Effects of acute hyperosmolality on blood-brain barrier function in ovine fetuses and lambs

We examined the effects of hyperosmolality on blood-brain barrier (BBB) permeability during development to test the vulnerability of the immature barrier to stress. The BBB response to hyperosmolality was quantified using the blood-to-brain transfer constant (Ki) with alpha-aminoisobutyric acid in fetuses at 60% and 90% gestation, premature, newborn, and older lambs. Ki plotted against osmolality increased as a function of increases in osmolality in all groups and brain regions. The relationship was described (P < 0.05) by a segmented regression model. At lower osmolalities, changes in Ki were minimal, but after a break point (threshold) was reached, the increase (P < 0.05) was linear. We examined the responses of Ki to hyperosmolality within each brain region by comparing the thresholds and slopes of the second regression segment. Lower thresholds and higher slopes imply greater vulnerability to hyperosmolality in the younger groups. Thresholds increased (P < 0.05) with development in the thalamus, superior colliculus, pons, and spinal cord, and slopes of the second regression segment decreased (P < 0.05) in the cerebellum, hippocampus, inferior colliculus, medulla, and spinal cord. BBB resistance to hyperosmolality increased (P < 0.05) with development in most brain regions. The pattern of the Ki plotted against osmolality was (P < 0.05) heterogenous among brain regions in fetuses and premature and newborn lambs, but not in older lambs. We conclude that 1) BBB permeability increased as a function of changes in osmolality, 2) the barrier becomes more resistant to hyperosmolality during development, and 3) the permeability response to hyperosmolality is heterogenous among brain regions in fetuses and premature and newborn lambs.     

Effects of duration of positive-pressure ventilation on blood-brain barrier function in premature lambs.

We have been studying the ontogeny of the blood-brain barrier function in ovine fetuses and lambs. During these studies, we have found that the duration of ventilation also influences blood-brain barrier permeability in premature lambs. Chronically instrumented hysterotomy-delivered surfactant-treated premature lambs were studied at 90% or 137 days of gestation (n = 9). Blood-brain barrier function was quantified with the blood-to-brain transfer constant K(i) to alpha-aminoisobutyric acid. Linear regression analysis was used to compare the K(i) values in the brain regions, as the dependent variable, to the duration of ventilation, as the independent variable. There were direct correlations (P < 0.05) between the K(i) values and the duration of ventilation [306 min (mean), 162-474 min (range)] in the cerebral cortex, cerebellum, medulla, caudate nucleus, hippocampus, superior colliculus, inferior colliculus, thalamus, pons, cervical spinal cord, and choroid plexus, but not in the pituitary gland. Ventilatory pressures and rates were established before the onset of the permeability studies. Calculated mean airway pressures [14 cmH(2)O (mean), 7-20 cmH(2)O (range)] from similarly studied premature lambs did not correlate with the duration of positive-pressure ventilation. We conclude that increases in the duration of positive-pressure ventilation predispose premature lambs to increases in regional blood-brain barrier permeability. These alterations in barrier function occur over relatively short time intervals (minutes to hours). In our study, these changes in permeability are most likely not attributable to changes in mean airway pressure.     

Studies on blood-brain barrier permeability after microwave-radiation

Summary Since the reported alterations of permeability of the blood-brain barrier by microwave radiation have implications for safety considerations in man, studies were conducted to replicate some of the initial investigations. No transfer of parenterally-administered fluorescein across the blood-brain barrier of rats after 30 min of 1.2-GHz radiation at power densities from 2–75 mW/cm² was noted. Increased fluorescein uptake was seen only when the rats were made hyperthermic in a warm-air environment. Similarly, no increase of brain uptake of¹⁴C-mannitol using the Oldendorf dual isotope technique was seen as a result of exposure to pulsed 1.3-GHz radiation at peak power densities up to 20 mW/cm², or in the continuous wave mode from 0.1–50 mW/cm². An attempt to alter the permeability of the blood-brain barrier for serotonin with microwave radiation was unsuccessful. From these studies it would appear that the brain must be made hyperthermic for changes in permeability of the barrier induced by microwave radiation to occur.The research reported in this paper was conducted by personnel of the Radiation Sciences Division, USAF School of Aerospace Medicine, Brooks AFB, Tex. 78235. The animals involved in the study were procured, maintained, and used in accordance with the Animal Welfare Act of 1970 and the Guide for the Care und Use of Laboratory Animals prepared by the Institute of Laboratory Animal Resources, National Research Council     

Effects of lipopolysaccharide on blood-brain barrier permeability during pentylenetetrazole-induced epileptic seizures in rats

We investigated the effects of lipopolysachharide (LPS) on functional and structural properties of the blood-brain barrier (BBB) during pentylenetetrazole (PTZ)-induced epileptic seizures in rats. Arterial blood pressure was significantly elevated during epileptic seizures irrespective of LPS pretreatment. Plasma levels of interleukin (IL)-1, interleukin (IL)-6, nitric oxide (NO) and malondialdehyde (MDA) increased while catalase concentrations decreased in animals treated with LPS, PTZ and LPS plus PTZ. The significantly increased BBB permeability to Evans blue (EB) dye in the cerebral cortex, diencephalon and cerebellum regions of rats by PTZ-induced seizures was markedly reduced upon LPS pretreatment. Immunoreactivity for tight junction proteins, zonula occludens-1 and occludin, did not change in brain vessels of animals treated with PTZ and LPS plus PTZ. Glial fibrillary acidic protein immunoreactivity was increased in LPS, but not in PTZ and LPS plus PTZ. These results indicate that LPS pretreatment reduces the passage of EB dye bound to albumin into the brain, at least partly, by increasing plasma NO and IL-6 levels during PTZ-induced epileptic seizures. We suggest that LPS may provide protective effects on the BBB integrity during epileptic seizures through transcellular pathway, since the paracellular route remained unaffected by LPS and LPS plus PTZ.     

Effects of radiofrequency radiation exposure on blood-brain barrier permeability in male and female rats

During the last several decades, numerous studies have been performed aiming at the question of whether or not exposure to radiofrequency radiation (RFR) influences the permeability of the blood-brain barrier (BBB). The objective of this study was to investigate the effect of RFR on the permeability of BBB in male and female Wistar albino rats. Right brain, left brain, cerebellum, and total brain were analyzed separately in the study. Rats were exposed to 0.9 and 1.8 GHz continuous-wave (CW) RFR for 20 min (at SARs of 4.26 mW/kg and 1.46 mW/kg, respectively) while under anesthesia. Control rats were sham-exposed. Disruption of BBB integrity was detected spectrophotometrically using the Evans-blue dye, which has been used as a BBB tracer and is known to be bound to serum albumin. Right brain, left brain, cerebellum, and total brain were evaluated for BBB permeability. In female rats, no albumin extravasation was found in in the brain after RFR exposure. A significant increase in albumin was found in the brains of the RF-exposed male rats when compared to sham-exposed male brains. These results suggest that exposure to 0.9 and 1.8 GHz CW RFR at levels below the international limits can affect the vascular permeability in the brain of male rats. The possible risk of RFR exposure in humans is a major concern for the society. Thus, this topic should be investigated more thoroughly in the future.     

Effects of radiofrequency radiation exposure on blood-brain barrier permeability in male and female rats

During the last several decades, numerous studies have been performed aiming at the question of whether or not exposure to radiofrequency radiation (RFR) influences the permeability of the blood-brain barrier (BBB). The objective of this study was to investigate the effect of RFR on the permeability of BBB in male and female Wistar albino rats. Right brain, left brain, cerebellum, and total brain were analyzed separately in the study. Rats were exposed to 0.9 and 1.8?GHz continuous-wave (CW) RFR for 20?min (at SARs of 4.26?mW/kg and 1.46?mW/kg, respectively) while under anesthesia. Control rats were sham-exposed. Disruption of BBB integrity was detected spectrophotometrically using the Evans-blue dye, which has been used as a BBB tracer and is known to be bound to serum albumin. Right brain, left brain, cerebellum, and total brain were evaluated for BBB permeability. In female rats, no albumin extravasation was found in in the brain after RFR exposure. A significant increase in albumin was found in the brains of the RF-exposed male rats when compared to sham-exposed male brains. These results suggest that exposure to 0.9 and 1.8?GHz CW RFR at levels below the international limits can affect the vascular permeability in the brain of male rats. The possible risk of RFR exposure in humans is a major concern for the society. Thus, this topic should be investigated more thoroughly in the future.     

Effects of hypoxia-reoxygenation on rat blood-brain barrier permeability and tight junctional protein expression

Cerebral microvessel endothelial cells that form the blood-brain barrier (BBB) have tight junctions (TJs) that are critical for maintaining brain homeostasis. The effects of initial reoxygenation after a hypoxic insult (H/R) on functional and molecular properties of the BBB and TJs remain unclear. In situ brain perfusion and Western blot analyses were performed to assess in vivo BBB integrity on reoxygenation after a hypoxic insult of 6% O2 for 1 h. Model conditions [blood pressure, blood gas chemistries, cerebral blood flow (CBF), and brain ATP concentration] were also assessed to ensure consistent levels and criteria for insult. In situ brain perfusion revealed that initial reoxygenation (10 min) significantly increased the uptake of [14C]sucrose into brain parenchyma. Capillary depletion and CBF analyses indicated the perturbations were due to increased paracellular permeability rather than vascular volume changes. Hypoxia with reoxygenation (10 min) produced an increase in BBB permeability with associated alterations in tight junctional protein expression. These results suggest that H/R leads to reorganization of TJs and increased paracellular diffusion at the BBB, which is not a result of increased CBF, vascular volume change, or endothelial uptake of marker. Additionally, the tight junctional protein occludin had a shift in bands that correlated with functional changes (i.e., increased permeability) without significant change in expression of claudin-3, zonula occludens-1, or actin. H/R-induced changes in the BBB may result in edema and/or associated pathological outcomes.     

Streptozotocin-induced diabetes progressively increases blood-brain barrier permeability in specific brain regions in rats

This study investigated the effects of streptozotocin-induced diabetes on the functional integrity of the blood-brain barrier in the rat at 7, 28, 56, and 90 days, using vascular space markers ranging in size from 342 to 65,000 Da. We also examined the effect of insulin treatment of diabetes on the formation and progression of cerebral microvascular damage and determined whether observed functional changes occurred globally throughout the brain or within specific brain regions. Results demonstrate that streptozotocin-induced diabetes produced a progressive increase in blood-brain barrier permeability to small molecules from 28 to 90 days and these changes in blood-brain barrier permeability were region specific, with the midbrain most susceptible to diabetes-induced microvascular damage. In addition, results showed that insulin treatment of diabetes attenuated blood-brain barrier disruption, especially during the first few weeks; however, as diabetes progressed, it was evident that microvascular damage occurred even when hyperglycemia was controlled. Overall, results of this study suggest that diabetes-induced perturbations to cerebral microvessels may disrupt homeostasis and contribute to long-term cognitive and functional deficits of the central nervous system.     

Chronic nicotine exposure alters blood-brain barrier permeability and diminishes brain uptake of methyllycaconitine

Methyllycaconitine (MLA) is reported to be a selective antagonist for the nicotinic acetylcholine receptor alpha7 subtype and has been found in animal behavioral studies to reduce nicotine self-administration and attenuate nicotine withdrawal symptoms. While MLA crosses the blood-brain barrier (BBB), no studies have assessed brain uptake in animals subjected to chronic nicotine exposure. Given that chronic nicotine administration has been reported to alter BBB parameters that may affect the kinetic BBB passage of MLA, we evaluated MLA brain uptake in naive and S-(-)nicotine-exposed rats (4.5 mg/kg/day for 28 days; osmotic minipumps) using in situ rat brain perfusions. Our results demonstrate that in situ(3)H-MLA brain uptake rates in naive animals approximate to intravenous kinetic data (K(in), 3.24 +/- 0.71 x 10(-4) mL/s/g). However, 28-day nicotine exposure diminished (3)H-MLA brain uptake by approximately 60% (K(in), 1.29 +/- 0.4 x 10(-4) mL/s/g). This reduction was not related to nicotine-induced (3)H-MLA brain efflux or BBB transport alterations. Similar experiments also demonstrated that the passive permeation of (14)C-thiourea was diminished approximately 24% after chronic nicotine exposure. Therefore, it appears that chronic nicotine exposure diminishes the blood-brain passive diffusion of compounds with very low extraction rates (i.e. permeability-limited compounds). These findings imply that the pharmacokinetics of neuropharmaceutical agents that are permeability limited may need to be re-evaluated in individuals exposed to nicotine.     

Comparison of blood-brain barrier permeability in mice and rats using in situ brain perfusion technique

Here we present a method for measuring the permeability coefficient-surface area product (PS) values at the blood-brain barrier in mice, using the in situ brain perfusion technique originally developed for rats by Takasato et al. (Am J Physiol Heart Circ Physiol 247: H484-H493, 1984). Retrograde infusion into the right external carotid artery increased the carotid perfusion pressure in proportion to the perfusion rate. Intravascular volume and cerebral perfusion fluid flow at a perfusion rate of 1.0 ml/min in mice were similar to those in rats. In addition, the contribution of systemic blood to total flow in the hemisphere was small (only 3. 2%). These findings indicated that this perfusion rate is suitable for mice. The PS values of more than 20 different compounds were determined in mice by using the in situ brain perfusion technique, and comparisons were made with data from rats. There was a close relationship (1:1) between the PS values in mice and rats, indicating that brain capillary permeabilities are similar in mice and rats.     

Effect of atrial natriuretic factor on blood-brain barrier permeability

Recent studies have demonstrated receptors for atrial natriuretic factor on endothelium of intracerebral vessels. The physiological role of these receptors is not known. The present study was undertaken to determine whether atrial natriuretic factor has an effect on blood-brain barrier permeability to protein and ions using horseradish peroxidase and lanthanum as markers of permeability alterations. This study does not demonstrate a significant effect of atrial natriuretic factor on blood-brain barrier permeability mechanisms in steady states.     

Effect of growth retardation on the permeability of the blood-brain barrier in the newborn rat exposed to lead

Postnatal administration of lead to young rats via maternal milk increases the permeability of the blood-brain barrier to trypan blue. However, since this regimen delays postnatal maturation, the question arises whether growth retardation per se could explain the altered permeability to the dye. The present investigation was undertaken to examine this possibility. A first group of newborn rats were fed by dams having free access to normal food; a second group was fed by dams receiving 3% lead as the acetate salt in their food; a third group was fed by dams whose normal diet was restricted to the amount taken daily by dams of the second group. Signs of encephalopathy as shown by urinary incompetence and hind-limb paralysis were observed only in your pups exposed to lead; similarly, only the latter showed increased brain permeability to trypan blue. These results suggest that the altered permeability of the blood-brain barrier in young rats is the direct consequence of lead toxicity and not of growth retardation secondary to a nutritional effect of lead.     

Effects of losartan on the blood-brain barrier permeability in long-term nitric oxide blockade-induced hypertensive rats

Hypertension is closely associated with vascular endothelial dysfunction. The aim of this study was to investigate the effects of Angiotensin II (ANG II) receptor antagonist losartan on the blood-brain barrier (BBB) permeability in L-NAME-induced hypertension and/or in ANG II-induced acute hypertension in normotensive and hypertensive rats. Systolic blood pressure was measured by tail cuff method before, during and following L-NAME treatment (1 g/L). Losartan (3 mg/kg) was given to the animal for five days. Acute hypertension was induced by ANG II (60 microg/kg). Arterial blood pressure was directly measured on the day of the experiment. BBB disruption was quantified according to the extravasation of the albumin-bound Evans blue dye. Losartan significantly reduced the mean arterial blood pressure from 169 +/- 3.9 mmHg to 82 +/- 2.9 mmHg in L-NAME and from 171 +/- 2.9 mmHg to 84 +/- 2.9 in L-NAME plus losartan plus ANG II groups (p < 0.05). The content of Evans blue dye in the cerebral cortex significantly increased in L-NAME (p < 0.01). Moreover, the content of Evans blue dye markedly increased in the cerebellum (p < 0.001) and slightly increased in diencephalon region (p < 0.05) in L-NAME plus ANG II. Losartan reduced the increased BBB permeability to Evans blue dye in L-NAME (p < 0.01) and L-NAME plus ANG II (p < 0.001). These results indicate that L-NAME and L-NAME plus ANG II both lead to an increase in microvascular Evans blue dye efflux to brain, and losartan treatment attenuates this protein-bound dye transport into brain tissue presumably due to its protective effect on endothelial cells of brain vessels.