INTERVENTION OF BRAIN CORTEX PHOSPHOLIPIDS IN PYRIDOXAL PHOSPHATE-DEPENDENT REACTIONS

We have examined the role of brain cortex phospholipids in regulating some enzymic reactions specific to the CNS. The study was carried out at the level of the reactions concerned with GABA formation, both in vivo and in vitro, and included investigation of the specificity of the effect. It was found that the brain cortex phospholipids enhance the transformation of exogenous vitamin B₆ into pyridoxal-5-phosphate by activating the pyridoxal 5-phosphate-kinase enzyme, in contrast to other phospholipids of different origins. The possible role of brain cortex phospholipids in regulating an enzyme contained in the soluble fraction is discussed. Moreover, it is suggested that the specific effect of the phospholipids from various sources is linked to their fatty acid composition and to be therefore dependent on the aliphatic chains.     

Effect of lysophosphatidylserine on immunological histamine release

The effect of lysophosphatidylserine on immunological histamine release has been studied in rat peritoneal mast cells actively sensitized with horse serum and in human basophils challenged with anti-IgE. In contrast to other lysophospholipids, lysophosphatidylserine enhances the immunological histamine release in rat mast cells. The effect shows the kinetics of a saturable process with an apparent Km for lysophosphatidylserine of 0.26 microM. A similar Km value (0.21 microM) is found when measuring the non-immunological histamine release activated by lysophosphatidylserine plus nerve growth factor. A comparison with phosphatidylserine shows that a half-maximal response to lysophosphatidylserine occurs at a concentration 4-times lower. In addition, the magnitude of the response is higher. At variance with rat mast cells, lysophosphatidylserine does not influence the histamine release elicited by immunological and non-immunological stimuli in human basophils. The histamine secretion in these cells is instead affected by a calcium ionophore or tetradecanoylphorbolacetate, a compound producing activation of protein kinase C.     

Synergistic effect of phosphatidylserine with γ-aminobutyric acid in antagonizing the isoniazid-induced convulsions in mice

The influence of phosphatidylserine (PS) on the isoniazid-induced convulsions has been studied in mice. Sonicated dispersions of this phospholipid given intravenously do not show anticonvulsant activity but they do so when -aminobutyric acid (GABA) is simultaneously injected. GABA alone is inactive. The synergism between PS and GABA is influenced by the structure of the phospholipid liposomes. In contrast to multilamellar vesicles, oligolamellar vesicles are active. Under these conditions the effect shows head group specificity, in that the neutral phosphatidylcholine (PC) or the acidic phosphatidylinositol (PI) are inactive, either in the presence or in the absence of GABA. Lysophosphatidylserine (lysoPS), the deacylated PS derivative, shows increased efficacy as an isoniazid antagonist in the presence of GABA, and has anticonvulsant activity also in the absence of GABA. Other lysophospholipids are inactive. It is suggested that PS, after its metabolic conversion to lysoPS, enhances the anticonvulsant effect of GABA.     

Biochemical changes of rat brain membranes with aging

Modification of membrane composition and enzymatic activities both in total brain homogenate and purified synaptic plasma membrane of 3 and 24 month old rats has been investigated. Protein, cholesterol and phospholipid content and (Na+, K+)ATPase and 2',3' cyclic nucleotide phosphohydrolase activities were determined. The major changes occurred in the whole homogenate where a general increase in total protein and cholesterol content with age and a significant increase of the cholesterol/phospholipids molar ratio has been detected. In S.P.M. aging process induced a decrease of protein, cholesterol and phospholipids content associated with an increased membrane viscosity and a decrease of delta E. These data are consistent with a change in the structural organization and in the distribution pattern of different cell population in the aging brain. A possible artifactual effect of freezing on the reported parameter is also discussed.     

Aspects of neural plasticity in the central nervous system—IV. Chemical anatomical studies on the aging brain

Some effects of aging processes on the neurochemical features of central transmitter-identified neuronal populations have been investigated by means of immunocytochemistry and receptor autoradiographic techniques coupled with image analysis. A selective decrease of tyrosine hydroxylase immunoreactivity in the ventrolateral region of the arcuate nucleus in aged rats was observed. The level and turnover (recovery after irreversible blockade of monoamine receptors with the peptide coupling agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline) of 2-adrenergic ([³H]paraaminoclonidine binding) and D2 dopamine ([³H]spiperone binding) receptors were reduced in most regions of the rat brain. Peptide receptors showed a more complex pattern of change, since while μ opiate receptors (preferentially labeled with [³H]etorphine binding) were reduced in the old animals, δ opiate ([³H]DSTLenkephalin binding) receptors were affected only in certain areas. The effect of irreversible blockade of monoamine receptors on μ and δ opiate receptors was also studied in young adult and aged rats. A δ but not μ opiate receptor up-regulation was observed after monoamine receptor blockade in the young adult animals. This effect was greatly reduced in the n. caudatus-putamen, n. accumbens and tuberculum olfactorium of the old animals.     

Excitatory amino acid receptor agonists stimulate membrane inositol phospholipid hydrolysis and increase cytoplasmic free Ca2+ in primary cultures of retinal neurons

A variety of neurotransmitters are believed to elicit effects through receptor-stimulated inositol phospholipid metabolism. It appears that most major types of retinal neurons receive a direct glutamatergic input. The aim of the present studies was to characterize excitatory amino acid (EAA) receptor-mediated breakdown of inositol phospholipids and changes in Ca2+ homeostasis in primary avian retinal cell cultures. Cell monolayers, prepared from 8-day-old chick embryo neural retina, were labelled with [3H]inositol for 48 h, and used after 7 days in vitro. Kainic acid stimulated the accumulation of inositol phosphates in a time- and dose-dependent manner (ED50 = 30 microM). The EAA receptor agonists glutamate, N-methyl-D-aspartate (NMDA), ibotenate and quisqualate were all active, with the rank order: glutamate greater than kainate greater than NMDA much greater than ibotenate approximately quisqualate. External Ca2+ was required for these effects. Agonist actions were inhibited by type-specific antagonists, and also Mg2+ in the case of glutamate and NMDA. Glutamate, NMDA and kainate also elevated cytosolic free Ca2+ in individual retinal cells loaded with the Ca2(+)-sensitive dye Fura-2, as assessed by digital fluorescence ratio imaging microscopy. The agonist-induced increases in [Ca2+]i were largely dependent on extracellular Ca2+, independent of membrane depolarization and were blocked by Mg2+ for glutamate and NMDA. These results demonstrate that vertebrate retinal cells possess EAA receptors coupled to intracellular signal transduction pathways.     

Changes in rabbit cerebrum and cerebellum gangliosides during postnatal life. A study especially referring to alkali labile gangliosides

The present study deals with the developmental behaviour of cytosolic and membrane-bound gangliosides, especially the alkali labile species, in rabbit cerebrum and cerebellum from birth to 6 months of life. At all ages the amount of cytosolic gangliosides was less than 0.5% of total gangliosides. The proportion of alkali labile gangliosides on the total membrane-bound ganglioside content and the profile of the individual alkali labile gangliosides during postnatal life were different in cerebellum and cerebrum. In cerebellum the proportion of alkali labile gangliosides progressively increased from 4.6% at birth to 16.7% at 6 months; in cerebrum the proportion decreased from 8.9% at birth to a minimum of 5.5% at 10 days, then slowly increased up to 8.1% at 6 months.All the major alkali labile gangliosides in cerebellum, especially O-Ac-GT1b and O-Ac-GQ1b, tended to accumulate during postnatal life. In cerebrum only two alkali labile gangliosides, namely O-Ac-GT1b and a species not yet identified, increased starting from the 10th day of life, while the other ones progressively diminished after birth.     

Disposition of exogenous tritium-labelled GM1lactone in the rat.

The disposition of labelled [3H]GM1lactone, the inner ester of ganglioside GM1, was studied in the rat. After i.v. administration [3H]GM1lactone was quickly converted to its corresponding open form most likely by plasma esterases, and then displayed a pharmacokinetic profile identical to [3H]GM1. Following intramuscular administration of [3H]GM1lactone [3H]GM1 levels in plasma and in tissues were higher than those obtained after the administration of an equivalent dose of [3H]GM1. This increased bioavailability means that GM1lactone can be considered as a potential prodrug of GM1.