Decreased intrinsic excitability of cerebellar Purkinje cells following optokinetic learning in mice
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Decreased intrinsic excitability of cerebellar Purkinje cells following optokinetic learning in mice Yong Gyu Kim1,2 and Sang Jeong Kim1,2*
Abstract The optokinetic response (OKR), a reflexive eye movement evoked by a motion of the visual field, is known to adapt its strength to cope with an environmental change throughout life, which is a type of cerebellum-dependent learning. Previous studies suggested that OKR learning induces changes in in-vivo spiking activity and synaptic transmission of the cerebellar Purkinje cell (PC). Despite the recent emphasis on the importance of the intrinsic excitability related to learning and memory, the direct correlation between the intrinsic excitability of PCs and OKR learning has not been tested. In the present study, by utilizing the whole-cell patch-clamp recording, we compared the responses of cerebellar PCs to somatic current injection between the control and learned groups. We found that the neurons from the learned group showed a significant reduction in mean firing rate compared with neurons in the control group. In the analysis of single action potential (AP), we revealed that the rheobase current for the generation of single AP was increased by OKR learning, while AP threshold, AP amplitude, and afterhyperpolarization amplitude were not altered. Taken together, our result suggests that the decrease in the intrinsic excitability was induced in the cerebellar PC of learned group by an increase in the current threshold for generating AP. Keywords: Intrinsic excitability, Cerebellum, Purkinje cell, Oculomotor learning Main text The optokinetic response (OKR) is a reflex of eye movement that follows the motion of the visual field, which stabilizes an image on the retina. The OKR is exhibited to adapt to changes in the environment throughout life. The cerebellum is well-known to participate in this motor learning as an adaptive controller [1]. The cerebellar Purkinje cell (PC) lies in the center of the adaptive controlling unit. PCs are the sole output of the cerebellum that converge two primary afferent pathways, the parallel fiber (PF) pathway carrying vestibular signals and climbing fiber carrying the error signal in their dendrites. Due
*Correspondence: [email protected] 1 Department of Physiology, Seoul National University College of Medicine, 103 Daehangno, Jongro‑gu, Seoul 03080, Republic of Korea Full list of author information is available at the end of the article
to the significance of PCs in neural circuitry modulating OKR, many studies have attempted to find cellular traces of OKR memory in PCs. Early studies performed in vivo unit recording from cerebellar PCs of rabbits in OKR learning, which revealed that spiking activities of PCs were altered after OKR learning in response to optokinetic stimuli [2]. More recently, several studies observed structural and functional changes in PF-PC synapses after OKR learning [3, 4]. However, although it has been suggested that the intrinsic excitability is considered as a crucial cellular cor
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