Browsing by Author "Johnstone, Andrew F.M."

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Behaviorally mediated, warm adaptation: A physiological strategy when mice behaviorally thermoregulate
(Pergamon-Elsevier, 2014-08) Gordon, Christopher J.; Repasky, Elizabeth A.; Kokolus, Kathleen M.; Dheyongera, Geoffrey; Johnstone, Andrew F.M.; Aydın, Cenk; Uludağ Üniversitesi/Veterinerlik Fakültesi/Temel Bilimler Bölümü.; 7005426982
Laboratory mice housed under standard vivarium conditions with an ambient temperature (T-a) of similar to 22 degrees C are likely to be cold stressed because this T-a is below their thermoneutral zone (TNZ). Mice raised at T(a)s within the TNZ adapt to the warmer temperatures, developing smaller internal organs and longer tails compared to mice raised at 22 degrees C. Since mice prefer T(a)s equal to their TNZ when housed in a thermocline, we hypothesized that mice reared for long periods (e.g., months) in a thermocline would undergo significant changes in organ development and tail length as a result of their thermoregulatory behavior. Groups of three female BALB/c mice at an age of 37 days were housed together in a thermocline consisting of a 90 cm long aluminum runway with a floor temperature ranging from 23 to 39 degrees C. Two side-by-side thermoclines allowed for a total of 6 mice to be tested simultaneously. Control mice were tested in isothermal runways maintained at a T-a of 22 degrees C. All groups were given cotton pads for bedding/nest building. Mass of heart, lung, liver, kidney, brain, and tail length were assessed after 73 days of treatment. Mice in the thermocline and control (isothermal) runways were compared to cage control mice housed 3/cage with bedding under standard vivarium conditions. Mice in the thermocline generally remained in the warm end throughout the daytime with little evidence of nest building, suggesting a state of thermal comfort. Mice in the isothermal runway built elaborate nests and huddled together in the daytime. Mice housed in the thermocline had significantly smaller livers and kidneys and an increase in tail length compared to mice in the isothermal runway as well as when compared to the cage controls. These patterns of organ growth and tail length of mice in the thermocline are akin to warm adaptation. Thus, thermoregulatory behavior altered organ development, a process we term behaviorally mediated, warm adaptation. Moreover, the data suggest that the standard vivarium conditions are likely a cold stress that alters normal organ development relative to mice allowed to select their thermal preferendum.
Episodic ozone exposure in adult and senescent Brown Norway rats: Acute and delayed effect on heart rate, core temperature and motor activity
(Taylor & Francis, 2014-06) Gordon, Christopher J.; Johnstone, Andrew F.M.; Phillips, Pamela M.; MacPhail, Robert C.; Kodavanti, Urmila P.; Ledbetter, Allen D.; Jarema, Kimberly A.; Aydın, Cenk; Uludağ Üniversitesi/Veterinerlik Fakültesi/Temel Bilimler Bölümü.; 7005426982
Setting exposure standards for environmental pollutants may consider the aged as a susceptible population but the few published studies assessing susceptibility of the aged to air pollutants are inconsistent. Episodic ozone (O-3) is more reflective of potential exposures occurring in human populations and could be more harmful to the aged. This study used radiotelemetry to monitor heart rate (HR), core temperature (T-c) and motor activity (MA) in adult (9-12 months) and senescent (20-24 months) male, Brown Norway rats exposed to episodic O-3 (6 h/day of 1 ppm O-3 for 2 consecutive days/week for 13 weeks). Acute O-3 initially led to marked drops in HR and T-c. As exposures progressed each week, there was diminution in the hypothermic and bradycardic effects of O-3. Senescent rats were less affected than adults. Acute responses were exacerbated on the second day of O-3 exposure with adults exhibiting greater sensitivity. During recovery following 2 d of O-3, adult and senescent rats exhibited an elevated Tc and HR during the day but not at night, an effect that persisted for at least 48 h after O-3 exposure. MA was elevated in adults but not senescent rats during recovery from O-3. Overall, acute effects of O-3, including reductions in HR and T-c, were attenuated in senescent rats. Autonomic responses during recovery, included an elevation in T-c with a pattern akin to that of a fever and rise in HR that were independent of age. An attenuated inflammatory response to O-3 in senescent rats may explain the relatively heightened physiological response to O-3 in younger rats.
Thermal stress and toxicity
(Wiley, 2014-07) Gordon, Christopher J.; Johnstone, Andrew F.M.; Aydın, Cenk; Uludağ Üniversitesi/Veterinerlik Fakültesi/Temel Bilimler Bölümü.; 7005426982
Elevating ambient temperature above thermoneutrality exacerbates toxicity of most air pollutants, insecticides, and other toxic chemicals. On the other hand, safety and toxicity testing of toxicants and drugs is usually performed in mice and rats maintained at sub-thermoneutral temperatures of similar to 22 degrees C. When exposed to chemical toxicants under these relatively cool conditions, rodents typically undergo a regulated hypothermic response, characterized by preference for cooler ambient temperatures and controlled reduction in core temperature. Reducing core temperature delays the clearance of most toxicants from the body; however, a mild hypothermia also improves recovery and survival from the toxicant. Raising ambient temperature to thermoneutrality and above increases the rate of clearance of the toxicant but also exacerbates toxicity. Furthermore, heat stress combined with work or exercise is likely to worsen toxicity. Body temperature of large mammals, including humans, does not decrease as much in response to exposure to a toxicant. However, heat stress can nonetheless worsen toxic outcome in humans through a variety of mechanisms. For example, heat-induced sweating and elevation in skin blood flow accelerates uptake of some insecticides. Epidemiological studies suggest that thermal stress may exacerbate the toxicity of airborne pollutants such as ozone and particulate matter. Overall, translating results of studies in rodents to that of humans is a formidable task attributed in part to the interspecies differences in thermoregulatory response to the toxicants and to thermal stress. Published 2014.