Center for Molecular and Behavioral Neuroscience, Rutgers, The State University of New Jersey, Newark, NJ, USA.
J Neurophysiol. 2012 Dec;108(12):3196-205. doi: 10.1152/jn.00514.2012. Epub 2012 Sep 12.
Recent findings implicate the central lateral amygdala (CeL) in conditioned fear. Indeed, CeL contains neurons exhibiting positive (CeL-On) or negative (CeL-Off) responses to fear-inducing conditioned stimuli (CSs). In mice, these cells differ in their expression of protein kinase Cδ (PKCδ) and physiological properties. CeL-Off cells are PKCδ(+) and late firing (LF), whereas CeL-On cells are PKCδ(-) and express a regular-spiking (RS) or low-threshold bursting (LTB) phenotype. However, the scarcity of LF cells in rats raises questions about the correspondence between the organization of CeL in mice and rats. Therefore, we studied the PKCδ expression, morphological properties, synaptic responsiveness, and fear conditioning-induced plasticity of rat CeL neurons. No PKCδ(+) LF cells were encountered, but ≈20-25% of RS and LTB neurons were PKCδ(+). Compared with RS neurons, a higher proportion of LTB cells projected to central medial amygdala (CeM) and they had fewer primary dendritic branches, yet the amplitude of excitatory postsynaptic potentials (EPSPs) evoked by lateral amygdala (LA) stimulation was similar in RS and LTB cells. In contrast, LA-evoked inhibitory postsynaptic potentials (IPSPs) had a higher amplitude in LTB than RS neurons. Finally, fear conditioning did not induce plasticity at LA inputs to RS or LTB neurons. These findings point to major species differences in the organization of CeL. Since rat LTB cells are subjected to stronger feedforward inhibition, they are more likely to exhibit inhibitory CS responses than RS cells. This is expected to cause a disinhibition of CeM fear output neurons and therefore an increase in fear expression.
最近的研究结果表明，中央外侧杏仁核（CeL）在条件性恐惧中起作用。事实上，CeL 包含对引起恐惧的条件刺激（CS）表现出正（CeL-On）或负（CeL-Off）反应的神经元。在小鼠中，这些细胞在蛋白激酶 Cδ（PKCδ）的表达和生理特性上存在差异。CeL-Off 细胞是 PKCδ(+)和晚期放电（LF），而 CeL-On 细胞是 PKCδ(-)，并表达规则放电（RS）或低阈值爆发（LTB）表型。然而，大鼠中 LF 细胞的稀缺性引发了关于小鼠和大鼠 CeL 组织对应关系的问题。因此，我们研究了大鼠 CeL 神经元的 PKCδ 表达、形态特性、突触反应性以及恐惧条件反射诱导的可塑性。没有遇到 PKCδ(+) LF 细胞，但 ≈20-25%的 RS 和 LTB 神经元是 PKCδ(+)。与 RS 神经元相比，LTB 细胞中有更高比例投射到中央内侧杏仁核（CeM），它们的初级树突分支较少，但外侧杏仁核（LA）刺激诱发的兴奋性突触后电位（EPSP）的幅度在 RS 和 LTB 细胞中相似。相比之下，LA 诱发的抑制性突触后电位（IPSP）在 LTB 神经元中的幅度高于 RS 神经元。最后，恐惧条件反射没有诱导 LA 输入到 RS 或 LTB 神经元的可塑性。这些发现表明 CeL 组织存在主要的物种差异。由于大鼠 LTB 细胞受到更强的前馈抑制，它们比 RS 细胞更有可能表现出抑制性 CS 反应。这预计会导致 CeM 恐惧输出神经元的去抑制，从而增加恐惧表达。
