Also, it is a gross oversimplification of things just to look at levels of one or more neurotransmitters and assign values such as 'low' or 'high' (outside of quite obviously pathological such as neurotransmitter/hormone-secreting tumors like phaeochromocytomas [a type of adrenal gland tumor which secretes massive, potentially fatal levels of noradrenaline, causing very high blood pressure and heart rate, can lead to strokes for example, and additionally in this particular case can tie into violence, with people ending up having hair-trigger tempers, or believing themselves in danger due to the constant fight-or-flight response caused by a phaeochromocytoma]
Things such as overall neurological architecture, sensitivities of receptors in synapses, distribution and trafficking of neuron types, (this is often altered in many neurological diseases of genetic origin, where the neurons meant to migrate to a particular area fail to get the full way, or are altered in performance, are of altered morphology etc,) are a lot more important than simplistic interpretations such as 'has low/high XYZ'. And not only that, but the same neurotransmitter can and usually does do different things in different areas of the brain. For example dopamine, a catecholamine neurotransmitter; is responsible for both inhibitory control over movement in the area of the brain known as the substantia nigra, located, along with the striatum, in the nigro-striatal tract, here DA blocks spurious movement signalling and allows conscious, voluntary movement to be fluid and to proceed as it should (impairment hear is a prototypical feature of parkinson's disease) whereas DA signalling in the prefrontal cortex is strongly associated with attention and focus, whilst within the nucleus accumbens (you could, crudely, think of this area as a 'pleasure center', in a manner of speaking) is associated with rewarding and highly reinforcing effects. Many, perhaps even most, of the drugs of abuse having addictive properties such as cocaine, heroin, amphetamines, methylphenidate/ritalin, these cause large releases of DA within the nucleus accumbens.
So simple neurotransmitter levels don't tell the whole story, in fact they usually don't tell you very much at all, the WHEN, the WHY and critically, the WHERE are far more important.
