Kir3 channel blockade in the cerebellar cortex suppresses performance of classically conditioned Purkinje cell responses

Fredrik Johansson,Germund Hesslow

doi:10.1038/s41598-020-72581-8

Abstract

In the eyeblink conditioning paradigm, cerebellar Purkinje cells learn to respond to the conditional stimulus with an adaptively timed pause in its spontaneous firing. Evidence suggests that the pause is elicited by glutamate released from parallel fibers and acting on metabotropic receptors (mGluR7) which initiates a delayed-onset suppression of firing. We suggested that G protein activation of hyperpolarizing Kir3 channels (or ‘GIRK’, G protein-coupled inwardly-rectifying K+ channels) could be part of such a mechanism. Application of the Kir3 antagonist Tertiapin-LQ locally in the superficial layers of the cerebellar cortex in decerebrate ferrets suppressed normal performance of Purkinje cell pause responses to the conditional stimulus. Importantly, there was no detectable effect on spontaneous firing. These findings suggest that intact functioning of Kir3 channels in the cerebellar cortex is required for normal conditioned Purkinje cell responses.

Highlights

In the eyeblink conditioning paradigm, cerebellar Purkinje cells learn to respond to the conditional stimulus with an adaptively timed pause in its spontaneous firing
When the Purkinje cells responded to the conditional stimulus (CS) with characteristic pause conditional blink response (CR) (Fig. 1a), usually after 2–3 h of conditioning, drugs were applied in a nanoliter range (~ 0.5–1.5 nl) injected 15 μm from the tip of the recording electrode
A considerably increased spontaneous firing rate or otherwise altered firing behavior could plausibly be disruptive for the expression of a Purkinje cell CR

Summary

Introduction

In the eyeblink conditioning paradigm, cerebellar Purkinje cells learn to respond to the conditional stimulus with an adaptively timed pause in its spontaneous firing. If a conditional stimulus (CS), repeatedly precedes an unconditional blink-eliciting stimulus (US), at a fixed delay, it acquires the ability to elicit a conditional blink response (CR) that peaks near the expected time of the U S1–3 This learning depends on the cerebellar c ortex[4] where Purkinje cells receive information about the CS and US via mossy/ parallel fibers and climbing fibers, r espectively[5,6,7,8]. Purkinje cells learn adaptively timed CRs to a CS consisting of a uniform train of stimuli repetitively applied to the same parallel fibers, i.e. when the upstream network is bypassed[21]. The evidence suggests that timed Purkinje cell CRs are mediated by a mechanism intrinsic to the Purkinje cell, which is activated by parallel fiber release of glutamate acting on mGluR722

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