Department of Neuroanatomy, Institute for Anatomy, University Medical Center, Georg-August-University, D-37075 Göttingen, Germany.
Department of Basic Neurosciences, University of Geneva, CH-1211, Geneva, Switzerland.
Cereb Cortex. 2017 Oct 1;27(10):4851-4866. doi: 10.1093/cercor/bhw281.
Layer IV (LIV) of the rodent somatosensory cortex contains the somatotopic barrel field. Barrels receive much of the sensory input to the cortex through innervation by thalamocortical axons from the ventral posteromedial nucleus. In the reeler mouse, the absence of cortical layers results in the formation of mispositioned barrel-equivalent clusters of LIV fated neurons. Although functional imaging suggests that sensory input activates the cortex, little is known about the cellular and synaptic properties of identified excitatory neurons of the reeler cortex. We examined the properties of thalamic input to spiny stellate (SpS) neurons in the reeler cortex with in vitro electrophysiology, optogenetics, and subcellular channelrhodopsin-2-assisted circuit mapping (sCRACM). Our results indicate that reeler SpS neurons receive direct but weakened input from the thalamus, with a dispersed spatial distribution along the somatodendritic arbor. These results further document subtle alterations in functional connectivity concomitant of absent layering in the reeler mutant. We suggest that intracortical amplification mechanisms compensate for this weakening in order to allow reliable sensory transmission to the mutant neocortex.
鼠类体感皮层的第四层（LIV）包含了躯体感觉皮层柱。皮层柱通过来自腹后内侧核的丘脑皮质轴突的支配接收了大部分的感觉输入。在 Reeler 小鼠中，由于皮层层的缺失导致了错位的桶状神经元簇的形成，这些神经元簇是 LIV 命运决定的神经元。尽管功能成像表明感觉输入激活了皮层，但对于 Reeler 皮层中已鉴定的兴奋性神经元的细胞和突触特性知之甚少。我们使用体外电生理学、光遗传学和亚细胞通道视紫红质-2辅助电路映射（sCRACM）研究了 Reeler 皮层中棘星形（SpS）神经元的丘脑输入特性。我们的结果表明，Reeler SpS 神经元接收来自丘脑的直接但减弱的输入，其在树突体树突上的空间分布是分散的。这些结果进一步证明了在 Reeler 突变体中，功能连接存在微妙的改变，而这种改变与不存在分层有关。我们认为，皮层内的放大机制弥补了这种减弱，从而使感觉信息能够可靠地传递到突变的新皮层。
