Tuberoinfundibular pathway

Serotonin 2A antagonism may reverse dopamine 2 antagonism in the tuberoinfundibular pathway. There is an antagonistic and reciprocal relationship between serotonin and dopamine in the control of prolactin secretion from the pituitary lactoroph cells. That is, dopamine inhibits prolactin release by stimulating D2 receptors (Fig. 11—30), whereas serotonin promotes prolactin release by stimulating 5HT2A receptors (Fig. 11—31). 

Fig. 19.3 Sagittal brain section illustrating dopaminergic pathways. I. Mesolimbic pathway (overactive in psychotic illness according to the dopamine hypothesis of schizophrenia).VTA= ventrotegmental area. 2. Nigrostriatal pathway (involved in motor control, underactive in Parkinson s Disease and associated with extrapyramidal motor symptoms). 3. Tuberoinfundibular pathway (inhibits prolactin release from the hypothalamus).

A further totally separate DA pathway arises from A12 in the arcuate nucleus and forms the tuberoinfundibular tract in the median eminence to the pituitary gland for controlling prolactin release. This is partly achieved by DA being released into capillaries of the hypothalamic-hypophyseal portal system and then inhibiting the prolactin releasing cells (lactotrophs) of the anterior pituitary. 

Four well-defined dopamine pathways in the brain are shown in Figure 10—7. They include the mesolimbic dopamine pathway, the mesocortical dopamine pathway, the nigrostriatal dopamine pathway, and the tuberoinfundibular dopamine pathway. 

The dopamine neurons that project from the hypothalamus to the anterior pituitary are known as the tuberoinfundibular dopamine pathway (Fig. 10—13). Normally, these neurons are active and inhibit prolactin release. In the postpartum state, however, their activity is decreased, and therefore prolactin levels can rise during breastfeeding, so that lactation will occur. If the functioning of tuberoinfundibular dopamine neurons is disrupted by lesions or drugs, prolactin levels can also rise. Elevated prolactin levels are associated with galactorrhea (breast secretions), amenorrhea,... 

FIGURE 10—13. The tuberoinfundibular dopamine pathway from hypothalamus to anterior pituitary regulates prolactin secretion into the circulation. Dopamine inhibits prolactin secretion. 

FIGURE 11—6. The tuberoinfundibular dopamine pathway controls prolactin secretion. When dopamine 2 receptors in this pathway are blocked by dopamine 2 antagonists, prolactin levels rise, sometimes so much so that women may begin lactating inappropriately, a condition known as galactorrhea. 

The tuberoinfundibular dopamine pathway mediates the secretion of prolactin. True or False. 

Tuberoinfundibular DA pathway—neurones in the median eminence that project to the pituitary. 

There are three major central DA pathways the nigrostriatal, which is affiliated with motor effects produced by antipsychotic drugs the tuberoinfundibular tract, which is asso-... 

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