The Involvement Of Neuropeptides In Depression Genesis And Development

Depression is an incapacitating disorder,primarily characterized by a lowering of mood and an inhibition of both mental and physical activities.The incidence of depression has increased year by year and with a younger trend.The illness often results in huge emotional and financial consequences.WHO predicts that by 2020 depression will become one of the 2 major diseases leading to human death and disability.For complex causes and polymorphism symptoms,its pathogenesis has not yet entirely clear.Current major hypothesis considers that stress enhance the HPA axis, cause monoamine neurotransmitter systems decline,finally lead to depression.But present antidepressants designed base on monoamine neurotransmitters doctrine exist many limitations,such as poor specification,drug interactions,side effects,and tolerance.Recent research has focused on a new kind of antidepressant drugs which directly act on the relevant receptors.Neuropeptide is a kind of peptide to deliver message,widely exist in the nervous system and various parts of the body,involved in the regulation of stress response,cardiovascular activities and so on.It significantly impacts neurotransmitter metabolism and function,is considered to monoamine neurotransmitter upstream regulatory factors,and its incidence in the course of depression is being strong concerned.In this study,first we use forced swim,tail suspension,chronic unpredictable miled stress and olfactory bulbectomy to establish depression model of rats,Open-field behavior test was used to detect the locomotion activity,Sugar consumption was measured to observe the degree of happiness and reward.The method of Morris water Maze was used to assay the ability of learning and memory,and HPLC-UV was employed to analyze the level of blood serum corticosterone.The results showed that compared with the control group,the body weight,sugar consumption,locomotion activity,learning and short term memory ability for chronic stress and olfactory bulbectomy models decreased extremely,the level of serum corticosterone increased evidently,and no apparent difference in the long term memory.While,the body weight,sugar consumption,locomotion activity,learning and short term memory ability,level of serum corticosterone for forced swim and tail suspension models were not significantly changed.These results suggested that both chronic stress and olfactory bulbectomy could cause rats depression,were effective model building methods,but forced swim and tail suspension were not.In second part of research work:The chronic unpredictable stress model of rats was adopted.The method of DNA microarray,RT-PCR and fluorescence quantitative PCR were used to test the expression of Neuropeptides and their receptors in hypothalamus, dorsal raphe nucleus and hippocampus.The results showed that the expression of CRF and its receptor1 in hypothalamus,dorsal raphe nucleus and hippocampus increased obviously.The expression of GAL and its receptor1,receptor2 increased except GAL receptor 1 in hypothalamus and hippocampus decreased.The expression of NPY and its receptor NPYR1,NPYR2 and NPYR5 increased.The expression of AVP and its receptor AVPR1a,AVPR1b increased except AVP in hippocampus didn't change.These results suggested that in the course of depression,CRF,GAL and NPY are likely involved in the regulation of neuronal function.Our third part of research work aim to verify the function of CRF,GAL and NPY in depression.1.Chronic intra-cerebral ventricular administration of CRF in normal rats for 21 days were performed and compared with the depression model of chronic unpredictable miled stress(CUMS)in rats.2.Chronic intra-cerebral ventricular adininistration of GAL,GAL2-11(the specific receptor-2 agonist)and NPY respectively in CUMS model were performed and compared with intra-cerebral ventricular administration of aCSF in CUMS model.Open-field behavior test was used to detect the locomotion activity.The method of Morris water Maze was used to assay the ability of learning and memory.The results showed that,1.The rats with chronic administration of CRF consistently decreased the weight gain,locomotion activity and the ability of spatial learning and memory as the CUMS model.2.The CUMS model chronic intra-cerebral ventricular administration of GAL,GAL2-11 (the specific receptor-2 agonist)and NPY respectively increased the locomotion activity obviously.Meanwhile,GAL2-11 significantly improved the ability of learning for CUMS model.These results suggested that sustained elevation of CRF induced by stress may be the chief factor for depression.The higher expression for GAL,GAL receptor 2 and NPY in some brain area may be the protective response for depression.Through the CRF receptor R1,GAL receptor 2 and the NPY system to explore antidepressant drug targets,with broad prospects.The fourth part of our study aim to explore the role of CRF and corticosterone in the hippocampus-related depression mechanism.1.The chronic unpredictable stress and olfactory bulbectomy model of rats were adopted.The results of LTP and LTD in hippocampus CA1 were recorded to observe the synaptic plasticity of hippocampus neurons.HPLC-FLU was employed to analyze the level of 5-HT and NE in hippocampus.2.Optical microscopy and transmission electron microscopy were used to observe the hippocampus cells structure for CUMS model,OB model and CRF icv rats.3.The method of primary hippocampal nerve cell culture was used to observe the effect of CRF and corticosterone.The results showed that,1.The synaptic plasticity of hippocampus neurons for two models decreased significantly,the level of 5-HT in hippocampus decreased evidently and Neurotransmitter disordered.2.The hippocampus cells structure for CUMS model,OB model and CRF icv rats were all seriously damaged,nuclear pyknosis or dissolved,cytoplasm and hollowing out of internal mitochondria,mitochondria swelled and reduced;synaptic reduced, postsynaptic membrane thicken.3.On hippocampal neurons,different concentrations of CRF did no significant impact;Low concentration(10^-8mol / L)of corticosterone had protective effect,when greater than 10^-7mol / L,reflected dose dependent injury. These results indicate that stress firstly infect hippocampus,cause the release of CRF, then Cortisol or corticosterone generate and directly damage the structure of hippocampal neurons,cell necrosis or apoptosis,which eventually led to hippocampus dysfunction and even depression.Conclusions:1.Both chronic stress and olfactory bulbectomy could cause rats depression,in a variety of evaluation have consistency,were effective model building means;2.Sustained elevation of CRF induced by stress may be the chief factor for depression.The higher expression for GAL,GAL receptor 2 and NPY in some brain area may be the protective response.Through the CRF receptor R1,GAL receptor 2 and the NPY system to explore antidepressant drug targets,with broad prospects;3.Stress caused hippocampus substantial damaged,which indicate that stress firstly infect hippocampus,cause the release of CRF,then Cortisol or corticosterone generate and directly damage the structure of hippocampal neurons,cell necrosis or apoptosis,which eventually led to hippocampus dysfunction and even depression.