INVESTIGATION OF FEEDING-STATUS DEPENDENT MODULATION OF GABA<SUB>A</SUB>RΑ5 AND GAT3 PROTEINS IN THE VENTROMEDIAL HYPOTHALAMUS

The ventromedial hypothalamus (VMH) is crucial for regulating metabolic activities such as satiety, glucose and insulin homeostasis, and energy expenditure, and for modulating the metabolic response through neurotransmitters and neuromodulators such as γ-Aminobutyric acid (GABA) and BDNF. The extrasynaptic GABAergic signaling in the VMH is shaped by the relation between GABA_ARα5 and the astrocytic transporter GAT3, which regulates tonic inhibition. Our aim is to investigate dynamic alterations in GABA_ARα5 and GAT3 levels in the VMH region of fed and 24-hour-fasted mice to assess GABAergic circuit plasticity in response to metabolic state. Coronal VMH brain slices from 24-hour fasted and fed mice were collected and analyzed by western blot and immonohistochemistry-immunofluorescence (IHC-IF) experiments. The images were acquired by confocal microscopy and analyzed with Fiji 1.54 and IMARIS 9.7. Our results indicate that 24-hour fasting significantly increased GAT3-colocalized surface area and volume in VMH astrocytes. Morphological assessments and Sholl analysis showed that fasting-induced remodeling is characterized by a significant reduction in structural complexity, especially in the number of branches and mean Sholl radius, despite a trend toward increased total surface area and volume. GABA_ARα5 levels in synaptic and extrasynaptic areas remain unchanged between feeding conditions. In conclusion, these results suggest that VMH astrocytes undergo morphological and molecular remodeling during fasting to modulate GABAergic signaling, predominantly through GAT3-mediated pathways rather than through alterations in GABA_ARα5 expression. This project is funded by TUBITAK 2232 Early-Stage Researchers Grant and TUBITAK 1001 Grant (Project Numbers 121C128 and 124Z284, respectively).