Stress enhances expression of calcium-binding proteins and NMDAR subunit genes in the rat hippocampus

Oxidative stress impairs the function of calcium-binding proteins and deregulates calcium signaling in living organisms. We have previously explored the overexpression of calcium-binding protein genes in a reactive oxygen and nitrogen species-induced in vitro cell model of stress that leads to apoptosis. However, in in vivo models, low levels of stress leads to depressive-like behavior. Here, we aimed to analyze gene expression of major calcium-binding proteins (calcineurin, calmodulin, calsyntenin, synaptotagmin, and calreticulin) and N-methyl-d-aspartic acid (NMDA) receptor subunits (glutamate receptor ionotropic [GluN] GluN1, GluN2A, and GluN2B) in the hippocampus of stress-induced rats.

Six-week-old male Wistar rats were assigned to two stress induction groups and a control group without stress (n = 6). Stress was induced by using H₂O₂ (3% in water) or by immobilization (using a sticky mat) over a period of 30 days. Expression of calcium-binding protein genes in the hippocampus, antioxidant assays, structural alterations in hippocampal neurons, and depressive-like behavior were determined.

Expression of genes encoding calcium-binding proteins calcineurin, calsyntenin, synaptotagmin and NMDA receptor subunit GluN1 was enhanced in both chemical and physical stress-induced rats compared with control rats (4.25 ± 0.05 vs. 1.03 ± 0.02, p < 0.05, 2.05 ± 0.08 vs. 1.03 ± 0.02, p < 0.005; 2.2 ± 0.4 vs. 1.02 ± 0.03, p < 0.05, 1.98 ± 0.07 vs. 1.02 ± 0.03, p < 0.005; 1.4 ± 0.6 vs. 1.15 ± 0.09, p < 0.05, 1.39 ± 0.05 vs. 1.15 ± 0.09, p < 0.005), respectively. In stress-induced rats, neurons in the CA2 region of the hippocampus were fewer and appeared disorganized compared with control rats. Furthermore, stress-induced rats showed decreased mobility and lower sucrose preference in behavioral studies compared with control rats.

Lower levels of reactive oxygen and nitrogen species (RONS) can also lead to stress in rats by affecting their calcium signaling, buffering capacity in the neurons leading to depressive symptoms.