The Expression Of N-methyl-D-aspartate Receptor Subunit2B(NR2B) And Hippyragranin(HGN) In Hippocampus Of Rat Offspring Caused By Propofol Or Ketamine Exposure During Early Gestation Period

Objective To explore the mechanism of learning and memory impairment inrat offspring after propofol or ketamine exposure in early gestation period byobserving the ultrastructural change of hippocampus and expression ofN-methyl-D-aspartate receptor subunit2B(NR2B) and hippyragranin(HGN) inhippocampus.Methods210femal SD rats of clean grade in the5th-7thday of gestation wererandomly divided into7groups (n=30, respectively) according to administratedanesthetics and the anesthesia time, namely, group Ket2(ketamine,2h), groupKet4(ketamine,4h), group Ket8(ketamine,8h), group Prop2(propofol,2h), groupProp4(propofol,4h), group Prop8(propofol,8h) and the control group (physiologicalsaline). Morris water maze experiment was performed to evaluate the learning andmemory ability of their offspring in postpartum30days. Then the hippocampustissues of those offspring were collected to do histopathology and transmissionelectron microscopy. And expression of NR2B and HGN in hippocampus tissue wasdetected by immunohistochemistry.Result (1) Compared with the control group, the escape latency, the targetquadrant traveling time and the platform-crossing frequencies of the offspring rats ingroup Prop2showed no significant difference (P>0.05). However, with the extensionof the anesthesia duration, the escape latency of the offspring in group Prop4andProp8were longer than that in the control group (P<0.05), the target quadranttraveling time and the platform-crossing frequencies of the offsprings in group Prop4and Prop8were obviously less than that in the control group (P<0.05), though nosignificant difference was abserved among the later three groups. Compared with thecontrol group, the escape latency of the offspring rats in group Ket2, Ket4and Ket8were prolonged significantly (P<0.05). The target quadrant traveling time and theplatform-crossing frequencies of the offspring rats in group Ket2, Ket4and Ket8reduced significantly when compared with the control group (P<0.05)，though nosignificant difference could be seen among the later three groups.(2) As showed in transmission electron microscopy (TEM) studies, there was no significant differencebetween group Prop2and the control group. The neuron number decreased and theirregular shape of nerve cell nucleus were observed in group Prop4and Prop8.Moreover, intercellular space dilated and mitochondria dissolved were observed ingroup Prop8. TEM studies showed that, the change of hippocampus tissueultrastructure in the ketamine group was characterized by the decreased neuronnumber. In group Ket2, the irregular shape of nerve cell nucleus, heterochromatinincreased, mitochondria dissolved and swollen, and endoplasmic reticulum dilationcould be observed through electron microscope. With the extension of the anesthesiaduration, in group Ket4, intercellular space dilated, nuclear membrane disrupted,karyopyknosis irregular, the chromatin of nucleus were massed and margined weremore than group Ket2, endoplasmic reticulum and mitochondria became moreswollen, and appeared dissolution and empty bubbles. In group Ket8, more seriousdamages were shown, such as disappearance of nuclear membrane, chromatinscattered in the cytoplasm, and the formation of apoptotic bodies.(3) Expression ofNR2B and HGN protein can be detected in the hippocampus of offspring rats in eachgroup. The expression level of NR2B protein in offspring rats’ hippocampus of groupProp2was showed no significant difference when compared with the control group(P>0.05). The expression level of NR2B protein in offspring rats’ hippocampus ofgroup Prop4(0.085±0.016) and Prop8(0.070±0.015) was significantly lower than thecontrol group (0.092±0.018)(P<0.05). Comparison between the Prop groups foundthat the expression level of NR2B protein in offspring rats’ hippocampus in groupProp8was significantly lower than the group Prop2and Prop4(P<0.05). Theexpression level of NR2B protein in offsprings rats’ hippocampus of group Ket2(0.077±0.014), Ket4(0.073±0.013) and Ket8(0.056±0.014) were obviously lowerthan the control group (0.092±0.018)(P<0.05). Comparison between the Ket groupsfound that the expression level of NR2B protein in offspring rats’ hippocampus ingroup Ket8was significantly lower than the group Ket2and Ket4(P<0.05). Theexpression level of HGN protein in offspring rats’ hippocampus in group Prop2wasshowed no significant difference when compared with the control group (P>0.05).The expression level of HGN protein in offspring rats’ hippocampus of group Prop4 (0.109±0.015) and Prop8(0.120±0.020) were obviously more than the control group(0.093±0.022)(P<0.05). Comparison between the Prop groups found that theexpression level of HGN protein in offspring rats’ hippocampus of group Prop4wasobviously more than the group Prop2, and group Prop8was obviously more than thegroup Prop4(P<0.05). The expression level of HGN protein in offsprings rats’hippocampus of group Ket2(0.110±0.029), Ket4(0.111±0.014) and Ket8(0.135±0.021) were obviously more than that in the control group (0.093±0.022)(P<0.05). Comparison between the Ket groups found that the expression level ofHGN protein in offspring rats’ hippocampus of group Ket8was obviously more thanthe group Ket2and group Ket4(P<0.05). The ratio of NR2B/HGN protein expressionin offspring rats’ hippocampus in group Prop2was showed no significant differencewhen compared with the control group (P>0.05). The ratio of NR2B/HGN proteinexpression in offspring rats’ hippocampus of group Prop4and group Prop8wasobviously more than the control group (P<0.05). Comparison between the Propgroups found that the ratio of NR2B/HGN protein expression in offspring rats’hippocampus of group Prop4was significantly lower than the group Prop2, and groupProp8was significantly lower than the group Prop4(P<0.05). The ratio ofNR2B/HGN protein expression in offspring rats’ hippocampus of group Ket2, Ket4and Ket8were obviously lower than the control group (P<0.05). Comparison betweenthe Ket groups found that the ratio of NR2B/HGN protein expression in offspringsrats’ hippocampus of group Ket8was significantly lower than the group Ket2andgroup Ket4(P<0.05).Conclusion Under this experimental condition, propofol or ketamine exposureof pregnant rats could damage the learning and memory function of rats offspring.The mechanism is that propofol or ketamine damages neurons in hippocampus of ratsoffspring, down-regulates the expression of NR2B protein and up-regulates theexpression of HGN protein, then breaks the balance between learning and memorypositive/negative regulation.