Temperature stressors

The final point is perhaps the most critical as well as the most overlooked. Even under normal circumstances the fish thyroid cascade responds to a wide array of environmental variables and changes in whole-animal physiologic state. In fact, much fish thyroid literature (unrelated to ecotoxicants) documents thyroidal responses to variables such as temperature, stressors, nutritional availability and sexual state. The thyroidal system is also pivotal in the total endocrine network. Consequently,... 

Present the mouse with a stressor, such as a novel cage, and document the change in internal temperature (see Note 30). 

Temperature measurements should be performed at the same time due to circadian rhythm. Baseline body temperature is significantly higher during the night. If testing occurs during the dark phase, there may be an interference with the amplitude of hyperthermia when the stressor is presented (21). 

The above protocol may be modified for the testing of anxiolytic drugs. Sixty minutes prior to the first temperature measurement, inject the mouse with the desired drug. The first temperature measurement serves as an acute stressor and is followed after 10 min with a second temperature measurement (34). 

Many of the factors that can affect organisms adversely are inherent stressors, including availability of nutrition, water quality, temperature and other climatic extremes, disease, and predation. It is important to be able to separate effects of inherent stressors from those of toxic chemicals. There are often important synergistic relationships between inherent stressors and the effects of toxic chemicals. Organisms that are under stress from inherent stressors are likely to be more susceptible to the effects of xenobiotic toxicants. 

Menezes S., Soares A.M.V.M., Guilhermino L., Peck M.R. (2006) Biomarker responses of the estuarine brown shrimp Crangon crangon L. to non-toxic stressors temperature, salinity and handling stress effects. Journal of Experimental Marine Biology and Ecology 335(1) 114-122. 

A stressor is a substance, circumstance, or energy field that causes impacts, either positive or negative, upon a biological system. Stressors could be as wide ranging as chemical effects, ionizing radiation, or rapid changes in temperature. 

For chemical stressors, the exposure scenario usually involves consideration of sources, environmental transport, partitioning of the chemical among various environmental media, chemical/biological transformation or speciation processes, and identification of potential routes of exposure (e.g., ingestion). For nonchemical stressors such as water level or temperature changes or physical disturbance, the exposure scenario describes the ecological components exposed and the general temporal and spatial patterns of their co-occurrence with the stressor. For example, for habitat alterations, the exposure scenario may describe the extent and distributional... 

During stressor characterization, one considers not only the primary stressor but also secondary stressors that can arise as a result of various processes. For example, removal of riparian (stream-side) vegetation not only alters habitat structure directly, but can have additional ramifications such as increased siltation and temperature rise. For chemicals, secondary stressors can be produced by a range of environmental fate processes. 

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