Center for Learning and Memory, The University of Texas at Austin, Austin, Texas 78712, USA.
J Neurosci. 2010 Dec 15;30(50):16922-37. doi: 10.1523/JNEUROSCI.3644-10.2010.
Mnemonic persistent activity in the prefrontal cortex (PFC) constitutes the neural basis of working memory. To understand how neuromodulators contribute to the generation of persistent activity, it is necessary to identify the intrinsic properties of the layer V pyramidal neurons that transfer this information to downstream networks. Here we show that the somatic dynamic and integrative properties of layer V pyramidal neurons in the rat medial PFC depend on whether they project subcortically to the pons [corticopontine (CPn)] or to the contralateral cortex [commissural (COM)]. CPn neurons display low temporal summation and accelerate in firing frequency when depolarized, whereas COM neurons have high temporal summation and display spike frequency accommodation. In response to dynamic stimuli, COM neurons act as low-pass filters, whereas CPn neurons act as bandpass filters, resonating in the theta frequency range (3-6 Hz). The disparate subthreshold properties of COM and CPn neurons can be accounted for by differences in the hyperpolarization-activated cyclic nucleotide gated cation h-current. Interestingly, neuromodulators hypothesized to enhance mnemonic persistent activity affect COM and CPn neurons distinctly. Adrenergic modulation shifts the dynamic properties of CPn but not COM neurons and increases the excitability of CPn neurons significantly more than COM neurons. In response to cholinergic modulation, CPn neurons were much more likely to display activity-dependent intrinsic persistent firing than COM neurons. Together, these data suggest that the two categories of projection neurons may subserve separate functions in PFC and may be engaged differently during working memory processes.
前额叶皮层（PFC）中记忆痕迹的持续活动构成了工作记忆的神经基础。为了理解神经调质如何有助于产生持续活动，有必要确定将信息传递到下游网络的 V 层锥体神经元的内在特性。在这里，我们表明，大鼠内侧 PFC 的 V 层锥体神经元的体动态和整合特性取决于它们是否向桥脑（皮质桥核[CPn]）或对侧皮层（连合[COM]）投射。CPn 神经元表现出低时间总和，并在去极化时加速放电频率，而 COM 神经元具有高时间总和并表现出频率适应。对于动态刺激，COM 神经元充当低通滤波器，而 CPn 神经元充当带通滤波器，在 theta 频率范围内（3-6 Hz）共振。COM 和 CPn 神经元的亚阈值特性的差异可以用超极化激活环核苷酸门控阳离子 h 电流的差异来解释。有趣的是，假设增强记忆痕迹持续活动的神经调质对 COM 和 CPn 神经元的影响不同。肾上腺素能调制改变 CPn 但不改变 COM 神经元的动态特性，并使 CPn 神经元的兴奋性显著增加，而对 COM 神经元的兴奋性增加则不明显。对胆碱能调制的反应，CPn 神经元比 COM 神经元更有可能显示与活动相关的内在持续放电。总之，这些数据表明，这两种投射神经元可能在 PFC 中发挥不同的功能，并且在工作记忆过程中可能以不同的方式参与。
