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Biomedical subjects

M Baudry

Publications and source records attributed to M Baudry.

At least 199 records · Page 11Linked to original sources
PubMed1985

Olfactory discrimination learning is blocked by leupeptin, a thiol protease inhibitor.

Rats were trained on successive two-odor discriminations with the cues randomly located in an 8-arm radial maze. After several days of training using different odor pairs, the thiol protease inhibitor leupeptin was infused into the ventricles and testing continued. Leupeptin caused a pronounced, dose-dependent and reversible deficit in performance in this task. Previous studies have shown that these drug concentrations do not influence spontaneous activity, feeding and drinking, or the acquisition and retention of avoidance conditioning. The results are interpreted as supporting the hypothesis that a calcium-sensitive proteinase is involved in certain forms of memory that require modification of telencephalic circuitries.

Animals↗
PubMed1985

Electrophysiological and neurochemical investigations on the action of carbamazepine on the rat hippocampus.

Carbamazepine moderately depressed the input fiber volley resulting in attenuation of the dendritic epsp and the population spike in CA1 of rat hippocampal slices with a threshold concentration of 20 microM. The depressant effect on the population spike was not antagonized by the adenosine receptor blocker caffeine. Paired-pulse inhibition was not affected by carbamazepine (40 microM). Epileptic-like rhythmic discharge of CA1 neurons in medium containing low Ca2+/high Mg2+ was attenuated at even lower concentrations of carbamazepine (8 microM) indicating that there was also a postsynaptic site of action. Imipramine being significantly more potent than carbamazepine in the rabbit corneal test for local anaesthetic activity had no effect on the population spike (20 microM). In neurochemical studies, carbamazepine reduced the [22Na]- and [3H]L-glutamate efflux induced by potassium and veratridine from hippocampal slices with a threshold concentration of 10 microM. The drug (400 microM) failed to affect Na+-dependent binding of [3H]L-glutamate to hippocampal synaptic membranes. In conclusion, the present findings demonstrate pre- and postsynaptic depressant actions of carbamazepine in CAI of hippocampus.

Anesthetics, Local↗
PubMed1985

Regional distribution of soluble calcium activated proteinase activity in neonatal and adult rat brain.

Calcium dependent proteolytic activity in the soluble fraction of various rat brain regions was assayed using 14C-radiolabelled denatured casein as a substrate. Two forms of activity, distinguishable by their calcium requirement for half maximal activation (5 and 80 microM), were found; both were blocked by sulfhydryl alkylating agents and thiol proteinase inhibitors. Preincubation at 58 degrees C for 10 min also eliminated the high threshold activity. These characteristics are identical to those reported for calcium activated neutral proteinases ('calpains') found in other tissues. Calpain activity varied markedly across brain regions. The greatest values for the high threshold enzyme were found in pons-medulla followed by cerebellum/mesencephalon and finally the telencephalon. The low threshold enzyme had low levels of activity throughout the brainstem and diencephalon and was barely detectable in telencephalic structures. In contrast, a previously described endogenous inhibitor of calpain, 'calpastatin', was found not to vary in its activity across brain regions. Calpain activity was high in the prenatal brain, but while the hindbrain maintained high levels of activity into adulthood, the activity in the forebrain dropped 80% during the early postnatal period. The differences between forebrain and hindbrain activity levels were evident during the first 5 days of the neonatal period, suggesting that glial cell differentiation is not responsible for the regional variations found in the adult. These results are discussed with regard to the possibility that the turnover of anatomical structures differs between brain regions.

Animals↗
PubMed1985

[Effect of hypothyroidism on mitochondrial energy metabolism and nuclear synthesis of RNA in the liver of Cynomolgus monkeys].

The effects of hypothyroidism and of replacement therapy with T4 or T3 were studied on the enzymatic activities of liver subcellular fractions isolated from Cynomolgus monkeys. Animals were sacrificed 20 days after thyroidectomy. In mitochondria, thyroidectomy decreased significantly the respiratory chain activity (succinate cytochrome c-reductase), the transfer of cytosolic reducing equivalents (glycerol-3-phosphate dehydrogenase) and the phosphorylating capacity (oligomycin-sensitive ATPase and state 3 respiratory rate). The activity of nucleolar and nucleoplasmic RNA polymerases dropped by about 50% in hypothyroid monkeys. In T4 (2.5 micrograms/kg/d) or T3 (1 microgram/kg/d) treated thyroidectomized animals, the iodothyronine concentrations and the activity of mitochondria and nuclei enzymes were halfway between normal and hypothyroid values. Thus, the mitochondrial effects of thyroidectomy in monkey are, as in rat, at least partly secondary to a decrease in nucleocytoplasmic protein synthesis.

Animals↗
PubMed1984

Inhibitors of lysosomal enzymes: accumulation of lipofuscin-like dense bodies in the brain.

Injections of leupeptin (a thiol proteinase inhibitor) or chloroquine (a general lysosomal enzyme inhibitor) into the brains of young rats induced the formation of lysosome-associated granular aggregates (dense bodies) which closely resembled the ceroid-lipofuscin that accumulates in certain disease states and during aging. The dense material increased in a dose- and time-dependent fashion and was differentially distributed across brain regions and cell types. These observations provide clues to the origins of ceroid-lipofuscin and suggest means for studying the consequences of its accumulation.

Animals↗
PubMed1984

Low concentrations of potassium inhibit the Na-dependent [3H]glutamate binding to rat hippocampal membranes.

Potassium at low concentrations was found to inhibit the Na-dependent [3H]L-glutamate binding to rat hippocampal synaptic membranes. This inhibition was probably due to a competition between potassium and sodium at the ionic locus of the recognition site for glutamate of the uptake process. In addition, potassium inhibited the high-affinity [3H]L-glutamate uptake in hippocampal synaptosomes. These results provide an additional mechanism for the spreading of depression which accompanies seizure activity in the hippocampus.

Animals↗
PubMed1984

The biochemistry of memory: a new and specific hypothesis.

Recent studies have uncovered a synaptic process with properties required for an intermediate step in memory storage. Calcium rapidly and irreversibly increases the number of receptors for glutamate (a probable neurotransmitter) in forebrain synaptic membranes by activating a proteinase (calpain) that degrades fodrin, a spectrin-like protein. This process provides a means through which physiological activity could produce long-lasting changes in synaptic chemistry and ultrastructure. Since the process is only poorly represented in the brain stem, it is hypothesized to be responsible for those forms of memory localized in the telencephalon.

Animals↗
PubMed1984

A comparative study of L[3H]-glutamate and L[3H]-cysteine sulfinate binding sites in subcellular fractions of rat brain.

A comparative study of the binding of L-cysteine sulfinic acid (CSA) and L-glutamic acid (GLU) to various subcellular fractions of membranes from rat brain was made. Kinetic parameters were determined in all fractions for both types of binding. The effects of membrane preincubation, freezing, and thawing were also examined. The GLU and CSA specific binding levels increased in medium-density (C) and high-density (D) synaptic membranes as compared to the crude mitochondrial/synaptosomal membranes (wP2). Freezing and thawing reduced CSA binding in all tested subcellular fractions. GLU binding is reduced in wP2, C, and D. Binding to the "light" synaptic membranes (B) was not significantly affected, suggesting the presence of two GLU sites. Kinetics of the GLU binding indicated that the temperature-sensitive and -insensitive sites have Kd of 600 nM and 1,100/nM, respectively. Preincubation of fresh membranes conversely affected CSA and GLU binding to the various subcellular fractions, increasing CSA binding in wP2, B, C and decreasing it in D suggesting the existence of distinct sites for GLU and CSA. Preincubation of previously frozen membranes similarly modified CSA and GLU binding except in B fractions. CSA and GLU binding exhibited different pH sensitivities in both fresh and frozen membranes. These results indicate that multiple acid amino acid binding sites exist in membranes and that they can be differentiated according to their sensitivity to temperature. They also suggest the existence of distinct sites for CSA and GLU in fresh membranes, giving further support to the hypothesis that CSA may also serve a neurotransmitter role in the rat central nervous system.

Animals↗
PubMed1984

Leupeptin, a thiol proteinase inhibitor, causes a selective impairment of spatial maze performance in rats.

The effects of chronic intraventricular infusion of leupeptin, a potent inhibitor of thiol proteinases, were tested on ingestive behaviors, escape and avoidance conditioning, and spatial memory in rats. The drug did not detectably influence feeding, drinking, body temperature, or the latency to escape from a mild footshock or inhibitory avoidance behavior. However, rats treated with leupeptin made numerous errors ( reentries ) in an eight-arm spatial maze. These results are interpreted as supporting the hypothesis that calcium-activated thiol proteinases are involved in the formation of certain types of memory.

Animals↗
PubMed1984

Brain fodrin: substrate for calpain I, an endogenous calcium-activated protease.

The calcium-activated thiol-protease calpain I, which is present in cytosolic and membrane preparations from rat brain, was tested for its capacity to degrade the neuronal spectrin-like protein fodrin. In the presence of micromolar calcium concentrations purified calpain I degraded both purified fodrin and the fodrin present in hippocampal and cerebellar membranes. Fodrin was identified as a high molecular weight protein present in brain membranes by the following criteria: (i) comigration on NaDodSO4/polyacrylamide gels with purified fodrin, (ii) reactivity with antibodies to purified fodrin, and (iii) a proteolytic map following calpain activation comparable to that found after calpain-mediated degradation of purified fodrin. The fodrin breakdown was selective in that calpain I did not affect at least 15 other membrane-associated polypeptides. Fodrin degradation by the protease was rapid and was accompanied by the appearance of a lower molecular weight breakdown product. Calpain I had a high affinity for fodrin, with a Km for degradation of about 50 nM. Purified calpain I also degraded purified spectrin and the spectrin present in erythrocyte membranes. Calpain I-mediated degradation of spectrin-like proteins could provide a mechanism by which brief increases in intracellular free calcium levels modify the structure of the submembraneous cytoskeleton and the distribution of cell surface receptors and alter cell shape.

Animals↗
PubMed1984

Classical conditioning of the rabbit eyelid response increases glutamate receptor binding in hippocampal synaptic membranes.

Hippocampal pyramidal neurons exhibit a rapid within-trial increase in firing frequency during classical conditioning of the rabbit eyelid response. It has been proposed that the cellular mechanisms responsible for hippocampal long-term potentiation (LTP) may also mediate this learning-dependent increase in neuronal activity. The induction of LTP in rat hippocampal slices results in an increase in the number of [3H]glutamate-binding sites in the potentiated region. The present study investigates the kinetics of [3H]glutamate binding to hippocampal synaptic membranes after eyelid conditioning in the rabbit. We report that the regional distribution of [3H]glutamate binding across the layers of rabbit hippocampus is compatible with a dendritic localization. The pharmacological and ionic properties of the binding suggest that it is associated with an excitatory amino acid receptor. After eyelid conditioning, the maximal number of hippocampal [3H]glutamate-binding sites is increased in animals receiving paired presentations of the tone conditioned stimulus and corneal air-puff unconditioned stimulus relative to that found in naive or unpaired control animals. These results strengthen the hypothesis that an LTP-like mechanism underlies the increase in hippocampal firing frequency during rabbit eyelid conditioning.

Animals↗
PubMed1983

Irreversibility and time course of calcium stimulated [3H]glutamate binding to rat hippocampal membranes.

Previous studies have indicated that calcium ions induce an irreversible increase of [3H]glutamate binding to rat hippocampal membranes. The present study was intended to provide an estimate of the time-course for this effect. The calcium chelator EGTA and the proteinase inhibitor leupeptin were introduced at various times during the incubation of hippocampal membranes with calcium and the binding of [3H]glutamate subsequently assayed. Both compounds totally blocked the calcium-induced increase in binding when added at the beginning of the incubation period but produced progressively less inhibition when added after longer delays. This method indicates that calcium produces its maximal effect between 5 and 10 min of incubation, a time-course compatible with the hypothesis that calcium stimulates a membrane-bound proteinase which results in the unmasking of [3H]glutamate binding sites.

Animals↗
PubMed1983

Regulation by calcium ions of glutamate receptor binding in hippocampal slices.

Hippocampal slices were incubated in a Krebs-bicarbonate buffer with various concentrations of calcium and [3H]glutamate receptor binding was measured in crude synaptic membranes derived from these slices. Increasing the calcium concentration from 0 to 2.5 mM resulted in a 2.2-fold increase in the maximal number of the Na-independent [3H]glutamate binding sites without changes in their affinity for [3H]glutamate. This effect was totally blocked by the addition of the protease inhibitor leupeptin (50 microM) to the slice incubation medium. No effect was observed on the Na-dependent [3H]glutamate binding nor on the Na-independent [ 3H ]glutamate binding measured in the presence of a concentration of calcium of 250 microM. Increasing the calcium concentration also resulted in an increased proteolytic activity which was inhibited by about 70% by the addition of leupeptin. Finally, increasing the calcium concentration induced the degradation of high-molecular weight proteins, the microtubule-associated proteins (MAPs) and the 220 000 dalton doublet protein corresponding to fodrin. Both effects were partially prevented by the addition of leupeptin in the slice incubation medium. These results indicate that the same calcium-dependent processes which were previously shown to regulate [ 3H ]glutamate receptor binding to hippocampal membranes occur in the hippocampal slice preparation, and they suggest a mechanism by which fluctuations in calcium levels can activate a calcium-dependent proteinase, the degradation of cytoskeletal-associated proteins and the unmasking of additional glutamate receptors. The participation of such processes in various forms of plasticity is discussed.

Animals↗
PubMed1983

Effects of glucagon on basal metabolic rate and oxidative phosphorylation of rat liver mitochondria.

Glucagon produced fast but transient stimulation of respiration rates in state 3 and state 4 rat liver mitochondria when either succinate or beta-hydroxybutyrate was used as substrate. Stimulation was already detectable 7.5 minutes after glucagon injection. Glucagon also clearly activated basal metabolic rate, and its effects on oxygen consumption rates reached their maximum 20 to 30 minutes after injection. Pretreatment with cycloheximide blocked most activation by glucagon of both oxidative phosphorylation and basal metabolic rate, but did not affect its enhancement of glycaemia. The rise in basal metabolic rate was the direct result of glucagon's effect on mitochondria, which was secondary to nucleocytoplasmic protein synthesis.

Animals↗
PubMed1983

Effects of glucagon and 3,5,3'-triiodo-L-thyronine on oxidative phosphorylation of thyroidectomized rat liver mitochondria.

In normal or thyroidectomized rat liver mitochondria, glucagon produced fast but transient stimulation of respiration rates in state 3 and state 4 whatever the substrates. Stimulation reached its maximum 20 to 30 minutes after glucagon injection. However, the effects of glucagon are less marked after removal of the thyroid gland, since the increases observed in the oxygen consumption and basal metabolic rates were only half those shown in normal rats. The activating effects of triiodothyronine and glucagon on the ADP phosphorylation rates were found to be additive. Pretreatment with cycloheximide blocked the activation induced by glucagon but not that induced by triiodothyronine. Both hormones therefore stimulate oxidative phosphorylation but by different mechanisms. Thyroidectomy did not alter the early rise in glycaemia observed in response to glucagon. It may therefore be assumed that the hypothyroid rat's sensitivity to glucagon is not directly connected with the change in cAMP metabolism.

Animals↗
PubMed1983

Purification from synaptosomal plasma membranes of calpain I, a thiol protease activated by micromolar calcium concentrations.

Synaptosomal plasma membranes (SPMs) were prepared from whole rat brain and assayed for calcium-stimulated proteolytic activity. Addition of calcium to SPMs caused a dose-dependent increase in trichloroacetic acid-soluble protein. Two peaks of protease activity directed against a casein substrate were detectable when SPMs were incubated with low-ionic-strength buffer and the extract was fractionated on DEAE-cellulose. The enzyme in peak 1 required less than 1/10 the calcium concentration for activation as the peak 2 protease (Kact1 = 35 microM; Kact2 = 500 microM). The specific thiol-protease inhibitors leupeptin and antipain and the alkylator iodoacetate blocked enzyme activity. The low-sensitivity protease was converted to a high-sensitivity enzyme (Kact = 20 microM) by substrate affinity chromatography in the presence of calcium. This protease was purified 550-fold from SPMs. The high- and low-sensitivity membrane-associated calcium-dependent proteases are part of a family of enzymes, the calpains, previously reported in cytosolic fractions of several tissues.

Animals↗