N-甲基-D-天冬氨酸(NMDA)及荷包牡丹碱对不同年龄蝙蝠下丘神经元听反应的影响

THE EFFECTS OF NMDA AND BICUCULLINE ON THE AUDITORYRESPONSES OF BAT INFERIOR COLLCULIAR NEURONSDURING POSTNATAL DEVELOPMENT

分别对出生后第２周和第４周的中华鼠耳蝠（Ｍｙｏｔｉｓｃｈｉｎｅｎｓｉｓ）中脑下丘中央核１２１个听神经元进行了考察，同时与成年动物进行比较。结果表明，微电泳ＮＭＤＡ对下丘中央核绝大部分听神经元（２周龄、４周龄和成年动物分别为９６％、９５％和９６％）具有易化性影响，表现为听反应脉冲发放率增加、反应阈值下降、频率调谐曲线增宽。ＮＭＤＡ的易化性效应部分地与动物的周龄相关，表现为对听反应阈值和听反应脉冲发放率的易化效应在出生后２－４周逐渐增强，但４周以后的易化效应趋缓；微电泳ＧＡＢＡＡ受体的特异性拮抗剂Ｂｉｃｕｃｕｌｉｎｅ，对神经元的听反应也呈现易化性影响，表现为听反应脉冲发放率增加，反应阈值降低和频率调谐曲线增宽等。实验结果还提示，ｂｉｃｕｃｕｌｉｎｅ对下丘神经元听反应的易化作用，在出生后早期呈持续增强趋势。ＮＭＤＡ和ｂｉｃｕｃｕｌｉｎｅ的效应与动物周龄之间的关系略有差异，是否提示着下丘中央核ＮＭＤＡ受体和ＧＡＢＡＡ受体在出生后的发育进程有所差别，尚待进一步探讨。

The effects of NMDA and bicuculline on auditory response properties of the inferior collicular neurons were examined in 2 and 4 weeks old and adult bats,Myotis chinensis.Iontophoretic application of NMDA resulted in enhancement of auditory reponses of 96%,95%,96% neurons in the central nucleus of inferior colliculus(ICc) in 3 groups respectively.These excitory effects partly correlated with increasing of age in weeks.The effects of NMDA on reducing response threshold and increasing discharge rate were enhanced within 4 postnatal weeks;Iontophoretic application of bicuculline, an antagonist of GABAA receptor,also resulted in enhancement of auditory response.The facilitatory effect of bicuculline on reducing response threshold,increasing discharge rate and reducing Q10-dB value were keeping enhanced till adult.The different development trends between the effects of NMDA and bicuculline suggest that the postnatal development course of NMDA receptor and GABAA receptor in ICc may be different.