Recovery From Schizophrenia: Psychiatry And Political Economy

222 TREATMENTdopamine-2 receptor. Observable reduction in psychotic symptoms occurswhen 65 per cent or more of the dopamine-2 receptors are blocked. 7(2) The stimulant drug, amphetamine, which increases the release of dopamineand other catecholamines in the brain, will produce in humans an acutepsychosis that is very similar to schizophrenia if it is taken in sufficient amounts.The drug can also bring about an exacerbation of psychotic symptoms inpeople with schizophrenia.Dopaminergic fibers are to be found in a number of major tracts in the centralnervous system. Two of these pathways, the mesolimbic and the mesocorticaltracts, are considered to be possible sites of defective dopamine activity inschizophrenia. A disturbance in the mesolimbic system, in particular, can result inan inability to filter out multiple environmental stimuli—a characteristic disorderin schizophrenia. 8 Damage to the limbic system, or electrical stimulation of thispathway, can result in a number of other schizophrenia-like symptoms, includinghallucinations, disturbances in thinking and emotion, paranoia, depersonalizationand perceptual distortion. 9DOPAMINE SUPERSENSITIVITYResearchers refer to “dopamine dysregulation” as being an underlying problem inschizophrenia. They use this term because, while it is clear that dopamine activityis elevated in the mesolimbic system, it is not clear whether this is all a result of anincreased synthesis and release of dopamine or if it is partly due to an increasedsensitivity of the dopamine-2 receptors to the effects of stimulation. 10 Forexample, it is possible that there is an excess of the type of dopamine-2 receptorswith a high affinity for this neurotransmitter. Regardless of whether or notdopamine supersensitivity proves to be an important underlying problem inschizophrenia, it is clear that treatment with the standard antipsychotic drugsproduces such a supersensitivity. Continuous use of these drugs leads to atolerance to their effect, so that bigger doses have to be used to achieve the samedegree of dopamine blockade—a phenomenon which researchers refer to as “upregulation”of the dopamine system. 11 This is how it happens. Dopamine releaseis stimulated by stress and exposure to new situations. 12 Ordinarily the effect ofdopamine activity is damped down by means of a negative feedback process inwhich the neuronal system attempts to prevent overload by minimizing the effectof the neurotransmitter through a reduction in dopamine turnover. 13Malfunctioning of the interneurons that bring about this negative feedback isbelieved to be one of the problems leading to dopamine dysregulation inschizophrenia. By blocking dopamine receptors the standard antipsychotic drugsdiminish the activity of dopaminergic neurons and reduce the symptoms ofpsychosis. The dopamine-blocking action, however, eliminates the feedbackprocess that has been keeping dopamine turnover at a low level. With theadministration of these drugs dopamine turnover promptly increases. 14 This is not