University of Texas at Houston evolutionary biologist and behavioral neuroscientist Robyn Crook, PhD BSc’s broad research focus is evolution and function of complex behaviors, and the study of injury, nociception and pain in both invertebrate and vertebrate animals. Dr. Crook self-describes as being primarily a behavioralist, with interests in neural plasticity and higher cognitive processing, and her research examines mechanisms of neural plasticity involved in learning, memory, pain and affective states, contrasting cellular and behavioral changes after injury that vary among invertebrate and vertebrate animals.
Generally Dr. Crook’s work seeks to understand how and why mechanisms of neural plasticity might be conserved across taxonomically diverse species with vastly different brains and behaviors, and how different selective pressures drive the evolution of these mechanisms in distantly related species.
In her current research, Dr. Crook uses neurophysiological and behavioral techniques to examine nociception (detecting noxious or unpleasant stimuli) and nociceptive sensitization in invertebrates and mammals. She notes that sensitization resulting from tissue injury or from noxious stimuli can be expressed both as changes to the neurons that detect these stimuli, and as a change to the animals behavior. By studying both nociceptors and the behaviors they influence, she and her team aim to understand how sensitisation might function to provide a fitness benefit for affected animals.
Dr. Crook observes that Invertebrate animals are used widely in scientific research, but unlike vertebrate animals, their use is generally loosely regulated — based partly on the historical and still prevalent view that invertebrate animals lack sufficient neural complexity to experience pain, distress, or other negative affective states when subjected to the same experimental manipulations that might cause pain in mammals or other vertebrates. However, she contends that we still know very little about how invertebrates respond to noxious sensations, noting that many scientists think invertebrates are capable only of nociception (reflexive avoidance that involves no cognitive awareness), whereas others think they might experience pain (a negative emotional state associated with noxious sensations), and that distinguishing these experimentally requires a good understanding of sensory physiology and neurobiology, which is still largely missing for cephalopods.
“As concern for the welfare of invertebrates increases,” maintains Dr. Crook, “there is a critical need for careful study of the way invertebrates process and respond to potentially noxious and injurious stimuli. Parts of our work aim to clarify how cephalopods respond to different types of sensory stimuli, so that we and others can assess objectively whether cephalopods experience the emotional. subjective aspect that defines pain, or whether their responses are the result of reflexes that do not encompass emotional states.”
An Institute for Labratory Animal Research paper entitled “Nociceptive behaviour and physiology of molluscs: animal welfare implications” (PMID: 21709311 [PubMed – indexed for MEDLINE]) co-authored by Dr. Crook and Edgar T. Walters, PhD, a professor in the Department of Integrative Biology and Pharmacology at the University of Texas Medical School at Houston, they note that Molluscs have proven to be invaluable models for basic neuroscience research, yielding fundamental insights into a range of biological processes involved in action potential generation, synaptic transmission, learning, memory, and, more recently, nociceptive biology.
Drs. Crook and Walters observe that evidence suggests nociceptive processes in primary nociceptors are highly conserved across diverse taxa, making molluscs attractive models for biomedical studies of mechanisms that may contribute to pain in humans, but also exposing them to procedures that might producepainlike sensations.
In the free access paper, the co-authors review the physiology of nociceptors and behavioral responses to noxious stimulation in several molluscan taxa, and discuss the possibility that nociception may result in painlike states in at least some molluscs that possess more complex nervous systems, noting that few studies have directly addressed possible emotionlike concomitants of nociceptive responses in molluscs, and because the definition of pain includes a subjective component that may be impossible to gauge in animals quite different from humans, firm conclusions about the possible existence of pain in molluscs may be unattainable.
The researchers suggest that evolutionary divergence and differences in lifestyle, physiology, and neuroanatomy suggest that painlike experiences in molluscs, if they exist, should differ from those in mammals, but reports indicate that some molluscs exhibit motivational states and cognitive capabilities that may be consistent with a capacity for states with functional parallels to pain. Consequently, they recommend that investigators attempt to minimize the potential for nociceptor activation and painlike sensations in experimental invertebrates by reducing the number of animals subjected to stressful manipulations and by administering appropriate anesthetic agents whenever practicable, welfare practices similar to those for vertebrate subjects.e definition of pain includes a subjective component that may be impossible to gauge in animals quite different from humans, firm conclusions about the possible existence of pain in molluscs may be unattainable.
Drs. Crook and Walters found that all molluscs examined have shown a capacity for nociception as demonstrated by behavioral responses and/or by direct recording from nociceptors and other neurons, and that nociception and nociceptive sensitization at the level of primary nociceptors make use of neuronal mechanisms that appear to be highly conserved and widespread throughout the animal kingdom, but that not all mechanisms related to nociceptive biology are widely shared. For example, they note that analgesic-like effects mediated by true opioids and opioid receptors may be absent in invertebrates (Dores et al. 2002), and vertebrates may possess some synaptic mechanisms that are absent in invertebrates (Ryan and Grant 2009). Moreover, they observe that the sharing of many basic molecular building blocks does not imply sharing of higher order processes that depend on those building blocks. For example, nearly all known brain functions in most phyla depend on action potentials generated by the operation of highly conserved sodium channels, but only a few species have brains with the capacity to learn a spoken language or do arithmetic, ergo: voltage-gated sodium channels are essential for learning German or solving equations, but their presence does not imply the capacity for proficiency in German or algebra. At some level this must also be true for the capacity to experience pain.
Given the capabilities of relatively simple molluscan nervous systems, and if a key to the experience of pain is the size and complexity of the nervous system, Drs. Crook and Walters contend that one must seriously consider the possibility that cephalopods can experience some form of pain, noting that in the laboratory, molluscs are often subjected to manipulations that produce nociceptive responses, either as the aim of an experiment or as a byproduct. They observe that profound differences between molluscs and mammals in the size, complexity, and structure of their nervous systems, as well as their lifestyles and evolutionary history, suggest that painlike phenomena, if they exist in some molluscs, are likely to be quite different from pain in mammals, although it does not follow that molluscs are incapable of experiencing pain, pointing out that astropod and cephalopod molluscs have shown long-lasting behavioral alterations induced by noxious experience, which probably involve motivational states that can be used exibly to alter defensive and appetitive responses.
This suggests, they maintain, that some mollusks may be capable not only of nociception and nociceptive sensitization, but also of neural states that have some functional similarities to emotional states associated with pain in humans, and while it seems improbable that any mollusc has a capacity to feel pain equivalent to that evident in social mammals, the existence of some similarities in nociceptive physiology between molluscs and mammals, the paucity of systemic investigations into painlike behavior in molluscs, and the logical impossibility of disproving the occurrence of conscious experience in other animals all suggest that it is appropriate to treat molluscs as if they are susceptible to some form of pain during experimental procedures.
In conclusion, Drs. Crook and Walters recommend that the design of experiments using molluscs, particularly those with larger and more complex ganglia or brains (especially cephalopods but also gastropods), take into account the possibility of a capacity for painlike experience in these animals, and suggest that effective anesthetics (e.g., magnesium chloride) should be used during dissections and, to the extent possible, during any procedure that produces tissue damage or possible stress, and that investigators whose experiments unavoidably produce noxious stimulation should employ efforts similar to those required for vertebrate subjects to reduce both the number of animals and the potential for suffering to the minimum needed to test their hypotheses. Further that balancing the benefits derived from knowledge gained in molluscan experiments with the potential for inflicting pain and distress in the experimental subjects should be an explicit consideration in molluscan studies.
The paper’s full text can be accessed at:
Another study report by Drs. Crook and Walters coauthored with Robert T. Hanlon of the Program in Sensory Physiology and Behavior at the Marine Biological Laboratory in Woods Hole, Massachusetts became the Journal of Neuroscience June 12th 2013 issue’s cover story.
The study, titled: “Squid Have Nociceptors That Display Widespread Long-Term Sensitization and Spontaneous Activity after Bodily Injury” (The Journal of Neuroscience, 12 June 2013, 33(24): 10021-10026; doi: 10.1523/JNEUROSCI.0646-13.2013) notes that bodily injury in mammals often produces persistent pain that is driven at least in part by long-lasting sensitization and spontaneous activity (SA) in peripheral branches of primary nociceptors near sites of injury, and that while nociceptors have been described in lower vertebrates and invertebrates, outside of mammals there is limited evidence for peripheral sensitization of primary afferent neurons, and there are no reports of persistent SA being induced in primary afferents by noxious stimulation.
The researchers observe that cephalopod molluscs are the most neurally and behaviorally complex invertebrates, with brains rivalling those of some vertebrates in size and complexity, and that has fostered the opinion that cephalopods may experience pain, leading some governments to include cephalopods under animal welfare laws. However, they note that it is not known that cephalopods possess nociceptors, or whether their somatic sensory neurons exhibit nociceptive sensitization.
In their paper, Drs. Crook, Walters and Hanlon demonstrate that squid possess nociceptors that selectively encode noxious mechanical but not heat stimuli, and that show long-lasting peripheral sensitization to mechanical stimuli after minor injury to the body. As in mammals, injury in squid can cause persistent SA in peripheral afferents. However, while squid exhibit peripheral alterations in afferent neurons similar to those that drive persistent pain in mammals, robust changes far from sites of injury in squid suggest that persistently enhanced afferent activity provides much less information about the location of an injury in cephalopods than it does in mammals.
The field of pain sentience in invertebrate animals is also a research focus of
Professor Robert Elwood of the School of Biological Sciences at Queens University in Belfast, Northern Ireland.
A paper published in the Journal of Experimental Biology titled “Shock avoidance by discrimination learning in the shore crab (Carcinus maenas) is consistent with a key criterion for pain” (JEB, Vol. 216, No. 3, 01.02.2013, p. 353-358), co-authored by Dr. Elwood with School of Biological Sciences colleague Barry Magee, notes that nociception allows for immediate reflex withdrawal, whereas pain allows for longer-term protection via rapid learning. The researchers examine whether shore crabs placed within a brightly lit chamber learn to avoid one of two dark shelters when that shelter consistently results in shock.
In the experiments, crabs were randomly selected to receive shock or not prior to making their first choice and were tested again over 10 trials. They found those that received shock in trial 2, irrespective of shock in trial 1, were more likely to switch shelter choice in the next trial and thus showed rapid discrimination.
Elwood and Magee note that during trial 1, many crabs emerged from the shock shelter and an increasing proportion emerged in later trials, thus avoiding shock by entering a normally avoided light area. In a final test, the researchers switched distinctive visual stimuli positioned above each shelter and/or changed the orientation of the crab when placed in the chamber for the test. The visual stimuli had no effect on choice, but crabs with altered orientation now selected the shock shelter, indicating that they had discriminated between the two shelters on the basis of movement direction. These data, and those of other recent experiments, are consistent with key criteria for pain experience and are broadly similar to those from vertebrate studies.
A New Scientist report by Tamar Stelling this week notes that while some people are horrified by the common practices of boiling lobsters alive or the tearing claws from live crabs before tossing them back into the sea, there is very little scientific knowledge as to whether these creatures actually suffer, and that researchers are either certain the animals feel pain or certain they don’t, and that while the global food industry farms or catches billions of invertebrates every year, unlike their vertebrate cousins, invertebrates, which make up 98 percent of all animal species, have virtually no legal protection.
Ms Stelling cites the research by Dr. Elwood and colleagues at Queens University Belfast, and Dr. Crook at UT Houston as shedding some light on the issue, but notes that when an animal responds to something humans would consider painful, it doesn’t necessarily mean the animal is in pain, and the response might be a simple reflex, where signals do not travel all the way to the brain, and bypass the parts of the nervous system connected with the conscious perception of pain, and that the focus of Dr. Elwood’s research was to try and detect responses that went beyond reflex. She nots that based on their respective research findings, both Dr. Elwood and t. Crook have changed the way they treat the invertebrates in their labs, now using as few animals as possible and taking pains to keep potential for suffering to a minimum — and pushing others to do the same.
On his UTHSC Webpage, Dr. Edgar Walters notes that his researches and those of others has revealed striking similarities in how the nociceptors of invertebrates and vertebrates detect and “remember” injury-related stimulation. Molluscs offer well-known advantages for relating the properties of identifiable cells to behavioral functions. We use the large marine snail, Aplysia, to define cellular signaling pathways important for the induction and long-term maintenance of hyperexcitability in the cell body, axon, and peripheral and central terminals of identified nociceptors. Some of these signals also contribute to long-term alterations in vertebrate nociceptors, including the cAMP-PKA-CREB and NO-cGMP-PKG pathways. Others have not yet been investigated in vertebrates, such as a potent pathway that depends upon local depolarization (and protein synthesis) but not calcium signals. We found recently that another mollusc, the longfin Atlantic squid, displays long-term nociceptive sensitization of defensive behavior paralleled by sensitization of the peripheral branches of nociceptors. Comparisons of behavioral alterations and nociceptor memory in squid, Aplysia, and rats point to shared functions that have shaped the evolution of nociceptor plasticity and to conserved mechanisms that may be fundamental to many memory-like phenomena, including some forms of chronic pain.
University of Texas at Houston
University of Texas Medical School at Houston
School of Biological Sciences at Queens University, Belfast, Northern Ireland
Institute for Labratory Animal Research
Journal of Neuroscience
Journal of Experimental Biology
Robyn Crook, University of Texas at Houston
School of Biological Sciences at Queens University,