Special issue: Cephalopod BiologyPreliminary in vitro functional evidence for reflex responses to noxious stimuli in the arms of Octopus vulgaris☆
Introduction
The sea floor (benthic) habitat of most species of octopus and the extensive use made of the arms for foraging, often out of sight (Packard, 1972, Yarnall, 1969), means that the distal parts of the arms are the most likely part of the body to encounter potentially tissue damaging noxious stimuli. Typically, such noxious stimuli are categorised as mechanical, chemical or thermal (Sherrington, 1906). Physical damage is most likely caused by predators, prey or features of the environment such as sharp rocks and coral. Withdrawal and “shaking of the arms” has been reported in Eledone coming into contact with sea anemones so the chemical(s) released by the nematocysts may also constitute a noxious stimulus (Boycott, 1954) as in theory could heat in species inhabiting hydrothermal vents (e.g. Muusoctopus hydrothermalis, Voight, 2012).
Although the arms in octopus are potentially vulnerable to injury, animals in general have a number of defensive responses to minimise the possibility of tissue damage. One defensive response is mediated by nociceptors detecting stimuli that are either causing tissue damage or have the potential to cause such damage. A nociceptor is “a receptor preferentially sensitive to a noxious stimulus or to a stimulus which would become noxious if prolonged” (IASP Task Force on Taxonomy, 2011) and although it is highly likely that the octopus arm will be exposed to noxious stimuli (see above) there is a paucity of hard evidence for the presence of nociceptors (see Andrews et al., 2013-this volume for review; Crook and Walters, 2011, Crook et al., 2011). Nociceptors can be activated by mechanical, chemical (e.g. acid, capsaicin) and thermal stimuli (Smith and Lewin, 2009) and are classified as polymodal if an individual nociceptive neurone responds to multiple classes of stimulus. In fish skin polymodal nociceptors are in the majority and this has been ascribed to the nature of the aquatic environment (Sneddon, 2004). Nociceptors sensitive to mechanical, chemical (e.g. acid, capsaicin) or thermal (heat and cold) stimuli have been described in selected invertebrates: Caenorhabditis elegans, Drosophila melanogaster, Hirudo medicinalis, and Aplysia californica (Smith and Lewin, 2009); there is no equivalent molecular or neurophysiological evidence for the presence of nociceptors in cephalopods.
A range of responses result from noxious stimuli with the main ones being: i. Defensive motor reactions present in both vertebrates (e.g. reflex withdrawal of a stimulated limb in cat, Sherrington, 1906) and invertebrates (e.g. gill-withdrawal in Aplysia, Walters, 1987); ii. An unpleasant sensation assumed to occur in all vertebrates and which in humans is described as pain. The unpleasant sensation also induces a learned aversion to the stimulus leading to avoidance if encountered again and such conditioned responses to an electric shock (presumed to activate nociceptors) have been exploited in studies of learning in cephalopods (Boycott, 1954). Knowledge of the responses to noxious stimuli and characteristics of nociceptors in any species is relevant to understanding the potential that particular experimental procedures (including surgery) may have for the induction of pain, suffering, distress or lasting harm. Such procedures will become regulated in cephalopods in 2013 by Directive 2010/63/EU (Andrews, 2011, Andrews et al., 2013, Smith et al., 2013).
As a prelude to a neurophysiological investigation of nociceptors in the arm of Octopus vulgaris, we undertook a pilot study of the responses of the isolated arm to mechanical (pinch/compression) and chemical (acid) stimuli shown to activate nociceptors in some invertebrates (Smith and Lewin, 2009) and vertebrates including fish (Mettam et al., 2012). A hypotonic challenge (tap water) was also investigated as although Wells (1963) showed that O. vulgaris could discriminate salt and fresh water, and Walker et al. (1970) reported violent motor reactions and severe damage in Octopus maya immersed in fresh water.
Section snippets
Animals
Ten O. vulgaris, Cuvier 1797 of both sexes (7 males and 3 females; weight 261 ± 33 g [mean ± s.e.m.]) caught in the Bay of Naples, Italy were used in this study. They were housed individually in tanks (30 × 50 × 100 cm) constantly supplied with fresh sea water (Fiorito et al., 1990). They were fed with a small live crab (Carcinus mediterraneus) three times per week.
The animals used in this study were captured for other studies in the laboratory and were used post mortem (see below) for the in vitro study
Results
The descriptions below summarise the effects of challenge with each stimulus tested on at least 4 arms taken from different animals to ensure reproducibility of the responses.
Discussion
This study has demonstrated that the isolated arm of O. vulgaris is capable of “withdrawing” from potentially noxious chemical (acid), osmotic (hypotonic) and mechanical (compression) stimuli. Although the stimuli are applied to the distal part of the arm the withdrawal is mediated by coordinated contraction of muscle in the more proximal part of the arm and the formation of a bend (c.f. “quasi-joint” described by Sumbre et al., 2005) clearly visible in the horizontally mounted preparations
Acknowledgements
PLRA and TH wish to thank ASSEMBLE (Association of European Marine Biological Laboratories) for funding the preliminary study of nociception in O. vulgaris. We also wish to acknowledge the assistance of Drs Euan Brown, Graziano Fiorito, and Giovanna Ponte at SZN in providing facilities for these studies and stimulating discussions. [SS]
References (36)
- et al.
The identification and management of pain, suffering and distress in cephalopods, including anesthesia, analgesia and humane killing
J. Exp. Mar. Biol. Ecol.
(2013) - et al.
Problem solving ability of Octopus vulgaris Lamarck (Mollusca, Cephalopoda)
Behav. Neural Biol.
(1990) - et al.
Using ultrasound to estimate brain size in the cephalopod Octopus vulgaris Cuvier in vivo
Brain Res.
(2007) - et al.
Cephalopod research and EU Directive 2010/63/EU: Requirements, impacts and ethical review
J. Exp. Mar. Biol. Ecol.
(2013) Evolution of nociception in vertebrates: comparative analysis of lower vertebrates
Brain Res. Rev.
(2004)- et al.
Octopuses use a human-like strategy to control precise point-to-point arm movements
Curr. Biol.
(2006) Aspects of behaviour of Octopus cyanea Gray
Anim. Behav.
(1969)Control of accept and reject reflexes in Octopus
Nature
(1971)Laboratory invertebrates: only spineless, or spineless and painless? Introduction
ILAR J.
(2011)- et al.
A Catalogue of Body Patterning in Cephalopoda
Learning in Octopus vulgaris and other cephalopods
Pubbl. Staz. Zool. Napoli
The UFAW Handbook on the Care and Management of Cephalopods in the Laboratory
Modulation of acid-sensing ion channels: molecular mechanisms and therapeutic potential
Int. J. Physiol. Pathophysiol. Pharmacol.
Nociceptive behavior and physiology of molluscs: animal welfare implications
ILAR J.
Peripheral injury induces long-term sensitization of defensive responses to visual and tactile stimuli in the squid Loligo pealeii, Lesueur 1821
J. Exp. Biol.
Receptors in suckers of octopus
Nature
Patterns of motor activity in the isolated nerve cord of the octopus arm
Biol. Bull.
Acid sensing by visceral afferent neurones
Acta Physiol (Oxf.)
Cited by (26)
Behavioral Analysis of Learning and Memory in Cephalopods
2017, Learning and Memory: A Comprehensive ReferenceArm injury produces long-term behavioral and neural hypersensitivity in octopus
2014, Neuroscience LettersCitation Excerpt :Elevated spontaneous activity is present in all arms after one is injured, thus it is not clear if it is implicated in wound-directed attention, as occurs in mammals [29]. Noxious mechanosensation appears to be coded by increased firing of multiple distinct units in arms, probably a mixed population of primary sensory neurons and interneurons [19]; further work is needed to identify true nociceptors and circuitry driving peripherally-mediated reflexive avoidance [30,31]. In the mantle we identified putative primary afferents, as the mantle does not contain peripheral cell bodies outside stellate ganglia [32].
The identification and management of pain, suffering and distress in cephalopods, including anaesthesia, analgesia and humane killing
2013, Journal of Experimental Marine Biology and EcologyCitation Excerpt :Rowell also reported that a “painful stimulus” (needle prick or electric shock) to a sucker caused immediate withdrawal and, if continued, there was “a general movement of the arm away from it”. Using a similar preparation Hague et al. (2011, 2013) demonstrated reflex withdrawal of an isolated arm on exposure of the tip (~ 1 cm) to acetic acid (1–5%), hypotonic tap water and a strong pinch with forceps. Although the stimulus was applied at the tip, the arm withdrew by contraction of the proximal muscles forming a “joint” in the proximal arm as is observed in intact animals during withdrawal of the arm (Sumbre et al., 2005).
Hierarchical Control and Learning of a Foraging CyberOctopus
2023, Advanced Intelligent SystemsOctopus arm search strategies over complex surfaces
2023, bioRxiv
- ☆
This article is part of a special issue on Cephalopod Biology published under the auspices of CephRes-ONLUS (www.cephalopodresearch.org).