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The Journal of Neuroscience, August 8, 2007, 27(32):8719-8732; doi:10.1523/JNEUROSCI.1630-07.2007

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Cellular/Molecular
Dendritic HCN2 Channels Constrain Glutamate-Driven Excitability in Reticular Thalamic Neurons

Shui-Wang Ying,¹ Fan Jia,¹ Syed Y. Abbas,¹ Franz Hofmann,² Andreas Ludwig,³ and Peter A. Goldstein¹

¹C. V. Starr Laboratory for Molecular Neuropharmacology, Department of Anesthesiology, Weill Medical College, Cornell University, New York, New York 10021, ²Institut für Pharmakologie und Toxikologie, 80802 München, Germany, and ³Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany

Correspondence should be addressed to Dr. Peter A. Goldstein, Department of Anesthesiology, Weill Medical College, Cornell University, 1300 York Avenue, Room A-1050, New York, NY 10021. Email: pag2014{at}med.cornell.edu

Hyperpolarization activated cyclic nucleotide (HCN) gated channels conduct a current, I_h; how I_h influences excitability and spike firing depends primarily on channel distribution in subcellular compartments. For example, dendritic expression of HCN1 normalizes somatic voltage responses and spike output in hippocampal and cortical neurons. We reported previously that HCN2 is predominantly expressed in dendritic spines in reticular thalamic nucleus (RTN) neurons, but the functional impact of such nonsomatic HCN2 expression remains unknown. We examined the role of HCN2 expression in regulating RTN excitability and GABAergic output from RTN to thalamocortical relay neurons using wild-type and HCN2 knock-out mice. Pharmacological blockade of I_h significantly increased spike firing in RTN neurons and large spontaneous IPSC frequency in relay neurons; conversely, pharmacological enhancement of HCN channel function decreased spontaneous IPSC frequency. HCN2 deletion abolished I_h in RTN neurons and significantly decreased sensitivity to 8-bromo-cAMP and lamotrigine. Recapitulating the effects of I_h block, HCN2 deletion increased both temporal summation of EPSPs in RTN neurons as well as GABAergic output to postsynaptic relay neurons. The enhanced excitability of RTN neurons after I_h block required activation of ionotropic glutamate receptors; consistent with this was the colocalization of HCN2 and glutamate receptor 4 subunit immunoreactivities in dendritic spines of RTN neurons. The results indicate that, in mouse RTN neurons, HCN2 is the primary functional isoform underlying I_h and expression of HCN2 constrains excitatory synaptic integration.

Key words: I_h block; HCN2 knock-out; synaptic integration; RTN; immunohistochemistry; AMPA receptor

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Received Dec. 22, 2006; revised June 27, 2007; accepted June 27, 2007.

Correspondence should be addressed to Dr. Peter A. Goldstein, Department of Anesthesiology, Weill Medical College, Cornell University, 1300 York Avenue, Room A-1050, New York, NY 10021. Email: pag2014{at}med.cornell.edu

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