Lyon Neuroscience Research Center, CNRS UMR 5292 - INSERM U 1028 - Université Claude Bernard Lyon 1, Centre Hospitalier Le Vinatier - Bâtiment 462 - Neurocampus, 95 Boulevard Pinel, 69675 Bron Cedex, France.
Lyon Neuroscience Research Center, CNRS UMR 5292 - INSERM U 1028 - Université Claude Bernard Lyon 1, Centre Hospitalier Le Vinatier - Bâtiment 462 - Neurocampus, 95 Boulevard Pinel, 69675 Bron Cedex, France
eNeuro. 2022 Apr 1;9(2). doi: 10.1523/ENEURO.0401-21.2021. Print 2022 Mar-Apr.
In the olfactory bulb, mitral cells (MCs) display a spontaneous firing that is characterized by bursts of action potentials (APs) intermixed with silent periods. Intraburst firing frequency and duration are heterogeneous among MCs and increase with membrane depolarization. By using patch-clamp recording on rat slices, we dissected out the intrinsic properties responsible for this bursting activity. We showed that the threshold of AP generation dynamically changes as a function of the preceding trajectory of the membrane potential. In fact, the AP threshold became more negative when the membrane was hyperpolarized and had a recovery rate inversely proportional to the membrane repolarization rate. Such variations appeared to be produced by changes in the inactivation state of voltage-dependent Na channels. Thus, AP initiation was favored by hyperpolarizing events, such as negative membrane oscillations or inhibitory synaptic input. After the first AP, the following fast afterhyperpolarization (AHP) brought the threshold to more negative values and then promoted the emission of the following AP. This phenomenon was repeated for each AP of the burst making the fast AHP a regenerative mechanism that sustained the firing, AHP with larger amplitudes and faster repolarizations being associated with larger and higher-frequency bursts. Burst termination was found to be because of the development of a slow repolarization component of the AHP (slow AHP). Overall, the AHP characteristics appeared as a major determinant of the bursting properties.
在嗅球中，僧帽细胞（MCs）表现出一种自发的放电活动，其特征是动作电位（APs）爆发与沉默期交替出现。爆发内的放电频率和持续时间在 MCs 之间存在异质性，并随膜去极化而增加。通过在大鼠切片上进行膜片钳记录，我们分离出负责这种爆发活动的内在特性。我们表明，AP 产生的阈值随膜电位的先前轨迹动态变化。实际上，当膜超极化时，AP 阈值变得更负，并且恢复率与膜复极化率成反比。这种变化似乎是由电压依赖性 Na 通道的失活状态变化引起的。因此，AP 起始受到去极化事件的促进，例如负膜振荡或抑制性突触输入。在第一个 AP 之后，随后的快速后超极化（AHP）将阈值带到更负的值，然后促进下一个 AP 的发射。这种现象在爆发的每个 AP 中重复，使快速 AHP 成为维持放电的再生机制，具有更大幅度和更快复极化的 AHP 与更大和更高频率的爆发相关。爆发的终止是因为 AHP 的慢去极化成分（慢 AHP）的发展。总的来说，AHP 的特性似乎是爆发特性的主要决定因素。
