Role Of Dopamine In Schizophrenia

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Affecting 1 in 100 individuals, the prolonged mental disorder, schizophrenia, is characterised by altered thoughts and experience from reality. Schizophrenia typically influences the ideas, perceptions and behaviour of individuals and also hindering their ability to perform regular tasks. While the symptoms of schizophrenia are diverge in multiple groups; positive, negative and cognitive, the following piece strives to shed light on the positive symptoms. While the negative symptoms involved The positive symptoms of the disorder takes into account the symptoms that add to an individuals state of being. These symptoms includes, delusions; which refer to the illogical and peculiar line of thinking and hallucinations; involving the experiencing of sounds and other perceptions as real, whilst only existing in the mind of the patient. The signs of the mental condition are usually to start between the ages 16 – 30 and both males and females are equally likely to develop the disorder, however, males may tend to experience it slightly earlier than females. Nevertheless, while genetic inheritance, external factors; such as family relationships and abuse, and drug consumption all contribute to the on-set of schizophrenia. This piece endeavours to place great emphasis on the chemical imbalances that consequently lead to schizophrenia, specifically the imbalance of dopamine. Dopamine is a neurotransmitter produced in the substantia nigra, a nucleus in the midbrain. The neurotransmitter is responsible for many functions, including voluntary movement, motivation, sleep, dreaming, mood, attention, memory and learning. Hence, it receives a great amount of attention in research studies, as an imbalance in such a multifaceted can result to numerous abnormalities and dysfunctions in individuals. According to a myriad of studies, it is hypothesised that the over-production of dopamine in the brain results to schizophrenic symptoms. This was referred to as the dopamine hypothesis of schizophrenia. Nevertheless, the various neuroleptic treatments, receptor binding studies, dopamine synthesis studies and recreational drug evidences will be explored to project the involvement of dopamine in the development of schizophrenia.

Neuroleptic drugs, also referred to antipsychotics, are utilised to manage symptoms of psychosis such as; schizophrenia and bipolar disorders, temporarily. The ‘neuroleptic’ reference to the drugs originated due to its ability to produce a neurolepsis – an altered state of consciousness characterised by inactivity, decrease in motor functioning and reduction of anxiety. The tranquillising effects of neuroleptics occur as the drugs hinders the dopamine neurotransmitters from exciting action, via binding to the dopamine receptors and blocking it.The implementation of antipsychotics to treat schizophrenic patients, through the blockage of the dopamine receptors in the brain, (Haddad & Correll, 2018) studies reveal that antipsychotics are effective in the treatment of symptoms of psychosis – in particular schizophrenia. Furthermore, antipsychotics are branched off in two divisions; typical and atypical. Typical antipsychotics are also known to be first-generation neuroleptics, these are the drugs responsible for managing positive symptoms of schizophrenia. Where as, atypical neuroleptics, also – second-generation antipsychotics – are used to treat the negative schizophrenic symptoms.While both are dopamine antagonists, when examining the effectiveness of both typical and atypical neuroleptics, Nowinska’s study found that there was no significant difference in the motor function of schizophrenic patients when treated with typical neuroleptic, in comparison to the schizophrenic patients who were treated with atypical neuroleptics.(Nowinska et al., 2012). Thus, suggesting there is no significant difference in the efficacy of first-generation antipsychotics in comparison to second-generation antipsychotics.

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Receptor binding in schizophrenia involves the antipsychotic drugs potency to bind to the receptors of dopaminergic pathways in order to prevent the firing of dopamine. Dopaminergic pathways are the set of neurons that are responsible for producing and releasing the neurotransmitter dopamine, in the substantia nigra. While there are approximately four different dopaminergic pathways, mesolimbic pathway is responsible for positive symptoms of schizophrenia. Additionally, this specific plays a key role in the emotions, motivation and rewards, hence the excessive production of the neurotransmitter, dopamine, prompts psychotic indicators. (Howes et al., 2013a) According to recent studies, researchers convey that tyrosine hydroxylase, a rate-limiting enzyme in the substantia nigra, is significantly greater amongst patients with schizophrenia in comparison to patients with depression and healthy controls. Furthermore, the study stipulates that there is, thus, an increase in dopamine D2 receptors in schizophrenic patients. Hence playing a significant role in the excessive synthesis of dopamine. Consequently, all antipsychotic drugs have the ability to reduce dopaminergic neurotransmission as they convey an antagonistic effect on neurotransmitters through attaching to the d2 receptors. This is done via a method referred to as receptor binding. Nonetheless, studies found a significantly reduced D2 receptor binding in the basal ganglia of drug naive schizophrenic patients as compared to age matched control subjects. (Vita et al., 1995). The experiment suggests that those who have been administered with neuroleptic drugs have a lower amount of dopamine receptor bindings, as a result of the antipsychotics preventing the release of excessive dopamine in the brain. Overall, leading to a decrease in the prevalence of schizophrenic symptoms in participants.

Recreational drug often refers to the drugs used without medical order, due to its psychoactive effects in the belief that the occasional use of the drug is not addictive or habit-forming. Despite marijuana being an illicit substance in many states globally, it contrarily has many medicinal and recreational use as well. Stemming from the hemp plant, many chemicals are found in the plant. The most dominant, known as tetrahydrocannabinol or THC. According to studies, there is an association between the constituent of cannabis – THC- and the symptoms of schizophrenia. (D’Souza et al., 2005). Through carrying out a double-blind, placebo-controlled study on antipsychotic-treated schizophrenic patients, results suggested that THC increased


Cannabis use would be a crucial factor for the development or for the precipitation of psychosis in an otherwise not so compromised brain (Hadden, LeDrew, Hogan & Thomas, 2016)  


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