Department of Neuroanatomy, Graduate School of Medicine, Yokohama City University, Yokohama.
Eur J Histochem. 2022 Mar 24;66(2):3370. doi: 10.4081/ejh.2022.3370.
The thalamic reticular nucleus (TRN) projects inhibitory signals to the thalamus, thereby controlling thalamocortical connections. Few studies have examined the development of TRN projections to the anterior thalamic nuclei with regard to axon course and the axon terminal distributions. In the present study, we used parvalbumin (PV) immunostaining to investigate inhibitory projections from the TRN to the thalamus in postnatal (P) 2- to 5-week-old rats (P14-35). The distribution of PV-positive (+) nerve fibers and nerve terminals markedly differed among the anterior thalamic nuclei at P14. Small, beaded nerve terminals were more distributed throughout the anterodorsal nucleus (AD) than in the anteroventral nucleus (AV) and anteromedial nucleus (AM). PV+ fibers traveling from the TRN to the AD were observed in the AV and AM. Nodular nerve terminals, spindle or en passant terminals, were identified on the axons passing through the AV and AM. At P21, axon bundles traveling without nodular terminals were observed, and nerve terminals were distributed throughout the AV and AM similar to the AD. At P28 and P35, the nerve terminals were evenly distributed throughout each nucleus. In addition, DiI tracer injections into the retrosplenial cortex revealed retrogradely-labeled projection neurons in the 3 nuclei at P14. At P14, the AD received abundant projections from the TRN and then projected to the retrosplenial cortex. The AV and AM seem to receive projections with distinct nodular nerve terminals from the TRN and project to the retrosplenial cortex. The projections from TRN to the AV and AM with nodular nerve terminals at P14 are probably developmental-period specific. In comparison, the TRN projections to the AD at P14 might be related to the development of spatial navigation as part of the head orientation system.
丘脑网状核（TRN）向丘脑投射抑制性信号，从而控制丘脑皮质连接。很少有研究检查 TRN 投射到前丘脑核的发育情况，包括轴突过程和轴突末端分布。在本研究中，我们使用 parvalbumin（PV）免疫染色来研究出生后（P）2 至 5 周龄大鼠（P14-35）TRN 到丘脑的抑制性投射。在 P14，PV 阳性（+）神经纤维和神经末梢在前丘脑核中的分布明显不同。小而珠状的神经末梢在前背侧核（AD）中的分布比在前腹侧核（AV）和前内侧核（AM）中更广泛。从 TRN 到 AD 的 PV+纤维在 AV 和 AM 中观察到。在穿过 AV 和 AM 的轴突上发现了结节状神经末梢、梭形或沿途末梢。在 P21，观察到没有结节状末梢的轴突束，并且神经末梢在前 AV 和 AM 中分布均匀，类似于 AD。在 P28 和 P35，神经末梢均匀分布在每个核中。此外，将 DiI 示踪剂注入后扣带回皮层，在 P14 时在 3 个核中发现了逆行标记的投射神经元。在 P14，AD 从 TRN 接收丰富的投射，然后投射到后扣带皮层。AV 和 AM 似乎从 TRN 接收具有独特结节状神经末梢的投射，并投射到后扣带皮层。P14 时，具有结节状神经末梢的 TRN 投射到 AV 和 AM 的投射可能是特定于发育时期的。相比之下，P14 时 TRN 对 AD 的投射可能与作为头部定向系统一部分的空间导航发育有关。
