Nagel Katherine I, Wilson Rachel I
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115
J Neurosci. 2016 Apr 13;36(15):4325-38. doi: 10.1523/JNEUROSCI.3887-15.2016.
Local inhibitory neurons control the timing of neural activity in many circuits. To understand how inhibition controls timing, it is important to understand the dynamics of activity in populations of local inhibitory interneurons, as well as the mechanisms that underlie these dynamics. Here we describe the in vivo response dynamics of a large population of inhibitory local neurons (LNs) in the Drosophila melanogaster antennal lobe, the analog of the vertebrate olfactory bulb, and we dissect the network and intrinsic mechanisms that give rise to these dynamics. Some LNs respond to odor onsets ("ON" cells) and others to offsets ("OFF" cells), whereas still others respond at both times. Moreover, different LNs signal odor concentration fluctuations on different timescales. Some respond rapidly, and can track rapid concentration fluctuations. Others respond slowly, and are best at tracking slow fluctuations. We found a continuous spectrum of preferred stimulation timescales among LNs, as well as a continuum of ON-OFF behavior. Using in vivo whole-cell recordings, we show that the timing of an LN's response (ON vs OFF) can be predicted from the interplay of excitatory and inhibitory synaptic currents that it receives. Meanwhile, the preferred timescale of an LN is related to its intrinsic properties. These results illustrate how a population of inhibitory interneurons can collectively encode bidirectional changes in stimulus intensity on multiple timescales, and how this can arise via an interaction between synaptic and intrinsic mechanisms.
Most neural circuits contain diverse populations of inhibitory interneurons. The way inhibition shapes network activity will depend on the spiking dynamics of the interneuron population. Here we describe the dynamics of activity in a large population of inhibitory interneurons in the first brain relay of the fruit fly olfactory system. Because odor plumes fluctuate on multiple timescales, the drive to this circuit can vary over a range of frequencies. We show how synaptic and cellular mechanisms interact to recruit different interneurons at different times, and in response to different temporal features of odor stimuli. As a result, inhibition is recruited over a range of conditions, and there is the potential to tune the timing of inhibition as the environment changes.
局部抑制性神经元控制着许多神经回路中神经活动的时间。为了理解抑制作用如何控制时间，了解局部抑制性中间神经元群体的活动动态以及这些动态背后的机制非常重要。在这里，我们描述了果蝇触角叶中大量抑制性局部神经元（LN）的体内反应动态，触角叶相当于脊椎动物的嗅球，并且我们剖析了产生这些动态的网络和内在机制。一些LN对气味开始作出反应（“开启”细胞），另一些对气味结束作出反应（“关闭”细胞），而还有一些在这两个时间点都会作出反应。此外，不同的LN在不同的时间尺度上对气味浓度波动进行信号传递。一些反应迅速，能够追踪快速的浓度波动。另一些反应缓慢，最擅长追踪缓慢的波动。我们发现LN之间存在连续的偏好刺激时间尺度谱，以及开启 - 关闭行为的连续统。使用体内全细胞记录，我们表明可以根据LN所接收的兴奋性和抑制性突触电流的相互作用来预测其反应时间（开启与关闭）。同时，LN的偏好时间尺度与其内在特性相关。这些结果说明了一群抑制性中间神经元如何能够在多个时间尺度上共同编码刺激强度的双向变化，以及这如何通过突触和内在机制之间的相互作用而产生。
大多数神经回路包含不同类型的抑制性中间神经元群体。抑制作用塑造网络活动的方式将取决于中间神经元群体的放电动态。在这里，我们描述了果蝇嗅觉系统第一个脑中继中大量抑制性中间神经元的活动动态。由于气味羽流在多个时间尺度上波动，该回路的驱动可以在一系列频率范围内变化。我们展示了突触和细胞机制如何相互作用，在不同时间招募不同的中间神经元，并对气味刺激的不同时间特征作出反应。结果，在一系列条件下都会招募抑制作用，并且随着环境变化有调整抑制时间的潜力。
