bims-climfi 2020-08-02 papers

Issue of 2020‒08‒02
two papers selected by
Jun Maruta
Mount Sinai Health System

Neuroscience. 2020 Jul 22. pii: S0306-4522(20)30462-0. [Epub ahead of print]

Ocular Reflex Adaptation as an Experimental Model of Cerebellar Learning -- In Memory of Masao Ito -.

Masao Ito proposed a cerebellar learning hypothesis with Marr and Albus in the early 1970s. He suggested that cerebellar flocculus (FL) Purkinje cells (PCs), which directly inhibit the vestibular nuclear neurons driving extraocular muscle motor neurons, adaptively control the horizontal vestibulo-ocular reflex (HVOR) through the modification of mossy and parallel fiber-mediated vestibular responsiveness by visual climbing fiber (CF) inputs. Later, it was suggested that the same FL PCs adaptively control the horizontal optokinetic response (HOKR) in the same manner through the modification of optokinetic responsiveness in rodents and rabbits. In 1982, Ito and his colleagues discovered the plasticity of long-term depression (LTD) at parallel fiber (PF)-PC synapses after conjunctive stimulation of mossy or parallel fibers with CFs. Long-term potentiation (LTP) at PF-PC synapses by weak PF stimulation alone was found later. Many lines of experimental evidence have supported their hypothesis using various experimental methods and materials for the past 50 years by many research groups. Although several controversial findings were presented regarding their hypothesis, the reasons underlying many of them were clarified. Today, their hypothesis is considered as a fundamental mechanism of cerebellar learning. Furthermore, it was found that the memory of adaptation is transferred from the FL to vestibular nuclei for consolidation by repetition of adaptation through the plasticity of vestibular nuclear neurons. In this article, after overviewing their cerebellar learning hypothesis, I discuss possible roles of LTD and LTP in gain-up and gain-down HVOR/HOKR adaptations and refer to the expansion of their hypothesis to cognitive functions.

Keywords: cerebellar learning; cognitive function; long-term depression and potentiation; motor memory; ocular reflex; synapse plasticity

DOI: https://doi.org/10.1016/j.neuroscience.2020.07.021

Neuroscience. 2020 Jul 24. pii: S0306-4522(20)30470-X. [Epub ahead of print]

Striped distribution pattern of Purkinje cells of different birthdates in the mouse cerebellar cortex studied with the Neurog2-CreER transgenic line.

Zhang J, Tran-Anh K, Hirata T, Sugihara I.

Heterogeneity of Purkinje cells (PCs) that are arranged into discrete longitudinally-striped compartments in the cerebellar cortex is related to the timing of PC generation. To understand the cerebellar compartmental organization, we mapped the PC birthdate (or differentiation timing) in the entire cerebellar cortex. We used the birthdate-tagging system of Neurog2-CreER (G2A) mice hybridized with the AldocV strain which visualizes the zebrin (aldolase C) longitudinal striped pattern. The birthdate-specific distribution pattern of PCs was arranged into longitudinally-oriented stripes consistently throughout almost all lobules except for the nodulus, paraflocculus, and flocculus, in which distinct stripes were observed. Boundaries of the birthdate stripes coincided with the boundary of zebrin stripes or located in the middle of a zebrin stripe. Each birthdate stripe contained PCs born in a particular period between embryonic day (E) 10.0 and E 13.5. In the vermis, PCs were chronologically distributed from lateral to medial stripes. In the paravermis, PCs of early birthdates were distributed in the long lateral zebrin-positive stripe (stripe 4+//5+) and the medially neighboring narrow zebrin-negative substripe (3d-//e2-), while PCs of late birthdates were distributed in the rest of all paravermal areas. In the hemisphere, PCs of early and late birthdates were intermingled in the majority of areas. The results indicate that the birthdate of a PC is a partial determinant for the zebrin compartment in which it is located. However, the correlation between the PC birthdate and the zebrin compartmentalization is complex and distinct among the vermis, paravermis, hemisphere, nodulus, and flocculus.

Keywords: Neurog2; Purkinje cells; aldolase C; cerebellar cortex; mice; neuronal birthdate; zebrin

DOI: https://doi.org/10.1016/j.neuroscience.2020.07.028