seratonin

The Involvement of Serotonin in Canine Aggression

Serotonin, or 5-hydroxytryptamine (5-HT), is a monoamine. Its adjective is serotonergic.

Composition
Chemically, Serotonin is created in seratonergic neurons in the CNS.

Serotonin is synthesized from tryptophan by the enzyme tryptophan hydroxylase (TPH), which produces 5-hydroxytryptophan (5-HTP) and then the action of 5-HTP decarboxylase to create 5-HT.

Sertonergic neurons are mostly found in the raphe nuclei of midbrain, pons and medulla.

There are nine types of seratonertic receptors with varying effect, for example 5-HT1B and 5-HT1D are presynaptic autoreceptors. All receptors are metabotropic, except for the ionotropic 5-HT1A.

Serotonin along with dopamine and norepinephrine are neurotransmitters, involved in the transmission of nerve impulses ("messages") among brain cells. It is a natural chemical manufactured in the body on an ongoing basis in response to pleasure-giving experiences, in a normally healthy system. Neurotransmitters are extremely important, since they carry impulses between nerve cells. The substance that processes the neurotransmitter called serotonin is the amino acid tryptophan. It increases the amount of serotonin made by the brain. Serotonin provides a wide range of control of emotions including anger, aggression, body temperature, pain, mood, sleep, appetite, and metabolism. In the spinal fluid of dominant -aggressive dogs Serotonin has been found to exist in lower concentrations in comparison to normal non aggressive dogs.

High serotonin levels makes you happy but if that system becomes less than healthy, the seratonin levels can drop. Serotonin plays a very important role in the neurochemical role of aggression, especially when a component of impulsivity is present. Research done in humans and animals demonstrates a relationship between low levels of Serotonin and the rise of impulsivity(Lesch,2000, Miczek 1998, Stanley B 2000). A recent study in dogs reveals low levels of 5-HIAA, a seratonin metabolite, in dominant aggressive dogs, especially those that bite without warning. (Reisner 1996) (3)

Deficits in serotonin, seem to play an important role in the control of aggression and mood changes in the brain, especially when certain other conditions that affect impulsive behaviours are present. Restoring the chemical balance is not easy, since serotonin cannot successfully be administered as a shot or pill. In human beings, there has been a good deal of success controlling such conditions with drugs that keep the serotonin already in the brain from being broken down and reabsorbed around the nerve endings. This, in effect, increases the amount of serotonin available for use by the neural system. The class of drugs that do this is known as “serotonin reuptake inhibitors” or SRI’s. The best known of these is Prozac (1) (a type of anti-depressant).

Many authors have suggested that high protein diets may have a role to play in aggressive behaviour in dogs but only a few scientific studies have been performed to demonstrate the benefits of low protein diets.

Diets that are lower in protein and/or supplementing with tryptophan may also help in decreasing aggression. This recommendation is based on findings which show that diets low in protein actually increase availability of the amino acid tryptophan, which in turn, induces serotonin synthesis. Increased serotonin levels seems to be associated with calmer emotional processes and less impulsive behaviour, thereby controlling aggression (Lindsay 2000).(2)

Why should dietary protein affect aggressive behaviour ?
It is known that some amino acid concentrations in the brain (eg tryptophan) can affect behaviour and cause aggression . Amino acids are the primary chemical units that are linked together to form proteins and many are essential nutrients that must be supplied by the diet. Altering the type and amount of protein intake can increase or decrease specific amino acid availability.

It is known that high ammonia concentrations in the blood can affect the brain and cause aggression. Ammonia is a nitrogen-containing breakdown product following protein metabolism, and its blood concentrations increase in some forms of disease eg liver disease and a vascular abnormality called a portocaval shunt.

What is the scientific evidence so far ?
More work needs to be done , but from the studies published so far it appears that :

1. Dogs fed a "low" protein ration may show a decrease in territorial aggression behaviour
2. A "low" protein ration may be helpful in managing dogs with dominance aggression
3. A ration supplemented with the amino acid tryptophan may be helpful in managing dogs with dominance aggression or territorial aggression

Nutritional Effects on Serotonin and Behavioural Aggression in Dogs	In Vivo Evaluation of Serotonin-2a Receptors in Normal Canine Brain	Benefiting Brain Chemistry with L-Tryptophan	Fear Aggression: Behaviour Products and Drug Therapy
Neurobiology of Domestic Canine Aggression: A review of the Literature To Date	Early recognition and prevention of canine aggression	Fluoxetine

Source
1. Mood-altering drugs and our dogs By Stanley Coren     http://www.moderndogmagazine.com/articles/pill-popping-pups/753
2. Recognition and Management of Common Aggressive Behavioral Problems in Dogs   http://dspace.library.cornell.edu:8080/bitstream/1813/2779/1/2003%20Sosa.pdf
3. Impusivity in Dogs   http://www.wheelmeon.org/donna1218.pdf
4. Dietary Protein and Aggression in Dogs http://www.provet.co.uk/petfacts/healthtips/proteinaggression.htm