Pape H C, McCormick D A
Institut für Physiologie, Otto-von-Guericke-Universitaet, Magdeburg, Germany.
Neuroscience. 1995 Oct;68(4):1105-25. doi: 10.1016/0306-4522(95)00205-w.
We investigated the electrophysiological and pharmacological properties of morphologically identified and putative interneurons within laminae A and A1 of the cat dorsal lateral geniculate nucleus maintained in vitro. These intralaminar interneurons possess unique electrophysiological characteristics, including (1) action potentials of a short duration (average width at half amplitude of 0.34 ms). (2) the ability to generate high-frequency trains of action potentials exceeding 500 Hz, without strong spike frequency adaptation, and (3) a low-threshold regenerative response with variable magnitude of expression, ranging from a subthreshold depolarization towards the generation of one to several action potentials in different cells. The low-threshold regenerative depolarization following a hyperpolarizing current pulse was increased in size by application of 4-aminopyridine, was reduced by nickel, and was not influenced by extracellular cesium. These findings indicate that this event is mediated by an underlying Ca(2+)-dependent mechanism, such as a low-threshold Ca(2+) current, that is regulated by the activation of opposing transient K+ currents. Every interneuron tested responded to glutamate, kainate, quisqualate, or N-methyl-D-aspartate with depolarization and action potential discharge. In contrast, we did not observe a postsynaptic response to activation of the metabotropic receptors with 1S,3R-(+/-)-1-amino-cyclopentane-1,3-dicarboxylate. Application of gamma-amino-butyric acid (GABA) strongly inhibited spike firing through a biphasic hyperpolarization and increase in membrane conductance, a response that reversed close to the presumed chloride equilibrium potential and was imitated by the GABAA receptor agonist muscimol. The GABAB receptor agonist baclofen evoked only a weak membrane hyperpolarization from rest and suppression of spontaneous spike activity. Application of acetylcholine, or the muscarinic agonist acetyl-beta-methylcholine, inhibited spontaneous action potential activity through hyperpolarization of the membrane potential, presumably resulting from an increase in membrane potassium conductance. In contrast, application of serotonin only slightly facilitated tonic activity in a subpopulation of interneurons, histamine induced a small slow depolarization apparently through activation of presynaptic excitatory pathways, and noradrenaline and adenosine had no detectable effect on the spontaneous firing or resting potential of interneurons. We suggest that intralaminar interneurons may function in a relatively linear manner to transform retinal and cortical inputs into a local field of inhibition in the dorsal lateral geniculate and that the excitability of these neurons is largely controlled by retinal, cortical, GABAergic, and cholinergic (brainstem) afferents.
我们研究了在体外培养的猫背外侧膝状核A层和A1层中形态学上已确定的以及假定的中间神经元的电生理和药理学特性。这些层内中间神经元具有独特的电生理特征，包括：（1）动作电位持续时间短（半幅处平均宽度为0.34毫秒）；（2）能够产生超过500赫兹的高频动作电位序列，且无明显的放电频率适应现象；（3）具有低阈值再生反应，其表达幅度可变，在不同细胞中表现为从阈下去极化到产生一至数个动作电位。超极化电流脉冲后的低阈值再生去极化在应用4 - 氨基吡啶后幅度增大，在应用镍后减小，且不受细胞外铯的影响。这些发现表明，该事件由一种潜在的钙依赖机制介导，如低阈值钙电流，它受相反的瞬时钾电流激活的调节。每个被测试的中间神经元对谷氨酸、海人藻酸、quisqualate或N - 甲基 - D - 天冬氨酸均有去极化和动作电位发放反应。相反，我们未观察到用1S,3R - (+/-)-1 - 氨基环戊烷 - 1,3 - 二羧酸激活代谢型受体后的突触后反应。应用γ - 氨基丁酸（GABA）通过双相超极化和膜电导增加强烈抑制动作电位发放，该反应在接近假定的氯平衡电位处反转，且可被GABAA受体激动剂蝇蕈醇模拟。GABAB受体激动剂巴氯芬仅从静息状态诱发微弱的膜超极化并抑制自发动作电位活动。应用乙酰胆碱或毒蕈碱激动剂乙酰 - β - 甲基胆碱通过膜电位超极化抑制自发动作电位活动，推测这是由于膜钾电导增加所致。相反，应用5 - 羟色胺仅轻微促进了一部分中间神经元的紧张性活动，组胺显然通过激活突触前兴奋性通路诱导了小的缓慢去极化，而去甲肾上腺素和腺苷对中间神经元的自发放电或静息电位无明显影响。我们认为层内中间神经元可能以相对线性的方式发挥作用，将视网膜和皮质输入转化为背外侧膝状核中的局部抑制场，并且这些神经元的兴奋性在很大程度上受视网膜、皮质、GABA能和胆碱能（脑干）传入纤维的控制。
