Effects Of Exercise On HPA Axis Secretion, Hippocampus-Associated Proteins And Signal Molecules

Objectives:Exercise enables the adaptation of the body,and stress can be said to be the basis of body adaptation,according to the stress reaction stages,i.e.,the alert stage,the resistance stage and the failure stage.On the other hand,the hippocampus of the central nervous system is a sensitive part of stress;stress may lead to hippocampal damage.The process of stress is characterized by increased adrenal hormones.The hippocampus is rich in glucocorticoid receptors,and plays an important role in the two-way adjustment of excitatory neurons,in apoptosis,in long-term synaptic potentiation,and in learning and memory formation.Stress induces changes in hippocampal glucocorticoid receptors,and affects protein synthesis through hormone response elements and excitatory neurons in the hippocampus.The hippocampus,rich in glutamate neurons,releases excitatory amino acids,and,through NMDA receptors,affects the permeability of cell membranes on ions,calcium ions in particular.Normal NMDA receptors activity and the calcium levels of hippoeampal neurons is the basis of hippoeampal learning and memory;in severe stress injury,the activity of excitatory amino acids or NMDA receptors increases,which causes calcium ion overload in cells and mitochondria,which,in turn,witnesses de-coupling effects of oxidative phosphorylation and generates free radicals,which further leads to oxidative damage of tissues(i.e.,oxidative stress). Calcium ions and reactive oxygen species rapidly initiate the mechanism for neural protection,such as both nuclear factor kappa B and estrogen.Estrogen itself is an antioxidant;at the same time,through non-genomic(fast) and genomic(slow) mechanisms,estrogen plays a role in neural protection and may regulate the HPA axis against body stress.The objective of the present study,which observes the effects of environment and exercise on indicators of hippocampal functions and HPA axis hormones under stress through the swimming exercise model in terms of water environment, investigates the effects of stress on hippocampal functions,and the mechanism for neural protection and HPA axis regulation to provide the basis for exercise-induced central fatigue theory.Methods:To test the above hypothesis,male SD rats were selected,and the effects of acute exercise were observed for the acute exercise and endurance training conditions.The points of observation in the experimental design were 15min exercise, immediately after exhaustive exercise,lhr after exhaustive exercise,and 24hr after exhaustive exercise.The rats in the control group were exposed to the water environment,and the effects observed for the acute water environment and long-term water environment,with four points of observation designated.Two separate pools were used,and while the endurance training rats were swimming,the control group rats were immersed in water(free) to minimize the interference of non-experimental factors like water temperature and the biological rhythm of hormones.However,the water depth of the control group was only the level that reached the lower ear edges of the control rats(about 15-20cm).The intensity on the weight-bearing swimming lactate threshold intensity model was designated as the intensity of endurance training and exhaustive exercise.Increased hemoglobin levels,exhaustive swimming ability and lactate threshold intensity were designated as indicators of a successful model.Radioimmunoassay was used for determination of the levels of some hormones in the rats,including corticotropin-releasing hormone(CRH),corticosterone and estradiol in the hypothalamus,and adrenocorticotropin,corticosterone and testosterone in the serum.The electron microscope ultrastructures of the cells of the hippocampal CAI neurons were observed.Paramagnetic resonance techniques were used for determination of the intensity of hydroxyl radical signals in the hippocampus CA1 area.Western blot was used for determination of hippocampal glucocorticoid receptors(GR),estrogen receptor alpha(ERα),nuclear factor kappa B(NF-κB), N-methyl-D-aspartate receptor subtype 2A(NMDAR2A) and calmodulin kinaseⅡalpha subtypes(CaMKⅡα).To enrich the lactic acid threshold intensity exercise model,high-density lipoprotein cholesterol levels were tested.Results:Animal exercise model.6 weeks after weight-bearing swimming at 90%of the lactate threshold intensity for 30min,6 times a week,the time that the rats reached exhaustion was delayed(trained rats 44.42±32.29min,and untrained rats 21.32±20.12 min,p＜0.05),hemoglobin levels were significantly higher in the trained rats than in the untrained rats(trained 146.08±7.35g / L,and untrained 134.50±8.33g / L,p＜0.05).Form of pyramidal cells of the hippocampal CA1 area.Both the acute and chronic water environment conditions,and the acute and chronic exercise conditions led to changes in the ultrastructures.The extent of change differed;no obvious nuclear condensation,nuclear fragmentation or dissolution of nuclear apoptosis occurred.In the acute water environment condition,the form of pyramidal cells in the hippocampal CA1 area changed,such as unclear outer membranes of cell,and damage to intracellular organdies occurred,such as the disappearance of nuclear membranes and mitochondrial vacuolization.In terms of the effects of time,cell damage was more serious 15min and lhr,but less so immediately and 24hr after the acute environment condition.The results in the chronic water environment were similar.In the acute exercise condition,the form of pyramidal cells of the hippocampal CA1 area changed,such as deformation of the outer membranes of cells and that of nuclear membranes,and swelling of the endoplasmic reticula and mitochondria. Immediately and 1hr after acute exercise,damage to cells was the most serious,and the form of cells returned to normal 24hr after acute exercise.In the chronic exercise condition,the deformation of the structures of pyramidal cells of the hippocampal CA1 area was the most serious 15min and 24hr after exercise,while the damage proved small immediately and lhr after exercise.Hippocampus hydroxyl radicals.No significant differences in the intensity of hippocampus hydroxyl radicals occurred in the long-term water environment re-treated with acute,in the untreated condition re-treated with acute,and in the endurance training condition and the untrained re-treated with acute exhaustive exercise condition.The effects of water environment and exercise were parallel. However,the intensity was significantly higher in the endurance training rats than in the untrained rats immediately after exercise.No difference between the long-term water environment condition and and the untreated condition immediately after the factor.Hormones.No significant difference in hypothalamus CRH occurred under the conditions,but hypothalamus CRH averages were higher in the trained rats than in the untrained rats immediately after exhaustive training(with no significant difference). The overall significance of hypothalamus corticosterone levels was higher in the endurance exercise rats than in the long-term water environment rats;hypothalamus corticosterone levels were significantly higher in the rats immediately after than 15min after exercise;corticosterone in the hypothalamus was significantly lower in the untrained rats lhr after than immediately after exercise,and the levels of corticosterone in the hypothalamus were higher in the endurance training rats.Serum ACTH levels were not significantly different in the conditions.Serum corticosterone levels were significantly lower immediately after than 15min after the water environment or exercise condition,and significantly higher immediately after than lhr after the water or exercise condition.Correlation analysis of hypothalamus corticosterone and serum corticosterone showed that the two displayed a mildly negative correlation,R=-0.228,p＜0.05.Estrogen in the hypothalamus were higher in the endurance training and water environment rats than in the single water environment or single exercise rats,but only the ratio of the long-term water environment to single was significantly different;significantly higher in the single water environment,long-term acute water environment after long-term water environment,single exercise and endurance training immediately,lhr and 24hr after acute exercise than 15min,and up to 24hr after exercise,serum testosterone was significantly higher in a single water environment significantly higher than that in the long-term,acute exercise and endurance training acute exercise rats.serum testosterone reached its maximum levels 24hr after exercise in the various groups with significant difference.Hippocampal signal protein content.Hippocampal estrogen receptor levels in the single water environment,long-term water environment and single exercise conditions were significantly higher immediately after the factors than 15min,1hr and 24hr after the factors,whereas a decreasing trend emerged immediately after exercise and an increase occurred 24hr after exercise.Hippocampal glucocorticoid receptors saw the same trend in the endurance training rats as the other rats,at the same points of sampling but with insignificant difference.As a whole,Hippocampus NF-κB was not significantly different when the factors and points of sampling were considered, but was significantly lower immediately after than lhr and 24hr after the single water environment,and significantly lower than in the long-term water environment,single exercise and endurance training conditions immediately after exercise.24hr after exercise,hippocampal NF-κB was significantly higher in the endurance training rats than in the untrained rats.In addition,NF-κB was the highest in the untrained rats immediately after exercise,and in the endurance training rats 24hr after exercise.In terms of hippocampus NMDAR2A,the overall significance was higher in the endurance training rats than in the single exercise rats,in the endurance training rats than in the long-term water environment rats immediately after exhaustive exercise, and in the endurance training and untrained rats immediately after than 1hr and 24hr after exercise.A significant difference in CaMKⅡαlevels occurred between the single acute exercise rats and the single water environment rats,between the long-term water environment rats and the single water environment rats,between 24hr after the factors and immediately and 1hr after the factors;the levels were significantly higher in the endurance training rats than in the long-term water environment rats and the untrained rats 24hr after exercise.Correlation analysis.The time for exhaustive swimming in the rats correlated with hypothalamus CRH and hippoeampus ERα,the partial correlation coefficient being 0.573,p＜0.001 and-0.584,p＜0.001,respectively.Other significant bivariate Pearson correlations were:NF-κB and CaMKⅡα(r= 0.253,p＜0.05),ERα,and GR, estrogen in the hypothalamus,and hypothalamus corticosterone(r= 0.428,p＜0.001; r=-0.250,p＜0.05;r=-0.219,p＜0.05),hydroxyl radical hippocampal signal intensity and serum testosterone and corticosterone(r= 0.232,p＜0.05;r=0.443,p＜0.001), serum eorticosterone and eorticosterone in the hypothalamus(r=-0.220,p＜0.05), corticosterone in the hypothalamus and CRH(r=0.214,p＜0.05).Conclusion:CRH and hypothalamus corticosterone,rather than serum corticosterone,play an important role in the regulation of HPA axis hormones;increased hypothalamic stress (increased corticosterone) levels accompanied with increased estradiol levels.The ultrastructures of the hippocampus may change due to environment and swimming excitation,which may return to normal within a short period of time.It may not be damage change,but more likely to be stage adaptation in the process of learning and memory.The negative feedback regulation of the hippocampus on the HPA axis is related to the overall hippocampal functions,and hippocampus ERαand hydroxyl free radicals are related to the negative feedback regulation of HPA.NF-κB may more important in delayed repair that may affect adaption progress.ERαin hippocampal is closely related to exercise ability(probably the first piece of empirical evidence).The above conclusion is generalizable to male SD rats.