The Dopamine Hypothesis of Schizophrenia
This is the question:
The prevailing hypothesis for schizophrenia implicates the neurotransmitter dopamine as playing a key role in the development of the disease. Dopamine acts on several areas of the brain with differing effects. Please outline the key dopamine pathways and the implications of antipsychotic use on each pathway.
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The dopamine hypothesis of schizophrenia
Schizophrenia is typically characterized by positive symptoms, such as hallucinations or delusions; disorganized speech; negative symptoms, such as a flat affect, and impairments in cognition, including attention, memory, and executive functions (Fischer & Buchanan, 2021). The dopamine hypothesis of schizophrenia postulates that an excess of dopamine subcortically is associated with the positive symptoms, and at the same time, the negative and cognitive symptoms of schizophrenia are thought to arise from a deficit of dopamine in the cortex. The dopamine producing neurons are located in the midbrain nuclei; mainly ventral tegmental area (VTA) and substantia nigra pars compacta (Ranjbar-Slamloo & Fazlali, 2020). Below are the four major dopamine pathways for schizophrenia:
The Mesolimbic pathway: The pathway projects from the Ventral tegmental area (VTA) that innervate many forebrain areas to the nucleus accumbens in the limbic system. The hyperactivity of dopamine in the mesolimbic pathway mediates positive symptom in schizophrenia including emotions, reward, and motivation.
Implications of antipsychotic use: D2 antagonists reduce positive symptoms of schizophrenia on the mesolimbic pathway by blocking the D2 receptors.
The Mesocortical pathway: This pathway projects from VTA to the prefrontal cortex. It projects into both dorsolateral prefrontal cortex which regulates cognition and executive functioning, and into ventromedial prefrontal cortex which regulates emotions and affect. Therefore, mesocortical pathway is believed to be associated with negative and cognitive symptoms of schizophrenia with hypofunction of the mesocortical pathway.
Implications of antipsychotic use: The dopaminergic antagonist effect on the mesocortical pathway creates mental deficiencies and a lack of emotions. Blocking or decreasing activity in this pathway can create difficulties with thought and speech, apathy, reduction in a drive to be social, decreased motivation, and an inability to feel pleasure.
The Nigrostriatal pathway: This projects from the dopaminergic neurons in the substantia nigra to the basal ganglia or striatum. The nigrostriatal system contains about 80% of the brain’s dopamine. This tract projects from cell bodies in the pars compacta of the substantia nigra to terminals that innervate the striatum (caudate and putamen). This pathway is believed to mediate motor movements / purposeful movements.
Implications of antipsychotic use: D2 antagonism induces extrapyramidal symptoms, therefore, blockade of dopamine D2 receptor in this pathway can lead to dystonia, parkinsonian symptoms, and akathisia.
The Tuberoinfundibular Pathway: This transmits dopamine from hypothalamus to the pituitary gland. The role of dopamine release in the tuberoinfundibular pathway is to inhibit prolactin release.
Implications of antipsychotic use: Antipsychotic use in this pathway causes blockade of D2 receptors which increase prolactin levels (hyperprolactinemia), and this can manifest as amenorrhea, galactorrhea, and sexual dysfunction. Also, long term use of such medication can be associated with osteoporosis (Rege, 2022).
The Dopamine Hypothesis of Schizophrenia
I like how the post approaches and discusses how neurotransmitter dopamine plays a significant role in the development of Schizophrenia. The post brings out an excellent point about how excess dopamine is highly linked to positive symptoms of Schizophrenia. I agree with the post that the cognitive and negative symptoms of schizophrenia rise due to the deficit of dopamine in the cortex. Most of the studies that have paid attention to dopamine and Schizophrenia have resulted from an overactive dopamine system in the brain. Dopamine has been a neurotransmitter that has inhibitory impacts in the study and diagnosis of (Schizophrenia Maia and Frank, 2017). Having a lot of dopamine concentrated in the brain leads to the subcortical release of dopamine, resulting in Schizophrenias symptoms such as delusions and hallucinations. The producing neurons are located in the midbrain nuclei.
The post has clearly outlined the four major dopamine pathways for Schizophrenia and the implications of antipsychotic use for each. The four dopamine pathways include the mesolimbic, mesocortical, nigrostriatal, and tuberoinfundibular pathways (Stępnicki, Kondej, and Kaczor, 2018). The Mesocortical transfers from the VT area to the prefrontal cortex. The mesolimbic transfers dopamine from the ventral tegmental (VT) region and innervates to the nucleus accumbens. It leads to positive psychotic symptoms. The tuberoinfundibular transfers dopamine from the hypothalamus to the pituitary gland. The nigrostriatal transmits from dopaminergic neurons to the striatum.
I agree with the post that antipsychotic use in the dopamine pathways can lead to blockade of D2 receptors and reduce the positive symptoms of Schizophrenia. This is because the antipsychotic compounds tend to influence the dopaminergic transmission in the pathways. Blocking the dopamine D2 receptors diminishes psychotic symptoms and normalizes the reward substances. The post has taken an interesting approach in addressing the hypothesis on how dopamine plays an essential role in the development of Schizophrenia. Additionally, Schizophrenia treatment approach should focus on the transcultural model of care since it’s a culture-bound illness. Transcultural concepts in nursing care help in striving for effective care that meets the patient’s cultural needs (Andrews et al., 2020). Therefore, care providers need to focus on transcultural care differences in culture that can affect how Schizophrenia manifests.
Andrews, L. L., Boyle, J. S., & Collins, J. (2020). Transcultural Concepts in Nursing Care (8th Ed.). Wolters Kluwer.
Maia, T. V., & Frank, M. J. (2017). An integrative perspective on the role of dopamine in Schizophrenia. Biological psychiatry, 81(1), 52-66.
Stępnicki, P., Kondej, M., & Kaczor, A. A. (2018). Current concepts and treatments of Schizophrenia. Molecules, 23(8), 2087.