Systematic analysis of mushroom body-innervating dopaminergic neuron activity in different physiological states in...

Thirst and hunger are fundamental survival drives that modulate various aspects of animal behavior through specific neural circuits. Previous studies have demonstrated that dopaminergic neurons (DANs) innervating the mushroom body (MB) in the Drosophila brain play essential roles in innate and learned thirst- and hunger-dependent behaviors, with most experiments focusing on acute water or food deprivation. However, it is unclear whether acute water or food deprivation alters dopamine production and neural activity in MB-innervating DANs.

We genetically expressed green fluorescent protein (GFP) in MB-innervating DANs using broadly and specifically labeled GAL4 lines under satiety, thirst, and hunger states. The brains were immunostained with anti-tyrosine hydroxylase (TH) to assess dopamine biosynthesis. Additionally, the transcriptional reporter of intracellular Ca²⁺ (TRIC) was expressed in these DANs using the same GAL4 lines to monitor neural activity under different internal states. Normalized anti-TH and TRIC signals in specific MB compartments were compared between the satiety and thirst groups and between the satiety and hunger groups using unpaired two-tailed t-tests.

Neither TH levels nor neural activity in the 13 subtypes of MB-innervating DANs exhibited significant differences during the satiety, thirst, and hunger conditions.

This study suggests that 16-h water deprivation or 24-h food deprivation does not significantly alter dopamine production and neural activity in MB-innervating DANs. These findings offer insights into the independence of baseline dopaminergic activity from internal states in thirst- or hunger-related behaviors.