Loop diuretics mitigate juvenile immobilization treatment-induced hippocampal dysfunction

Juvenile traumatic experiences can lead to adult cognitive impairments, including learning deficits and increased anxiety risk. Dysfunction of the hippocampus is crucial in stress-induced behavioral disorders, and recent evidence suggests that disrupted chloride homeostasis through the chloride transporter NKCC1 may alter GABAergic signaling and contribute to neuropathology. This study investigates the role of NKCC1 in long-term hippocampal dysfunction induced by juvenile immobilization (J_IMO). Male C57BL/6 mice underwent J_IMO treatment at five weeks of age and were assessed at six and twelve weeks using inhibitory avoidance (IA), open field tests (OFT), extracellular recording, qPCR, and Western blot analyses. Following J_IMO treatment, mice exhibited significant learning deficits in IA, with no notable differences in total movement distance in the OFT. Electrophysiological analysis revealed a marked increase in long-term potentiation (LTP) within the hippocampal Schaffer collateral pathway, while paired-pulse facilitation remained unchanged. An altered input-output curve indicated post-synaptic dysregulation in J_IMO-treated mice. Additionally, Western blot and qPCR analyses showed significant upregulation of Slc12a2 (NKCC1) expression, primarily localized to neural cells, as confirmed by double-staining immunohistochemistry. These findings suggest that NKCC1 plays a pivotal role in J_IMO-induced hippocampal dysfunction, particularly by impairing GABAergic inhibitory neurotransmission. The GABA_A agonist isoguvacine's inhibitory effect on the fEPSP was diminished in J_IMO-treated mice but restored with NKCC1 inhibitor co-treatment, indicating that altered NKCC1 function undermines GABAergic inhibitory neurotransmission in this stress model. In conclusion, our results indicate that NKCC1 contributes to J_IMO-induced hippocampal dysfunction by diminishing GABAergic inhibitory neurotransmission. NKCC1 inhibitors may significantly alleviate these dysfunctions.