Browsing by Author "Gordon, Christopher J."

Now showing 1 - 6 of 6

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.
Effect of physical restraint on the limits of thermoregulation in telemetered rats
(Wiley, 2011-11) Gordon, Christopher J.; Grace, Curtis E.; Aydın, Cenk; Uludağ Üniversitesi/Veteriner Fakültesi/Fizyoloji Anabilim Dalı.; 0000-0002-3090-0099; 7005426982
Physical restraint of rodents is needed for nose-only exposure to airborne toxicants and is also used as a means of psychological stress. Hyperthermia is often observed in restrained rats, presumably as a result of impairments in heat dissipation. However, such a hyperthermic response should be dependent on the prevailing ambient conditions. To understand how ambient temperature (Ta) affects the thermoregulatory response to restraint, core temperature (Tc) and heart rate (HR) were monitored by telemetry in rats subjected to 1 h of physical restraint while Ta was maintained at 1430 degrees C in 2 degrees C increments. The Tc of unrestrained rats was unaffected by Ta. During restraint, Tc was elevated at ambient temperatures with the exception of 14 degrees C, at which the rats became mildly hypothermic. There was an inverse relationship between Ta and HR in both unrestrained and restrained rats; however, HR was significantly elevated in restrained rats at all ambient temperatures except 22 and 24 degrees C. Heat loss from the tail, estimated from Tc and tail skin temperature, was markedly reduced at all but the highest ambient temperatures in restrained rats. The data suggest that the Ta limits of normothermia are narrowed in the restrained rat. That is, between 16 and 20 degrees C, the rat maintains a relatively stable Tc that is slightly elevated above that of the unrestrained rat. At ambient temperatures above or below this range, the rat shows signs of hyperthermia and hypothermia, respectively. In contrast, the limits of normothermia for unrestrained rats range from 14 (or lower) to 30 degrees C. Overall, the ideal Ta for restrained rats appears to be 20 degrees C and no higher than 22 degrees C for the thermoregulatory system to maintain a regulated Tc in rats well adapted to physical restraint.
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.
Pulmonary sensitivity to ozone exposure in sedentary versus chronically trained, female rats
(Taylor & Francis, 2016-03-04) Gordon, Christopher J.; Phillips, Pamela M.; Beasley, Tracey E.; Ledbetter, A.; Snow, Samantha J.; Kodavanti, Urmila P.; Johnstone, Andrew F.; Aydın, Cenk; Uludağ Üniversitesi/Veteriner Fakültesi/Fizyoloji Anabilim Dalı.; 7005426982
Epidemiological data suggest that a sedentary lifestyle may contribute to increased susceptibility for some environmental toxicants. We developed an animal model of active versus sedentary life style by providing female Sprague-Dawley rats with continuous access to running wheels. Sedentary rats were housed in standard cages without wheels. After training for 12 wks, rats were exposed to 0, 0.25, 0.5 or 1.0ppm ozone [O-3 for 5 h/d, 1 d/wk, for 6 wk (N = 10 per group)]. Body composition (%fat, lean and fluid) was monitored noninvasively over the course of the study. Ventilatory parameters [tidal volume, minute ventilation, frequency and enhanced pause (Penh)] were assessed using whole-body plethysmography prior to O-3 and 24 h after the 5th O-3 exposure. Trained rats lost similar to 2% body fat after 12 wk of access to running wheels. Peak wheel activity was reduced by 40% after exposure to 1.0ppm O-3. After the 5th O-3 exposure, body weight and % fat were reduced in sedentary but not trained rats. Penh was significantly elevated in sedentary but not trained rats the day after exposure to 1.0 ppm O-3. However, lung lavage cell counts and biomarkers of pulmonary inflammation measured 1 day after the final exposure were inconsistently affected by training. Wheel running led to marked physiological responses along with some indication of improved pulmonary recovery from O-3 exposure. However, wheel running with O-3 exposure may also be a detriment for some pulmonary endpoints. Overall, a sedentary lifestyle may increase susceptibility to O-3, but additional studies are needed.
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.
Thermoregulatory, cardiovascular, and metabolic responses to mild caloric restriction in the Brown Norway rat
(Wiley, 2013-07-01) Aydın, Cenk; Gordon, Christopher J.; AYDIN, CENK; Uludağ Üniversitesi/Veteriner Fakültesi/Fizyoloji Anabilim Dalı; 0000-0002-3090-0099; DWC-5118-2022
Caloric restriction (CR) has been demonstrated to prolong the life span of a variety of species. CR-induced reduction in core temperature (Tc) is considered a key mechanism responsible for prolonging life span in rodents; however, little is known about the regulation of CR-induced hypothermia as a function of the circadian cycle. We assessed how mild CR that resulted in a 10% reduction in body weight affected the 24 h patterns of Tc as well as heart rate (HR) and motor activity (MA) of the Brown Norway rat. Telemetered rats were allowed to feed for 20 weeks ad libitum (AL) or given a CR diet. Tc, HR, and MA of CR rats exhibited nocturnal reductions and diurnal elevations, opposite to that of AL rats. The effects of CR appeared to peak at similar to 4 weeks. Metabolic rate (MR) and respiratory exchange ratio (RER) were measured overnight after 18 weeks of CR. MR and RER were elevated markedly at the time of feeding in CR rats and then declined during the night. We found that the pattern of Tc was altered with CR, characterized by elimination of high nocturnal Tc's typically observed in AL animals. In terms of mechanisms to prolong life span in CR animals, we suggest that the shift in the pattern of Tc during CR (i. e., elimination of high Tc's) may be as critical as the overall mean reduction in Tc. Future studies should address how the time of feeding may affect the thermoregulatory response in calorically restricted rats.