time-elapsed and cumulative manner pre- and post-AMPH treatment in four different caloric states including acute and chronic schedules of feeding and hunger. Both locomotor and motor neuron activities were compared in all four states in both fish lines.

Findings: Our results show that locomotion and motor neuron activity increased in both chronic and acute food deprivation post-AMPH treatment cumulatively. A steady increase in locomotion was observed in acute food deprivation compared to an immediate abrupt increase in chronic food-deprivation state. The ad libitum-fed larvae exhibited a moderate increase both in locomotion and motor neuron activity. Conversely to all other caloric states, food-sated (acute feeding after chronic food deprivation) larvae moved moderately less and exhibited a mild decrease in motor neuron activity after AMPH treatment.

Conclusion: These results reveal the importance of cohesive effects of feeding schedule and AMPH treatment by revealing the changes in stimulatory characteristics of AMPH on locomotion and motor neuron activity in acute and chronic feeding states.