The 9 dopaminergic pathways of the brain: types, functions and associated disorders.
Lesions of these networks of neurons produce disorders such as schizophrenia or Parkinson's disease.
Our brain is a complex network of neurons which are grouped in 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 with respect to the pathways by which it circulates is dopamine. In this article we are going to review the different dopaminergic pathways present in our brain..
The dopamine
Before discussing 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 in our nervous system to communicate with each other.
We are dealing with one of the most important neurotransmitters for the human being and its survival, since its functions are multiple.Its functions are multiple and of great importance in allowing us to regulate our behavior: participating in aspects such as the perception of pleasure (in fact, it has often been called the hormone of pleasure), influencing emotions and personality, allowing memory and creativity and being fundamental in regulating behavior and orienting it towards goals.
It is a hormone that is naturally present in our organism, although it can also be synthesized artificially. This hormone is a catecholaminederived 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 in the substantia nigra. And there are multiple pathways by which it circulates.
The 4 major dopaminergic pathways
Although dopamine can be found in very different nervous pathways, there are four major dopaminergic nervous 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. It is in this pathway that we find a large part of the brain's reward system. we find a great part of the brain reward system, which allows us to feel pleasure and motivation.which allows us to feel pleasure and motivation for our behavior.
This pathway connects a large number of areas and regions of great relevance, among them the ventral tegmental area (which is also part of the mesocortical pathway), the nucleus accumbens (area in which most drugs act), the amygdala, the 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. that make us repeat our behavioral patterns, learning. It is also linked to the management of emotions.
However, the hyperexcitability of this pathway can generate hallucinations and other perceptual alterations and aggressiveness. Also disorganized behaviors or the realization of risky behaviors. In fact, the positive symptoms of schizophrenia the positive symptoms of schizophrenia are associated with an excess of dopamine in this pathway.. The pursuit of its activation can also lead to the acquisition of addictions and behavioral problems.
Mesocortical pathway
The mesocortical pathway is particularly linked to cognitive. This pathway, 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 remarkable are the dorsolateral and ventromedial prefrontal cortex).
Closely linked to the mesolimbic pathway, the mesocortical pathway is also involved in affect and emotion, as well as in the abilities and use of executive functions.
The presence of excessively low levels of dopamine in this pathway generates profound alterations at the cognitive level producing poor thinking, difficulties in the use of logic and reasoning and poor 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, incongruence between what is lived and what is felt, anguish and anxiety.incongruence 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 whole brain is generated. This pathway runs from the substantia nigra to the basal ganglia (specifically the striatal nucleus).
The nigrostriatal pathway is especially linked to motor control, its degeneration being the main cause of disorders such as Parkinson's disease and choreic movements, as in the case of chorea.as in the case of Huntington's chorea.
4. Tuberoinfundibular pathway
This nerve pathway, strongly influenced by dopamine, is found connecting the tuberal region of the medial hypothalamus to the infundibular region of the medial 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, when taking neuroleptics we can observe that one of the side effects that can occur due to the decrease in dopamine are sexual alterations such as galactorrhea and different sexual dysfunctions derived from a decrease in dopamine. sexual dysfunctions derived from an increase in prolactin synthesis.. 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. 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 cingulum, 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 are of less importance than the previous ones, which also include some of its processes to a certain extent. But it would be very useful to analyze their 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 utilize it can lead to diseases and disorders.. Among the most relevant are the following.
1. Schizophrenia
As we have 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 to an excess of dopamine in the mesolimbic pathway, while negative symptoms would correspond to a deficit of this neurotransmitter in the mesocortical pathway. The other two main pathways would not have, in principle, any alteration per se.
2. Parkinson's
Parkinson's is another of the disorders that is most often linked to the dopaminergic pathways, specifically the nigrostriatal pathway. In fact, it is the degeneration of the dopaminergic neurons of the substantia nigra that generates the symptomatology.
3. ADHD
Different investigations have insinuated that may be influenced by alterations in the mesocortical and mesolimbic pathways in ADHD. in 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 acquisition and maintenance of addictionsThe brain's reward circuitry is in its pathways. This includes especially substance addictions, but also more behavioral addictions such as pathological gambling.
5. Hyperprolactinemia
It has been observed that the decrease of dopamine levels in the tuberoinfundibular pathway generates hyperprolactinemia, something that has a variety of 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 one of the above pathways. For example, have been associated with the manifestations of movement disorders such as Tourette's syndrome, or 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 de Psicopatología. 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). Psicología Clínica. Manual CEDE de Preparación PIR, 02. CEDE. Madrid.
- Vallejo, J. (2006). Introduction to psychopathology and psychiatry (6th edition). Elsevier, Spain.
(Updated at Apr 14 / 2024)