Human Behaviour, Dopamine & DNA

Dopmine is a neuurotransmitter and hormone -its a precursor molecule in adrenaline/noradrenaline production

• abnomral ow levels re associated with Parkinson's disease - treatment is the administration of dopamine precursor L-dopa
• raised dopmine levels are linked to the developemnt of mental health problems such as Schizophrenia - patients with Parkinson's disease treated with L-dopa are prone to behavioural changes such as compulsive gambling. Dopamine increases general arousal, decreases inhibition, leading to an increase in creativity in conjunction with cerebral activity

A range of activites are affect by Dopamine (largely due to the number of variations within dopamine receptors - there are 5 receptors called DRD1 to DRD5, each of which is coded for by a separate gene)

The binding of dopamine to its receptor is involved in a number fo processes, including the control of motivation and learning, and is linked to regulatory effects on other neurotransmitter release. A number of antipsychotic drugs work by blocking dopamine receptors

There are 50 known variants of the gene. The variants differ in a specific sequence known as variable number tandem repeats. A short section of nucleotides shows a different number of repeats in each variant

A number of studies have shown that some of these variants are implicated in certain human behavioural conditions. it it thought that the inheritance of particular variants of the DRD4 gene affects the levels and action of dopamine in the brain

Attention Deficit Hyperactivity Disorder (ADHD):- drugs such as Ritalin are used to treat it. ADHD affects dopamine levels in the brain. In a number of studies, a particular dopamine recpetor variant of DRD4, has been shown to be more frequent in individualssuffering from ADHD

Addicive and Risk Behaviours:- A number of studies have suggested that some variants of DRD4 receptor gene are implicated in increased likelihood of addictive behaviours like smoking. A study into the effects of administering L-dopa to one group of individuals and haloperidol (a drug that blocks dopamine recepors ) to another group showed not only a difference in general arousal, but also a significant difference in the risk-taking levels of the individuals

The interest in DRD4 and Dopmaine has stimulated research into other possible links between behviour and genetic constituion.

• OCD is though to result from a deficienc in the levels of the neurotransmitter seratonin. In 2007, a genome wide scan for DNA sequences related to OCD was carried out when the DNA from 1008 peopl from 219 families was analysed. Eight gentic markers were found that appear to be linked to OCD