GABAergic synaptic communication in the GABAergic and non-GABAergic cells in the deep cerebellar nuclei

doi:10.1016/j.neuroscience.2008.07.060

Neuroscience

Volume 156, Issue 3, 15 October 2008, Pages 537-549

https://doi.org/10.1016/j.neuroscience.2008.07.060 Get rights and content

Abstract

The deep cerebellar nuclei (DCN) are the final integrative units of the cerebellar network. The strongest single afferent to the DCN is formed by GABAergic Purkinje neuron axons whose synapses constitute the majority of all synapses in the DCN, with their action strongly regulating the intrinsic activity of their target neurons. Although this is well established, it remains unclear whether all DCN cell groups receive a functionally similar inhibitory input.

We previously characterized three types of mouse DCN neurons based on the expression of glutamic acid decarboxylase isoform 67 (GAD67), their active membrane properties and morphological features. Here we describe the GABAergic synapses in these cell groups and show that spontaneous GABAergic synaptic activity can be seen in all three cell types. Since the majority of DCN neurons fire action potentials spontaneously at high frequencies both in vivo and in vitro, we expected that spontaneous GABAergic synaptic activities mediated by intra-DCN synaptic connections could be uncovered by their sensitivity to TTX. However, TTX had little effect on spontaneous synaptic activity. It seems, therefore that functional GABAergic connectivity within the DCN is sparse and/or weak at least under our experimental conditions. Even though present in all cell types, the spontaneous GABAergic events showed significant differences between the cell types. The synaptic currents in GABAergic cells had lower amplitude, lower frequency and slower kinetics than those of non-GABAergic cells. These differences could not be sufficiently explained by considering only cell size differences or a differential GABA_A-receptor α-subunit composition. Rather, the main differentiating factor appears to be the dendritic localization of GABAergic synapses in the GABAergic cells.

Section snippets

Slice preparation

The acute DCN slice is a notoriously difficult preparation that allows systematic patch-clamp studies in juvenile animals only. Young mice between postnatal days 14 and 21 from a GAD67-GFP knock in line (Tamamaki et al., 03) were anesthetized with halothane and decapitated. To ensure that all animals had reached the same minimal developmental stage, only animals with fully open eyes were used. The cerebellum was quickly removed and mounted for sectioning with a vibratome (Leica VT100S, Leica

Spontaneous, TTX-insensitive post-synaptic activity in the DCN cells

In all three previously-described DCN cell types (Uusisaari et al., 2007) spontaneous PSCs were observed in whole-cell voltage-clamp recording at V_h=−65 mV using high-Cl⁻ patch electrodes (n=53, 36, and 61 cells for GADnL, GADnS and GAD+ cells, respectively). Typical examples of PSCs are shown in the upper panel of Fig. 1. They were on the whole resistant to addition of 1 μM TTX to the bath solution (n=4 cells for each group) (Fig. 1, lower panel), and thus were mostly independent of

Different frequency of IPSCs in GAD+ and GAD− cells

The frequency of IPSCs was much higher in GAD− than in GAD+ cells. Smaller cells can physically accommodate fewer synapses and this could translate into fewer spontaneous synaptic events. The observed difference in IPSC frequency could therefore simply reflect the smaller membrane area of GAD+ cells. Comparing the individual cell body sizes and event frequencies revealed that the difference in cell body size between the GAD+ and GADnS cells is not sufficient to explain the almost 10-fold

Acknowledgments

We thank all members of the Laboratory for Neuronal Circuit Dynamics for helpful comments and suggestions and Dr. Steve Middleton in particular for language advice. The work was supported by intramural funds provided by RIKEN BSI.

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Cellular neuroscienceGABAergic synaptic communication in the GABAergic and non-GABAergic cells in the deep cerebellar nuclei

Abstract

Section snippets

Slice preparation

Spontaneous, TTX-insensitive post-synaptic activity in the DCN cells

Different frequency of IPSCs in GAD+ and GAD− cells

Acknowledgments

Neuron

Mol Brain Res

Neuropharmacology

Prog Neurobiol

Neuron

Neurosci Lett

Neuropharmacology

Brain Res

Biophys J

Trends Neurosci

Neuron

Brain Res

Brain Res

Rapid, synaptically driven increases in the intrinsic excitability of cerebellar deep nuclear neurons

Nat Neurosci

Morphological correlates of intrinsic electrical excitability in neurons of the deep cerebellar nuclei

J Neurophysiol

Interaction of Kv3 potassium channels and resurgent sodium current influences the rate of spontaneous firing of Purkinje neurons

J Neurosci

Subcellular localization of the voltage-gated potassium channels Kv3.1b and Kv3.3 in the cerebellar dentate nucleus of Gad67-Gfp transgenic mice

Postsynaptic currents in deep cerebellar nuclei

J Neurophysiol

Transgenic mouse lines subdivide medial vestibular nucleus neurons into discrete, neurochemically distinct populations

J Neurosci

Desensitization and binding properties determine distinct alpha1beta2gamma2 and alpha3beta2gamma2 GABAA receptor-channel kinetic behavior

Eur J Neurosci

Differential number of glycine- and GABA-immunopositive neurons and terminals in the deep cerebellar nuclei of normal and Purkinje cell degeneration mutant mice

J Comp Neurol

Kinetic and pharmacological properties of GABAA receptors in single thalamic neurons and GABAA subunit expression

J Neurophysiol

Inhibitory synaptic transmission differs in mouse type A and B medial vestibular nucleus neurons in vitro

J Neurophysiol

Cerebellar dentate nucleus: organization, cytology and transmitters

Colocalization of neurotransmitters in the deep cerebellar nuclei

J Neurocytol

Two types of neurons in the rat cerebellar nuclei as distinguished by membrane potentials and intracellular fillings

J Neurophysiol

Postsynaptic targets of Purkinje cell terminals in the cerebellar and vestibular nuclei of the rat

Eur J Neurosci

Cellular neuroscience
GABAergic synaptic communication in the GABAergic and non-GABAergic cells in the deep cerebellar nuclei