Morphological and Electrophysiological Properties of GABAergic and Non-GABAergic Cells in the Deep Cerebellar Nuclei

Abstract

The deep cerebellar nuclei (DCN) integrate inputs from the brain stem, the inferior olive, and the spinal cord with Purkinje cell output from cerebellar cortex and provide the major output of the cerebellum. Despite their crucial function in motor control and learning, the various populations of neurons in the DCN are poorly defined and characterized. Importantly, differences in electrophysiological properties between glutamatergic and GABAergic cells of the DCN have been largely elusive. Here, we used glutamate decarboxylase (GAD) 67-green fluorescent protein (GFP) knock-in mice to unambiguously identify GABAergic (GAD-positive) and non-GABAergic (GAD-negative, most likely glutamatergic) neurons of the DCN. Morphological analysis of DCN neurons patch-clamped with biocytin-containing electrodes revealed a significant overlap in the distributions of the soma sizes of GAD-positive and GAD-negative cells. Compared with GAD-negative DCN neurons, GAD-positive DCN neurons fire broader action potentials, display stronger frequency accommodation, and do not reach as high firing frequencies during depolarizing current injections. Furthermore, GAD-positive cells display slower spontaneous firing rates and have a more shallow frequency-to-current relationship than the GAD-negative cells but exhibit a longer-lasting rebound depolarization and associated spiking after a transient hyperpolarization. In contrast to the rather homogeneous population of GAD-positive cells, the GAD-negative cells were found to consist of two distinct populations as defined by cell size and electrophysiological features. We conclude that GABAergic DCN neurons are specialized to convey phasic spike rate information, whereas tonic spike rate is more faithfully relayed by the large non-GABAergic cells.

Rescue of Motor Coordination by Purkinje Cell-Targeted Restoration of Kv3.3 Channels inKcnc3-Null Mice RequiresKcnc1

“…5E) are SMI-32 positive and GAD67 negative (data not shown). DCN neurons with areas of more than ϳ300 m 2 are consistently GAD67 negative (Uusisaari et al, 2007). These observations support the notion that the large neurons identified by Alexa Fluor 488 fills after intracellular recording (Fig.…”

“…Glutamatergic projection neurons were evidenced by their large size (Chan-Palay, 1977;Kumoi et al, 1988;Batini et al, 1992;Aizenman et al, 2003). In contrast to other brain areas in the DCN, it is the large neurons that are relatively fast spiking (Uusisaari et al, 2007). We restricted our analysis to the apparent murine counterpart of the weak-burst subtype classified in rat (Molineux et al, 2006 and by their distinctive electrophysiological signature in response to depolarizing current injection steps or upon relief of hyperpolarizing current steps (Fig.…”

“…For this to be the case, Kv3.1 and Kv3.3 subunits must be expressed in the same cells, presumably large, glutamatergic projection neurons, which are inferred to be those endowed with especially brief action potentials (Uusisaari et al, 2007). To determine the distribution of Kv3 channels in the DCN and validate the neurochemical identity of large cells, we performed immunostaining with Kv3 channel-specific antibodies.…”

“…These cells could be another locus where redundancy could account for the behavior; however, action potentials of wild-type GAD67-positive neurons are already considerably broader than in large neurons (Uusisaari et al, 2007). Finally, another factor that could explain the lack of a coordination rescue in Ϫ/Ϫ; Ϫ/Ϫ mice is the presence of other, superimposed motor phenotypes that may be independent of cerebellar function.…”

Plasma Membrane Ca2+ATPase 2 Contributes to Short-Term Synapse Plasticity at the Parallel Fiber to Purkinje Neuron Synapse

“…PNs were filled with biocytin (Sigma, Poole, UK) and processed (Uusisaari et al, 2007) before visualization with a C1si spectral confocal (Nikon, Tokyo, Japan). Images were collected at 1 m depth intervals, reconstructed, and analyzed with ImagePro 6 (Media Cybernetics, Bethesda, MD).…”