Dopamine is a neurotransmitter, which transmits signals between brain neurons. Scientists report that very few cells are responsible for making dopamine, and the death of substantia-nigra is associated with the dysfunction of the body and formation of disease cells such as Parkinson’s disease. This paper studies the roles and effects of dopamine in the human brain while utilizing the literature review done by other scholars.
Dopamine
Central dopamine (DA-containing neurons) has been thought to be involved in human diseases such as schizophrenia and Parkinson’s disease. The neurons are also thought to act as the sites of action of the drugs of abuse. Consequently, scholars wanted to test the report and study the DA receptors in the Candate–putamen (CP) and Substantia Nigra (SN) of the rat. The DA receptor binding was measured with agonists and antagonists labeled (Wang 2001). The selective lesion of the nigrostriatal projection (NSP) was also measured whereby the DA receptors in the structures were labeled. The study revealed that the lesions that are put at the NSP axons cause near complete anterograde and retrograde degeneration of the system’s cell bodies and terminals. The scholar posited that the method of study used was safer than previous methods since it avoided damage to the areas, which were studied. The study, which used rat brains, revealed that dopamine causes diseases such as schizophrenia in the brain.
Delegate your assignment to our experts and they will do the rest.
Additionally, Jaber, Robinson, &Caron (1996) state that dopamine plays a vital role in the central nervous system as it controls such activities as locomotion, cognition, control, and secretion of the neuroendocrine. The actions of the substance are mediated by five-receptor subtypes, which all belong to the G-protein receptor family. D 1 -like and D 2 -like receptors are the two main subclasses of dopamine receptors. The two align to the G s and G i transduction systems in the central nervous system. Notably, the different receptor subtypes have precise anatomical distributions: D 1 -like receptors are post-synaptic while D 2 -like receptions are pre-synaptic as well as postsynaptic. In addition, these two dopamine receptors are the most common in the central nervous system; they are mostly expressed in distinct neurons. To monitor the dopaminergic activities in the central nervous system, scholars in many studies have used dynorphin and substance P, which are contained in neurons that contain D 1 receptor and preproenkephalin that is contained in D 2 receptors (Jaber, Robinson, &Caron,1996).
Zabberoni et al. 2017 in their recent study stated that the early functioning of the Parkinson’s disease is relatively independent of the activities of the dopamine brains networks. They state that the disease is mainly accompanied by cognitive deficits such as mild cognitive impairment, dementia, visual-spatial abilities, as well as episodic memory. Nevertheless, they suggested that studies should be done that combine different paradigms of study such as verbal fluency and associative priming.
According to the research findings by Jaber, Robinson, &Caron (1996), dopamine, which is released from the hypothalamus, is responsible for the control, secretion, and synthesis of prolactin. The action is done via the D 2 receptors to the anterior pituitary. Additionally, these scholars claim that although dopamine is associated with mental disorders such as schizophrenia, none of its receptor subtypes is specifically identified for the same. However, they claim that more studies will be conducted, especially following the characterization of the D 3 and D 4 dopamine receptors, which are mostly found in the areas of the CNS, which mediate cognition and show high affinity for some neuroleptics. Since there has been a production of animals, which are genetically derived, and which lack some of the receptors, studies will help elucidate the precise physiological paradigms, which the several receptors mediate.
On the other hand, Wise & Rompre (1989) indicated that studies implicate that neurons that contain dopamine are active in reward phenomenon. Dopamine is cited as one of the catecholamine-neuron- transmitters; the cell group’s dopaminergic actions are the ones that project forward from the midbrain to several forebrain structures. Wise & Rompre (1989) further posit that subsets of the neurons are also associated with several aspects of motivated behaviors. Additionally, the abnormal functioning of the dopaminergic neurons has been associated with the development of Parkinson’s disease, depression, mania and, schizophrenia. The study suggests that understanding the role played by the dopaminergic neurons in reward are a step forward in determining the role that dopamine plays in the mood and movement of a living being. Wise & Rompre (1989) focus on the role of rewards, which are said to exert strong control over the human thoughts and behaviors. Two powerful rewards that activate the central rewards circuitry directly and not via the peripheral nerves are rewards that have direct electrical stimulation and the rewards of habit-forming drugs. The final summary of the Wise & Rompre (1989) study indicated that dopamine projections are a vital part of the mediation of rewarding effects. However, although dopamine plays a vital role in rewarding the brain stimulation, the exact role of the element is unclear. The study also revealed that dopamine is not the only reward transmitter and dopaminergic neurons are definitely not the final common path for all rewards.
Wang et. al. (2001) conducted a similar study and posited that the cerebral mechanists that lead people to overeat pathologically and suffer obesity could be associated with dopamine. They noted that dopamine is a neurotransmitter that plays an active role in the modulation of the rewarding properties of food. The study hypothesis that obese people have abnormalities in the dopamine activity of their brains. The study focused on the D 2 receptors whose availability was measured using NaN raclopride positron emission tomography (PET). Notably the former is a radiogland for the receptor. The scholars in the study also assessed 2-deoxy-2[18F] fluoro-D-glucose to check the glucose metabolism in the brain. The findings of the study were there the D 2 receptors were lower in the ten obese people used in the study than in the control group. The Body Mass Index (BMI) of the individuals had a negative correlation with their D 2 receptors; the person with the lowest D 2 receptor level had the highest BMI level. Contrastingly, the whole brain or striatal metabolism did not differ between the obese people and their controls. The interpretation of the finding is that the availability of the D 2 receptors was low in obese people in proportion to their BMI levels. Since dopamine modulates reward and motivating circuits, its deficiency in obese people may propagate pathological and unreasonable eating so that the people can compensate for the decreased activation of the said circuits. As such, the improvement of dopamine functions in obese people should be focused on, as that will reduce the health issues associated with obesity.
Conclusion
Dopamine plays major roles in the human brain. The ventral tegmental area (VTA) neurons help the brain learn about rewards. As such, drug abuse causes dopamine release leading to addictive tendencies among individuals. Additionally, the dysfunction of the dopamine-producing cells in the brain results in such effects as obesity and development of the Parkinson's disease. It is vital for the dopamine levels and functions to be kept at the right level in the human brain.
References
Jaber, M., Robinson, S., Missale, C &Caron, M., (1996). Dopamine receptors and brain function, Neuropharmacology 35 (11) 1503-1519.
Wang, G., Volkow, N. D., Pappas, N. R., Netusil, N., Wong, C. T., Logan, J., & ... Zhu, W. (2001). Brain dopamine and obesity. Lancet , 357 (9253), 354.
Wise, R., & Rompre, P. (1989). BRAIN DOPAMINE AND REWARD. Annual Review Of Psychology, 40(1), 191.
Zabberoni, S., Carlesimo, G. A., Peppe, A., Caltagirone, C., & Costa, A. (2017). Does Dopamine Depletion Trigger a Spreader Lexical-Semantic Activation in Parkinson’s Disease? Evidence from a Study Based on Word Fluency Tasks. Parkinson's Disease (20420080) , 1-6. doi:10.1155/2017/2837685
