The 9 dopaminergic pathways of the brain: types, functions and associated disorders

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

Among the neurotransmitters, one of the most studied is the route by which it circulates is dopamine. In this article we will review the different dopaminergic pathways present in our brain.

    Dopamine

    Before we start talking about the pathways that carry it, it may help to remember that this is dopamine. It is a neurotransmitter, a hormone used by different neurons in our nervous system to communicate with each other.

    we are in front one of the most important neurotransmitters for humans and their survival, 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 is often called the pleasure hormone) , influence emotions and personality, allow memory and creativity and be fundamental in regulating behavior and guiding it towards goals.

    It is a hormone naturally present in our body, although it can also be synthesized artificially. This hormone is a catecholamine, Derived from doping and before that from tyrosine. And it can be found in many parts of the brain. One of the main points in which it is synthesized is in the midbrain and in the substantia nigra. And there are many roads.

      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. Mesolimbic route

      One of the most well-known dopaminergic pathways in the brain is the mesolimbic pathway. And it is that this way we find a large part of the brain’s reward system, Which allows us to feel pleasure and motivation in our behavior.

      This route connects a large number of areas and regions of great importance, emphasizing among them the ventral tegmental area (which also includes the mesocortical route), the nucleus accumbens (area in which the majority of drugs act), the amygdala, the hippocampus, and prefrontal cortex.

      Thanks to it, we can feel motivated to do something or to address specific situations or stimuli, learn on the basis of stimulation and make associations that make us repeat our patterns of behavior, learn. It is also linked to the management of emotions.

      However, over-arousal in this pathway can generate hallucinations and other perceptual alterations and attacks. Also disorganized behavior or risky behavior. In fact, positive symptoms of schizophrenia are associated with excess dopamine in this pathway. The search for its activation can also lead to the acquisition of addictions and behavioral problems.

        2. Mesocortical route

        The mesocortical route is mainly linked to the. This pathway, which begins in the ventral tegmental zone (which, as we have also said, is part of the mesolimbic pathway), reaches the frontal lobe and the cerebral cortex, in particular the dorsolateral and ventromedial cortices of the prefrontal).

        Closely related to the mesolimbic pathway, the mesocortical pathway is also related to ailments 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 cognitive level producing poverty of thought, difficulties in the use of logic and reasoning, and poverty of speech. In fact, it is believed that the negative symptoms of schizophrenia are largely due to the lack of dopamine in this brain pathway. The appearance of the sausage is frequent, not very expressive, Incongruity between what is experienced and what is felt, anxiety and laziness.

        3. Your black band

        The black streak pathway is one of the main and most important dopaminergic pathways, in fact being the pathway where most dopamine is generated throughout the brain. This pathway goes from the substantia nigra to the basal ganglia (especially the striatal nucleus).

        The black striped channel is particularly linked to engine control, its degeneration being the main cause of disorders such as Parkinson’s disease and chorionic movements, As in the case of Huntington’s Korea.

          4. Your tuberoinfundibularis

          This nerve path, with a great influence of dopamine, connects the tubal region of the middle hypothalamus to the infundibular region of the latter. Widely it connects different parts of the hypothalamus and pituitary. This pathway is of great importance because 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 the synthesis of prolactin and promotes the production of somatotropin. In fact, with the consumption of neuroleptics, we can see that one of the side effects that can occur with the decrease in dopamine are sexual disorders such as galactorrhea and various sexual dysfunctions resulting from increased synthesis of prolactin. It greatly affects fertility.

          The other dopaminergic pathways

          When asked about the existing dopaminergic pathways, most people with knowledge on the subject refer only to those mentioned above. But the truth is, while 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.

          More precisely, we can find a nerve path which goes from the ventral tegmental zone to the amygdala, another which goes from the ventral tegmental zone to the hippocampus, another which would circulate again between the ventral tegmental zone and the cingulate, a connection between the substantia nigra and the subthalamus and a last which would connect the ventral tegmental zone with the olfactory bulb.

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

          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 lead to diseases and disorders. The most relevant are the following.

          1. Schizophrenia

          As mentioned above, the main symptoms of schizophrenia appear to be related 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 correspond to a deficiency of this neurotransmitter in the mesocortical pathway. The other two main routes would, in principle, not have any changes per se.

            2. Parkinson’s

            Parkinson’s disease is another of the disorders most closely linked to the dopaminergic pathways, particularly black spot. In fact, it is degeneration of dopaminergic neurons in the substantia nigra the one that generates the symptomatology.

              3. ADHD

              Different research has suggested that there may be an influence of alterations in the mesocortical pathway and the mesolimbic 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. Dependencies

              Dopaminergic pathways are deeply associated with the acquisition and maintenance of addictions, With the brain reward circuit their journeys. This includes substance addictions in particular, but also those of a more behavioral type such as gambling addiction.

                5. Hyperprolactinemia

                It has been observed that the decrease in dopamine levels in the tuberofibular pathway results in hyperprolactinemia, which it has several effects in areas such as reproduction. Among the most well-known symptoms are menstruation and fertility alterations or galactorrhea

                6. Other disorders

                There are many other issues that have been associated in one way or another with the dysfunction of some of the above pathways. For example, have been observed to be related to manifestations of movement disorders like Tourette’s syndrome or tics, and even in some cases with obsessive-compulsive disorder.

                Bibliographical references:

                • Belloch, Sandín and Ramos (2008). Manual of psychopathology. McGraw-Hill. Madrid.
                • Kandel, ER; Schwartz, JH; Jessell, TM (2001). Principles of neuroscience. Madrid: McGraw Hill.
                • Sants, JL; Garcia, LI; Calderon, MA; Sanz, LJ; of rivers, P .; Left, S .; Román, P .; Hernangómez, L .; Navas, E .; Lladre, A and Álvarez-Cienfuegos, L. (2012). Clinical Psychology. CEDE PIR preparation manual, 02. CEDE. Madrid.
                • Vallejo, J. (2006). Introduction to psychopathology and psychiatry (6th edition). Elsevier, Spain.

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