The Effects Of Subarachnoid Block On Excitatory Amino Acids And Inhibitory Amino Acids In Spinal Cord

The neuraxial blockade combined general anesthesia has been widely used in anesthesiapractice due to its good properties. It was found that the spinal anesthesia had sedate effect,but its mechanismis still not clear. The theory basis of sedative drugs such as propofolcould reinforce the inhibitory synaptic transmission and inhibit the excitatory synaptictransmission which exist in spinal dorsal horn of mammals.New research shows that localanesthetics not only act on ion channels, but also acts on central nervous systemneurotransmitter/receptor system such as γ-aminobutyric acid (GABA) andN-methyl-D-aspartate (NMDA)of the spinal cord and so on. Therefore, we assume that theimpact of local anesthetic through the spinal excitatory and inhibitory amino acidneurotransmitter/receptor system to produce sedation.The study is divided into twoparts,firstly,molecular biology techniques is used to study the effect of bupivacaine on therelease of excitatory and inhibitory amino acid in the spinal cord;secondly,behavioralexperiments is used to study the effect of bupivacaine on GABAA receptor and NMDAreceptors using the intrathecal injection of bicuculline andNMDA(N-Methyl-D-Aspartate,NMDA);,thus, revealing the mechanism of sedation ofsubarachnoid block initially. Part1: Intrathecal Injection of Bupivacaine on the content of excitatory and inhibitoryamino acids of spinal cord in ratsObjective: To investigate the effects of subarachnoid injection of0.5%bupivacaine onthe content of excitatory amino acid aspartate (Asp) and glutamate (Glu) and inhibitoryamino acid γ-aminobutyric acid (GABA) and glycine (Gly) in the rat spinal cord.Method:24male Sprague-Dawley(SD) rats were randomly divided into3groups: control group(Cgroup, n=8), Saline group(NS group, n=8),0.5%bupivacaine group(B group, n=8).the ratswere intrathecally administrated25μL of saline and25μL of0.5%Bupivacaine in thegroup NS and group B,respectively.10minutes after injection,the rats were decapitated,andremoved lamina and took out the Spinal cord, then placed the spinal cord below T10in thevials of1.8ml.Numbered the samples and preserved them in the-80degrees freezer.Use theAutomatic amino acid analyzer to detect the the content of excitatory amino acid aspartate(Asp) and glutamate (Glu) and inhibitory amino acid γ-aminobutyric acid (GABA) andglycine (Gly) in the rat spinal cord.Results: The content of γ-aminobutyric acid(GABA)in the rats spinal cord in group B （0.65±0.10）μg/mg were significantly increasedcomparing with group C （0.48±0.12）μg/mg and group NS（0.49±0.12）μg/mg，(P＜0.01,P＜0.05);The content of glycine (Gly) in the rats spinal cord in group B （1.13±0.20）μg/mg were significantly increased comparing with group C （0.91±0.16）μg/mgand group NS（0.76±0.13）μg/mg，(P＜0.05,P＜0.01);however,the content of glutamate(Glu) in the rats spinal cord in group B （0.91±0.16）μg/mg were significantly decreasedcomparing with group C （1.07±0.12）μg/mg and group NS（1.14±0.67）μg/mg，(P＜0.05,P＜0.01);comparing the content of Aspartate(Asp) in the rats spinal cord in group B（1.21±0.15）μg/mg with group C （1.20±0.16）μg/mg and group NS（1.20±0.18）μg/mg，there were no significant differences.(P＞0.05,P＞0.05).Conclusion: Bupivacaine spinal anesthesia can affect the release of amino acids in spinal,and increase the content ofinhibitory amino acid(γ-aminobutyric acid ane glycine)and decrease the content ofexcitatory amino acid(glutamate). Part2: Intrathecal Injection of Bicuculline and NMDA on Sedation of Propofol inRatsObjective: To investigate the effects of intrathecal injection of Bicuculline and NMDAon sedation of propofol in rats.Methods:40male Sprague-Dawley(SD) rats were randomlydivided into5groups: control group(C group, n=8), Saline group(NS group, n=8),0.5%bupivacaine group(B group, n=8), Bicuculline+0.5%bupivacaine group (Bic group,n=8),NMDA+0.5%bupivacaine group(NMDA group, n=8). To establish the rats model ofsubarachnoid block, the rats were intrathecally administrated20μL of saline or20μL of0.5%Bupivacaine in the group NS and group B,respectively; and the rats were intrathecallyinjected with an effective dose of bicuculline10μL and NMDA10μL in the group Bicand group NMDA, respectively;which were before15minutes of the injecting of0.5%bupivacaine20μL intrathecally; the five groups of rats were all received intravenousinjection of propofol after10minutes, the dosage of propofol and the time required to ablatethe eyelid reflex and compard among the five groups.Results: The dosage of propofolrequired to ablate the eyelid reflex in group B (6.72±0.77)mg·kg-1were significantlydecreased comparing with group C (10.94±0.9) mg·kg-1and group NS(10.51±1.01)(P＜0.01)The dosage of propofol required to ablate the eyelid reflex in group Bic (9.25±1.03)mg·kg-1were significantly decreased comparing with group C (10.94±0.91) mg·kg-1and group NS (10.51±1.01)(P＜0.01); still were significantly increased comparing with groupB (6.72±0.77) mg·kg-1(P＜0.01); The dosage of propofol required to ablate the eyelidreflex in group NMDA (17.02±1.25) mg·kg-1were significantly increased comparing withgroup C (10.94±0.91) mg·kg-1and group NS (10.51±1.01) and group B (6.72±0.77)mg·kg-1(P＜0.01); however, there were no significant difference between group C andgroup NS (P＞0.05) Conclusions Intrathecal Injection of bupivacaine can reduce the dosageof Propofol on Sedation; the sedation produced by the Subarachnoid block of rats may beassociated with GABAAreceptor of the spinal cord, while regardless of the NMDA receptor.