Serotonergic Modulation of the Olfactory Bulb The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Provost, Allison. 2015. Serotonergic Modulation of the Olfactory Bulb. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences. Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:17463145 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA Serotoninergic Modulation of the Olfactory Bulb A dissertation presented by Allison Christine Provost to The Division of Medical Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Neurobiology Harvard University Cambridge, MA March 2015 © 2015 – Allison Christine Provost All rights reserved ! ! Dissertation Advisor: Dr. Venkatesh N. Murthy Allison Christine Provost Serotoninergic modulation of the olfactory bulb Abstract Serotonin is a neuromodulator whose actions are thought to modulate mood and brain states. Growing evidence correlates perturbations in the serotonergic system with neuropsychiatric diseases ranging from depression to schizophrenia. The dorsal raphe nucleus (DRN), a serotonergic cluster of neurons in the brainstem, projects widely throughout anterior brain regions, including the olfactory bulb. Electrophysiological recordings from the DRN show that its activity fluctuates with behavior over hundreds of milliseconds. Study of serotonergic modulation of the olfactory bulb has focused on modulation on the timescale of brain states (minutes to hours). This dissertation describes our work to understand how serotonergic inputs affect olfactory bulb codes on the time scale of behavior. Here we show that the serotonergic system plays a role in olfactory bulb coding on fast time scales (hundreds of milliseconds to seconds). Mitral and tufted cells, the two primary types of olfactory bulb output neurons, send olfactory information to distinct downstream targets. Brief stimulation of the DRN led to excitation of tufted cells at rest and potentiation of their odor responses. While mitral cells at rest were also excited by DRN activation, their odor responses could be suppressed or potentiated. This bidirectional modulation led to improved pattern separation of mitral cell odor responses. In vitro whole-cell recordings revealed that specific optogenetic activation of raphe axons affected bulbar neurons through dual release of serotonin and glutamate. Our data indicate that the raphe nuclei, in addition to their role in neuromodulation of brain states, are also involved in fast sub-second top-down modulation, similar to cortical feedback. Notably, this modulation can differentially sensitize or decorrelate distinct output channels. """! ! ! This work sheds light on the function of the serotonergic system in healthy brains, and future work will explore how this modulatory signature in olfactory outputs may be altered in diseased states. "#! ! ! Table of contents Abstract iii Table of contents v Acknowledgments vi Chapter 1 1 Introduction Chapter 2 31 Rapid and distinct effects of serotonergic system activation on parallel olfactory bulb output channels! Chapter 3 73 The intersection of the serotonergic system and olfactory bulb processing Chapter 4 108 Concluding remarks Chapter 5 119 Appendix A: Functional and anatomical heterogeneous glomeruli in the OMP null mouse Citations 148 #! ! ! Acknowledgements I would like to thank Dr. Venkatesh Murthy for his support throughout my graduate career. I am extremely grateful for his investment in my success. I would also like to thank all the members of the Murthy lab for teaching me numerous scientific techniques and for their intellectual contributions and critical analysis of my work. In particular, I would like to acknowledge Vikrant Kapoor for invaluable technical support and fruitful collaborations. I am grateful for administrative support from the Program in Neuroscience, the Division of Medical Sciences, and the Graduate School of Arts and Sciences. I am also very thankful to Drs. Rachel Wilson, Nao Uchida, Bence Ölveczky, and Florian Engert for serving on various committees on my behalf. Their scientific and personal advice throughout the years has guided my research and future plans. I particularly thank Dr. Rachel Wilson for serving as the chair of all of my committee meetings, including my Dissertation Examination Committee. Also thank you to Drs. Michela Fagiolini, Robert Sandeep Datta, and Ian Davison for their participation on my Dissertation Examination Committee. I would also like to thank Harvard Graduate Women in Science and Engineering (HGWISE) for cultivating a wonderful campus community across labs and departments. I am thankful to Drs. Beate Lanske and Joanne Kamens who mentored me through the HGWISE Mentoring Program. I am grateful for their advice and efforts on my behalf. Finally, thanks to my family and friends for their love and encouragement. In particular, I must thank Peter Goldman for proofreading this thesis and being generally wonderful. Thank you to everyone who has been part of this journey. I have learned a tremendous amount and feel very lucky to have had the opportunity. This research was supported by fellowships from the National Science Foundation and the Dr. Mortimer and Theresa Sackler Foundation. #"! ! Chapter 1: Introduction In the 5th century BC, Plato hypothesized that smells could be classified along a spectrum with two extremes, painful and pleasant. Modern scientists supported his hypothesis and demonstrated that the classification of smells varies on along a spectrum RIµSOHDVDQWQHVV¶ (Khan et al., 2007; Koulakov et al., 2011). The study of smell has carried on over the millennia following Plato. Why are we, as humans and scientists, interested in understanding smell? Perhaps because it allows us to better understand ourselves. As the experience of tea and a PDGHOHLQHELVFXLWGURYHPHPRULHVRI3URXVW¶VFKLOGKRRGWRRYHUZKHOPKLPWKHVHQVHRIVPHOO enriches our lives and helps knit together the poignant memories and experiences that make us individuals. The direct projections from the early olfactory areas to cortical and subcortical brain regions, associated with cognitive and emotional processing, may be the anatomical substrates for the Proustian phenomenon. But whether or not this experience can be explained by science does not guide our exploration of the subject, but rather fuels our interest. In this introduction, I will review the basics of the olfactory bulb (OB) circuit, focusing particularly on the differentiating aspects of specific classes of principal neurons. Next, I will discuss the functional aspects of the serotonergic system and its influence on sensory processing and behavior. Serotonin is a utilitarian molecule implicated in multiple neural processes, behaviors, and disease states (Audero et al., 2008; Celada et al., 2013; Cools et al., 2008a; Jonnakuty and Gragnoli, 2008; Kim and Camilleri, 2000; Monti, 2011). Here, I explore its function in healthy brains in order to better understand aberrations that arise in diseased/disordered brains. The flow of olfactory information Olfactory information from the environment is transduced at the olfactory epithelium in the nasal cavity and then travels to the OB. The OB has many downstream targets (Fig. 1-1) including the anterior olfactory nucleus (also referred to as the anterior olfactory cortex), anterior and posterior piriform cortex, cortical amygdala (also referred to as the posterolateral amygdala), ! ʹ! )LJXUH-7KHIORZRIROIDFWRU\LQIRUPDWLRQ'LDJUDPRIWKHROIDFWRU\EXOE 2% SURMHFWLRQ WDUJHWVDQGRULJLQVRIIHHGEDFNWRWKH2%&RQQHFWLRQVEHWZHHQEUDLQUHJLRQVGRZQVWUHDPIURP WKH2%DUHQRWGHSLFWHG$QWHULRUROIDFWRU\QXFOHXV $21 $QWHULRUSLULIRUPFRUWH[ $3& 3RVWHULRUSLULIRUPFRUWH[ 33& (QWRUKLQDOFRUWH[ (QWR %DVDOIRUHEUDLQ %) 'RUVDOUDSKH QXFOHXV '51 /RFXVFRHUXOHXV /& &RUWLFDODP\JGDOD &R$ 2OIDFWRU\WXEHUFOH 27 0RGLILHGZLWKSHUPLVVLRQIURPRULJLQDOE\&*HRII/DX ! ͵! olfactory tubercle (a subdivision of the striatum), and entorhinal cortex ((Ghosh et al., 2011; Miyamichi et al., 2011; Sosulski et al., 2011) see (Haberly, 2001a; Wilson and Mainen, 2006) for review). This is a diverse set of efferent targets, and each locus is likely to distinctly contribute to experience and perception (Anderson et al., 2003; Haberly, 2001a; Poellinger et al., 2001). Some of these areas, such as the entorhinal cortex, amygdala, olfactory tubercle, and piriform cortex, are considered cognitive and emotional centers of the brain. It is impressive that projections from the OB, which are a single synapse into the central nervous system, reach these high level areas associated with cognition. This is in stark contrast to the visual and auditory systems that send information through at least 5 synapses before reaching cognitive EUDLQUHJLRQV,WPD\EHWKDWLQIRUPDWLRQH[LWLQJWKH2%WRKLJKHUEUDLQDUHDVLVUHODWLYHO\µUDZ¶ but also that odor features are isolated by the efficient microcircuits in the OB. In addition to a plurality of downstream targets, the OB also receives immense amounts of feedback from the cortex and brainstem and midbrain neuromodulatory areas (Fig. 1-1). These feedback fibers ramify throughout the OB, likely influencing all aspects of odor processing there. In this thesis, I will focus on serotonergic feedback particularly,