Gray C M, Skinner J E
Department of Neurology, Baylor College of Medicine, Houston, TX 77030.
Exp Brain Res. 1988;69(2):378-86. doi: 10.1007/BF00247583.
The influences of centrifugal projections to the olfactory bulb were examined on the bulbar EEG and mitral-tufted cell activity in waking rabbits. Each of 6 rabbits was implanted, under surgical anesthesia, with fine wire electrodes for recording of the EEG and mitral-tufted cell unit activity and for stimulating the lateral olfactory tract. Two cooling probes, for reversible cryogenic blockade, were implanted on either side of the left olfactory peduncle. Records of EEG and unit activity were taken for 200 s before, during and after cooling of the probes to 3 degrees centigrade. Antidromic evoked potentials were used to assess the efficacy of the blockade. During the cryogenic blockade bursts of EEG activity, evoked in the bulb by inspiration through the nose, were augmented in amplitude and reduced in frequency. Mitral-tufted cell unit activity was reduced in rate but was more highly correlated with the phase and amplitude of the EEG bursts. Analysis of individual EEG bursts revealed that the variance in frequency of bulbar activity was significantly reduced in the isolated state. The data demonstrate that oscillatory bursting activity in the olfactory bulb is intrinsically maintained within a relatively fixed frequency range during receptor input and does not depend on centrifugal projections for its electrogenesis. Changes in EEG frequency, amplitude and correlation with unit activity support the hypothesis that centrifugal projections act in part to inhibit mitral-tufted cell output by direct excitation of granule cells. These findings are supported by a theoretical model in which distributed feedback to the granule cells from more central olfactory structures acts to regulate the coherency of bulbar activity.
在清醒的家兔中，研究了离心投射对嗅球的影响，观察其对嗅球脑电图（EEG）以及二尖瓣-簇状细胞活动的作用。6只家兔在手术麻醉下，植入细钢丝电极用于记录EEG和二尖瓣-簇状细胞单位活动，以及刺激外侧嗅束。在左嗅脚两侧植入两个用于可逆性低温阻断的冷却探头。在将探头冷却至3摄氏度之前、期间和之后，记录200秒的EEG和单位活动。采用逆向诱发电位来评估阻断效果。在低温阻断期间，通过鼻腔吸气在嗅球诱发的EEG活动爆发，其幅度增大而频率降低。二尖瓣-簇状细胞单位活动的速率降低，但与EEG爆发的相位和幅度相关性更高。对单个EEG爆发的分析表明，在隔离状态下，嗅球活动频率的方差显著降低。数据表明，在受体输入期间，嗅球中的振荡爆发活动在相对固定的频率范围内内在维持，其电活动并不依赖于离心投射。EEG频率、幅度以及与单位活动相关性的变化支持了这样一种假说，即离心投射部分地通过直接兴奋颗粒细胞来抑制二尖瓣-簇状细胞的输出。这些发现得到了一个理论模型的支持，在该模型中，来自更中枢嗅结构对颗粒细胞的分布式反馈作用于调节嗅球活动的连贯性。
