Dopamine is a catecholamine neurotransmitter found in the central nervous system, sympathetic ganglia and retina and works inside the brain’s reward as well as pleasure centers to facilitate regulation of movements and emotions. In addition, dopamine also allows us to see rewards and also initiate actions to more in their direction. Deficiency or dearth of dopamine causes Parkinson’s disease, while individuals having poor dopamine actions are likely to be more inclined to addiction. In addition, the existence of a specific type of dopamine receptor is also related to sensation-seeking.
In fact, several areas of the brain, counting the ventral tegmental area (VTA) – a group of neurons present at the center of the brain, and substantia nigra (a densely pigmented area in the midbrain), produce dopamine. In addition, dopamine is also a neurohormone (hormones produced by specific nervous tissue instead of the endocrine glands) that is discharged by the hypothalamus. As a hormone, the primary function of dopamine is to slow down the discharge of prolactin from the anterior (frontal) lobe of the pituitary.
Akin to several neurotransmitters (chemicals that communicate messages from one nerve in the brain to another or the muscles), dopamine too possesses many dissimilar functions. Dopamine performs a vital role in the normal functioning of the central nervous system and is also connected with the intricate system of stimulus and reward of the brain. When the levels of dopamine in the brain are changed, it may result in an assortment of problems and symptoms, varying from Parkinson’s disease to Attention Deficit Disorder (ADD).
It may be noted that dopamine was discovered as a separate neurotransmitter in Sweden in 1952. This neurotransmitter belongs to the catecholamine family of neurotransmitters, which also includes adrenaline as well as noradrenaline. Together all these neurotransmitters are categorized as monoamines, denoting that their chemical arrangement comprises an amino group connected with an aromatic ring. Dopamine is biosynthesized by the brain, leveraging precursors manufactured or introduced into the body.
From being in the territory of the central nervous system, dopamine facilitates the smooth functioning of the body. Any decline in the level of dopamine has been typically related to Parkinson’s disease, an ailment which is distinguished by difficulties with the central nervous system. Deficiency or absence of dopamine makes the patients feeble, trembling as well as confused. In effect, several patients suffering from Parkinson’s disease have inadequate or flawed control over their body.
Dopamine is also known to have an important role in addiction, since this neurotransmitter is an element of the brain’s system of stimulation. There are a number of medications that promote dopamine production resulting in augmented dopamine levels as well as a matching high. However, when the drug goes out of the system, a sense of depression and a slowdown overtakes. Such a situation can only be cured by augmenting the dopamine levels once more. In effect, the brain has the aptitude to promptly find out the drugs that would promote production of dopamine and, thus, it results in an addiction.
In addition, dopamine is related to a number of psychological conditions, for instance schizophrenia (a grave mental disorder also known as dementia praecox) and psychosis (a mental disorder marked by symptoms like delusions or hallucinations). Besides, dopamine also appears to be concerned with attention maladies, such as ADD, normally in situations wherein reduced levels of dopamine make it troublesome for people to concentrate.
As dopamine is not able to pass through the ‘blood-brain barrier’, doctors are unable to simply give dopamine to their patients straightaway even when the neurotransmitter may be necessary in neurological therapy. As an alternative, the doctors provide precursors that are able to cross the ‘blood-brain barrier’, enabling the brain to synthesize dopamine all by itself. Occasionally, dopamine is also administered into the bloodstream to treat a number of health conditions, as it also works as a diuretic within the body, augmenting the blood pressure as well as enhancing the output by the kidneys.
This neurotransmitter is available in the form of intravenous medication, which acts on the sympathetic nervous system. Administration of the intravenous dopamine results in augmented heart rate as well as increased blood pressure. Nevertheless, since dopamine is not capable of passing through the ‘blood-brain barrier’, when it is given as a medication it does not have an effect on the central nervous system straightaway. In order to augment the levels of dopamine in the brain of patients suffering from Parkinson’s disease and dopa-responsive dystonia also known as DRD ((a genetic disorder that normally becomes perceptible from around 6 years to 16 years of age), a precursor of dopamine called L-DOPA is usually given, as it has the aptitude to pass through the ‘blood-brain barrier’ comparatively without much effort.
Functions in the brain
To be precise, dopamine performs numerous vital functions within the brain, for instance playing a crucial role in behaviour and reasoning/ understanding, motivation/ stimulus, voluntary movement, slowing down the production of prolactin (concerned with lactation as well as sexual gratification/ orgasm), punishment and reward, mood, sleep, attention, learning and working memory. Neurons whose main neurotransmitter is dopamine (Dopaminergic neurons) are present mainly in the ventral tegmental area (VTA) in the midbrain region, the arcuate nucleus of the hypothalamus and the substantia nigra pars compacta.
According to a hypothesis, dopamine sends out reward prediction error, though this theory has been questioned by many. According to this theory, the phase-wise response of dopamine neurons is visible when there is an unanticipated reward. Such responses pass on to the commencement of a conditional impetus following repetitive pairings with the reward. In addition, dopamine neurons are rundown when the reward, which was anticipated, is missed or cancelled. Therefore, it appears that dopamine neurons are able to encrypt the forecast error of rewarding consequences. We naturally learn to replicate behaviours that result in capitalizing rewards. Hence, it is believed that dopamine provides a teaching indication to the different brain parts that are responsible for obtaining a fresh behaviour. Chronological knowledge difference offers a calculation model illustrating the manner in which dopamine’s prediction error is utilized as a technical indicator.
In insects, instead of dopamine, the reward system – a set of structures in the brain that try to synchronize and control behaviour by means of producing gratifying effects, makes use of octopamine, which is supposed to be arthropod homolog of norepinephrine. The role of dopamine is reversed in the case of insects, where it works as a signal for punishment and is essential to develop antagonistic memories.