Biomedical subjects

N Sarda

Publications and source records attributed to N Sarda.

At least 37 records · Page 2Linked to original sources

PubMed1993

[Implication of melatonin in the control of the interdigestive ileocecal-colic electromyographic profile in rats].

In the interdigestive period, intestinal motility displays myoelectrical complexes occurring cyclically at a constant rhythm. Since it is established that the pineal gland plays an important role in the control of circadian rhythms via its melatonin secretion, we decided to study the effects of pinealectomy and melatonin on the organization of the ileo-ceco-colic electromyogram of the rat. Pinealectomy resulted in the disappearance of ileal myoelectrical complexes and, concurrently, an excitomotor effect on the cecocolic tract. In pinealectomized rats a single intravenous injection of melatonin during lighting period induced an immediate recovery of the ileal myoelectrical complexes and a progressive return to the control electromyographic pattern of the ceco-colic tract. The melatonin action was definitive.

Animals↗

PubMed1992

Evidence for adenosine A2b receptors in the rat pineal gland.

We describe the effects of 5'-N-ethylcarboxamidoadenosine (NECA), a mixed A2a/A2b adenosine receptor agonist and 2-[p-(carboxyethyl)-phenylethylamino]-5'-N-ethylcarboxamidoaden osin e (CGS 21680), a selective A2a agonist, on cyclic AMP and N-acetylserotonin synthesis in rat pineal gland. NECA, 1 and 10 microM, increased cyclic AMP by 5- and 25-fold and N-acetylserotonin by 40- and 60-fold respectively, whereas CGS 21680 at the same concentrations was ineffective. These results argue for the presence of adenosine A2b receptors in rat pinealocytes.

Adenosine↗

PubMed1992

Brain protein synthesis in the conscious rat using L-[35S]methionine: relationship of methionine specific activity between plasma and precursor compartment and evaluation of methionine metabolic pathways.

The method previously developed for the measurement of rates of methionine incorporation into brain proteins assumed that methionine derived from protein degradation did not recycle into the precursor pool for protein synthesis and that the metabolism of methionine via the transmethylation pathway was negligible. To evaluate the degree of recycling, we have compared, under steady-state conditions, the specific activity of L-[35S] methionine in the tRNA-bound pool to that of plasma. The relative contribution of methionine from protein degradation to the precursor pool was 26%. Under the same conditions, the relative rate of methionine flux into the transmethylation cycle was estimated to be 10% of the rate of methionine incorporation into brain proteins. These results indicate the following: (a) there is significant recycling of unlabeled methionine derived from protein degradation in brain; and (b) the metabolism of methionine is directed mainly towards protein synthesis. At normal plasma amino acid levels, methionine is the amino acid which, to date, presents the lowest degree of dilution in the precursor pool for protein synthesis. L-[35S]-Methionine, therefore, presents radiobiochemical properties required to measure, with minimal underestimation, rates of brain protein synthesis in vivo.

Animals↗

PubMed1991

Docosahexaenoic acid (cervonic acid) incorporation into different brain regions in the awake rat.

A quantitative method is presented to examine the localization, in individual brain regions of awake rats, of docosahexaenoic acid (22:6 n-3 or cervonic acid), the main polyunsaturated fatty acid of the nervous system together with arachidonic acid. Following the intravenous injection of 10 microCi [14C]22:6 n-3 (around 0.2 mumol/rat). 0.11-0.28% of the initial radioactivity was located in specific brain areas after detection from 10 to 240 min. Brain regional radioactivity determined by quantitative autoradiography indicated that 60 min after injection, [14C]22:6 n-3 concentrations ranged from 13.75 nCi/g of tissue in inferior olive to 5.59 nCi/g in frontal cortex. The results indicate a higher incorporation into the auditory system: inferior colliculus, central cochlear nucleus, lateral lemniscus, into neuroendocrine structures: paraventricular and supraoptic nuclei, and into certain circumventricular organs such as the pineal gland and neurohypophysis. Analysis of the Bligh and Dyer lipid extracts of rat brain revealed that 60 min after injection, 80-85% of the radioactivity was in choline and ethanolamine phosphoglycerides. These observations suggest that intravenous injection of [14C]22:6 n-3 may be used to study the brain lipid compartmental metabolism in vivo in order to visualize alterations of structural lipid components.

Animals↗

PubMed1991

Fatty acid composition of the rat pineal gland. Dietary modifications.

When compared to brain, the fatty acid composition of the rat pineal gland revealed that the total proportion of n-6 polyunsaturated fatty acids (PUFA) was 2.3-fold higher, whereas the proportion of n-3 fatty acids was similar. Specifically, 20:4(n-6) and 18:2(n-6) were respectively 1.56- and 11.80-fold higher in the pineal than in the brain, while the proportions of 22:6(n-3) were similar in both tissues. In addition, 18:1(n-9) was found 2.15-fold lower in the pineal. Feeding adult rats with fish oil concentrates induced a significant alteration of the polyunsaturated fatty acid composition of the pineal. There was a reciprocal replacement of the n-6 by the n-3 fatty acids. Conversely, in rats fed a n-3 fatty acid-deficient diet (sunflower oil or coconut oil diet), the pineal gland contained reduced proportions of n-3 fatty acids. We conclude that the pineal gland (i) differs from the brain in containing much higher proportions of 18:2(n-6) and from the other tissues for its high proportions of 22:6(n-3) and (ii) is highly sensitive to the n-3 fatty acid diet in contrast to what is known for the brain. These findings are discussed in the context of melatonin biosynthesis, the major hormone of the pineal gland.

Animals↗

PubMed1991

Detection of the release of 5-hydroxyindole compounds in the hypothalamus and the n. raphe dorsalis throughout the sleep-waking cycle and during stressful situations in the rat: a polygraphic and voltammetric approach.

In the present work, voltammetric method combined with polygraphic recordings were used in animals under long-term chronic conditions; the extracellular concentrations of 5-hydroxyindole compounds (5-OHles) and in particular 5-hydroxyindoleacetic acid (5-HIAA) were measured in the hypothalamus and in the nucleus Raphe Dorsalis (n.RD). The hypothesis that extracellular detection of 5-HIAA, in animals under physiological conditions, might reflect serotonin (5-HT) release is suggested by the following observations: serotoninergic neurons are reported to contain only monoamine oxidase type B (MAO-B);--an inhibitor of such an enzyme, MDL 72145 (1 mg/kg), fails to decrease the extracellular 5-HIAA peak 3 height:--MAO type A is contained in non-5-HT cells or neurons;--only the inhibitor of this last type of enzyme (Clorgyline 2.5 mg/kg) induces a complete disappearance of the voltammetric signal. The 5-HIAA measured in the extracellular space thus comes from the 5-HT released and metabolized outside the 5-HT neurons. Throughout the sleep-waking cycle, 5-OHles release occurs following two different modes: 1--during sleep, in the vicinity of the 5-HT cellular bodies in the n.RD; this release might come from dendrites and be responsible for the 5-HT neuronal inhibition occurring during sleep; 2--during waking, at the level of the axonal nerve endings impinging on the hypothalamus; this release might be related to the synthesis of "hypnogenic factors". Finally, we have observed that in the hypothalamus, 30 min. of immobilization-stress (IS) induces a larger increase of the voltammetric signal (+80%) than a painful stimulation of the same duration (+30%); the possible link between the 5-OHles release occurring in this area during an IS and the subsequent paradoxical sleep rebound is discussed.

Allylamine↗

PubMed1991

The role of 5-hydroxytryptophan (5-HTP) in the regulation of the sleep/wake cycle in parachlorophenylalanine (p-CPA) pretreated rat: a multiple approach study.

In the rat, the insomnia which follows the administration of parachlorophenylalanine (p-CPA), a serotonin synthesis inhibitor, is transiently reversed either by intra-cisternal injection of L-5-HTP or by an associated injection of 5-HTP and an L-aromatic-acid-decarboxylase inhibitor (benserazide). Histochemical, immunohistochemical and chemical investigations showed that 5-HTP administration does not lead to a detectable increase in cerebral 5-HT. These findings suggest that the restoration of sleep after p-CPA treatment could be mediated by the central action of 5-HTP.

5-Hydroxytryptophan↗

PubMed1991

[Brain protein synthesis in awake rats: equilibrium of L-methionine between plasma and direct precursor pool].

After 1 hr. of continuous infusion of L-(35S)methionine the specific activities of L-methionine in plasma and tissue-free and tRNA-bound L-methionine in brain were in the same range. This result indicates that, under steady-state conditions, dilution of the precursor pool for protein synthesis (L-methionyl-tRNA) by L-methionine derived from a source other than plasma can be considered as negligible.

Animals↗

PubMed1990

Time-course variations induced by pargyline on the 5-hydroxyindole compounds measured in the nucleus raphe dorsalis and in blood: a voltammetric and HPLC approach in the rat.

Ninety min after pargyline (Pargy, 75 mg/kg) injection, the +300 mV voltammetric signal, measured in the nucleus raphe dorsalis (nRD) of freely moving rats, disappeared completely. This effect was also followed (2-7 h post-injection) by the reappearance of a peak (post-Pargy-peak) at the same +300 mV potential. The height of this post-Pargy signal was still decreased by Pargy (30 or 75 mg/kg). Endogenous 5-hydroxyindoleacetic acid (5-HIAA) contents, measured with HPLC in the nRD of Pargy-treated rats, exhibited analogous variations. Inhibition of monoamine oxidases by Pargy seems thus to be effective in blocking 5-HIAA production over only 2 h. The 15-fold increase of 5-HT endogenous content in the nRD (3 h after injection) was not reflected in the voltammetric extracellular measurements performed 90 min to 7 h after Pargy injection; this increase is suspected to be mainly intracellular.

Animals↗

PubMed1990

Voltammetric detection of the release of 5-hydroxyindole compounds throughout the sleep-waking cycle of the rat.

In the present work, differential pulse voltammetry (DPV) measurements of the extracellular fraction of 5-hydroxyindole compounds were performed in rats under long-term chronic conditions. In the nucleus Raphe Dorsalis (n.RD), the voltammetric signal measured at +300 mv (peak 3) disappeared completely 70 to 90 min after injection of Clorgyline (10 mg/kg), a monoamine oxidase inhibitor type A (MAOI-A); the signal measured in such conditions is thus dependent upon extracellular 5-hydroxyindoleacetic acid (5-HIAA peak 3). Deprenyl, an MAOI type B, at the same dose, induced only a slight increase in peak 3 height; according to the fact that MAO-B is selectively located in the 5-HT neurons and since their inhibition does not decrease 5-HIAA peak 3 nor the endogenous 5-HIAA content as measured with High Performance Liquid Chromatography (HPLC), 5-HIAA measured with DPV in the extracellular fluid of untreated animals might come from 5-HT released and metabolized by MAO-A outside the 5-HT neurons. In animals implanted for measurements of both voltammetric and polygraphic parameters, the 5-HIAA peak 3 measured mainly in the anterior and ventral part of the n.RD exhibited large increases in its height during slow-wave sleep (SWS: +39%) and paradoxical sleep (PS = +71%) as compared to the waking state (W = 100%); these variations could reflect the dendritic release of 5-HT. In the Caudate nucleus (n.Cd) the same voltammetric signal presented reverse fluctuations, i.e. an increase during W and a decrease during SWS and PS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1990

Characterization of A-2 receptors in postmortem human pineal gland.

We have examined the binding of the adenosine agonist radioligands [3N]N6-cyclohexyladenosine ([3H]CHA) and [3H]5'-N-ethylcarboxamidoadenosine ([3H]NECA) to membranes prepared from postmortem human pineal glands. The results showed that the A-1-specific ligand CHA did not bind to membranes. By contrast, [3H]NECA, a nonselective A-1/A-2 ligand, gave 68% specific binding of the total binding. This specific binding was nearly insensitive to the N-ethyl-maleimide pretreatment method. To characterize this binding, we used cyclopentyladenosine (50 nM). Under those conditions [3H]NECA binding at 30 degrees C was rapid and reversible; the KD determined from the kinetic studies was 141 nM. In postmortem human pineal gland, the rank order of potency of adenosine analogues and drugs competing with [3H]NECA showed the specificity for an A-2 receptor: NECA greater than 2-chloroadenosine greater than L-N6(2-phenylisopropyl)adenosine greater than 8-phenyltheophylline greater than 3-isobutyl-1-methylxanthine greater than caffeine. Guanylylimidodiphosphate (100 microM) induced a decrease in the affinity of [3H]NECA, a result suggesting the involvement of a G protein mechanism in the coupling of the adenosine receptor to other components of the receptor complex. Scatchard analysis revealed one class of binding sites for [3H]NECA with KD and Bmax ranging from 175 to 268 nM and 11.0 to 14.1 pmol/mg protein, respectively. The binding of [3H]NECA was not affected by age, sex, or postmortem delay. [3H]NECA should be a useful tool to assess brain A-2 receptor density in a variety of neuropsychiatric disorders.

Adenosine↗

PubMed1989

Adenosine analogs elevate N-acetylserotonin and melatonin in rat pineal gland.

Adenosine, S-adenosyl-L-homocysteine, adenosine analogs such as 5'-N-ethylcarboxamidoadenosine and mioflazine, a nucleoside transport inhibitor, injected intraperitoneally at 09.00 h during the light period increased melatonin levels in the pineal gland of the rat. The largest increase occurred with 1 mg/kg 5'-N-ethylcarboxamidoadenosine. A representative time-response curve with 5'-N-ethylcarboxamidoadenosine (1 mg/kg) showed a maximal peak of N-acetylserotonin and melatonin 2 and 4 h after injection, respectively. These results are discussed in relation with the possible modulation through A2 receptors of melatonin synthesis in the pineal gland.

Adenosine↗

PubMed1989

Regulation of S-adenosyl methionine synthesis in the mouse embryo.

In early embryos, methylation is involved in "gamete imprinting" and inactivation of artificially introduced foreign genes. We studied the biosynthesis of the universal methylation cofactor: S-Adenosyl methionine (SAM). In the mouse, SAM conversion from methionine is limited by saturation of the methionine endogenous pool. SAM is present at a practically unchanged level from the unfertilized oocyte to early morula. SAM synthesis is increased at the time of compaction. In blastocysts, although methionine uptake is increased, the conversion rate from methionine is lowered. We observed no differences between C57 Black and Swiss albino random bred strains. In few experiments with human unfertilized oocytes and spared embryos, we observed higher methionine incorporation, and higher conversion to SAM. Next, the effect of two methylation inhibitors was tested, on early mouse embryonic development, at the one-cell and the two-cell stage. We found that ethionine is very toxic, even at the lowest tested concentration of 25 microM. Homocysteine is more potent at the one-cell stage than at the 2-cell stage, and it only partially blocks blastocyst formation from the 2-cell stage even at a concentration of 500 microM. It clearly acts as a methylation inhibitor; it lowers the SAM pool and the methylation index, SAH/SAM ratio (SAH: S-Adenosyl Homocysteine). We also found that homocysteine is an unexpected competitor for methionine influx and efflux.

Animals↗

PubMed1989

Identification of adenosine receptor in rat pineal gland: evidence for A-2 selectivity.

We have examined the binding of the adenosine agonist radioligands [3H]cyclohexyladenosine [( 3H]CHA), R-N6-[3H]phenylisopropyladenosine [( 3H]R-PIA), and 5'-N-ethylcarboxamido[3H]adenosine [( 3H]NECA) to membranes prepared from rat pineal gland. The results showed that the A-1-selective ligands (CHA and R-PIA) had less than or equal to 10% specific binding. By contrast, [3H]NECA, a nonselective A-1/A-2 ligand, gave 72% specific binding of the total binding. This specific binding was insensitive to cyclopentyladenosine (50 nM) or R-PIA (50 microM). To characterize this binding, we used the N-ethylmaleimide pretreatment method. Under these conditions, this binding was of high affinity with a KD of 51 +/- 10 nM and an apparent Bmax of 1,060 +/- 239 fmol/mg of protein. Specific binding was unaffected by the presence of MgCl2 (10 mM) but was sensitive to guanylylimidodiphosphate (100 microM) (-25%), a result suggesting the involvement of an N-protein mechanism in the coupling of the adenosine receptor labeled by [3H]NECA to other components of the receptor complex. The rank of activity of adenosine analogues in displacing specific [3H]NECA binding was NECA greater than 2-chloroadenosine greater than S-adenosyl-L-homocysteine greater than CHA. Binding was also displaced by 3-isobutyl-1-methylxanthine (IC50 = 23.6 microM). These findings are consistent with the selective labeling by [3H]NECA of an A-2-type adenosine receptor in rat pineal membranes.

2-Chloroadenosine↗

PubMed1989

S-adenosylmethionine, S-adenosylhomocysteine and adenosine system. Age-dependent availability in rat brain.

The changes in activity of N-methyltransferase 1 and [3H]-S-adenosylhomocysteine binding were determined in cortical membranes preparations from newborn and 1-, 2- and 10-month-old rats. These parameters were significantly higher: +130 and 200%, respectively, in 1-day compared to 2-month-old rats (adult). With maturation, S-adenosylmethionine levels decreased (-24%) whereas adenosine levels increased gradually from 0.17 to 6.10 nmol/mg protein in forebrain or whole brain between 1-day and 10-month-old rats. The ontogenesis of adenosine receptors was studied. The A2 receptors were not detectable at 1 day. For A1 receptors, Kd and Bmax increased with age while for A2 receptors Kd and Bmax were similar between 9 days and 2 months of age.

Adenosine↗

PubMed1989

[Role of hypothalamic adenosinergic systems in regulating states of wakefulness in the rat].

Immunohistochemical localization of adenosine deaminase (ADA), marker for the putative neurotransmitter/neuromodulator adenosine, has revealed a population of ADA-positive neurons in the ventrolateral hypothalamus in the rat brain. These posterior neurons possess adenosine uptake sites. We have studied the effects of local injections of adenosinergic drugs on the sleep-wake cycle in the rat. Microinjection of erythro-9-(hydroxy-2, nonyl-3) adenine (EHNA), a specific inhibitor of adenosine deaminase, resulted in a significant decrease in wakefulness (W) and an increase in deep slow wave sleep (SWS, or S2) and paradoxical sleep (SP). On the other hand, microinjections of soluflazine, a nucleoside transport inhibitor, increased W and decreased total sleep. These opposite modifications may reflect opposite variations in the extracellular concentrations of Ado and consequently different responses of A1/A2 adenosine receptors.

Adenine↗

PubMed1988

Changes in the rat sleep-wake cycle produced by D,L-beta-(1-naphthyl)alanine, a tryptophan analog.

The effects of i.p. injections of D,L-beta-(1-naphthyl)alanine, a synthetic analog of tryptophan were tested on the rat sleep-waking cycle. Administration of 30, 60 and 120 mg/kg resulted in a significant increase in slow-wave sleep (SWS) and a decrease in paradoxical sleep (PS). These modifications were dose-dependent. These results were compared with those previously obtained with L-tryptophan and several analogs and discussed in relation with possible changes in central serotonergic activity.

Alanine↗

PubMed1986

Possible involvement of the S-adenosyl-L-homocysteine metabolites, adenosine and L-homocysteine, in sleep in rats.

The effects of i.p. injections of adenosine (Ado) and homocysteine at 17.00 h were tested on the rat sleep-waking cycle. Administration of 7 and 50 mg/kg of Ado resulted in a significant increase in sleep in otherwise saline male rats during the environmental-dark period (18.00-06.00 h). Increments of paradoxical sleep were maximal with the smaller dose of Ado. The larger dose increased slow-wave sleep during the first 2 h. In contrast, administration of homocysteine (7 mg/kg) had no effect while a larger dose (50 mg/kg) induced a slight but significant long-lasting decrease of paradoxical sleep. These results were compared with those previously obtained with S-adenosyl-L-homocysteine (SAH), an intracellular precursor of Ado and L-homocysteine. It is proposed that the reported hypnotic action of exogenous SAH in rats could be mediated by Ado receptors.

Adenosine↗