Progressive postnatal dilation of brain ventricles in spontaneously hypertensive rats

Cross-sectional areas of the forebrain ventricles were measured from coronal sections in spontaneously hypertensive rats (SHRs) 4, 8, 12, 16, 21 and 56 weeks of age and in age-matched Wistar-Kyoto (WKY) and Sprague-Dawley (SD) normotensive rats. Progressive ventricular dilation and associated attrition of brain tissue was observed in SHRs of both sexes after 4 weeks of age, and was present in animals obtained from two different suppliers. In some SHRs, ventricle size was increased to 270% of control. Hence, it seems likely that some systemic and behavioral signs which are concomitant with hypertension in the SHR may be attributable to hydrocephalus and its neuropathological correlates.     

Transport of 5-aminolevulinic acid between blood and brain

Little is known about the movement of 5-aminolevulinic acid (delta-aminolevulinic acid; ALA) between blood and brain. This is despite the fact that increases in brain ALA may be involved in generating the neuropsychiatric symptoms in porphyrias and that systemic administration of ALA is currently being used to delineate the borders of malignant gliomas. The current study examines the mechanisms involved in the movement of [(14)C]ALA across the blood-brain and blood-CSF barriers in the rat. In the adult rat, the influx rate constant (K(i)) for [(14)C]ALA movement into brain was low ( approximately 0.2 microl/g per min), was unaffected by increasing plasma concentrations of non-radioactive ALA or probenecid (an organic anion transport inhibitor) and, therefore, appears to be a diffusional process. The K(i) for [(14)C]ALA was 3-fold less than that for [(14)C]mannitol, a molecule of similar size. This difference appears to result from a lower lipid solubility rather than saturable [(14)C]ALA transport from brain to blood. The K(i) for [(14)C]ALA for uptake into the neonatal brain was 7-fold higher than in the adult. However, again, this was unaffected by increasing plasma ALA concentrations suggesting a diffusional process. In contrast, at the blood-CSF barrier, there was evidence of carrier-mediated [(14)C]ALA transport from blood to choroid plexus and blood to CSF. Both processes were inhibited by administration of non-radioactive ALA and probenecid. However, experiments in choroid plexus epithelial cell primary cultures indicated that transport in these cells was polarized with [(14)C]ALA uptake from the apical (CSF) side being about 7-fold greater than uptake from the basolateral (blood) side. In total, these results suggest that the brain is normally fairly well protected from changes in plasma ALA concentration by the very low blood-brain barrier permeability of this compound and by a saturable efflux mechanism present at the choroid plexus.     

Zn localization in rat brain after intracerebroventricular injection of Zn-histidine

Previous studies have shown that ⁶⁵Zn uptake in the brain expressed relative to plasma ⁶⁵Zn level is enhanced by histidine infusion into the blood vessel. To study the effect of histidine on zinc uptake in the brain parenchyma via the CSF, the brains of rats injected intracerebroventricularly with ⁶⁵Zn-His were subjected to autoradiography. Six days after injection, the radioactivity from ⁶⁵Zn-His was distributed in the major part of the brain parenchyma higher than that from ⁶⁵ZnCl₂, and relatively concentrated in the hippocampal formation, globus pallidus and hypothalamus. The radioactivity of the aqueduct was also higher in the ⁶⁵Zn-His group, indicating that CSF clearance of the ⁶⁵Zn-His group may be lower than that of the ⁶⁵ZnCl₂ group. These results suggest an enhancement by histidine on zinc uptake in the brain parenchyma via the CSF.     

Structural alterations of tight junctions are associated with loss of polarity in stroke-prone spontaneously hypertensive rat blood–brain barrier endothelial cells

The mechanisms leading to stroke in stroke-prone spontaneously hypertensive rats (SHRSP) are not well understood. We tested the hypothesis that the endothelial tight junctions of the blood–brain barrier are altered in SHRSP prior to stroke. We investigated tight junctions in 13-week-old SHRSP, spontaneously hypertensive stroke-resistant rats (SHR) and age-matched Wistar–Kyoto rats (WKY) by electron microscopy and immunocytochemistry. Ultrathin sections showed no difference in junction structure of cerebral capillaries from SHRSP, SHR and WKY, respectively. However, using freeze-fracturing, we observed that the blood–brain barrier specific distribution of tight junction particles between P- and E-face in WKY (58.7±3.6%, P-face; 41.2±5.59%, E-face) and SHR (53.2±19.3%, P-face; 55.6±13.25%, E-face) was changed to an 89.4±9.9% predominant E-face association in cerebral capillaries from SHRSP. However, the expression of the tight junction molecules ZO-1, occludin, claudin-1 and claudin-5 was not changed in capillaries of SHRSP. Permeability of brain capillaries from SHRSP was not different compared to SHR and WKY using lanthanum nitrate as a tracer. In contrast, analysis of endothelial cell polarity by distribution of the glucose-1 transporter (Glut-1) revealed that its abluminal:luminal ratio was reduced from 4:1 in SHR and WKY to 1:1 in endothelial cells of cerebral capillaries of SHRSP. In summary, we demonstrate that early changes exist in cerebral capillaries from a genetic model of hypertension-associated stroke. We suggest that a disturbed fence function of the tight junctions in SHRSP blood–brain barrier endothelial cells may lead to subtle changes in polarity. These changes may contribute to the pathogenesis of stroke.     

Cd transport in rat brain

The brain distribution of ¹⁰⁹CdCl₂ following administration into either the tail vein, the lateral ventricle or the olfactory bulb was studied to clarify permeability of the brain barrier system to cadmium (Cd) and Cd movement in the cerebrospinal fluid (CSF) and the brain extracellular fluid. One hour after intravenous (i.v.) injection, ¹⁰⁹Cd was largely concentrated in the choroid plexus, and ¹⁰⁹Cd concentration in the major part of the brain parenchyma, except for the circumventricular organs such as the pineal gland and the regions around them, was low. Six days after i.v. injection, ¹⁰⁹Cd concentration in the choroid plexus was still high, and ¹⁰⁹Cd was also detected highly in the pineal gland and small part around the median eminence. ¹⁰⁹Cd concentration in the major part of the brain parenchyma was decreased in parallel with that in the blood. In the case of injection of ¹⁰⁹CdCl₂ into the lateral ventricle, a large portion of ¹⁰⁹Cd was detected in the ventricular system 6 days after injection, and ¹⁰⁹Cd concentration in the major part of the brain parenchyma was less than the detection limit. These results suggest that Cd cannot easily get into the brain and is blocked not only by the blood—brain and the blood—CSF barriers, but also by the ependymal and pial surfaces. In the case of injection of ¹⁰⁹CdCl₂ into the olfactory bulb, a large portion of ¹⁰⁹Cd was detected in the injected area 24 h after injection, and, the next 24 h later, ¹⁰⁹Cd distribution in the brain was not changed appreciably. These results suggest that Cd cannot easily move in the brain extracelular space, and is taken up into the brain parenchyma.     

Leptin transport at the blood–cerebrospinal fluid barrier using the perfused sheep choroid plexus model

Leptin is secreted by adipose tissue and thought to regulate appetite at the central level. Several studies have explored the central nervous system (CNS) entry of this peptide across the blood–brain and blood–cerebrospinal fluid (CSF) barriers in parallel, but this is the first to explore the transport kinetics of leptin across the choroid plexus (blood–CSF barrier) in isolation from the blood–brain barrier (BBB). This is important as the presence of both barriers can lead to ambiguous results from transport studies. The model used was the isolated Ringer perfused sheep choroid plexus. The steady-state extraction of [¹²⁵I]leptin (7.5 pmol l⁻¹) at the blood face of the choroid plexus was 21.1±5.7%, which was greater than extraction of the extracellular marker, giving a net cellular uptake for [¹²⁵I]leptin (14.0±3.7%). In addition, trichloroacetic acid precipitable [¹²⁵I] was detected in newly formed CSF, indicating intact protein transfer across the blood–CSF barrier. Human plasma concentrations of leptin are reported to be 0.5 nM. Experiments using 0.5 nM leptin in the Ringer produced a concentration of leptin in the CSF of 12 pM (similar to that measured in humans). [¹²⁵I]Leptin uptake at the blood–plexus interface using the single-circulation paired tracer dilution technique (uptake in <60 s) indicated the presence of a saturable transport system, which followed Michaelis–Menten-type kinetics (K_m=16.3±1.8 nM, V_max=41.2±1.4 pmol min⁻¹ g⁻¹), and a non-saturable component (K_d=0.065±0.002 ml min⁻¹ g⁻¹). In addition, secretion of new CSF by the choroid plexuses was significantly decreased with leptin present. This study indicates that leptin transport at the blood–CSF barrier is via saturable and non-saturable mechanisms and that the choroid plexus is involved in the regulation of leptin availability to the brain.     

Zinc distribution in the brain of Nagase analbuminemic rat and enlargement of the ventricular system

⁶⁵ZnCl₂ was intravenously injected into Nagase analbuminemic rats (NAR), which have a genetical mutation affecting albumin mRNA processing and lack serum albumin, to test the hypothesis that albumin is necessary for zinc (Zn) transport into the brain. One hour after injection, ⁶⁵Zn was largely concentrated in the choroid plexus of NAR as well as normal parental Sprague–Dawley rats (SDR). Six days after injection, in both groups, the ⁶⁵Zn concentration in the choroid plexus decreased, with increases in other brain regions. The finding that there was no significant difference in brain distribution of ⁶⁵Zn between NAR and SDR suggests that Zn transport into the brain and its distribution through the blood–cerebrospinal fluid barrier as well as the blood–brain barrier are not dependent on serum albumin. A most interesting observation was that the cerebral ventricles were considerably enlarged in NAR.     

The activity of catecholamine synthesis in the hypothalamus of female normotensive Wistar Kyoto and spontaneously hypertensive rats

The activity of catecholamine synthesis in the hypothalamus, as determined by the rate of 3,4-dihydroxyphenylalanine (DOPA) accumulation after the administration of a DOPA decarboxylase inhibitor, was compared among Wistar, spontaneously hypertensive (SH), and genetically matched normotensive Wistar Kyoto (WKY) rats. DOPA accumulation in the median eminence, an index of the activity of tuberoinfundibular dopaminergic neurons, was greater in SH rats than Wistar and WKY rats while DOPA accumulation in the medial preoptic area was smaller in Wistar rats than SH and WKY rats. No strain difference was found in DOPA accumulation in the corpus striatum, which represents the activity of nigrostriatal dopaminergic neurons. These results suggest that there are differences in catecholamine synthesis in the hypothalamus not only between SH and WKY rats but also between WKY and Wistar rats.     

Role of choroid plexus epithelium in the removal of valproic acid from the central nervous system

Previous experiments suggest the primary route of valproic acid (VPA) removal from the rabbit central nervous system (CNS) is by probenecid-sensitive transporters at the blood-brain barrier but not at the choroid plexus. The purpose of this study was to determine if other transport mechanisms at the choroid plexus played a significant role in the removal of VPA from the CNS. In six rabbits, silicone oil was perfused into both cerebral ventricles and out through the cisterna magna to physically block exchange of VPA between cerebrospinal fluid (CSF) and blood and between brain and CSF. In six control rabbits, perfusion was performed with mock CSF. Both groups received a loading dose followed by continuous intravenous infusion of VPA for 2.10 min. Ventriculocisternal perfusion with silicone oil had no significant effect on the steady-state brain concentrations or brain-to-plasma concentration ratios of VPA, further confirming that efflux of VPA at the choroid plexus is negligible.     

Kinetics and distribution of [Fe–I]transferrin injected into the ventricular system of the rat

We examined the kinetics and distribution of [⁵⁹Fe–¹²⁵I] rat Tf and unlabelled human Tf injected into a lateral cerebral ventricle (i.c.v. injection) in the rat. [⁵⁶Fe–¹³¹I]Tf injected intravenously served as a control of blood–brain barrier (BBB) integrity. In CSF of adult rats, ⁵⁹Fe and [¹²⁵I]Tf decreased to only 2.5% of the dose injected after 4 h. In brain parenchyma, [¹²⁵I]Tf had disappeared after 24 h, whereas approximately 18% of i.c.v.-injected ⁵⁹Fe was retained even after 72 h. The elimination pattern of [¹²⁵I]Tf from the CSF corresponded to that of [¹³¹I]albumin injected i.c.v., suggesting a nonselective washout of CSF proteins. [¹³¹I]Tf was hardly detectable in the brain, reflecting an unimpaired BBB during the experiments. Morphologically, ⁵⁹Fe and i.c.v. injected human Tf were confined to the ventricular surface and meningeal areas, whereas grey matter regions at distances more than 2–3 mm from the ventricles and the subarachnoid space were unlabelled. However, accumulation of ⁵⁹Fe was observed in the anterior thalamic and the medial habenular nuclei, and in brain regions with synaptic communications to these areas. In the newborn rats aged 7 days (P7) injected i.c.v. with [⁵⁹Fe–¹²⁵I]Tf and examined after 24 h, the amounts of [¹²⁵I]Tf in CSF were approximately 3.5 times higher than in adult rats collected after the same time interval, whereas the amounts of ⁵⁹Fe in CSF were at the same level in P7 and adult rats. In the brain tissue of the i.c.v. injected P7 rats, both [¹²⁵I]Tf and ⁵⁹Fe were retained to a significantly higher degree compared to that seen in adult brains. The rapid washout and lack of capability for i.c.v. injected [¹²⁵I]Tf to penetrate deeply into the brain parenchyma of the adult brain question the importance of Tf of the CSF, and choroid plexus-derived Tf, for Fe neutralization and delivery of Fe–Tf to TfR-containing neurons and other cells in the CNS. However, it may serve these functions in young animals due to a lower rate of turnover of CSF.     

Biotin and biocytin uptake into cultured primary calf brain microvessel endothelial cells of the blood–brain barrier

The uptake of biotin and the closely related biocytin was characterized in primary cultures of calf brain microvessel endothelial (CBME) cells. Biotin uptake was found to be Na⁺-gradient dependent and independent of changes in the membrane potential. Concentration dependence revealed a single saturation mechanism with a K_m of 47 μM and a V_max of 101 pmol/min/mg. Inhibition studies demonstrated dependence on metabolic energy and the necessity for a free carboxyl group for transport activity. The anticonvulsants primidone and carbamazepine had no inhibitory effect. Biotin uptake into CBME cells is a secondary active, electroneutral, saturable and specific process. Biocytin which accumulates in biotinidase deficiency, a human congenital disorder, did not inhibit biotin uptake and was not transported into these cells. The presence of human serum with normal biotinidase activity significantly reduced biotin uptake by about 50%. Further, added biocytin was hydrolyzed to biotin, which accumulated intracellularly but to a lesser extent than added free biotin. Biotin uptake after addition of plasma of biotinidase-deficient patients was not different from that in the presence of normal serum. These results indicate that the absence of biotinidase activity in serum does not reduce blood–brain barrier transport of biotin.     

Expression of the hexose transporters GLUT1 and GLUT2 during the early development of the human brain

We used immunohistochemistry with anti-glucose transporter antibodies to document the presence of facilitative hexose transporters in the fetal human brain. GLUT1 is expressed in all regions of the fetal brain from ages 10 to 21 weeks. GLUT1 was present in the endothelial cells of the brain capillaries, the epithelial cells of the choroid plexus and neurons. High expression of GLUT2 was observed in the granular layer of the cerebellum in brains 21 weeks old, but GLUT2 immunoreactivity was absent at earlier stages. GLUT3 and GLUT4 immunoreactivities were absent at all stages studied. GLUT5 immunoreactivity was evident only in the cerebellar region of 21-week old fetal brains. We conclude that GLUT1 plays a fundamental role in early human brain development. The data also suggest that the cerebellum of the developing brain has the capacity to transport fructose, a substrate that has not been previously identified as a source of metabolic energy in the adult human brain.     

Carrier-mediated processes in blood–brain barrier penetration and neural uptake of paraquat

Due to the structural similarity to N-methyl-4-phenyl pyridinium (MPP⁺), paraquat might induce dopaminergic toxicity in the brain. However, its blood–brain barrier (BBB) penetration has not been well documented. We studied the manner of BBB penetration and neural cell uptake of paraquat using a brain microdialysis technique with HPLC/UV detection in rats. After subcutaneous administration, paraquat appeared dose-dependently in the dialysate. In contrast, MPP⁺ could not penetrate the BBB in either control or paraquat pre-treated rats. These data indicated that the penetration of paraquat into the brain would be mediated by a specific carrier process, not resulting from the destruction of BBB function by paraquat itself or a paraquat radical. To examine whether paraquat was carried across the BBB by a certain amino acid transporter, -valine or -lysine was pre-administered as a co-substrate. The pre-treatment of -valine, which is a high affinity substrate for the neutral amino acid transporter, markedly reduced the BBB penetration of paraquat. When paraquat was administered to the striatum through a microdialysis probe, a significant amount of paraquat was detected in the striatal cells after a sequential 180-min washout with Ringer’s solution. This uptake was significantly inhibited by a low Na⁺ condition, but not by treatment with putrescine, a potent uptake inhibitor of paraquat into lung tissue. These findings indicated that paraquat is possibly taken up into the brain by the neutral amino acid transport system, then transported into striatal, possibly neuronal, cells in a Na⁺-dependent manner.     

Altered gene expression in cerebral capillaries of stroke-prone spontaneously hypertensive rats

Stroke-prone spontaneously hypertensive rats (SHRSP) are a well-characterized, genetic model for stroke. We showed earlier that the structure and function of the tight junctions in SHRSP blood–brain barrier endothelial cells is disturbed prior to stroke. To investigate the molecular events leading to endothelial dysfunction in SHRSP cerebral capillaries, we carried out suppression subtractive hybridization (SSH) in combination with a cDNA filter screening step. We identified two cDNA fragments that were upregulated in SHRSP, compared to stroke-resistant spontaneously hypertensive rats (SHR), and found open reading frames of 133 and 138 amino acids, respectively. These peptides did not match any known proteins in public databases. A third upregulated SHRSP cDNA fragment was identified as the rat sulfonylurea receptor 2B (SUR2B). We also isolated and cloned the cDNA of the rat homologue for the mouse G-protein signaling 5 (RGS5) regulator. This regulator was downregulated in SHRSP. We used in situ hybridization to show that rat RGS5 is expressed in the brain capillary endothelium and in the choroid plexus. Our findings may lead to the identification of new stroke-related genes.     

P-Glycoprotein on astrocyte foot processes of unfixed isolated human brain capillaries

Sites of immunoreactive P-glycoprotein associated with human brain microvasculature were identified by labeling of unfixed isolated human brain capillaries, allowing visualization of the three-dimensional capillary structure by confocal microscopy. Capillaries isolated from human autopsy brain were dual-labeled with the MRK16 mouse monoclonal antibody (against human P-glycoprotein) and rabbit polyclonal antisera against the human brain microvascular glucose transporter (GLUT1), or glial fibrillary acidic protein (GFAP) on astrocyte foot processes. MRK16 and GLUT1 dual-labeling showed no signal overlap, identical to the staining pattern observed for dual-labeling with anti-GFAP and anti-GLUT1 antibodies: both GFAP and MRK16 labeling were discrete, discontinuous, and not co-localized with continuous GLUT1 labeling of capillary endothelium. In contrast, complete overlap of MRK16 and GFAP labeling demonstrated P-glycoprotein localization on astrocyte foot process remnants at the abluminal face of the brain microvasculature.     

Mosquito repellent (pyrethroid-based) induced dysfunction of blood–brain barrier permeability in developing brain

Pyrethroid-based mosquito repellents (MR) are commonly used to protect humans against mosquito vector. New born babies and children are often exposed to pyrethroids for long periods by the use of liquid vaporizers. Occupational and experimental studies indicate that pyrethroids can cause clinical, biochemical and neurological changes, and that exposure to pyrethroids during organogenesis and early developmental period is especially harmful. The neurotoxicity caused by MR has aroused concern among public regarding their use. In the present study, the effect of exposure of rat pups during early developmental stages to a pyrethroid-based MR (allethrin, 3.6% w/v, 8h per day through inhalation) on blood-brain barrier (BBB) permeability was investigated. Sodium fluororescein (SF) and Evan's blue (EB) were used as micromolecular and macromolecular tracers, respectively. Exposure during prenatal (gestation days 1-20), postnatal (PND1-30) and perinatal (gestation days 1-20 + PND1-30) periods showed significant increase in the brain uptake index (BUI) of SF by 54% (P < 0.01), 70% (P < 0.01), 79% (P < 0.01), respectively. This increase persisted (68%, P < 0.01) even 1 week after withdrawal of exposure (as assessed on PND37). EB did not exhibit significant change in BBB permeability in any of the group. The results suggest that MR inhalation during early prenatal/postnatal/perinatal life may have adverse effects on infants leading to central nervous system (CNS) abnormalities, if a mechanism operates in humans similar to that in rat pups.     

Cyclooxygenase 2 mRNA expression in rat brain after peripheral injection of lipopolysaccharide

Inducible cyclooxygenase 2 (COX 2) converts arachidonic acid to prostaglandins, which are thought to mediate various peripheral lipopolysaccharide (LPS)-induced central effects, including generation of fever and activation of the hypothalamic–pituitary–adrenal axis. To localize prostaglandin production in the brain following peripheral LPS administration, COX 2 mRNA expression was examined by in situ hybridization histochemistry in rats injected intraperitoneally (i.p.) or intravenously (i.v.) with various doses of LPS or saline. Constitutive expression of COX 2 mRNA was found in neurons of cortex, hippocampus, and amygdala, but not in cells of the blood vessels. COX 2 mRNA levels were not altered in saline-injected animals as compared to non-injected controls. In LPS-injected animals, no consistent changes of neuronal COX 2 mRNA expression were observed. COX 2 mRNA expression appeared ex novo at 0.5-h post-injection in cells closely associated with blood vessels, however, ex novo labeling of the number of labeled cells increased to a peak at 2 h and subsided gradually to basal levels by 24 h. Initially, labeling was observed in cells comprising major surface-lying blood vessels and meninges. Later, vascular and perivascular cells associated with smaller penetrating blood vessels were labeled. This pattern of COX 2 mRNA induction is independent of the route and dose of the LPS injection. The induced COX 2 mRNA producing cells are identified as endothelial and leptomeningeal cells. Changes in COX 2 mRNA expression were not observed in circumventricular organs. These results suggest that peripheral LPS induces a rapid increase in COX 2 production throughout the vasculatures of the brain, which could affect the neuronal activity of widespread brain regions by elevating the levels of prostaglandins.     

Molecular anatomy of intercellular junctions in brain endothelial and epithelial barriers: electron microscopist’s view

In this review, we have tried to summarize the current knowledge on the distribution of important molecular components of intercellular junctions—both tight junctions (TJs) and adherens junctions (AJs)—at the level of ultrastructure. For this purpose, immunogold procedure was applied to ultrathin sections of brain samples obtained from mice, rats, and humans and embedded in hydrophilic resin Lowicryl K4M. The results of our observations performed with transmission electron microscopy (EM) are discussed and compared with findings of other authors. Although the main structures responsible for the barrier and fence functions of the blood–brain barrier (BBB) and blood–CSF barrier are TJs present between endothelial cells (ECs) of brain capillaries and epithelial cells of the choroid plexus, their functional characteristics (e.g. tightness of the barrier evaluated by electrical resistance) differ significantly. Therefore, our main attention is focused on the presence and distribution of both intrinsic, i.e. integral membrane (transmembrane), molecules such as occludin, claudins, and junctional adhesion molecule (JAM) in TJs, and cadherins in AJs, as well as peripheral molecules of both types of junctions, e.g. zonula occludens (ZO) proteins and catenins. The latter group of molecules connects transmembrane proteins with the cell cytoskeleton. A close spatial association of the TJ proteins with those of AJs indicates that both junctional types are intermingled in the BBB type of endothelium. One of most important purposes of this work is to find out the junction-associated molecules that can serve as sensitive markers of normal or disturbed function of brain barriers. Understanding the structural–functional relations between molecular components of junctional complexes in physiological and experimental conditions of both barriers can provide important information about the etiology of various pathological conditions of the central nervous system and also help to elaborate new therapeutic approaches.     

Increased transfer ofCa into brain and cerebrospinal fluid from plasma during chronic hypocalcemia in rats

Recent studies have shown regulation of central nervous system [Ca] after chronic hypo- and hypercalcemia. To investigate the mechanism of this regulation , 3-week-old rats were fed diets for 8 weeks that contained low or normal levels of Ca. Plasma [Ca] was 40% less in rats fed the low Ca diet than in animals fed normal diet. Unidirectional transfer coefficients for Ca (K_Ca) and Cl (K_Cl) into cerebrospinal fluid (CSF) and brain were determined from the 10 min uptake of intravenously injected⁴⁵Ca and³⁶Cl in awake animals. K_Ca for CSF was 68% greater in low-Ca rats than in normal rats. Likewise, the values of K_Ca for brain regions with areas adjacent to the ventricles like the hippocampus and pons-medulla were 50% higher than in normal animals. On the other hand, K_Cas for parietal cortex, a brain region distant from the choroid plexus and not expected to be influenced by Ca entry into CSF, were similar between the groups. Comparison of the regional ratios of K_Ca/K_Cl revealed that a selective increase of Ca transport occurred into CSF and all brain regions except the parietal cortex in Ca-deficient rats. The results suggest that Ca homeostasis of CSF and brain [Ca] during chronic hypocalcemia is due to increased transfer of Ca from blood to brain, and that the regulation occurs via the CSF, possibly at the choroid plexus, but not via the cerebral capillaries.     

Intra-uterine growth restriction differentially regulates perinatal brain and skeletal muscle glucose transporters

Employing Western blot analysis, we investigated the effect of maternal uterine artery ligation causing uteroplacental insufficiency with asymmetrical intrauterine growth restriction (IUGR) upon fetal (22d) and postnatal (1d, 7d, 14d and 21d) brain (Glut 1 and Glut 3) and skeletal muscle (Glut 1 and Glut 4) glucose transporter protein concentrations. IUGR was associated with a 42% decline in fetal plasma glucose (p<0.05) and a 25% decrease in fetal body weights (p<0.05) with no change in brain weights when compared to the sham operated controls (SHAM). In addition, IUGR caused a 45% increase in fetal brain Glut 1 (55 kDa) with no change in Glut 3 (50 kDa) protein concentrations. This fetal brain Glut 1 change persisted, though marginal, through postnatal suckling stages of development (1d–21d), with no concomitant change in brain Glut 3 levels at day 1. In contrast, in the absence of a change in fetal skeletal muscle Glut 1 levels (48 kDa), a 70% increase was observed in the 1d IUGR with no concomitant change in either fetal or postnatal Glut 4 levels (45 kDa). The change in skeletal muscle Glut 1 levels normalized by d7 of age. We conclude that IUGR with hypoglycemia led to a compensatory increase in brain and skeletal muscle Glut 1 concentrations with a change in the brain preceding that of the skeletal muscle. Since Glut 1 is the isoform of proliferating cells, fetal brain weight changes were not as pronounced as the decline in somatic weight. The increase in Glut 1 may be protective against glucose deprivation in proliferating fetal brain cells and postnatal skeletal myocytes which exhibit ‘catch-up growth', thereby preserving the specialized function mediated by Glut 3 and Glut 4 towards maintaining the intracellular glucose milieu.