Brain area-specific changes in glucose metabolism in rats after acute stress

Stress is known to be one of the main risk factors for neuropsychiatric disorders. The stress response is a physiological mechanism of adaptation essential for survival but, when the stressful event is prolonged or overwhelming, maladaptive mechanisms could occur, thus increasing the risk to develop a stress-related pathology. Several human and ex vivo animal studies tried to investigate how brain responds to stressors and which cerebral areas are involved, but only in the last years, with the recent progress in neuroimaging techniques such as Positron Emission Tomography (PET), it has been possible to study metabolic and neurobiological changes induced in vivo by stress. Compelling evidence shows that energy metabolism and mitochondrial activity are affected by stress: at a cellular level stress results to be linked to premature cellular ageing and shortened telomeres. Because mitochondria actively regulate synaptic transmission, brain seems to be vulnerable to bioenergetic fluctuations and mitochondrial defects induced by stress. Main aim of the present study was to evaluate the effect of acute foot shock (FS) stress on brain glucose metabolism in rats. We took advance of [18F]FDG-PET studies on FS-stressed rats to highlight which brain areas were activated/inactivated by stress. Our results showed an increase of energy consumption in rostral regions, while in more caudal areas acute stress induced a decrease in glucose metabolism. In order to understand whether these changes in activation of selected brain areas were related with modifications in synaptic glucose metabolism, thus suggesting changes in synaptic function, we measured enzymatic activity of hexokinase, the rate-limiting enzyme for glycolysis in the brain. In line with previous results, hexokinase activity resulted to be increased by acute stress in synaptosomes from prefrontal cortex and dorsal hippocampus while showing an opposite trend in those from ventral hippocampus. Moreover, as we wanted to investigate ex vivo whether our previous results reflected real changes in synaptic glucose consumption, we analyzed synaptic glucose uptake by measuring the uptake of the glucose analogous 2-Deoxy [3H] glucose in perfused purified synaptosomes from stressed rats. Data from the uptake of 2-Deoxy [3H] glucose are also consistent with previous results. Taken together, these results suggest that acute stress induces area-specific changes in glucose metabolism, immediately after the stress episode.