Behavioral effects of clinical doses of the general Anesthetic isoflurane on Octopus vulgaris

Anesthesia of cephalopods is more in discussion 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 anaesthetized. For example, 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 (CF2HOCClHCF3) reduce L-type calcium currents and potassium currents in a dose-dependent manner in the pulmonate mollusk 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=8) of about 400 g. Using a web camera we recorded the animals response to a touch stimuli eliciting withdrawal responses of the arms and siphon and observed changes in the respiratory rate and the chromatophore pattern over time during the anesthetic application. We found that different animals of the same size respond showing 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=1). After application of 2.5% isoflurane (for a maximum of 5 minutes), when all the responses indicated deep anesthesia, the animals recovered rapidly (within 10-15 minutes) in fresh aerated sea water. Gray (1970) proposed that the vertical lobe of Octopus vulgaris has integrative functions and receives two input fibers one of which comes from lower subvertical centers and is thought to mediate “pain”. The suggestion that the subvertical lobe is involved in pain is supported by our finding of the expression of estradiol receptors in the subvertical lobe allied to recent studies that demonstrate that estradiol can modulate the anesthetic actions.