Tan M L, Theeuwes H P, Feenstra L, Borst J G G
Department of Neuroscience, Erasmus MC, Rotterdam, The Netherlands.
J Neurophysiol. 2007 Jul;98(1):443-53. doi: 10.1152/jn.01273.2006. Epub 2007 May 16.
The inferior colliculus (IC) is a large auditory nucleus in the midbrain, which is a nearly obligatory relay center for ascending auditory projections. We made in vivo whole cell patch-clamp recordings of IC cells in young-adult anesthetized C57/Bl6 mice and Wistar rats to characterize their membrane properties and spontaneous inputs. We observed spikelets in both rat (18%) and mouse (13%) IC neurons, suggesting that IC neurons may be connected by electrical synapses. In many cells, spontaneous postsynaptic potentials were sufficiently large to contribute to spike irregularity. Cells differed considerably in the number of simultaneous spontaneous postsynaptic potentials that would be needed to trigger an action potential. Depolarizing and hyperpolarizing current injections showed six different types of firing patterns: buildup, accelerating, burst-onset, burst-sustained, sustained, and accommodating. Their relative frequencies were similar in both species. In mice, about half of the cells showed a clear depolarizing sag, suggesting that they have the hyperpolarization-activated current I(h). This sag was observed more often in burst and in accommodating cells than in buildup, accelerating, or sustained neurons. Cells with I(h) had a significantly more depolarized resting membrane potential. They were more likely to fire rebound spikes and generally showed long-lasting afterhyperpolarizations following long depolarizations. We therefore suggest a separate functional role for I(h).
下丘是中脑中一个较大的听觉核团，它几乎是听觉上行投射的必经中继中心。我们对年轻成年麻醉状态下的C57/Bl6小鼠和Wistar大鼠的下丘细胞进行了体内全细胞膜片钳记录，以表征其膜特性和自发输入。我们在大鼠（18%）和小鼠（13%）的下丘神经元中均观察到了尖峰电位，这表明下丘神经元可能通过电突触相连。在许多细胞中，自发的突触后电位足够大，足以导致动作电位的发放不规则。不同细胞触发动作电位所需的同时发生的自发突触后电位数量差异很大。去极化和超极化电流注入显示出六种不同的放电模式：逐渐增强、加速、爆发起始、爆发持续、持续和适应。两种物种中这些模式的相对频率相似。在小鼠中，约一半的细胞表现出明显的去极化凹陷，这表明它们具有超极化激活电流I(h)。与逐渐增强、加速或持续放电的神经元相比，这种凹陷在爆发放电和适应放电的细胞中更常见。具有I(h)的细胞静息膜电位明显更去极化。它们更有可能发放反弹尖峰，并且在长时间去极化后通常表现出持久的超极化后电位。因此，我们认为I(h)具有独立的功能作用。
