Brain pathways are routes that connect different regions of the brain. In this article we will learn about one of the dopaminergic pathways, the tubero-infundibular pathway . This pathway is related to a very important hormone: prolactin.

We will see how important this pathway is, and we will also learn about the other three most important dopaminergic pathways, which are closely related to schizophrenia or other psychotic disorders.

Dopaminergic pathways

The tubero-infundibular pathway is one of the four dopaminergic pathways in the brain. The other three are: the mesolimbic, mesocortical and nigrostriatal pathways.

Each dopaminergic pathway is actually a brain pathway of neurons that transmit dopamine from one area of the brain to another . Dopamine has been and is one of the neurotransmitters most closely related to schizophrenia, as we will see later on.

Tube-infundibular track: characteristics

At the neuroanatomical level, the tuberous-infundibular pathway projects from the hypothalamus to the anterior pituitary gland. More specifically, it runs from a very specific nucleus of the mid-basal hypothalamus, called the arcuato nucleus (also called the tubal region), to the medial eminence or infundibular region. On the other hand, the term “infundibular” refers to the infundibulum, a structure from which the pituitary gland develops .

The tubero-infundibular pathway influences the secretion of some hormones by the pituitary gland, such as prolactin (this is a hormone that, among other functions, secretes milk during maternity), and which is secreted more specifically in the adeno-pituitary gland.

Thus, the dopaminergic neurons in this pathway are usually active and inhibit the release of prolactin ; that is, the presence of dopamine in the tuber-infundibular pathway inhibits prolactin synthesis, and also favours somatotrophin synthesis.

Blockage of the pathway: hyperprolactinemia

Classic antipsychotics that act by reducing dopamine in patients with psychosis or schizophrenia , end up generating the side effect of an abnormal increase in prolactin levels. This occurs because they block the D2 (dopamine) receptors, reducing its level and by extension, inhibiting the functioning of the tubero-infundibular pathway.

Increased levels of prolactin in the blood through the tuber-infundibular pathway, called hyperprolactinemia, involve a number of symptoms:

On the one hand, there is an increase in the secretion of milk in postpartum stages (during breastfeeding), as well as the presence of galactorrhea (spontaneous mammary secretions outside the period of breastfeeding), gynecomastia (increase in mammary glands) and mastodynia (breast pain).

In addition, hyperprolactinemia can also produce irregularities in the menstrual cycle of women, visual problems, headache , amenorrhea and other possible problems, such as sexual dysfunction (for example, it significantly affects fertility and reduces sexual desire).

Hyperprolactinemia occurs in both men and women.

The other dopaminergic pathways

In addition to the tuber-infundibular pathway, there are three other dopaminergic pathways that are involved in different hormonal and organismal processes ; moreover, and as we have mentioned, some of them have been significantly related to schizophrenia.

Destination and origin

The mesocortical pathway runs from the ventral tegmental area (VTA) of the trunk to various areas of the cortex, especially the limbic and dorsolateral prefrontal cortex. The mesolimbic pathway runs from the dopaminergic cell bodies in the ventral tegmental area (VTA) to the limbic areas of the brain, such as the nucleus accumbens. Finally, the nigrostriatal pathway goes from the substantia nigra to the basal or striatal ganglia (extrapyramidal system).

Relationship to Schizophrenia and Parkinson’s

The hyperfunctioning of the mesolimbic dopamine pathway has been related to the positive symptomatology of schizophrenia (remember that positive symptoms include hallucinations, delusions, disorganized behaviour, etc.).

In contrast, hypofunction of the mesocortical dopamine pathway has been associated with the negative symptoms of schizophrenia (abulia, anhedonia, tendency to isolate, affective flattening, etc.).

On the other hand, the nigrostriatal pathway has been associated with other pathologies such as Parkinson’s (its blockage implies a reduction in dopamine levels, and this is related to Parkinson’s, producing symptoms such as akathisia and dystonia). In contrast, an increase in dopamine in the nigrostriatal pathway is associated with hyperkinetic disorders such as chorea or tics. If the DA2 receptor in this pathway is chronically blocked, tardive dyskinesia appears.

Bibliographic references:

  • Carlson, N.R. (2005). Behavioral physiology. Madrid: Pearson Educación.
  • Netter, F. (1989). Nervous system. Anatomy and physiology. Barcelona: Salvat.
  • Rosenweig, M., Breedlove, S., Watson, N. (2005). Psychobiology: an introduction to behavioural, cognitive and clinical neuroscience. Barcelona: Ariel.