Endocrine functions of brain in adult and developing mammals

The main prerequisite for organism’s viability is the maintenance of the internal environment despite changes in the external environment, which is provided by the neuroendocrine control system. The key unit in this system is hypothalamus exerting endocrine effects on certain peripheral organs and anterior pituitary. Physiologically active substances of neuronal origin enter blood vessels in the neurohemal parts of hypothalamus where no blood-brain barrier exists. In other parts of the adult brain, the arrival of physiologically active substances is blocked by the blood-brain barrier. According to the generally accepted concept, the neuroendocrine system formation in ontogeny starts with the maturation of peripheral endocrine glands, which initially function autonomously and then are controlled by the anterior pituitary. The brain is engaged in neuroendocrine control after its maturation completes, which results in a closed control system typical of adult mammals. Since neurons start to secrete physiologically active substances soon after their formation and long before interneuronal connections are formed, these cells are thought to have an effect on brain development as inducers. Considering that there is no blood-brain barrier during this period, we proposed the hypothesis that the developing brain functions as a multipotent endocrine organ. This means that tens of physiologically active substances arrive from the brain to the systemic circulation and have an endocrine effect on the whole body development. Dopamine, serotonin, and gonadotropin-releasing hormone were selected as marker physiologically active substances of cerebral origin to test this hypothesis. In adult animals, they act as neurotransmitters or neuromodulators transmitting information from neuron to neuron as well as neurohormones arriving from the hypothalamus with portal blood to the anterior pituitary. Perinatal rats—before the blood-brain barrier is formed—proved to have equally high concentration of dopamine, serotonin, and gonadotropin-releasing hormone in the systemic circulation as in the adult portal system. After the brain-blood barrier is formed, the blood concentration of dopamine and gonadotropin-releasing hormone drops to zero, which indirectly confirms their cerebral origin. Moreover, the decrease in the blood concentration of dopamine, serotonin, and gonadotropin-releasing hormone before the brain-blood barrier formation after the microsurgical disruption of neurons that synthesize them or inhibition of dopamine and serotonin synthesis in the brain directly confirm their cerebral origin. Before the blood-brain barrier formation, dopamine, serotonin, gonadotropin-releasing hormone, and likely many other physiologically active substances of cerebral origin can have endocrine effects on peripheral target organs—anterior pituitary, gonads, kidney, heart, blood vessels, and the proper brain. Although the period of brain functioning as an endocrine organ is not long, it is crucial for the body development since physiologically active substances exert irreversible effects on the targets as morphogenetic factors during this period. Thus, the developing brain from the neuron formation to the establishment of the blood-brain barrier functions as a multipotent endocrine organ participating in endocrine control of the whole body development.     

Developing Brain as an Endocrine Organ: A Paradoxical Reality

The maintaining of homeostasis in the organism in response to a variable environment is provided by the highly hierarchic neuroendocrine-immune system. The crucial component of this system is the hypothalamus providing the endocrine regulation of key peripheral organs, and the adenohypophysis. In this case, neuron-derived signaling molecules (SM) are delivered to the blood vessels in hypothalamic “neurohaemal organs” lacking the blood–brain barrier (BBB), the posterior lobe of the pituitary and the median eminence. The release of SM to the blood vessels in most other brain regions is prohibited by BBB. According to the conventional concept, the development of the neuroendocrine system in ontogenesis begins with the “maturation” of peripheral endocrine glands which first are self-governed and then operate under the adenohypophysial control. Meantime, the brain maturation is under the control of SM secreted by endocrine glands of the developing organism and coming from the placenta and maternal organism. The hypothalamus is involved in the neuroendocrine regulation only after its full maturation that is followed by the conversion of the opened-looped neuroendocrine system to the closed-looped system as in adulthood. Neurons of the developing brain begin to secrete SM shortly after their origin and long before the establishment of specific interneuronal relations providing initially autocrine and paracrine morphogenetic influence on differentiating target neurons. Taking into account that the brain lacks BBB over this ontogenetic period, we hypothesized that it operates as the multipotent endocrine gland secreting SM to the general circulation and thereby providing the endocrine regulation of peripheral organs and the brain. The term “multipotent” means that the spectrum of the brain-derived circulating SM and their occupancy at the periphery in the developing organism should greatly exceed those in adulthood. In order to test this hypothesis, gonadotropin-releasing hormone (GnRH), dopamine (DA), and serotonin (5-hydroxytryptamine, 5-HT) were chosen as the markers of the presumptive endocrine function of the brain in ontogenesis. According to our data, the concentrations of GnRH, DA, and 5-HT in the rat general circulation during the perinatal period, i.e. before the establishment of BBB, was as high as those in the portal circulation in adulthood. The concentrations of circulating GnRH and DA dropped to almost undetectable level after the development of BBB suggesting their brain origin. This suggestion has been proven by showing an essential decrease of GnRH, DA, and 5-HT concentrations in general circulation of perinatal rats after microsurgical elimination of synthesizing neurons or the inhibition of specific syntheses in the brain before the establishment of BBB. GnRH, DA, and 5-HT apparently as dozens of other brain-derived SM appear to be capable of providing the endocrine influence on their peripheral targets like the adenohypophysis, gonads, kidney, heart, blood vessels, and the brain (endocrine autoregulation). Although the ontogenetic period of the brain operation as the multipotent endocrine gland is relatively short, the brain-derived SM are thought to be capable of providing long-lasting morphogenetic effects on peripheral targets and the brain. Thus, the developing brain operates as the multipotent endocrine gland from the onset of neurogenesis to the establishment of BBB providing the endocrine regulation of the developing organism.     

Features of blood-brain barrier formation affected by the modulation of HIF activity in astroglial and neuronal cells in vitro

Barriergenesis is the process of maturation of the primary vascular network of the brain responsible for the establishment of the blood-brain barrier. It represents a combination of factors that, on the one hand, contribute to the process of migration and tubulogenesis of endothelial cells (angiogenesis), on the other hand, contribute to the formation of new connections between endothelial cells and other elements of the neurovascular unit. Astrocytes play a key role in barriergenesis, however, mechanisms of their action are still poorly examined. We have studied the effects of HIF-1 modulators acting on the cells of non-endothelial origin (neurons and astrocytes) on the development of the blood-brain barrier in vitro. Application of FM19G11 regulating expression of HIF-1 activity and GSI-1 suppressing gamma-secretase and/or proteasomal activity resulted in the elevated expression of thrombospondins and matrix metalloproteinases in the developing blood-brain barrier. However, it caused the opposite effect on VEGF expression thus promoting barrier maturation in vitro.     

Developing Brain as a Giant Multipotent Endocrine Gland

The brain of adult mammals is composed of neuronal ensembles, which are intergrated in the course of synaptic transmission by chemical signals (CSs). Among them, there are classical neurotransmitters, neuropeptides, etc. In addition, neurosecretory neurons secrete the same CSs to the blood vessels in the brain areas lacking the blood-brain barrier (BBB), though their spectrum is greatly limited. According to the conventional conception, the brain lacks the neuroendocrine function over the ontogenetic period lasting from the genesis of neuronal units to the development of neuron-to-neuron synaptic connections (synaptogenesis) and BBB. Nevertheless, some recent data contradict this concept making reasonable its that CSs and receptors are expressed in the neurons just after their origin and long before the establishment of BBB. During this period, CSs are considered diffusive inductors of the brain development, which provide the paracrine regulation of the neuronal differentiation. Although this regulation is beyond doubt, some data do not agree with the concept. For example, the receptors of CSs are transiently expressed in many areas of the developing brain, though there are no neuronal sources of the respective CSs in close vicinity. This might be explained by the CS transfer from the synthesizing neurons toward the target neurons via the circulation, i.e., due to the neuroendocrine autoregulation. According to our hypothesis, the neurons serve as endocrine cells, and the brain can be considered a giant multipotent endocrine gland providing the neuroendocrine regulation of the development of the brain itself and peripheral target organs over the period preceding synaptogenesis and the establishment of BBB. The term “giant multipotent” means that the spectrum of the brain-derived circulating CSs and their occupancy at the periphery in the developing organism should greatly exceed those in adulthood. Gonadotropin-releasing hormone (GnRH)-producing and dopaminergic neurons, the most representative populations of peptidergic and monoaminergic neurons were used for testing our hypothesis. According to the age dynamics of GnRH and dopamine (DA) in general circulation in rats, the concentrations of these agents were sufficiently great for the regulation of the target cells before the establishment of BBB, but they dropped to an undetectable level after the BBB appearance. Furthermore, the microsurgical lesion of most GnRH and DA-ergic neurons in the developing brain resulted in a dramatic drop of both CSs in the blood, confirming that the brain is the principal but not the only source of circulating CSs. Potential targets for the brain-derived circulating CSs, including GnRH and DA, should be neurons and peripheral cells. For example, the gonads begin to express the GnRH receptors simultaneously with the onset of GnRH synthesis in the brain in fetal rats. The DA-sensitive cells in the developing organism are, e.g., represented by neurons of the suprachiasmatic nucleus in the brain and epithelial cells of the kidney. Both cell types transiently express D₂ receptors before the establishment of BBB and the related fall of circulating DA. Thus, differentiating neurons and the developing brain play roles of secretory cells and of the endocrine gland, respectively, before the development of interneuronal synaptic connections and maturation of BBB. Neirofiziologiya/Neurophysiology, Vol. 37, No. 3, pp. 257–270, May–June, 2005.     

Neurothelin: molecular characteristics and developmental regulation in the chick CNS.

Neurothelin has recently been identified as a cell surface protein specific for chick endothelial cells forming the blood-brain barrier. Neurons of the adult brain are essentially devoid of neurothelin. In contrast, neurons of the chick retina, which lack blood vessels and accessory astrocytes, express neurothelin. Here we demonstrate that during chick brain development initially neurothelin is expressed probably in all neuroblasts. With proceeding cytodifferentiation, such as vascularization and gliogenesis, brain neurons become neurothelin negative. Coincidentally the endothelial cells forming the blood-brain barrier start to synthesize neurothelin. In contrast to brain neurons, in retina neurons, neurothelin expression increases by one order of magnitude during the course of histogenesis. Coculturing of chick retinal cells with purified rat astrocytes in vitro results in reduction of neural neurothelin expression as quantified by ELISA. Conversely, disruption of the glia-neuron interactions by culturing brain neurons as individualized cells in vitro leads to a reexpression of neurothelin. This is consistent with the hypothesis that astrocytes inhibit neurothelin expression in neurons. Biochemical characterization classifies neurothelin as an integral membrane protein. Temperature-induced-detergent phase separation, phospholipase C digestion and sodium carbonate treatment were employed to distinguish between integral membrane proteins, lipid-anchored proteins and peripheral membrane proteins. Two-dimensional gel electrophoresis reveals an isoelectric point of about 6.4 for neurothelin. Polysaccharide analysis by glycosidase digestion and lectin binding indicates that neurothelin is highly glycosylated. The relative molecular mass of glycosylated neurothelin is 41 x 10(3), whereas the peptide backbone is only 25 x 10(3). The very strict spatiotemporal regulation of neurothelin expression in the central nervous system suggests that neurothelin fulfils possibly a crucial function such as transport of low relative molecular mass components that are essential for neuronal metabolism. The proposed biological activity of neurothelin might be specifically affected by some of its distinct biochemical features.     

Astrocyte-endothelial interactions at the blood-brain barrier

The blood-brain barrier, which is formed by the endothelial cells that line cerebral microvessels, has an important role in maintaining a precisely regulated microenvironment for reliable neuronal signalling. At present, there is great interest in the association of brain microvessels, astrocytes and neurons to form functional 'neurovascular units', and recent studies have highlighted the importance of brain endothelial cells in this modular organization. Here, we explore specific interactions between the brain endothelium, astrocytes and neurons that may regulate blood-brain barrier function. An understanding of how these interactions are disturbed in pathological conditions could lead to the development of new protective and restorative therapies.     

Specific AHNAK expression in brain endothelial cells with barrier properties

The blood-brain barrier (BBB) is essential for maintaining brain homeostasis and low permeability. Because disruption of the BBB may contribute to many brain disorders, they are of considerable interests in the identification of the molecular mechanisms of BBB development and integrity. We here report that the giant protein AHNAK is expressed at the plasma membrane of endothelial cells (ECs) forming specific blood-tissue barriers, but is absent from the endothelium of capillaries characterized by extensive molecular exchanges between blood and extracellular fluid. In the brain, AHNAK is widely distributed in ECs with BBB properties, where it co-localizes with the tight junction protein ZO-1. AHNAK is absent from the permeable brain ECs of the choroid plexus and is down-regulated in permeable angiogenic ECs of brain tumors. In the choroid plexus, AHNAK accumulates at the tight junctions of the choroid epithelial cells that form the blood-cerebrospinal fluid (CSF) barrier. In EC cultures, the regulation of AHNAK expression and its localization corresponds to general criteria of a protein involved in barrier organization. AHNAK is up-regulated by angiopoietin-1 (Ang-1), a morphogenic factor that regulates brain EC permeability. In bovine cerebral ECs co-cultured with glial cells, AHNAK relocates from the cytosol to the plasma membrane when endothelial cells acquire BBB properties. Our results identify AHNAK as a protein marker of endothelial cells with barrier properties.     

Neuro-steroids: 3β-hydroxy-Δ5-derivatives in the rodent brain

Pregnenolone, dehydroepiandrosterone and their sulfate esters have been characterized in the rat brain. Their formation or accumulation depend on in situ mechanisms unrelated to the peripheral endocrine glands. Although their functions are still poorly understood, they may affect the brain by metabolism to sex steroid hormones and they may be functionally related to sexual behavior, possibly through direct modulations of the firing rates of neurons.     

Permeability properties of a three-cell type in vitro model of blood-brain barrier

We previously found that RBE4.B brain capillary endothelial cells (BCECs) form a layer with blood-brain barrier (BBB) properties if co-cultured with neurons for at least one week. As astrocytes are known to modulate BBB functions, we further set a culture system that included RBE4.B BCECs, neurons and astrocytes. In order to test formation of BBB, we measured the amount of 3H-sucrose able to cross the BCEC layer in this three-cell type model of BBB. Herein we report that both neurons and astrocytes induce a decrease in the permeability of the BCEC layer to sucrose. These effects are synergic as if BCECs are cultured with both neurons and astrocytes for 5 days, permeability to sucrose decreases even more. By Western analysis, we also found that, in addition to the canonical 60 kDa occludin, anti-occludin antibodies recognize a smaller protein of 48 kDa which accumulates during rat brain development. Interestingly this latter protein is present at higher amounts in endothelial cells cultured in the presence of both astrocytes and neurons, that is in those conditions in which sucrose permeation studies indicate formation of BBB.     

Adrenomedullin in the cerebral circulation.

The central nervous system requires an effective autoregulation of cerebral circulation in order to meet the critical and unusual demands of the brain. In addition, cerebral microvessels has a unique feature, the formation of the blood-brain barrier, which contributes to the stability of the brain parenchymal microenvironment. Many factors are known to be involved in the regulation of cerebral circulation and blood-brain barrier functions. In the last few years a new potential candidate, adrenomedullin, a hypotensive peptide was added to this list. Adrenomedullin has a potent vasodilator effect on the cerebral vasculature, and it may be implicated in the pathologic mechanism of cerebrovascular diseases. In this review, we describe current knowledge about the origin and possible role of adrenomedullin in the regulation of cerebral circulation and blood-brain barrier functions.     

Saturable Retention of Vasopressin by Hippocampus Vessels In Vivo, Associated with Inhibition of Blood-Brain Transfer of Large Neutral Amino Acids

Vasopressin receptors have been reported in the endothelium of brain capillaries. The function of these receptors is not known. To test the prediction that vasopressin receptors in brain capillary endothelium affect amino acid transport across the blood-brain barrier and to assess the role of vasopressin transport across the cerebral vascular endothelium, we measured (a) the endothelial permeability to the large neutral amino acid leucine in the absence and presence of arginine vasopressin (AVP) and (b) the permeability of the blood-brain barrier to AVP relative to manitol. In brain regions protected by the blood-brain barrier, after circulation for 20 s, coinjection of leucine and AVP intravenously led to a decrease of leucine transport unrelated to changes of blood flow. The decrease was most pronounced in hippocampus (42%) and least pronounced in olfactory bulb and colliculi (17 and 19%, respectively). In the latter regions, the endothelial permeability to AVP did not significantly exceed that of mannitol. In hippocampus and in regions with no blood-brain barrier (pituitary and pineal glands), AVP retention in excess of mannitol retention was blocked by unlabeled AVP. The findings do not contradict the hypothesis of a role for AVP in the regulation of large neutral amino acid transfer into brain tissue.     

Brain is a source of blood serotonin in rats during perinatal development

The aim of this study was to test our hypothesis that the brain functions as an endocrine organ before the blood-brain barrier is formed. A model of drug-inhibited serotonin synthesis in the brain using a single stereotactic administration of p-chlorophenylalanine, an inhibitor of serotonin synthesis, was developed. The inhibitor dose inducing the maximum effect in the brain and no effect on serotonin synthesis in the periphery was experimentally selected. The concentration of serotonin and its metabolites (5-hydroxytryptophan and 5-hydroxy-indoleacetic acid) was studied by high performance liquid chromatography in the brain, duodenum, and blood (separately in plasma and platelets). The optimal p-chlorophenylalanine dose (200 mg/kg) was shown to induce a sharp decrease in the brain level of serotonin (70%), a moderate decrease in plasma (16%) and platelets (26%), and an insignificant decrease in the duodenum (12%). At the same time, this dose did not decrease the 5-hydroxytryptophan level in the intestine. This suggests that the decrease in the blood level of serotonin was due to the inhibition of its synthesis in the brain, whereas the decrease in the duodenum level of serotonin was due to the compensatory release to blood while its synthetic rate remained unaltered. Thus, the developing brain before the blood-brain barrier formation was shown to secrete serotonin into blood.     

Production and effects of platelet-activating factor in the rat brain

The synthesis of platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) in rat brain was evaluated. Extracted PAF was characterized using standard HPLC and TLC techniques, and by correlation of its bioactivity with the acetylation state of the 2-position of the molecule. PAF was quantified by bioassay, its ability to cause [3H]serotonin release from washed rabbit platelets. The low basal level of PAF (0.25 +/- 0.15 pmol/g wet wt., mean +/- S.E.) in the brain of the intact rat was greatly increased by intraperitoneal injection of the chemoconvulsant drugs picrotoxin or bicuculline, to levels of 10.68 +/- 2.18 and 4.97 +/- 0.75 pmol/g wet wt., respectively. Electroconvulsion also increased brain PAF, to 1.76 +/- 0.30 pmol/g wet wt. Equivalent experiments using bicuculline in the isolated perfused rat brain yielded qualitatively similar results, indicating that the production of PAF in the brain is independent of systemic metabolism. When a 32P-labeled nerve-ending (synaptosome) preparation from rat brain was challenged with synthetic PAF (denoted AGEPC) at 0.1 nM concentration, responses were observed consistent with accelerated turnover of polyphosphoinositides. AGEPC also caused an increase in the Na+-Ca2+ exchange of synaptic membrane vesicles. Furthermore, AGEPC infused into the vasculature of the isolated perfused rat brain caused changes consistent with an increase in blood-brain barrier permeability, although AGEPC did not itself significantly penetrate the blood-brain barrier. It is concluded from these studies that PAF is synthesized within the rat brain in response to convulsant stimuli and that one of its effects is to accelerate synaptic polyphosphoinositide turnover. In addition, circulating PAF can influence blood-brain barrier permeability without itself penetrating the blood-brain barrier.     

The brain is one of the most important sources of dopamine in general circulation during perinatal ontogenesis in rats

This study was aimed to test our hypothesis that dopamine synthesized in the neurons of the brain is delivered to the general circulation in rats during prenatal and early postnatal periods, i.e. before the establishment of the blood-brain barrier. Using the high performance liquid chromatography, it was demonstrated that the dopamine concentration and content in the peripheral blood in fetuses and neonatal rats (i.e. before the establishment of the blood-brain barrier) greatly exceeded those in adult rats. Moreover, the establishment of the blood-brain barrier was accompanied by the significant increase of the dopamine concentration in the brain. A drop of the dopamine concentration in fetal plasma after the microsurgical lesion of the forebrain and mesencephalon (encephalectomy) are considered as direct evidence in favour of our hypothesis.     

Evaluation of blood-brain barrier thiamine efflux using the in situ rat brain perfusion method

Thiamine is an essential, positively charged (under physiologic conditions), water-soluble vitamin requiring transport into brain. Brain thiamine deficiency has been linked to neurodegenerative disease by subsequent impairment of thiamine-dependent enzymes used in brain glucose/energy metabolism. In this report, we evaluate brain uptake and efflux of [3H]thiamine using the in situ rat brain perfusion technique. To confirm brain distribution was not related to blood-brain barrier endothelial cell uptake, we compared parenchymal and cell distribution of [3H]thiamine using capillary depletion. Our work supports previous literature findings suggesting blood-brain barrier thiamine uptake is via a carrier-mediated transport mechanism, yet extends the literature by redefining the kinetics with more sensitive methodology. Significantly, [3H]thiamine brain accumulation was influenced by a considerable efflux rate. Evaluation of the efflux mechanism demonstrated increased stimulation by the presence of increased vascular thiamine. The influx transport mechanism and efflux rate were each comparable throughout brain regions despite documented differences in glucose and thiamine metabolism. The observation that [3H]thiamine blood-brain barrier influx and efflux is regionally homogenous may have significant relevance to neurodegenerative disease linked to thiamine deficiency.     

Zinc homeostasis and functions of zinc in the brain

The brain barrier system, i.e., the blood-brain and blood-cerebrospinal fluid barriers, is important for zinc homeostasis in the brain. Zinc is supplied to the brain via both barriers. A large portion of zinc serves as zinc metalloproteins in neurons and glial cells. Approximately 10% of the total zinc in the brain, probably ionic zinc, exists in the synaptic vesicles, and may serve as an endogenous neuromodulator in synaptic neurotransmission. The turnover of zinc in the brain is much slower than in peripheral tissues such as the liver. However, dietary zinc deprivation affects zinc homeostasis in the brain. Vesicular zinc-enriched regions, e.g., the hippocampus, are responsive to dietary zinc deprivation, which causes brain dysfunctions such as learning impairment and olfactory dysfunction. Olfactory recognition is reversibly disturbed by the chelation of zinc released from amygdalar neuron terminals. On the other hand, the susceptibility to epileptic seizures, which may decrease vesicular zinc, is also enhanced by zinc deficiency. Therefore, zinc homeostasis in the brain is closely related to neuronal activity. Even in adult animals and probably adult humans, adequate zinc supply is important for brain functions and prevention of neurological diseases.     

Syncytial perforations of human embryo membranes

An electron microscopy study of the anlage of cerebral cortex of human embryo has been carried with the aim of determining the presence of syncytial interneuronal connections in embryogenesis. It has been determined that, in part of the neurons, the glial embryo is absent and their external cell membranes are directly attached to each other by forming elongated or dotted tight junctions. Sometimes these junctions are perforated and, on their basis, the true syncytial interneuronal connections are formed. Natural structural properties of these connections are the following: formation of the base of tight membrane contacts, obligatory rounding of perforation edges, and the presence of residual particles in the form of spherical vesicles in the lumen of perforations. Results obtained allowed us to conclude that, in the anlage of cerebral cortex of embryos obtained during surgical abortion of pregnancy, apart from the formation of synaptic contacts, or until their formation, there is the possibility of syncytial interneuronal connections appearing. This should be considered during the transplantation of the developing brain.     

Neurosteroid dehydroepiandrosterone and brain function

In the past 30 years it has become clear that the brain tissue and the nervous system are steroidproducing structures. Steroids synthesized in the brain structures are called neurosteroids. This paper summarizes the results of studies on the biosynthesis and metabolism of dehydroepiandrosterone (DHEA), including its metabolism in the adipose tissue, where it serves as a substrate for intracellular formation of biologically active metabolites estradiol and testosterone. The role of sulfatase and sulfotransferase in mutual conversions of DHEA and DHEA sulfate (DHEAS) is described. Species-related differences in the synthesis of DHEA in the adrenal cortex are considered. The adrenal glands of primates (humans and monkeys, including the lower ones) produce large quantities of free and sulfated DHEA. Their synthesis proceeds by the Δ5 pathway: cholesterol → pregnenolone → 17-hydroxypregnenolone → DHEA. The adrenal glands of other species, including rats and mice, do not synthesize DHEA. Out point of view on the possible mechanisms of penetration of endogenous or exogenous DHEA sulfate into the brain structures is described: desulfurization of molecules to form free DHEA penetrating the blood-brain barrier and the possibility of penetration of the sulfate form into the hypothalamic structures, which are not protected by the blood-brain barrier. The results of studies of the use of DHEA as a neurosteroid in clinical practice and the analysis of its role in the development of Alzheimer’s disease, cognitive disorders, and other CNS disorders are also presented. The possible mechanisms underlying the effects of DHEA on the brain are considered. The main neurobiological effects of both forms, DHEA and DHEAS, on the brain structures, which were identified experimentally in various animal models, include the neuroprotective effects, neurogenesis and survival of neurons, apoptosis, and the effect on the synthesis and secretion of catecholamines. Neurosteroids also carry out antioxidative, antiinflammatory, and antiglucocorticoid activity.     

Evaluation of the Role of P-Glycoprotein in Ivermectin Uptake by Primary Cultures of Bovine Brain Microvessel Endothelial Cells

The P-glycoprotein efflux system located on the apical membrane of brain capillary endothelial cells functions as part of the blood-brain barrier. In this study, primary cultures of bovine brain microvessel endothelial cells (BMECs) were investigated for the presence of a P-glycoprotein system and its contribution in regulating ivermectin distribution across the blood-brain barrier. Results of rhodamine 123 uptake studies with cyclosporin A and verapamil as substrates indicated that a functional efflux system was present on BMECs. Immunoblot analysis with the C219 monoclonal antibody to the product of the multidrug resistant member 1(MDR1) gene also confirmed the expression of MDR1 in the BMECs. Unbound ivermectin was shown to significantly increase the uptake of rhodamine 123 in BMECs, however, the drug only modestly enhanced the transcellular passage of rhodamine. The results of these studies affirmed that unbound ivermectin is an inhibitor of the MDR1 efflux system in BMECs.