The neurobiology of pain and facial movements in rodents: Clinical applications and current research

Abstract

One of the most controversial aspects of the use of animals in science is the production of pain. Pain is a central ethical concern. The activation of neural pathways involved in the pain response has physiological, endocrine, and behavioral consequences, that can affect both the health and welfare of the animals, as well as the validity of research. The strategy to prevent these consequences requires understanding of the nociception process, pain itself, and how assessment can be performed using validated, non-invasive methods. The study of facial expressions related to pain has undergone considerable study with the finding that certain movements of the facial muscles (called facial action units) are associated with the presence and intensity of pain. This review, focused on rodents, discusses the neurobiology of facial expressions, clinical applications, and current research designed to better understand pain and the nociceptive pathway as a strategy for implementing refinement in biomedical research.

Rat Grimace Scale as a Method to Evaluate Animal Welfare, Nociception, and Quality of the Euthanasia Method of Wistar Rats

“…However, a possible explanation for why nociception/pain might be present could be due to the activation of peripheral nociceptors located in the skin and muscles of the cervical region of rodents and to the potential sensitization of nociceptors due to negative states derived from decapitation (e.g., fear). Although the loss of consciousness is fast after decapitation, before head detachment, tissular damage to said structures would trigger the nociceptive pathway (e.g., transduction, transmission, modulation, projection, and perception) culminating in pain perception for a couple of seconds before the cessation of nervous signaling [7,21,62]. It is known that after decapitation there is an anatomical disconnection between the mesencephalon and the cardiorespiratory centers-leading to death-and that the electric signaling present postdecapitation cannot solely be attributed to nociception since it has been found in healthy anesthetized animals or during REM sleep [14,33].…”

“…Currently, studying pain facial expressions in domestic and wildlife species is a trend derived from Darwin's studies regarding emotion and its association with facial expressions [19]. This has led to the development of "grimace scales", scoring systems that categorize movements of facial muscles-called Facial Action Units (FAUs)-related to pain [20][21][22][23]. For rats, Sotocinal et al [22] developed the Rat Grimace Scale (RGS), using as a basis the Mouse Grimace Scale (MGS), a validated tool that uses four FAUs to determine the pain level: 1. ear change; 2. orbital tightening; 3. nose/cheek flattening; and 4. whisker change.…”

Antioxidants from microalgae and their potential impact on human well-being

“…Oxidative stress can damage DNA, leading to mutations and potentially harmful consequences. Microalgae-derived antioxidants may aid in DNA repair mechanisms, preventing long-term damage and maintaining genetic integrity [70].…”

Assessment of Pain and Inflammation in Domestic Animals Using Infrared Thermography: A Narrative Review

“…An important field of research where IRT could help to refine and promote animal welfare is during the slaughter or euthanasia of farm, companion, and laboratory animals in order to prevent pain and negative emotional states [ 74 , 139 , 140 ]. Weschenfelder et al [ 74 ] have used infrared ocular thermography in pigs during slaughter to associate the physiological response with meat quality.…”