Brown C E, Dyck R H
Department of Psychology, Hotchkiss Brain Institute, University of Calgary, 2500 University Drive, NW, Calgary, Alberta, Canada T2N 1N4.
Neuroscience. 2005;134(2):355-9. doi: 10.1016/j.neuroscience.2005.05.011.
The cortical representation of the body surface is not fixed, but rather, is continuously modified by ongoing changes in sensory experience. Although the cellular and molecular mechanisms that subserve these changes are uncertain, increasing evidence suggests that synaptically-released zinc may play a role. Zinc is released from a subset of glutamatergic neurons and can modulate postsynaptic excitability by regulating the activation of glutamate and GABA receptor-gated ion channels. Previously, we have shown that whisker plucking, a manipulation commonly used to induce cortical map plasticity, results in a rapid and robust increase in staining levels for synaptic zinc in deprived regions of the barrel cortex. In the present study, we examined the effect of increased whisker activity, analogous to what may happen during tactile learning or exploratory behavior in a natural setting, on synaptic zinc levels in the adult barrel cortex. Our results indicate that stimulation of whiskers caused a selective decrease in zinc levels within layer 4 of the barrel hollow corresponding to the stimulated whisker. Quantitatively, levels of staining were significantly reduced at 3 h, and showed even greater reductions following 12 and 24 h of stimulation. However, these changes were not long-lasting, as levels of staining in the stimulated barrel returned to control values within 24 h after stimulation had ceased. These data indicate that zincergic circuits are highly sensitive to ongoing changes in sensory experience and may participate in moment-to-moment changes in the functional connectivity of the cerebral cortex.
体表的皮质表征并非固定不变，而是会随着感觉体验的持续变化而不断改变。尽管支持这些变化的细胞和分子机制尚不确定，但越来越多的证据表明，突触释放的锌可能发挥了作用。锌从一部分谷氨酸能神经元中释放出来，并可通过调节谷氨酸和GABA受体门控离子通道的激活来调节突触后兴奋性。此前，我们已经表明，触须拔除是一种常用于诱导皮质图谱可塑性的操作，会导致桶状皮质剥夺区域中突触锌的染色水平迅速且显著升高。在本研究中，我们研究了增加触须活动（类似于在自然环境中的触觉学习或探索行为中可能发生的情况）对成年桶状皮质中突触锌水平的影响。我们的结果表明，刺激触须会导致对应于受刺激触须的桶状凹陷第4层内锌水平选择性降低。从数量上看，染色水平在3小时时显著降低，在刺激12小时和24小时后降低得更明显。然而，这些变化并非持久不变，因为在刺激停止后24小时内，受刺激桶状区域的染色水平恢复到了对照值。这些数据表明，锌能回路对感觉体验的持续变化高度敏感，可能参与了大脑皮质功能连接的即时变化。
