Fourcaud-Trocmé Nicolas, Courtiol Emmanuelle, Buonviso Nathalie, Voegtlin Thomas
INSERM, U1028, Lyon Neuroscience Research Center, Olfactory Coding and Memory Team, Lyon F-69000, France.
J Physiol Paris. 2011 Jan-Jun;105(1-3):59-70. doi: 10.1016/j.jphysparis.2011.07.009. Epub 2011 Aug 6.
In the rat olfactory bulb (OB), fast oscillations of the local field potential (LFP) are observed during the respiratory cycle. Gamma-range oscillations (40-90 Hz) occur at the end of inspiration, followed by beta-range oscillations (15-30 Hz) during exhalation. These oscillations are highly stereotypical, and their frequencies are stable under various conditions. In this study, we investigate the effect of stimulus intensity on activity in the OB. Using a double-cannulation protocol, we showed that although the frequency of the LFP oscillation does depend on the respiratory cycle phase, it is relatively independent of the intensity of odorant stimulation. In contrast, we found that the individual firing rate of mitral OB cells dramatically changed with the intensity of the stimulation. This suggests that OB fast oscillation parameters, particularly frequency, are fully determined by intrinsic OB network parameters. To test this hypothesis, we explored a model of the OB where fast oscillations are generated by the interplay between excitatory mitral/tufted cells and inhibitory granule cells with graded inhibition. We found that our model has two distinct activity regimes depending on the amount of noise. In a low-noise regime, the model displays oscillation in the beta range with a stable frequency across a wide range of excitatory inputs. In a high-noise regime, the model displays oscillatory dynamics with irregular cell discharges and fast oscillations, similar to what is observed during gamma oscillations but without stability of the oscillation frequency with respect to the network external input. Simulations of the full model and theoretical studies of the network's linear response show that the characteristics of the low-noise regime are induced by non-linearities in the model, notably, the saturation of graded inhibition. Finally, we discuss how this model can account for the experimentally observed stability of the oscillatory regimes.
在大鼠嗅球（OB）中，在呼吸周期期间可观察到局部场电位（LFP）的快速振荡。伽马波段振荡（40 - 90赫兹）出现在吸气末期，随后在呼气期间出现贝塔波段振荡（15 - 30赫兹）。这些振荡具有高度的刻板性，并且它们的频率在各种条件下都很稳定。在本研究中，我们研究了刺激强度对OB活动的影响。使用双插管方案，我们表明尽管LFP振荡的频率确实取决于呼吸周期阶段，但它相对独立于气味刺激的强度。相反，我们发现OB二尖瓣细胞的个体放电率随刺激强度而显著变化。这表明OB快速振荡参数，特别是频率，完全由OB内在网络参数决定。为了验证这一假设，我们探索了一个OB模型，其中快速振荡是由兴奋性二尖瓣/簇状细胞和具有分级抑制的抑制性颗粒细胞之间的相互作用产生的。我们发现我们的模型根据噪声量有两种不同的活动状态。在低噪声状态下，该模型在贝塔波段显示振荡，在广泛的兴奋性输入范围内频率稳定。在高噪声状态下，该模型显示出具有不规则细胞放电和快速振荡的振荡动力学，类似于在伽马振荡期间观察到的情况，但振荡频率相对于网络外部输入不稳定。完整模型的模拟和网络线性响应的理论研究表明，低噪声状态的特征是由模型中的非线性引起的，特别是分级抑制的饱和。最后，我们讨论了该模型如何解释实验观察到的振荡状态的稳定性。
