Lasting effects of early chronic caffeine feeding on rats' behavior and brain in later life

Pregnant dams were fed a 20% protein diet with caffeine (2 mg/100 g b.wt.), starting on day 9 of gestation. At birth, each dam with 8 assigned pups was fed this diet until weaning, day 22. On day 22, female rats were caged and fed this diet until day 93. Starting on day 93, the caffeine-supplemented diet was replaced with a caffeine-free, 20% protein diet until day 388. Starting on day 31, each animal was placed in a photoactivity cage, and locomotive activity was measured until day 375. On day 388, the animals were killed, and their brains were removed and divided into 7 regions. The weight, DNA, protein and zinc contents, and alkaline phosphatase activity of each region were determined. Locomotive activity of the caffeine-fed group was higher than in the noncaffeine control group. Accumulative activity scores showed 3 subgroups (high, medium, and low) in both groups at day 93. The medium activity subgroup in the caffeine group was greater than the controls from day 72 to day 93. These differences reappeared 5 weeks after cessation of caffeine supplementation and continued until day 375. The differences in activity were minimum in the high and low subgroups. Chronic caffeine intake in early life permanently affected the medium activity subgroup. Furthermore, various regions of the brain were biochemically altered in spite of the feeding of a noncaffeine diet for almost 300 days after caffeine.

Increased levels of leukotriene C4 in retinal pigment epithelium are correlated with early events in photoreceptor shedding in Xenopus laevis

The levels of 5-lipoxygenase products of arachidonic acid, leukotriene (LT) B4 and LTC4 in retinal pigment epithelia (RPE) from Xenopus laevis were measured by radioimmunoassay (RIA). RPE were isolated during various stages of photoreceptor renewal to determine possible alterations in 5-lipoxygenase activity concurrent with photoreceptor detachment and phagocytosis. Both LTC4 and LTB4 were released to RPE incubation media, although levels of LTB4 in unstimulated RPE were close to the limits of detection by RIA. Incubation of RPE with the calcium ionophore A23187 increased the levels of both LTB4 and LTC4. When animals were maintained on a cycle of 12 hr light/dark, normal photoreceptor shedding, as measured by histological quantitation of the appearance of phagosomes in the RPE, occurred 1 hr after light onset. Levels of LTC4 in RPE were lower 1 hr after light onset, as compared to 1 hr prior to light onset. Due to the low levels of LTB4, no significant differences could be detected. However, when LTB4 levels were elevated with A23187, LTB4 also declined 1 hr after light onset. When animals were maintained in constant light for 5 days, then exposed to 2 hr dark and 2 hr light, a massive shedding response occurred. Levels of LTC4 were stimulated 5 min after light onset (prior to detectable shedding) and declined below dark levels as shedding progressed. These data suggest a correlation between 5-lipoxygenase activity and the events of photoreceptor shedding and phagocytosis.

Synthesis of leukotrienes in frog retina and retinal pigment epithelium

Leukotrienes (LT) were identified in the intact frog (Rana pipiens) retinal pigment epithelium (RPE), retina, isolated rod outer segments (ROS), and ROS-free (neuronal) retina. Levels of endogenous LTC4 were measured by radioimmunoassay (RIA) in both unpurified incubation medium and in incubation medium purified by reverse-phase high-performance liquid chromatography (HPLC). The purified LTC4 exhibited characteristic ultraviolet absorption spectrum with lambda max at 280 nm. The Ca2+ ionophore A23187 (10 microM) increased LTC4 production in intact and ROS-free retina and RPE but had no effect on LTC4 levels in isolated ROS. This lack of effect suggests that LTC4 is present but not synthesized in ROS. Synthesis of radiolabeled LTC4 in frog retina and RPE prelabeled in vivo by intravitreal injection of [1-14C]arachidonic acid (20:4, n-6) provided an additional verification of the presence of LTC4 in these tissues. The physiological significance of the presence of these biologically active derivatives of arachidonic acid in photoreceptor cells and retinal pigment epithelium may be related to the interactions between these cells, consisting of photoreceptor membrane shedding and phagocytosis.

Metabolism of phosphoinositides and inositol polyphosphates in rabbit corneal epithelium

The synthesis of phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2) was studied in the rabbit cornea using 32P and [3H]myo-inositol as precursors. Also, the formation of water-soluble products of the degradation of inositol lipids, inositol-1-phosphate, -1,4-bisphosphate and -1,4,5-trisphosphate, was shown. Corneal epithelium displayed the most active inositol lipid metabolism and endothelium the least when the cornea layers were separately incubated (stroma had intermediate values). In corneal epithelium incubated with [3H]myo-inositol, tritiated glycerophosphorylinositol and water-soluble inositol phosphates were formed. 10 mM LiCl promotes an increase in the inositol phosphates consistent with an inhibitory effect on inositol phosphatase. Cell-free preparations of epithelium incubated with [gamma-32P]ATP detected the presence of diacylglycerol kinase, PI kinase and PIP kinase. Endogenous PI was rapidly phosphorylated to PIP within 1 min of incubation, whereas PIP was phosphorylated more slowly. In conclusion, the components of the inositol lipid cycle are present in the cornea, particularly in the epithelium. It is proposed that the control of these pathways may be involved in the transduction of cell signals through the plasma membrane, intracellular calcium ionization and epithelial cell proliferation and differentiation, particularly in wound healing.

Inhibition of phosphatidylinositol-4-phosphate kinase by its product phosphatidylinositol-4,5-bisphosphate

Phosphatidylinositol 4,5-bisphosphate (PIP2) is enzymatically produced when high speed supernatant fraction from bovine retina is incubated with [gamma-32P]ATP and phosphatidylinositol 4-phosphate (PIP) as substrates. Exogenously added PIP2 inhibits PIP kinase activity 50% at equimolar concentrations of product and substrate. Ca2+-dependent phosphodiesteratic activity, resulting in the loss of PIP2 and PIP and concommitant increase in myo-inositol 1,4,5-trisphosphate and myo-inositol 1,4-bisphosphate, was observed when soluble retinal fractions were incubated with heat-inactivated 32P-prelabeled guinea pig nerve ending membranes as substrate. It is suggested that polyphosphoinositides are under stringent and complex control and that upon receptor activation-mediated stimulation of phosphodiesteratic degradation release of the feedback inhibition shown here may occur and result in the synthesis and replenishment of PIP2.

Effect of hypoxia on the superficially exposed carbohydrates of subcellular fractions of guinea pig cerebral cortex

Experimental hypoxia led to changes in carbohydrate-containing macromolecules located on the microsomal and synaptosomal membrane surface. It was found that hypoxia reduced the external membrane-bound sialic acid content in microsomal and synaptosomal fractions. On the other hand, a decrease in fucose content of proteins in hypoxic synaptosomal fraction was found. Similarly, a decrease was observed in the amount of 3H-labeled concanavalin A bound to the microsomal and synaptosomal glycoprotein fractions. Treatment of microsomal and synaptosomal fractions with galactose oxidase followed by reduction with tritiated potassium borohydride resulted in a significantly higher incorporation rate of tritium into the hypoxic membranes. This was accompanied by an increase in the endogenous glycoprotein galactose transferase activity both in microsomal and synaptosomal fractions.

Effect of modification of synaptosomal membrane glycoproteins on adenylate cyclase activity

The effect of the modification of synaptosomal membrane glycoproteins on the activity of adenylate cyclase was studied. It was found that the binding of concanavalin A to unmodified guinea pig cerebral cortex synaptosomal membrane did not change adenylate cyclase activity. Concanavalin A binding to synaptosomal membrane of hypoxic brain cortex resulted in no decrease of enzyme activity. The level of protein-bound sialic acid in these synaptosomal fractions was 20% lower than in the control. Treatment of synaptosomal membranes with neuraminidase resulted in a decrease of sialic acid content by about 70%, but it had no significant effect on adenylate cyclase activity. The modification with concanavalin A of sugar end groups exposed by neuraminidase treatment resulted in significant decrease of both basal and fluoride-stimulated adenylate cyclase activity. These results seem to indicate that some component of the adenylate cyclase complex of brain synaptosomal membranes is closely interacting with a carbohydrate-containing macromolecule on the cell surface.

Role of glycoproteins in the uptake of L-14C-leucine by a synaptosomal fraction

The present study deals with the effect of modification of membrane glycoproteins on the accumulation of amino acids by isolated synaptosomal fractions, measured by the uptake of 14C-leucine. Superficial sugar receptors were modified by concanavalin A, neuraminidase, and neuraminidase followed by concanavalin A binding. It is demonstrated that neuraminidase treatment followed by concanavalin A binding results in significant diminution of 14C-leucine uptake. A similar effect was observed in experimental hypox followed by concanavalin A binding to isolated synaptosomal fractions. In this case, however, (Na+-K+) -ATPase activity remained unchanged. These results seem to indicate that 14C-leucine uptake was dependent on integrity of glycoprotein structure of synaptosomal membranes.

Studies on the glycoprotein component of (Na+-k+) atpase from guinea pig brain

In this study an attempt was made to elucidate the possible mechanism of the brain microsomal (Na+-K+)ATPase inhibition based on the assumption that glycoprotein part of the enzyme is exposed on the outer membrane surface. In our experiments the modification with concanavalin A of sugar end groups exposed by neuraminidase treatment resulted in a significant decrease of the brain (Na+-K+)ATPase activity. The percentage of the enzyme inhibition by concanavalin A binding to the neuraminidase-treated preparation corresponds to the amount of liberated sialic acids. The modification of the glycoprotein part of the brain (Na+-K+)ATPase complex by neuraminidase and concanavalin A treatments did not affect K+-nitrophenylphosphatase activity.

Effect of hypoxia and ischemia on the distribution of protein in brain cellular fractions

The effect of postdecapitative ischemia (5 min at 37 degrees) and hypoxia (5% O2, 95% N2, 30 min) on the distribution of protein radioactivity in the cellular fractions of guinea pig cerebral cortex was studied. Ischemic conditions resulted in the increase of total radioactivity level and protein content in the mitochondrial fraction. In the cytosol the opposite effect was observed; the radioactivity and protein content were decreased. The amino acid analysis of microsomal proteins and the distribution of glucose-6-phosphatase activity, differing from those in control animals, suggest structural disturbances in the microsomal fraction. The results indicate a different sedimentation of proteins in the given experimental conditions. After hypoxia such effects were not observed.