The Efficacy And Mechanism Of Hyperbaric Oxygen On Depression Rat Model Induced By Chronic Stress

ObjectiveDepression has a high incidence, and it has been burdening too much on the society as well as the patients. So far, drugs play a dominant role to cure Depression Major, especially to cure those with endogenous reasons. The drugs include:â‘ tricylic antidepressants (TCAs);â‘¡monoamine oxidase inhibitors (MAOIs);â‘¢selective serotonin reuptake inhibitors (SSRIs). They mainly make influences by increasing the concentration of 5-hydroxytryptamine (5-HT) or norepinephrine (NE) in brain's synaptic clefts, and downward regulating their receptors'sensitivity. A very small number of antidepressants, such as Bupropion, have a pharmacological mechanism related to the monomine dopamine (DA).Whatever drug administrated, a big problem baffles the therapy: it will cost the patient about 2 weeks for the drug to make a difference.Besides, we can see some patients have no reaction to normal anti-depressants. So, many efforts have been done to find new paths to cure depression.Hyperbaric oxygen (HBO) can magnify the solution and diffusion in organisms, improve the microcirculation, and influence the cell's ultramicrostructure, making extensive effects on nervous, endocrine and cardiovascular systems. HBO has successfully cured some diseases, or played a supporting but important role to treat many diseases.HBO has a significant influence to central nervous system, and it can improve the permeability of blood-brain barrier (so, it can magnify the pharmacodynamic action of psychotropic drugs). So, we are considering using HBO to treat depression, whose etiology has much to do with the pathological changes of mesolimbic system. Due to the popularization of HBO chambers in China, HBO will have a bright future to benefit the patients, if it has a curative effect for depression.So, we decided to make a depressed rat model, and then treat it with HBO, and compare the effectivity with which of a classic anti-depressant, and look for the mechanism of the effectivity (if there is any).Methods1. Eighty male SD rats were selected by open-field test, etc., from 120 ones, to be randomized distributed into 5 groups: Control, Model, HBO treatment, Fluoxetine treatment, Combined treatment (both HBO and Fluoxetine). The Control group was normally bred, receiving only tests, not stimuli or therapies. The other 4 groups of rats received chronic unpredicted mild stress (CUMS) with corresponding therapies:HBO was taken by both HBO group and Combined group: Sodium lime was put at the bottom of the small animal HBO chamber to absorb CO2; pure oxygen was consumed to"wash"the chamber, and then was used to lift the inside pressure to 0.2MPa. 60min passed (during the span, pure oxygen was used to ventilate the chamber for 10min), 5min was taken to reduce the pressure to normal. One time a day, 7 days a course. When the rats were treated with HBO, the Model group or Fluoxetine group were put into a similar box, which was put into another chamber of the same making, but the chamber gate was open, and no pure oxygen was supplied.Fluoxetine, a classic anti-depressant, was given to Fluoxetine group and Combined group, with a dosage of 1.8 mg/kg for every morning (the dose was changed every 10d according to the body weight measured), by gavage. The Model group and the HBO group were given a gavage of distilled water of the same volume with the drug. The Control group didn't receive gavage.2. Behavioral tests were administrated every 10 days, to monitor the emergence, changes or fadeaway of depression symptoms. 3. Thirty days later, behavioral changes showed that the animal model had been successfully established. Then, the stress was ceased. 50 days later, all of the animals were executed with mercy, and plasma or brain samples were taken, to detect plasma stress hormone such as cortisol (CORT) and adrenocorticotrophic hormone (ACTH) by radioimmunoassay (RIA), and to detect brain monoamine neurotransmitters such as 5-HT, NE and DA by high performance liquid chromatography (HPLC), and to detect the concentration of tryptophan hydroxylase (TPH) and tyrosine hydroxylase (TH) by enzyme linked immunosorbent assay (ELISA), and to detect the activity of monoamine oxidase (MAO) by spectrophotometer. Last but not least, a Nyssl's staining was conducted to observe the morphological changes of the neurons in hippocampal CA1, CA3 and dentate gyrus area.Results1. Since D30, the bodyweight of Control group was very significantly heavier than those of another 4 groups ( P<0.001); Compared with Control group, Model group had a lower sucrose preference ( P<0.05) and fewer horizontal locomotion ( P<0.05), fewer vertical activities ( P<0.01), fewer grooming acts ( P<0.001) . These changes manifested the depression rat modeling was successful. Then, the stimuli were ceased, only therapies continued.2. Since D40, the 3 groups with therapies had their sucrose preference higher than Model group ( P<0.01) ; HBO group had their grooming acts much more than the other 3 experimental groups ( P<0.01) , and kept this advantage till the end. On D50, the horizontal locomotion of HBO group and Fluoxetine group was significantly frequent than Model group ( P<0.05) ; the vertical activities of HBO group was better than Model group ( P<0.05), while that of Fluoxetine had no this difference.The interaction between HBO and Fluoxetine were a little complicated. On D20, the vertical activities of Combined group were fewer than that of Control group ( P<0.05), while the other 2 experimental groups had no such a difference; On D30, the vertical activities of Combined group were not only fewer than Control group ( P<0.01) , but also than HBO group (P<0.05). As for sucrose preference, Combined group didn't show such a change, on the contrary, it kept this indicator significantly higher than Model group, while the other 2 groups with therapies showed no significant difference with Model group (since Model group also lifted its sucrose sucrose preference after the stimuli ceased). These two opposite changes indicates that Fluoxetine with HBO can improve rats'responsiveness to pleasant sensation or"rewards", but in the meantime, the combination maybe reduce depressed rats'activeness. We have to deal with this conclusion cautiously, because Combined group showed fewer intitial rearings (although the difference was not statistically significant). Another phenomenon also interested us, that the Combined group continuously had a lower grazing rate: on D20, lower than Model group ( P<0.01), HBO group (P<0.01) or Fluoxetine group (P<0.01); On D30, lower than HBO group (P<0.05); On D40, lower than Model group (P<0.01), indicating the combination with HBO perhaps synergized the anorectic effect of Fluoxetine.3. The 5-HT concentration of different brain areas of different groups (P>0.05), but the NE concentration showed some difference: in hypothalamus, HBO group was higher than Model group (P<0.05); in temporal lobe, Model group was lower than Control and Combined (P<0.05); in parietal lobe, Model group was lower than Combined and Fluoxetine (P<0.05). As for the concentration of DA, in hippocampus, HBO group was lower than Control group (P<0.05); in temporal lobe, HBO group was lower than Control group (P<0.05) and Fluoxetine group (P<0.01), Combined group was lower than Control group (P<0.05), Model group (P<0.05) and Fluoxetine group (P<0.01).4. The TH concentration had no significant difference among those groups in any brain areas (P>0.05). The TPH concentration of Control group and which of Model group were lower than HBO group, Fluoxetine group or Combined group (P<0.05). MAO activity was not activated in Control, HBO or Fluoxetine group, while it was highly lifted up in Model and Combined groups (P<0.001). Conclusions1. The CUMS-induced depression rats modeling was successful.2. HBO showed some therapeutic effect for chronic stress depression rats: compared with Fluoxetine, it was better to improve appetite, it had similar effects to cure anhedonia, motivelessness, inactiveness, and it had a faster respondence of depressed rats to improve self-satisfaction and exploratory activities.3. HBO maybe cure those depression symptoms by increasing the concentration of NE, the neurotransmitter, in brain. It suggests that HBO's anti-depressant mechanisms are different from which of Fluoxetine, the prototypical anti-depressant classified as SSRIs. The evidence includes: HBO didn't lifted up ACTH, CORT level in plasm, while Fluoxetine did; HBO increased NE concentration in hypothalamus, temporal lobe and parietal lobe, while Fluoxetine only did that in temporal lobe; HBO reduced DA concentration in hippocampus and temporal, while Fluoxetine increased the concentration in temporal lobe. Besides, HBO showed some protecting effects to the pathologically morphological changes caused by CUMS.4. HBO increased NE concentration in brain, perhaps by inhibiting MAO (which decomposes NE), other than by increasing TH (which synthesize NE).5. As a serendipity, we also confirmed Fluoxetine can increase TPH in rat brain, beside of its SSRI pharmacology.