Apelin-13 confers Neuropeptide Y-mediated neuroprotection and preserves learning and allocentric memory in D-glutamic acid-induced excitotoxicity in rats.

Glutamate-mediated excitotoxicity leads to mitochondrial dysfunction, apoptosis, and neuronal cell death. This study aims to investigate whether NPY2 receptors (NPY2R) and NPY5 receptors (NPY5R) enhance the effects of Apelin-13/APJ signaling pathways as modulatory cofactors in the neuroprotection provided by Apelin-13 against excitotoxic damage and in the prevention of learning-memory disorders. D-Glutamic acid-induced excitotoxicity was established in 42 male Sprague-Dawley rats (6-8 weeks, 200-250 g). Animals were randomly divided into six groups (n = 7); Control (C; 0.9% NaCl, i.p), D-Glutamic Acid (G; 4 mg/kg, i.p), Apelin-13 (A; 300 µg/kg, i.p), D-Glutamic Acid + Apelin-13 (GA), D-Glutamic Acid + Apelin-13 + NPY2R antagonist (GAN2; 1,5 mg/kg, i.p) and D-Glutamic Acid + Apelin-13 + NPY5R antagonist (GAN5; 1,5 mg/kg, i.p). Locomotor activity were evaluated with the Open Field (OFT), short/long-term memory and learning performance, allocentric-egocentric orientation were assesed with novel object recognition (NORT) and Morris water maze (MWM) tests. All parameters were normalized to the C group, and statistical significance between groups was assesed. In group G, a significant decrease (p < 0.001) in Extracellular Signal Regulatory Kinase (ERK1/2) and Protein Kinase B-1 (AKT-1) levels and an increase (p < 0.001) in Caspase-3 were observed. Oxidative parameters increased in the G and GAN2 groups. Antioxidant parameters were also elevated in GA and GAN5, similar to C and A groups. An increase in MWM latency to the target quadrant (p < 0.001) and a decrease in NORT discrimination index (p < 0.001) were found in the G and GAN2 groups compare to the C and A. Histochemical staining scores showed that the protection of Apelin-13 was mediated by NPY2R. In GAN2, blocking NPY2R reduces Apelin-13's neuroprotection, which is sustained only via NPY5R with limited effect. In GAN5, Apelin-13's protection was enhanced through NPY2R, as shown with NPY5R blockade. Accordingly, Apelin-13 exerts its neuroprotective effects primarily through NPY2R, its modulatory influence via NPY5R appears to be comparatively limited.