The extracellular space and blood-eye barrier in an insect retina: An ultrastructural study

Summary (1) The distribution of the extracellular space (ECS) in the outer part of the locust compound eye has been mapped with lanthanum and ruthenium red, applied to the retina. (2) In the photoreceptor zone, about 2.4% of the volume is ECS, in agreement with radiotracer and electrical estimates. Of this ECS, about 70% lies in lacunae between ommatidia, but only 1–2% adjacent to the photosensitive rhabdom. The lacunae are filled with material which binds applied tracers, and are thought to be structural spaces. (3) It has been suggested several times that such a small cation pool is insufficient to sustain more than a few large photoresponses, but this is shown to be incorrect. Enough Na⁺ lies within the rhabdomal ECS and within rapid diffusional access to it, to impose no immediate limitation. (4) The palisade vacuoles surrounding the rhabdom are intracellular, and are typical of light as well as dark-adapted eyes. (5) Tracers fail to penetrate more than about 30 m into the axon zone, in agreement with electrical, dye and radiotracer indications of a blood-eye barrier near this point. Septate and gap junctions between glial membranes proliferate at this level, the lacunae disappear, and the axonal clefts narrow, but no tight junctions were seen. Comparison is made with the barrier around the nerve cord. (6) The secondary pigment cells in the retina may function as osmotic/ionic buffers, in conjunction with the blood-eye barrier.     

Changes in glomerular structure after sexual maturation and seawater adaptation in males of the euryhaline teleost Gasterosteus aculeatus L.

Summary In sexually mature male sticklebacks, the renal tubular cells are transformed from ion reabsorbing to mucus secreting cells and in these fish concomitant changes take place in the glomeruli.The present study compares glomerular structure of immature males in fresh water (controls) to those of mature males in fresh water and to immature male sticklebacks in seawater. Glomerular structure is markedly altered in the latter two groups and the changes are similar to a large extent. In these two groups the renal capsules and glomeruli are smaller and the lumina of the glomerular capillaries decrease in diameter, while the number and size of the endothelial fenestrations are reduced. Mesangial cells proliferate and the mesangial matrix greatly expands in both the centrolobular region and the subendothelial space around the capillaries. The secretory activity of the podocytes is enhanced and is responsible for the observed increase in thickness of the outer layer of the basal lamina, the lamina rara externa. The area covered by the filtration slit membranes is reduced, probably as a consequence of fusion of the pedicels of the podocytes. The permeability characteristics of the glomerular filtration barrier for macromolecules, as studied with ferritin injections, remain unaltered. However, the observed differences point to a reduction of the glomerular filtration rate (GFR) during maturation in male sticklebacks, as well as during adaptation of sticklebacks to seawater. This conclusion is in line with physiological evidence.     

Evidence for a cholecystokinin gut-brain axis with modulation by bombesin

The relationship between cerebrospinal fluid and plasma cholecystokinin (CCK) levels was investigated by simultaneous withdrawal of CSF and blood from anesthetized mongrel dogs and measurement of CCK immunoreactivity by radioimmunoassay. A significant correlation occurred between CSF and plasma levels of CCK. During a CCK IV infusion, a statistically significant inverse correlation was noted between CSF and plasma values, while no significant relationship was noted during a bombesin (BBS) IV infusion. When infusion data were analyzed together with the appropriate baseline data, polynomial analysis revealed significant biphasic relationships for both CCK and BBS infusion studies. Intraventricular infusion of CCK did not alter plasma levels. These data suggest the existence of a mechanism relating CSF to plasma CCK levels (a gut to brain axis) with possible modulation or suppression by BBS.     

Uptake and Storage of Choline by Rat Brain: Influence of Dietary Choline Supplementation

In order to elucidate the regulation of the levels of free choline in the brain, we investigated the influence of chronic and acute choline administration on choline levels in blood, CSF, and brain of the rat and on net movements of choline into and out of the brain as calculated from the arteriovenous differences of choline across the brain. Dietary choline supplementation led to an increase in plasma choline levels of 50% and to an increase in the net release of choline from the brain as compared to a matched group of animals which were kept on a standard diet and exhibited identical arterial plasma levels. Moreover, the choline concentration in the CSF and brain tissue was doubled. In the same rats, the injection of 60 mg/kg choline chloride did not lead to an additional increase of the brain choline levels, whereas in control animals choline injection caused a significant increase; however, this increase in no case surpassed the levels caused by chronic choline supplementation. The net uptake of choline after acute choline administration was strongly reduced in the high-choline group (from 418 to 158 nmol/g). Both diet groups metabolized the bulk (greater than 96%) of newly taken up choline rapidly. The results indicate that choline supplementation markedly attenuates the rise of free choline in the brain that is observed after acute choline administration. The rapid metabolic choline clearance was not reduced by dietary choline load. We conclude that the brain is protected from excess choline by rapid metabolism, as well as by adaptive, diet-induced changes of the net uptake and release of choline.     

Uptake and Distribution of Iron and Transferrin in the Adult Rat Brain

Brain uptake of iron-59 and iodine-125-labelled transferrin from blood in the adult rat has been investigated using graphical analysis to determine the blood-brain barrier permeability to these tracers in experiments that lasted between 5 min and 8 days. The blood-brain barrier permeability (K(in)) to 59Fe was 89 x 10(-5) ml/min/g compared to the value of 7 x 10(-5) ml/min/g for 125I-transferrin, which is similar to that of albumin, a plasma marker. The autoradiographic distribution of these tracers in brain was also studied to determine any regional variation in brain uptake after the tracers had been administered either systemically or applied in vitro. No regional uptake was seen for 125I-transferrin even after 24 h of circulation. In contrast, 59Fe showed selective regional uptake by the choroid plexus and extra-blood-brain barrier structures 4 h after administration. After 24 h of circulation, 59Fe distribution in brain was similar to the transferrin receptor distribution, as determined in vitro, but was unlike the distribution of nonhaem iron determined histochemically. The data suggest that brain iron uptake does not involve any significant transcytotic pathway of transferrin-bound iron into brain. It is proposed that the uptake of iron into brain involves the entry of iron-loaded transferrin to the cerebral capillaries, deposition of iron within the endothelial cells, followed by recycling of apotransferrin to the circulation. The deposited iron is then delivered to brain-derived transferrin for extracellular transport within the brain, and subsequently taken up via transferrin receptors on neurones and glia for usage or storage.     

Effect of Ozone on the Activities of Reactive Oxygen Scavenging Enzymes in Rbc of Ozone Exposed Japanese Charr (Salvelinus Leucomaenis)

The effect of ozone exposure on the activities of reactive oxygen scavenging enzymes (SOD†, catalase, GSH-Px) in RBC of Japanese charr (Salvelinus leucomaenis) was examined. Ozone (0, 0.4 and 0.7 ppm as initial concentrations) was exposed to Japanese charr for 30 min, which definitely caused serious membrane damage to RBC of fish. Ozone exposure at 0.4 and 0.7 ppm decreased activities of both catalase and GSH-Px by 80 to 57+ of the control. On the other hand, the activities of SOD remained unaffected even by 0.7 ppm ozone exposure. A hypothesis on the RBC membrane damage and participation of SOD and heme-iron was proposed.     

Effect of antioxidants on chemiluminescence produced by reactive oxygen species

Luminol chemiluminescence was used to evaluate the scavenging of superoxide, hydroxyl and alkoxy radicals by four antioxidants: dipyridamole, diethyldithiocarbamic acid, (+)catechin, and ascorbic acid. Different concentrations of these compounds were compared with well-known oxygen radical scavengers in their capacity to inhibit the chemiluminescence produced in the reaction between luminol and specific oxygen radicals. Hydroxyl radicals were generated using the Fenton reaction and these produced chemiluminescence which was inhibited by diethyldithiocarbamate. Alkoxy radicals were generated using the reaction of tert-butyl hydroperoxide and ferrous ion and produced chemiluminescence which was inhibited equally by all of the compounds tested. For the determination of superoxide scavengers we describe a new, simple, economic, and rapid chemiluminescence method consisting of the reaction between luminol and horseradish peroxidase (HRP). With this method it was found that 40 nmol/l dipyridamole, 0.18 μmol/l ascorbic acid, 0.23 μmol/l (+)catechin, and 3 μmol/l diethyldithiocarbamic acid are equivalent to 3.9 ng/ml superoxide dismutase (specific scavenger of superoxide) in causing the same degree of chemiluminescence inhibition. These results not only indicated that the antioxidative properties of these compounds showed different degrees of effectiveness against a particular radical but also that they may exert their action against more than one radical.     

An analog of ACTH/MSH (4–9), ORG-2766, reduces cerebral uptake of morphine

The uptake of morphine was significantly reduced in most regions of the brains of conscious, unrestrained rats within 10 minutes after treatment with an analog of ACTH/MSH (4–9), ORG-2766. The effect was most obvious in regions with significant densities of enkephalin receptors, namely basal ganglia, hippocampus and cortex. The results explain, in part, how some fragments and analogs of ACTH/MSH may antagonize behavioral actions of morphine, even though some of these peptides lack significant opiate receptor binding properties. We believe that this effect of ORG-2766 is related to an action on the permeability characteristics of the brain microvasculature. The underlying mechanism is unknown.     

Kinetics of Neutral Amino Acid Transport Through the Blood-Brain Barrier of the Newborn Rabbit

Abstract: Since protein synthesis in the developing brain may, under certain conditions, be limited by amino acid availability, the present studies were undertaken to characterize the kinetics of large neutral amino acid transport through the blood-brain barrier (BBB) of the newborn rabbit. The K_m, V_max, and K_D of the transport of eight amino acids were determined by a nonlinear regression analysis of data obtained with the carotid injection technique. Compared with kinetic parameters observed for the adult rat, the K_m, V_max, and K_D of amino acid transport were all two- to threefold higher in the newborn. Albumin was found to bind tryptophan actively in vitro , but had no inhibitory effect on tryptophan transport through the newborn BBB. Glutamine was transported through the BBB of the newborn at rates severalfold higher than are seen in the adult rat. However, glutamine transport was not inhibited by high concentrations of N -methylaminoisobutyric acid (NMAIB), a model amino acid that is specific for the alanine-preferring or A-system present in peripheral tissues. In conclusion, these studies show that the BBB neutral amino acid transport system of the newborn rabbit has a lower affinity and higher capacity than does the BBB of the adult rat. Under conditions of high plasma amino acids, the increased capacity of the newborn transport system allows for a higher rate of amino acid transport into brain than would occur via the lower capacity system present in the adult rat brain.     

Uptake of 36Cl and 22Na by the Brain-Cerebrospinal Fluid System: Comparison of the Permeability of the Blood-Brain and Blood-Cerebrospinal Fluid Barriers

Abstract: Transport and permeability properties of the blood-brain and blood-CSF barriers were determined by kinetic analysis of radioisotope uptake from the plasma into the CNS of the adult rat. Cerebral cortex and cerebellum uptake curves for ³⁶Cl and ²²Na were resolved into two components. The fast component (t_½ 0.02–0.05 h, fractional volume 0.04–0.08) is comprised of the vascular compartment and a small perivascular space whereas the slow component (t_½ 1.06–1.69 h, fractional volume 0.92–0.96) represents isotope movement across the blood-brain barrier into the brain extracellular and cellular compartments. Uptake curves of both ³⁶Cl and ²²Na into the CSF were also resolved into two components, a fast component (t_½ 0.18 h, fractional volume 0.24) and a slow component (t_½ 1.2 h, fractional volume 0.76). Evidence suggests that the fast component represents isotope movement across the blood-CSF barrier, i.e., the choroid plexuses, whereas the CSF slow component probably reflects isotope penetration primarily from the brain extracellular fluid into the CSF. The extracellular fluid volume of the cerebral cortex and cerebellum was estimated as ?13% from the initial slope of the curve of brain space versus CSF space curve for both ³⁶Cl and ²²Na. Like the choroid plexuses, the glial cell compartment of the brain appears to accumulate Cl from 2 to 6 times that predicted for passive distribution. The relative permeability of the blood-CSF and blood-brain barriers to ³⁶Cl, ²²Na, and [³H]mannitol was determined by calculating permeability surface-area products (PA). Analysis of the PA values for all three isotopes indicates that the effective permeability of the choroidal epithelium (blood/CSF barrier) is significantly greater than that of the capillary endothelium in the cerebral cortex and cerebellum (blood-brain barrier).