γ-氨基丁酸对家鸽(Columba livia)顶盖脑片Ⅲ层神经元电活动的影响

THE EFFECTS OF GABA UPON LAYER Ⅲ NEURONS IN PIGEON (Cilumba livia) OPTIC TECTUM SLICES

在２５只家鸽的离体顶盖脑片上，用玻璃微电极胞外记录到顶盖Ⅲ层神经元自发放电单位５５个，观察了γ氨基丁酸（ｇａｍｍａａｍｉｎｏｂｕｔｙｒｉｃ，ＧＡＢＡ）及其拮抗剂以及电刺激Ⅱａ～ｆ亚层对Ⅲ层神经元电活动的作用．作用显示：脑片灌流ＧＡＢＡ（１０－６ｍｏｌ／Ｌ，３ｍｉｎ）后，１６／２１个单位（占７６．２％）放电频率减少，１／２１个单位（占４．８％）放电频率增加，４／２１个单位（占１９．６％）放电频率无变化．ＧＡＢＡ的这种减频作用可被１０－６ｍｏｌ／Ｌ荷包牡丹碱（ｂｉｃｕｃｕｌｉｎｅ，ＢＩＣ）逆转．１４个被Ⅱａ～ｆ亚层刺激传入减频的Ⅲ层神经元，其中１１个单位（占７８．６％）的减频作用可被ＢＩＣ阻断，另３个单位则不产生阻遏作用．上述药物的作用具有可逆性和重复性．结果表明：家鸽顶盖Ⅲ层中可能有ＧＡＢＡ能纤维的到达，Ⅲ层内存在ＧＡＢＡ敏感神经元．

spontaneous discharging units are recorded extracellularly in the layer Ⅲ of 25 pigeons optic tectum slices with glass micropitettes. The effects of putative transmitter, gamma aminobutyric acid (GABA), its antagonist perfused, and electric stimulating sublayer Ⅱ a f  on the layer Ⅲ neurons are investigated. The results are as follows: Most of layer Ⅲ neurons (16/21,76.2%) are inhibited by GABA (10 -6 mol/L, 3 min), 1/21 unit (4.8%) is excited, and the other four cells are unaffected. The effects of GABA can be blocked by bicuculline (BIC, 10 -6 mol/L). The inhibiting effects of 11 out of 14 layer Ⅲ units (78.6%) stimulating sublayer Ⅱ a f  can be blocked by BIC, but not as of the other 3 units are not blocked. These results show posibility of the GABA ergic fibres afferenting to pigeon optic tectum layer Ⅲ. GABA may act as an excitatory transmitter through GABA A receptor between sublayer Ⅱ a f  and layer Ⅲ neurons.