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The Journal of Neuroscience, May 2, 2007, 27(18):4910-4918; doi:10.1523/JNEUROSCI.5528-06.2007

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Behavioral/Systems/Cognitive
Serotonergic Modulation of Plasticity of the Auditory Cortex Elicited by Fear Conditioning

Weiqing Ji and Nobuo Suga

Department of Biology, Washington University, St. Louis, Missouri 63130

Correspondence should be addressed to Nobuo Suga, Department of Biology, Washington University, One Brookings Drive, St. Louis, MO 63130. Email: suga{at}biology.wustl.edu

In the awake big brown bat, 30 min auditory fear conditioning elicits conditioned heart rate decrease and long-term best frequency (BF) shifts of cortical auditory neurons toward the frequency of the conditioned tone; 15 min conditioning elicits subthreshold cortical BF shifts that can be augmented by acetylcholine. The fear conditioning causes stress and an increase in the cortical serotonin (5-HT) level. Serotonergic neurons in the raphe nuclei associated with stress and fear project to the cerebral cortex and cholinergic basal forebrain. Recently, it has been shown that 5-HT_2A receptors are mostly expressed on pyramidal neurons and their activation improves learning and memory. We applied 5-HT, an agonist (-methyl-5-HT), or an antagonist (ritanserin) of 5-HT_2A receptors to the primary auditory cortex and discovered the following drug effects: (1) 5-HT had no effect on the conditioned heart rate change, although it reduced the auditory responses; (2) 4 mM 5-HT augmented the subthreshold BF shifts, whereas 20 mM 5-HT did not; (3) 20 mM 5-HT reduced the long-term BF shifts and changed them into short-term; (4) -methyl-5-HT increased the auditory responses and augmented the subthreshold BF shifts as well as the long-term BF shifts; (5) in contrast, ritanserin reduced the auditory responses and reversed the direction of the BF shifts. Our data indicate that the BF shift can be modulated by serotonergic neurons that augment or reduce the BF shift or even reverse the direction of the BF shift. Therefore, not only the cholinergic system, but also the serotonergic system, plays an important role in cortical plasticity according to behavioral demands.

Key words: bat; best frequency; neuromodulatory systems; reorganization; stress; tonotopic map

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Received Dec. 20, 2006; revised March 29, 2007; accepted April 2, 2007.

Correspondence should be addressed to Nobuo Suga, Department of Biology, Washington University, One Brookings Drive, St. Louis, MO 63130. Email: suga{at}biology.wustl.edu

This article has been cited by other articles:

				N. Suga The neural circuit for tone-specific plasticity in the auditory system elicited by conditioning Learn. Mem., March 20, 2008; 15(4): 198 - 201. [Full Text] [PDF]

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