Post 1:
Mesolimbic and Mesocortical Pathways:
According to Boyle et al., “The mesocortical pathway involves dopaminergic neurons that project from the ventral tegmental area (VTA) to cortical regions, including the orbitofrontal cortex (OFC), ventromedial prefrontal cortex (vmPFC), medial prefrontal cortex (mPFC), and anterior cingulate cortex (ACC) (Boyle et al., 2023). However, in simpler terms, as presented in our lesson, the Mesocortical pathway projects to the cerebral cortex from the VTA for motivation, concentration, executive function, and emotions, which play a role in processing reward. With this understanding, providers can choose the correct medications that can either increase or decrease dopamine in conditions such as depression or schizophrenia.
The pathway that is most often associated with reward is the mesolimbic dopamine pathway. The VTA is the primary source of dopamine production. It uses the mesolimbic dopamine pathway to connect the nucleus accumbens, strongly associated with emotional expression, learning and reinforcement, and hedonic capacity (Travis & Daroff, 2003, p. 202). This nucleus is located in the ventral Striatum. When one experiences something rewarding or uses an addictive drug, the dopamine neurons in the VTA are activated. They are projected to the nucleus accumbens via the mesolimbic dopamine pathway, which causes dopamine to rise (Neuroscientifically Challenged, 2015). The role in pharmacology the mesolimbic pathway plays is using medications that can treat ADHD or addiction that can help with the dysregulation of dopamine.
References
Boyle, C., Bower, J., Eisenberger, N., & Irwin, M. (2023). Stress to inflammation and anhedonia: Mechanistic insights from preclinical and clinical models. Neuroscience & Biobehaviroal Reveiws, 152(105307). Retrieved March 13, 2024, from to inflammation and anhedonia: Mechanistic insights from preclinical and clinical models
Neuroscientifically Challenged. (2015, February 15). 2-Minute Neuroscience: Reward System [Video]. Youtube.
Travis, A., & Daroff, R. (2003). Mood Disorders, Biology (M. Aminoff, Ed.). Academic Press.
Post 2:
What is the difference between pharmacokinetics and pharmacodynamics? How does this influence how you might prescribe a medication?
Pharmacokinetics is how a medication is absorbed, distributed, metabolized, and excreted. In other words, it is what the body does to a drug after it is administered, and it leaves the body. Pharmacodynamics is how a drug exerts itself within the systems of the body or what effects (including side effects) the medication causes. Each influences how drugs are prescribed.
Some medications circumvent the more common routes of administration to avoid the first-pass effect. Delivering medication directly to where you want it, as with a local anesthetic, not only increases the amount of bioavailable drugs but also allows for anesthesia without general sedation. It is also well known that certain compounds can aid in the absorption of another drug. For example, they take vitamin C with an iron supplement or vitamin D with calcium. A slow, steady absorption could be the best way to deliver a drug into circulation. In addition, an intramuscular injection can also erase questions of patient compliance. The two reasons above are what make long-acting injectables viable.
Distribution matters tremendously in psychiatry and neurology because medications will likely have to cross the blood-brain barrier at some point. In obstetrics, distribution across the placental barrier is a huge variable to consider when conscientiously prescribing. Lastly, “Protein binding can also act as a reservoir as the drug is released slowly, causing a prolonged action” (Ernstmeyer K & Christman E, 2023). It can also change the tissues to which a drug is distributed.
Metabolism changes how one prescribes a drug, as drugs that are processed intensely in the kidney will be a second choice for elderly patients. Ghaemi (2019) states, “Kidney function is naturally affected by age, with a 1% decline per year in excretion capacity.” Similarly, liver function must be included in decisions about prescribing. For example, alternatives to benzodiazepines should be considered first in a patient with fatty liver disease.
It is reasonable to consider excretion in prescribing as humans, unlike many other living things, requires adequate hydration to excrete waste or drugs through urine.
Side effects from the pharmacodynamics of the medication, whether subjective or objective, play a huge role in compliance for psychiatric patients (Ghaemi, 2019).
Ernstmeyer K & Christman E. Nursing Pharmacology [Internet]. 2nd edition. Eau Claire (WI): Chippewa Valley Technical College; 2023. Chapter 1 Pharmacokinetics & Pharmacodynamics. Available from:
Ghaemi, S. N. (2019). Clinical psychopharmacology: principles and practice. Oxford University Press.
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