Brain Areas Without a Blood Brain Barrier.
All areas of the brain do not have a blood-brain barrier. The structures located at strategic positions in the midline of the ventricular system and lack the BBB are collectively referred to as circumventricular organs (CVOs). In these non-barrier regions, the tight junctions between endothelial cells are discontinuous thus allowing entry of molecules. Many of these areas participate in hormonal control.
Areas of brain without a blood-brain barrier:
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Pituitary gland
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biogenic amines, including the catecholamines (norepinephrine, dopamine and epinephrine), serotonin, acetylcholine and gamma-aminobutyric acid (GABA).
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Median eminence
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The median eminence is a very unusual neural structure: although it contains nerve terminals and glial cells, it is virtually devoid of synapses and it has structural properties that distinguish it from other brain regions. We provide information about the molecular, anatomical and physiological features of the median eminence, and their age-related changes. The hypothalamic system controlling reproduction through the release of the gonadotropin-releasing hormone (GnRH) peptide from nerve terminals in the median eminence. The hypothalamic-pituitary-gonadal (HPG) axis of females includes GnRH cells and terminals in hypothalamus; the pituitary gonadotropes which produce the gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH); and the ovary, which produces steroid (particularly estradiol and progesterone) and protein hormones. All of the HPG levels must function normally for reproduction to occur, and during aging, each of these levels undergoes changes that may conribute to reproductive dysfunction and ultimately failure.
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Area postrema
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The area postrema, one of the ,circumventricular organs detects toxins in the blood and acts as a vomit-inducing center. The area postrema is a critical homeostatic integration center for humoral and neural signals. Recent studies have implicated its function as a chemoreceptor trigger site for vomiting in response to emetic drugs. It is a densely vascularized structure that lacks tight junctions between endothelial cells, thereby allowing it to detect various toxins in the blood as well as in the cerebrospinal fluid.
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The area postrema’s position outside of the blood–brain barrier makes this particular region of the medulla a key player in the autonomic control of various physiological systems, including the cardiovascular system and the systems controlling feeding and metabolism. A recent study has indicated the existence of prolactin-binding sites specific to the area postrema. The result of the current study has implicated the area postrema as a prolactin target area at which vascular prolactin has the ability to openly associate with neuronal components. Prolactin is a peptide hormone known in lower animals to play a significant role in osmoregulation, originally functioning to influence electrolyte balance, and may now be believed to stimulate reproductive behaviors such as the water-drive before ovoposition in amphibians and lactation in mammals.[5] Another recent study found that the administration of angiotensin II causes a dose-dependent increase in the arterial blood pressure without producing considerable changes in the heart rate. Evidence from this study reveals that the change in the arterial blood pressure depends on the integrity of the area postrema and that this site partially contributes to the action of angiotensin.
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Preoptic recess
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Molecules like dopamine stimulate cells in this portion of the preoptic area, and when stimulated, these neurons regulate male sexual behavior. Animal studies have shown that stimulation results in copulation behavior and the release of compounds like gonadotropin-releasing hormone. Higher dopamine stimulation is seen in response to testosterone levels, as well as by sensory stimulation, such as the presence of a female.
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Paraphysis
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Pineal gland
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The pineal gland, also known as the pineal body, conarium or epiphysis cerebri, is a small endocrine gland in the vertebrate brain. It produces the serotonin derivative melatonin, a hormone that affects the modulation of sleep patterns in the circadian rhythms and seasonal functions
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Unlike much of the rest of the mammalian brain, the pineal gland is not isolated from the body by the blood–brain barrier system; it has profuse blood flow, second only to the kidney.
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The choroid plexus plays a wide range of roles in brain development, maturation, aging process, endocrine regulation, and pathogenesis of certain neurodegenerative diseases [1]. The choroid plexuses consist of a single layer of epithelial cells enclosing a vascular core that together form the blood-cerebrospinal fluid barrier [2]. The choroidal capillary is a single layer of endothelial cells interrupted by “pores” which exhibit a diaphragm between the lumen and the interstitial space. Study shows that choroid plexus endothelial cells express high Glut1 glucose transporter [3]. The high glucose transport densities in choroids plexus endothelial cells is consistent with the suggestion that choroids epithelial and endothelial cells provide a metabolic work capability for maintaining ionic gradients and secretory functions across the blood-cerebrospinal fluid barriers.
http://www.jci.org/a...canned-page/145
Transport of hormones across BBB
http://www.ncbi.nlm....8?dopt=Abstract
Small amounts of glutamate cross bbb.
http://www.ncbi.nlm....1?dopt=Abstract
Small amounts of glutamate cross bbb.
http://www.ncbi.nlm....9?dopt=Abstract
Glutamate across bbb
http://www.ncbi.nlm....7?dopt=Abstract
Glutamate across bbb
http://ajpcell.physi...pe2=tf_ipsecsha
Glutamate across bbb
http://www.ncbi.nlm....les/PMC3001209/
Melatonin passes through bbb.
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