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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Preferred Name

Romie D. Powell

Date of Award

Summer 2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Biology

Advisor(s)

Justin Brown

Mark Gabriele

T.J. Hyn

Abstract

Laboratory animals are housed at ambient temperatures ranging from 20°C – 26°C per recommended guidelines. Rats in particular typically prefer ambient temperatures (Tamb) of ~27°C (Brown et al, 2011). When rats undergo surgical instrumentation for experimental use, they often recover at normal room temperature (~21°C). While this is comfortable to those maintaining them, it may lead to a cold thermal stress for the rats. It is hypothesized that housing rats at ambient temperatures away from their preferred Tamb could lead to a thermal stress, which adversely affects surgical recovery. To address this, rats (220g-350g) were surgically instrumented with a radiotelemetry probe (DSI), which allows non-invasive measurement of core temperature (Tc). A cannula (21ga) was also inserted into the brainstem to allow microinjection of drugs as part of a separate project. For at least 1 week post-surgery, the rats were housed at either 21°C, 24°C, 27°C (control), 30°C, or 33°C Tamb while Tc, food and water intake, and body weight changes were measured. Rats housed at 21°C and 24°C struggled to recover a normal Tc initially, which delayed the onset of normal circadian cycling in the 21°C group. Warmer Tamb (30°C & 33°C) did not alter recovery of circadian Tc rhythms. Rats held at 21°C steadily increased food intake, while those at 33°C consumed less as the recovery period continued, suggesting that colder rats needed more caloric intake to thermoregulate, while those at warmer Tamb did not. Rats in the 30°C and 33°C groups consumed more water after post-surgical Day 3 compared to the other groups. This was due to more evaporative water loss at the higher Tamb versus the rats held at lower Tamb. The return of body weight to pre-surgical levels in rats housed at 33°C was delayed due to heat stress. The control group (27°C) returned to pre-surgical weight earlier than the other groups. These data suggest that rats maintained at 27°C recovered from surgical stress more readily. These rats returned to pre-surgical body weight more quickly and demonstrated a normal thermoregulatory circadian rhythm earlier than the cold (21°C) rats. The rats housed at 33°C were exposed to a heat stress, which affected weight gain and surgical recovery initially but did not affect circadian cycling during recovery. Rats housed at 21°C were cold stressed, which affected weight gain and thermoregulatory recovery. It is suggested that rats be maintained at their preferred Tamb of 27 °C during the week following surgery to minimize thermal stress and thereby facilitate recovery. This reduction in thermal stress would facilitate the return to a normal physiologic state and consequently enables more reliable data collection from these animals.

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