Tuberoinfundibular

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. 

Control (inhibition) of prolactin release Tuberoinfundibular tract from A12 in the arcuate nucleus of the median eminence to pituitary Humans Hypoprolactaemia Humans Hyperprolactaemia Galactorrhoea Amenorrhoea D2 ... 

Li C.S., Kaba H., Saito H. and Seto K. (1992b). Estrogen infusions into the amygdala potentiate excitatory transmission from the accessory olfactory bulb to tuberoinfundibular arcuate neurons in the mouse. Neurosci Lett 143, 48-50. 

Dopamine blocking (mesolimbic) Dopamine blocking (mesocortical) Dopamine blocking (tuberoinfundibular)... 

The intermediate length systems include the tuberoinfundibular system, which projects from the arcuate and periventricular nuclei into the intermediate lobe of the pituitary and the median eminence. This system is responsible for the regulation of such hormones as prolactin. The inter hypothalamic neurons send projections to the dorsal and posterior hypothalamus, the lateral septal nuclei and the medullary periventricular group, which are linked to the dorsal motor nucleus of the vagus such projections may play a role in the effects of dopamine on the autonomic nervous system. 

Appears to act selectively on cortical and mesolimbic DA neuronal systems (in preference to the nigrostriatal and tuberoinfundibular areas). 

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. 

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). 

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

In addition to being synthesized in the peripheral nervous system, dopamine is synthesized in the corpus striatum and in the mesocortical, mesolimbic, and tuberoinfundibular systems. Norepinephrine is synthesized and stored primarily in sympathetic noradrenergic nerve terminals, as well as in the brain and the adrenal medulla. Epinephrine is synthesized and stored primarily in the adrenal medulla and, to a certain extent, in the hypothalamic nuclei. 

Dopamine agonists decrease pituitary prolactin secretion through a dopamine-mimetic action on the pituitary at two central nervous system loci (1) they decrease dopamine turnover in the tuberoinfundibular neurons of the arcuate nucleus, generating increased hypothalamic dopamine and (2) they act directly on pituitary dopamine receptors to inhibit prolactin release. 

Labrie F, Ferland L, Veilleux R, Euvrard C, Boissier J (1979) Influence of estrogens on tuberoinfundibular and striatal dopaminergic systems in the rat. Acta Psychiatr Belg 79 623-637... 

The tuberoinfundibular system, which originates in the arcuate nucleus of the hypothalamus and projects to the median eminence. 

The results of such studies suggest that the major classes of neuroleptics in therapeutic use owe their activity to their ability to block D2 and/or D, receptors, particularly in the mesocortical and mesolimbic regions of the brain. Side effects, such as parkinsonism and increased prolactin release, would seem to be associated with the antagonistic effects of these drugs on D2 and/or Dj receptors in the nigrostriatal and tuberoinfundibular systems. 

Maternal prolactin via the milk is required for normal development of the tuberoinfundibular neuronal system of the hypothalamus during the neonatal period in rats (Shyr et al., 1986). Blocking the suckling-induced rise in maternal prolactin levels causes abnormal tuberoinfundibular function, with decreased inhibition by dopamine of prolactin secretion in the offspring later in life. The resulting chronically elevated prolactin levels cause prostatitis in the male offspring (Tangbanluekal Robinette, 1993). 

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