| Abstract No.: | C-E3166 |
| Country: | Canada |
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| Title: | THE INTER- AND INDEPENDENCE OF TEMPERATURE AND BRAIN STATE IN RATS UNDER URETHANE ANAESTHESIA |
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| Authors/Affiliations: | 1 Tara Whitten*; 1 Anthony Guico; 1 Laura Martz; 1 Jill Miko; 1 Nicole Gervais; 1 Clayton Dickson;
1 University of Alberta, Edmonton, AB, Canada
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| Content: | Objectives: During sleep, warm-blooded animals exhibit cyclic alternations between rapid-eye-movement (REM) sleep and non-rapid-eye-movement (non-REM) sleep, which are characterized by distinct behavioural and electroencephalographic (EEG) characteristics. Interestingly, alternations between these two brain states are coupled to fluctuations of core, brain and skin temperatures. Recently we have shown that urethane-anaesthetized rats display cyclic alternations between activated and deactivated forebrain states that are highly similar in both EEG and physiological characteristics to REM and non-REM sleep states respectively. Our most recent experiments suggest that these alternations are also coupled to fluctuations in core body temperature. In the present study, the objective was to evaluate the degree of coupling between these two parameters through manipulations of both temperature and EEG state.
Materials and Methods: Hippocampal and neocortical local field potential recordings were obtained from Sprague Dawley rats anaesthetized with urethane. Core body temperature was maintained using a servo-controlled heating pad connected to a rectal probe. Both core body temperature and peripheral skin temperatures were manipulated within this system to assess the effect on brain state. Brain state was also ‘clamped’ through stimulation of brain sites inducing activated EEG states. Body temperature was ‘clamped’ through the use of a non-feedback heating system.
Results: Core body temperature could be manipulated in various ways without disrupting the coupling between temperature and brain state such that the activated state predominated when body temperature was rising whereas the deactivated state predominated while body temperature was falling. To investigate the mechanism of coupling between core body temperature and brain state, the effect of peripheral thermal stimuli on brain state was tested. Cooling of the scrotum elicited a sharp state transition into the deactivated state, while warming elicited an activated state. The strong coupling of temperature and brain state could be disrupted however by ‘clamping’ brain state, which resulted in a unitary EEG state while body temperature continued to fluctuate, or by ‘clamping’ body temperature, which resulted in spontaneous state changes which were uncorrelated with temperature fluctuations.
Conclusion: Just like in natural sleep, there is a coupling between temperature and brain state in rats under urethane anaesthesia. Peripheral thermal stimuli can drive alternations of brain state, however in the absence of thermal stimuli spontaneous alternations of brain state can still occur.
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