Department of Biology, Institute for Systems Research, University of Maryland, College Park, Maryland 20742, USA.
J Neurosci. 2009 Dec 9;29(49):15479-88. doi: 10.1523/JNEUROSCI.4471-09.2009.
The functional connectivity of the cerebral cortex is shaped by experience during development, especially during a critical period early in life. In the prenatal and neonatal cortex, transient neuronal circuits are formed by a population of subplate neurons (SPNs). However, SPNs are absent in the adult cortex. While SPNs are crucial for normal development of the cerebral cortex and of thalamocortical synapses, little is known about how they are integrated in the developing thalamocortical circuit. We therefore investigated SPNs in vitro in thalamocortical slices of A1 and medial geniculate nucleus (MGN) in mouse from postnatal day 1 (P1) to P13. We found that SPNs can fire action potentials at P1 and that their intrinsic membrane properties are mature after P5. We find that SPNs receive functional excitatory inputs from the MGN as early as P2. The MGN projections to SPNs strengthen between P2 and P13 and are capable of inducing action potentials in SPNs. Selective activation of SPNs by photostimulation produced EPSCs in layer 4 neurons, demonstrating a functional excitatory connection. Thus, SPNs are tightly integrated into the developing thalamocortical circuit and would be a reliable relay of early spontaneous and sound-evoked activity. The role of SPNs in development likely results from their strong excitatory projection to layer 4, which might function to regulate activity-dependent processes that enable mechanisms required for the functional maturation and plasticity of the developing cortex and thereby contribute to the development of normal cortical organization.
大脑皮层的功能连接是由发育过程中的经验塑造的，尤其是在生命早期的关键时期。在产前和新生儿皮层中，亚板神经元（SPN）形成了短暂的神经元回路。然而，成年皮层中不存在 SPN。虽然 SPN 对于大脑皮层和丘脑皮质突触的正常发育至关重要，但对于它们如何整合到发育中的丘脑皮质回路中知之甚少。因此，我们在从出生后第 1 天（P1）到第 13 天的 A1 和内侧膝状体核（MGN）的体外鼠丘脑皮质切片中研究了 SPN。我们发现 SPN 在 P1 时可以产生动作电位，并且它们的内在膜特性在 P5 后成熟。我们发现 SPN 最早在 P2 时就从 MGN 接收功能性兴奋性输入。MGN 对 SPN 的投射在 P2 和 P13 之间增强，并且能够在 SPN 中诱导动作电位。通过光刺激选择性地激活 SPN 可在第 4 层神经元中产生 EPSC，证明了功能兴奋性连接。因此，SPN 紧密整合到发育中的丘脑皮质回路中，将成为早期自发和声音诱发活动的可靠中继。SPN 在发育中的作用可能源于其对第 4 层的强烈兴奋性投射，这可能有助于调节活动依赖性过程，从而为发育中的皮层的功能成熟和可塑性提供机制，并有助于正常皮层组织的发育。
