id_945. RELAXIN-3 AND OXYTOCIN SIGNALING IN THE VENTRAL DENTATE GYRUS: NEUROCHEMICAL CHARACTERIZATION AND OPPOSING ROLES IN STRESS AND ANXIETY
Kinga Przybylska1,2, Aleksandra Trenk1, Anna Gugula1, Aleksandra Nogaj1,2, Gabriela Stopka1,2, Mohammed Akhter Hossain3, Andrew L. Gundlach3, Anna Blasiak1
1 Department of Neurophysiology and Chronobiology, Institute of Zoology and Biomedical Research, Jagiellonian University, Cracow, Poland
2 Doctoral School of Exact and Natural Sciences, Jagiellonian University, Cracow, Poland
3 The Florey Institute of Neuroscience and Mental Health, and Florey Department of Neuroscience and Mental Health, The University of Melbourne, Parkville, Victoria, Australia
INTRODUCTION: The ventral hippocampus (vHPC) plays a critical role in regulating stress and anxiety, with interneuron dysfunction implicated in anxiety-related disorders. The vHPC receives substantial innervation from the nucleus incertus (NI), the primary source of relaxin-3 (RLN3) in the rat brain. RLN3 signaling in vHPC has been shown to promote anxiety and social avoidance. In contrast, oxytocin (OXT) signaling within vHPC enhances social bonding and reduces stress, highlighting opposing neuromodulatory effects of these neuropeptides. However, their interaction within this structure remains poorly understood.
AIM(S): This study aimed to characterize the neurochemical profile and functional connectivity of the NI–vHPC pathway and determine how RLN3/RXFP3 and OXT/OXTR signaling interact to modulate vHPC neuronal activity.
METHOD(S): Anatomical, molecular, and electrophysiological approaches were employed in rats, including viral based tract-tracing, immunohistochemistry, HiPlex in situ hybridization (ISH), and ex vivo multi-electrode array (MEA) recordings.
RESULTS: Immunohistochemistry and viral tract-tracing revealed dense RLN3-positive and NI-originating fibers in the ventral dentate gyrus (vDG), particularly within the hilus. ISH demonstrated that RXFP3 and OXTR mRNAs are expressed in GABAergic (vGAT1-positive) neurons, including subpopulations expressing somatostatin and/or parvalbumin. Notably, we also observed co-expression of RXFP3, OXTR, and KCNQ2 mRNA in individual vDG neurons. MEA recordings revealed opposing effects of RLN3 and OXT on vDG neural activity, with RLN3 exerting inhibitory and OXT excitatory effects. Furthermore, the blockade of KCNQ channels with XE991 reduced both of these responses.
CONCLUSIONS: These findings demonstrate that RLN3 and OXT directly modulate vDG neuronal activity and exert antagonistic effects via common molecular effector, KCNQ channels. This interaction may represent a molecular substrate underlying the regulation of stress- and anxiety-related behaviors.
FINANCIAL SUPPORT: National Science Centre Poland: UMO-2023/49/B/NZ4/01885, MiniGrant2023 ID.UJ