Effects of experience on the early development of the olfactory system

In collaboration with Dr. Alan Fine, Department of Physiology & Biophysics

Olfactory cues play essential roles in psychosocial development. For instance, mother-infant bonding and mate selection are shaped by early olfactory experience; studies also show olfactory deficits associated with a large range of disorders such as autism, depression, anxiety, schizophrenia, obsessive compulsive disorder and various psychopathologies and lead to the hypothesis that disabilities in olfactory perception contribute to clinical aspects of these diseases. And yet, the olfactory system remains poorly understood and we are currently unable to explain, much less remediate, olfactory dysfunctions associated with serious medical and social consequences. Much of this lack of understanding can be traced to the extraordinary complexity of olfaction system with hundreds of genes uniquely expressed in the olfactory system of humans and other mammals. Fortunately, zebrafish, which have proven to be valuable models for understanding many other systems in our body, can also be exploited to better understand the sense of smell. While zebrafish share many genes and much of its basic neuroanatomy with humans, they have an olfactory system with only about 1/10 as many receptor genes and processing units (glomeruli) as found in most mammals. Here we propose to use zebrafish to examine how the ability to detect, discriminate and remember odours changes during early development. We will focus specifically on how early experience with odours changes both the ability to smell and the underlying circuitry of the brain. We anticipate that the results of these studies will help us better understand not only how we smell but also why odours that we first encountered as children can elicit powerful memories and shape social behaviours when presented decades later. Tools and concepts developed in this research will, in turn, permit us to examine how and why olfactory dysfunction contributes to the development of psychosocial problems associated with the disorders listed above.

Form and function of the olfactory and larval nervous systems in molluscs

The nervous systems of molluscs show a diversity which surpasses any other phylum, except perhaps the chordates. The brains and behaviours of cephalopods like the octopus were subjects of fascination for Aristotle, while those of sedentary chitons can be described only as rudimentary at best. And yet, we currently know very little about how the molluscan nervous system develops or how such diversity is generated through evolution. Moreover, knowledge of neural development derived from model organisms such as flies, worms and certain vertebrates appears inadequate to resolve this issue. This application proposes two lines of research aim at better understanding neural evolution and development within the molluscs. The first line will investigate the olfactory system and look for the basic units of sensory processing (glomeruli) as described in arthropods and vertebrates but largely unknown outside these two groups. Work on molluscs will not only inform us about how olfaction may have evolved in these animals but may provide insights into our own sense of smell. The second line involves investigation of the larval nervous system, which plays a critical role in early life and provides a scaffold on which the adult nervous system is built. The larval nervous system of molluscs is known to share similarities with larval nervous systems from across the animal kingdom and thus serves as a basis for comparison of animals with otherwise diverse body forms. Our work focuses on identification and morphology of cells which use acetylcholine and histamine as transmitters, and then examines their roles in behaviours that allow larvae to orient to chemicals, light, currents and gravity. Both lines of research will depend upon the use of multiple, combinational staining techniques coupled with high resolution microscopy and 3D reconstruction. As both the most varied and also the largest phylum in the Lophotrochozoa, the molluscs offer an important and unique perspective from current model species. While aimed largely at a better understanding of the diversity of life around us, the work also has implications for understanding larval and adult molluscs as major components of our ocean ecosystems and even as prized foods from aquaculture.

Autonomic nervous system control of cardiac output in zebrafish

In collaboration with Dr. Frank Smith, Department of Medical Neuroscience

Cardiac output is modulated by the autonomic nervous system (ANS driving the intracardiac nervous system (ICNS), the final common pathway for cardiac control. Neural regulation of the 4-chambered mammalian heart is complex, and because the ICNS is distributed throughout both atria and cannot be accessed in its entirety for study, our understanding of neural control of the mammalian heart is incomplete. With two chambers rather than the four of the mammalian heart, the hearts of zebrafish offer a more accessible experimental model for analyzing the neural control of cardiac output. Similar to the mammalian heart, fish hearts are dually innervated by the sympathetic and parasympathetic limbs of the ANS; the overall functions of these limbs also similar to their functions in mammalian hearts. In this study we aim to refine and elaborate upon previously established anatomy through identification of neural pathways in the zebrafish and the myocardial targets of autonomic innervation. In combination with immunohistochemical methods, electrophysiology and optical imaging will elucidate the types of responses evoked in the ICNS by vagal stimulation and the contribution of each limb of the ANS. It will thus be possible to eventually identify all the components of specific functional pathways that control heart rate or myocardial contractility, identification as yet not possible in the mammalian heart.

Effects of different modalities of simulated microgravity on the development of zebrafish

In collaboration with Dr. Frank Smith, Department of Medical Neuroscience

Given limited opportunities for space flights, ground based experiments represent an important means for providing initial data regarding the effects of microgravity to guide future work in space. Currently there are four commonly used methods to simulate microgravity for periods sufficient to investigate developmental processes: the rotating wall vessel (RWV), 2- and 3-D clinostats and the random positioning machine (RPM). To date most research simulating microgravity has been performed on cell cultures and suggests that simulated microgravity induces changes in the rates of cellular proliferation and differentiation. In this study we aim to test whether these effects were present in whole organisms. Our laboratory is currently developing protocols for the use of zebrafish embryos in the 3-D clinostat, as well as in the 2-D clinostat and RPM to test whether this trend is observed in other modalities of simulated microgravity (SMG). Our results will allow the first comparison of the effects of the different methods of simulating microgravity on whole-embryo development. These findings will provide insights into how zebrafish may develop in space, permitting better formulation of experiments to test the mechanisms by which microgravity affects ontogeny in this model organism.

Photos

Ctenophores

Molluscs

Urochordates

Zebrafish

Effects of wall compliance on functions of the swimbladder in zebrafish

In collaboration with Dr. Frank Smith, Department of Medical Neuroscience

Zebrafish use gas-filled swimbladders to maintain nearly neutral buoyancy and three-dimensional orientation (pitch and roll). The two-chambered swimbladder also contributes to hearing of the fish, via the Weberian apparatus which connects the anterior chamber to the acoustic labyrinth. Swimbladder volume, and thus its contributions to all these functions, varies with depth-related pressure as described by Boyle’s Law. The swimbladder volume at a given depth also depends on the elasticity of the swimbladder wall. In this study the effects of pressure on swimbladder volume, both in vivo and in situ, and the behaviour of the whole animal were observed, using pressure tanks which allowed simulations of vertical movement within the water column to a depth of 300 cm and a return to surface from a depth of 300 cm; results showing the anterior chamber to be highly compliant in contrast to a minimally compliant posterior chamber. Future work will focus on the active control of the swimbladder through autonomic nervous system control of this organ. Ongoing experiments on zebrafish hearing have shown repeatable increases in swimming activity (arousal) in adult zebrafish during exposure to noise stimuli. Comparison of the results of these tests to zebrafish tested after simulated depth changes will elucidate any effects that changes in swimbladder volume may have on auditory function of these fish.