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

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

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 place to another in the brain.

To be more precise, the nigrostriatal pathway is the one whose beams project from the black substance to the striated body, specifically to the caudate nucleus and the putamen. This pathway has a fundamental role in motor control , being the stimulation of intentional movement the main function of this one.

The injuries or alterations typical of disorders such as Parkinson’s disease or chorea, affect the nigrostriatal pathway generating numerous symptoms. Likewise, D2 dopamine antagonists can 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. Black substance

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

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

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

2. Grooved body

Also called the striated nucleus, the striated body forms the subcortical part of the brain. This structure is distinguished by the fact that it is essential in transmitting information to the basal ganglia.

The set of structures that form the striated body are the caudate nucleus, the putamen and the nucleus accumbens . However, this article will only describe the former because they are an essential part of the functioning of the nigrostriatal pathway.

3. Caudate nucleus

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

Traditionally, the basal ganglia has 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 also a system 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 has an important influence on operant conditioning and recent studies label it as the origin of feelings of love and hate.

Role in brain function

As we have seen, the nigrostriatal road, and those structures that make it up, are responsible for governing and favouring 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 the voluntary movements, the involuntary ones and the reflexes. However, in this case it is the voluntary movements that are controlled by the nigrostriatal route.

Voluntary movements are carried out with the intention of achieving an objective, i.e. they are purposeful. Moreover, most of these movements can be learned and improved through practice

Clinical implications and associated disorders

Already knowing the structures related to the mesocortical pathway and the functions it performs, it will be much easier for us to understand what effects or consequences the decrease in activity in these neural networks entails.

This decrease in activity level can occur either by the administration of D2 dopamine antagonist drugs or by the progressive degeneration of the pathway, which gives rise to diseases such as Korean 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 performance as a dopamine antagonist can lead to unwanted extrapyramidal effects such as dystonia or pseudoparkinsonian-type movements.

Koreas

Koreas are a group of neurological conditions that are distinguished by the fact that they cause people to make a series of strange, involuntary movements in their hands and feet. These impulses are caused by a series of intermittent and uneven muscle contractions , that is, 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, the benign familial chorea or familial inverted cheoathetosis.

Parkinson’s Disease

Parkinson’s disease is a motor disorder that is relatively common in people over 60. The origin of this disease is found in a decrease in dopamine production, especially in the nigrostriatal pathway, which is no longer sufficient to supply the demands of the brain.

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

  • Tremors in upper and lower extremities , hands, feet, jaw and face.
  • Hardening of the muscles in the arms, legs and trunk.
  • Slow movement.
  • Alterations in balance and coordination.