Effects And Possible Mechanisms Of Habenula On The Depressed Rats

With the fast rhythm of modern society, the onset of depression is relevant to the chronic stress, the activity of HPA axis and the change of transmitter of amino acids. Some nucleus relating to the stress in the CNS may participate in the morbidity of depression. Limbic system is the center of emotional response, and the habenula, which is relevant to the stress reaction, is an important hinge between limbic forebrain and brain stem. The habenula have the connection of neuron fiber and function with hippocampus and raphe nuclei. Therefore, we investigated the effect of habenula on the depression and possible related transmitter. The research went as follow: ⅠThe choice and establishment of animal model of depression The choice of animal model is the base of study. A good animal model can simulate the clinical symptom effectively. Associated application of different models could make results more accurate. Therefore we used two depressed models-CIM depressed model and chronic stress depressed model, to investigate the effect of habenula on the mechanisms of depression. Stressful life events are the main cause of depression, on which chronic stress depressed model was based. Chronic unpredictable stress was applied on animals that would be in a state of anxiety, horror and helplessness. Finally, depression occurred. We improved the method of document according to the response of rats to chronic stress. We changed time of the food deprivation from 48 hours to 40 hours and the switch time from 15 minutes to 30 minutes. And these got better model effects. The results showed that the crossing times of improved methods was 14.38±11.22 times/3 minutes,less than 21.89±9.25 times/3 minutes of the model of document; the rearing time was 6.63±5.29 times/3 minutes, less than 7.00±3.57 times/3 minutes of the model of document. These proved that the depressed effects of model induced by our improved method were better than the method of document. The model was established successfully through results. 1 Influence of chronic variable stress on rat's weight: weight of rats in model group(204.17±9.75g)was lighter than that in control group(263.33±16.43g)and there was a notable significance between them(p<0.001). 2 Influence of chronic variable stress on rat's intake of sucrose: On the 22nd day of stress, rat's intake amount of sucrose in model group(10.25±3.99 ml)was fewer than that in control group(19±3.70ml)and there was a notable significance between them (p<0.001). 3 Influence of chronic variable stress on open field of rats: On the 22nd day of chronic stress, crossing times of model group(14.38±11.22) reduced compared with control group(50.13±23.65),(p<0.01). Rearing times of model group(6.63±5.29)decreased significantly in comparison with control group(16.29±7.02),(p<0.01). Grooming time of model group(0.63±1.19)was shorter than thatof control group(8.88±7.99),(p<0.05).Defecation times of model group(4.13±2.42)increased compared with that(2.13±0.83)of control group(p<0.05). 4 Influence of chronic variable stress on swimming of rats: After chronic variable stress on rats for 21 days, the immobility time of model group(165±42s)was longer than that(88.9±48.27s)of control group(p<0.01). The climbing time of model group(40.22±23.14s)was longer than that(93.7±69.12s)of control group while there had no difference of swimming time between two groups. The prolonged time of immobility indicated that rats were in a state of despair, which proved that rats had symptoms of depression. 5 Influence of chronic variable stress on weight of adrenal gland and concentration of cortisol in serum: On the 22nd day of chronic stress, weights of adrenal gland of model group were heavier than that of control group(p<0.001)and the concentration of cortisol in serum was about two times than that of control group(p<0.01). Above results showed that improved chronic stress model used in our experiments was a more effective and incredible model. CIM depressed model was established by giving neonate rats tricyclic antidepressants, which caused symptoms similar to endogenous depression after adults. This model has more selective and incredible characters and is widely used throughout the world. ⅡEffect of habenula in depression and its possible mechanisms( Ⅰ) Relationship between functional state of habenula and depression in rats 1 Effect of habenular lesion on depressed behavior of rats We applied two models: CIM depressed rats and chronic stress depressed rats to investigate the influence of lateral habenula damaged by electricity on depressed behavior of rats. We investigated rats'behavior after lateral habenula was damaged by electricity and swimming time, immobility and climbing time was observed in forced swimming test. Results showed that immobility times of rats decreased significantly from 180.75±51.99s to 95.63±61.50s after lateral habenula was damaged by electricity(p<0.05). Swimming time obviously prolonged after lateral habenula was damaged by electricity. It increased from 112.88±50.92s to 168.38±44.23s(p<0.05). The results of forced swimming test of rats induced by chronic stress depression also showed that immobility time distinctly decreased from 167.5±6.46s to 131±21.94 after lateral habenula lesion. Swimming time and climbing time had prolonged trends after lateral habenula lesion. Moreover, the rearing and crossing times of stress depressed rats had increased trends after lateral habenula lesion. Two types of model both indicated that damaged lateral habenula could ameliorate depressed behavior of rats. As the decrease of 5-HT in raphe nuclei is the main reason of depression and raphe nuclei is controlled by habenula, depressionon raphe nuclei is relieved after habenula lesion, which will increase the synthesis and release of 5-HT in raphe nuclei. This may be one of the reasons that why habenula lesion can ameliorate depressed behavior of rats. 2 Change of amino acid transmitters and c-fos expression in habenula of depressed rats There are relationships of function and structure between habenula and raphe nuclei and habenula could project excitable amino acid transmitters to raphe nuclei. Research showed that activity of habenula increased in depression. So we analyzed contents of amino acid transmitters in habenula of depressed rats induced by chronic stress depression in a state of anesthesia in vivo. Results of microanalysis showed that peak area of glutamate in habenula of rats in model group obviously increased (0.43±0.18v.s). It was two times of that in control group(0.22±0.07v.s) and there was a notable significance between them. Peak area of glutamine in habenula of model group distinctly increased (10.41±4.57v.s). It was more than two times of that in control group (4.22±0.23v.s) and there was a notable significance between them (p<0.05). Thus it was known that the increase of habenular excitability participated in the onset of depression, which also proved that why habenula lesion could ameliorate depressed behavior of rats. The possible reason is that the increase of habenular excitability inhibits activity of monaminergic neuron in raphe nuclei. After habenula lesion, inhibition on raphe nuclei was eliminated anddepressed behavior was ameliorated. It indicated that content of glutamate in habenula of rats induced by chronic stress depression increased, nevertheless c-fos expression is seen as a symbol of activation of glutamate receptor. So we analyzed change of c-fos expressive content in habenula of depressed rats induced by chronic stress at different times by immunohistochemistry after the last stress. Our results showed that c-fos expression in habenula obviously increased in comparison with control at 0.5h, 1h, 2h and 3h after the last stress and there was a notable significance between them (p<0.01). At the same time the content of glutamate was also found higher than control group. It indicated that their contents were increased simultaneously. So we speculated that activity of habenula was strengthened after every stimulus in chronic stress and excessive released glutamate facilitated c-fos expression. It could lead to the decrease of monoamine transmitter release in monaminergic neuron of raphe nuclei dominated by habenula and resulted in depression. ( Ⅱ) Change of amino acid neurotransmitter in hippocampus of depressed rats induced by habenula lesion 1. Effect of habenula lesion on content of glutamate in hippocampus Compared with control, the peak area of glutamate in CA3 of rats in model group obviously increased from 0.17±0.07v.s to 0.59±0.33 v.s. It was more than three times of that in control group and had...