van Neerven J, Pompeiano O, Collewijn H
Department of Physiology I, Erasmus University Rotterdam, The Netherlands.
Prog Brain Res. 1991;88:485-97. doi: 10.1016/s0079-6123(08)63829-7.
The role of the vesitibulo-cerebellum of the rabbit in the control of the vestibulo-ocular response (VOR) and optokinetic response (OKR) reflexes was investigated by bilateral microinjections, into the flocculus, of substances affecting GABAergic or noradrenergic neurotransmission. GABA, the main transmitter through which cerebellar interneurons inhibit Purkinje cells directly or indirectly, acts normally through GABAA receptors (mainly located in the granular layer) and GABAB receptors (predominantly located in the molecular layer). Despite this different distribution, floccular injections of the GABAA agonist muscimol and of the GABAB agonist baclofen had a similar effect, presumably by profound inhibition of Purkinje cells. This effect consisted of a reduction in the gain of the VOR (in darkness and in light) as well as of the OKR by at least 50%. This provides firm evidence that the net effect of normal Purkinje-cell activity in the flocculus is to enhance the VOR and OKR, rather than to inhibit these responses, as is sometimes supposed. Intrafloccular injections of the beta-noradrenergic agonist isoproterenol or the beta-noradrenergic antagonist sotalol did not affect the basic magnitude of the VOR and OKR. However, these substances markedly affected the adaptive processes, which cause the VOR and OKR to change its magnitude when this is no longer adequate in stabilizing the retinal image. By a suitable combination of vestibular and optokinetic stimuli, consistent upward changes in the gain of these reflexes could be reliably and reproducibly induced in uninjected animals. Floccular injections of sotalol impaired these adaptive changes markedly, whereas injections of isoproterenol enhanced the adaptation, particularly of the VOR measured in darkness. These findings strongly suggest that the effectuation of adaptive changes of vestibular, and possibly other, motor control systems is strongly facilitated by the noradrenergic innervation of the flocculus, which is normally provided by the locus coeruleus (LC), by way of the beta-receptor system, although the activity of this system does not directly affect the signal transmission supporting the basic reflexes as such.
通过向兔绒球双侧微量注射影响γ-氨基丁酸（GABA）能或去甲肾上腺素能神经传递的物质，研究了兔前庭小脑在控制前庭眼反射（VOR）和视动反射（OKR）中的作用。GABA是小脑中间神经元直接或间接抑制浦肯野细胞的主要递质，通常通过GABAA受体（主要位于颗粒层）和GABAB受体（主要位于分子层）发挥作用。尽管分布不同，但向绒球注射GABAA激动剂蝇蕈醇和GABAB激动剂巴氯芬具有相似的效果，可能是通过对浦肯野细胞的深度抑制实现的。这种效果包括在黑暗和光照条件下VOR以及OKR的增益至少降低50%。这提供了确凿的证据，表明绒球中正常浦肯野细胞活动的净效应是增强VOR和OKR，而不是像有时所认为的那样抑制这些反应。向绒球内注射β-肾上腺素能激动剂异丙肾上腺素或β-肾上腺素能拮抗剂索他洛尔并不影响VOR和OKR的基本幅度。然而，这些物质显著影响了适应性过程，当稳定视网膜图像不再足够时，适应性过程会使VOR和OKR改变其幅度。通过适当组合前庭和视动刺激，在未注射的动物中可以可靠且可重复地诱导这些反射增益持续向上变化。向绒球注射索他洛尔显著损害了这些适应性变化，而注射异丙肾上腺素则增强了适应性，特别是在黑暗中测量的VOR的适应性。这些发现强烈表明，绒球的去甲肾上腺素能神经支配（通常由蓝斑核通过β受体系统提供）极大地促进了前庭以及可能其他运动控制系统适应性变化的实现，尽管该系统的活动本身并不直接影响支持基本反射的信号传递。
