Barmack Neal H, Pettorossi Vito Enrico
Department of Physiology & Pharmacology, Oregon Health & Science University, Portland, OR, United States.
Section of Human Physiology and Biochemistry, Department of Experimental Medicine, University of Perugia, Perugia, Italy.
Front Neurol. 2021 Mar 9;12:635259. doi: 10.3389/fneur.2021.635259. eCollection 2021.
Vestibular and optokinetic space is represented in three-dimensions in vermal lobules IX-X (uvula, nodulus) and hemisphere lobule X (flocculus) of the cerebellum. Vermal lobules IX-X encodes gravity and head movement using the utricular otolith and the two vertical semicircular canals. Hemispheric lobule X encodes self-motion using optokinetic feedback about the three axes of the semicircular canals. Vestibular and visual adaptation of this circuitry is needed to maintain balance during perturbations of self-induced motion. Vestibular and optokinetic (self-motion detection) stimulation is encoded by cerebellar climbing and mossy fibers. These two afferent pathways excite the discharge of Purkinje cells directly. Climbing fibers preferentially decrease the discharge of Purkinje cells by exciting stellate cell inhibitory interneurons. We describe instances adaptive balance at a behavioral level in which prolonged vestibular or optokinetic stimulation evokes reflexive eye movements that persist when the stimulation that initially evoked them stops. Adaptation to prolonged optokinetic stimulation also can be detected at cellular and subcellular levels. The transcription and expression of a neuropeptide, corticotropin releasing factor (CRF), is influenced by optokinetically-evoked olivary discharge and may contribute to optokinetic adaptation. The transcription and expression of microRNAs in floccular Purkinje cells evoked by long-term optokinetic stimulation may provide one of the subcellular mechanisms by which the membrane insertion of the GABAA receptors is regulated. The neurosteroids, estradiol (E2) and dihydrotestosterone (DHT), influence adaptation of vestibular nuclear neurons to electrically-induced potentiation and depression. In each section of this review, we discuss how adaptive changes in the vestibular and optokinetic subsystems of lobule X, inferior olivary nuclei and vestibular nuclei may contribute to the control of balance.
前庭和视动空间在小脑的蚓部小叶IX - X（悬雍垂、小结）和半球小叶X（绒球）中以三维形式呈现。蚓部小叶IX - X利用椭圆囊耳石和两个垂直半规管对重力和头部运动进行编码。半球小叶X利用关于半规管三个轴的视动反馈对自身运动进行编码。在自我诱导运动受到干扰时，需要对该神经回路进行前庭和视觉适应以维持平衡。前庭和视动（自我运动检测）刺激由小脑攀缘纤维和苔藓纤维进行编码。这两条传入通路直接兴奋浦肯野细胞的放电。攀缘纤维通过兴奋星状细胞抑制性中间神经元优先减少浦肯野细胞的放电。我们描述了行为水平上的适应性平衡实例，其中长时间的前庭或视动刺激会引发反射性眼球运动，当最初引发这些运动的刺激停止时，这些运动仍会持续。在细胞和亚细胞水平也能检测到对长时间视动刺激的适应。一种神经肽，促肾上腺皮质激素释放因子（CRF）的转录和表达受视动诱发的橄榄核放电影响，可能有助于视动适应。长期视动刺激诱发的绒球浦肯野细胞中微小RNA的转录和表达可能提供了一种调节GABAA受体膜插入的亚细胞机制。神经甾体，雌二醇（E2）和二氢睾酮（DHT），影响前庭核神经元对电诱导增强和抑制作用适应。在本综述的每个部分，我们讨论小叶X、下橄榄核和前庭核的前庭和视动子系统中的适应性变化如何可能有助于平衡控制。
