DOPAMINE

Dopamine



Dopamine

Introduction

Dopamine, identified as a central nervous system agent in 1959, is a neurotransmitter (nerve-signaling molecule) the body makes from the amino acid tyrosine. Dopamine in turn serves as the molecule the body uses to make adrenaline and noradrenaline. In addition to operating in nervous system signaling, it also acts as a hormone in an area of the brain called the hypothalamus, regulating release of the hormone prolactin, which is involved in parenting behavior and milk production. The body regulates dopamine' activity in the brain in part by using proteins called dopamine transporters, which can take up dopamine and dump it back into a cell, preventing the signalling molecule from exerting its activity. The body also has five types of proteins, called dopamine receptors, responsible for recognizing the dopamine molecule, binding to it, and transmitting its signal to the cell. Dopamine is at the centre of the development of a number of psychiatric disorders, including addiction and schizophrenia, and it also plays a prominent role in the manifestations of Parkinson's disease.

Discussion and Analysis

The brain produces dopamine in three primary areas: the substantia nigra, the ventral tegmental area, and the arcuate nucleus. The first two are of particular interest in terms of psychiatric disorders; the arcuate nucleus is associated with dopamine's role as a neurohormone in prolactin regulation. Disorders associated with dopamine signaling have a biological basis in the brain that appears to be site-specific. The brain has four major dopamine-signaling pathways. (White, 1996, pp. 921-949)

The mesocortical pathway connects the ventral tegmental area to the cortex, the part of the brain involved in cognition and that may play a role in motivation. This pathway features in hypotheses of dopamine's association with schizophrenia.

The mesolimbic pathway also begins in the ventral tegmental area, which is linked to the nucleus accumbens, the largest component of the ventral striatum. Much research has associated the nucleus accumbens and the mesolimbic pathway with brain reward processes and addiction and also with different aspects of schizophrenia.

The nigrostriatal pathway connects the dopamine-producing nigrostriatal area with the striatum and plays a high-profile role in the development of Park-sinon's symptoms.

The tuberoinfundibular pathway involves the hypothalamus and dopamine as a neurohormone.

In terms of neuropsychiatric disorders, dopamine is probably best known as the neurotransmitter underlying the development and persistence of addiction as part of the mesolimbic reward pathway. In brief, experiences we find rewarding, such as food or sex, can become associated with increased dopamine, as can some pathological behaviors, such as compulsive gambling. Some drugs also directly elicit an increase in dopamine, setting off the reward pathway and leading more use of the drug. Ultimately, some people become addicted to substances or behaviors because of the dopamine release they trigger and the feelings of euphoria or tension relief that can follow the release. (Sell, 2000, pp. 207-216)

Anatomically, these distinct dopamine-signaling pathways, variously involved in specific pathologies, may overlap with one another. For example, there is some comorbidity among schizophrenia, depression, and drug dependence and some anatomical overlap in the dopamine-signaling areas ...