Neuroscience Program, University of Colorado School of Medicine, Aurora, Colorado 80045, USA.
J Neurophysiol. 2012 Oct;108(7):1999-2007. doi: 10.1152/jn.00322.2012. Epub 2012 Jul 18.
Many sensory systems are endowed with mechanisms of neural plasticity that are restricted to a sensitive period in the young developing animal. In this study, we performed experiments in slices of the main olfactory bulb (OB) from rats to examine possible age-dependent cellular mechanisms of plasticity in the olfactory system. We focused on the neurotransmitter norepinephrine (NE), shown to be important in different forms of olfactory learning, examining whether two specific cellular effects of NE previously observed in rats less than P14 extended to older animals. These included an acute reduction in GABAergic synaptic transmission from granule cells (GCs) onto output mitral cells (MCs) and an enhancement in gamma frequency (30-70 Hz) oscillations that persists long after removal of NE. We found that NE failed to reduce GC-to-MC transmission or enhance gamma oscillations in older rats at P18-23. The loss of NE actions on both phenomena appeared to reflect an age-dependent loss of function of α(2)-adrenergic receptors. In addition, we found that NE induced an age-dependent enhancement of transient excitation in MCs, providing a mechanism to link the acute decrease in GC-to-MC inhibition to the long-term increase in gamma oscillations through increases in intracellular calcium. The age-dependent cellular mechanisms that we describe could underlie an olfactory-sensitive period in newborn rodents.
许多感觉系统都具有神经可塑性机制，这些机制仅限于年轻发育中的动物的敏感时期。在这项研究中，我们在大鼠的主要嗅觉球（OB）切片上进行了实验，以检查嗅觉系统中可能存在的依赖年龄的细胞可塑性的机制。我们专注于神经递质去甲肾上腺素（NE），它在不同形式的嗅觉学习中被证明很重要，研究了先前在小于 P14 天的大鼠中观察到的 NE 的两种特定细胞效应是否扩展到了年龄较大的动物。这些包括从颗粒细胞（GC）到输出僧帽细胞（MC）的 GABA 能突触传递的急性减少，以及在去除 NE 后持续很长时间的伽马频率（30-70 Hz）振荡增强。我们发现，在 P18-23 天的年龄较大的大鼠中，NE 未能减少 GC 到 MC 的传递或增强伽马振荡。两种现象中 NE 作用的丧失似乎反映了α（2）-肾上腺素能受体功能的依赖年龄的丧失。此外，我们发现 NE 诱导了 MC 中瞬时兴奋的依赖年龄的增强，通过增加细胞内钙，为将 GC 到 MC 抑制的急性减少与伽马振荡的长期增加联系起来提供了一种机制。我们描述的依赖年龄的细胞机制可能是新生啮齿动物嗅觉敏感时期的基础。
