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Biomedical subjects

G Pepeu

Publications and source records attributed to G Pepeu.

At least 91 records · Page 5Linked to original sources
PubMed1993

Effect of idebenone on adenosine outflow and adenine nucleotide level in hippocampal slices under ischemia-like conditions.

The effect of idebenone on the changes in adenosine and nucleotide metabolism occurring in hippocampal slices after ischemia-like conditions (superfusion with glucose-free Krebs solution gassed with 95% N2-5% CO2) and during reperfusion with normal Krebs solution was investigated by measuring adenosine and inosine outflow, and adenosine and adenine nucleotide levels by HPLC. Five minutes of ischemia-like conditions brought about an 8- and 4-fold increase in adenosine and inosine outflow 10 min after reperfusion and a 75% increase in the tissue level of adenosine, a 40% decrease in ATP, and a 50% increase in AMP at the end of the ischemic period. Ten minutes after reperfusion, ATP and AMP returned to control values. Idebenone (25-100 microM) brought about a concentration-dependent increase in adenosine and inosine outflow evoked by ischemia-like conditions. Idebenone (50 microM) also increased the adenosine content in hippocampal slices after both ischemia (+150%) and reperfusion (+320%). An 82% increase in ADP, 174% in AMP, and 56% in the total sum of nucleotides, 10 min after reperfusion were found in idebenone treated slices. These results suggest that idebenone enhances adenosine formation after ischemia-like conditions from sources other than AMP, and improves phosphorylating activity during reperfusion. Idebenone, by increasing adenosine and total nucleotide levels, may protect brain tissue from ischemic damage.

Adenine Nucleotides↗
PubMed1993

Effect of K+ depolarization, tetrodotoxin, and NMDA receptor inhibition on extracellular adenosine levels in rat striatum.

Extracellular adenosine in the striatum of adult male rats was measured by the use of a microdialysis fibre inserted transversely in the striatum. The adenosine concentration in samples of perfusate was determined by HPLC coupled to U.V. detection. The adenosine concentration (corrected for recovery) decreased after implantation of the probe. Two hours later it was 1.83 +/- 0.22 in anaesthetized rats, whereas it was 40% higher in rats in which anaesthesia had been discontinued. Twenty-four hours later the adenosine concentration was 0.124 +/- 0.09 microM; the addition of dipyridamole (100 microM), an adenosine uptake blocker, to the perfusate resulted in a 76% increase in adenosine concentration in the effluent, whereas addition of the adenosine deaminase inhibitor erythro-2-(hydroxy-3-nonyl) adenine (100 microM) caused a 260% increase. The addition of tetrodotoxin (1 microM) was followed by a decrease in basal adenosine concentration and a partial inhibition of the increase in adenosine evoked by K+ depolarization. The increase induced by high K+ was markedly inhibited by the NMDA receptor antagonist D(-)-amino-7-phosphoeptanoic acid (1 mM, D-AP7). These findings indicate that the extracellular adenosine level is influenced by neuronal activity, and that under strong depolarizing conditions the increase in adenosine level involves NMDA receptor activation.

2-Amino-5-phosphonovalerate↗
PubMed1993

Lesions of the nucleus basalis magnocellularis in immature rats: short- and long-term biochemical and behavioral changes.

Short- and long-term effects of unilateral lesions of the nucleus basalis magnocellularis (NBM) on cortical choline acetyltransferase (ChAT) activity and passive avoidance conditioned responses were examined in immature rats. The lesions were made by stereotaxic injection of quisqualic acid on postnatal days 14 (P14), 17 (P17), and 21 (P21). A marked loss of ChAT activity was found 7 days after surgery in all age groups of lesioned rats. Unoperated P14 rats were unable to perform the passive avoidance conditioned responses. Acquisition began on P17. Lesions made on P17 and P21 strongly impaired the acquisition and retention of the task, evaluated 7 days postoperation. No biochemical but a partial behavioral recovery was observed 3 months after surgery in rats lesioned on P14. On the contrary, despite a persistent decrease in cortical ChAT activity, rats lesioned on P21 were able to acquire and retain the passive avoidance conditioned response. These results indicate that destruction of NBM cholinergic neurons shortly after birth is not compensated for by the developmental plasticity of the residual neurons but results in permanent cholinergic hypofunction. They also demonstrate that cholinergic NBM neurons play an important role in the acquisition and retention of a passive avoidance task; nevertheless, a behavioral recovery may take place 3 months after the lesion, even in the presence of a persistent cholinergic hypofunction.

Animals↗
PubMed1993

Long-term ethanol consumption by rats: effect on acetylcholine release in vivo, choline acetyltransferase activity, and behavior.

The extent and duration of cholinergic hypofunction induced by long-term ethanol consumption was investigated in the rat. Ethanol (20% v/v) was administered to male adult Wistar rats as a sole source of fluid for three or six months. Control rats received tap water. The body weight, food and fluid intake in ethanol-treated rats were lower than in control rats throughout the treatment. After three months of ethanol consumption, and one week withdrawal, acetylcholine release in freely moving rats, investigated by microdialysis technique coupled to high-performance liquid chromatography quantification, was significantly decreased by 57 and 32% in the hippocampus and cortex, respectively, while choline acetyltransferase activity was significantly decreased (-30%) only in the hippocampus. A complete recovery of choline acetyltransferase activity and acetylcholine release was found after four ethanol-free weeks. Conversely, after four weeks of withdrawal following six months of ethanol treatment, the recovery in acetylcholine release was not accompanied by that in choline acetyltransferase activity, which remained significantly lower than in control rats in both cortex and hippocampus. The ability of rats to negotiate active and passive avoidance conditioned response tasks, tested after four ethanol-free weeks, was strongly impaired in both three- and six-month ethanol-treated rats. In conclusion, our experiments demonstrate that the development of a long-lasting cholinergic hypofunction requires at least six months of ethanol administration. The hypofunction affects choline acetyltransferase activity and acetylcholine release differently, and undergoes a remarkable recovery.

Acetylcholine↗
PubMed1993

Investigations into the adenosine outflow from hippocampal slices evoked by ischemia-like conditions.

The characteristics of adenosine and inosine outflow evoked by 5 min of ischemia-like conditions in vitro (superfusion with glucose-free Krebs solution gassed with 95% N2/5% CO2) were investigated on rat hippocampal slices. The viability of the slices after "ischemia" was evaluated by extracellular recording of the evoked synaptic responses in the CA1 region. The evoked dendritic field potentials were abolished after 5 min of superfusion under "ischemia" but a complete recovery occurred after 5 min of reperfusion with normal oxygenated Krebs solution. No recovery took place after 10 min of "ischemia." The addition of the adenosine A1 receptor antagonist 8-phenyltheophylline to the superfusate antagonized the depression of the evoked field potentials caused by 5 min of "ischemia." Five minutes of "ischemia" brought about a six- and fivefold increase in adenosine and inosine outflow, respectively, within 10 min. Tetrodotoxin reduced the outflow of adenosine and inosine by 42 and 33%, respectively, whereas the removal of Ca2+ caused a further increase. The NMDA receptor antagonist D(-)-2-amino-7-phosphonoheptanoic acid and the non-NMDA antagonist 6,7-dinitroquinoxaline-2,3-dione brought about small, not statistically significant decreases of adenosine and inosine outflow. The glutamate uptake inhibitor dihydrokainate did not affect the outflow of adenosine and inosine. Inhibition of ecto-5'-nucleotidase by alpha,beta-methylene ADP and GMP did not affect basal adenosine outflow but potentiated "ischemia"-evoked adenosine outflow. It is concluded that ischemia-like conditions in vitro evoke a Ca(2+)-independent adenosine and inosine outflow, through a mechanism that partly depends on propagated nervous activity but does not involve excitatory amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)

5'-Nucleotidase↗
PubMed1993

The brain cholinergic system in ageing mammals.

The complex picture of age-associated brain cholinergic deficiency in humans and animals, and the possibilities of correcting it, are presented in this article. The changes that occur during ageing and senile dementias in cholinergic neurones and receptors and in the release and synthesis of acetylcholine are described and discussed. The drugs that have so far been administered to humans to correct cholinergic deficiency are listed and the effects of cholinesterase inhibitors, nerve growth factor and phosphatidylserine are discussed in some detail.

Acetylcholine↗
PubMed1992

Effect of scopolamine and nootropic drugs on rewarded alternation in a T-maze.

The effects of different doses of scopolamine, and of the nootropic drugs oxiracetam and aniracetam, were investigated on the performance of male Wistar rats in a T-maze requiring a spatial discrimination in the stem (reference memory) and an alternate discrimination in the arms (working memory). Criterion (90% correct responses) was reached within 3 days of daily training for stem and 9 days for arm discrimination. Scopolamine (0.1, 0.2, 0.6, and 1.0 mg/kg, SC, 60 min before session) significantly impaired working memory, as shown by a decrease in the number of correct alternations, without affecting reference memory. Both nootropic drugs (25-50 and 100 mg/kg PO) 30 min before scopolamine) attenuated the working memory impairment induced by scopolamine.

Animals↗
PubMed1992

Serotonin blocks the long-term potentiation induced by primed burst stimulation in the CA1 region of rat hippocampal slices.

The effect of 5-hydroxytryptamine on the induction of long-term potentiation by a train of high frequency pulses (100 Hz; 1 s) or by a stimulation consisting of one burst of five pulses at 100 Hz delivered 170 ms after a single pulse (primed burst) was investigated in the CA1 region of the rat hippocampal slice in vitro with extracellular recordings. Superfusion with 5-hydroxytryptamine (3-30 microM) produced a concentration-dependent decrease in amplitude of the population spikes evoked by test stimuli. The presence of 5-hydroxytryptamine (30 microM) did not affect the magnitude of long-term potentiation produced by the high-frequency stimulation but it prevented the long-term potentiation induced by a primed burst. The action of 5-hydroxytryptamine was mimicked by the 5-hydroxytryptamine1A agonist 5-carboxamidotryptamine (0.3 microM) and blocked by the 5-hydroxytryptamine2/5-hydroxytryptamine1A antagonist spiperone (3 microM) or by the 5-hydroxytryptamine1/5-hydroxytryptamine2 antagonist methiothepin (1-10 microM). The selective 5-hydroxytryptamine2 antagonist ritanserin (1 microM) did not antagonize the block of long-term potentiation produced by 5-hydroxytryptamine. The selective 5-hydroxytryptamine3 antagonists (3-tropanyl)-1H-indole-3-carboxylic acid ester (ICS 205-930; 1 nM) and ondansetron (GR-38032; 30 nM) did not affect the reduction in the population spike produced by application of 5-hydroxytryptamine. In contrast, a primed burst delivered at the fifth minute of 5-hydroxytryptamine application in the presence of a 5-hydroxytryptamine3 antagonist induced a long-term potentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Release of endogenous glutamate and aspartate from the frog spinal cord in vitro.

The release of the endogenous excitatory amino acids aspartate and glutamate from an in vitro slice preparation of the frog spinal cord was investigated by using high performance liquid chromatography (HPLC). Spinal slices were incubated at 4 degrees C to minimize amino acid uptake; samples of the bathing solution were collected at 10 min intervals for amino acid assay. In each experiment electrophysiological responses were recorded continuously from ventral roots after stimulation of an adjacent dorsal root, so that changes in the profile of amino acid release could be correlated with electrophysiological responses. At rest the release of glutamate and aspartate was 52.9 +/- 5.8 and 66.9 +/- 5.6 pmol/10 min, respectively, and was unaffected by low Ca2+ media or tetrodotoxin. After trains of high frequency stimulation applied to a dorsal root the release of glutamate and aspartate was significantly and reproducibly enhanced by 33 +/- 13 and 49 +/- 18%, respectively. The stimulus-dependent release was blocked by low Ca2+ media, tetrodotoxin or topical application of the neuropeptide thyrotropin releasing hormone. The present study provides direct evidence to support the role of glutamate and aspartate as neurotransmitters in the spinal cord.

Animals↗
PubMed1991

Phosphatidylserine reverses the age-dependent decrease in cortical acetylcholine release: a microdialysis study.

In vivo basal acetylcholine (ACh) and choline (Ch) output from the parietal cortex of 3- and 19-month-old freely moving rats was measured by microdialysis. A dialysis tubing was inserted transversally through the parietal cortex 24 h before the experiment. ACh and Ch concentrations were determined in the same perfusate samples by HPLC with electrochemical detection. In 19-month-old rats treated with Tris buffer, ACh and Ch outputs were 39 and 16% lower, respectively, than in 3-month-old rats. Phosphatidylserine (PtdSer) administration (15 mg/kg i.p. daily) for 8 days to 19-month-old rats markedly attenuated the decrease in ACh release. The same treatment did not affect ACh and Ch outputs in 3-month-old rats. ACh and Ch outputs in 19-month-old rats administered either phosphatidylcholine (PtdCho) or o-phospho-dl-serine (P-Ser) (15 mg/kg i.p. daily) for 8 days were as low as in 19-month-old rats receiving Tris buffer only. It is possible that chronic PtdSer treatment improve ACh release in aging rats by increasing the availability of Ch for ACh synthesis.

Acetylcholine↗
PubMed1991

Endogenous adenosine release from hippocampal slices: excitatory amino acid agonists stimulate release, antagonists reduce the electrically-evoked release.

The effect of excitatory amino acids and their antagonists on adenosine and inosine release has been investigated on unstimulated and electrically stimulated hippocampal slices. On unstimulated slices N-methyl-D-aspartate (NMDA), quisqualate and glutamate concentration-dependently evoked the release of adenosine and inosine. The effect of NMDA and quisqualate was antagonized by the NMDA receptor antagonist D(-)-2-amino-7-phosphonoheptanoic acid (D-AP7; 100 mumol/l) and the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX; 10 mumol/l) respectively. Glutamate (2 and 10 mmol/l)-evoked adenosine and inosine release was not antagonized by the NMDA and non-NMDA receptor antagonists indicating that the effect of glutamate is due to a metabolic rather than a receptor-mediated effect. Electrical field stimulation at 10 Hz also evoked a release of endogenous adenosine and inosine. Tetrodotoxin (0.5 mumol/l) abolished and absence of Ca2+ markedly reduced the electrically evoked release of adenosine and inosine. Adenosine and inosine release evoked by electrical stimulation at 20 Hz was significantly reduced in the presence of the NMDA receptor antagonist D-AP7, while at 10 Hz no consistent decrease was seen. In the presence of D-AP7 plus DNQX the 10 Hz-evoked adenosine and inosine release was reduced to about half. These data suggest that the electrically evoked release of adenosine and inosine is partly mediated by the release of excitatory amino acids which act at both non-NMDA and NMDA receptors.

Adenosine↗
PubMed1991

A decrease in brain catecholamines prevents oxiracetam antagonism of the effects of scopolamine on memory and brain acetylcholine.

The effect of oxiracetam on passive avoidance conditioned response and acetylcholine (ACh) levels in rats with selective lesions of the central monoaminergic pathways was investigated. The lesions were followed by a marked decrease in cortical serotonin (-88%), noradrenaline (-54%) and striatal dopamine (-57%) levels, while neither the performance of a passive avoidance conditioned response nor brain ACh levels were affected. Scopolamine (hyoscine) administration (0.63 mg/kg, s.c.) to lesioned rats exerted the expected amnesic effect, associated with a decrease in hippocampal, cortical and striatal ACh levels. In the rats with degeneration of dopaminergic and noradrenergic but not serotoninergic pathways, oxiracetam (50 and 100 mg/kg, s.c.) was unable to prevent both amnesia and the decrease in brain ACh levels caused by scopolamine. The effect of oxiracetam was prevented by haloperidol (0.2 mg/kg, s.c.). Our findings support the hypothesis that an interaction between monoaminergic and cholinergic neurotransmitter systems may be involved in the actions of nootropic drugs on cognitive functions.

Acetylcholine↗
PubMed1991

Effect of thyrotropin releasing hormone (TRH) on acetylcholine release from different brain areas investigated by microdialysis.

1. The effect of thyrotropin releasing hormone (TRH) administration upon acetylcholine (ACh) release in freely moving rats was investigated by means of transversal microdialysis coupled to h.p.l.c. TRH administered either s.c. or via local perfusion increased the ACh release from cortex and hippocampus but not from the striatum. The increase in ACh release was maintained after 7 days of s.c. administration of TRH. 2. After s.c. injection of the neuropeptide, the increase in ACh release was dose-dependent and reached a maximum at 40 min after administration. The maximal percentage increases were 18, 52, 66 and 89% at doses of 1, 2.5, 5 and 10 mg kg-1 and 35, 48 and 54% at doses of 2.5, 5 and 10 mg kg-1 in the cortex and hippocampus, respectively. The effect of TRH was dependent on neuronal activity since it was completely inhibited by perfusion with tetrodotoxin (TTX), 5 X 10(-7) M. 3. Perfusion with TRH, 2.5 micrograms microliters-1, caused 198% and 150% increase in ACh release 60 and 80 min after the beginning of the perfusion in the cortex and hippocampus, respectively. After this initial peak, a 100% increase in ACh release persisted throughout the perfusion. 4. Systemic TRH administration was followed by marked hyperactivity and stereotyped behaviour that showed a time course shorter than that of the increase in ACh release. 5. These findings demonstrate that TRH exerts a strong stimulant action on cortical and hippocampal cholinergic pathways.

Acetylcholine↗
PubMed1990

Regional differences in the electrically stimulated release of endogenous and radioactive adenosine and purine derivatives from rat brain slices.

The release of both radioactive and endogenous purines was investigated in rat brain cortical, hippocampal and striatal slices at rest and following stimulation with electrical fields. Purines were labelled by incubating the slices with 3H-adenine. The purine efflux at rest and that evoked by electrical stimulation (10 Hz. 5 min) was analyzed by HPLC with ultraviolet absorbance detection. Both radioactive and endogenous purines in the effluent consisted mainly of hypoxanthine, xanthine, inosine and adenosine. No qualitative differences in the composition of the released purines were found in the three areas investigated. Electrical stimulation evoked a net increase in both radioactive and endogenous purine release. However the increase in 3H-adenosine following electrical stimulation was twice as large as that of endogenous adenosine. The electrically evoked release of both radioactive and endogenous purines was greatest in hippocampal slices and progressively smaller in cortical and striatal slices. In the three areas the addition of 0.5 microM tetrodotoxin to the superfusing Krebs solution brought about a similar (83-100%) reduction in evoked 3H-purine and endogenous purine release. Superfusion of the slices with calcium-free Krebs solution containing 0.5 mM EGTA reduced evoked release of 3H-purines by 58-60% and that of endogenous purine components by 54-89%. The results demonstrate similar characteristics for both radioactive and endogenous purine release but indicate that the most recently synthetized adenosine is the most readily available for release. The features of the electrically evoked purine release support a neuronal origin of adenosine and derivatives and are consistent with the hypothesis of discrete regional differences in adenosine neuromodulation.

Adenosine↗
PubMed1990

Oxiracetam and D-pyroglutamic acid antagonize a disruption of passive avoidance behaviour induced by the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovalerate.

Intracerebroventricular administration (6 micrograms/2 microliters) of D-2-amino-5-phosphonovalerate (AP-5), a specific antagonist of the NMDA receptors, prior to training impaired the passive avoidance in a retention test in rat. Pretreatment with oxiracetam and D-pyroglutamic acid at doses ranging from 50 to 500 mg/kg SC dose-dependently prevented the disruptive effect of AP-5. This finding indicates that an interaction with excitatory amino acid NMDA type receptors may be important in behavioural effects of the two pyrrolidinone derivatives.

Animals↗