Adenosine A2A receptor neurons in the olfactory bulb mediate odor-guided behaviors in mice

doi:10.1016/j.brainres.2021.147590

Brain Research

Volume 1768, 1 October 2021, 147590

https://doi.org/10.1016/j.brainres.2021.147590 Get rights and content

Highlights:

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OB A_2AR neurons regulate odor-mediated food exploration in mice.
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OB A_2AR neurons mediate olfaction habituation and dishabituation in mice.
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OB A_2AR neurons are functionally connected to the OT and the Pir via excitatory glutamatergic release.

Abstract

Depression, rapid eye movement (REM) sleep behavior disorder, and altered olfaction are often present in Parkinson's disease. Our previous studies demonstrated the role of the olfactory bulb (OB) in causing REM sleep disturbances in depression. Furthermore, adenosine A_2A receptors (A_2AR) which are richly expressed in the OB, play an important role in the regulation of REM sleep. Caffeine, an adenosine A₁ receptors and A_2AR antagonist, and other A_2AR antagonists were reported to improve olfactory function and restore age-related olfactory deficits. Therefore, we hypothesized that the A_2AR neurons in the OB may regulate olfaction or odor-guided behaviors in mice. In the present study, we employed chemogenetics to specifically activate or inhibit neuronal activity. Then, buried food test and olfactory habituation/dishabituation test were performed to measure the changes in the mice's olfactory ability. We demonstrated that activation of OB neurons or OB A_2AR neurons shortened the latency of buried food test and enhanced olfactory habituation to the same odors and dishabituation to different odors; inhibition of these neurons showed the opposite effects. Photostimulation of ChR2-expressing OB A_2AR neuron terminals evoked inward current in the olfactory tubercle (OT) and the piriform cortex (Pir), which was blocked by glutamate receptor antagonists 2-amino-5-phosphonopentanoic acid and 6-cyano-7nitroquinoxaline-2,3-dione. Collectively, these results suggest that the OB mediates olfaction via A_2AR neurons in mice. Moreover, the excitatory glutamatergic release from OB neurons to the OT and the Pir were found responsible for the olfaction-mediated effects of OB A_2AR neurons.

Graphical abstract

Introduction

Recent studies have identified abnormalities in olfaction, depression, and rapid eye movement (REM) sleep disorders in Parkinson’s disease (PD) (Musiek and Holtzman, 2016). However, the underlying mechanisms of these symptoms in PD are not well characterized. The olfactory bulb (OB), an important center for processing olfactory information, contains multiple receptors such as adenosine A_2A receptors (A_2AR) (Wang et al., 2017). A_2AR play an important role in neuromuscular disorders (NMDs) which related to activities such as sleep-wake as well as anxiety anddepression (Carvalho et al., 2019, Kaster et al., 2015, Kim et al., 2019, Moreira-de-Sá et al., 2021). CGS21680, a highly selective yet blood–brain-barrier impermeable A_2AR agonist, was shown to promote sleep (Scammell et al., 2001). Caffeine, an adenosine A₁ receptors (A₁R) and A_2AR antagonist, induced wakefulness depending on A_2AR (Huang et al., 2005). These results suggest a predominant role of A_2AR neurons in regulating sleep (Huang et al., 2014, Li et al., 2020). Furthermore, in our previous studies, A_2AR in the OB was shown to suppress REM sleep in rodents (Wang et al., 2017). The above results indicate an important role of A_2AR in regulating sleep and wakefulness. Furthermore, it was also shown that caffeine could improve olfactory function in both close relatives of PD patients and healthy individuals (Berendse and Ponsen, 2006, Stafford and Orgill, 2020). Interestingly, for irregular caffeine consumers, caffeine enhanced olfactory sensitivity but reduced their capabilities to discriminate different odors. Moreover, caffeine, along with A_2AR antagonist ZM241385, successfully reversed the olfactory dysfunction caused by aging in rodents (Prediger et al., 2005). Based on the effects of A_2AR antagonists on olfactory function and involvement of A_2AR in the regulation of behaviors related to NMDs, we hypothesized that the A_2AR in the OB plays an important role in regulating olfaction.

To explore the role of OB in olfactory regulation and the underlying mechanism, we used designer receptors that are exclusively activated by designer drugs to specifically activate or inhibit OB neurons or OB A_2AR neurons. The results showed that chemogenetic activation or inhibition of the OB enhanced or attenuated olfaction, respectively. Furthermore, we found that specific activation or inhibition of the OB A_2AR neurons can enhance or reduce olfaction. Using electrophysiological recording combined with optogenetics, we found that the OB A_2AR neurons are functionally connected to the olfactory tubercle (OT) and the piriform cortex (Pir) via excitatory glutamatergic release. In summary, our results provide evidence of the involvement of OB A_2AR neurons in regulating olfaction through the excitatory pathway to the OT and the Pir.

Section snippets

Chemogenetic activation of OB neurons shortened BFT latency and enhanced olfactory habituation and dishabituation in WT mice

To investigate the role of OB neurons in olfaction, we employed the chemogenetic approach to regulate the activity of OB neurons. After a 3-week recovery from AAV-hSyn-hM3Dq-mCherry-WPRE-pA microinjections, WT mice were injected with clozapine-N-oxide (CNO) or vehicle and subjected to buried food test (BFT) and olfactory habituation and dishabituation test (OHDT) (Fig. 1 and Fig. 2A). Immunofluorescence staining of brain tissues showed that OB neurons expressed mCherry and DAPI (stained blue),

Discussion

We used chemogenetic experiments to demonstrate the important role of OB in the olfaction. Furthermore, bilateral chemogenetic specifically activated OB A_2AR neurons enhanced olfactory function. However, the opposite effect was observed after inhibition of OB A_2AR neurons, indicating the important role of OB A_2AR neurons in regulating olfaction. Previously, mice were injected intraperitoneally with A_2AR antagonists caffeine and ZM241385 before the behavioral tasks, including discrimination of

Animals

Male C57BL/6J mice (age: 6–8 weeks) were obtained from the Laboratory Animal Center, Chinese Academy of Sciences. We consider that the hormone status of female animals may affect sensory input to produce uncertain olfactory behavior (Dey et al., 2015), so this article only uses male animals for experiments. Mice were housed in individual cages under standardized conditions [temperature: 22 ± 2 ℃; relative humidity: 60% ± 2%; 12 h light–dark cycle (lights on at 07:00 Hrs, illumination intensity:

CRediT authorship contribution statement

Xiao Sun: Conceptualization, Methodology, Formal analysis, Writing - original draft, Visualization. Lei Li: Methodology, Formal analysis, Visualization. Hu-Yun-Long Zhang: Methodology, Formal analysis, Writing - original draft, Data curation. Wei He: Methodology, Formal analysis, Writing - original draft, Data curation. Dian-Ru Wang: Methodology, Formal analysis, Data curation, Visualization. Zhi-Li Huang: Writing - review & editing, Supervision. Yi-Qun Wang: Conceptualization, Writing - review

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We express our appreciation to Jiang-fan Chen and Cheng-wei Liu for providing A_2AR-cre mice.

Funding sources

This study was supported in part by grants-in-aid for scientific research from the National Natural Science Foundation of China (81871037, 82020108014 and 32070984), the National Key Research and Development Program of China (2020YFC2005301), Shanghai Municipal Science and Technology Major Project (2018SHZDZX01) and ZJLab, Program for Shanghai Outstanding Academic Leaders (to Z.-L.H), Shanghai Science and Technology Innovation Action Project (201409001800).

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¹: Xiao Sun and Lei Li contributed equally to this work.

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