Nigrostriatal pathway of the brain: structures and functions.

This set of neural circuits in the brain plays a role in movement control.

Dopamine is one of the main neurotransmitters in the brain, known mainly for its involvement in processes related to pleasure and reward systems. However, its role in motor control is fundamental, using different dopaminergic pathways to travel through the brain.

One of these neural networks is the nigrostriatal pathway.. Throughout this article we will discuss what structures compose it, as well as its role in brain function and the clinical implications of its impairment.

What is the nigrostriatal pathway?

The nigrostriatal pathway is one of the four pathways that make up the dopaminergic system. Together with the mesolimbic pathway, the mesocortical pathway and the tuberoinfundibular pathway, it is responsible for transporting dopamine from one part of the brain to another.

To be more precise, the nigrostriatal pathway is the one whose bundles project from the substantia nigra to the striatum, specifically to the caudate nucleus and putamen. This pathway plays a fundamental role in motor controlbeing the stimulation of intentional movement the main function of this pathway.

The lesions or alterations inherent to disorders such as Parkinson's disease or chorea affect the nigrostriatal pathway, generating numerous symptoms. D2 dopaminergic antagonists can also induce extrapyramidal symptoms associated with pseudoparkinsonism.

Related structures

As mentioned above, the nigrostriatal pathway runs through the brain from the substantia nigra to the caudate nucleus and putamen, located in the striatum.

1. Substance nigra

The substantia nigra corresponds to a brain area located in the midbrain, which stores dopamine-producing neurons. It is called substantia nigra because its tone is darker than the rest of the surrounding areas, because its neuromelanin levels are the highest in the area..

The main function of the substantia nigra is related to eye movements, motor control, reward seeking, learning and addiction. However, most of these are also mediated by the striatum.

When this structure begins to disintegrate or starts a process of degeneration, conditions such as Parkinson's disease appear, conditions such as Parkinson's diseasewhich leads to numerous motor and cognitive disorders.

2. Striatum

Also called the striatum, the striatum forms the subcortical part of the telencephalon. This structure is distinguished by the fact that it is essential for transmitting information to the basal ganglia.

The group of structures that form the striatum are the caudate nucleus, the putamen and the nucleus accumbens.. However, in this article only the first ones will be described because they are an essential part of the functioning of the nigrostriatal pathway.

3. Caudate nucleus

The structures known as the caudate nuclei are located approximately in the center of the brain. located approximately in the center of the brain, very close to the thalamus.. We speak of nuclei in plural because there are two different nuclei within each of the hemispheres of the brain.

Traditionally, the basal ganglia have been associated with higher order motor control. Within these functions, the caudate nucleus participates in the domain of voluntary control, as well as in learning processes and memory.

4. Putamen

The putamen is a system also located in the central area of the brain, which plays an essential role in the control of movements, specifically in the control and direction of fine voluntary movements.

In addition, the correct functioning of the putamen exerts an important influence on operant conditioning and recent studies label it as the and recent studies label it as the origin of the feelings of love and hate.

Role in brain functioning

As we have seen, the nigrostriatal pathway, and those structures that comprise it, are responsible for governing and promoting the control of voluntary movements..

In general, movement control is the result of the successful combination of sensory and motor information coordinated by the central nervous system (CNS).

Within this motor control we find voluntary, involuntary and reflex movements. However, in this case it is the voluntary movements that are controlled by the nigrostriatal pathway.

Voluntary movements are made with the intention of achieving a goal, i.e. they are purposeful. Moreover, most of these movements can be learned, most of these movements can be learned and improved through practice.

Clinical implications and associated disorders

Knowing the structures related to the mesocortical pathway and the functions it performs, it will be much easier to understand the effects or consequences of decreased activity in these neural networks.

This decrease in the level of activity can occur in the following ways either by the administration of dopaminergic D2 antagonist drugs or by progressive degeneration of the pathway, leading to diseases such as chorea or Parkinson's disease. of the pathway, which gives rise to diseases such as chorea or Parkinson's disease.

D2 antagonists

D2 antagonists are commonly used in the treatment of gastric problems such as nausea, vomiting or Gastrointestinal problems. However, their action as a dopamine antagonist may cause undesirable extrapyramidal effects such as dystonia or pseudoparkinsonian-like movements.

Koreas

Choreas are a group of neurological conditions that are distinguished by causing a series of strange involuntary movements in the feet and hands. These impulses are caused by a series of intermittent and uneven muscle contractions, i.e., they do not present a pattern.They do not present a repetitive or rhythmic pattern, but seem to be transmitted from one muscle to another.

Within this group is the well-known Huntington's chorea, familial benign chorea or familial inverted choreoathetosis.

Parkinson's disease

Parkinson's disease is a motor disorder of relatively frequent occurrence in people over 60 years of age. The origin of this disease lies in a decrease in dopamine production, especially in the nigrostriatal pathway, which is no longer sufficient to meet the demands of the brain.

It is a disease that develops progressively, affecting first one side of the body to act later on the other. The main symptoms of this disease are:

• Tremors in upper and lower extremitieshands, feet, jaw and face.
• Stiffening of the muscles of the arms, legs and trunk.
• Slowness of movement.
• Alterations in balance and coordination.