Raising cytosolic Cl⁻in cerebellar granule cells affects their excitability and vestibulo-ocular learning

Abstract

Cerebellar cortical throughput involved in motor control comprises granule cells (GCs) and Purkinje cells (PCs), both of which receive inhibitory GABAergic input from interneurons. The GABAergic input to PCs is essential for learning and consolidation of the vestibulo‐ocular reflex, but the role of GC excitability remains unclear. We now disrupted the Kcc2 K‐Cl cotransporter specifically in either cell type to manipulate their excitability and inhibition by GABAA‐receptor Cl− channels. Although Kcc2 may have a morphogenic role in synapse development, Kcc2 disruption neither changed synapse density nor spine morphology. In both GCs and PCs, disruption of Kcc2, but not Kcc3, increased [Cl−]i roughly two‐fold. The reduced Cl− gradient nearly abolished GABA‐induced hyperpolarization in PCs, but in GCs it merely affected excitability by membrane depolarization. Ablation of Kcc2 from GCs impaired consolidation of long‐term phase learning of the vestibulo‐ocular reflex, whereas baseline performance, short‐term gain‐decrease learning and gain consolidation remained intact. These functions, however, were affected by disruption of Kcc2 in PCs. GC excitability plays a previously unknown, but specific role in consolidation of phase learning.

Dissociation of locomotor and cerebellar deficits in a murine Angelman syndrome model

“…45 and for review In particular, the deficits observed in AS mice are strikingly similar to those identified in a recently reported mouse mutant with a granule cell-specific mutation in the KCC2 KCl cotransporter gene; this genetic manipulation depolarizes granule cells by increasing their cytosolic chloride concentration. Like AS mice, these mutants also show severely impaired phase-reversal learning, while their OKR, VOR, and VVOR basic motor performance and gain-decrease learning are unaffected (38). Together, these findings suggest that defective Golgi cell functioning might contribute to the observed cerebellar phase-reversal learning deficits in AS mice.…”

GABAA receptors increase excitability and conduction velocity of cerebellar parallel fiber axons

“…In other neurons, such as neocortical pyramidal cells, where GABA has been shown to depolarize axons, it is unclear whether NKCC1 is expressed in adults; however, KCC2 protein is excluded from the axonal compartments (Szabadics et al 2006). In the adult cerebellar cortex, both KCC2 and NKCC1 mRNA are present in granule cells (Mikawa et al 2002), and KCC2 protein appears to be completely absent in PFs (Seja et al 2012). Thus, either the presence of NKCC1 or the absence of KCC2 from PFs likely accounts for the compartmental differences in chloride reversal potential.…”

Cation-chloride cotransporters in neuronal development, plasticity and disease

“…For instance, in the simultaneous presence of KCC-mediated Cl − extrusion and GABA A receptor (GABA A R)-mediated Cl − influx, a dynamic steady state will be established in which changes in Cl − conductance or KCC activity will be reflected in [Cl − ] i . This classical pump–leak relationship 273 is made use of in experiments addressing the transport capacity of KCC2 and NKCC1 by experimentally inducing an exogenous excess or deficit of Cl − , respectively, in a neuron 5,146,185,274,275 .…”

“…1a). Nevertheless, the physiological roles of KCC3 in neurons remain largely unknown 5,6,51,116,117 (TABLE 1). The idea that KCC3 has important roles in the healthy nervous system is strongly supported by the fact that peripheral neuropathy associated with agenesis of the corpus callosum (ACCPN; also known as Andermann syndrome) is caused by genetic impairment of KCC3 (REFS 46,116,118).…”