Octopuses and cuttlefish are quite sensitive and smart - for these reasons, scientists are forced to work with them in the same way as with mammals, in particular, to immobilize and anesthetize animals during experiments.
Cephalopods - octopus, squid and cuttlefish - have the most developed nervous system and the largest ratio of brain mass to body weight among all invertebrates. The peculiarities of the nervous system, in particular the giant axons and giant squid synapses, made cephalopods in the early 20th century popular among laboratory physiologists.
In addition to the nervous system, scientists are attracted by the vision device of cephalopods (especially their “inverted” eyes), the ability to camouflage,regeneration and even examples of unique symbiosis with microorganisms, as is the case with the luminous organs of squid. For these reasons, cephalopods are often kept in laboratories as experimental animals. Perhaps the most intriguing feature of cephalopods is their “consciousness” - something other than that of vertebrates, the structure of the nervous system does not prevent distant relatives of snails from showing remarkable acumen.
Certain types of cephalopods can certainly be attributed to the presence of intelligence - for example, octopuses are capable of developing conditioned reflexes (in fact, for training) and have been “caught” in the use of tools. When keeping octopuses in captivity, many funny cases were described when, for example, animals were selected from their aquarium, purposefully climbed into an aquarium with crabs, ate those and returned to their aquarium.
The recognition of cephalopods by scientists led to the fact that already in 1986 in the UK, the common octopus was included in the list of laboratory animals mentioned in the Animal Treatment Act in scientific experiments (ASPA - Animals (Scientific Procedures) Act 1986).When working with these animals, an ethics committee's opinion is necessary, their conditions of detention are strictly regulated, and when conducting potentially painful procedures and killing animals, the use of anesthesia is necessary. Cephalopods are currently included in relevant lists in most European countries and in Canada, which represents a unique precedent for invertebrates.
For many laboratory animals, such as mice and rats, isoflurane or other means of inhalation anesthesia, such as ether, is the standard method of anesthesia. When working with cephalopods, researchers do it easier — they pour alcohol or magnesium chloride into an aquarium. It is known that these substances quickly immobilize octopuses and cuttlefish, but nobody actually checked whether they provide pain relief.
In their work, a group of American researchers from the University of San Francisco decided to find out whether the drugs used to work with cephalopods are actually anesthetized. Scientists have found that in addition to magnesium chloride and ethyl alcohol, their colleagues sometimes use diethyl ether, tricaine fish anesthetic (MS-222), or simply cold sea water to immobilize mollusks.
Animals that were used in the anesthesia selection experiment
Hanna M. Butler-Struben et al / Front. Physiol. 2018
Researchers non-invasively attached electrodes to the mantle nerves of three representatives of cephalopods — dwarf cuttlefish and two types of octopus, in order to record the transmission of a signal to and from the central nervous system. The absence of signals in both directions in the presence of stimuli would mean that the animal does not feel pain and is “unconscious”. As stimulation, the researchers poked animals with a stick at regular intervals for some time after adding drugs to the aquarium.
It turned out that magnesium chloride, although it quickly immobilizes, begins to provide pain relief only 15 minutes after the animal stopped moving. Thus, the widely used protocol for anesthesia with this drug had to be rewritten. Alcohol was the best anesthetic - it simultaneously immobilized and anesthetized octopuses, but before that the animals showed clear signs of irritation. "No wonder," explains one of the authors of the work, "imagine that you have dripped vodka into your eye."
Ether and tricain were quite toxic to animals in an effective dose, and cold water did not work at all. Also, scientists have found that lidocaine is well suited for local anesthesia of octopuses - a drug that is used in medicine for the same purpose.
According to the results of their experiments, the authors of the work prepared a set of recommendations for anesthesia of cephalopod mollusks, and they hope that these recommendations will be taken into account by their colleagues and legislators in the preparation of the following versions of documents regulating work with laboratory animals.
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