Heat Stress Effects on the Kinetics of Olfactory Responses

Abstract

Temperature is one of the most challenging stressors, affecting human and animal health. Extreme heat stress can damage the olfactory sensory neurons. In this work, we examined the effects of elevated temperature on the kinetic properties of rat olfactory sensory receptors in vitro by the recording of electroolfactogram (EOG) of the olfactory epithelium (OE) removed from the animals before and after the heat stress at 45 ºC for 25 minutes. EOG were evoked by an odorant mixture of ethyl butyrate, eugenol, and (+) and (−) carvone. The biochemical properties of the animal blood related to heat stress were characterized. Exposure of rats to high temperature resulted in a significant increase of body temperature. The mean body temperatures of rats before and immediately after heat stress were 36.7±0.07 ºC and 40.3 ±0.17 ºC, respectively. The kinetic properties of electrical responses to odorant were significantly changed in animals subjected to heat stress. The mean half‐rise (tr)and –decay times (td) of control OE were 328±11 and 660±20 ms, respectively. The rise and decay of EOG peak amplitude after heat stress were much faster, being reduced by 175 %, and 72 %, respectively. Heat stress did not result in a change of IL‐1β; IL‐6, TNF‐α, INF‐γ cytokines level. However, a significant increase of the IL‐10 level was found in rats exposed to heat. The level of lipopolysaccharides (LPS) was significantly increased in the serum of heat‐stressed animals compared to control animals. The concentration of free vesicles in animal blood increased after exposure to heat stress from (1.4±0.2)×106 to (3.8±0.3)×106 vesicles μl−1, indicating a faster conversion of erythrocytes into echinocytes. The kinetic properties found in this work are consistent with the kinetics of cultured mouse olfactory neurons 1. The effect of elevated temperature on the kinetic properties of olfactory receptors is also consistent with those seen in other neurons2–4. Detrimental effects of elevated temperatures on olfaction are shown in other animals5. The change in kinetic properties of olfactory receptors as a result of elevated temperature is consistent with those in other neurons2–4. Cytokines were found to cause neurodegeneration of the olfactory bulb6. We conclude that heat stress causes a strong irreversible modulation of olfactory responses.Support or Funding InformationSupported by grant from the National Institute of Standards and Technology: 70NANB14H324