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J Physiol Volume 581, Number 2, 709-724, June 1, 2007 DOI: 10.1113/jphysiol.2007.129106
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NEUROSCIENCE

Intrinsic properties and mechanisms of spontaneous firing in mouse cerebellar unipolar brush cells

 Marco J. Russo1,2, Enrico Mugnaini1,2 and Marco Martina1

1 Department of Physiology
2 Department of Cellular and Molecular Biology, Feinberg School of Medicine, Northwestern University, 303 E. Chicago Avenue, Chicago, IL 60611, USA

Neuronal firing patterns are determined by the cell's intrinsic electrical and morphological properties and are regulated by synaptic interactions. While the properties of cerebellar neurons have generally been studied in much detail, little is known about the unipolar brush cells (UBCs), a type of glutamatergic interneuron that is enriched in the granular layer of the mammalian vestibulocerebellum and participates in the representation of head orientation in space. Here we show that UBCs can be distinguished from adjacent granule cells on the basis of differences in membrane capacitance, input resistance and response to hyperpolarizing current injection. We also show that UBCs are intrinsically firing neurons. Using action potential clamp experiments and whole-cell recordings we demonstrate that two currents contribute to this property: a persistent TTX-sensitive sodium current and a ruthenium red-sensitive, TRP-like cationic current, both of which are active during interspike intervals and have reversal potentials positive to threshold. Interestingly, although UBCs are also endowed with a large Ih current, this current is not involved in their intrinsic firing, perhaps because it activates at voltages that are more hyperpolarized than those associated with autonomous activity.

(Received 30 January 2007; accepted after revision 19 March 2007; first published online 22 March 2007)
Corresponding author M. Martina: Department of Physiology, Northwestern University Feinberg School of Medicine, 303 E. Chicago Avenue, Chicago, IL 60611, USA. Email m-martina{at}northwestern.edu

This paper has online supplemental material.






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