See below for a list of our peer-reviewed publications, including a summary or what we found and a link to the full paper. Most recent paper at top
Urea nitrogen recycling via gut symbionts increases in hibernating ground squirrels over the winter fast.
Regan MD, Chiang E, Liu Y, Tonelli M, Verdoorn KM, Gugel SR, Suen G, Carey HV, Assadi-Porter FM.
Science 375 (6579), 460-463, 2022.
What we found: Hibernating mammals harness their gut microbes to recycle nitrogen from waste urea to help maintain tissue protein during hibernation, when they lack activity and a dietary nitrogen source.
Linking environmental salinity to respiratory phenotypes and metabolic rate in fishes: a data mining and modeling approach.
Harter TS, Damsgaard C, Regan MD.
Journal of Experimental Biology 225, 2022.
What we found: Freshwater fishes have less efficient gills than seawater fishes but can nevertheless attain similar levels of aerobic performance and hypoxia tolerance thanks to hemoglobins with higher oxygen affinities.
How the gut and liver hibernate.
Kurtz CC, Otis JP, Regan MD, Carey HV.
Comparative Biochemistry and Physiology A 253, 2021.
What we found: A graphical review summarizing the causes and consequences of hibernation-related modifications to the GI tract, its microbial inhabitants, and its main accessory organ, the liver.
Shallow metabolic depression and human spaceflight: a feasible first step.
Regan MD, Flynn-Evans EE, Griko YV, Kilduff TS, Rittenberger JC, Ruskin K, Buck CL.
Journal of Applied Physiology 128, 637-647, 2020.
What we found: An alternative model for hibernation applications to human spaceflight that enhances biological and logistical feasibility, based on the premise of metabolic depression as a continuous variable.
The utility and determination of Pcrit in fishes.
Ultsch GR, Regan MD.
Journal of Experimental Biology 222, 2019.
What we found: A review of the theory underlying the critical oxygen tension (Pcrit) as a hypoxia tolerance metric, and an evidence-based guide for best experimental and mathematical practices when running Pcrit ex experiments.
Shifts in metabolic fuel use coincide with maximal rates of ventilation and body surface rewarming in arousing hibernators.
Regan MD, Chiang D, Martin SL, Porter WP, Assadi-Porter FM, Carey HV.
American Journal of Physiology 316, R764-R775, 2019.
What we found: To fuel the massive 400-fold increase in metabolic rate when arousing from torpor, hibernators recruit fast-burning carbohydrates to supplement their hallmark use of slow-burning lipids.
Don't throw the fish out with the respirometry water.
Regan MD, Mandic M, Dhillon RS, Lau GY, Farrell AP, Schulte PM, Seibel BA, Speers-Roesch B, Ultsch GR, Richards JG.
Journal of Experimental Biology 222, 2019.
What we found: The critical oxygen tension (Pcrit) remains a useful method for quantifying and comparing an animal's aerobic contributions to hypoxia tolerance.
Can variation among hypoxic environments explain why different fish species use different hypoxic survival strategies?
Mandic M, Regan MD.
Journal of Experimental Biology 221, 2018.
What we found: Distantly related species from similar hypoxic environments employ similar metabolic strategies of hypoxic survival, while closely related species from dissimilar hypoxic environments employ dissimilar strategies. Predation threat and aerial access also contribute to the strategies used.
Synthetic torpor: A method for safely and practically transporting experimental animals aboard spaceflight missions to deep space.
Griko YV, Regan MD.
Life Sciences in Space Research 16, 101-107, 2018.
What we found: We proposed the use of metabolic control technologies to reversibly depress the metabolic rates of experimental animals while in transit aboard spacecraft. We estimated the savings this could bring to spacecraft capacities and discussed the space-specific health benefits that torpor could confer to the animals (atrophy resistance, radiation resistance). We also explored current metabolic control technologies and delved into some of the major questions and obstacles that will likely appear should this idea be pursued..
Metabolic depression and the evolution of hypoxia tolerance in the threespine stickleback, Gasterosteus aculeatus.
Regan MD, Gill IS, Richards JG.
Biology Letters 13, 2017.
What we found: Stickleback from a recently-invaded hypoxic lake have the ability to depress metabolism to achieve a twofold greater hypoxia-tolerance than stickleback from a non-hypoxic lake, suggesting metabolic depression can evolve rapidly in response to environmental change.
Rates of hypoxia induction alter mechanisms of O2 uptake and the critical O2 tension of goldfish.
Regan MD, Richards JG.
Journal of Experimental Biology 220, 2017.
What we found: Goldfish exposed to low rates of hypoxia induction had more time to initiate acclimatory responses than goldfish exposed to high rates of induction, allowing them to maintain routine rates of aerobic metabolism at oxygen levels twice as low as fish exposed to high rates of hypoxia induction (ie, a twofold lower critical oxygen tension, Pcrit).
Calorespirometry reveals that goldfish prioritize aerobic metabolism over metabolic depression in all but near-anoxic environments.
Regan MD, Gill IS, Richards JG.
Journal of Experimental Biology 220, 564-572, 2017.
What we found: Goldfish, champions of hypoxia tolerance, rely almost exclusively on aerobic metabolism in all hypoxic environments despite their exceptional capacities for anaerobic metabolism and metabolic depression. They employ hibernation-like metabolic depression only in anoxic (ie, no oxygen) environments.
Ambient CO2, fish behavior and GABAergic neurotransmission: what happens when a hypercapnia dweller, Pangasianodon hypophthalmus, is taken down to low CO2?
Regan MD, Turko AJ, Heras J, Kuhlmann Andersen M, Lefevre S, Wang T, Bayley M, Brauner CJ, Huong DTT, Phuong NT, Nilsson GE.
Journal of Experimental Biology 219, 109-118, 2016.
What we found: Fish exposed to low-CO2 water displayed abnormal behaviour in a variety of tests. This was related to the way certain ions (chloride and bicarbonate) distributed across brain cell membranes, which affected the release of an important neurotransmitter, GABA. When we treated these fish with a drug that blocked the suspected membrane ion exchanger, these behaviours were reduced. These results were supported by a series of theoretical calculations.
Characterizing the metabolic capacity of the anoxic hagfish heart
Gillis T, Regan MD, Cox G, Harter T, Brauner CJ, Richards JG, Farrell AP.
Journal of Experimental Biology 218, 3754-3761 2015.
What we found: Hagfish are exceptionally tolerant of hypoxia, enabled in part via hearts that remain at routine levels of metabolism over 16+ hours of anoxia exposure.
Biochemical correlates of aggressive behaviour in the Siamese fighting fish.
Regan MD, Dhillon RS, Toews DPL, Speers-Roesch B, Sackville MA, Pinto S, Bystriansky JS, Scott GR.
Journal of Zoology 297, 99-107 2015.
What we found: Winners of mock fights supply their muscle cells with more energy than losers do, exploiting both aerobic and anaerobic energy-supplying pathways to greater extents. Additionally, a key enzyme in the aerobic supply of energy (citrate synthase) functions at a significantly higher activity level in winners than it does in losers.
Osmoregulatory bicarbonate secretion exploits H+-sensitive haemoglobins to autoregulate intestinal O2 delivery in euryhaline teleosts.
Cooper CA, Regan MD, Brauner CJ, De Bastos ESR, Wilson RW.
Journal of Comparative Physiology B 184, 856-876, 2014.
What we found: The euryhaline flounder is able to enhance O2 delivery to the energetically expensive intestinal cells by up to 42% by exploiting special hemoglobins (Root effect hemoglobins) and a mechanism of divalent ion regulation.
A simple and affordable calorespirometer for measuring the metabolic rates of fishes.
Regan MD, Gosline JM, Richards JG.
Journal of Experimental Biology 216, 4507-4513, 2013.
What we found: We designed and built an apparatus called a calorespirometer to precisely measure the metabolic rates of hypoxic-exposed fishes via metabolic heat and oxygen consumption rate.
The evolution of Root effect haemoglobins in the absence of protective red blood cell bNHE: Insights from primitive fishes.
Regan MD, Brauner CJ.
Journal of Comparative Physiology B 180, 695-706 2010.
What we found: Extant primitive fish species have Root effects that are induced only at very low blood pHs, which preserves O2 uptake despite an absence of red blood cell bNHE activity.
The transition in haemoglobin proton-binding characteristics within the basal actinopterygian fishes.
Regan MD, Brauner CJ.
Journal of Comparative Physiology B 180, 521-530 2010.
What we found: Extant primitive fish species use different combinations of intrinsic buffering and the Haldane effect to bind protons to hemoglobin and facilitate CO2 transport in the blood.
The effect of dietary canola oil replacement on swimming performance and metabolic response to hypoxia in spring Chinook salmon parr.
Regan MD, Kuchel LJ, Huang SSY, Higgs D, Wang J, Schulte P, Brauner CJ.
Aquaculture 308, 183-189, 2010.
What we found: In farmed salmon feed, replacing the fish oil component with canola oil has no effect on the fish's swimming performance, metabolic rate or hypoxia tolerance. Though this replacement alters the fish's whole body fatty acid profiles, it does not alter the polar lipids that comprise the cellular lipid membranes, which likely explains the lack of physiological effects.
Top image: Autumn in the Botanical Garden of Montréal. Photo credit: Matthew Regan.