The Study On Effects And Mechanisms Of Dexmedetomidine On Acute And Long-term Cognitive Function In Neonatal Rats Anaesthetized By Sevoflurane

Background:The effect of anaesthesia on the neonates neurodevelopment is one of the most popular topics in clinical medicine nowadays.Sevoflurane is mainly inhalational anesthetic for infants.Many previous clinical and animal studies have shown that general anesthesia early after born may cause neonatal cognitive dysfunction and neurodevelopmental damage.The early anaesthesia by sevoflurane may lead to an increasement of autism and anxiety in adulthood.Sevoflurane anesthesia in neonates caused neonatal endocrine,cardiovascular and neurological abnormalities by stress,the main mechanism may be the Hypothalamic-pituitary-adrenal axis?HPA?excited and Gamma aminobutyric acid A receptor?GABAAR?enhanced excitability by anesthesia.Dexmedetomidine?DEX?is a new type of alpha 2 adrenergic receptor agonist,has the effect of central anti-sympathetic,inhibiting stress response,stabilizing hemodynamics,reducing the dosage of anesthetics,and the effect similar to natural sleep no respiratory depression.It also has the characteristics of protecting heart,kidney and brain function.Now it is widely used in clinical medicine.The drug exerts sedative and anti-anxiety effects by activating endogenous sleep pathways during anesthesia and inhibiting norepinephrine release by inhibiting ion channels.Purpose:In this study,monitoring EEG,elevated plus maze test,pre-pulse inhibition test and ELISA were used to investigate the effect and the mechanism of dexmedetomidine on sevoflurane anesthesia in neonatal rats with acute and long-term cognitive dysfunction.MethodsPart one:electroencephalogram monitoring1 Experimental groupeThe rats postnatal 4 to 6 days,were divided into 6 groups of males and females respectively,and 8 rats in each group.?1?control group?intraperitoneal injection saline 5?l/g?C group?2?sevoflurane group S group?3?Dexmedetomidine?25?g/kg,intraperitoneal?+Sevoflurane D+S group?4?Dexmedetomidine?25?g/kg,intraperitoneal?+alpha2 receptor antagonist Atipamezole?250?g/kg,intraperitoneal?+sevoflurane D+A+S group?5?Dexmedetomidine?25?g/kg,intraperitoneal?+alpha_2A receptor antagonist BRL44408?1.5 mg/kg,intraperitoneal?+sevoflurane D+B+S group?6?Dexmedetomidine?25?g/kg,intraperitoneal?+alpha_2C receptor antagonist JP1302?3 mg/kg,subcutaneous injection?+sevoflurane D+J+S group2 Electroencephalogram monitoring durin g anesthesiaAfter 2%isoflurane anesthesia,the electroencephalogram amplifier was fixed in cranial sagittal suture and coronal suture to monitor brain electrical activity in frontal lobe of the rats postnatal 4 to 6 days.6%sevoflurane was induced for 3 minutes,and2.1%sevoflurane was anesthetized for 57 mins,total 1 hour.The number and length of epileptic waves in electroencephalogram were recorded.3 Corticosterone testAfter the electroencephalogram?EEG?examination,the blood were getted by broken head immediately to detect blood gas.The concentration of corticosterone in blood was tested by enzyme-linked immunosorbent assa?ELISA?.The second part:behavioral test1 Experimental groups and methodPostnatal 4-6 days rats were divided into 8 groups,each group of 36 newborn male rats.?1?Negative control group C group?2?sevoflurane+saline group?5?l/g,intraperitoneal injection?S group?3?saline?5?l/g,intraperitoneal injection?+maternal separation for 6 hours,without sevoflurane anesthesia M group?4?Sevoflurane+dexmedetomidine?25?g/kg,intraperitoneal injection?D+S group?5?Dexmedetomidine?25?g/kg,intraperitoneal injection?+maternal separation D+M group?6?Atipamezole?250?g/kg,intraperitonealinjection?+sevoflurane+dexmedetomidine?25?g/kg,intraperitoneal injection?D+A+S group?7?Dexmedetomidine+alpha_2AreceptorantagonistBRL44408?1.5mg/kg,intraperitoneal injection?+sevoflurane D+B+S group?8?Dexmedetomidine+alpha_2C receptor antagonist JP1302?3mg/kg,subcutaneous injection?+sevoflurane D+J+S group2 Elevated plus mazePostnatal 4-6 days rats were anesthetized by 2.1%sevoflurane for 6 hours totally?after 6%minutes of sevoflurane induction for 3 minutes?.12 rats were randomly selected for blood gas analysis,and the remaining 24 rats were kept in routine feeding.The elevated cross maze test?elevated plus-maze,EPM?was performed on the 60th day after birth.3 Prepulse inhibition,PPIOn the 70 day after birth,the rats were subjected to prepulse inhibition?PPI?test to detect the effects of sevoflurane anesthesia and experimental drug on sensorimotor gating function in rats,and to evaluate cognitive function.4 Corticosterone test after restriction experimentAfter behavioral testing,the rats were fed until postnatal 80 days.12 rats were randomly selected and bound with restraint bags for 30 minutes,after that the rats tails were cut off for blood collection.Then corticosterone concentration was measured by ELISA.Results1 Results of electroencephalogram monitoringDuring sevoflurane anesthesia,the results of blood gas analysis in neonatal rats were normal,and there was no significant difference among the other groups?P>0.05?.the epileptic wave,the number and duration of epileptic waves increased significantly in neonatal rats in S group?P<0.05?.The corticosterone concentration in S group were significantly higher than control group?P<0.05?.The total duration of epileptic wave in the D+S group was significantly decreased?P<0.05?,and the concentration of corticosterone was significantly lower than that of the S group?P<0.05?.After given dexmedetomidine antagonist Atipamezole and alpha_2A receptor antagonistBRL44408,totaldurationofepilepticwavesincreased significantly?P<0.05?;After given alpha_2C receptor antagonist JP1302,total duration of epileptic waves do not change obviously compared with D+S group?P>0.05?.The corticosterone changing trend is similar with each experimental epileptic waves changing trend.2 Behavioral experimental resultsDuring sevoflurane anesthesia,the results of blood gas analysis in neonatal rats were also normal,and there was no significant difference among the groups?P>0.05?.In the elevated plus maze test,The time of S group and M group rats stay in the open arm was shorter than the C group?P<0.05?,and The time stay in the open arm of D+S group and D+M group increased similarly to control group?P<0.05?.The time stay in the open arm of the D+A+S group and D+B+S group was shortening?P<0.05?,while the time stay in the open arm of D+J+S group does not change obviously?P>0.05?.In the prepulse inhibition test,the PP3 value of the neonatal rats after sevoflurane anesthesia was lower than the C group?P<0.05?.The PP3 value of the neonatal rats in the D+S group increased after given dexmedetomidine?P<0.05?.Atipamezole and BRL44408 significantly reversed the effects of dexmedetomidine on sensorimotor gating system injured by sevoflurane?P<0.05?,JP1302 also reversed the effects of dexmedetomidine on sensorimotor gating system injured by sevoflurane but not significantly?P>0.05?.The corticosterone concentration of the experimental groups changed similarly with PPI.Conclusions1.sevoflurane can shorten the duration of open arms and increase anxiety behavior of adult rats anesthetized in neonates,but the dexmedetomidine may relieve anxiety caused by sevoflurane.2.sevoflurane can make sensorimotor gating system injury in adult rats anesthetized in neonates,and dexmedetomidine may relieve the damage of sensorimotor gating system.3.sevoflurane leads to the increase of corticosterone concentration in neonatal rats and adult rats after stress,and dexmedetomidine may reduce the elevated corticosterone.