Anesthesia and Pain in Advanced Invertebrates


Cephalopod mollusks and decapod crustaceans are believed to the most developed and intelligent invertebrates and may be sentient animals. They are legally protected by a number of national and trans-national organizations, such as the European Union.

In the proposed research topic we would start by attempting to define sentience/consciousness, probably in relation to what we understand in marine vertebrates, which may be very different from that in land-based forms. Given that many mollusks, including cephalopods, and crustaceans are model animals in neuroscience and species of interest for aquaculture, definitions and mechanisms of action of anesthetics and analgesics acquire an added value for the project.

One of the features of sentient beings is that they feel pain, but this is largely a central nervous phenomenon, a consequence of nociception. Therefore the evolution of nociception in invertebrates and the presence of opioids in their nervous systems needs to be elaborated as a basis for considering the welfare of mollusks and crustaceans, particularly under laboratory conditions.

This leads us on to the very difficult problem of how we assess pain in invertebrates – a withdrawal response to a noxious stimulus could be a simple reflex reaction in simpler animals, but at what point in the evolution of nervous systems does the subjective sensation of pain arise? This leads to further questions as to how should the more advanced invertebrates be anesthetized and should we use clinical general anesthetics on them? To understand more of this we need to comprehend the basis of clinical anesthesia and analgesia. We should then consider the substances used as anesthetics in invertebrates and their suitability to the species involved, both crustaceans and mollusks.

Other questions also arise as to whether anesthetics and/or analgesics affect learning and memory in mollusks and crustaceans and these issues are presumably related to consciousness, if present, in advanced invertebrates. One view of anesthesia in mammals is that its effects may be differentiated so that, loss of consciousness appears to be associated with the cerebral cortex, amnesia with the limbic system and immobility and analgesia with the spinal cord. Do equivalent divisions occur within the nervous systems of advanced invertebrates, and if so, with which parts of their nervous systems are they associated? Finally, if advanced invertebrates are conscious/sentient, then there must be numerous different neural systems with which consciousness is associated, so would this enlighten us on the general nature of consciousness? What sort of neural matrix is required for a creature to become sentient?

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