Schwarz C, Schmitz Y
Sektion für Visuelle Sensomotorik, Neurologische Universitätsklinik Tübingen, Germany.
J Comp Neurol. 1997 May 12;381(3):320-34. doi: 10.1002/(sici)1096-9861(19970512)381:3<320::aid-cne5>3.0.co;2-4.
The pontine nuclei (PN) and the nucleus reticularis tegmenti pontis (NRTP) are sources of an excitatory projection to the cerebellar cortex via mossy fibers and a direct excitatory projection to the cerebellar nuclei. These precerebellar nuclei, in turn, receive a feedback projection from the cerebellar nuclei, which mostly originate in the lateral nucleus (LN). It has been suggested that the feedback projection from the LN partially uses gamma-aminobutyric acid (GABA) as a transmitter. We tested this hypothesis by using a combination of anterograde tracing (biotinylated dextran amine injection into the LN) and postembedding GABA and glutamate immunogold histochemistry. The pattern of labeling in the PN and the NRTP was compared with that of cerebellonuclear terminals in two other target structures, the parvocellular part of the nucleus ruber (RNp) and the ventromedial and ventrolateral thalamus (VM/VL). The projection to the inferior olive (IO), which is known to be predominantly GABAergic, served as a control. A quantitative analysis of the synaptic terminals labeled by the tracer within the PN, the NRTP, and the VL/VM revealed no GABA immunoreactivity. Only one clearly labeled terminal was found in the RNp. In contrast, 72% of the terminals in the IO were clearly GABA immunoreactive, confirming the reliability of our staining protocol. Correspondingly, glutamate immunohistochemistry labeled the majority of the cerebellonuclear terminals in the PN (88%), the NRTP (90%), the RNp (93%), and the VM/VL (63%) but labeled only 5% in the IO. These data do not support a role for GABAergic inhibition either in the feedback systems from the LN to the PN and the NRTP or within the projections to the RNp and the VM/VL.
脑桥核（PN）和脑桥被盖网状核（NRTP）是通过苔藓纤维向小脑皮质发出兴奋性投射以及直接向小脑核发出兴奋性投射的来源。这些小脑前核又接受来自小脑核的反馈投射，其中大部分起源于外侧核（LN）。有人提出，来自LN的反馈投射部分使用γ-氨基丁酸（GABA）作为递质。我们通过结合顺行示踪（将生物素化葡聚糖胺注入LN）和包埋后GABA和谷氨酸免疫金组织化学来验证这一假设。将PN和NRTP中的标记模式与另外两个靶结构——红核小细胞部（RNp）以及丘脑腹内侧核和腹外侧核（VM/VL）中的小脑核终末的标记模式进行比较。已知主要为GABA能的向下橄榄核（IO）的投射作为对照。对PN、NRTP和VL/VM内被示踪剂标记的突触终末进行定量分析，未发现GABA免疫反应性。在RNp中仅发现一个标记清晰的终末。相比之下，IO中72%的终末GABA免疫反应性清晰，证实了我们染色方案的可靠性。相应地，谷氨酸免疫组织化学标记了PN（88%）、NRTP（90%）、RNp（93%）和VM/VL（63%）中大多数小脑核终末，但在IO中仅标记了5%。这些数据不支持GABA能抑制在从LN到PN和NRTP的反馈系统中或在向RNp和VM/VL的投射中起作用。
