The stinging response of the honeybee: effects of morphine, naloxone and some opioid peptides

Drug effect and addiction research with insects - From Drosophila to collective reward in honeybees

Animals and humans share similar reactions to the effects of addictive substances, including those of their brain networks to drugs. Our review focuses on simple invertebrate models, particularly the honeybee (Apis mellifera), and on the effects of drugs on bee behaviour and brain functions. The drug effects in bees are very similar to those described in humans. Furthermore, the honeybee community is a superorganism in which many collective functions outperform the simple sum of individual functions. The distribution of reward functions in this superorganism is unique - although sublimated at the individual level, community reward functions are of higher quality. This phenomenon of collective reward may be extrapolated to other animal species living in close and strictly organised societies, i.e. humans. The relationship between sociality and reward, based on use of similar parts of the neural network (social decision-making network in mammals, mushroom body in bees), suggests a functional continuum of reward and sociality in animals.

Animal sentience

'Sentience' sometimes refers to the capacity for any type of subjective experience, and sometimes to the capacity to have subjective experiences with a positive or negative valence, such as pain or pleasure. We review recent controversies regarding sentience in fish and invertebrates and consider the deep methodological challenge posed by these cases. We then present two ways of responding to the challenge. In a policy-making context, precautionary thinking can help us treat animals appropriately despite continuing uncertainty about their sentience. In a scientific context, we can draw inspiration from the science of human consciousness to disentangle conscious and unconscious perception (especially vision) in animals. Developing better ways to disentangle conscious and unconscious affect is a key priority for future research.

Degradation of an appetitive olfactory memory via devaluation of sugar reward is mediated by 5-HT signaling in the honey bee

Conditioned taste aversion (CTA) learning induces the devaluation of a preferred food through its pairing with a stimulus inducing internal illness. In invertebrates, it is still unclear how this aversive learning impairs the memories of stimuli that had been associated with the appetitive food prior to its devaluation. Here we studied this phenomenon in the honey bee and characterized its neural underpinnings. We first trained bees to associate an odorant (conditioned stimulus, CS) with appetitive fructose solution (unconditioned stimulus, US) using a Pavlovian olfactory conditioning. We then subjected the bees that learned the association to a CTA training during which the antennal taste of fructose solution was contingent or not to the ingestion of quinine solution, which induces malaise a few hours after ingestion. Only the group experiencing contingent fructose stimulation and quinine-based malaise exhibited a decrease in responses to the fructose and a concomitant decrease in odor-specific retention in tests performed 23 h after the original odor conditioning. Furthermore, injection of dopamine- and serotonin-receptor antagonists after CTA learning revealed that this long-term decrease was mediated by serotonergic signaling as its blockade rescued both the responses to fructose and the odor-specific memory 23 h after conditioning. The impairment of a prior CS memory by subsequent CTA conditioning confirms that bees retrieve a devaluated US representation when presented with the CS. Our findings further highlight the importance of serotonergic signaling in aversive learning in the bee and uncover mechanisms underlying aversive memories induced by internal illness in invertebrates.

Increased aggression and reduced aversive learning in honey bees exposed to extremely low frequency electromagnetic fields

Honey bees, Apis mellifera, are a globally significant pollinator species and are currently in decline, with losses attributed to an array of interacting environmental stressors. Extremely low frequency electromagnetic fields (ELF EMFs) are a lesser-known abiotic environmental factor that are emitted from a variety of anthropogenic sources, including power lines, and have recently been shown to have a significant impact on the cognitive abilities and behaviour of honey bees. Here we have investigated the effects of field-realistic levels of ELF EMFs on aversive learning and aggression levels, which are critical factors for bees to maintain colony strength. Bees were exposed for 17 h to 100 μT or 1000 μT ELF EMFs, or a sham control. A sting extension response (SER) assay was conducted to determine the effects of ELF EMFs on aversive learning, while an intruder assay was conducted to determine the effects of ELF EMFs on aggression levels. Exposure to both 100 μT and 1000 μT ELF EMF reduced aversive learning performance by over 20%. Exposure to 100 μT ELF EMFs also increased aggression scores by 60%, in response to intruder bees from foreign hives. These results indicate that short-term exposure to ELF EMFs, at levels that could be encountered in bee hives placed under power lines, reduced aversive learning and increased aggression levels. These behavioural changes could have wider ecological implications in terms of the ability of bees to interact with, and respond appropriately to, threats and negative environmental stimuli.

Cooperative defence operates by social modulation of biogenic amine levels in the honey bee brain

The defence of a society often requires that some specialized members coordinate to repel a threat at personal risk. This is especially true for honey bee guards, which defend the hive and may sacrifice their lives upon stinging. Central to this cooperative defensive response is the sting alarm pheromone, which has isoamyl acetate (IAA) as its main component. Although this defensive behaviour has been well described, the neural mechanisms triggered by IAA to coordinate stinging have long remained unknown. Here we show that IAA upregulates brain levels of serotonin and dopamine, thereby increasing the likelihood of an individual bee to attack and sting. Pharmacological enhancement of the levels of both amines induces higher defensive responsiveness, while decreasing them via antagonists decreases stinging. Our results thus uncover the neural mechanism by which an alarm pheromone recruits individuals to attack and repel a threat, and suggest that the alarm pheromone of honey bees acts on their response threshold rather than as a direct trigger.

Pheromones modulate responsiveness to a noxious stimulus in honey bees

Pheromones are chemical substances released into the environment by an individual, which trigger stereotyped behaviors and/or physiological processes in individuals of the same species. Yet, a novel hypothesis has suggested that pheromones not only elicit innate responses but also contribute to behavioral plasticity by affecting the subjective evaluation of appetitive or aversive stimuli. To test this hypothesis, we exposed bees to three pheromonal components whose valence was either negative (i.e. associated with aversive events: isopentyl acetate and 2-heptanone) or positive (i.e. associated with appetitive events: geraniol). We then determined the effect of this exposure on the subjective evaluation of aversive stimuli by quantifying responsiveness to a series of increasing electric shock voltages before and after exposure. Two experiments were conducted varying the time lapse between shock series (15 min in experiment 1, and 24 h in experiment 2). In experiment 1, we observed a general decrease of shock responsiveness caused by fatigue, due to the short lapse of time between the two series of shocks. This decrease could only be counteracted by isopentyl acetate. The enhancing effect of isopentyl acetate on shock responsiveness was also found in experiment 2. Conversely, geraniol decreased aversive responsiveness in this experiment; 2-heptanone did not affect aversive responsiveness in any experiment. Overall, our results demonstrate that certain pheromones modulate the salience of aversive stimuli according to their valence. In this way, they would affect the motivation to engage in aversive responses, thus acting as modulators of behavioral plasticity.

Aversive gustatory learning and perception in honey bees

Taste perception allows discriminating edible from non-edible items and is crucial for survival. In the honey bee, the gustatory sense has remained largely unexplored, as tastants have been traditionally used as reinforcements rather than as stimuli to be learned and discriminated. Here we provide the first characterization of antennal gustatory perception in this insect using a novel conditioning protocol in which tastants are dissociated from their traditional food-reinforcement role to be learned as predictors of punishment. We found that bees have a limited gustatory repertoire via their antennae: they discriminate between broad gustatory modalities but not within modalities, and are unable to differentiate bitter substances from water. Coupling gustatory conditioning with blockade of aminergic pathways in the bee brain revealed that these pathways are not restricted to encode reinforcements but may also encode conditioned stimuli. Our results reveal unknown aspects of honey bee gustation, and bring new elements for comparative analyses of gustatory perception in animals.

The defensive response of the honeybee Apis mellifera

Honeybees (Apis mellifera) are insects living in colonies with a complex social organization. Their nest contains food stores in the form of honey and pollen, as well as the brood, the queen and the bees themselves. These resources have to be defended against a wide range of predators and parasites, a task that is performed by specialized workers, called guard bees. Guards tune their response to both the nature of the threat and the environmental conditions, in order to achieve an efficient trade-off between defence and loss of foraging workforce. By releasing alarm pheromones, they are able to recruit other bees to help them handle large predators. These chemicals trigger both rapid and longer-term changes in the behaviour of nearby bees, thus priming them for defence. Here, we review our current understanding on how this sequence of events is performed and regulated depending on a variety of factors that are both extrinsic and intrinsic to the colony. We present our current knowledge on the neural bases of honeybee aggression and highlight research avenues for future studies in this area. We present a brief overview of the techniques used to study honeybee aggression, and discuss how these could be used to gain further insights into the mechanisms of this behaviour.

In search of evidence for the experience of pain in honeybees: A self-administration study

Despite their common use as model organisms in scientific experiments, pain and suffering in insects remains controversial and poorly understood. Here we explore potential pain experience in honeybees (Apis mellifera) by testing the self-administration of an analgesic drug. Foragers were subjected to two different types of injuries: (i) a clip that applied continuous pressure to one leg and (ii) amputation of one tarsus. The bees were given a choice between two feeders, one offering pure sucrose solution, the other sucrose solution plus morphine. We found that sustained pinching had no effect on the amount of morphine consumed, and hence is unlikely to be experienced as painful. The amputated bees did not shift their relative preference towards the analgesic either, but consumed more morphine and more solution in total compared to intact controls. While our data do not provide evidence for the self-administration of morphine in response to pain, they suggest that injured bees increase their overall food intake, presumably to meet the increased energy requirements for an immune response caused by wounding. We conclude that further experiments are required to gain insights into potential pain-like states in honeybees and other insects.

Social signals and aversive learning in honey bee drones and workers

The dissemination of information is a basic element of group cohesion. In honey bees (Apis mellifera Linnaeus 1758), like in other social insects, the principal method for colony-wide information exchange is communication via pheromones. This medium of communication allows multiple individuals to conduct tasks critical to colony survival. Social signaling also establishes conflict at the level of the individual who must trade-off between attending to the immediate environment or the social demand. In this study we examined this conflict by challenging highly social worker honey bees, and less social male drone honey bees undergoing aversive training by presenting them with a social stress signal (isopentyl acetate, IPA). We utilized IPA exposure methods that caused lower learning performance in appetitive learning in workers. Exposure to isopentyl acetate (IPA) did not affect performance of drones and had a dose-specific effect on worker response, with positive effects diminishing at higher IPA doses. The IPA effects are specific because non-social cues, such as the odor cineole, improve learning performance in drones, and social homing signals (geraniol) did not have a discernible effect on drone or worker performance. We conclude that social signals do generate conflict and that response to them is dependent on signal relevance to the individual as well as the context. We discuss the effect of social signal on learning both related to its social role and potential evolutionary history.

Heat Perception and Aversive Learning in Honey Bees: Putative Involvement of the Thermal/Chemical Sensor AmHsTRPA

The recent development of the olfactory conditioning of the sting extension response (SER) has provided new insights into the mechanisms of aversive learning in honeybees. Until now, very little information has been gained concerning US detection and perception. In the initial version of SER conditioning, bees learned to associate an odor CS with an electric shock US. Recently, we proposed a modified version of SER conditioning, in which thermal stimulation with a heated probe is used as US. This procedure has the advantage of allowing topical US applications virtually everywhere on the honeybee body. In this study, we made use of this possibility and mapped thermal responsiveness on the honeybee body, by measuring workers' SER after applying heat on 41 different structures. We then show that bees can learn the CS-US association even when the heat US is applied on body structures that are not prominent sensory organs, here the vertex (back of the head) and the ventral abdomen. Next, we used a neuropharmalogical approach to evaluate the potential role of a recently described Transient Receptor Potential (TRP) channel, HsTRPA, on peripheral heat detection by bees. First, we applied HsTRPA activators to assess if such activation is sufficient for triggering SER. Second, we injected HsTRPA inhibitors to ask whether interfering with this TRP channel affects SER triggered by heat. These experiments suggest that HsTRPA may be involved in heat detection by bees, and represent a potential peripheral detection system in thermal SER conditioning.

Association of Amine-Receptor DNA Sequence Variants with Associative Learning in the Honeybee

Octopamine- and dopamine-based neuromodulatory systems play a critical role in learning and learning-related behaviour in insects. To further our understanding of these systems and resulting phenotypes, we quantified DNA sequence variations at six loci coding octopamine-and dopamine-receptors and their association with aversive and appetitive learning traits in a population of honeybees. We identified 79 polymorphic sequence markers (mostly SNPs and a few insertions/deletions) located within or close to six candidate genes. Intriguingly, we found that levels of sequence variation in the protein-coding regions studied were low, indicating that sequence variation in the coding regions of receptor genes critical to learning and memory is strongly selected against. Non-coding and upstream regions of the same genes, however, were less conserved and sequence variations in these regions were weakly associated with between-individual differences in learning-related traits. While these associations do not directly imply a specific molecular mechanism, they suggest that the cross-talk between dopamine and octopamine signalling pathways may influence olfactory learning and memory in the honeybee.

Ethanol-induced effects on sting extension response and punishment learning in the western honey bee (Apis mellifera)

Acute ethanol administration is associated with sedation and analgesia as well as behavioral disinhibition and memory loss but the mechanisms underlying these effects remain to be elucidated. During the past decade, insects have emerged as important model systems to understand the neural and genetic bases of alcohol effects. However, novel assays to assess ethanol's effects on complex behaviors in social or isolated contexts are necessary. Here we used the honey bee as an especially relevant model system since bees are typically exposed to ethanol in nature when collecting standing nectar crop of flowers, and there is recent evidence for independent biological significance of this exposure for social behavior. Bee's inhibitory control of the sting extension response (SER) and a conditioned-place aversion assay were used to study ethanol effects on analgesia, behavioral disinhibition, and associative learning. Our findings indicate that although ethanol, in a dose-dependent manner, increases SER thresholds (analgesic effects), it disrupts the ability of honey bees to inhibit SER and to associate aversive stimuli with their environment. These results suggest that ethanol's effects on analgesia, behavioral disinhibition and associative learning are common across vertebrates and invertebrates. These results add to the use of honey bees as an ethanol model to understand ethanol's effects on complex, socially relevant behaviors.

Individual responsiveness to shock and colony-level aggression in honey bees: evidence for a genetic component

The phenotype of the social group is related to phenotypes of individuals that form that society. We examined how honey bee colony aggressiveness relates to individual response of male drones and foraging workers. Although the natural focus in colony aggression has been on the worker caste, the sterile females engaged in colony maintenance and defense, males carry the same genes. We measured aggressiveness scores of colonies and examined components of individual aggressive behavior in workers and haploid sons of workers from the same colony. We describe for the first time, that males, although they have no stinger, do bend their abdomen (abdominal flexion) in a posture similar to stinging behavior of workers in response to electric shock. Individual worker sting response and movement rates in response to shock were significantly correlated with colony scores. In the case of drones, sons of workers from the same colonies, abdominal flexion significantly correlated but their movement rates did not correlate with colony aggressiveness. Furthermore, the number of workers responding at increasing levels of voltage exhibits a threshold-like response, whereas the drones respond in increasing proportion to shock. We conclude that there are common and caste-specific components to aggressive behavior in honey bees. We discuss implications of these results on social and behavioral regulation and genetics of aggressive response.

Pharmacological modulation of aversive responsiveness in honey bees

Within a honey bee colony, individuals performing different tasks exhibit different sensitivities to noxious stimuli. Noxious-stimulus sensitivity can be quantified in harnessed bees by measuring the sting extension response (SER) to a series of increasing voltages. Biogenic amines play a crucial role in the control of insect responsiveness. Whether or not these neurotransmitters affect the central control of aversive responsiveness, and more specifically of electric-shock responsiveness, remains unknown. Here we studied the involvement of the biogenic amines octopamine, dopamine and serotonin, and of the ecdysteroid 20-hydroxyecdisone in the central control of sting responsiveness to electric shocks. We injected pharmacological antagonists of these signaling pathways into the brain of harnessed bees and determined the effect of blocking these different forms of neurotransmission on shock responsiveness. We found that both octopamine and 20-hydroxyecdisone are dispensable for shock responsiveness while dopamine and serotonin act as down-regulators of sting responsiveness. As a consequence, antagonists of these two biogenic amines induce an increase in shock responsiveness to shocks of intermediate voltage; serotonin, can also increase non-specific responsiveness. We suggest that different classes of dopaminergic neurons exist in the bee brain and we define at least two categories: an instructive class mediating aversive labeling of conditioned stimuli in associative learning, and a global gain-control class which down-regulates responsiveness upon perception of noxious stimuli. Serotonergic signaling together with down-regulating dopaminergic signaling may play an essential role in attentional processes by suppressing responses to irrelevant, non-predictive stimuli, thereby allowing efficient behavioral performances.

Effects of morphine on associative memory and locomotor activity in the honeybee (Apis mellifera)

Morphine can modulate the processes underlying memory in vertebrates. However, studies have shown various modulations by morphine: positive, negative and even neutral. The honeybee is a potential platform for evaluating the effects of drugs, especially addictive drugs, on the nervous system. However, the involvement of morphine in learning and memory in insects or other invertebrates is poorly understood. The current work evaluated whether morphine affects memory acquisition, consolidation and retrieval in honeybees, using the proboscis extension response (PER) paradigm. We demonstrated that morphine treatment (5 μg/bee) before training decreased the percentage of correct PERs and the response latency related to aversive rather than rewarding odors when tested after 1 or 24 h. Morphine treatment after training also caused a decrease in this latency when tested after 24 h. Meanwhile, morphine treatment reduced the ambulation distance when tested after 30 min. Our findings suggest that morphine impairs the acquisition of short- and long-term associative memory and slightly disrupts the consolidation of long-term memory in honeybees. These negative effects cannot be explained by reduced locomotion but by impaired memory associated with aversion.

General Stress Responses in the Honey Bee

The biological concept of stress originated in mammals, where a “General Adaptation Syndrome” describes a set of common integrated physiological responses to diverse noxious agents. Physiological mechanisms of stress in mammals have been extensively investigated through diverse behavioral and physiological studies. One of the main elements of the stress response pathway is the endocrine hypothalamo-pituitary-adrenal (HPA) axis, which underlies the “fight-or-flight” response via a hormonal cascade of catecholamines and corticoid hormones. Physiological responses to stress have been studied more recently in insects: they involve biogenic amines (octopamine, dopamine), neuropeptides (allatostatin, corazonin) and metabolic hormones (adipokinetic hormone, diuretic hormone). Here, we review elements of the physiological stress response that are or may be specific to honey bees, given the economical and ecological impact of this species. This review proposes a hypothetical integrated honey bee stress pathway somewhat analogous to the mammalian HPA, involving the brain and, particularly, the neurohemal organ corpora cardiaca and peripheral targets, including energy storage organs (fat body and crop). We discuss how this system can organize rapid coordinated changes in metabolic activity and arousal, in response to adverse environmental stimuli. We highlight physiological elements of the general stress responses that are specific to honey bees, and the areas in which we lack information to stimulate more research into how this fascinating and vital insect responds to stress.

Behavioral and neurophysiological study of olfactory perception and learning in honeybees

The honeybee Apis mellifera has been a central insect model in the study of olfactory perception and learning for more than a century, starting with pioneer work by Karl von Frisch. Research on olfaction in honeybees has greatly benefited from the advent of a range of behavioral and neurophysiological paradigms in the Lab. Here I review major findings about how the honeybee brain detects, processes, and learns odors, based on behavioral, neuroanatomical, and neurophysiological approaches. I first address the behavioral study of olfactory learning, from experiments on free-flying workers visiting artificial flowers to laboratory-based conditioning protocols on restrained individuals. I explain how the study of olfactory learning has allowed understanding the discrimination and generalization ability of the honeybee olfactory system, its capacity to grant special properties to olfactory mixtures as well as to retain individual component information. Next, based on the impressive amount of anatomical and immunochemical studies of the bee brain, I detail our knowledge of olfactory pathways. I then show how functional recordings of odor-evoked activity in the brain allow following the transformation of the olfactory message from the periphery until higher-order central structures. Data from extra- and intracellular electrophysiological approaches as well as from the most recent optical imaging developments are described. Lastly, I discuss results addressing how odor representation changes as a result of experience. This impressive ensemble of behavioral, neuroanatomical, and neurophysiological data available in the bee make it an attractive model for future research aiming to understand olfactory perception and learning in an integrative fashion.

Visual conditioning of the sting extension reflex in harnessed honeybees

Visual performances of honeybees have been extensively studied using free-flying individuals trained to choose visual stimuli paired with sucrose reward. By contrast, harnessed bees in the laboratory were not thought to be capable of learning a Pavlovian association between a visual stimulus (CS) and sucrose reward (US). For reasons as yet unknown, harnessed bees only learn visual cues in association with sucrose if their antennae are ablated. However, slow acquisition and low retention performances are obtained in this case. Here, we established a novel visual conditioning protocol, which allows studying visual learning and memory in intact harnessed bees in the laboratory. This protocol consists of conditioning the sting extension reflex (SER) by pairing a visual stimulus (CS+) with an electric shock punishment (US), and a different visual stimulus (CS–) with the absence of shock. Bees with intact antennae learned the discrimination between CS+ and CS– by using chromatic cues, achromatic cues or both. Antennae ablation was not only unnecessary for learning to occur but it even impaired visual SER conditioning because of a concomitant reduction of responsiveness to the electric shock. We thus established the first visual conditioning protocol on harnessed honeybees that does not require injuring the experimental subjects. This novel experimental approach opens new doors for accessing the neural correlates of visual learning and memory in honeybees.

Odour aversion after olfactory conditioning of the sting extension reflex in honeybees

In Pavlovian conditioning, an originally neutral stimulus (conditioned stimulus or CS) gains control over an animal's reflex after its association with a biologically relevant stimulus (unconditioned stimulus or US). As a consequence, a conditioned response is emitted by the animal upon further CS presentations. In such a situation, the subject exhibits a reflex response, so that whether the CS thereby acquires a positive or a negative value for the animal is difficult to assess. In honeybees, Apis mellifera, an odour (CS) can be associated either with sucrose solution (US) in the appetitive conditioning of the proboscis extension reflex (PER), or with an electric shock (US) in the aversive conditioning of the sting extension reflex (SER). The term ;aversive' may not apply to the latter as bees do not suppress SER as a consequence of learning but, on the contrary, start emitting SER to the CS. To determine whether the CS acquires a positive or a negative value in these conditioning forms, we compared the orientation behaviour of freely walking honeybees in an olfactory-cued Y-maze after training them with an odour-sucrose association (PER conditioning) or an odour-shock association (SER conditioning). We show that the same odours can acquire either a positive value when associated to sucrose, or a negative value when associated to an electric shock, as bees respectively approach or avoid the CS in the Y-maze. Importantly, these results clearly establish the aversive nature of SER conditioning in honeybees.

Reappraising social insect behavior through aversive responsiveness and learning

Background

The success of social insects can be in part attributed to their division of labor, which has been explained by a response threshold model. This model posits that individuals differ in their response thresholds to task-associated stimuli, so that individuals with lower thresholds specialize in this task. This model is at odds with findings on honeybee behavior as nectar and pollen foragers exhibit different responsiveness to sucrose, with nectar foragers having higher response thresholds to sucrose concentration. Moreover, it has been suggested that sucrose responsiveness correlates with responsiveness to most if not all other stimuli. If this is the case, explaining task specialization and the origins of division of labor on the basis of differences in response thresholds is difficult.

Methodology

To compare responsiveness to stimuli presenting clear-cut differences in hedonic value and behavioral contexts, we measured appetitive and aversive responsiveness in the same bees in the laboratory. We quantified proboscis extension responses to increasing sucrose concentrations and sting extension responses to electric shocks of increasing voltage. We analyzed the relationship between aversive responsiveness and aversive olfactory conditioning of the sting extension reflex, and determined how this relationship relates to division of labor.

Principal Findings

Sucrose and shock responsiveness measured in the same bees did not correlate, thus suggesting that they correspond to independent behavioral syndromes, a foraging and a defensive one. Bees which were more responsive to shock learned and memorized better aversive associations. Finally, guards were less responsive than nectar foragers to electric shocks, exhibiting higher tolerance to low voltage shocks. Consequently, foragers, which are more sensitive, were the ones learning and memorizing better in aversive conditioning.

Conclusions

Our results constitute the first integrative study on how aversive responsiveness affects learning, memory and social organization in honeybees. We suggest that parallel behavioral modules (e.g. appetitive, aversive) coexist within each individual bee and determine its tendency to adopt a given task. This conclusion, which is at odds with a simple threshold model, should open new opportunities for exploring the division of labor in social insects.

The 3R principle and the use of non-human primates in the study of neurodegenerative diseases: the case of Parkinson's disease

The aim of this paper is to offer an ethical perspective on the use of non-human primates in neurobiological studies, using the Parkinson's disease (PD) as an important case study. We refer, as theoretical framework, to the 3R principle, originally proposed by Russell and Burch [Russell, W.M.S., Burch, R.L., 1959. The Principles of Humane Experimental Technique. Universities Federation for Animal Welfare Wheathampstead, England (reprinted in 1992)]. Then, the use of non-human primates in the study of PD will be discussed in relation to the concepts of Replacement, Reduction, and Refinement. Replacement and Reduction result to be the more problematic concept to be applied, whereas Refinement offers relatively more opportunities of improvement. However, although in some cases the 3R principle shows its applicative limits, its value, as conceptual and inspirational tool remains extremely valuable. It suggests to the researchers a series of questions, both theoretical and methodological, which can have the results of improving the quality of life on the experimental models, the quality of the scientific data, and the public perception from the non-scientist community.

The mandible opening response: quantifying aggression elicited by chemical cues in ants

Social insects have evolved efficient recognition systems guaranteeing social cohesion and protection from enemies. To defend their territories and threaten non-nestmate intruders, ants open their mandibles as a first aggressive display. Albeit chemical cues play a major role in discrimination between nestmates and non-nestmates, classical bioassays based on aggressive behaviour were not particularly effective in disentangling chemical perception and behavioural components of nestmate recognition by means of categorical variables. We therefore developed a novel bioassay that accurately isolates chemical perception from other cues. We studied four ant species: Camponotus herculeanus, C. vagus, Formica rufibarbis and F. cunicularia. Chemical analyses of cuticular extracts of workers of these four species showed that they varied in the number and identity of compounds and that species of the same genus have more similar profiles. The antennae of harnessed ants were touched with a glass rod coated with the cuticular extract of (a) nestmates, (b) non-nestmates of the same species, (c) another species of the same genus and (d) a species of a different genus. The mandible opening response (MOR) was recorded as the aggressive response. In all assayed species, MOR significantly differed among stimuli, being weakest towards nestmate odour and strongest towards odours originating from ants of a different genus. We thus introduce here a new procedure suitable for studying the chemical basis of aggression in ants.

Flight and fight: a comparative view of the neurophysiology and genetics of honey bee defensive behavior

Honey bee nest defense involves guard bees that specialize in olfaction-based nestmate recognition and alarm-pheromone-mediated recruitment of nestmates to sting. Stinging is influenced by visual, tactile and olfactory stimuli. Both quantitative trait locus (QTL) mapping and behavioral studies point to guarding behavior as a key factor in colony stinging response. Results of reciprocal F1 crosses show that paternally inherited genes have a greater influence on colony stinging response than maternally inherited genes. The most active alarm pheromone component, isoamyl acetate (IAA) causes increased respiration and may induce stress analgesia in bees. IAA primes worker bees for 'fight or flight', possibly through actions of neuropeptides and/or biogenic amines. Studies of aggression in other species lead to an expectation that octopamine or 5-HT might play a role in honey bee defensive response. Genome sequence and QTL mapping identified 128 candidate genes for three regions known to influence defensive behavior. Comparative bioinformatics suggest possible roles of genes involved in neurogenesis and central nervous system (CNS) activity, and genes involved in sensory tuning through G-protein coupled receptors (GPCRs), such as an arrestin (AmArr4) and the metabotropic GABA(B) receptor (GABA-B-R1).

Aversive learning in honeybees revealed by the olfactory conditioning of the sting extension reflex

Invertebrates have contributed greatly to our understanding of associative learning because they allow learning protocols to be combined with experimental access to the nervous system. The honeybee Apis mellifera constitutes a standard model for the study of appetitive learning and memory since it was shown, almost a century ago, that bees learn to associate different sensory cues with a reward of sugar solution. However, up to now, no study has explored aversive learning in bees in such a way that simultaneous access to its neural bases is granted. Using odorants paired with electric shocks, we conditioned the sting extension reflex, which is exhibited by harnessed bees when subjected to a noxious stimulation. We show that this response can be conditioned so that bees learn to extend their sting in response to the odorant previously punished. Bees also learn to extend the proboscis to one odorant paired with sugar solution and the sting to a different odorant paired with electric shock, thus showing that they can master both appetitive and aversive associations simultaneously. Responding to the appropriate odorant with the appropriate response is possible because two different biogenic amines, octopamine and dopamine subserve appetitive and aversive reinforcement, respectively. While octopamine has been previously shown to substitute for appetitive reinforcement, we demonstrate that blocking of dopaminergic, but not octopaminergic, receptors suppresses aversive learning. Therefore, aversive learning in honeybees can now be accessed both at the behavioral and neural levels, thus opening new research avenues for understanding basic mechanisms of learning and memory.

Can Invertebrates Suffer? or, How Robust is Argument-By-Analogy?

It is a popular notion that, compared to vertebrates, invertebrates have a reduced capacity to experience suffering. This is usually based on arguments that invertebrates show only simple forms of learning, have little memory capacity, do not show behavioural responses to stimuli that would cause ‘higher’ vertebrates to exhibit responses indicative of pain, and have differences in their physiology that would preclude the capacity for suffering. But, how convincing is this ‘evidence’ of a reduced capacity to suffer? Suffering is a negative mental state - a private experience - and, as such, it cannot be measured directly. When assessing the capacity of an animal to experience suffering, we often compare the similarity of its responses with those of ‘higher’ animals, conceptualized in the principle of argument-by-analogy. By closely examining the responses of invertebrates, it can be seen that they often behave in a strikingly analogous manner to vertebrates. In this paper, I discuss published studies that show that invertebrates such as cockroaches, flies and slugs have short- and long-term memory; have age effects on memory; have complex spatial, associative and social learning; perform appropriately in preference tests and consumer demand studies; exhibit behavioural and physiological responses indicative of pain; and, apparently, experience learned helplessness. The similarity of these responses to those of vertebrates may indicate a level of consciousness or suffering that is not normally attributed to invertebrates. This indicates that we should either be more cautious when using argument-by-analogy, or remain open-minded to the possibility that invertebrates are capable of suffering in a similar way to vertebrates.

The opiate system in invertebrates

The presence in diverse species of a similar mode of communication, that of a soluble messenger binding to a receptor, raises the question as to whether the specific components of this system are equally widespread. Do invertebrates use the same hormones and receptors as vertebrates do? Invertebrates ranging from unicellular organisms to insects have been shown to contain opiate-like peptides and binding sites, and they exhibit biological responses to opiates. However, critical genetic data are lacking. It is not known how signal systems arise phylogenetically, but it is conceivable that signal molecules that are already present cause the formation of their own receptors from membrane proteins.

Opiate effect on the threat display in the crab Carcinus mediterraneus

The well-known defense response of a crab (laterus merus display, LMD) was easily evoked in Carcinus mediterraneus by striking the cephalothoraxic protogastric region between the eyestalks. Following a program aimed at investigating the regulatory action of diverse neuromodulators on the LMD of this crab, a study on the role of opioids was started by testing the effect of morphine administration. Injection of morphine HC1 (MP) (40, 50, 60, 70, or 100 micrograms/g) produced a dose-dependent reduction of the LMD so elicited that dissipated with the postinjection time. Only MP doses higher than 50 micrograms/g were effective 30 min after drug administration. The MP-induced inhibition of LMD was blocked by a 4.8-micrograms naloxone HC1/g dose injected 10 min before MP. These results and those previously obtained as the action of GABA on the LMD of this crab are discussed in connection with results reporting a similar effect of these drugs on another agonistic item of behavior in the crab Chasmagnatus granulatus. The possibility of demonstrating habituation of the LMD to an iterated stimulation in C. mediterraneus and of using such a process to elucidate the acting paths of the drugs is discussed.

Morphine analgesia, tolerance and addiction in the cricket Pteronemobius sp. (Orthoptera, Insecta)

The escape reaction time (ERT) of the cricket Pteronemobius sp. from the heated box begins at 48 degrees and increases with temperature until 56 degrees C, beyond which there is no further increase. The ERT (2.2 +/- 1.39 s) from the hot box at 54 degrees C is used as a model for studying the analgesic effects of opiates. Results of the present paper show that the ERT did not change after injecting the insect in the abdominal haemocoel with 0.9% saline solution, but ERT increased when 0.32, 0.52 or 0.69 mg/g of morphine is injected in the same place. The maximum ERT increase is reached at 90 min after drug injection, and the drug effect disappears 3 h after the injection. At 90 min after drug injections, the dose of 0.50 mg/g of morphine produces 50% of ERT increase, and it is referred to as the median analgesic dose (D50). 1.05 mg/g of morphine produces an ERT longer than 30 s that results in an irreversible damage to the insect. Sixty-four micrograms/g of naloxone given in addition to D50 of morphine fully blocked the effect of morphine during its 3-h action. However, more than 64 micrograms/g of naloxone alone also increase the ERT in the cricket, similar to what has been described for vertebrates. Four daily morphine injections of D50 decreased ERT in such a way that, at the fourth day, the ERT is similar to the ERT produced by saline solution; i.e., tolerance is shown. The suppression of daily morphine injections of D50 during the fifth day produced a hyperresponse to vibration (big jumps) not shown in the case of the injections of saline solution; i.e., addiction is shown.

Central effect of morphine pretreatment on short- and long-term habituation to a danger stimulus in the crab Chasmagnathus

Morphine is believed to inhibit the crab's escape response to a danger stimulus due to central drug action. To test alternative explanations of such an effect in terms of afferent and/or efferent impairment, experiments were conducted using the crab's optokinetic response as indicator. Doses of morphine with maximal detrimental effect on the escape response (75-100 micrograms/g) showed no effect on the optokinetic response, both by measuring the crab's eyestalk displacement and by recording its body rotation, supporting the hypothesis of a morphine central action on the danger-induced escape response. As regards the effect on habituation, a 75 micrograms morphine/g injection administered 30 min before the first trial produced a parallel shift of the short-term (within-session) habituation curve, suggesting a modulatory central drug action that would mimic a putative endogenous opioid action. A 100 morphine micrograms/g dose injected 30 min before training sharply reduced reactivity during training and impaired the acquisition of long-term (between-session) habituation. It may be speculated that the decrease in the danger meaning of the stimulus due to morphine explains both effects in terms of a stimulation impairment during training.

Effect of morphine and naloxone on a defensive response of the crab Chasmagnathus granulatus

Male crabs (Chasmagnathus granulatus) exhibited a defensive response (DR) to an electric shock (8 V, 50 Hz, 1 sec). The DR so elicited was used as a model for studying the antinociceptive effect of morphine. Injections of morphine-HCl (MP) (25, 50, 100 and 150 micrograms/g) were administered and the DR was examined at 2, 7.5, 15, 30, 45 and 75 min post-injection. (a) MP produced a dose-dependent reduction of the crab's sensitivity to the nociceptive stimulus. (b) A 100 micrograms/g dose of MP caused a 50% response inhibition with an injection-shock interval of 30 minutes, but no inhibition occurred when the same dose was administered with 1.6 micrograms/g of naloxone-HCl, suggesting that MP acts through an opiate receptor. (c) The ED50 at 2 min post-injection was roughly 33 micrograms/g and the threshold dose was estimated to be 6.8 micrograms/g. These doses are lower than ED50 values reported for other arthropods (90 to 930 micrograms/g) and approach those of vertebrates. (d) The peak MP effect was reached quickly, within 2 min post-injection. The duration of the MP effect was calculated to be 45.0-75.0 min depending on the dose, and an indirect estimate of half-life elimination was 15.7 min. These values are remarkably lower than those reported for vertebrates. The shorter duration of the MP peak effect is attributable to a greater permeability of the arthropod blood-brain barrier as compared to that of vertebrates.

Habituation in the crab Chasmagnathus granulatus: effect of morphine and naloxone

The escape response decrement shown by the crab Chasmagnathus granulatus as a consequence of repeated shadow presentation, meets five of the seven tested parametric criteria of habituation. Results concerning stimulus generalization and dishabituation strongly suggest that neither motor fatigue nor sensory adaptation can account for the response waning. The effects of morphine and naloxone on performance were also studied. Neither 50 nor 5 micrograms morphine/g exerted any modulatory effect on memory retention. A dose of 50 micrograms morphine/g produced an anterograde detrimental effect on responsiveness but no long-term training effects could be detected after the drug's period of action. A dose of naloxone of 1.6 micrograms/g did not antagonize the effect of morphine. The potential value of the response habituation as a model for studying both habituation dynamics and the mechanisms that subserve it, and also for elucidating the effects of opiates on this memory process, is discussed.

Passive avoidance learning in the crab Chasmagnathus granulatus

Male crabs Chasmagnathus granulatus were trained by means of a method similar to the standard inhibitory avoidance technique widely used in vertebrates. Each crab was placed in the dark compartment (DC) of a double-chamber device, allowed to move towards the light compartment (LC) and latency to enter measured. Experimental crabs received a shock in LC, but controls were not punished. After 1 min, both experimental and control crabs were free to return to DC. On completion of 1, 2, 3 or 24 hr intertrial interval in DC a retention test was administered and latency to enter LC was measured. A single trial was proven enough to establish a LC-shock association that was detected up to 3 hr later, but no retention was proved after 24 hr. Memory was disrupted when crabs were removed from the apparatus during the 3 hr intertrial interval. Similarities and differences between the passive avoidance method used with crabs and that used with vertebrates are discussed.

Opioid involvement in the control of feeding in an insect, the American cockroach

Administration of the kappa opiate agonist, U-50,488H (0.10-10 mg/kg), produced over three hours a significant dose-dependent increase in the ingestive responses of free feeding American cockroaches, Periplaneta americana. These effects could be decreased by the opiate antagonist, naloxone (1.0 mg/kg), with naloxone by itself blocking the augmented feeding responses of food-deprived cockroaches. The mu opiate agonist, morphine (1.0-20 mg/kg) caused a significant dose-dependent and naloxone-reversible increase in the locomotory activity of cockroaches. These results suggest that opioid systems may be involved in the control of the feeding in cockroaches in a manner analogous to that proposed for vertebrates.

Opiate receptor in praying mantis: effect of morphine and naloxone

A praying mantis displays a "frightening reaction" called deimatic reaction (DR), any time that it is faced with a patterned visual stimulus that represents a potential damage for the insect. Results of the present paper show that the DR could be also elicited by an actual noxious (an electrical shock) and that this response is similar to that elicited by a potential nociceptive stimulus (a patterned visual stimulus). The DR elicited by the electric shock was used as a model for studying the analgesic effect of opiates. The mantis was placed in an apparatus that allowed us to give the insect an electrical shock and to measure the strength of its DR. During a first session the voltage threshold necessary to induce a full DR was determined, and then, the insect was injected with a certain solution. The voltage threshold was tested one, two and four hours after injection. Mantises that were injected with only distilled water showed no changes in their voltage threshold during the three tests. Injections of 300, 350 and 400 micrograms/g of morphine-HCl increased the voltage threshold in both a time-dependent and a dose related manner. A dose of 350 micrograms/g of morphine-HCl produced 50% of response inhibition after two hours of injections and is referred to as the median antinoxious dose ( AD50 ). Sixteen micrograms/g of naloxone given in conjunction with an AD50 of morphine, partially blocked the effect of morphine during the first hour and fully blocked it during the second hour. Thirty-two micrograms/g of naloxone fully blocked the morphine effect during the first and the second hour. However, more than 48 micrograms/g of naloxone alone also increased the voltage threshold in insects, similar to those described for vertebrates.