The 9 dopaminergic pathways of the brain: types, functions and associated disorders
Our brain is a complex network of neurons They are grouped into different structures and nerve pathways, and they communicate with each other by means of electrochemical impulses generated and largely mediated by neurotransmitters. These neurotransmitters do not appear from nowhere, but they are also synthesized and received in and by the different structures and pathways of the brain.
Among the neurotransmitters, one of the most studied is regarding the pathways through which circulates is dopamine. In this article let's review the different dopaminergic pathways present in our brain .
- Related article: "Parts of the human brain (and functions)"
Dopamine
Before talking about the routes that transmit it, it may be useful to remember that it is dopamine. It is a neurotransmitter, a hormone used by the different neurons of our nervous system to communicate with each other.
We are facing One of the most important neurotransmitters for human beings and their survival , since its functions are multiple and of great importance 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 the personality, allowing memory and creativity and being fundamental when regulating behavior and guiding 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 the dopa and before that from the tyrosine. And it can be found in many parts of the brain. One of the major points in which it is synthesized is in the mesencephalon and in the substantia nigra. And there are many ways through which it circulates.
- Related article: "Catecholamines: types and functions of these neurotransmitters"
The 4 major dopaminergic pathways
Although dopamine can be found in very different nerve pathways, there are four major dopaminergic nerve pathways, which govern the synthesis and transmission of this hormone and in which it has great effects.
1. Via mesolimbic
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 , that allows us to feel pleasure and motivation before our behavior.
This road connects a large number of areas and regions of great relevance, including the ventral tegmental area (which is also part of the mesocortical path), the nucleus accumbens (area where most drugs act), the amygdala, the hippocampus and the prefrontal cortex.
Thanks to it we can feel motivated to do something or 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 the management of emotions.
However, hyperexcitation of this pathway can generate hallucinations and other perceptual alterations and aggression. Also disorganized behaviors or the performance of risky behaviors. In fact, positive symptoms of schizophrenia are associated with an excess of dopamine in this way . The search for their activation, likewise, can lead to the acquisition of addictions and behavioral problems.
- Related article: "Mesolimbic path (brain): anatomy and functions"
2. Via mesocortical
The mesocortical pathway is especially linked to the cognitive . It is via, which starts in 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 the dorsolateral and ventromedial cortex of the prefrontal cortex).
Closely linked to the mesolimbic pathway, the mesocortical pathway also has a relationship with affections and emotions, as well as with the capabilities and use of executive functions.
The presence of excessively low levels of dopamine in this way generate profound alterations at the cognitive level producing poverty of thought, difficulties in the use of logic and reasoning and poverty of speech. In fact, it is considered that the negative symptoms of schizophrenia are largely explained by the lack of sufficient dopamine in this brain pathway. It is frequent the appearance of dullness, little expressiveness , incongruity between the lived and the felt, anguish and bradypsychia.
3. Via nigroestriada
The nigrostriatal pathway is one of the main and most important dopaminergic pathways, being in fact the pathway where most of the brain's dopamine is generated.This pathway goes from the substantia nigra to 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 Huntington's Korea.
- Related article: "Nigrostriatal pathway of the brain: structures and functions"
4. Tuberoinfundibular pathway
This nerve pathway, strongly influenced by dopamine, is found connecting the tuberal region of the middle hypothalamus to the infundibular region thereof. Roughly connects different parts of the hypothalamus and the pituitary gland . This route is of great importance, since it influences the secretion of hormones by the pituitary gland. One of the hormones most affected by the functioning of this pathway is prolactin.
The presence of dopamine in this way 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 happen before the decrease of dopamine are sexual alterations such as galactorrhea and different Sexual dysfunctions resulting from an increase in the synthesis of prolactin . It greatly affects fertility.
The other dopaminergic pathways
When asked about the dopaminergic pathways, most people with knowledge about the subject only refer to those cited above. But the truth is that although the mesolimbic, mesocortical, nigrostriatal and tuberoinfundibular are the main routes 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 pathway that goes from the ventral tegmental area to the amygdala, another that goes from the ventral tegmental area to the hippocampus, another that would again circulate between the ventral and cingulate tegmental area, a connection between the substantia nigra and the subthalamus and a last one that would connect the ventral tegmental area with the olfactory bulb.
Their functions are much less studied and have less importance than the previous ones, which also include some of their processes to some extent. But it would be very useful to analyze its importance in greater depth.
Disorders associated with these neural networks
Dopamine is a neurotransmitter essential for the normative functioning of the human being, as well as other animals. The presence of dysfunctions in the pathways that synthesize and use it can generate diseases and disorders . Among the most relevant are the following.
1. Schizophrenia
As we mentioned earlier, 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 mesolimbic pathway, while the negative ones would do so with a deficit of this neurotransmitter in the mesocortical pathway. The other two main roads would not, in principle, have any alteration per se.
- You may be interested: "The 6 types of schizophrenia and associated characteristics"
2. Parkinson
Parkinson's is another of the disorders that is most linked to the dopaminergic pathways, specifically the nigrostriatal. In fact, it is the degeneration of the dopaminergic neurons of the substantia nigra the one that generates the symptomatology.
- Related article: "Parkinson: causes, symptoms, treatment and prevention"
3. ADHD
Different investigations have insinuated that there may be influence of alterations in the mesocortical pathway and in the mesolimbic pathway in attention deficit hyperactivity disorder, having an effect on the difficulties of individuals with this disorder in terms of motivation, attention span, planning or inhibition of behavior.
4. Addictions
The dopaminergic pathways are deeply associated with the acquisition and maintenance of addictions , being the brain reward circuit in its tracks. This especially includes addictions to substances, but also those of a more behavioral type such as pathological gambling.
- Maybe you're interested: "Addiction: disease or learning disorder?"
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 of menstruation and fertility or galactorrhea are some of the most well-known symptoms
6. Other disorders
There are many other problems that have been associated in some way with the malfunctioning of any of the previous routes. For example, have been related to the manifestations of movement disorders such as Tourette's syndrome or tic disorders, and even in some cases with obsessive-compulsive disorder.
Bibliographic references:
- Belloch, Sandín and Ramos (2008). Manual of Psychopathology. McGraw-Hill. Madrid.
- Kandel, E.R .; Schwartz, J.H .; Jessell, T.M. (2001). Principles of Neuroscience. Madrid: McGraw Hill.
- Santos, J.L. ; García, L.I. ; Calderón, M.A. ; Sanz, L.J .; de los Ríos, P .; Left, S .; Román, P .; Hernangómez, L .; Navas, E .; Thief, A and Álvarez-Cienfuegos, L. (2012). Clinical psychology. CEDE Preparation Manual PIR, 02. CEDE. Madrid.
- Vallejo, J. (2006). Introduction to psychopathology and psychiatry (6th edition). Elsevier, Spain.
