Hypothalamic dopamine neuron activity is modulated by caloric states and amphetamine abuse in zebrafish larvae

Dopaminergic (DA) neuron activity is affected by reward and stress-inducing entities such as food and drugs of abuse, and different DA neuron populations can respond distinctly to these stimuli. Interaction between both stimuli significantly alters the dynamics of DA release in different DA populations. Additionally, these stimulating entities can affect the interconnections among different DA populations by impairing their correspondence with each other. However, limited studies have been performed that could point to the effect of interaction between AMPH and caloric states on DA neurons and their inter-correlation. This study explores the individual and interactive effect of two caloric states, ad-libitum fed (AL) and food deprived (FD), and acute exposure to a stimulant drug (amphetamine) in two different DA neurons in the hypothalamus of zebrafish larvae. We used a transgenic zebrafish line Tg(th2:GCaMP7s), which expresses a calcium indicator (GCaMP7s) in A11(Posterior Tuberculum) and a part of A14 (Caudal Hypothalamus and Intermediate Hypothalamus) DA populations located in the hypothalamus of the larval zebrafish. The larvae were subjected to acute FD and ad AL feeding followed by acute treatment with 0.7uM and 1.5uM doses of AMPH. We recorded calcium activity and quantified fluorescence change, activity duration, peak rise/fall time, and latency in the spikes of the DA neurons. Our results show that baseline DA neuron activity amplitude, spike duration, and correlation between inter- and intra-DA neurons were higher in the FD than in the AL state. Dose-dependent AMPH treatment further increased the activity intensity of the aforementioned parameters in the neuron spikes in the FD state. The DA activity correlation and spike latency were dose-dependently impaired in both DA populations. These results suggest that different DA populations in the brain exhibit a similar activity trend in response to caloric states and AMPH, where the AMPH-mediated intensity change in the activity was dose-dependent.