大鼠丘脑前核内海马下托复合体谷氨酸能传入终末与皮质投射神经元的突触联系

THE RELATIONSHIP BETWEEN GLUTAMATE INPUTS FROM THE SUBICULAR COMPLEX AND THALAMOCORTICAL PROJECTION NEURONS IN THE ANTERIOR THALAMIC NUCLEUS OF THE RAT

目的探讨大鼠丘脑前核-海马下托复合体神经元环路的突触结构及谷氨酸分布特征。方法应用HRP束路追踪结合包埋后胶体金免疫电镜技术。结果在丘脑前核内,可见HRP顺行标记的海马下托复合体传入轴突终末,终末多为卵圆形,内含圆形透亮突触小泡和数个线粒体。其做为突触前成分与HRP标记的树突或非HRP标记的树突形成非对称性突触。在谷氨酸胶体金免疫反应切片上,胶体金颗粒标记胞体、树突、轴突终末等。HRP标记的轴突终末和一些非HRP标记的与突触后成分形成非对称性突触的轴突终末(GrayⅠ型)内,胶体金颗粒密度明显大于背景(胞体、树突、GrayⅡ型轴突终末等)的胶体金颗粒密度。其平均胶体金颗粒密度为突触后树突的3倍多,为对称性轴突终末(GrayⅡ型)的6倍多。在两张邻近的连续切片,γ-氨基丁酸(GABA)胶体金免疫反应切片上,GABA胶体金颗粒浓重标记GrayⅡ型轴突终末,背景标记极少;而非对称性轴突终末(GrayⅠ型)胶体金颗粒标记极弱。谷氨酸胶体金免疫反应切片上,GrayⅡ型轴突终末胶体金颗粒标记极弱。GABA阳性轴突终末与HRP标记的树突形成对称性突触,在同一树突上可见GABA能轴突终末形成的对称性突触和其他轴突终末形成的非对称性突触。结论丘脑前核内来自海马下托复合体投射神经元的轴突终末是谷氨酸能的;来自海马下托复合体皮质投射神经元轴突终末,在丘脑前核与投射至海马下托皮质的神经元树突形成非对称性轴-树突触。

Objective To examine the synaptic structure and glutamatergic transmitter of the pathway linking the anterior thalamic nucleus（ATN） and the subicular complex. Methods The HRP tracing and post embedding immunogold technique were used. Results In the anterior thalamic nucleus, anterograde HRP labelled terminals contained clear round synaptic vesicles and several mitochondria, and formed asymmetric synaptic contacts with HRP-labelled or non-HRP labelled dendrites. The highest densities of immunogold particles following glutamate immunostaining were found in HRP-labelled terminals and similar axon terminals devoid of HRP reaction product, They formed asymmetric synaptic contacts（ Gray type Ⅰ ） with dendrites. The average density of those immunogold particles was more than 3 times higher than that of the gold particles in the dendrites of their contacts and over 6 times higher than that of the particles in the terminals that formed symmetric synapses （ Gray type Ⅱ ）. In two serial GABA immunogold reactive sections, Gray tpye Ⅱ terminals were heavily labeled whereas Gray type Ⅰ terminals displayed a very slight labelling. In glutamate immunogold reactive sections, Gray type Ⅱ terminals were slightly labeled. A GABA positive terminal which formed symmetric synapses with HRP-labeled dendrites and the terminal which formed asymmetric synapses converged on the same dendrite. Conclusion The terminals of projection neurons in the pathway linking the anterior thalamic nucleus and the subicular complex are glutamatergic. In anterior thalamic nucleus corticothalamic projection neuron terminals form asymmetric synaptic contacts with HRP-labelled thalamocortical projection neurons by axo-dendritic synapses.