Tuberoinfundibular system

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. 

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. 

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. 

Marcos P, Corio M, Covenas R, Tramu G (1996b) Neurotensin and tyrosine hydroxylase in the tuberoinfundibular system of the guinea pig hypothalamus with special emphasis to lactation status. Peptides 17 138-146. 

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. 

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

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... 

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). 

Dawson R, Valdes JJ, Annau Z (1985) Tuberohypophyseal and tuberoinfundibular dopamine systems exhibit differential sensitivity to neonatal monosodium glutamate treatment. Pharmacology 37 17-23. 

Shieh K-R, Pan J-T (1997) Nicotinic control of tuberoinfundibular dopaminergic neuron activity and prolactin secretion diurnal rhythm and involvement of endogenous opioidergic system. Brain Res 756 266-272. 

Shieh K-R, Pan J-T (1998) Ontogeny of the diurnal rhythm of tuberoinfundibular dopaminergic neuronal activity in peripubertal female rats possible involvement of cholinergic and opioidergic systems. Neuroendocrinology 65 395 402. 

Ethyl benzene is an inducer of the cytochrome P450 and cytochrome c reductase enzyme systems. Ethyl benzene acts as a mitochondrial-uncoupling agent. It is believed that ethyl benzene metabolites are capable of interfering with dopamine catabolism in the brain. The tuberoinfundibular dopaminergic system may be a target for these metabolites. 

Serum prolactin (PRL) has been shown to be a possible biomarker of manganese action of dopamine neurotransmission (Smargiassi and Mutti 1999). Manganese acts on the tuberoinfundibular dopaminergic system which exerts tonic inhibition of PRL secretion. Serum PRL levels observed in workers occupationally exposed to manganese were shown to be consistent with mechanistic studies as they were distinctly higher than unexposed workers. It is still unclear whether or not serum PRL levels indicate recent... 

Hypothalamus and Endocrine Systems Endocrine changes occur because of effects of antipsychotic drugs on the hypothalamus or pituitary, including their antidopaminergic actions. Most older antipsychotics and risperidone increase prolactin secretion, probably due to a blockade of the pituitary actions of the tuberoinfundibular dopaminergic neurons. These neurons project from the arcuate nucleus of the hypothalamus to the median eminence, where they deliver DA to the anterior pituitary via the hypophyseoportal blood vessels. Dj receptors on lactotropes in the anterior pituitary mediate the tonic prolactin-inhibiting action of DA (see Chapter 55). 

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