Neurotransmitters and Receptor Theory Sample Paper

Transmission of electrical impulses from one neuron across the synapse to a different neuron or a cell is facilitated by neurotransmitters. Examples of neurotransmitters that facilitate central nervous functions include amino acids (GABA, aspartate, and glutamate), amines (catecholamines, acetylcholine, and serotonin), peptides (neuropeptide Y) and gases such as nitric oxide (Sheffler, Reddy & Pillarisetty, 2020). These neurotransmitters have specific receptors which bind to psychopharmacologic agents to either cause agonistic or antagonistic actions as illustrated hereafter.

Agonist-to-antagonist Spectrum of Action of Psychopharmacologic Agents

Psychopharmacologic agents are drugs used in the management of a wide spectrum of psychiatric disorders including behavioral disorders, depression, anxiety or stressor-related conditions. The drugs can either exhibit agonistic or antagonistic activities at the receptor site (Katzung, 2018). While agonists activate the receptors, antagonists block the receptors. For example, in the etiology of Schizophrenia, the Dopamine hypothesis is widely accepted. It is believed that excess Dopamine neurotransmission causes the Schizophrenic symptoms.

This has been evidenced by the presence of higher levels of Dopamine receptors in Schizophrenic patients. Management of Schizophrenia therefore utilizes drugs that block the Dopamine receptors (antagonists) for example Chlorpromazine (Katzung, 2018). Contrarily, the pathophysiology of neurodegenerative diseases such as Parkinson disease (PD) reveals decreased dopamine levels and receptor (Katzung, 2018). Therefore, dopamine agonists such as Levodopa are used in the management of PD.

Partial agonists bind and activate receptors but only have partial efficacy (Berg & Clarke, 2018). An example, used as an anxiolytic is Buspirone. Partial agonists exhibit both agonistic and antagonistic actions for example, while Buspirone is a partial agonist for 5HTA1 receptors; it’s an antagonist for D2 receptors (Katzung, 2018)). Therefore, it can be used both as an anxiolytic and antidepressant drug. Inverse agonists bind to receptors however, produces effects opposite to the agonist (Berg & Clarke, 2018). Naltrexone, a partial inverse agonist is used in the management of opioid addiction.

G-coupled proteins and Ion-gated Channels

G-protein receptors and ligand gated ion channels are both cell surface receptors. They are both found on the membrane of the cells. While ligand gated ion channels are controlled by neurotransmitters to release ions, a G-protein depends on the second messenger system to act (Miller & Lappin, 2020).

Therefore, due to the difference in the mechanism of stimulation, ligand gated ion channels take less time (milliseconds) to be activated compared to G-protein receptors which take a bit longer time (seconds). Additionally, examples of ligand gated ion channels include nicotinic acetylcholine receptors and GABA A receptors while G-coupled receptors examples include muscarinic acetylcholine receptors and adrenoceptors (Katzung, 2018; Miller & Lappin, 2020).

Role of Epigenetics in Pharmacologic Action

It has been shown that the gene environment influences its expression. Epigenetics, an emerging scientific area is the study of how the environment, child development, aging or diet influences the changes in gene expression (Ganesan et al., 2019). Epigenetic variations have been linked to multiple conditions such as a variety of cancers and psychiatric disorders.

Therefore, understanding the multiple epigenetic mechanisms and pathways involved is the key to treating such conditions. Drugs such as Decitabine have been used as epigenetic anticancer drugs (Ganesan et al., 2019). This drug manipulates the epigenetic changes and genes therefore, capable of halting the neoplastic progression. Currently, the epigenetic drugs are used alongside routine therapy, an approach which has produced myriad beneficial effects.

Significance of the Information

The information about the pharmacology of drugs is crucial in healthcare. A competent care provider must know the mechanism of actions and potential adverse effects of the drugs. For example, in the management of PD, the nurse must be aware of the pathophysiological mechanisms; the dopamine levels and its receptors. In this case, a nurse is aware that Dopamine agonists are indicated for the management and Dopamine antagonists would worsen the effects.

References

Berg, K. A., & Clarke, W. P. (2018). Making sense of pharmacology: Inverse agonism and functional selectivity. The International Journal of Neuropsychopharmacology, 21(10), 962–977. doi:10.1093/ijnp/pyy071
Ganesan, A., Arimondo, P. B., Rots, M. G., Jeronimo, C., & Berdasco, M. (2019). The timeline of epigenetic drug discovery: from reality to dreams. Clinical Epigenetics, 11(1), 174. doi:10.1186/s13148-019-0776-0
Katzung, B. (2018). Basic & clinical pharmacology (14th ed.). New York: McGraw-Hill.
Miller, E. J., & Lappin, S. L. (2020). Physiology, Cellular Receptor. In StatPearls. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK554403/#_NBK554403_pubdet_
Sheffler, Z. M., Reddy, V., & Pillarisetty, L. S. (2021). Physiology, Neurotransmitters. In StatPearls. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK539894/