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Cerebral Cortex Advance Access published online on October 26, 2005
Cerebral Cortex, doi:10.1093/cercor/bhj065
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© The Author 2005. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Article

High-Frequency Stimulation Together with Adrenoceptor Activation Facilitates the Maintenance of Long-Term Potentiation at Visual Cortical Inhibitory Synapses

Kazumasa Yamada 1, Tsuyoshi Inagaki 1, Rie Funahashi 1, Yumiko Yoshimura 1, and Yukio Komatsu 1*

1 Department of Visual Neuroscience, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan

* To whom correspondence should be addressed.
Yukio Komatsu, E-mail: komatsu{at}riem.nagoya-u.ac.jp


  Abstract

Long-term potentiation (LTP) at inhibitory synapses of rat visual cortex requires firing of presynaptic cells for maintenance, at least at a low frequency. We examined the roles of adrenoceptors in this LTP maintenance. Although high-frequency stimulation (HFS) failed to produce LTP in normal Ca2+ medium, it produced pathway-specific LTP with addition of noradrenaline to the medium soon after HFS. However, this LTP disappeared after washout of noradrenaline. HFS applied during noradrenaline application produced LTP persisting even after washout, indicating that HFS together with adrenoceptor activation makes the adrenergic facilitation enduring. After washout, LTP was produced further by HFS of the conditioned, but not the unconditioned, pathway by the first HFS. Pharmacological examination demonstrated that {alpha}2 and {beta}, but not {alpha}1, receptors facilitated LTP maintenance synergistically. Bath application, but not postsynaptic loading, of either the adenylyl cyclase activator forskolin or the protein kinase C (PKC) activator phorbol ester facilitated LTP maintenance. These results suggest that adrenergic facilitation of LTP maintenance is mediated by presynaptic adrenoceptors via a subfamily of adenylyl cyclases stimulated by Gs{alpha}, Gi{beta}{gamma}, and PKC. Thus, it is likely that the activity of noradrenergic afferents takes part in the control of LTP duration at visual cortical inhibitory synapses.

Keywords: adrenergic; inhibitory synapses; LTP; maintenance; visual cortex.
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