Elsevier

Journal of Veterinary Behavior

Volume 7, Issue 6, November–December 2012, Pages 348-352
Journal of Veterinary Behavior

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

https://doi.org/10.1016/j.jveb.2012.01.005Get rights and content

Abstract

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.

Introduction

Canine aggression is the most common reason for the referral of dogs to animal behaviorists (Bamberger and Houpt, 2006, Fatjó et al., 2007). Dog bites represent an important problem for public health (Overall and Love, 2001, Palacio et al., 2005). They also pose a problem in the field of animal welfare, as a significant proportion of aggressive dogs is euthanized or abandoned (Hunthausen, 1997, Mikkelsen and Lund, 2000). If these problems are to be prevented and effectively managed, it is necessary to deepen the understanding of the biological basis of canine aggression.

Serotonergic neurotransmission is believed to play a critical role in the control of aggression in several species (Ferrari et al., 2005). Low concentrations of the main serotonin (5-HT) metabolite 5-hydroxyindoleacetic acid in cerebrospinal fluid (CSF) have been associated with low thresholds for aggression or impulsivity in human and nonhuman primates (Mehlman et al., 1994, Stanley et al., 2000, Soderstrom et al., 2001, Howell et al., 2007) as well as in dogs (Reisner et al., 1996).

Technical and ethical restrictions linked to the study of the serotonergic system in psychiatric disorders through CSF and neurohistochemical studies have led scientists to search for more easily accessible biological samples. The platelet where blood 5-HT is mainly stored (Kema et al., 2000) has been proposed as a peripheral marker of the serotonergic neuron (Plein and Berk, 2001). Although blood 5-HT does not cross the hematoencephalic barrier, a correlation between blood and CSF serotonergic parameters has been found in humans (Sarrias et al., 1990). In the realm of human aggression, the measurement of blood 5-HT has offered inconclusive results, as both low (Goveas et al., 2004) and high (Golubchik et al., 2009) concentrations have been found to be linked to aggressive behavior in different populations. In canine species, 2 recent studies have reported low serum serotonin concentrations in aggressive individuals (Çakiroglu et al., 2007, Rosado et al., 2010a).

The aim of the present study was 2-fold. First, to assess the suitability of different types of blood samples for measuring circulating 5-HT in clinical studies in canine species. Second, to further investigate the relationship between the serotonergic system and canine aggression. To this end, the assessment of 5-HT was simultaneously carried out in serum, plasma, and platelets of aggressive and nonaggressive dogs.

Section snippets

Aggressive animals

Two Spanish veterinary teaching hospitals (Universidad de Zaragoza and Cardenal Herrera-CEU, Valencia) contributed to the collection of cases. Dogs included in the present study were referred to the Companion Animal Behavior Services within the respective hospitals owing to problems of aggression toward people and/or other dogs. Displaying any other type of behavioral problem did not constitute an exclusion criterion. Animals showing an underlying causative medical condition to the problem of

Results

The unifactorial multivariate analysis of variance showed a significant effect of the factor “aggression” on 5-HT concentrations (P < 0.01). Aggressive animals showed lower 5-HT concentrations in serum, plasma, and platelets than nonaggressive animals. The higher mean 5-HT concentration was detected in serum samples. Serotonin results according to the type of sample are summarized in Table.

Serotonin concentration in platelets was positively correlated with that in serum (r = 0.465; P < 0.01)

Discussion

In the present study, the assessment of 5-HT in serum, plasma, and platelets was carried out both in aggressive and nonaggressive dogs. Regardless of the type of sample, aggressive dogs showed significantly lower concentrations of circulating 5-HT than nonaggressive dogs. This finding agrees with previous studies that found an association between high aggression or impulsivity and low concentrations of CSF 5-hydroxyindoleacetic acid and circulating 5-HT in primates (CSF: Mehlman et al., 1994,

Acknowledgment

The authors are grateful to María Yetano for language support.

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