Intrinsic Excitability Increase in Cerebellar Purkinje Cells after Delay Eye-Blink Conditioning in Mice

Abstract

Cerebellar-based learning is thought to rely on synaptic plasticity, particularly at synaptic inputs to Purkinje cells. Recently, however, other complementary mechanisms have been identified. Intrinsic plasticity is one such mechanism, and depends in part on the downregulation of calcium-dependent SK-type K ϩ channels, which contribute to a medium-slow afterhyperpolarization (AHP) after spike bursts, regulating membrane excitability. In the hippocampus, intrinsic plasticity plays a role in trace eye-blink conditioning; however, corresponding excitability changes in the cerebellum in associative learning, such as in trace or delay eye-blink conditioning, are less well studied. Whole-cell patch-clamp recordings were obtained from Purkinje cells in cerebellar slices prepared from male mice ϳ48 h after they learned a delay eye-blink conditioning task. Over a period of repeated training sessions, mice received either paired trials of a tone coterminating with a periorbital shock (conditioning) or trials in which these stimuli were randomly presented in an unpaired manner (pseudoconditioning). Purkinje cells from conditioned mice show a significantly reduced AHP after trains of parallel fiber stimuli and after climbing fiber evoked complex spikes. The number of spikelets in the complex spike waveform is increased after conditioning. Moreover, we find that SK-dependent intrinsic plasticity is occluded in conditioned, but not pseudoconditioned mice. These findings show that excitability is enhanced in Purkinje cells after delay eye-blink conditioning, and point toward a downregulation of SK channels as a potential underlying mechanism. The observation that this learning effect lasts at least up to 2 d after training shows that intrinsic plasticity regulates excitability in the long term.

Decreased intrinsic excitability of cerebellar Purkinje cells following optokinetic learning in mice

“…Taken our results together, it would be expected that a decrease in the intrinsic excitability was induced in the cerebellar PC of the OKR learning group by an increase in the current threshold for generating AP. Our result supports the emerging hypothesis that cerebellar memory may be implemented not only by a change in synaptic transmission in the Purkinje cell, but also change in the intrinsic excitability [ 5 – 8 , 13 , 14 ]. Given that the intrinsic excitability of neurons is influenced by the conductance of various transmembrane ion channels that affect the passive and active membrane properties of the neuron, a further attempt should be made to determine the ion conductance that mediates the reduced excitability of cerebellar PCs after OKR learning.…”

“…To address our question, we utilized an ex vivo approach, in which whole-cell patch-clamp recordings were performed from PCs in acute cerebellar slices prepared from mice that underwent OKR learning of 50 min. A similar ex vivo approach has been already taken to elucidate a role of intrinsic excitability in delay eye-blinking conditioning, another form of cerebellum-dependent learning [ 7 , 8 ].…”

Heterogeneity of intrinsic plasticity in cerebellar Purkinje cells linked with cortical molecular zones

“…Ca 2+ then activates PLCβ4 further and also protein phosphatase 1 (PP1), protein phosphatase 2A (PP2A), and protein phosphatase 2B (PP2B), which induce LTP of the PF-PC synaptic transmission ( Belmeguenai et al., 2010 ). Furthermore, these phosphatases also suppress the small conductance Ca 2+ -activated K channel (SK channel) putatively involved in the mAHP ( Belmeguenai et al., 2010 ; Grasselli et al., 2020 ; Titley et al., 2020 ). The present result showed specific involvement of the SK channel in the LTP-IE of Z- PCs, thereby suggesting that the blockade of the SK channel by these phosphatases activated by Ca 2+ is the mechanism of the enhanced LTP-IE in Z- PCs.…”

Differential spatiotemporal development of Purkinje cell populations and cerebellum-dependent sensorimotor behaviors

“…LTD can be readily induced in the anterior regions of juvenile PCs ( Kim, 2013 ) and LTD-deficient mice do not have impaired EBC, arguing against a central role for LTD in the EBC impairment in juvenile mice. Intrinsic excitability is increased after EBC ( Schreurs et al, 1997 ; Titley et al, 2020 ) and deletion of calcium-activated potassium channel SK2 ablated this plasticity of intrinsic excitability (intrinsic plasticity) and resulted in impaired EBC, but enhanced VOR adaptation ( Grasselli et al, 2020 ), a phenotype that is in line with the juvenile phenotype ( Hesslow, 1994b ). Thus, a lack of ability to reach higher levels of excitability by young anterior Z– PCs could explain the lower performance in the P21 animals.…”