Effects Of Urocortin On Striatal Nerve Electrical Activity And Neural Function In Chronic Hypoxic Rats

ObjectiveThe purpose of this study was to investigate the effects of neuro-active peptide——Urocortin(URO)on motor function,learning and memory in rats with chronic hypoxia,and the effects of URO on the electrical activity of Striatum(STR)neurons,the possible electrophysiological mechanism was discussed.The results will provide experimental basis for the pathogenesis of chronic hypoxic diseases and drug targets for the improvement of neural function after hypoxia.MethodsThe chronic hypoxia model of rats was established by 0.05% Carbon dioxide(CO2)chronic accumulation and retention.The experimental animals were randomly divided into 5 groups,the rats were divided into control group(BC group),chronic hypoxia model group(CHM group),low and high dose URO treatment groups(URO-L,URO-H group),and positive control group--Glutathione + CO2 chronic hypoxia group(GSH-P group).Each group was given different drugs every day for 2 weeks,and then the chronic hypoxia model of CO2 retention was made.The effects of URO on bio-chemical indexes after chronic hypoxia,including oxygenation(Sp O2),lactate dehydrogenase(LDH),hepatic glycogen(HGC)and muscle glycogen(MGC),were measured.The activities of glucose transporter-4(GLUT-4)and glutathione peroxidase(GSH-Px)were measured by enzyme linked immune sorbent assay(ELISA).Moreover,the effects of URO on learning and memory in rats with chronic hypoxia were measured by morris water maze behavior test.And the electrical activity of STR neurons was measured,the electrophysiological method of multi-tube micro-electrophoresis was used,these include the effect of URO on spontaneous firing of STR neurons and the interaction of dopamine(DA)and acetylcholine(ACH)in STR neurons.Corticotropin releasing factor(CRF)and Notch signaling agonist(VAS)and antagonist(TAN)were used to observe the mechanism of URO on the function of STR neurons after chronic hypoxia.At last the histopathological changes of STR neurons after chronic hypoxia were observed.Results1.The effect of URO on the general state of chronic hypoxia was better,body weight and Sp O2 increased in different doses of URO group,and there was difference between URO and CHM group(P <0.05).2.The effects of URO on the indexes of exercise behavior after chronic hypoxia:(1)In the tail suspension test of rats,URO-L group,URO-H and GSH-P positive control group,compared with the CHM hypoxia group,were significantly increased,the experimental results showed that the experimental animals’ struggling time was prolonged,the total struggling times were increased,and the quiet time was shortened,which had statistical significance(P <0.05).(2)URO significantly prolonged the clockwise,counter-clockwise and even accelerating rotation time of the stick,and prolonged the stay time on the stick in the chronic hypoxic rats.The data had statistical significance between URO and CHM group(P <0.05).3.The effects of URO on learning and memory after chronic hypoxia: in morris water maze training for 1-5 days and space exploration experiment for6 th day,the total swimming path of rats in URO-L and URO-H groups was shortened,the swimming-time of rats in the original platform was longer,the escape latency was shortened,and the swimming time in the original platform quadrant as a percentage of the total swimming-time was increased.The data had statistical significance between URO and CHM group(P <0.05).4.The effect of URO on the discharge of STR neurons after chronic hypoxia:(1)The discharge frequency was 5.85±0.72 Hz in the BC group,and increased to 9.85±0.72 Hz in the CHM group,however,the firing frequencies of URO-L(6.45±1.76 Hz)and URO-H(6.10±1.23 Hz)STR neurons were significantly lower than those of the control group(P <0.05).(2)The effect of URO on neurotransmitter in STR neurons of rat showed that the discharge frequency of URO was significantly decreased in neurons which had inhibitory effect on DA,and the inhibition was decreased after URO was administered again.In addition,microelectrophoresis URO and URO could decrease the rise of discharge frequency induced by ACH(P < 0.05).The results suggested that there was interaction between URO and DA and ACH in STR.It could inhibit DA synergistically and decrease ACH excitability.(3)The original inhibition of URO by microelectrophoresis CRF receptor blocker AST-2B disappears,and the administration of URO by microelectrophoresis Notch pathway agonist during VAS has synergistic inhibition of neuronal discharge,but during microelectrophoresis Notch signal pathway blocker TAN,the firing frequency of STR neurons increased,and the original inhibitory effect of URO decreased(P<0.05).5.Effects of URO on blood biochemical indexes and energy metabolism indexes in chronic hypoxic rats:(1)URO could significantly decrease the serum levels of BUN and LDH,and increase the contents of HGC and MGC;(2)URO could increase the activities of GLUT-4 and GSH-Px,which was significantly higher than that of CHM group(P <0.05).6.The effect of URO on the pathological damage of brain tissue in chronic hypoxic rats: the number of URO neurons was normal,and were arranged orderly,which had protective effect on the neurons of chronic hypoxic rats.Conclusions1.URO could decrease the contents of BUN and LDH,increase the levels of MGC and HGC,and increase the activities of GLUT-4 and GSH-Px in chronic hypoxic rats.2.URO could prolong the time of rotating the stick and the time of hanging the rat tail,shorten the total swimming path and escape latency,which proves that URO can improve the motor function and the ability of learning and memory in hypoxic rats.3.URO could decrease the spontaneous firing of STR neurons in chronic hypoxia rats,and converge with DA and ACH neurotransmitters in STR neurons.The possible mechanism is through CRF-Notch signaling pathway.