Brief anesthesia, but not voluntary locomotion, significantly alters cortical temperature

Abstract

Changes in brain temperature can alter electrical properties of neurons and cause changes in behavior. However, it is not well understood how behaviors, like locomotion, or experimental manipulations, like anesthesia, alter brain temperature. We implanted thermocouples in sensorimotor cortex of mice to understand how cortical temperature was affected by locomotion, as well as by brief and prolonged anesthesia. Voluntary locomotion induced small (∼ 0.1 °C) but reliable increases in cortical temperature that could be described using a linear convolution model. In contrast, brief (90-s) exposure to isoflurane anesthesia depressed cortical temperature by ∼ 2 °C, which lasted for up to 30 min after the cessation of anesthesia. Cortical temperature decreases were not accompanied by a concomitant decrease in the γ-band local field potential power, multiunit firing rate, or locomotion behavior, which all returned to baseline within a few minutes after the cessation of anesthesia. In anesthetized animals where core body temperature was kept constant, cortical temperature was still > 1 °C lower than in the awake animal. Thermocouples implanted in the subcortex showed similar temperature changes under anesthesia, suggesting these responses occur throughout the brain. Two-photon microscopy of individual blood vessel dynamics following brief isoflurane exposure revealed a large increase in vessel diameter that ceased before the brain temperature significantly decreased, indicating cerebral heat loss was not due to increased cerebral blood vessel dilation. These data should be considered in experimental designs recording in anesthetized preparations, computational models relating temperature and neural activity, and awake-behaving methods that require brief anesthesia before experimental procedures.

Brain heating induced by near-infrared lasers during multiphoton microscopy

“…The temperature was 36.8°C 30 min after recovery from anesthesia (N ϭ 2 mice), consistent with previous reports (Shirey et al 2015).…”

“…Brain temperature 500 m below the cranial window was 35.3°C in awake head-fixed mice in the absence of objective immersion, which reduced to 34.3°C with room temperature immersion water placed above the window and a microscope objective immersed (N ϭ 2 mice). Anesthesia induces prolonged brain cooling for up to 30 min after recovery (Shirey et al 2015). We found that 1.25% isoflurane anesthesia reduced brain temperature 500 m below the dura to 33.8°C and 34.4°C in the presence and absence of immersion water, respectively, while core temperature was maintained at 37°C (N ϭ 2 mice).…”

“…The amount of heating tolerable in a given experiment depends on many factors, such as the duration and duty cycle of the experiment and the physiological variables being measured. For example, power limits may differ in anesthetized vs. awake animals due to the neuroprotective effects of anesthesia (Sanders et al 2005) and its concomitant reduction in brain temperature (Shirey et al 2015;Yenari and Han 2012). In this study we investigated the threshold for lasting histological damage in awake mice, finding damage onset in the range of 250 -300 mW for 20-min continuous illumination, corresponding to a steady-state temperature rise of ϳ5°C.…”

Interhemispheric resting-state functional connectivity of the claustrum in the awake and anesthetized states

“…During the experimental setup, the rat was briefly anesthetized by isoflurane (2%) to secure the head and body in a restraining system with a built-in coil. Isoflurane was discontinued immediately after each rat was restrained, and sufficient time was given so that all rats were fully awake during imaging sessions (Shirey et al 2015). Body temperature was maintained at 37 °C by a feedback controlled heating pad while the rats were imaged.…”

“…This concentration induces a deep anesthetic plane, characterized by loss of withdrawal reflexes, as well as a significant decrease in thalamic and cortical activity (Detsch et al 1999; 2002; Shirey et al 2015). Furthermore, 1.5–2% isoflurane produces an anesthetic state in which the electrocorticogram signal is dominated by a 1–2 Hz signal in the power spectrum, which is consistent with a loss of consciousness (Friedburg et al 1999; Smith et al 2012a; Alloway et al 2014).…”