Effects of age and treadmill exercise in chronic diabetic stages on neuroblast differentiation in a rat model of type 2 diabetes

The Impact of Exercise Training on the Brain and Cognition in Type 2 Diabetes, and its Physiological Mediators: A Systematic Review

BACKGROUND

Type 2 diabetes (T2DM) affects brain structure and function, and is associated with an increased risk of dementia and mild cognitive impairment. It is known that exercise training has a beneficial effect on cognition and brain structure and function, at least in healthy people, but the impact of exercise training on these aspects remains to be fully elucidated in patients with T2DM.

OBJECTIVE

To determine the impact of exercise training on cognition and brain structure and function in T2DM, and identify the involved physiological mediators.

METHODS

This paper systematically reviews studies that evaluate the effect of exercise training on cognition in T2DM, and aims to indicate the most beneficial exercise modality for improving or preserving cognition in this patient group. In addition, the possible physiological mediators and targets involved in these improvements are narratively described in the second part of this review. Papers published up until the 14th of January 2025 were searched by means of the electronic databases PubMed, Embase, and Web of Science. Studies directly investigating the effect of any kind of exercise training on the brain or cognition in patients with T2DM, or animal models thereof, were included, with the exception of human studies assessing cognition only at one time point, and studies combining exercise training with other interventions (e.g. dietary changes, cognitive training, etc.). Study quality was assessed by means of the TESTEX tool for human studies, and the CAMARADES tool for animal studies.

RESULTS

For the systematic part of the review, 22 papers were found to be eligible. 18 out of 22 papers (81.8%) showed a significant positive effect of exercise training on cognition in T2DM, of which two studies only showed significant improvements in the minority of the cognitive tests. Four papers (18.2%) could not find a significant effect of exercise on cognition in T2DM. Resistance and endurance exercise were found to be equally effective for achieving cognitive improvement. Machine-based power training is seemingly more effective than resistance training with body weight and elastic bands to reach cognitive improvement. In addition, BDNF, lactate, leptin, adiponectin, GSK3β, GLP-1, the AMPK/SIRT1 pathway, and the PI3K/Akt pathway were identified as plausible mediators directly from studies investigating the effect of exercise training on brain structure and function in T2DM. Via these mediators, exercise training induces multiple beneficial brain changes, such as increased neuroplasticity, increased insulin sensitivity, and decreased inflammation.

CONCLUSION

Overall, exercise training beneficially affects cognition and brain structure and function in T2DM, with resistance and endurance exercise having similar effects. However, there is a need for additional studies, and more methodological consistency between different studies in order to define an exercise program optimal for improving cognition in T2DM. Furthermore, we were able to define several mediators involved in the effect of exercise training on cognition in T2DM, but further research is necessary to unravel the entire process.

Two weeks of moderate intensity locomotor training increased corticosterone concentrations but did not alter the number of adropin-immunoreactive cells in the hippocampus of diabetic type 2 and control rats

Adropin (ADR) plays a role in metabolism regulation and its alterations in obesity and diabetes have been found. Treatment with ADR was beneficial in metabolic diseases, and physical exercise increased ADR concentrations in obese patients. However, data on the distribution of ADR in the brain are sparse. The role of metabolic status and physical exercise on its expression in the brain is undiscovered. We hypothesized that diabetes type 2 (DM2) and/or exercise will alter number of ADR-immunoractive (-ir) cells in the rat brain. Animals were divided into groups: diabetes type 2 (receiving high-fat diet and injections of streptozotocin) and control (fed laboratory chow diet; C). Rats were further divided into: running group (2 weeks of forced exercise on a treadmill) and non-running group. Body mass, metabolic and hormonal profiles were assessed. Immunohistochemistry was run to study ADR-ir cells in the brain. We found that: 1) in DM2 animals, running decreased insulin and increased glucose concentrations; 2) in C rats, running decreased insulin concentrations and had no effect on glucose concentration in blood; 3) running increased corticosterone (CORT) concentrations in DM2 and C rats; 4) ADR-ir cells were detected in the hippocampus and ADR-ir fibers in the arcuate nucleus of the hypothalamus, which is a novel location; 5) metabolic status and running, however, did not change number of these cells. We concluded that 2 weeks of forced moderate intensity locomotor training induced stress response present as increased concentration of CORT and did not influence number of ADR-ir cells in the brain.

Hypothyroidism increases cyclooxygenase-2 levels and pro-inflammatory response and decreases cell proliferation and neuroblast differentiation in the hippocampus

The present study investigated the effects of hypothyroidism on cyclooxygenase-2 (COX-2) and pro‑inflammatory cytokines in the dentate gyrus to elucidate the roles of COX‑2 in the hypothyroid hippocampus. Hypothyroidism was induced in rats by treating with 0.03% 2‑mercapto‑1‑methyl‑imidazole dissolved in drinking water for 5 weeks. The animals were sacrificed at 12 weeks of age. Hypothyroidism rats exhibited decreased triiodothyronine and thyroxine levels in the serum, while the levels of thyroid‑stimulating hormone and the weight of thyroid glands were significantly higher in the hypothyroid rats compared with those in the vehicle‑treated group. COX‑2 immunoreactivity was significantly increased in the hippocampal CA2/3 region and the dentate gyrus compared with the vehicle‑treated group. Levels of pro‑inflammatory cytokines including interleukin (IL)‑1β, IL‑6 and tumor necrosis factor‑α were significantly higher in the hippocampal homogenates of hypothyroid rats. Cell proliferation and neuroblast differentiation based on Ki67 and doublecortin immunohistochemistry were decreased in the dentate gyrus of hypothyroid rats compared with those in the vehicle‑treated group. These results suggested that hypothyroidism‑mediated COX‑2 expression affected hippocampal plasticity by upregulating the levels of pro‑inflammatory cytokines in the hippocampus. Therefore, COX‑2 may be suggested as a candidate molecule for preventing hypothyroidism‑induced neurological side effects.

Comparison of Adult Hippocampal Neurogenesis and Susceptibility to Treadmill Exercise in Nine Mouse Strains

The genetic background of mice has various influences on the efficacy of physical exercise, as well as adult neurogenesis in the hippocampus. In this study, we investigated the basal level of hippocampal neurogenesis, as well as the effects of treadmill exercise on adult hippocampal neurogenesis in 9 mouse strains: 8 very commonly used laboratory inbred mouse strains (C57BL/6, BALB/c, A/J, C3H/HeJ, DBA/1, DBA/2, 129/SvJ, and FVB) and 1 outbred mouse strain (ICR). All 9 strains showed diverse basal levels of cell proliferation, neuroblast differentiation, and integration into granule cells in the sedentary group. C57BL/6 mice showed the highest levels of cell proliferation, neuroblast differentiation, and integration into granule cells at basal levels, and the DBA/2 mice showed the lowest levels. The efficacy of integration into granule cells was maximal in ICR mice. Treadmill exercise increased adult hippocampal neurogenesis in all 9 mouse strains. These results suggest that the genetic background of mice affects hippocampal neurogenesis and C57BL/6 mice are the most useful strain to assess basal levels of cell proliferation and neuroblast differentiation, but not maturation into granule cells. In addition, the DBA/2 strain is not suitable for studying hippocampal neurogenesis.

Diabetes-Induced Dysfunction of Mitochondria and Stem Cells in Skeletal Muscle and the Nervous System

Diabetes mellitus is one of the most common metabolic diseases spread all over the world, which results in hyperglycemia caused by the breakdown of insulin secretion or insulin action or both. Diabetes has been reported to disrupt the functions and dynamics of mitochondria, which play a fundamental role in regulating metabolic pathways and are crucial to maintain appropriate energy balance. Similar to mitochondria, the functions and the abilities of stem cells are attenuated under diabetic condition in several tissues. In recent years, several studies have suggested that the regulation of mitochondria functions and dynamics is critical for the precise differentiation of stem cells. Importantly, physical exercise is very useful for preventing the diabetic alteration by improving the functions of both mitochondria and stem cells. In the present review, we provide an overview of the diabetic alterations of mitochondria and stem cells and the preventive effects of physical exercise on diabetes, focused on skeletal muscle and the nervous system. We propose physical exercise as a countermeasure for the dysfunction of mitochondria and stem cells in several target tissues under diabetes complication and to improve the physiological function of patients with diabetes, resulting in their quality of life being maintained.

Age-associated alterations in constitutively expressed cyclooxygenase-2 immunoreactivity and protein levels in the hippocampus

Cyclooxygenase-2 (COX-2) is a known inducible inflammatory mediator. COX-2 is constitutively expressed in the hippocampus and may regulate synaptic plasticity. The present study investigated the age‑associated alterations in white blood cell counts and hippocampal COX‑2 expression in healthy mice using immunohistochemical and western blot analyses at 1 month postnatal (PM1), PM3, PM6, PM12 and PM24. White blood cell counts were significantly decreased in the PM24 group when compared with the PM1 group. In addition, lymphocyte counts were decreased in the PM24 group when compared with all other groups. By contrast, monocyte, neutrophil and eosinophil counts were increased in the PM24 group; however, this did not reach statistical significance. COX‑2 expression was identified in the granule cells of the dentate gyrus and in the pyramidal cells of the hippocampal CA2/3 region. COX‑2 immunoreactivity was maintained until PM18, however, the levels significantly decreased by PM24. These results suggest that, despite alterations in the differential white blood cell counts, the significant decrease in constitutive COX‑2 expression in the hippocampus may be associated with degenerative age-associated alterations in synaptic plasticity in the hippocampus.

Up-regulated fractalkine (FKN) and its receptor CX3CR1 are involved in fructose-induced neuroinflammation: Suppression by curcumin

Recent studies suggest that diet-induced fractalkine (FKN) stimulates neuroinflammation in animal models of obesity, yet how it occurs is unclear. This study investigated the role of FKN and it receptor, CX3CR1, in fructose-induced neuroinflammation, and examined curcumin's beneficial effect. Fructose feeding was found to induce hippocampal microglia activation with neuroinflammation through the activation of the Toll-like receptor 4 (TLR4)/nuclear transcription factor κB (NF-κB) signaling, resulting in the reduction of neurogenesis in the dentate gyrus (DG) of mice. Serum FKN levels, as well as hypothalamic FKN and CX3CR1 gene expression, were significantly increased in fructose-fed mice with hypothalamic microglia activation. Hippocampal gene expression of FKN and CX3CR1 was also up-regulated at 14d and normalized at 56d in mice fed with fructose, which were consistent with the change of GFAP. Furthermore, immunostaining showed that GFAP and FKN expression was increased in cornu amonis 1, but decreased in DG in fructose-fed mice. In vitro studies showed that GFAP and FKN expression was stimulated in astrocytes, and suppressed in mixed glial cells exposed to 48h-fructose, with the continual increase of pro-inflammatory cytokines. Thus, increased FKN and CX3CR1 may cause a cross-talk between activated glial cells and neurons, playing an important role in the development of neuroinflammation in fructose-fed mice. Curcumin protected against neuronal damage in hippocampal DG of fructose-fed mice by inhibiting microglia activation and suppressed FKN/CX3CR1 up-regulation in the neuronal network. These results suggest a new therapeutic approach to protect against neuronal damage associated with dietary obesity-associated neuroinflammation.

Reduction of adult hippocampal neurogenesis is amplified by aluminum exposure in a model of type 2 diabetes

In this study, we investigated the effects of chronic aluminum (Al) exposure for 10 weeks on cell proliferation and neuroblast differentiation in the hippocampus of type 2 diabetic rats. Six-week-old Zucker diabetic fatty (ZDF) and Zucker lean control (ZLC) rats were selected and randomly divided into Al- and non-Al-groups. Al was administered via drinking water for 10 weeks, after which the animals were sacrificed at 16 weeks of age. ZDF rats in both Al- and non-Al-groups showed increases in body weight and blood glucose levels compared to ZLC rats. Al exposure did not significantly affect body weight, blood glucose levels or pancreatic β-cells and morphology of the pancreas in either ZLC or ZDF rats. However, exposure to Al reduced cell proliferation and neuroblast differentiation in both ZLC and ZDF rats. Exposure to Al resulted in poor development of the dendritic processes of neuroblasts in both ZLC and ZDF rats. Furthermore, onset and continuation of diabetes reduced cell proliferation and neuroblast differentiation, and Al exposure amplified reduction of these parameters. These results suggest that Al exposure via drinking water aggravates the impairment in hippocampal neurogenesis that is typically observed in type 2 diabetic animals.

Vanillin and 4-hydroxybenzyl alcohol promotes cell proliferation and neuroblast differentiation in the dentate gyrus of mice via the increase of brain-derived neurotrophic factor and tropomyosin-related kinase B

4-Hydroxy-3-methoxybenzaldehyde (vanillin) and 4-hydroxybenzyl alcohol (4-HBA) are well-known phenolic compounds, which possess various therapeutic properties and are widely found in a variety of plants. In the present study, the effects of vanillin and 4-HBA were first investigated on cell proliferation, as well as neuronal differentiation and integration of granule cells in the dentate gyrus (DG) of adolescent mice using Ki-67, doublecortin (DCX) immunohistochemistry and 5-bromo-2′-de-oxyuridine (BrdU)/feminizing Locus on X 3 (NeuN) double immunofluorescence. In both the vanillin and 4-HBA groups, the number of Ki-67⁺ cells, DCX⁺ neuroblasts and BrdU⁺/NeuN⁺ neurons were significantly increased in the subgranular zone of the DG, as compared with the vehicle group. In addition, the levels of brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB), a BDNF receptor, were significantly increased in the DG in the vanillin and 4-HBA groups compared with the vehicle group. These results indicated that vanillin and 4-HBA enhanced cell proliferation, neuroblast differentiation and integration of granule cells in the DG of adolescent mice. These neurogenic effects of vanillin and 4-HBA may be closely associated with increases in BDNF and TrkB.

Sitagliptin protects proliferation of neural progenitor cells in diabetic mice

Sitagliptin (SIT) is a dipeptidyl peptidase-4 (DPP-4) inhibitor that enhances the effects of incretin hormones, such as Glucose-dependent Insulinotropic Peptide (also known as Gastric Inhibitory Polypeptide, GIP) and Glucagon-Like Peptide 1 (GLP-1). We have now evaluated the effect of SIT on proliferation of neural progenitors in diabetic mice. A condition resembling the non-obese type 2 diabetes mellitus (D2) was achieved by a combination of streptozotocin and nicotinamide (NA-STZ), whereas a type 1-like disease (D1) was provoked by STZ without NA. Non-diabetic mice received vehicle injections. Cell proliferation was estimated by bromodeoxyuridine (BrdU) incorporation in two different regions of the subventricular zone (SVZ), the largest reserve of neural stem cells in the adult brain. SIT treatment did not modify the high fasting blood glucose (BG) levels and intraperitoneal glucose tolerance test (IPGTT) of D1 mice. By contrast, in D2 mice, SIT treatment significantly reduced BG and IPGTT. Both D1 and D2 mice showed a substantial reduction of BrdU labeling in the SVZ. Remarkably, SIT treatment improved BrdU labeling in both conditions. Our findings suggest that SIT would protect proliferation of neural progenitor cells even in the presence of non-controlled diabetic alterations.

Effects of exercise on brain functions in diabetic animal models

Human life span has dramatically increased over several decades, and the quality of life has been considered to be equally important. However, diabetes mellitus (DM) characterized by problems related to insulin secretion and recognition has become a serious health problem in recent years that threatens human health by causing decline in brain functions and finally leading to neurodegenerative diseases. Exercise is recognized as an effective therapy for DM without medication administration. Exercise studies using experimental animals are a suitable option to overcome this drawback, and animal studies have improved continuously according to the needs of the experimenters. Since brain health is the most significant factor in human life, it is very important to assess brain functions according to the different exercise conditions using experimental animal models. Generally, there are two types of DM; insulin-dependent type 1 DM and an insulin-independent type 2 DM (T2DM); however, the author will mostly discuss brain functions in T2DM animal models in this review. Additionally, many physiopathologic alterations are caused in the brain by DM such as increased adiposity, inflammation, hormonal dysregulation, uncontrolled hyperphagia, insulin and leptin resistance, and dysregulation of neurotransmitters and declined neurogenesis in the hippocampus and we describe how exercise corrects these alterations in animal models. The results of changes in the brain environment differ according to voluntary, involuntary running exercises and resistance exercise, and gender in the animal studies. These factors have been mentioned in this review, and this review will be a good reference for studying how exercise can be used with therapy for treating DM.

Treadmill exercise is associated with reduction of reactive microgliosis and pro-inflammatory cytokine levels in the hippocampus of type 2 diabetic rats

OBJECTIVES

In the present study, we investigated the effects of treadmill exercise on microglial activation and the subsequent release of tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-6 and IL-1-beta in the hippocampus in a rat model of type 2 diabetes.

METHODS

At 30 weeks of age, diabetic (Zucker diabetic fatty, ZDF) rats and their littermate control (Zucker lean control, ZLC) rats were either placed on a stationary treadmill or made to run for 1 hour/day at 12-16 m/minute on five consecutive days, for 10 weeks. Once the rats reached 40 weeks, they were perfused and their hippocampus collected for immunohistochemistry or hippocampus collected fresh for the Western blotting or enzyme-linked immunosorbent assay (ELISA).

RESULTS

The whole blood glucose levels in exercised ZDF rats were significantly higher than in the sedentary or exercised ZLC rats, but were significantly lower than in the sedentary ZDF rats. In the sedentary ZLC and exercised ZLC rats, ionised calcium-binding adapter molecule 1 (Iba-1) immunoreactive microglia showed normal morphology which had small cytoplasm with ramified processes. In the sedentary ZDF rats, some Iba-1 immunoreactive microglia showed abnormal morphology which had hypertrophied cytoplasm with retracted processes. However, exercised ZDF rats had small cytoplasm with highly ramified processes. Levels of TNF-alpha, IL-6 and IL-1beta in the hippocampal homogenates were significantly increased in sedentary ZDF rats compared to sedentary ZLC rats, respectively. However, TNF-alpha, IL-6 and IL-1beta levels in the exercised ZDF rats were significantly decreased compared with those of sedentary ZDF rats, respectively.

DISCUSSION

These results suggest that exercise in type 2 diabetic rats reduces microglial activation and the subsequent increase of pro-inflammatory cytokine levels in the hippocampus.

Activation of microglia and induction of pro-inflammatory cytokines in the hippocampus of type 2 diabetic rats

OBJECTIVES

The majority of immune cells in the brain are comprised of microglia, which undergo morphological changes when activated to remove damaged neurons and infectious agents from the brain tissue. In this study, we investigated the effects of type 2 diabetes on microglial activation and the subsequent secretion of pro-inflammatory cytokines, such as interferon-gamma (IFN-gamma) and interleukin-1beta (IL-1beta), in the hippocampus using Zucker diabetic fatty (ZDF) rats and Zucker lean control (ZLC) rats at various diabetic stages.

METHODS

Zucker lean control and Zucker diabetic fatty rats were sacrificed at 12 (early diabetic stage), 20, or 30 weeks of age (chronic diabetic stage), and the hippocampus was obtained via transcardiac perfusion or dissection for immunohistochemistry and western blot analysis, respectively.

RESULTS

Zucker diabetic fatty rats demonstrated significantly higher glucose levels at 12 and 30 weeks of age compared to ZLC rats. Microglia immunoreactive to ionized calcium-binding adapter molecule 1 (Iba-1) had hypertrophied cytoplasm with retracted processes at 30 weeks of age. In contrast, Iba-1-immunoreactive microglia displayed similar morphology in ZDF and ZLC rats at 12 and 20 weeks of age. Similarly, IFN-gamma and IL-1beta protein levels were significantly increased in ZDF rats compared to ZLC rats at 30 weeks of age, but not at 12 and 20 weeks of age. Interleukin-1beta immunoreactivity in the ZDF rats predominantly increased in the dentate gyrus and CA1 region of the hippocampus compared to that of ZLC rats at 30 weeks of age. In addition, IL-1beta immunoreactive structures in ZDF rats at 30 weeks of age were detected near the astrocytes and microglia.

CONCLUSION

These results suggest that chronic diabetes activates microglia and significantly increases pro-inflammatory cytokine levels in the hippocampus.

Neural stem cells in the diabetic brain

Experimental diabetes in rodents rapidly affects the neurogenic niches of the adult brain. Moreover, behavioral disorders suggest that a similar dysfunction of the neurogenic niches most likely affects diabetic and prediabetic patients. Here, we review our present knowledge about adult neural stem cells, the methods used for their study in diabetic models, and the effects of experimental diabetes. Variations in diet and even a short hyperglycemia profoundly change the structure and the proliferative dynamics of the neurogenic niches. Moreover, alterations of diabetic neurogenic niches appear to be associated with diabetic cognitive disorders. Available evidence supports the hypothesis that, in the adult, early changes of the neurogenic niches might enhance development of the diabetic disease.

Differential effects of treadmill exercise on cyclooxygenase-2 in the rat hippocampus at early and chronic stages of diabetes

Cyclooxygenase-2 (COX-2) is believed to be a multifunctional neural modulator that affects synaptic plasticity in the hippocampus. In the present study, we investigated the differential effects of treadmill exercise on COX-2 immunoreactivity in the dentate gyrus in early and chronic diabetic stages in Zucker diabetic fatty (ZDF) rats and lean control (ZLC) rats. To this end, ZLC and ZDF rats at 6 or 23 weeks of age were put on a treadmill with or without running for 1 h/day for 5 consecutive days at 16-22 m/min for 5 weeks or 12-16 m/min for 7 weeks, respectively. Treadmill exercise in prediabetic and chronic diabetic rats significantly reduced blood glucose levels. In particular, exercise in the prediabetic rat blocked the onset of diabetes. COX-2 immunoreactivity was mainly detected in the granule cell layer of the dentate gyrus and stratum pyramidale of the CA3 region in all groups. COX-2 immunoreactivity was significantly increased in these regions of ZLC and ZDF rats after treadmill exercise in the early diabetic stage. However, COX-2 immunoreactivity was not changed in these regions in ZDF rats after treadmill exercise in the chronic stage. These results suggest that treadmill exercise in diabetic animals in the chronic stage has limited ability to cause plasticity in the dentate gyrus.

Differential effects of treadmill exercise on calretinin immunoreactivity in type 2 diabetic rats in early and chronic diabetic stages

In this study, we investigated the effects of treadmill exercise on calretinin (CR), a marker of early postmitotic neurons, immunoreactivity in the dentate gyrus (DG) of Zucker diabetic fatty (ZDF) rats, before or after diabetes onset, and Zucker lean control (ZLC) rats. For this study, 6-week-old ZLC and prediabetic ZDF rats, and 22-week-old ZLC and ZDF rats were exercised on the treadmill. Sedentary ZLC and ZDF rats of the same age were used as exercise experiment controls. The exercised prediabetic ZDF rats did not show diabetes onset, while the sedentary prediabetic ZDF rats showed significantly increased blood glucose levels. The exercised diabetic ZDF rats exhibited a decrease in their blood glucose levels compared to the sedentary diabetic ZDF rats, but the levels were still above 20 mmol/l. ZLC rats of both ages were in the normoglycemic range. CR immunoreactivity was detected throughout the DG, including the subgranular zone and the polymorphic layer. Diabetic rats exhibited a significant decrease in the number of CR-immunoreactive cells and fibers in the DG. Exercise in the prediabetic ZDF rats significantly increased the number of CR-immunoreactive cells and fibers in the subgranular zone of the DG. In the ZLC and ZDF rats of chronic diabetic phase, exercise increased CR-immunoreactive neurons in the hilar region. These results suggest that diabetes significantly reduces the number of postmitotic CR-immunoreactive neurons and the intensity of immunoreactivity and that exercise increases these CR-related parameters in a diabetic stage-dependent manner.

Differential effects of treadmill exercise in early and chronic diabetic stages on parvalbumin immunoreactivity in the hippocampus of a rat model of type 2 diabetes

In the present study, we investigated the effects of treadmill exercise in early and chronic diabetic stages on parvalbumin (PV) immunoreactivity in the subgranular zone of the dentate gyrus of Zucker diabetic fatty (ZDF) and its lean control rats (ZLC). To investigate the effects, ZLC and ZDF rats at 6 or 23 weeks of age were put on a treadmill with or without running for 1 h/day/5 consecutive days at 16-22 m/min for 5 weeks or 12-16 m/min for 7 weeks, respectively. Physical exercise in pre-diabetic rats prevented onset of diabetes, while exercise in rats at chronic diabetic stage significantly reduced blood glucose levels. In addition, physical exercise in the pre-diabetic rats significantly increased PV immunoreactive fibers in the strata oriens and radiatum of the CA1-3 region and in the polymorphic and molecular layers of the dentate gyrus compared to that in sedentary controls. However, in rats at chronic stages, PV immunoreactivity was slightly increased in the CA1-3 region as well as in the dentate gyrus compared to that in the sedentary controls. These results suggest that physical exercise has differential effects on blood glucose levels and PV immunoreactivity according to diabetic stages. Early exercise improves diabetic phenotype and PV immunoreactive fibers in the rat hippocampus.

Effect of treadmill exercise on blood glucose, serum corticosterone levels and glucocorticoid receptor immunoreactivity in the hippocampus in chronic diabetic rats

Abnormal excess of glucocorticoid is one of feature characteristics in type 2 diabetes. In the present study, we investigated the effect of treadmill exercise at chronic diabetic stages on glucocorticoid receptor (GR) immunoreactivity in the hippocampal CA1 region and dentate gyrus, which are very vulnerable to diabetes. For this study, we used Zucker diabetic fatty (ZDF) rats and Zucker lean control (ZLC) rats. Twenty-three-week-old ZLC and ZDF rats were put on the treadmill with or without running for 7 weeks and sacrificed at 30 weeks of age. Treadmill exercise significantly decreased diabetes-induced blood glucose and serum corticosteroid levels although they did not drop to control levels. In sedentary ZLC rats, GR immunoreactivity was detected in pyramidal cells of the CA1 region as well as in granule cells of the dentate gyrus. In the sedentary ZDF rats, GR immunoreactivity was significantly increased in these regions. However, treadmill exercise significantly decreased GR immunoreactivity in these regions. These results indicate that treadmill exercise in chronic diabetic rats significantly decreased GR immunoreactivity in the hippocampal CA1 region and dentate gyrus, although blood glucose and serum corticosteroid levels did not fully recover to normal state.