Neuro-imaging the serotonin 2A receptor as a valid biomarker for canine behavioural disorders

The serotonergic system is disturbed in different mood and affective disorders, with especially the serotonin (5-HT) 2A receptor involved in impulsive aggressiveness and anxiety. The aim of the study was to evaluate the involvement of the brain 5-HT 2A receptor in dogs with different behavioural disorders.Three groups of drug naive dogs were studied: 22 dogs showing impulsive aggressive behaviour, 22 showing normal behaviour, and 22 showing anxious behaviour. The serotonin 2A receptor was evaluated with Single Photon Emission Computed Tomography (SPECT) and the serotonin 2A receptor-selective radiopharmaceutical ¹²³I-R91150. A serotonin 2A receptor binding index (BI), proportional to the cortical receptor density, was calculated. A receiver operating characteristic (ROC) analysis was performed to determine cut-off values at which optimal sensitivity and specificity are achieved and to evaluate the general performance of the BI in reflecting the state of the dog, i.e., impulsive aggressive, normal or anxious.Significantly (P < 0.0056) altered 5-HT 2A receptor binding indices were found in bilateral frontal, temporal and occipital cortical brain areas of the dogs behaving abnormally, with consistently increased BI in impulsive aggressive dogs and decreased BI in anxious dogs. These results provide clear evidence for a disturbed serotonergic balance in canine impulsive aggression and anxiety disorders. A right frontal cut-off value of ⩾1.92 with 86.4% sensitivity and 2.3% (1-specificity) was obtained for the impulsive aggressive dogs. Differentiating the anxious dogs from the rest of the population was possible with a cut-off value of ⩽1.73 with 86.4% sensitivity and 18.2% (1-specificity).We conclude that SPECT imaging with the radioligand ¹²³I-R91150 can be a helpful tool in evaluating the involvement of the serotonin 2A receptor in the complex mechanisms of impulsive aggressive and anxious behaviour. The 5HT-2A binding index of the right frontal cortex appears to be a valid biomarker in differentiating the studied canine behavioural disorders.     

Differences in serotonin serum concentration between aggressive English cocker spaniels and aggressive dogs of other breeds

Aggression is one of the most common behavioral problems in dogs and may have important negative effects on public health, human–animal bond, and animal welfare. There is ample evidence showing a negative correlation between serum serotonin concentration and aggressive behavior in a variety of species, including the domestic dogs. This negative correlation is particularly pronounced in dogs that show impulsive aggression. Data obtained in some previous studies suggest that the English cocker spaniel (ECS) is more likely to show impulsive aggression than other breeds. Therefore, the aim of this study was to analyze possible differences in serum serotonin levels between aggressive ECS and aggressive dogs of other breeds. Nineteen ECSs presented for aggression at the Animal Behavior Service (School of Veterinary Science, Barcelona, Spain) were evaluated and compared with 20 aggressive dogs of other breeds attended at the same center. Serum serotonin levels were measured using an enzyme-linked immunosorbent assay method. Statistical analysis was done using the SPSS 15.0 for Windows. Aggressive ECSs had significantly (P < 0.001) lower levels of serum serotonin than aggressive dogs of other breeds (318.6 ± 67.1 and 852.77 ± 100.58 ng/mL, respectively). Variances were not significantly different between ECSs and other breeds (standard deviation = 449.84 ng/mL vs. 292.47 ng/mL, P > 0.05). This finding may explain why ECSs are more likely to show impulsive aggression than other breeds, and suggests that the ECS could be a good model to study the neurophysiologic mechanisms underlying impulsive aggression.     

REGIONAL BINDING INDEX OF THE RADIOLABELED SELECTIVE 5-HT2A ANTAGONIST 123I-5-I-R91150 IN THE NORMAL CANINE BRAIN IMAGED WITH SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY

The pattern of the specific 5-HT2A (5-hydroxytryptamine 2A receptor) antagonist 123I-5-I-R91150 was measured in 10 healthy dogs without neurologic and behavior abnormalities. Eight cortical regions (left and right fronto-, temporo-, parieto-, and occipitocortical area), one global subcortical region (including the thalamic system) were compared with a reference region lacking receptors; that is, the cerebellum. The 123I labeled radioligand was injected intravenously 100-200 minutes before acquisition. Both transmission and emission data were obtained with a triple head gamma camera equipped with high-resolution fanbeam collimators. The emission data were corrected for scatter and attenuation. To delineate different cerebral regions more accurately, the regions of interest (ROI) defined in a former study on brain perfusion measured with 99mTc-ethyl cysteinate dimer (ECD) in the same dogs were used. The co-registration of the 99mTc-ECD and the 123I-5-I-R91150, obtained from each dog, was realized with the help of corresponding transmission maps. By normalizing each regional cerebral activity to the activity observed in the cerebellum, the regional radioactivity (binding index) could be relatively quantified. Highest brain uptake was noted in the frontocortical brain areas (right: 1.85, left: 1.89), followed by the temporocortical region (right: 1.58, left: 1.56). Least uptake was noted in the more caudal and middle brain regions [occipito- (right: 1.46, left: 1.41), parietocortical (right: 1.30, left: 1.26), and striatal region (1.19)]. No gender nor age influence was noted in this series. The 123I labeled serotonin-2A receptor ligand seems to have similar cortical binding in the normal canine brain, as shown in humans and other animal species. A frontocortical to occipitocortical (rostrocaudal) binding index gradient was identified within the dog, which has not been seen in imaging studies from humans and other animal species. The significance of these results will need further investigation. This normative data can be used to compare regional brain uptake of the 123I-radioligand to dogs with behavioral disorders related to the serotonergic system, in future studies.     

Effect of fluoxetine on blood concentrations of serotonin, cortisol and dehydroepiandrosterone in canine aggression

Canine aggression directed towards people is the most frequent reason for referral to behaviour practices. The serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis are believed to play an important role in controlling aggression. The selective serotonin reuptake inhibitor fluoxetine is the most commonly used drug in canine aggression. The aim of the present study was to assess the effect of a 30-day-long fluoxetine treatment on the peripheral serotonergic system and the HPA axis in canine aggression. To this end, the concentrations of serum serotonin (5-HT) and plasma cortisol and dehydroepiandrosterone (DHEA) were analysed in a group of aggressive (n = 22) and nonaggressive dogs (n = 9) during pre- (day 0) and posttreatment (day 30) conditions. Treatment caused a significant decrease in 5-HT concentrations (46% in the aggressive group and 32% in the control group). There was a trend towards a rise of DHEA/cortisol ratio values after treatment both in the aggressive and the control group. The determination of blood 5-HT and the DHEA/cortisol ratio could have important clinical applications in the future for deciding which animals might benefit from a given treatment as well as for monitoring the response. Further large-scale studies with this aim should be carried out to obtain sound conclusions.     

Differential serotonergic mediation of aggression in roosters bred for resistance and susceptibility to Marek’s disease

1. Serotonin (5-HT) is a primary regulating neurotransmitter involved in aggressive and impulsive behaviours in mammals. Previous studies have also demonstrated that the function of the serotonergic system in regulating aggression is affected by both genetic and environmental factors. The serotonergic system may display similar functions in chickens.

2. Our objective was to investigate the aggressive and impulsive behavioural response to antagonism of the 5-HT1A and 1B receptors in cocks bred for susceptibility and resistance to Marek’s disease (i.e. strain 7₂ and 6₃, respectively).

3. Cocks from strain 7₂ exhibited increased aggressive behaviours and lower brain 5-HT concentrations compared to strain 6₃ cocks.

4. Antagonism of 5-HT1A receptors increased aggressiveness and reduced serotonin turnover in strain 7₂, but not strain 6₃ cocks. 5-HT1B receptor antagonism had no effect on aggression or serotonin turnover in either strain.

5. Levels of the serotonin metabolite 5-HIAA, but not absolute central 5-HT levels, were altered in both strains following 5-HT1B antagonism, but only in strain 7₂ cocks following 5-HT1A antagonism.

6. The data suggest that 5-HT1A and 1B regulate aggression differently in high and low aggressive strains.     

Relationship between the serum concentrations of serotonin and lipids and aggression in dogs

The serum concentrations of serotonin and lipids--triglycerides, total cholesterol, low density lipoprotein, high density lipoprotein and very low density lipoprotein--were determined in 18 normal dogs and 23 dogs diagnosed as aggressive on the basis of interviews with their owners and an assessment of their behaviour with reference to a canine overt aggression chart. The serum serotonin levels in the aggressive dogs were significantly lower than in the normal dogs (P<0.01), but the differences in serum lipids between the two groups were not statistically significant.     

Fluoxetine combined with clorazepate dipotassium and behaviour modification for treatment of anxiety-related disorders in dogs

The effectiveness of clorazepate dipotassium combined with fluoxetine and a behaviour modification programme for the treatment of anxiety disorders in dogs was investigated. Forty dogs with anxiety disorders were initially enrolled and 36 dogs completed the trial. Dogs were classified into two behavioural categories (anxious dogs with aggression and anxious dogs without aggression) according to their presenting complaints, and were also subdivided into males, females, juveniles and adults. The dog owners were provided with a behaviour modification plan for their dogs to be commenced in the first week of therapy. Clorazepate dipotassium was administered PO at 1.0 mg/kg every 24 h for 4 weeks, and fluoxetine was administered PO at 1.0 mg/kg every 24 h for 10 weeks. Therapy with both drugs was initiated simultaneously. Improvement was reported in 25/36 dogs. Significant differences in treatment effects were observed between anxious dogs with aggression and anxious dogs without aggression (P < 0.05). Positive correlations between owner compliance with the treatment plan and reported improvement achieved during three periods of study were also noted.     

不同周龄蛋鸡攻击行为与五羟色胺、皮质酮的相关性分析

为探讨蛋鸡攻击行为与五羟色胺、皮质酮的相关性,选用1日龄京白939雏鸡96只,随机分为6个重复,每重复16只,采用瞬时观察法和连续观察法筛选不同周龄攻击行为有差异的蛋鸡,结合ELISA和qRT-PCR方法测定蛋鸡血清激素水平和5-HT1A受体mRNA表达量的变化。结果显示:蛋鸡的攻击行为随周龄的增加呈现逐渐上升的趋势(P<0.05);整体看,血清五羟色胺(5-HT)含量随周龄的增加呈下降趋势,皮质酮(CORT)呈现上升趋势(P<0.05),而下丘脑5-HT1A受体mRNA表达量随周龄增加有上升的趋势(P<0.05或P<0.01)。Pearson相关分析结果显示,蛋鸡攻击行为与血清五羟色胺(5-HT)呈极显著负相关(R=-0.741,P<0.01),与皮质酮(CORT)呈显著正相关(R=0.751,P<0.01)。综上所述,血清激素水平与蛋鸡攻击行为有一定联系,5-HT1A受体基因可能参与调控蛋鸡的攻击行为。     

Clomipramine and selegiline: do they influence impulse control?

Anxiety disorders in dogs are often accompanied by loss of impulse control and can result in inappropriate behaviour such as destructiveness, excessive barking and aggression. The reduction of these undesirable actions is the focus of behaviour therapy. Clomipramine and selegiline have been approved for the treatment of separation anxiety in dogs, but there are anecdotal reports that they produce inconsistent therapeutic effect. Hence, the aim of this study was to verify the efficacy of clomipramine and selegiline for regulating impulse control by using a rat model based on the delay of reward procedure. The principle is that the animal has to decide between an immediate small food reward, normally preferred by impulsive animals, and a delayed large food reward. In this study, acute effects of clomipramine (0.3-10.0 mg/kg), selegiline (0.3-3.0 mg/kg), and diazepam (1.0-3.0 mg/kg) on the impulsive behaviour of two breeding lines of rats with different anxiety-related behaviour were investigated. Neither clomipramine nor selegiline had an effect on impulse control in either breeding line. However, motor activity was decreased by clomipramine and increased by selegiline. Diazepam led to an increase in impulsive behaviour of one rat line concomitant with an increase in motor activity. The results of this rat model for studying impulsive behaviour suggest that a single administration of selegiline and clomipramine has no influence on impulsive behaviour.     

Assessment of serotonin in serum,plasma, and platelets of aggressive dogs

Canine aggression is the most common reason for the referral of dogs to behavior practices. In addition, dog bites represent an important problem for public health and animal welfare. The serotonergic system is believed to play an important role in modulating aggression. The aim of the present study was (1) to assess the suitability of different types of blood samples for measuring circulating serotonin in canine clinical studies, and (2) to investigate the relationship between the serotonergic system and canine aggression. The assessment of serotonin was simultaneously carried out in serum, plasma, and platelets of 28 aggressive and 10 nonaggressive dogs with an enzyme immunoassay technique. The mean serotonin concentration in aggressive dogs was significantly lower than in nonaggressive dogs in all the assayed samples. These findings suggest an inverse relationship between the activity of the serotonergic system and canine aggression. Considering the simplicity of the methodology, the authors propose sampling serum as the most suitable method for measuring circulating serotonin in dogs.     

Aggressive behavior in the English cocker spaniel

A high percentage of aggression problems and a tendency to display noninhibited aggression in the English cocker spaniel (ECS) have been suggested by many authors. The authors of this paper designed a retrospective study to analyze the aggressive behavior of 145 ECSs presented for aggression problems to the Animal Behavior Service at the Barcelona School of Veterinary Medicine's veterinary teaching hospital. Aggressive ECSs were compared with a population of dogs of the same breed presented for a behavior problem other than aggression and with a population of aggressive dogs of other breeds. The most common forms of aggression in the ECS were owner-directed aggression (67.6%), aggression toward unfamiliar people (18.4%), aggression toward unfamiliar dogs (10.1%), and aggression toward family dogs (3.3%).Owner-directed aggression was more common in the ECS than in other breeds, although in similar contexts. In the ECS, the golden coat color was more common in the aggressive dogs than in nonaggressive dogs. ECSs showed impulsive aggression more frequently than aggressive dogs of other breeds. The aim of the study was to analyze cases of aggressive ECSs seen in a referral practice.     

Association of pruritus with anxiety or aggression in dogs

OBJECTIVE: To evaluate the association between pruritus and anxiety-related and aggressive behaviors in dogs. DESIGN: Cross-sectional survey. ANIMALS: 238 dogs between 1 and 8 years old. PROCEDURES: Information including a score for general degree of pruritus (visual analogue scale from 0 to 10) and frequency of anxiety-related and aggressive behaviors was collected via a survey distributed to clients at 3 privately owned practices. RESULTS: Median score for pruritus was 2.4. Dogs were assigned to 2 groups on the basis of pruritus score (nonpruritic [0 to 2.4] and pruritic [2.5 to 10]). There was no significant difference between pruritic and nonpruritic dogs with regard to aggression or with regard to reactivity to being alone; to thunderstorms or noises; or to unfamiliar people, animals, or objects. Post hoc analysis revealed significantly more reactivity to thunderstorms or noises in dogs treated with glucocorticoids (18/37 [49%]) than in those not administered glucocorticoids (57/197 [29%]). CONCLUSIONS AND CLINICAL RELEVANCE: An association was not detected between pruritus and aggressive, anxious, or fearful behavior in dogs. There was greater reactivity to thunderstorms or noises in glucocorticoid-treated dogs. These findings do not preclude the possibility of a relationship between certain dermatoses or pruritic conditions and behavior. However, a concurrent behavioral abnormality cannot be assumed to result from a dermatosis and be expected to resolve with treatment of only the skin disease. Dogs with behavioral disorders and pruritic disease require primary treatment of both conditions. Additional studies to examine the effect of disease and glucocorticoids on canine behavior are warranted.     

Food intake and rumen motility in dwarf goats. Effects of some serotonin receptor agonists and antagonists

The serotonergic regulation of feeding behaviour has not so far been studied in ruminants. Therefore, the effects of some serotonin (5-HT) receptor agonists and antagonists on food intake and forestomach motility were studied in dwarf goats.Goats ate less food when treated intravenously (IV) with the 5-HT precursor 5-HTP (25 µg, 50 µg or 100 µg kg^–1 min^–1 over 15 min) than when they were treated with 5-HT (which does not pass the blood-brain barrier) or with saline. Accordingly, IV dexfenfluramine infusions (50 µg or 100 µg kg^–1 min^–1 over 15 min), which induces release of brain 5-HT, also led to dose-related reductions in food intake. In contrast, no anorectic effects were observed after IV infusions with the selective 5-HT reuptake inhibitor fluoxetine (100 µg kg^–1 min^–1 over 15 min), the selective 5-HT1A agonist 8-OH-DPAT (0.5 µg kg^–1 min^–1 over 15 min), or eltoprazine (4 or 8 µg kg^–1 min^–1 over 15 min), a mixed 5-HT1A/5HT1B receptor agonist. None of the 5-HT antagonists tested gave any increase in food consumption in this model. Interestingly, the non-selective 5-HT receptor antagonist methysergide (360 µg/kg IV) reduced food intake. This effect was most noticeable at 3 h after injection. The 5-HT3 receptor antagonist ondansetron (IV 10 µg kg^–1 min^–1 over 15 min) and the peripheral 5-HT2 receptor antagonist xylamidine (IV 100 µg kg^–1 min^–1 over 10 min) failed to modify food intake. These results provide evidence for central serotonergic involvement in the control of feeding. However, this control system differs markedly in goats and rodents.Dexfenfluramine, 5-HTP and eltoprazine administered at similar dose rates to those used in the food intake experiments induced some clinical signs including inhibition of forestomach contractions. These results, together with our earlierin vivo andin vitro observations, suggest that the inhibitory effects of serotonin receptor agonists on forestomach contractions are due to interactions with both peripheral and central serotonergic receptors. The change in smooth muscle tension, which leads to a change in the signals transmitted via vagal afferents to the central nervous system, appears not to modify feeding behaviour in dwarf goats.     

Contractile effects of 5-hydroxytryptamine (5-HT) in the equine jejunum circular muscle: functional and immunohistochemical identification of a 5-HT1A-like receptor

REASONS FOR PERFORMING STUDY: Prokinetic drugs used to treat gastrointestinal ileus in man have equivocal results in horses. In man, prokinetic drugs have 5-hydroxytryptamine4(5-HT4) receptors as their target, but little is known about the 5-HT-receptor subtypes in the equine small intestine. OBJECTIVE: Functional and immunohistochemical identification of the serotonin receptor subtype(s) responsible for the 5-HT induced contractile response in the equine circular jejunum. METHODS: Isometric organ-bath recordings were carried out to assess spontaneous and drug-evoked contractile activity of equine circular jejunum. Histological investigations by immunofluorescence analyses were performed to check for presence and localisation of this functionally identified 5-HT receptor subtype. RESULTS: Tonic contractions were induced by 5-HT in horse jejunal circular muscle. Tetrodotoxin, atropine and NG-nitro L-arginine did not modify this response. A set of 5-HT receptor subtype selective antagonists excluded interaction with 5-HT1B, 1D, 2A, 3, 4 and 7 receptors. The selective 5-HT1A receptor antagonists WAY 100635 and NAN 190 caused a clear rightward shift of the concentration-response curve to 5-HT. The contractile effect of 5-CT, that can interact with 5-HT1A, 1B, 1D, 5 and 7 receptors was also antagonised by WAY 100635, identifying the targeted 5-HT receptor as a 5-HT1A-like receptor. Immunohistology performed with rabbit polyclonal anti-5-HT1A receptor antibodies confirmed the presence of muscular 5-HT1A receptors in the muscularis mucosae, and both longitudinal and circular smooth muscle layers of the equine jejunum. CONCLUSIONS: Contractile responses in equine jejunal circular smooth muscle induced by 5-HT involves 5-HT1A-like receptors.     

Increased number of neurons expressing androgen receptor in the basolateral amygdala of pathologically aggressive dogs

The present study aimed to determine the extent to which the androgen receptor (AR) is directly involved in the hormonal modulation of pathological canine aggressive behaviour in the basolateral nuclear group (BNG) of the amygdaloid body. A stereological quantification of AR-positive neurons was performed in the BNGs of normally behaving and aggressive male dogs. The BNG was selected because it is involved in sexual and behavioural activities that are influenced by androgens. In the aggressive dogs the BNG contained a significantly higher number of AR-positive neurons compared with normally behaving dogs suggesting differences in androgen activity within the BNGs of both the groups. However, additional mechanisms are likely to be involved because the AR-negative fraction of BNG neurons was also increased in the aggressive dogs. It was concluded that most of the AR was unliganded because a cytoplasmic staining pattern of AR positivity was observed in the canine BNG neurons. This indicates that genomic androgen actions, which are mediated through the AR are of minor importance in the testosterone modulation of canine aggression within the BNG. Other non-genomic mechanisms through which androgens may exert their action in the BNG are discussed. The aromatase pathway is suggested to be the main mechanism through which testosterone exerts its action within the BNG.     

Modification of spontaneous contractility of smooth muscle preparations from the bovine abomasal antrum by serotonin receptor agonists

The effects of serotonin (5-hydroxytryptamine, 5-HT), a 5-HT2-receptor agonist, alpha-methyl-5-hydroxytryptamine (alpha-M-5-HT) and RS-67506, a 5-HT4 receptor partial agonist, on spontaneous contractility of bovine abomasal smooth muscle preparations were investigated in vitro. Preparations from the abomasal antrum of freshly slaughtered healthy dairy cows were cut parallel to the longitudinal fibres, suspended in isolated organ baths, and concentration-response curves were performed by cumulative application of the 5-HT receptor agonists. Blockade of 5-HT2-induced response was tested with atropine and hexamethonium. Serotonin evoked a significant increase in the area under curve (AUC), whilst the 5-HT2 receptor agonist alpha-M-5-HT significantly increased the AUC and resting tone (RT). RS-67506 induced a significant increase in AUC and RT and a significant decrease in the maximum force. The effect of alpha-M-5-HT was mediated by a muscarinic cholinergic pathway, as the effect of alpha-M-5-HT was inhibited in the presence of atropine but not hexamethonium. It is concluded that 5-HT2 and 5-HT4 receptors are present in the bovine abomasal antrum. Muscarinic receptors are involved in the increase in RT seen after 5-HT2 receptor stimulation.     

Aggressive dogs are characterized by low omega-3 polyunsaturated fatty acid status

Canine aggressive behaviour is one of the most common problems being reported by dog owners. However, the biochemical basis of this phenomenon remains unclear. In humans, alterations in omega-3 plasma polyunsatured fatty acids and elevated omega6/omega-3 ratio have been linked to behavioural alterations, including aggression. Thus far, however, the relationship between plasma polyunsatured fatty acid status and aggression has not been investigated in the dog. In the present study we sought to investigate whether polyunsatured fatty acid status could be altered in plasma of pathologically aggressive Canis familiaris. Eighteen adult male German Shepherd dogs, aged 4.9 ± 0.9 years, showing no clinical signs but aggression, were investigated. Eighteen healthy male dogs, aged 4.8 ± 0.7 years, with a negative history of behavioural and neurological disorders served as controls. Baseline fasting plasma polyunsatured fatty acid composition was determined by gas chromatography. Compared to normal dogs, aggressive dogs showed lower docosahexaenoic acid (22:6 n-3) concentrations and a higher omega6/omega-3 ratio. In addition, they showed reduced cholesterol and bilirubin concentrations compared to their normally behaving counterparts. Altogether, our results suggest that low omega-3 fatty acids may adversely impact behaviour in dogs, resulting in greater propensity to aggression. However, given the cross-sectional design of our study, we cannot claim any causal relationship between the presence of alterations in fatty acid status and canine aggressiveness. Whether omega-3 fatty acids supplementation may be useful to reduce aggressive behaviour in the dog deserves further investigation.     

Comparison of the efficacy of remote consultations and personal consultations for the treatment of dogs which are aggressive towards their owners

Two groups of 42 dogs which were aggressive towards their owners were enrolled into a study designed to compare the efficacy of remote consultations with direct personal consultations for the treatment of the aggressive behaviour. The level of aggression of the dogs was assessed before and after programmes designed to modify their behaviour. Both programmes resulted in a significant reduction in the aggressive behaviour of the dogs towards their owners, and there was no significant difference between the effectiveness of the recommendations, whether they were made without having seen the dog or during a personal consultation with the dog and its owner.     

Recognizing and assessing aggressive behaviour in dogs

Within the population the sensitivity to aggressive behaviour in dogs has increased. The authorities are confronted with a problem: if any incident occurs it is their task to decide whether the dogs involved constitute a threat to other people or whether the charge is only the result of a quarrel between neighbours. For this reason, an examination of the dogs with regard to their aggressive behaviour is necessary. Seen from the biological point of view, aggressive behaviour is one of four possibilities a dog can chose from to solve a conflict. The dog's intention in showing aggressive behaviour is to eliminate disturbances and to maintain a distance in space and time. Aggressive behaviour might also be necessary to acquire or defend resources essential to the dog's life. This is to secure its survival and its success in reproduction. One can see from this that aggressive behaviour is a very important and biologically necessary adjustment factor. However, when living together with man aggressive behaviour might become a problem. For the assessment and the therapy of the problem it is necessary to exa-mine the behaviour shown by the dog with regard to its cause. To be able to do this an exact anamnesis, a medical check, and an examination of the dog on the basis of its display in special situations are necessary. For this reason, exclusively veterinarians with a special further education in the field of behaviour should carry out the examination of dogs.     

Pain-related aggression in dogs: 12 clinical cases

The aim of this retrospective study was to describe the main features of pain-related aggression in dogs. Twelve dogs presented for aggressive problems at the Veterinary Hospital of the Autonomous University of Barcelona, Spain, were included, and a questionnaire was used to gather information on the context of the aggression, body posture during the attack, impulsiveness, and aggressive behavior before the onset of the pain-eliciting condition. The most common cause of pain was hip dysplasia (66.7%), but no relationship was found between the cause of pain and the characteristics of the aggressive behavior. Dogs were classified as having been aggressive before or after the onset of painful condition. Dogs that had not been aggressive before the onset of the pain-eliciting condition were more impulsive (df = 1, χ² = 5.3, P = 0.0209), showed aggression as a result of manipulation context more frequently (df = 1, χ² = 6, P = 0.0143), and adopted a defensive body posture more frequently (df = 1, χ² = 3.733, P = 0.0533) than dogs that had been aggressive before the onset of pain. These results suggest that previous expression of aggressive behavior has a major effect on the pattern of pain-related aggression in dogs.