Pain, Nociception and Analgesia in Reptiles When

CAN REPTILES EXPERIENCE PAIN? In a recent survey of members of the Association of Reptile and Amphibian Veterinarians, 98% of the respondents indicated their belief that reptiles do feel pain. However, only 39% of respondents in this survey reported using analgesics in > 50% of their patients subjected to surgical interventions. The reasons for failure to use analgesics were not specifically addressed in this study. However, some possibilities include a failure to recognize painful patients, concern of adverse effects from medications or lack of dose and pharmacokinetic information. Although reptile pain and nociception have not been extensively studied, there is very strong evidence that reptiles are capable of experiencing pain. The neuroanatomic components necessary for nociception have been described in reptiles. Endogenous antinociceptive mechanisms and a demonstrable modulation of pain with pharmacological agents known to be analgesics in other species have been demonstrated in reptiles. In lizards (Gekko gecko), spinal projections originating in the brain stem region (nucleus raphes inferior) that project to the superficial layers of the dorsal horn have been identified. These structures suggest the presence of inhibiting nociception mediating spinal tracts, similar to those found in mammals. Neurotransmitters that are important in pain modulation in mammals have been identified in reptiles. While endogenous opioids and opioid receptors involved in reproduction and thermoregulation have been identified in reptiles, there is little known of the role of opioids in nociception. Collectively, this information suggests, at the physiological level at least, that reptiles respond to nociceptive stimuli in a manner very similar to mammals. The assumption that an animal’s ability to experience pain is directly related to its position on the phylogenetic tree may be inaccurate. Rather, it may be that phylogenetic position is reflective of an animal’s ability to express pain. The benefits of providing adequate analgesia are well recognized in mammals. The consequences of untreated pain results in impaired homeostasis and this in turn can lead to alterations in numerous body systems. These alterations can result in negative energy balance, lead to immune system compromise, inhibit healing and interfere with normal behavioral process required for health. The benefits of preemptive analgesia have also been demonstrated and can not only reduce postoperative pain by decreasing central sensitization but may also facilitate healing and prevent and/or limit the actions of detrimental neurohumoral responses to pain postoperatively. In addition, many analgesics can be used as part of a balanced anesthesia to reduce the doses of other anesthetics. This can help reduce the negative cardiopulmonary effects of general anesthesia. Overall it has been demonstrated in humans and other mammals that appropriate analgesia is an important part of complete medical care in health and disease.