The use of animals in scientific research still raises doubts and controversy. This debate involves sensitive issues related to animal pain and welfare. But how can scientific necessity be balanced with ethical responsibility? To better understand this topic, Farmaco em Foco interviewed Prof. Dr. Stephen Hyslop, researcher and consultant of the Animal Use Ethics Committee (CEUA) at UNICAMP.
A career between toxins and ethical decisions
Prof. Stephen Hyslop is a professor at the Faculty of Medical Sciences (FCM) at UNICAMP, where he is also accredited in the Graduate Program in Pharmacology. With a degree in Biochemistry and Zoology from the University of Leeds and a PhD in Physiology from the University of London, Prof. Hyslop has built his career in a field known as toxinology.
Toxinology is the study of the effects of venoms and toxins produced by living organisms such as animals, plants, fungi, and bacteria. In Prof. Hyslop’s case, his focus is on snakes, scorpions, spiders, bees, and wasps.
Throughout his career, Prof. Hyslop has also played an important role as a member and, currently, consultant of the Animal Use Ethics Committee (CEUA) at UNICAMP. Within the CEUA, he participates in project evaluation and contributes to ensuring compliance with regulations governing animal experimentation in Brazil.
Prof. Hyslop explains how he became involved with the committee: “I have been on this committee for a long time, almost since the beginning. I ended up joining by nomination, because the different units that use animals at Unicamp need to have a representative there. At that time, someone was needed to represent the FCM.”
He also describes his current role: “Nowadays there are other people who also represent or have represented the FCM on this committee. But I remain there as an ad hoc consultant, as someone to assist when needed.”
What determines which animals are protected in science
When discussing the use of animals in scientific research, not all animals are treated equally. The guidelines that regulate animal use in laboratories are mostly focused on vertebrates: animals with a backbone, such as fish, amphibians, reptiles, birds, and mammals.
Prof. Hyslop comments: “All the legislation we have in Brazil is essentially focused on vertebrate animals. There is no legislation, neither in Brazil nor abroad, regarding invertebrates. Therefore, the use of laboratory animals and experimental animals requires several considerations that do not necessarily apply to invertebrates.”
But why is ethical protection mainly focused on vertebrates? Since animal research ethics aims to reduce pain and suffering, it makes sense that vertebrates are the primary focus. These animals have a more complex nervous system, and much of what we know about animal pain and suffering is related to nervous system complexity. In this context, legislation seeks to establish limits and criteria for the ethical use of vertebrates in experiments.
However, there is a group of invertebrates whose use in research is regulated by legislation: squids and octopuses. These animals have highly developed central nervous systems, great complexity, and evidence of advanced cognitive abilities (intelligence). This raises concerns about their capacity to experience pain.
Pain: the body’s alarm system that no one likes, but everyone needs
To understand why pain plays a central role in discussions about animal ethics, it is first necessary to understand what it is and how it works in the body. Far from being just an unpleasant sensation, pain is a mechanism for detecting aversive stimuli.
Aversive stimuli are those that cause discomfort or represent a threat, such as extreme heat or pressure. When we encounter these stimuli, we feel pain. Pain is essentially a signal sent by the nervous system. It is the way our nerves have evolved to say “WATCH OUT!”, prompting us to protect ourselves.
Pain perception involves a complex network of structures and chemical mediators. It begins with the activation of specific nerve endings (the terminal portions of neurons in the nervous system). In the case of pain, these endings are called nociceptors. Nociceptors are distributed throughout the skin, muscles, and organs, acting as sensors.
Nociceptors are activated when they detect something that may cause damage. When this happens, they send signals to the brain through nerve fibers. These fibers are like power cables connecting a switch (nociceptors) to a light bulb (the brain).
Throughout the pathway between nociceptors and the brain, neurons communicate through the release and recognition of chemical mediators such as glutamate and substance P. They act like letters sent from one neuron to another, saying: “Hey, we have a problem here! It looks like John put his finger in the fire and is going to get seriously burned if we don’t do something. Pass this message along until it reaches the brain.”
The brain is capable of receiving different stimuli and translating them into sensations such as heat, sweetness, or specific smells. In the case of signals from nociceptors, the brain interprets them as pain. You might think: “But does it really have to be something so unpleasant?” The reason is that pain must be a highly aversive signal for the body. Only then do we react quickly instead of remaining calm while burning our fingers.
Thus, when we touch a hot pan, the body generates pain to make us withdraw our hand immediately. If we step on something sharp by accident, we feel pain so we can lift our foot as quickly as possible before further injury occurs.
Pain plays a fundamental role in survival. Imagine if we did not feel pain. We would constantly injure ourselves more and more. In addition, pain also contributes to learning processes, helping the organism recognize and avoid similar situations in the future. If you have ever been stung by a wasp, you are likely much more careful not to experience it again, right?
Do insects feel pain?
Determining which animals can or cannot feel pain is not a simple task. It depends on the current state of scientific knowledge. Prof. Stephen comments: “It is easier to assess pain in vertebrates. This is because they have the nervous system structures and the mediators that we know are involved in pain. These are much better understood in vertebrates than in invertebrates.”
The possibility that insects and other invertebrates may feel pain is widely debated in science. Many researchers believe these animals are not capable of experiencing “true” pain, but rather only respond to noxious stimuli. Fruit flies and cockroaches, for example, quickly escape when exposed to very hot surfaces. In the past, it was almost unanimously accepted among scientists that this was merely an automatic response, without any suffering involved.
However, more recent studies are challenging this view. Research shows that some insects display complex behaviors, such as the formation of “memory” after negative experiences. For example, bees learn to avoid places where they previously received mild electric shocks. Cockroaches and grasshoppers may also rub or protect injured body parts to avoid further damage.
These behaviors may indicate that, although the nervous system of insects is simpler than that of vertebrates, their responses to injury may be more complex than mere automatic reactions. In this context, the debate remains open. Each new piece of evidence contributes to rethinking the ethical boundaries of using these animals in science.
Prof. Stephen comments: “Eventually, there may be other signaling pathways or neural networks in invertebrates that could be associated with pain. But generally, what is known from vertebrates is transferred to invertebrates to determine whether they feel pain or not. For now, this is the standard.”
The future of ethics
If today most legislation is centered on the protection of vertebrate animals, this scenario may be about to change in response to increasing evidence of the complexity of some invertebrates. The use of these animals is also growing in different contexts, from food production to scientific research. This has also created a need to reflect on the ethical use of these organisms.
Prof. Stephen comments: “I think that in the future we will have laws on the ethical use of invertebrates. We already see a lot of insect consumption in several countries, both for human consumption and as a protein source for pet food. The European Union already has legislation addressing the welfare of insect farming. And I don’t think it will take long before something appears related to the scientific use of these animals.”
Today, invertebrates are used in scientific research because they offer practical and experimental advantages. For example, they have lower maintenance costs, reproduce easily, and, due to the lack of specific legislation, their use involves fewer regulatory requirements than vertebrates. These characteristics allow large-scale and faster studies.
One of the ethical principles in animal research is the preference for less sentient species, meaning those with a lower capacity to experience pain and suffering. Whenever possible, it is recommended, for example, to replace vertebrates with invertebrates.
Even among vertebrates, this approach is encouraged: more complex vertebrates (such as rats and mice) should be replaced with less complex ones (such as fish). This logic has led researchers to increasingly use zebrafish in experiments.
Prof. Stephen notes that this is not without debate: “Some people argue that zebrafish are not an alternative model, because you are still using vertebrates. So that is a point of contention.”
Is the use of animals in research still necessary?
But, after all, is the use of animals in research really necessary? The answer involves a careful analysis that considers ethical criteria and the availability of alternative methods. With the advancement of new technologies, the possibility of replacing animals is increasing. However, there are still situations in which the complexity of a whole living organism cannot be fully replicated in the laboratory.
Among the main alternative methods to the use of animals in research are in vitro assays, such as cell culture. In vitro ((from Latin “in glass”) methods involve experiments conducted outside a living organism, such as in test tubes or culture plates. Cell culture consists of growing cells in the laboratory, allowing the study of biological processes, the testing of substances, and the assessment of toxicity in a controlled manner
Prof. Stephen explains the current scenario: “If we look at international recommendations and also in Brazil, the first step is to check whether there is an alternative method to animal use. But this alternative method must be well standardized, recognized, and accepted. It must be reliable and represent what would be evaluated in animals.”
He gives examples of cases where alternatives are not available: “For example, projects that propose investigating a substance that may reduce hypertension. You need a model in which it is possible to measure blood pressure. This cannot be done in cell culture or in vitro. You need the intact animal.”
He adds another example: “Or those working with tumor induction in animals. This also requires animals. It is difficult to reproduce in vitro. Because the advantage of using the animal is that you have, so to speak, the intact organism. The complete organism that allows you to see the various changes that occur due to the intervention.”
Some experiments are considered in vitro but use animal-derived samples. These are called isolated preparation experiments, as they use tissues or organs removed from humans or animals. For example, in studies of blood vessel contraction, arteries removed from animals may be used.
Prof. Stephen comments on these methods: “If you are evaluating vascular activity, for example, you will in some way have to sacrifice the animal to obtain that vessel for the in vitro study. Or sometimes we need certain types of inflammatory cells. The study outside the animal. So this is also animal use.”
Although many studies still depend on animal use, there are already fields in which alternative models predominate. One important example is the production of monoclonal antibodies through cell culture, widely used in research and drug development. This technique was developed in the 1970s by Argentine researcher César Milstein, in collaboration with Georges Köhler. The impact of this discovery was so significant that it earned the scientists the Nobel Prize.
Prof. Stephen gives other examples: “In cytotoxicity studies, it is possible to use cell culture. Whether for cardiac tissue, kidney tissue, or even neuronal tissue, some things can already be done in cells.” Cytotoxicity is the ability of a substance to cause damage to or kill cells.
Another important front in reducing animal use is the advancement of computational approaches. Today, simulation tools and artificial intelligence allow researchers to predict molecular behavior without the immediate need for animals. These methods make it possible, for example, to design new molecules and evaluate, in a virtual environment, their affinity for specific receptors, stability, and even potential toxic effects.
In practice, this stage works as an initial filter. Only the most promising molecules proceed to in vitro testing and later to animal an clinical (with human) studies. This workflow is widely adopted in the pharmaceutical industry, helping make drug development more efficient and ethical.
How ethical approval for animal research works
Before a study involving animals can even begin, it must go through a rigorous ethical review process. This assessment involves a set of criteria and procedures designed to ensure that animal use is justified, responsible, and conducted with the highest possible level of care. Only after approval from the Animal Use Ethics Committee (CEUA) can the research proceed.
Prof. Stephen explains the first step of the process at CEUA–UNICAMP: “The researcher must first complete an online CEUA course, in order to get at least a general understanding of the ethical principles involved in research. Without this certificate, it is impossible to submit a project to CEUA for evaluation.”
After that, the researcher must fill out a form describing the research project and submit it to CEUA. This document includes detailed information relevant to the ethical use of animals in research.
The form must include information about the experience of the research team. Proof of training is required. Researchers must be experienced in animal-related procedures to avoid unnecessary suffering or loss of animals, for example due to lack of skill in performing surgical procedures.
Among the first items in the form, the researcher must justify why animals are necessary for the study. At this stage, they must demonstrate that it is not possible to use alternative methods, such as cell culture or other in vitro approaches.
The form also requires a detailed description of the experimental design. This means the researcher must specify what will be done with each animal, the number required, and how this number was determined. Researchers cannot decide the number of animals arbitrarily; they must rely on a sample size calculation, mathematically demonstrating that the minimum number of animals will be used to obtain reliable scientific data.
In addition, the substances to be administered, their doses, routes of administration (oral, intramuscular injection, etc.), and all procedures must be described in detail.
Another key aspect of the evaluation concerns animal welfare. The researcher must specify which anesthetics and analgesics will be used and how pain will be monitored and controlled. If any surgical procedure is performed, the management of postoperative pain must also be described.
Based on this set of information, CEUA evaluates the project, prioritizing the reduction of animal suffering, the appropriate use of the number of individuals, and the scientific justification of the study.
Prof. Stephen explains how approval or rejection occurs:
“If there are no pending issues, the protocol is approved at the CEUA meeting. If there are issues, the process is sent back to the researcher. They must make the requested adjustments or provide clarifications. Then it can be resubmitted, usually limited to one resubmission. The entire process takes about one to two months to be approved.”
Once approved by CEUA, researchers may begin the project, but they must strictly follow what was previously approved. Failure to comply with the protocol can have serious consequences for both the researcher and the institution.
In Brazil, such violations may result in the immediate suspension of the project, a ban on the use of animals in future research, and even loss of funding and institutional affiliation. In addition, depending on severity, the case may fall under existing legislation, potentially leading to administrative and even criminal sanctions in cases of animal mistreatment.
Beyond legal implications, there are also ethical and scientific consequences. Data obtained irregularly may be invalidated, which undermines the credibility of both the research and the researcher.
From the laboratory to society: rethinking our relationship with animals
At the center of this debate is a legitimate concern shared by the public: animal pain and suffering, more than the mere use of animals itself. Prof. Stephen believes that what most often raises public concern is how these animals are treated throughout research. In this sense, ethical protocols and committees such as CEUA play a crucial role in ensuring that any discomfort is minimized as much as possible.
Prof. Stephen comments: “If, in any situation, pain and suffering become uncontrollable, the animal must be euthanized. This is precisely so that it does not have to go through that situation. I believe that showing that we take pain and suffering seriously, and that we take measures to control it, in a way greatly reduces most people’s concerns.”
At the same time, the topic becomes more complex when placed in perspective with the use of animals in society as a whole. In numerical terms, animal use for food consumption and other purposes far exceeds their use in scientific research. This comparison does not eliminate ethical questions in research, but it helps contextualize the debate and broaden reflection on the relationship between humans and other animals.
Finally, Prof. Stephen states: “We must always remember that over the past 100 years, the use of animals in research has led to medical advances that we still use and benefit from today. From heart transplantation, to the role of insulin, vaccines, and many other things. Many advances depended on the use of animals, and we must acknowledge that.”
This does not end the debate, but rather highlights its complexity. Between scientific necessity and ethical responsibility, the discussion is expected to continue evolving, alongside both technological advances and shifts in societal values.
This article was produced with the support of the São Paulo Research Foundation (FAPESP), Brazil. Grant No. 25/17158-3. The opinions, hypotheses, conclusions, or recommendations expressed in this material are the responsibility of the author(s) and do not necessarily reflect the views of FAPESP.
Further reading
Mechanisms of pain and nociception (DOI: 10.5380/avs.v13i1.11532)
Do insects feel pain? (DOI: 10.1016/bs.aiip.2022.10.001)
Arouca Law (Law No. 11.794/2008) – main Brazilian regulatory framework for the scientific use of animals
Brazilian Guide for the Use of Animals in Teaching and Research
Written by:
Mia Schezaro Ramos
Pharmacist. Ph.D. in Pharmacology. Science journalist, illustrator, trans, Nintendo enthusiast, K-pop fan, and dependent on physical exercise to stay sane.