Behavioral Neuroscience, Department of Psychology, Memorial University of Newfoundland, St. John's, USA.
Hippocampus. 2011 Nov;21(11):1250-62. doi: 10.1002/hipo.20816. Epub 2010 Jun 1.
Theta and gamma oscillations are thought to provide signal sets that promote neural coding of cognitive processes. Over 40 yrs ago, Jeffrey Gray reported event-related changes in a narrow band of hippocampal theta (7.5-8.5 Hz) which appeared to involve norepinephrine (NE) release from, the noradrenergic nucleus, the locus coeruleus (LC). These event-related alterations in EEG were elicited by novelty, attentional changes, the use of preparatory signals, and signal-mismatch events. Gray et al. have since provided indirect evidence that supports the role of NE in the modulation of 7.5- to 8.5-Hz oscillations in the hippocampus, but studies investigating the effects of direct LC activation in awake rats have been lacking. In the present study, dentate gyrus EEG was examined during glutamatergic activation of the LC in awake male rats in relation to plasticity effects on simultaneously recorded perforant path-evoked field potentials. Glutamate-injected animals were divided into three groups based on histological and plasticity outcomes; perforant path stimulated controls were also included. The three injected groups were: (1) rats with positive LC placements, demonstrating NE-LTP of the dentate gyrus evoked potential, (2) rats with positive LC placements, without NE-LTP, and (3) Non-LC injected controls. Activation of the LC in awake rats demonstrating NE-LTP increased the relative power of 7- to 9-Hz theta, a result masked in broader 4- to 12-Hz analysis. Comparatively, urethane-anesthetized rats showed an increase in 5-7 Hz, but not 7- to 9-Hz theta with LC activation. Discriminative analysis in the approximate theta band predicted by Gray (7.4-8.5 Hz) revealed that awake rats demonstrating NE-LTP had increased relative power in this narrow frequency compared to rats receiving perforant path only (noninjected) and Non-LC injected rats. Transiently reduced gamma (20-40 Hz) relative power was most commonly observed in rats with verified LC placements failing to express NE-LTP. Given current theories of LC function, these results suggest oscillatory tuning within the theta and gamma range may facilitate shifts in cognitive set.
θ 波和γ 波振荡被认为提供了促进认知过程神经编码的信号集。40 多年前，杰弗里·格雷（Jeffrey Gray）报告了海马体θ （7.5-8.5Hz）窄带中的与事件相关的变化，这些变化似乎涉及去甲肾上腺素（NE）从蓝斑核（LC）释放。这些与事件相关的脑电图改变是由新奇性、注意力变化、预备信号的使用以及信号不匹配事件引起的。此后，Gray 等人提供了间接证据，支持 NE 在调制海马体 7.5 至 8.5Hz 振荡中的作用，但缺乏研究直接激活 LC 在清醒大鼠中的作用。在本研究中，在清醒雄性大鼠中激活 LC 的谷氨酸能作用下，检查齿状回的 EEG，以研究其对同时记录的穿通路径诱发场电位的可塑性效应。根据组织学和可塑性结果，将谷氨酸注射动物分为三组；还包括穿通路径刺激对照。三个注射组为：（1）LC 位置阳性的大鼠，表现出齿状回诱发电位的 NE-LTP；（2）LC 位置阳性的大鼠，无 NE-LTP；（3）非 LC 注射对照。在清醒大鼠中激活 LC，表现出 NE-LTP，增加了 7 至 9Hzθ波的相对功率，这一结果在更广泛的 4 至 12Hz 分析中被掩盖。相比之下，在 LC 激活的麻醉大鼠中，5-7Hz 增加，但 7-9Hzθ波不增加。在 Gray（7.4-8.5Hz）预测的近似θ 波段的判别分析表明，与仅接受穿通路径（未注射）和非 LC 注射大鼠相比，表现出 NE-LTP 的清醒大鼠在这个狭窄的频率范围内具有增加的相对功率。在未能表达 NE-LTP 的经证实 LC 位置的大鼠中，γ （20-40Hz）相对功率短暂降低最为常见。鉴于 LC 功能的当前理论，这些结果表明，在θ 和γ 范围内的振荡调谐可能有助于认知状态的转变。
