Anesthesia of Octopus vulgaris with the volatile general anesthetic isoflurane.

Anesthesia of cephalopods is discussed more than ever before due to the work in progress for their welfare legislation. Different approaches to anesthesia in cephalopods have been tried by a number of scientists, but in most cases the animals were not truly anesthetized. Several workers have simply used muscle relaxants or simple hypothermia under the name anesthesia. This approach will not be adequate in the future. Inhalational anesthetics such as isoflurane (C3H2ClF5O) reduce L-type calcium currents and potassium currents in a dosedependent manner in the pulmonate mollusc Lymnaea stagnalis and there is evidence from cell culture that such anesthetics also block excitatory chemical synapses, more effectively than inhibitory synapses. Here we report, for the first time, on the effects of clinical doses of the inhalational anesthetic isoflurane on the behavioral responses of Octopus vulgaris. The volatile anesthetic isoflurane (0.5-2.5% v/v) was equilibrated into seawater (1600 ml) via an air stone to adult Octopus vulgaris (n=14) of about 400g. Using a web camera we recorded the animals response to touch stimuli eliciting withdrawal responses of the arms and siphon and observed changes in the respiratory rate and the chromatophoric pattern over time during the anesthetic application. We found that different animals of the same size responded with similar behavioral changes as the isoflurane concentration was gradually increased. Sudden application of the highest concentration of isoflurane can be lethal to the animal (n=2). After application of 2.5% isoflurane (5 minutes at the most), when all the responses indicated deep anesthesia, the animals recovered within 45 to 60 minutes in fresh aerated sea water. Based on previous findings in gastropods and the discovery of an L-type calcium channel sequence in the Octopus transcriptome, we believe that the molecular and electrophysiological bases of anesthesia induced by isoflurane are similar in that previously observed in Lymnaea. In the 30 minutes following anesthesia, the octopus can be handled without pain or distress, and an overdose of anesthetic can be used to euthanise the animal.