Romshin, A. M. | bioRxiv Science

bioRxiv2024

Relationship between Brain and Body Temperature in Anesthetized Animals Measured by Ultralocal Thermometry

Temperature is one of the least studied biophysical characteristics of the brain, although both the rate of biochemical reactions and the electrical activity of nervous tissue directly depend on it. The purpose of this study was to analyze the relationship between brain and body temperatures in anesthetized animals. Simultaneous measurement of brain and body temperature (rectally) was carried out at ambient temperature controlled with a thermal mat. The temperature of the deep layers of the somatosensory cortex was measured by ultralocal thermometry using a diamond thermometer. Under anesthesia, the body and brain temperature dropped to 27 C (4 degrees above ambient temperature). When the thermal mat was turned on, the brain and body began to heat up synchronously. The brain initially lagged behind, but when the critical temperature was reached, it began to release heat in quantities exceeding the influx from the blood, reaching physiological values of 37C. A reverse experiment with decreasing the temperature of the thermal mat showed a similar picture: a synchronous start of the decrease, but with reverse dynamics. Thus, we can distinguish two phases of the brains reaction to external heating: passive - when neuronal activity is decreased, and active - after internal regulatory mechanisms are triggered, which, in its turn, slows down the temperature drop. In general, the data obtained in the present work indicate that the temperature of neural tissue is not linearly related to body temperature.

neuroscience↗

bioRxiv2024

Rapid neurostimulation at micron scale with optically controlled thermal-capture technique

Precise control of cellular temperature at the microscale is crucial for developing novel neurostimulation techniques. Here, we study the effect of local heat on the electrophysiological properties of cells at the subcellular level using a cutting-edge micrometer-scale thermal probe, the diamond heater-thermometer (DHT). Experiments on primary neuronal cultures and HEK293 cells revealed that millisecond heat pulses could induce reversible changes in membrane potential and elicit ionic displacement currents. At local temperatures close to 50 {degrees}C, a rapid increase in cellular response by an order of magnitude was observed, attributed to local phase changes in the phospholipid membrane at the point of contact with the DHT. This allows the cell membrane to be effectively and reproducibly captured by temperature, referred to as thermal-capture mode (TCM). Once transition to TCM occurred, even lower temperatures (<35 {degrees}C) elicited depolarization up to 10 mV in neurons, sufficient for triggering action potentials with rates up to 30 Hz. Additionally, the impact of high temperatures beyond the physiological range on the electrophysiology of the cell was assessed. These findings enhance the understanding of how local heat affects cellular functions and provide insights into the thermal modulation of cell activity.

biophysics↗