Neuronal c-Fos Immunoreactivity as a Quantitative Measure of Stress or Pain

A significant development in the field of animal welfare is the detection of the protein product of the immediate early gene c-fos in nuclei of CNS neurones activated following stress or nociception. The activated neurones expressing c-fos can be visualised via immunohistochemistry on sections of the brain or spinal cord. The number of labelled neurones can be assessed using quantitative or semiquantitative techniques. While c-fos expression relating to nociceptive stimulation is located to the specific nociceptive pathways in the dorsal horn of the spinal cord and specific nociceptive areas of the brain, the kind of c-fos expression induced by stress is observed in a variety of brain regions, such as the limbic system, including the amygdala, and the hypothalamic paraventricular nucleus. Assuming that animal welfare is to be defined as a life without unnecessary stress and pain, this methodology seems to provide a valuable tool for evaluating animal welfare, since it is now possible to visualise neurones recently activated by stress or nociception.