Acoustic signal characteristic detection by neurons in ventral nucleus of the lateral lemniscus in mice

Under free field conditions, we used single unit extracellular recording to study the detection of acoustic signals by neurons in the ventral nucleus of the lateral lemniscus(VNLL) in Kunming mouse(Mus musculus). The results indicate two types of firing patterns in VNLL neurons: onset and sustained. The first spike latency(FSL) of onset neurons was shorter than that of sustained neurons. With increasing sound intensity, the FSL of onset neurons remained stable and that of sustained neurons was shortened, indicating that onset neurons are characterized by precise timing. By comparing the values of Q10 and Q30 of the frequency tuning curve, no differences between onset and sustained neurons were found, suggesting that firing pattern and frequency tuning are not correlated. Among the three types of rate-intensity function(RIF) found in VNLL neurons, the proportion of monotonic RIF is the largest, followed by saturated RIF, and non-monotonic RIF. The dynamic range(DR) in onset neurons was shorter than in sustained neurons, indicating different capabilities in intensity tuning of different firing patterns and that these differences are correlated with the type of RIF. Our results also show that the best frequency of VNLL neurons was negatively correlated with depth, supporting the view point that the VNLL has frequency topologic organization.

Responses from two firing patterns in inferior colliculus neurons to stimulation of the lateral lemniscus dorsal nucleus

The γ-aminobutyric acid neurons（GABAergic neurons） in the inferior colliculus are classified into various patterns based on their intrinsic electrical properties to a constant current injection. Although this classification is associated with physiological function, the exact role for neurons with various firing patterns in acoustic processing remains poorly understood. In the present study, we analyzed characteristics of inferior colliculus neurons in vitro, and recorded responses to stimulation of the dorsal nucleus of the lateral lemniscus using the wholecell patch clamp technique. Seven inferior colliculus neurons were tested and were classified into two firing patterns： sustained-regular（n = 4） and sustained-adapting firing patterns（n = 3）. The majority of inferior colliculus neurons exhibited slight changes in response to stimulation and bicuculline. The responses of one neuron with a sustained-adapting firing pattern were suppressed after stimulation, but recovered to normal levels following application of the γ-aminobutyric acid receptor antagonist. One neuron with a sustained-regular pattern showed suppressed stimulation responses, which were not affected by bicuculline. Results suggest that GABAergic neurons in the inferior colliculus exhibit sustained-regular or sustained-adapting firing patterns. Additionally, GABAergic projections from the dorsal nucleus of the lateral lemniscus to the inferior colliculus are associated with sound localization. The different neuronal responses of various firing patterns suggest a role in sound localization. A better understanding of these mechanisms and functions will provide better clinical treatment paradigms for hearing deficiencies.

Research Progress on Mechanisms in Regulating Anxiety-Related Neural Circuits

Anxiety is a common disease in the modern society which significantly affects people’s daily lives and function,thus it has become an increasingly highlighted issue.Anxiety is regulated by neural circuits in the brain.Therefore,the basal mechanism of anxiety has been studied,especially research based on the related neural circuits.For a long time,due to the limitations of science and technology,there was no breakthrough in research regarding anxiety.However,in recent years,due to the progress of technology,the research on anxiety neural circuits has made great progress.For example,the interaction among various brain regions,such as the central nucleus of the amygdala(CeA),the ventral tegmental area(VTA),the ventral hippocampus(vHPC),and so on.This article focuses on three brain regions:including BLA,BNST,and VTA,and illustrate their different roles and mechanisms in regulating anxiety.On this basis,this intensive study of anxiety will further promote the progress of anxiety research and provide therapeutic targets for the related treatment.

外侧丘系腹核在声信号加工和听觉上行传导中的作用

外侧丘系腹核(ventral nucleus of the lateral lemniscus,VNLL)是中枢听觉通路中连接耳蜗核等低位脑干和中脑下丘(inferior colliculus,IC)的重要核团,其神经元能够对声信号的不同参数进行检测与加工,进而形成多样的声反应特性。VNLL神经元对频率反应的调谐曲线有多种类型,但其锐化程度一般较低,对频率的分析亦不够精确;有关强度调谐的放电率函数分为两种类型:单调型与非单调型,它们对强度的加工和编码往往受到发放模式的影响;不同发放模式的VNLL神经元对时程的编码能力不同,其中起始型具有精确的时间特性,适合编码声刺激的起始时间信息,对蝙蝠的回声定位非常重要。VNLL接受来自低位核团的输入,并发出上行的抑制性投射至IC,在IC神经元的声信息检测过程中发挥重要作用。近来研究认为VNLL快速的抑制性投射延迟IC神经元的首次发放潜伏期,VNLL延迟的抑制性投射介导IC神经元的发放模式,但VNLL抑制性输入如何在IC进行整合,并增强IC神经元检测声信号能力的机制并不清楚,且缺乏VNLL对IC进行实时调控作用的直接证据。这些问题的研究有助于进一步认识上行输入在声信号加工过程中的作用,同时也是本实验室今后的研究重点。本文结合本实验室相关研究,围绕VNLL对听觉信号的加工和上行传导进行综述。