Higgs Matthew H, Slee Sean J, Spain William J
Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98105, USA.
J Neurosci. 2006 Aug 23;26(34):8787-99. doi: 10.1523/JNEUROSCI.1792-06.2006.
Neuronal firing is known to depend on the variance of synaptic input as well as the mean input current. Several studies suggest that input variance, or "noise," has a divisive effect, reducing the slope or gain of the firing frequency-current (f-I) relationship. We measured the effects of current noise on f-I relationships in pyramidal neurons and fast-spiking (FS) interneurons in slices of rat sensorimotor cortex. In most pyramidal neurons, noise had a multiplicative effect on the steady-state f-I relationship, increasing gain. In contrast, noise reduced gain in FS interneurons. Gain enhancement in pyramidal neurons increased with stimulus duration and was correlated with the amplitude of the slow afterhyperpolarization (sAHP), a major mechanism of spike-frequency adaptation. The 5-HT2 receptor agonist alpha-methyl-5-HT reduced the sAHP and eliminated gain increases, whereas augmenting the sAHP conductance by spike-triggered dynamic-current clamp enhanced the gain increase. These results indicate that the effects of noise differ fundamentally between classes of neocortical neurons, depending on specific biophysical properties including the sAHP conductance. Thus, noise from background synaptic input may enhance network excitability by increasing gain in pyramidal neurons with large sAHPs and reducing gain in inhibitory FS interneurons.
已知神经元放电取决于突触输入的方差以及平均输入电流。多项研究表明，输入方差或“噪声”具有一种分裂效应，会降低放电频率 - 电流（f - I）关系的斜率或增益。我们测量了电流噪声对大鼠感觉运动皮层切片中锥体神经元和快速放电（FS）中间神经元f - I关系的影响。在大多数锥体神经元中，噪声对稳态f - I关系具有乘法效应，增加了增益。相比之下，噪声降低了FS中间神经元的增益。锥体神经元中的增益增强随刺激持续时间增加，并且与慢后超极化（sAHP）的幅度相关，sAHP是放电频率适应的主要机制。5 - HT2受体激动剂α - 甲基 - 5 - HT降低了sAHP并消除了增益增加，而通过锋电位触发的动态电流钳增加sAHP电导则增强了增益增加。这些结果表明，噪声的影响在新皮层神经元类别之间存在根本差异，这取决于包括sAHP电导在内的特定生物物理特性。因此，来自背景突触输入的噪声可能通过增加具有大sAHP的锥体神经元的增益并降低抑制性FS中间神经元的增益来增强网络兴奋性。
