Wood Debra E, Manor Yair, Nadim Farzan, Nusbaum Michael P
Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6074, USA.
J Neurosci. 2004 Aug 25;24(34):7455-63. doi: 10.1523/JNEUROSCI.1840-04.2004.
Synaptic feedback from rhythmically active neuronal circuits commonly causes their descending inputs to exhibit the rhythmic activity pattern generated by that circuit. In most cases, however, the function of this rhythmic feedback is unknown. In fact, generally these inputs can still activate the target circuit when driven in a tonic activity pattern. We are using the crab stomatogastric nervous system (STNS) to test the hypothesis that the neuronal circuit-mediated rhythmic activity pattern in projection neurons contributes to intercircuit regulation. The crab STNS contains an identified projection neuron, modulatory commissural neuron 1 (MCN1), whose tonic stimulation activates and modulates the gastric mill (chewing) and pyloric (filtering of chewed food) motor circuits in the stomatogastric ganglion (STG). During tonic stimulation of MCN1, the pyloric circuit regulates both gastric mill cycle frequency and gastropyloric coordination via a direct synapse onto a gastric mill neuron in the STG. However, when MCN1 is spontaneously active, it has a pyloric-timed activity pattern attributable to synaptic input from the pyloric circuit. This pyloric-timed activity in MCN1 provides the pyloric circuit with a second pathway for regulating the gastric mill rhythm. At these times, the direct STG synapse from the pyloric circuit to the gastric mill circuit is not necessary for pyloric regulation of the gastric mill rhythm. However, in the intact system, these two pathways play complementary roles in this intercircuit regulation. Thus, one role for rhythmicity in modulatory projection neurons is to enable them to mediate the interactions between distinct but related neuronal circuits.
来自节律性活动神经元回路的突触反馈通常会使其下行输入呈现出该回路产生的节律性活动模式。然而，在大多数情况下，这种节律性反馈的功能尚不清楚。事实上，一般来说，当以紧张性活动模式驱动时，这些输入仍然可以激活目标回路。我们正在利用蟹类的口胃神经系统（STNS）来检验这一假设，即投射神经元中由神经元回路介导的节律性活动模式有助于回路间的调节。蟹类的口胃神经系统包含一个已确定的投射神经元，即调制连合神经元1（MCN1），对其进行紧张性刺激会激活并调节口胃神经节（STG）中的胃磨（咀嚼）和幽门（咀嚼食物过滤）运动回路。在对MCN1进行紧张性刺激期间，幽门回路通过直接突触作用于STG中的一个胃磨神经元，从而调节胃磨周期频率和胃幽门协调性。然而，当MCN1自发活动时，它具有归因于来自幽门回路突触输入的幽门定时活动模式。MCN1中的这种幽门定时活动为幽门回路提供了第二条调节胃磨节律的途径。在这些时候，从幽门回路到胃磨回路的直接STG突触对于幽门对胃磨节律的调节并非必需。然而，在完整系统中，这两条途径在这种回路间调节中发挥着互补作用。因此，调制投射神经元中的节律性的一个作用是使它们能够介导不同但相关的神经元回路之间的相互作用。
