Journal
JOURNAL OF NEUROSCIENCE
Volume 27, Issue 18, Pages 4910-4918Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.5528-06.2007
Keywords
bat; best frequency; neuromodulatory systems; reorganization; stress; tonotopic map
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Funding
- NIDCD NIH HHS [R56 DC000175, DC-000175, R01 DC000175] Funding Source: Medline
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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-HT2A receptors are mostly expressed on pyramidal neurons and their activation improves learning and memory. We applied 5-HT, an agonist (alpha-methyl-5-HT), or an antagonist (ritanserin) of 5-HT2A 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) alpha-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.
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