Our brain is a complex network of neurons that are grouped into different structures and nerve pathways, and which communicate with each other by means of electrochemical impulses generated and mediated to a large extent 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 is the way it circulates, dopamine. In this article we will review the different dopaminergic pathways present in our brain .

Dopamine

Before we go into the pathways that transmit it, it may be helpful to remember that it is dopamine. It is a neurotransmitter, a hormone used by the different neurons in our nervous system to communicate with each other.

We are dealing with 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 behaviour: 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 behaviour and orienting it towards goals.

It is a hormone that is naturally present in our body, although it can also be artificially synthesized. 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 where it is synthesized is in the midbrain and the substantia nigra. And there are multiple pathways through which it circulates.

The 4 major dopaminergic pathways

Although dopamine can be found in many 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. Mesolimbic pathway

One of the best known dopaminergic brain pathways is the mesolimbic pathway. In this pathway we find a large part of the brain’s reward system , which allows us to feel pleasure and motivation in our behaviour.

This pathway connects a large number of areas and regions of great relevance, highlighting among them the ventral tegmental area (which is also part of the mesocortical pathway), 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 to approach concrete situations or stimuli, learn based on stimulation and make associations that make us repeat our behavioural patterns, learning. It is also linked to the management of emotions.

However, hyperexcitation of this pathway can generate hallucinations and other perceptual disturbances and aggression. Also disorganized behavior or the performance of risky behaviors. In fact, the positive symptoms of schizophrenia are associated with an excess of dopamine in this pathway . The search for its activation may also lead to the acquisition of addictions and behavioural problems.

2. Mesocortical pathway

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

Closely linked to the mesolimbic pathway, the mesocortical pathway also has a relationship with affections and emotions, as well as in the capacities and use of executive functions.

The presence of excessively low levels of dopamine in this pathway generates 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 dulling, little expressiveness , incongruence between what is experienced and what is felt, anguish and bradypsychia.

3. Nigrostriatal track

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 whole brain is generated. This pathway runs from the substantia nigra to the basal ganglia (specifically the striatum).

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

4. Tube-infundibular track

This nerve pathway, heavily influenced by dopamine, is found connecting the tubal region of the mid-hypothalamus to the infundibular region of the mid-hypothalamus. Broadly speaking it connects different parts of the hypothalamus and the pituitary gland . This pathway is of great importance, as 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 pathway inhibits prolactin synthesis, in addition to favoring the generation of somatotropin. In fact, with the consumption of neuroleptics we can observe that one of the side effects that can occur with the decrease of dopamine 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 existence of dopaminergic pathways, most people with knowledge of 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. In 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 tegmental area and the cingulate, a connection between the substantia nigra and the subthalamus and a last one that would connect the ventral tegmental area with the olfactory bulb.

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

Disorders associated with these neural networks

Dopamine is an essential neurotransmitter for the regulatory functioning of humans, 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 mentioned above, the main symptoms of schizophrenia seem to be linked to alterations in the levels of dopamine in some of the dopaminergic nerve pathways . Specifically, positive symptoms seem to correspond with an excess of dopamine in the mesolimbic pathway, while negative symptoms would correspond with a deficit of this neurotransmitter in the mesocortical pathway. The other two main pathways would not, in principle, have any alteration per se.

  • You may be interested in: “The 6 Types of Schizophrenia and Associated Characteristics”

2. Parkinson’s

Parkinson’s is another disorder most closely linked to the dopamine pathways, specifically the nigrostriatal pathway. In fact, it is the degeneration of dopaminergic neurons in the substantia nigra that generates the symptoms.

3. ADHD

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

4. Addictions

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

  • You might be interested in: “Addiction: disease or learning disorder?”

5. Hyperprolactinemia

It has been observed that the decrease in dopamine levels in the tuber-infundibular pathway generates hyperprolactinemia, which has various effects in areas such as reproduction . 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 malfunctioning of one of the above routes. For example, have been linked to manifestations of movement disorders such as Tourette syndrome or tic disorders, and even in some cases to 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.; Izquierdo, S.; Román, P.; Hernangómez, L.; Navas, E.; Ladrón, A and Álvarez-Cienfuegos, L. (2012). Clinical Psychology. Manual CEDE de Preparación PIR, 02. CEDE. Madrid.
  • Vallejo, J. (2006). Introduction to psychopathology and psychiatry (6th edition). Elsevier, Spain.