Katie Gilmour - Research

My lab uses a range of physiological, biochemical and molecular approaches to address questions about stress in fish. We investigate the physiological consequences of social status in rainbow trout and zebrafish, focusing in particular on the impact of chronic behavioural stress on the ability of fish to cope with additional, acute stressors.  We are also interested in the physiological responses to environmental stressors, such as acid-base challenges.  A key player in responses to both social and environmental stressors is the hormone cortisol, the end-product of activation of the hypothalamic-pituitary-interrenal (HPI) axis.  We are characterizing regulation of the HPI axis in fish experiencing chronic stress, and focusing on the roles of cortisol in mediating both the effects of social stress and responses to acid-base challenges.  Areas of current research interest are described in more detail below.

Social stress in salmonid fish
We have been identifying the physiological costs of social interactions in fish and uncovering the mechanisms underlying these costs.  Salmonid fish readily form dominance hierarchies in the wild or under laboratory conditions. These pecking order social structures are established through aggressive interactions, with each fish being ranked according to its ability to out-compete other individuals within the group. Typically, dominant fish are able to monopolise essential but limited resources, such as food or shelter, while subordinate fish may be excluded from such resources. Behaviours associated with dominant social status are well characterised and include possession of choice positions within the environment, acquisition of a larger share of the available food, and aggression directed at fish of lower social status. Subordinate fish, by contrast, often exhibit behavioural inhibition including reductions in (or the absence of) activity, feeding, and aggression. Our interest lies in the physiological consequences of social status, particularly the impact of chronic behavioural stress (and resultant chronic elevation of the stress hormone cortisol) on the ability of subordinate fish to respond to acute stressors.  Most recently, we collaborated with S Currie (Mt Allison) to report that social interactions activate cellular stress responses. This work focuses on integrating behaviour into physiology, and through collaboration with S Cooke (Carleton), also attempts to translate lab-based studies of stress physiology into the field.   

Novel roles for cortisol
Our work on stress physiology has led us to ivestigate novel roles for cortisol  For example, we found that cortisol is important in regulating responses to acid-base disturbances, a significant finding because how pH imbalances are sensed and responses are initiated is poorly understood, especially in fish.  A collaboration with P Walsh (Ottawa), led to the finding that cortisol regulates expression of the recently discovered ammonia-transporting Rh proteins.  These studies are uncovering new functions for cortisol beyond its traditional roles in regulating metabolism and osmoregulation in fish.

Regulation of carbonic anhydrase in fish
Carbonic anhydrase (CA) catalyses the reversible hydration/dehydration reactions of CO2 and water to bicarbonate ions and protons.  Thus, CA plays a key role in a multitude of physiological processes ranging from calcification through metabolism and gas transfer, to ionic regulation and acid-base balance.  These varied roles reflect both the direct and indirect consequences of catalyzed CO2 reactions; for example, enhanced rates of HCO3- supply for metabolism or acid-base equivalents for acid-base balance, as well as faster movement of CO2 through fluid compartments and across membranes.  The differing demands of the many roles played by CA have resulted in the existence of multiple CA isoforms that vary in molecular sequence, kinetic properties, tissue distribution and subcellular localization.  With few exceptions, these isoforms share in common a catalytic mechanism reflecting specific molecular structures.  A major research interest has been identifying and characterizing CA isoforms in fish, examining the evolution of this key enzyme and its roles in CO2 excretion and acid-base balance.  For example, we cloned CA IV in dogfish (Squalus acanthias) and documented its role in CO2 excretion, proposing a novel model of CO2 excretion in which CA-catalyzed production of CO2 in plasma contributes to CO2 excretion.  More recently we have begun to explore the transcriptional and post-granslational mechanisms through which CA expression, protein levels and activity are regulated.