Halasy K, Somogyi P
Medical Research Council, Anatomical Neuropharmacology Unit, Oxford University, U.K.
J Hirnforsch. 1993;34(3):299-308.
The dentate gyrus has been shown to receive a laminated and target selective GABAergic input (Han et al., 1993; Halasy and Somogyi, 1993), but the numerical parameters of this innervation are not known. In order to establish the relative weight of GABAergic inputs to the dendritic versus somatic regions of granule cells the numerical density and proportion of GABA-immunopositive and immunonegative synaptic boutons and their postsynaptic targets were determined in the molecular and granule cell layers of the dentate gyrus using the postembedding immunogold method. The granule cell layer contained 9% of all synapses with the remaining 91% being in the molecular layer. Altogether 17% of all synaptic boutons were GABA-immunoreactive, and they formed either type 1 or type 2 synaptic junctions. About 88% of synaptic boutons in the granule cell layer and 7-8% in the molecular layer were GABA-positive. However, the numerical density (number of synapses per unit volume) of GABA-immunoreactive type 2 synapses was calculated to be only slightly less in the molecular layer than in the granule cell layer (100 x 10(6)/mm3 tissue in the granule cell layer and about 86 x 10(6)/mm3 in the molecular layer). In addition, GABA-positive type 1 synapses were found in lower number at the border region of the two layers. The mean volume of the molecular layer of the dentate gyrus in the Wistar rat was calculated to be nearly 4 times larger than the volume of the granule cell layer (West and Andersen, 1980). This means that 25-26% of all GABAergic type 2 synapses are located in the granule cell layer, and 74-75% in the molecular layer. The mean postsynaptic targets of the GABA-immunoreactive boutons in the granule cell layer were granule cell somata (46-60%), followed by dendritic shafts (26-29%), spines (up to 14%), and axon initial segments (7-9%). In the molecular layer the dominant postsynaptic targets of GABAergic synapses were dendritic shafts (63-72%), followed by dendritic spines (26-37%). About 2-3% of the targets of all GABA-immunoreactive synapses were GABA-immunoreactive dendritic shafts or somata. Up to 98% of all GABA-immunonegative synaptic boutons were found in the molecular layer, most of them terminating on dendritic spines. These results show that the dendritic region of the granule cells provides sites for GABAergic inhibition which in quantitative terms highly outnumber the somatic region in the dentate gyrus.
齿状回已被证明接受分层且具有靶标选择性的GABA能输入（Han等人，1993年；Halasy和Somogyi，1993年），但这种神经支配的数量参数尚不清楚。为了确定GABA能输入到颗粒细胞树突区域与胞体区域的相对权重，使用包埋后免疫金法在齿状回的分子层和颗粒细胞层中测定了GABA免疫阳性和免疫阴性突触小体及其突触后靶标的数量密度和比例。颗粒细胞层包含所有突触的9%，其余91%位于分子层。所有突触小体中总计17%是GABA免疫反应性的，它们形成1型或2型突触连接。颗粒细胞层中约88%的突触小体和分子层中7 - 8%的突触小体是GABA阳性的。然而，GABA免疫反应性2型突触的数量密度（每单位体积的突触数量）经计算在分子层仅略低于颗粒细胞层（颗粒细胞层中为100×10⁶/mm³组织，分子层中约为86×10⁶/mm³）。此外，在两层的边界区域发现GABA阳性1型突触数量较少。经计算，Wistar大鼠齿状回分子层的平均体积几乎是颗粒细胞层体积的4倍（West和Andersen，1980年）。这意味着所有GABA能2型突触中25 - 26%位于颗粒细胞层，74 - 75%位于分子层。颗粒细胞层中GABA免疫反应性突触小体的主要突触后靶标是颗粒细胞胞体（46 - 60%），其次是树突干（26 - 29%）、棘（高达14%）和轴突起始段（7 - 9%）。在分子层中，GABA能突触的主要突触后靶标是树突干（63 - 72%），其次是树突棘（26 - 37%）。所有GABA免疫反应性突触的靶标中约2 - 3%是GABA免疫反应性树突干或胞体。所有GABA免疫阴性突触小体中高达98%位于分子层，它们大多终止于树突棘上。这些结果表明，颗粒细胞的树突区域为GABA能抑制提供了位点，在数量上大大超过了齿状回中的胞体区域。
