Chronic restraint stress affected the whole body metabolism in adult male rats: the role of ventral hippocampus and hypothalamus

The brain’s functionality is supported by precise metabolic regulation and a continuous energy supply. Disruptions in these bioenergetic mechanisms have been associated with the development of Major Depressive Disorder. In this context, preclinical studies have shown that chronic mild stress (CMS) exposure in rats induces metabolic alterations in the ventral hippocampus (vHip), a brain area involved in emotional regulation and bioenergetics. Specifically, we recently observed a metabolic divergence between resilient and vulnerable individuals exposed to CMS [1]. Besides vHip, hypothalamus (Hyp) is a fundamental brain region involved in metabolic regulation. In this study, we aimed to investigate how prolonged exposure to stress may induce changes in the whole metabolic profile through indirect calorimetry in adult male rats. To achieve this objective, adult male Wistar rats were employed and exposed to chronic restraint stress (CRS) 1h twice a day for two weeks. After one week, half of the animals were transferred to metabolic cages for one week, while continuing the chronic stress exposure in parallel. Alterations in energy metabolism were assessed using the Promethion Metabolic Screening system (Sable Systems International), allowing continuous physiological parameter monitoring. The sucrose preference test was conducted weekly to evaluate changes in hedonic behavior. Metabolic data were processed with the CalR17 web-based platform and expressed as hourly means across light and dark cycles. 24h after last stressor, rats were sacrificed and vHip and Hyp were dissected for the targeted metabolomic analysis. Statistical analyses of behavioral and metabolic data were performed with the Unpaired t-test. After 1 week of CRS rats showed a reduction in sucrose preference (p < 0.05 vs No stress) and after one more week in the metabolic cages we found a decrease in the respiratory exchange ratio (RER) during both the light (p < 0.01 vs No stress) and dark (p < 0.05 vs No stress) phases. Considering the major classes of metabolites in the vHip, we observed a significant reduction in acylcarnitines (p<0.01 vs No stress) and amino acids (p < 0.05 vs No stress), while no changes for glycolysis class. Indeed, short-chain (p < 0.01 vs No stress), medium-chain (p < 0.01 vs No stress), and long-chain acylcarnitines (p < 0.01 No stress) were significantly reduced in CRS rats, together with a decrease in branched-chain amino acids (BCAA) (p<0.05 No stress) and in the C5/BCAA ratio (p<0.05 vs No stress). On the contrary, in the Hyp we found a significant increase specifically in glycolysis metabolites (p<0.01 vs No stress). These results indicate that CRS induced alterations in the whole metabolism and at central level the vHip was particularly affected. The altered metabolic profile in this brain region suggests a reduced availability of substrates for β-oxidation, potentially reflecting their impaired synthesis at peripheral level.