Dopamine Pathways of the Brain and their Importance with Antipsychotic Medications.
Dopamine plays an important role in five key pathways. These pathways include the mesolimbic, mesocortical, nigrostriatal, and the tuberoinfundibular dopamine pathways. Antipsychotics directly impact these dopamine pathways (Gabbard 2013, 193).
The mesolimbic dopamine pathway extends from the ventral tegmental area of the midbrain to the nucleus accumbens of the limbic system (Stahl 2013, 89). It is proposed that this pathway plays a role in the positive behaviors of psychosis such as delusions and hallucinations. Often referred to as the pleasure center of the brain, it is also important to note that this pathway is critical in the feelings of reward, pleasure, and motivation. (Stahl 2013, 89). Consequently, drugs that increase dopamine in this pathway can have an effect on behaviors that this pathway modulates. For example, increased dopamine levels by medications such as stimulants and amphetamines can eventually lead to an increase in positive symptoms that may eventually lead to psychosis or behaviors such as delusions and hallucinations, similar to those of paranoid schizophrenia. In contrast, medications such antipsychotics act as dopamine antagonists which decrease the amount of dopamine in-turn decreasing these positive behaviors. (Stahl 2013, 90) Unfortunately, first generation antipsychotics that block D2 receptors in this pathway not only reduce the positive symptoms but additionally block mechanisms of reward causing lack of motivation, interest, joy in social interactions, anhedonia and apathy similar to the negative symptoms in schizophrenia. (Stahl 2013, 133)
The nigrostriatal dopamine pathway extends from the substantia nigra to the striatum or basal ganglia which is part of the extrapyramidal nervous system. This pathway is important in controlling movement and motor function. (Stahl, 2013, 95) Decreased dopamine levels in this pathway lead to extrapyramidal symptoms (EPS) that mimic Parkinson’s Disease. Some of these Parkisonion-like symptoms or movement disorders are akinesia, bradykinesia, tremors, rigidity, dystonia, or akathisia. (Stahl, 2013, 95) Some drugs such as antipsychotics that are D2 receptor blocking agents decrease dopamine levels in this pathway and have a potential to cause drug induced movement disorders. First generation antipsychotics are some of the most common medications associated with EPS. (Stahl, 2013, 198) Although EPS occurs less frequently in atypical antipsychotics, the risk of EPS also increases with increased doses. Long term use of first generation antipsychotics can cause a permanent or irreversible change in D2 receptors in the nigrostriatal dopamine pathway causing tardive dyskinesia, a chronic often permanent movement disorder. (Stahl, 213, 134)
In contrast, increased levels can lead to symptoms similar to those of Huntington’s Disease such as dyskinesias, tics, or chorea. This impairment of the nigrostriatal dopamine pathway was evidenced by PET studies in which various dopamine markers were imaged in the brains of living patients. While Parkinson’s Disease can lead to decreased levels of dopamine, Huntington’s Disease is a biphasic disease in which there is an initial increase in dopamine and then a subsequent decline in dopamine. (Jamwal & Kumar, 2019)
The mesocortical dopamine pathway projects from the midbrain tegmentum to the areas of the prefrontal cortex. The significance of this pathway is that it controls cognition, negative, and affective symptoms. There are two branches in this pathway: the first branch goes into the dorsolateral prefrontal cortex and regulates the executive function and cognition and the second pathway goes to the ventromedial prefrontal cortex and mediates emotions and affect. (Stahl’s, 2013, 92) Dysfunction of this pathway may lead to poor concentration and the inability to make decisions. First generation antipsychotics can cause adverse behaviors such as neuroleptic induced deficit syndrome which appears to be very similar to that of the negative symptoms similar to those of schizophrenia. On the other hand, medications such as amphetamines increase dopamine or upregulate dopamine which increase cognition.
The tuberoinfundibular dopamine pathway extends from the hypothalamus to the anterior pituitary gland controlling prolactin hormone secretion. (Stahl, 2013, 95) The release of dopamine in this area inhibits prolactin hormone except only in a postpartum state where activity of dopamine neurons are decreased giving rise to increased prolactin levels for breastfeeding and lactation after birth. Some antipsychotics medications increase prolactin levels which may in turn produce amenorrhea, breast secretion and engorgement in females, sexual dysfunction, male gynecomastia, galactorrhea. (Lind, et al., 2005) Antipsychotic medications associated with the greatest risk of producing hyperprolactinemia include haloperidol, risperidone, and paliperidone. (Gabbard, 2013, 200)
Lastly, there is a fifth pathway called the thalamic pathway but its function is really not known. It extends from various areas in the brain (periaqueductal gray matter, ventral mesencephalon, hypothalamic nuclei, and lateral parabrachial nucleus to the thalamus.) Studies suggest that it may be involved in sleep and arousal. (Stahl’s, 2013, 96)
Dopamine levels play a key role in both the development and the treatment of disease in mental health. It is important to recognize the pathways and the specific implications they have with antipsychotic medications.
References
Gabbard, G.O. (2103). Gabbard’s Treatments of Psychiatric Disorders (5th ed.) American
Psychiatric Association Publishing
Jamwal, S., & Kumar, P. (2019). Insight Into the Emerging Role of Striatal Neurotransmitters in
the Pathophysiology of Parkinson’s Disease and Huntington’s Disease: A Review. Current neuropharmacology, 17(2), 165–175.
Lind, C. C., Carchedi, C. L., Staudenmeier, L. J., & Diebold, L. P. (2005). Atypical presentations
of atypical antipsychotics. Psychiatry (Edgmont (Pa. : Township)), 2(6), 32–39.
According to Lane (2019) the deaf and hearing impaired are considered a social group because they have a collective name: the Deaf-World. The Deaf- World offers easy communication, a positive identity, and a surrogate family amongst its members. Lane (2005) also asserts that the deaf have norms for behavior and distinct values like prizing one’s relation to the Deaf-World and acknowledging the contributions of those in the Deaf World. He believes that deaf people know when and with whom to use ASL and when to use English-marked varieties of sign language is an important part of being recognized as Deaf.
I recently heard about Black American Sign Language that developed in segregated African American communities. Black ASL today conveys an identity and sense of belonging that mirrors spoken language varieties of the African American hearing community. Different uses of space, hand use, directional movement, and facial expression are ways that Black ASL distinguishes itself as a vibrant dialect of American Sign Language (North Carolina Department of Health and Human Services, 2020). I think is important when providing care to any person to mindful of their cultural background, as well as if they are hearing impaired or deaf because they are 2 separate cultural groups.
References
Lane, H. (2019). Ethnicity, Ethics, and the Deaf-World. Journal of Deaf Studies and Deaf Education.
North Carolina Department of Health and Human Services. (2020, February 5). NCDHHS: Signing Black in America: The Story of Black American Sign Language.
Stahl, S. M. (2013). Stahl’s essential psychopharmacology: Neuroscientific basis and practical
applications (4th ed.). Cambridge University Press.
