Department of Functional and Structural Biology - Anatomy Division, Institute of Biosciences of Botucatu, São Paulo State University-UNESP, Botucatu, São Paulo, Brazil.
Medicine School, Federal University of Mato Grosso do Sul, UFMS-CPTL, Três Lagoas, Mato Grosso do Sul, Brazil.
Hear Res. 2024 Sep 1;450:109070. doi: 10.1016/j.heares.2024.109070. Epub 2024 Jun 14.
Cholinergic signaling is essential to mediate the auditory prepulse inhibition (PPI), an operational measure of sensorimotor gating, that refers to the reduction of the acoustic startle reflex (ASR) when a low-intensity, non-startling acoustic stimulus (the prepulse) is presented just before the onset of the acoustic startle stimulus. The cochlear root neurons (CRNs) are the first cells of the ASR circuit to receive cholinergic inputs from non-olivocochlear neurons of the ventral nucleus of the trapezoid body (VNTB) and subsequently decrease their neuronal activity in response to auditory prepulses. Yet, the contribution of the VNTB-CRNs pathway to the mediation of PPI has not been fully elucidated. In this study, we used the immunotoxin anti-choline acetyltransferase (ChAT)-saporin as well as electrolytic lesions of the medial olivocochlear bundle to selectively eliminate cholinergic VNTB neurons, and then assessed the ASR and PPI paradigms. Retrograde track-tracing experiments were conducted to precisely determine the site of lesioning VNTB neurons projecting to the CRNs. Additionally, the effects of VNTB lesions and the integrity of the auditory pathway were evaluated via auditory brain responses tests, ChAT- and FOS-immunohistochemistry. Consequently, we established three experimental groups: 1) intact control rats (non-lesioned), 2) rats with bilateral lesions of the olivocochlear bundle (OCB-lesioned), and 3) rats with bilateral immunolesions affecting both the olivocochlear bundle and the VNTB (OCB/VNTB-lesioned). All experimental groups underwent ASR and PPI tests at several interstimulus intervals before the lesion and 7, 14, and 21 days after it. Our results show that the ASR amplitude remained unaffected both before and after the lesion across all experimental groups, suggesting that the VNTB does not contribute to the ASR. The%PPI increased across the time points of evaluation in the control and OCB-lesioned groups but not in the OCB/VNTB-lesioned group. At the ISI of 50 ms, the OCB-lesioned group exhibited a significant increase in%PPI (p < 0.01), which did not occur in the OCB/VNTB-lesioned group. Therefore, the ablation of cholinergic non-olivocochlear neurons in the OCB/VNTB-lesioned group suggests that these neurons contribute to the mediation of auditory PPI at the 50 ms ISI through their cholinergic projections to CRNs. Our study strongly reinforces the notion that auditory PPI encompasses a complex mechanism of top-down cholinergic modulation, effectively attenuating the ASR across different interstimulus intervals within multiple pathways.
胆碱能信号对于介导听觉预脉冲抑制（PPI）至关重要，PPI 是一种感觉运动门控的操作性测量，指的是当低强度、非起始的声刺激（预脉冲）在起始声刺激之前呈现时，对声起始反射（ASR）的降低。耳蜗根神经元（CRNs）是第一个接收来自腹索体背核（VNTB）非橄榄耳蜗神经元的胆碱能输入的 ASR 回路细胞，随后响应听觉预脉冲降低其神经元活动。然而，VNTB-CRNs 通路对 PPI 介导的贡献尚未完全阐明。在这项研究中，我们使用免疫毒素抗胆碱乙酰转移酶（ChAT）-SAP 以及内侧橄榄耳蜗束的电解损伤来选择性地消除胆碱能 VNTB 神经元，然后评估 ASR 和 PPI 范式。逆行轨迹追踪实验精确地确定了投射到 CRNs 的 VNTB 神经元损伤的部位。此外，通过听觉脑反应测试、ChAT 和 FOS 免疫组织化学评估 VNTB 损伤和听觉通路的完整性。因此，我们建立了三个实验组：1）完整对照组大鼠（未损伤）、2）双侧橄榄耳蜗束损伤组大鼠（OCB 损伤组）和 3）双侧免疫损伤组大鼠影响橄榄耳蜗束和 VNTB（OCB/VNTB 损伤组）。所有实验组在损伤前和损伤后 7、14 和 21 天进行了 ASR 和 PPI 测试。我们的结果表明，在所有实验组中，ASR 幅度在损伤前后均不受影响，表明 VNTB 不参与 ASR。在对照组和 OCB 损伤组中，%PPI 在评估的时间点上均增加，但在 OCB/VNTB 损伤组中则没有。在 ISI 为 50ms 时，OCB 损伤组的%PPI 显著增加（p<0.01），而 OCB/VNTB 损伤组则没有。因此，在 OCB/VNTB 损伤组中，胆碱能非橄榄耳蜗神经元的消融表明，这些神经元通过其对 CRNs 的胆碱能投射，有助于介导 50ms ISI 的听觉 PPI。我们的研究强烈支持这样一种观点，即听觉 PPI 包含一种复杂的自上而下的胆碱能调制机制，通过多个通路在不同的刺激间隔内有效减弱 ASR。
