Journal
ENEURO
Volume 3, Issue 5, Pages -Publisher
SOC NEUROSCIENCE
DOI: 10.1523/ENEURO.0257-16.2016
Keywords
5-HT; odor discrimination; odor learning; operant behavior; psychophysics; reversal learning
Categories
Funding
- National Institute on Deafness and Other Communication Disorders, National Institutes of Health [100000055, R01DC014443, F31DC014615]
- National Institute of Mental Health, National Institutes of Health [100000025, R01MH062723, P50MH096972, F30MH099704]
- Case Western Reserve University [T32GM007250]
- National Science Foundation [IOS-1121471]
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The neurotransmitter serotonin (5-HT) is considered a powerful modulator of sensory system organization and function in a wide range of animals. The olfactory system is innervated by midbrain 5-HT neurons into both its primary and secondary odor-processing stages. Facilitated by this circuitry, 5-HT and its receptors modulate olfactory system function, including odor information input to the olfactory bulb. It is unknown, however, whether the olfactory system requires 5-HT for even its most basic behavioral functions. To address this question, we established a conditional genetic approach to specifically target adult brain tryptophan hydroxylase 2 (Tph2), encoding the rate-limiting enzyme in brain 5-HT synthesis, and nearly eliminate 5-HT from the mouse forebrain. Using this novel model, we investigated the behavior of 5-HT-depleted mice during performance in an olfactory go/no-go task. Surprisingly, the near elimination of 5-HT from the forebrain, including the olfactory bulbs, had no detectable effect on the ability of mice to perform the odor-based task. Tph2-targeted mice not only were able to learn the task, but also had levels of odor acuity similar to those of control mice when performing coarse odor discrimination. Both groups of mice spent similar amounts of time sampling odors during decision-making. Furthermore, odor reversal learning was identical between 5-HT-depleted and control mice. These results suggest that 5-HT neurotransmission is not necessary for the most essential aspects of olfaction, including odor learning, discrimination, and certain forms of cognitive flexibility.
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