New Research on Pitbull Aggression -- Neuroanatomy & Neurochemicals

New research on pitbull aggression….

I am guessing that everyone reading is hoping to find support to their “side” of the debate – whether pitbulls are inherently dangerous, if they are nanny dogs, or if it is all in how you raise them.  Just as a reminder – no dog is a “nanny dog”.  Watching children is the human’s responsibility.

But getting back to aggression….  The issues with the increased aggression we see in the US goes beyond pitbulls and bully breeds because there are genetic and neurochemical changes we are currently witnessing across many/all breeds resulting in increased aggression.  I have personally seen a lot more aggression overall (and more serious displays of aggression) in recent years across all breeds, and even in breeds that most people may not immediately associate with aggression, such as Golden Retrievers and Pugs. Obviously, large bully breeds -- which include pitbulls -- can do a LOT more damage than some other breeds, and we are also seeing an increase in dogs who have uninterruptible aggression intended to kill the victim.  This MUST be distinguished from inhibited bites that are intended to increase distance away from a stressor and not to seriously maim or kill the victim.  Regardless, there are increases in bites and aggression overall across breeds and mixes.  The genetic and neurochemical changes we are seeing in many breeds is on top of negative cultural changes that are occurring at the same time with how people raise their pets, such as reduced early and on-going socialization, reduced exercise, keeping them in tightly packed urban and suburban environments, unrealistic expectations of dogs’ behavior and the environments they should be placed in, and choosing pets based on looks instead of how their environmental perceptions and breed-specific behaviors may fit their lifestyle.  The culmination of all of this is highly stressed pets, many of whom are not prepared to deal with the stressors they will face in their daily lives.  Training -- whether reward-based or punitive -- is not going to solve aggression due to poor genetics, or neurochemical and/or neuroanatomical alterations.

Research reveals strong neurobiological causes behind aggression including brain shape and sizes of the regions, gene expression for modulating aggressive responses, synapse connectivity and connectivity between these brain regions that can either intensify or inhibit aggressive responses, and hormones and neurotransmitters that can affect perceptions and reactions to stimuli.  Üstündağ et al.’s (2026) research study specifically examined their neuroanatomy and neurobiology of pitbulls with stranger-directed aggression and dog-directed aggression.  It illuminates the issue of neuroanatomy and aggression, and it possibly sheds some light on common pitbull characteristics, temperament, and the issue of the heightened aggression.  It offered additional insight on things we typically things we see in large bully breeds, such as friendliness with their human caregivers, propensity for same-sex aggression, difficulties regulating emotions once excited/aroused, high levels of fearfulness, lack of warning in some bullies and pitbulls before escalation to aggression, and some pitbulls displaying intense or disproportionate aggression.  The dogs in this research had moderate levels of aggression, but they reportedly did not manifest the type of intense, uninterruptible aggression as seen in mauling cases that dominate the news headlines in the US and UK.

The research study from Turkey involved 53 pitbulls – 32 females, 21 males who were all spayed/neutered – between two and six years of age.  They all lived in apartments and spent the majority of each day with their owners.  Their owners completed a C-BARQ type questionnaire that included questions about specific aggressive behaviors toward familiar people, family, strangers, and other dogs to gain insight into their emotional states and motivations behind the behaviors.  Of the male group, one third displayed consistent strong aggressive behaviors based on the owners’ responses to the questionnaire.  Of the females, 15.6% displayed consistent strong aggressive behaviors.  Over 22% of dogs admitted into the study displayed heavy stranger-directed and dog-directed aggression according to their owners.  The researchers analyzed the MRIs and biochemicals of the four most aggressive females and three most aggressive males to gather insights into any potential mechanisms underlying the aggression.

Compared to the non-aggressive group, the more aggressive dogs had an unusually small prefrontal cortex and they had an abnormally large amygdala.  The amygdala is the fear center of the brain is where stimuli are assigned as salient and indicative of threat, and fight/flight responses originate.  Heightened amygdala activity is closely associated with hypervigilance, increased emotional reactivity and increased aggressive behavior in both dogs and humans.  The prefrontal cortex is the brain’s executive decision-making center where consequences are considered and thoughtful behavioral choices are made.  Decreases in the size and functionality are associated with lack of behavioral inhibition and increased aggression in humans.  The cortisol and adrenaline (stress hormone) levels of the dogs were at the lower end of the reference range, which the authors noted was possibly due to the comfort and safety the dogs may have felt when with their owners during the blood draw.  Testosterone levels in both the calm and aggressive groups were far above the reference range.  The calm group had testosterone levels 4 times the top of the reference range, and the aggressive group had levels over 13 times the upper end of the reference range!  No wonder we see same-sex aggression, even in neutered bullies, with some other type of endogenous testosterone production occurring.  Serotonin was low in both groups – low serotonin is indicated across research studies in heightened aggression -- but serotonin levels were slightly higher in the aggressive group.  Dopamine levels were higher in the aggressive group than the calmer/control group.  High levels of dopamine have been correlated in multiple studies on dogs and other mammals with increased aggressive phenotypes. 

These findings are consistent with previous research on pitbulls from Guvenc-Bayram et al.’s (2024) research study showing low serotonin, high dopamine, and low oxytocin levels in pitbulls being strongly linked with aggression.  These differences in levels were even more pronounced with the group of pitbulls in that study who were separated from the non-aggressive group (25% of the dogs) and aggressive group (43% of the dogs), and were classified as “dominant aggressive” (30% of the dogs) – meaning that they try to use aggression to control a situation, such as engaging in territorial or resource guarding.  They had even more pronounced differences in their neurochemical levels, and lower levels of the neuropeptide plasma nesfatin-1, which is closely associated with psychiatric conditions like anxiety and depression in humans.  Neurochemicals, hormones, and neuropeptides are important with how the brain regions communicate with one another and classifies situations, and modulate how the brain initiates stress pathway and behavioral responses to situations. 

On top of this, receptors can react differently (hypoactive or hyperactive) with receiving these neuropeptides and hormones, depending on genes and the gene expression.  Particular genes in English Cocker Spaniels, including RD1, HTR1D, HTR2C and SLC6A1, that affect serotonin and/or dopamine receptors are strongly correlated with behavioral impulsivity and human-directed aggressive behavior in dogs.  Additionally, gene expression can affect aggression modulation.  Three separate genes —UBE2V2, GLT1, and ZNF227— significantly influenced aggressive behavior when they had increased expression and affected the areas of the brain that were signaled for behavioral responses.  This was seen in English Cocker Spaniel and German Shepherd breeds, although a very small number of aggressive dogs were in the study.  Two separate genes —UBE2V2 and ZNF227— significantly influence aggressive behavior when they had increased expression in the animal, with varying gene expression between different sections of the brain and showing increased expression up-regulation in male dogs. An excitatory neurotransmitter linked to neuropsychiatric disorders -- GLT1 – had the largest expression differences between the various tissues with increased up-regulation in the amygdala and down-regulation in the hypothalamus. The researchers noted that the large number of genes showing differences in the levels of expression between the various brain tissues exceeded the normal differences in brain tissues between canid species. The brain tissue of dogs with increased gene expression were more alike to mice with similar gene expression than to another canid.

Dopamine is important for motivating individuals (including humans) to engage in behaviors essential for survival -- such as seeking food, mates, and learning about their environment -- in the pursuit of the feeling of reward and pleasure that dopamine provides.  These feelings of motivation and pleasure are imperative for positive reinforcement training during which the dog works for an appetitive stimulus.  Additionally, serotonin signaling from neurons in the hippocampus are essential for memory formation and plasticity.  Serotonin is also important for modulating social behaviors, with higher levels of serotonin correlating with increased prosocial behaviors.  Dopamine is important for the regulation of behaviors associated with risk versus reward.

These neuroanatomical differences are consistent with findings of aggression in humans, including Whittle et al.’s (2008) research study that found smaller prefrontal cortex and enlarged amygdalas in human adolescents displaying intense emotional and aggressive behavior toward their parents.  These neuroanatomical differences were more pronounced in males versus females.  Other research studies have separately linked low serotonin, decreased prefrontal cortex volume, and enlarged amygdala volume to heightened aggression in humans and various psychiatric disorders.  These changes affect how dogs’ levels of hypervigilance about their environment, shapes how they perceive the stimuli they observe, and affects their abilities to inhibit their locomotor responses including aggressive behavior.  These behaviors can be impulsive, explosive, and/or completely disproportionate to the situation without the brain’s various modulating functions operating effectively.  This is not to say that dogs have the same psychiatric conditions as humans.  The reason this is being pointed out is because one’s physical makeup is not a flaw in the character of the animal, and it is not a training situation.  It is something that humans are breeding animals to be. It would be good to also see more research on the roles of maternal and early life trauma in these neurophysiological phenomena. Regardless, these are all human factors that occur from birth or early in an animal's life. There may be veterinary psychopharmacological and emotional/behavioral modification solutions…or there may not be.  Aggression from genetic factors is likely in part behind the rising behavioral euthanasia and shelter euthanasia rates.  Some aggression may not be addressed to a level of consistency that keeps families and the community safe when some manifestations of aggression are not simply a learned behavior but is a result of the brain functionality itself.  There is a significant body of research across mammalian species seeing these same neuropeptides, hormones, and neuroanatomical changes linked to aggression modulation issues.    

Without these hormones at the appropriate levels, a dog would not be able to learn effectively or to engage in prosocial behaviors.  Not every dog with a behavioral issue is at the same starting point.  They may be unable to physically relax and settle with high dopamine levels triggering restlessness and reward-seeking drives, and low serotonin creating anxiety. They may have reduced ability to inhibit impulsivity and aggression to make thoughtful behavioral choices when confront with seeing a stressor, such as a stranger entering the property.  They may also be unable to effectively commit new learning to memory if serotonin levels were not at appropriate levels since serotonin signaling is essential to hippocampal memory formation.  This highlights the importance of working in conjunction with a veterinary behaviorist or behavior-focused veterinarian in addition to an applied animal behaviorist or animal behavior consultant (or a highly skilled trainer).  Some animals, including dogs, simply have genetics that negatively affect their hormones, and thus, their abilities to inhibit impulsive or aggressive behaviors.  Once this can be addressed by a veterinarian, often through SSRI medications (which is shown across numerous studies to reduce the aggressive behaviors associated with low serotonin in multiple mammalian species including dogs), then emotional and behavior modification are likely to be more successful.

Obviously, each dog is an individual and unique.  While particular human actions can often be identified in severe, unmodulated aggressive attacks, the dog’s proportionality in their behavioral response matters. There are MANY pitbulls and large bullies, German Shepherds, English Cockers, and those of other breeds indicated in the research (and across all breeds!) who do not show aggression at all, or they show normal levels of aggression with slow escalation in their responses to threats.  It is important to understand which mechanisms in the individual dogs are causing increased and/or unmodulated aggression – regardless of breed – so that this can potentially be addressed through improved breeding practices, human factors like better puppy raising and socialization, or through medical treatments.  Banning a breed will only result in creation of another breed with similar mechanisms and characteristics since people are selectively breeding these mechanisms into dogs, whether intentionally or inadvertently (e.g. selecting for a physical trait but that gene also influences neurophysiology and behavior in some way). 

Most people – whether for a pet, therapy, service dog, or sport dog -- want a dog who views the world as a friendly place, view other people and dogs in the community as neighbors who are safe and non-threatening, and to navigate social interactions with slow escalation instead of impulsivity.  I think that most people want to walk down their neighborhood street and feel safe that they and their dog will not be seriously maimed by a loose dog because this unfortunately happens EVERY DAY.   I think that most people want to feel safe to approach and leash a dog who is loose from their yard and not worry about serious harm coming to them.  These traits do not simply happen but can come about through socialization of a HEALTHY animal.  We need to breed physically and mentally healthy animals, both for the welfare of those animals and for communities at large.  Please support welfare laws including those requiring responsible breeding practices prioritizing health and temperament, which is a reflection of an animal’s mental health.

References:

• Bacqué-Cazenave, J., Bharatiya, R., Barrière, G., Delbecque, J.-P., Bouguiyoud, N., Di Giovanni, G., Cattaert, D., & De Deurwaerdère, P.  (2020).  Serotonin in Animal Cognition and Behavior.  International Journal of Molecular Sciences, 21(5), 1649. https://doi.org/10.3390/ijms21051649

• Bertsch, K., Florange, J. & Herpertz, S.C.  (2020).  Understanding Brain Mechanisms of Reactive Aggression. Curr Psychiatry Rep, 22, 81.  https://doi.org/10.1007/s11920-020-01208-6

• González-Martínez, Á., Muñiz de Miguel, S., Graña, N., Costas, X., & Diéguez, F. J.  (2023).  Serotonin and Dopamine Blood Levels in ADHD-Like Dogs.  Animals (Basel), 13(6), 1037.  https://doi.org/10.3390/ani13061037

• Guvenc-Bayram, G., Semen, Z., Polat-Dincer, P. F., Sertkaya, Z. T., Ustundag, Y., Ates, C., Aktas, B., & Yalcin, M.  The Relation between Plasma Nesfatin-1 Levels and Aggressive Behavior in Pit Bull Dogs.  Animals (Basel), 14(4), 632.  https://doi.org/10.3390/ani14040632

• Hasin, D., Pampori, Z. A., Aarif, O., Bulbul, K. H., Sheikh, A. A., & Bhat, I. A.  (2018).  Happy hormones and their significance in animals and man.  International Journal of Veterinary Sciences and Animal Husbandry, 3(5), 100-103.  https://www.veterinarypaper.com/pdf/2018/vol3issue5/PartB/3-5-15-355.pdf

• Kleszcz, A., Cholewińska, P., Front, G., Pacoń, J., Bodkowski, R., Janczak, M., & Dorobisz, T.  (2022).  Review on Selected Aggression Causes and the Role of Neurocognitive Science in the Diagnosis.  Animals (Basel), 12(3), 281.  https://doi.org/10.3390/ani12030281

• Liu, H., He, Y., Liu, H., Brouwers, B., Yin, N., Lawler, K., & Keogh, J. M.  (2024).  Neural circuits expressing the serotonin 2C receptor regulate memory in mice and humans.  Sci Adv, 10(26).  https://doi.org/10.1126/sciadv.adl2675

• Odore, R., Rendini, D., Badino, P., Gardini, G., Cagnotti, G., Meucci, V., Intorre, L., Bellino, C., & D’Angelo, A.  (2020).  Behavioral Therapy and Fluoxetine Treatment in Aggressive Dogs: A Case Study.  Animals, 10(5), 832. https://doi.org/10.3390/ani10050832

• Paliakkara, J., Ellenberg, Ursino, A., Smith, Evans, J., Strayhorn, J.  Faraone, S. V., & Zhang-James, Y.  (2024).  A Systematic Review of the Etiology and Neurobiology of Intermittent Explosive Disorder.  Psychiatric Research.  https://doi.org/10.1016/j.psychres.2025.116410

• Üstündağ, Y., Akar, D. C., Kartal, M., Yarol, R. C., Bariş, M. M., Di̇nçer, P. F. P.  (2026).  Neuroanatomical investigation of aggression in pit bulls.  Behavioural Processes, 239.  https://doi.org/10.1016/j.beproc.2026.105385

• Watanabe, N., Sakagami, M., & Haruno, M.  (2013).  Reward prediction error signal enhanced by striatum-amygdala interaction explains the acceleration of probabilistic reward learning by emotion.  J Neurosci, 33(10), 4487-93.  https://doi.org/10.1523/JNEUROSCI.3400-12.2013

• Våge, J., Bønsdorff, T. B., Arnet, E., Tverdal, A., & Lingaas, F.  (2010).  Differential gene expression in brain tissues of aggressive and non-aggressive dogs. BMC Vet Res, 6, 34.  https://doi.org/10.1186/1746-6148-6-34

• Våge, J., Wade, C., Biagi, T., Fatjó, J., Amat, M., Lindblad-Toh, K., & Lingaas, F.  (2010).  Association of dopamine- and serotonin-related genes with canine aggression.  Genes, Brain and Behavior, 9, 372-378.  https://doi.org/10.1111/j.1601-183X.2010.00568.x

• Whittle, S., Yap, M. B., Yücel, M., Fornito, A., Simmons, J. G., Barrett, A., Sheeber, L., & Allen, N. B.  (2008).  Prefrontal and amygdala volumes are related to adolescents' affective behaviors during parent-adolescent interactions.  Proc Natl Acad Sci U S A, 105(9), 3652-7.  https://doi.org/10.1073/pnas.0709815105

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Eileen Koval, CDBC, CBCC-KA, CPDT-KA, MSc (in Operations Management) is a fully certified dog behavior consultant with the International Association of Animal Behavior Consultants (IAABC). She is currently pursuing an M.S. in Applied Animal Behavior and Welfare at Husson University. Eileen believes that understanding each dog as an individual is the foundation of a good cross-species relationship. She enjoys helping humans and dogs communicate more effectively to create brilliant relationships filled with joy, purpose, and fulfillment for all involved. Eileen offers private consulting for serious dog behavior issues, obedience/manners, and agility training. She developed a unique online course to help pet parents and trainers teach reliable snake avoidance behavior off-leash through positive reinforcement techniques. These techniques have been applied by trainers worldwide to teach dogs to avoid dangerous environmental hazards and respect off-leash property boundaries. Eileen lives on a small ranch in Las Vegas, Nevada, with her husband and their Nederlandse Kooikerhondjes.