Cephalopods have nociceptors that respond maximally to an injurious stimulus but not to an innocuous
stimulus, and increase in sensitivity after tissue has
been injured to help the animal avoid further injury.
There is also some indication that the nociceptor rate of
firing or sensitivity is related to the sensitivity of the
tissue that they protect (Mather 2004). Cephalopods
can learn to avoid putatively painful stimuli (Young
1991), and have many of the neurotransmitters that are
involved in vertebrate pain reception and mediation
(Abbott et al. 1995).