Lo F S, Sherman S M
Department of Neurobiology State University of New York, Stony Brook 11794-5230.
Exp Brain Res. 1994;100(2):365-8. doi: 10.1007/BF00227207.
Feedback inhibition is generally believed to be a ubiquitous feature of brain circuitry, but few specific instances have been documented. An example in cats is the supposed feedback circuit involving relay cells of the lateral geniculate nucleus and cells of the perigeniculate nucleus (a part of the thalamic reticular nucleus): geniculate relay cells innervate the perigeniculate nucleus, which, in turn, provides an inhibitory, GABAergic projection back to the lateral geniculate nucleus. However, feedback inhibition at the single-cell level requires that a given perigeniculate cell project back onto the same geniculate relay cell that innervates it. We probed for this in an in vitro slice preparation of the cat's lateral geniculate nucleus. We evoked a single action potential in a geniculate cell via a brief, depolarizing pulse delivered through an intracellular recording electrode and looked for any evoked hyperpolarizations. For 6 of the 36 geniculate cells tested, we observed a long-lasting hyperpolarization after the action potential, and much of this was eliminated by application of bicuculline, suggesting synaptically activated inhibitory postsynaptic potentials. We interpreted this to be clear evidence that a given neuron may inhibit itself via circuitry mediating feedback inhibition in the cat's lateral geniculate nucleus.
反馈抑制通常被认为是脑回路中普遍存在的特征，但鲜有具体实例得到记载。猫的一个例子是推测存在的涉及外侧膝状体核中继细胞和膝周核细胞（丘脑网状核的一部分）的反馈回路：膝状体中继细胞支配膝周核，而膝周核又向外侧膝状体核提供抑制性的γ-氨基丁酸能投射。然而，单细胞水平的反馈抑制要求给定的膝周细胞投射回支配它的同一个膝状体中继细胞。我们在猫外侧膝状体核的体外脑片制备中对此进行了探究。我们通过细胞内记录电极施加一个短暂的去极化脉冲，在一个膝状体细胞中诱发单个动作电位，并寻找任何诱发的超极化。在测试的36个膝状体细胞中，有6个细胞在动作电位后出现了持续较长时间的超极化，并且其中大部分在应用荷包牡丹碱后消失，这表明是突触激活的抑制性突触后电位。我们将此解释为明确的证据，即给定的神经元可能通过介导猫外侧膝状体核反馈抑制的回路来抑制自身。
