Dopaminergic Pathways (Brain): Types, Functions, and Disorders

Our brain is a complex network of neurons. that are grouped into different structures and nerve pathways, and that communicate with each other through electrochemical impulses generated and largely mediated by neurotransmitters. These neurotransmitters do not appear out of nowhere, but are also synthesized and received in and by the different structures and pathways of the brain.

Among the neurotransmitters, one of the most studied regarding the pathways through which it circulates is the dopamine. In this article We are going to review the different dopaminergic pathways present in our brain.

• Related article: "Parts of the human brain (and functions)"

dopamine

Before starting to talk about the pathways that transmit it, it may be useful to remember what dopamine is. It is a neurotransmitter, a hormone used by the different neurons of our nervous system to communicate with each other.

we are before one of the most important neurotransmitters for humans and their survival, since its functions are multiple and of great depth when it comes to allowing us to regulate our behavior: participating in aspects such as the perception of pleasure (in fact, it has often been called the pleasure hormone), influencing emotions and personality, allowing memory and creativity and being fundamental when it comes to regulating behavior and directing it towards goals.

It is a hormone that is naturally present in our body, although it can also be synthesized artificially. This hormone is a catecholamine, derived from dopa and before that from tyrosine. And it can be found in numerous parts of the brain. One of the major points at which it is synthesized is in the midbrain and in the substantia nigra. And there are multiple routes through which it circulates.

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The 4 big dopaminergic pathways

Although dopamine can be found in many different nerve pathways, there are four major pathways. dopaminergic nerves, which govern the synthesis and transmission of this hormone and in which it has great effects.

1. mesolimbic pathway

One of the best known dopaminergic brain pathways is the mesolimbic pathway. And it is that in this way we found much of the brain reward system, which allows us to feel pleasure and motivation before our behavior.

This pathway connects a large number of areas and regions of great relevance, standing out among them the tegmental area. ventral (which is also part of the mesocortical pathway), the nucleus accumbens (area in which most of the drugs), the amygdala, he hippocampus and the prefrontal cortex.

Thanks to it we can feel motivated to do something or to approach specific situations or stimuli, learn based on stimulation and make associations that make us repeat our behavioral patterns, learning. It is also linked to managing emotions.

However, hyperarousal of this pathway can lead to hallucinations and other perceptual disturbances and aggression. Also disorganized behaviors or risk behaviors. In fact, the positive symptoms of schizophrenia are associated with an excess of dopamine in this pathway. The search for its activation, likewise, can lead to the acquisition of addictions and behavioral problems.

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2. mesocortical pathway

The mesocortical pathway is especially linked to the cognitive. This route, which starts at the ventral tegmental area (which, as we have said, is also part of the mesolimbic pathway), reaches the frontal lobe and the cerebral cortex (especially notable are the dorsolateral and ventromedial cortex of the prefrontal).

Closely linked to the mesolimbic pathway, the mesocortical pathway is also related to affects and emotions, as well as the abilities and use of executive functions.

The presence of excessively low levels of dopamine in this pathway generates profound alterations at the cognition producing poverty of thought, difficulties in the use of logic and reasoning and poverty of speaks. In fact, it is considered that the negative symptoms of schizophrenia are largely explained by the lack of sufficient dopamine in this brain pathway. The appearance of dullness is frequent, little expressiveness, incongruity between what is experienced and what is felt, anguish and bradypsychia.

3. nigrostriatal pathway

The nigrostriatal pathway is one of the main and most important dopaminergic pathways, being in fact the pathway where most of the dopamine in the entire brain is generated. This path goes from black substance until the basal ganglia (specifically the striated nucleus).

The nigrostriatal pathway is especially linked to motor control, its degeneration being the main cause of disorders such as Parkinson's and choreic movements, as in the case of the Huntington's chorea.

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4. tuberoinfundibular pathway

This nervous pathway, highly influenced by dopamine, is found connecting the tuberal region of the median hypothalamus to its infundibular region. Roughly connects different parts of the hypothalamus and pituitary gland. This pathway is of great importance, since it influences the secretion of hormones by the hypophysis. One of the hormones most affected by the functioning of this pathway is prolactin.

The presence of dopamine in this pathway inhibits the synthesis of prolactin, in addition to favoring the generation of somatotropin. In fact, before the consumption of neuroleptics we can observe that one of the side effects that can occur when dopamine decreases are sexual alterations such as galactorrhea and different sexual dysfunctions derived from an increase in the synthesis of prolactin. It greatly affects fertility.

The other dopaminergic pathways

When asked about the dopaminergic pathways that exist, most people with knowledge on the subject only refer to those mentioned above. But the truth is that although the mesolimbic, mesocortical, nigrostriatal and tuberoinfundibular pathways are the main ones, they are not the only ones that exist. For other areas of the brain there are other secondary dopaminergic pathways.

Specifically, we can find a nerve path that goes from the ventral tegmental area to the amygdala, another that goes from the ventral tegmental area to the hippocampus, another that again would circulate between the tegmental area ventral and cingulum, a connection between the substantia nigra and the subthalamus and a last one that would connect the ventral tegmental area with he olfactory bulb.

Its functions are much less studied and are less important than the previous ones, which also include some of its processes to a certain extent. But it would be very useful to analyze its importance in greater depth.

Disorders associated with these neural networks

Dopamine is an essential neurotransmitter for the normative functioning of humans, as well as other animals. The presence of dysfunctions in the pathways that synthesize and use it can cause diseases and disorders. Among the most relevant are the following.

1. Schizophrenia

As we have previously mentioned, the main symptoms of schizophrenia seem to be linked to alterations in dopamine levels in some of the dopaminergic nerve pathways. Specifically, the positive symptoms seem to correspond to an excess of dopamine in the pathway mesolimbic, while the negative ones would do so with a deficit of this neurotransmitter in the pathway mesocortical. The other two main routes would not have, in principle, any alteration per se.

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2. Parkinson's

Parkinson's is another of the disorders that is most linked to the dopaminergic pathways, specifically the nigrostriatal. In fact, it is degeneration of dopaminergic neurons of the substantia nigra the one that causes the symptoms.

• Related article: "Parkinson's: causes, symptoms, treatment and prevention"

3. ADHD

Various investigations have suggested that there may be influence of alterations in the mesocortical pathway and in the mesolimbic pathway in it attention deficit hyperactivity disorder, having an effect on the difficulties of individuals with this disorder in terms of motivation, attention span, planning or behavioral inhibition.

4. addictions

Dopaminergic pathways are deeply associated with the acquisition and maintenance of addictions, the brain reward circuit being in its pathways. This especially includes addictions to substances, but also those of a more behavioral type such as gambling.

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5. hyperprolactinemia

It has been observed that the decrease in dopamine levels in the tuberoinfundibular pathway generates hyperprolactinemia, which has various effects in areas such as reproductive. Alterations in menstruation and fertility or galactorrhea are some of the best known symptoms

6. Other disorders

There are many other problems that have been associated in some way with the malfunction of any of the above pathways. For example, have been related to manifestations of movement disorders such as the Tourette's syndrome or tic disorders, and even in some cases with obsessive-compulsive disorder.