Research Article | 10 Nov 2022

Imbalance in the ratio between mineralocorticoid and glucocorticoid receptors and neurodegeneration in the dentate gyrus of aged dogs

Shirley Jaqueline Szriber1, Leonardo Santana Novaes2, Nilton Barreto Dos Santos2, Carolina Demarchi Munhoz2, and Deise Carla Almeida Leite-Dellova1Show more
VETERINARY WORLD | pg no. 2543-2550 | Vol. 15, Issue 11 | DOI: 10.14202/vetworld.2022.2543-2550
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Abstract

          
Background and Aim: Cortisol binds to mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) found in the hippocampus. The balanced expression of these receptors is essential to neuronal survival as MR and GR activations have antiapoptotic and proapoptotic effects, respectively. Given the aging changes in dogs' dentate gyrus (DG) and the possible involvement of cortisol receptors in this process, this study aimed to evaluate the expression of MR and GR and neuronal degeneration in this hippocampal region of aged dogs.
Materials and Methods: This study included cadaveric histologic hippocampus sections from 12 dogs aged 10 years and older (AG group) and six young/adult dogs aged up to 8 years (YAd group). Nissl staining and immunohistochemistry were performed to identify cells and investigate MR and GR expression, respectively. Furthermore, fluorescent labeling (fluoro- Jade B) was used to detect degenerating neurons.
Results: The AG group's polymorphic layer of the DG had a lower cell count (16%) and more degenerating neurons than the YAd group. In addition to these cellular changes, the AG group had lower MR immunoreactivity and MR-to-GR ratio. Furthermore, the lowest MR expression was associated with neuronal degeneration in the polymorphic layer of the DG of dogs.
Conclusion: An imbalance in the MR-to-GR ratio was observed in the polymorphic layer of the DG of aged dogs, along with lower MR expression and a greater number of degenerating neurons. These findings have clinical implications for understanding the decline in hippocampal memory formation associated with cognitive changes in aged dogs. Keywords: aging, canine, cortisol receptors, hippocampus, neuronal loss.
          
Keywords: aging, canine, cortisol receptors, hippocampus, neuronal loss.