Search PubMed⌕ Search

Biomedical subjects

G Pepeu

Publications and source records attributed to G Pepeu.

At least 37 records · Page 2Linked to original sources
PubMed1999

Striatal A2A adenosine receptors differentially regulate spontaneous and K+-evoked glutamate release in vivo in young and aged rats.

The effect of the adenosine A2A receptor agonist CGS 21680 on glutamate and aspartate release was investigated in the striatum of young and old rats by microdialysis experiments. CGS 21680 (10 microM) significantly increased glutamate and aspartate spontaneous outflow in young but not in old rats. On the contrary, CGS 21680 induced the same decrease in K+-evoked glutamate outflow in both young and aged rats. A lower dose of CGS 21680 (1 microM) failed to modify either spontaneous or K+-evoked outflow. It is suggested that the opposite effects of the A2A agonist on excitatory amino acid outflow may be respectively mediated by striatal A2A adenosine receptors located on glutamatergic terminals and on the striatal indirect output pathway.

Adenosine↗
PubMed1999

Effects of novelty and pain on behavior and hippocampal extracellular ACh levels in male and female rats.

In vivo microdialysis was used to assess the effects of novelty and pain on hippocampal ACh release in male and female rats. Experiments were carried out during the dark phase and consisted of 2 days of tests: on Day 1, after Baseline 1, animals were exposed to a new cage (Novelty) to which, 30 min later, a plastic cylinder (Object) was introduced. On Day 2, after Baseline 2, the Formalin test (50 microl of formalin 10%, s.c. injected in the dorsal hindpaw) was carried out in the animal's home cage. All behaviors were recorded. The extracellular levels of ACh in the dorsal hippocampus were estimated, in 10-min samples, by assay of ACh in the dialysates by HPLC. On Day 1 the raw values of ACh were higher in females than in males, but no sex difference was present when the percentage of change was considered. In both sexes the Novelty and Object tests induced an increase in ACh levels with respect to Baseline. Higher levels of exploration were present in females than males during the first 10 min of Novelty. On Day 2, ACh release increased in both sexes during the Formalin test. No sex difference in either ACh raw values or the percentages of change were found. Females showed higher levels of licking and lower levels of activity than males. The present study shows that novelty and pain induce similar hippocampal cholinergic activation in male and female rats but different behaviors. The results are discussed in light of the several anatomical and functional sex differences present in the hippocampus.

Acetylcholine↗
PubMed1999

Peripheral administration of novel anti-inflammatories can attenuate the effects of chronic inflammation within the CNS.

In the present study we investigated whether nitroflurbiprofen (NFP) or nitro-aspirin can reduce the inflammatory response induced by continuous infusion of lipopolysaccharide (LPS) into the fourth ventricular space of the rat's brain for 30 days. The chronic LPS infusion produced an extensive inflammation that was particularly evident in the hippocampus, subiculum and entorhinal and piriform cortices. Daily peripheral administration of NFP dose-dependently, and significantly, attenuated the brain inflammation as indicated by the decreased density and reactive state of microglial cells. Daily peripheral administration of nitro-aspirin also attenuated the brain inflammation, but to a much lesser degree than NFP. The results demonstrated that nonsteroidal anti-inflammatory drugs (NSAIDs) could reduce brain inflammation and that NFP is an effective anti-inflammatory agent.

Animals↗
PubMed1999

Systemic chlorophenylpiperazine increases acetylcholine release from rat hippocampus-implication of 5-HT2C receptors.

The release of acetylcholine (ACh) from the hippocampus of freely moving rats was studied after the systemic and local administration of the 5-HT agonist chlorophenylpiperazine (mCPP), utilising the in vivo microdialysis coupled to HPLC. Intraperitoneally (i.p.) given mCPP at a dose of 8 mg kg(-1)increased the release of ACh from the hippocampus by approximately 96%. This effect was not observed when the agonist was delivered locally through the dialysis tube (reverse dialysis). The mCPP-induced increase of ACh release was prevented by i.p. mesulergine, a 5-HT2A/2C receptor antagonist, at a dose of 2 mg kg(-1). A similar effect was found with the i.p. administration of isoteoline-a putative serotonergic antagonist. Both mesulergine and isoteoline have been shown to prevent also the mCPP-induced increase of ACh release from rat cortex. In the cortex experiments both antagonists were inactive by themselves. In the hippocampus, however, isoteoline, unlike mesulergine, increased significantly the output of ACh when used alone. This effect was haloperidol-sensitive, which implies a possible dopaminergic mechanism. The results of the present work suggest that (i) the effect of mCPP on ACh release could be attributed to stimulation of 5-HT2C receptors located outside the hippocampus and (ii) isoteoline antagonizes this mCPP-induced effect irrespective of its own enhancing action on ACh release.

Acetylcholine↗
PubMed1999

Adenosine and memory storage: effect of A(1) and A(2) receptor antagonists.

RATIONALE: Caffeine is a non-selective A(1)/A(2 )adenosine receptor antagonist which is known to improve cognitive performance in humans. This effect of caffeine has been attributed to its antagonism of adenosine receptors. OBJECTIVE: The present study was devised to identify the role of A(1 )and A(2A) adenosine receptors in the facilitation of memory consolidation in mice performing a passive avoidance task. METHODS: Adult albino Swiss male mice were used. The mice were trained in a step-through inhibitory avoidance task in which they were punished by a foot-shock (0.4 mA, 5 Hz, for 3 s) delivered through the grid floor. Caffeine (0.1, 0.3, 1.0 and 3.0 mg/kg), SCH 58261 (0.1, 0.3, 1.0 and 3.0 mg/kg) and DPCPX (0.1, 0.3, 1.0 and 3.0 mg/kg) were injected IP immediately or 180 min after training. The retention test was performed 24 h after training. RESULTS: Caffeine and the selective A(2A) adenosine receptor antagonist SCH 58261 facilitated retention when administered immediately after training, but not when administered 180 min later. The dose response was a bell-shaped curve. Conversely, post-training administration of the selective A(1) adenosine receptor antagonist DPCPX did not affect retention. Caffeine and SCH 58261 had no effect in mice not given the foot-shock on the training trial, a finding indicating that the drug's effect on retention was specific. CONCLUSIONS: These results suggest that A(2A) but not A(1) adenosine receptors are involved in memory retention and consolidation.

Adenosine↗
PubMed1999

Interleukin-1beta activates forebrain glial cells and increases nitric oxide production and cortical glutamate and GABA release in vivo: implications for Alzheimer's disease.

Interleukin-1beta (10 U) was injected into the nucleus basalis of adult male Wistar rats. The inflammation-induced changes in glial cell morphology and expression of inducible nitric oxide synthase in the injected area, the release of acetylcholine, GABA and glutamate from the ipsilateral cortex, the production of nitrite levels in the injected area and ipsilateral cortex, and changes in motor activity were investigated. Saline-injected rats were used as control. Interleukin-1beta induced an activation of both microglia and astrocytes which was already evident 24 h after injection. Seven days after injection, many reactive microglial cells and astrocytes were seen in the injected area and in other brain regions of the same hemisphere. Microglia reaction, but not astrocyte activation, disappeared 30 days post-injection. Seven days after interleukin-1beta injection, many cells immunopositive for inducible nitric oxide synthase were found surrounding the injection site. Inducible nitric oxide synthase-positive cells were identified, by double staining immunohistochemistry, in the reactive microglial cells and, by electron microscope examination, in the perineuronal subpopulation of resident activated microglia. Microdialysis investigations revealed a transient increase in reactive nitrogen intermediates (at seven days post-injection), a delayed (at 30 days post-injection) increase in GABA and glutamate release, and no changes in acetylcholine release in the ipsilateral cortex in interleukin-1beta, but not saline, injected rats. Inhibition of inducible nitric oxide synthase expression by N(G)-nitro-L-arginine methyl ester administration prevented the increase in nitrogen intermediates and GABA release, but not in glutamate release. Our findings suggest that an inflammatory reaction of the basal forebrain facilitates GABA release through the production of nitric oxide.

Acetylcholine↗
PubMed1999

Effect of A2A adenosine receptor stimulation and antagonism on synaptic depression induced by in vitro ischaemia in rat hippocampal slices.

1. In the present study we investigated the role of A2A adenosine receptors in hippocampal synaptic transmission under in vitro ischaemia-like conditions. 2. The effects of adenosine, of the selective A2A receptor agonist, CGS 21680 (2-[p-(2-carboxyethyl)-phenethylamino]-5'-N-ethylcarboxamidoade nos ine ), and of selective A2A receptor antagonists, ZM 241385 (4-(2-[7-amino-2-(2-furyl)-¿1,2,4¿-triazolo¿2,3-a¿¿1,3, 5¿triazin-5-ylamino]ethyl)phenol) and SCH 58261 (7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2, 4-triazolo[1,5-c]pyrimidine), have been evaluated on the depression of field e.p.s.ps induced by an in vitro ischaemic episode. 3. The application of 2 min of in vitro ischaemia brought about a rapid and reversible depression of field e.p.s.ps, which was completely prevented in the presence of the A1 receptor antagonist DPCPX (1, 3-dipropyl-8-cyclopentylxanthine) (100 nM). On the other hand both A2A receptor antagonists, ZM 241385 and SCH 58261, by themselves did not modify the field e.p.s.ps depression induced by in vitro ischaemia. 4. A prolonged application of either adenosine (100 micronM) or CGS 21680 (30, 100 nM) before the in vitro ischaemic episode, significantly reduced the synaptic depression. These effects were antagonized in the presence of ZM 241385 (100 nM). 5. SCH 58261 (1 and 50 nM) did not antagonize the effect of 30 nM CGS 21680 on the ischaemia-induced depression. 6. These results indicate that in the CA1 area of the hippocampus the stimulation of A2A adenosine receptors attenuates the A1-mediated depression of synaptic transmission induced by in vitro ischaemia.

Adenosine↗
PubMed1999

Striatal outflow of adenosine, excitatory amino acids, gamma-aminobutyric acid, and taurine in awake freely moving rats after middle cerebral artery occlusion: correlations with neurological deficit and histopathological damage.

BACKGROUND AND PURPOSE: While a number of studies have investigated transmitter outflow in anesthetized animals after middle cerebral artery occlusion (MCAO) performed by craniectomy, studies have never been performed after MCAO induced by intraluminal filament. In addition, it has been reported that after MCAO, infarct volume correlates with functional outcome and with transmitter outflow, although there are no studies that demonstrate a direct correlation between transmitter outflow and functional outcome. The purpose of the present study was to assess excitatory amino acids, gamma-aminobutyric acid, taurine, and adenosine outflow in awake rats after intraluminal MCAO and to determine whether, in the same animal, outflow was correlated with neurological outcome and histological damage. METHODS: Vertical microdialysis probes were placed in the striatum of male Wistar rats. After 24 hours, permanent MCAO was induced by the intraluminal suture technique. The transmitter concentrations in the dialysate were determined by high-performance liquid chromatography. Twenty-four hours after MCAO, neurological deficit and histological outcome were evaluated. RESULTS: All transmitters significantly increased after MCAO. Twenty-four hours after MCAO, the rats showed a severe sensorimotor deficit and massive ischemic damage in the striatum and in the cortex (9+/-2% and 25+/-6% of hemispheric volume, respectively). Significant correlations were found between the efflux of all transmitters, neurological score, and striatal infarct volume. CONCLUSIONS: In this study, for the first time, amino acid and adenosine extracellular concentrations during MCAO by the intraluminal suture technique were determined in awake and freely moving rats, and a significant correlation was found between transmitter outflow and neurological deficit. The evaluation of neurological deficit, histological damage, and transmitter outflow in the same animal may represent a useful approach for studying neuroprotective properties of new drugs/agents against focal ischemia.

Adenosine↗
PubMed1998

Effect of subchronic treatment with metrifonate and tacrine on brain cholinergic function in aged F344 rats.

The effects of 21-day treatment with the acetylcholinesterase inhibitors metrifonate (80 mg kg(-1) per os (p.o.)) and tacrine (3 mg kg(-1) p.o.), twice daily, on cortical and hippocampal cholinergic systems were investigated in aged rats (24-26 months). Extracellular acetylcholine levels were measured by transversal microdialysis in vivo; choline acetyltransferase and acetylcholinesterase activities were measured ex vivo by means of radiometric methods. Basal cortical and hippocampal extracellular acetylcholine levels, measured 18 h after the last metrifonate treatment, were about 15 and two folds higher, respectively, than in control and tacrine-treated rats. A challenge with metrifonate further increased cortical and hippocampal acetylcholine levels by about three and four times, respectively. Basal extracellular acetylcholine levels, measured 18 h after the last treatment with tacrine were not statistically different from those of the control rats. A challenge with tacrine increased cortical and hippocampal extracellular acetylcholine levels by about four and two times. A 75% inhibition of cholinesterase activity was found 18 h after the last metrifonate administration, while only a 15% inhibition was detectable 18 h after the last tacrine administration. The challenge with metrifonate or tacrine resulted in 90 and 80% cholinesterase inhibition, respectively. These results demonstrate that in aging rats a subchronic treatment with metrifonate results in a long-lasting, cholinesterase inhibition, and a persistent increase in acetylcholine extracellular levels which compensate for the age-associated cholinergic hypofunction. Metrifonate is therefore a potentially useful agent for the cholinergic deficit accompanying Alzheimer's disease.

Acetylcholine↗
PubMed1998

Temporal correlation between adenosine outflow and synaptic potential inhibition in rat hippocampal slices during ischemia-like conditions.

The temporal correlation between adenosine outflow and changes in field excitatory post synaptic potentials (fEPSP) occurring during ischemia-like conditions was investigated in rat hippocampal slices. Five-minute long ischemia-like conditions resulted in a 100% depression of fEPSP amplitude, followed by a complete recovery after 6-7 min of reperfusion. By reducing the duration of the ischemic insult to 2 min, fEPSP was depressed by 50%. During both 5 and 2 min of ischemia-like conditions, a significant increase in adenosine outflow was detected. During reperfusion, when fEPSP amplitude recovered completely, the adenosine level in the extracellular fluid returned to basal values. The strict relationship between the increase in adenosine outflow and fEPSP inhibition supports the hypothesis that adenosine is largely responsible for the synaptic transmission depression during cerebral ischemia.

Adenosine↗
PubMed1998

Activation of non-NMDA receptors stimulates acetylcholine and GABA release from dorsal hippocampus: a microdialysis study in the rat.

The effect of the non-N-methyl-D-aspartate (NMDA) agonists (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and quisqualate (QUIS) on the release of acetylcholine (ACh), gamma-amino butyric acid (GABA), aspartate (Asp) and glutamate (Glu) from the hippocampus of freely moving rats was studied by transversal microdialysis. Intracerebroventricular (i.c.v.) administration of the non-NMDA receptor agonist AMPA (0.5 nmol) enhanced (by about 200%) ACh release from the hippocampus. The effect of AMPA was completely antagonized by 6-nitro-7-sulphamoyl-benz(f)quinoxaline-2,3-dione (NBQX; 2 nmol, i.c.v). No effect was seen when AMPA was perfused through the septum. However, AMPA (200 microM) locally applied to the hippocampus, increased (by about 200%) ACh release. QUIS (200 microM) applied locally to the hippocampus produced a long-lasting increase in the release of ACh (by about 215%) and GABA (by about 460%). Local infusion of tetrodotoxin (1 microM) decreased ACh and GABA basal extracellular levels, and abolished the QUIS-induced increase in ACh and GABA. Our results demonstrate that non-NMDA glutamatergic receptors in the hippocampus regulate hippocampal release of GABA and ACh.

Acetylcholine↗
PubMed1998

Acetylcholine release from the frontal cortex during exploratory activity.

The activation of the cortical cholinergic system was investigated in 3- and 25-month-old male Wistar rats, by measuring by transversal microdialysis the changes in cortical extracellular acetylcholine (ACh) levels during the performance of simple spontaneous tasks involving exploratory activity and working memory. Two days after implantation of the microdialysis probe in the frontal cortex, object recognition was investigated by either moving the rats from the home cage to the arena containing the objects or keeping the rats in the arena and introducing the objects. Spontaneous alternation was investigated in a Y runway. Young rats discriminated between familiar and novel objects and alternated in the Y runway, while aged rats were unable to discriminate. Whenever rats were moved from the home cage to the arena, ACh release increased (+70-80%) during the exploratory activity. Handling per se had no effect on extracellular ACh levels. When young rats were left in the arena, introduction of the objects caused some exploratory activity and object recognition but no increase in ACh release. ACh release increased by about 300% during spontaneous alternation. In aging rats basal extracellular ACh levels and their increase after placement in the arena were less than half that in young rats. Our work demonstrates that a novel environment activates the cortical cholinergic system, which presumably is associated with arousal mechanisms and selective attentional functions. It also demonstrates that in aging rats the cortical cholinergic hypofunction is associated with a loss of non-spatial working memory.

Acetylcholine↗
PubMed1998

C-fos expression in the rat nucleus basalis upon excitotoxic lesion with quisqualic acid: a study in adult and aged animals.

A unilateral quisqualic acid lesion was placed in the nucleus basalis magnocellularis of 3- and 24-month-old rats, and the animals were sacrificed at different times post-surgery. The morphology and the number of the cholinergic neurons of the nucleus basalis were analyzed by means of immunohistochemistry for cholineacetyltransferase, in order to evaluate the size and severity of the lesion. Immunohistochemistry for the immediate early gene c-fos was also performed in order to clarify its role in the process of neurodegeneration following the excitotoxin injection. The DNA laddering and TUNEL techniques were used to define the type of cell death involved. At short times (4 hr) the lesion induced alterations in the morphology of cholinergic neurons of the nucleus basalis. Subsequently, a significant decrease in the number of neurons was found in comparison to the contralateral unlesioned side. In the older animals the loss of cholineacetyltransferase immunoreactivity had an earlier onset (4 hr) than in the young (24 hr). C-fos expression was induced by the lesion and not by saline injection in the nucleus basalis and in neighbouring areas of the brain as early as 4 hr after surgery. The c-fos protein was no longer present by 24 hr. Furthermore, the c-fos gene product was consistently absent from the nuclei of cholinergic cells. The aged animals exhibited a slower and smaller increase in c-fos as measured by counting the labelled nuclei in the injected area. Analysis of DNA fragmentation did not provide any evidence for apoptosis as the type of cell death involved in the cholinergic degeneration. These results indicate that the c-fos protein might have a protective role in the response to excitotoxic lesions. Furthermore, we have shown that the aged brain displays a reduced ability to produce a c-fos-mediated plastic response to the lesion.

Aging↗
PubMed1998

Neurotensin modulation of acetylcholine and GABA release from the rat hippocampus: an in vivo microdialysis study.

The effects of neurotensin (NT) on the release of acetylcholine (ACh), aspartate (Asp), glutamate (Glu) and gamma-aminobutyric acid (GABA) from the hippocampus of freely moving rats were studied by transversal microdialysis. ACh was detected by High Performance Liquid Chromatography (HPLC) with electrochemical detection while GABA, glutamate and aspartate were measured using HPLC with fluorometric detection. Neurotensin (0.2 and 0.5 microM) administered locally through the microdialysis probe to the hippocampus produced a long-lasting and concentration-dependent increase in the basal extracellular levels of GABA and ACh but not of glutamate and aspartate. The increase in the extracellular levels of GABA and ACh produced by 0.5 microM neurotensin in the hippocampus reached a maximum of about 310% for GABA and 250% for ACh. This stimulant effect of NT was antagonized by the NT receptor antagonist SR 48692 (100 microg/kg, i.p.). Local infusion of tetrodotoxin (1 microM) decreased the basal release of ACh, GABA, Asp, Glu and prevented the 0.2 microM NT-induced increase in GABA and ACh release. The effect of NT on the release of ACh was blocked by the GABA(A) receptor antagonist bicuculline (2-10 microM). Our findings indicate for the first time that neurotensin plays a neuromodulatory role in the regulation of GABAergic and cholinergic neuronal activity in the hippocampus of awake and freely moving rats. The potentiating effects of neurotensin on GABA and ACh release in the hippocampus are probably mediated by (i) NT receptors located on GABAergic cell bodies and (ii) through GABA(A) receptors located on cholinergic nerve terminals.

Acetylcholine↗
PubMed1998

Long-term changes in the aggregation state and toxic effects of beta-amyloid injected into the rat brain.

The long-term effects of beta-amyloid peptide 1-40 injection into the rat forebrain were studied. Ten micrograms of pre-aggregated peptide were injected into the right nucleus basalis of male Wistar rats which were then killed four or six months later. Congo Red staining of histological sections showed that the peptide deposit was aggregated in a fibrillary form four months post-surgery, whereas at six months almost no trace of birefringency was detected at the deposit site, indicating a loss of fibril organization. This result was confirmed by electron microscopic analysis of the peptide deposits. The presence of the peptide at the injection site six months post-surgery was demonstrated by both Haematoxylin staining and beta-amyloid immunoreactivity. The number of choline acetyltransferase-immunoreactive neurons was reduced by 66% in the injected nucleus basalis four months after injection. A decrease in cortical acetylcholine release was also found at this time. Concomitantly with the loss of fibril conformation, a complete recovery of choline acetyltransferase immunoreactivity in the nucleus basalis and of acetylcholine release in the cortex was observed at six months. These data provide in vivo evidence that beta-amyloid neurotoxicity is related to the fibrillary conformation of the peptide aggregates, thus confirming previous in vitro studies.

Acetylcholine↗
PubMed1997

Increase of cortical acetylcholine release after systemic administration of chlorophenylpiperazine in the rat: an in vivo microdialysis study.

The changes in acetylcholine (ACh) release from the cortex of freely moving rats after systemic administration of chlorophenylpiperazine (mCPP), a 5-HT2C agonist, were measured utilising microdialysis coupled to high performance liquid chromatography. mCPP administered intraperitoneally (i.p.) increased cortical ACh release, but failed to do so when applied locally in the cortex. The effect of i.p. administered mCPP on cortical ACh release was prevented by i.p. injection of mesulergine, a 5-HT2A/2C receptor antagonist, and isoteoline, a compound previously shown to antagonize behavioural effects of mCPP. An increase of cortical ACh release was also found after the local administration of mCPP in nucleus basalis magnocellularis (NBM). The results of the present work suggest that 5-HT2C receptors located in NBM are involved in the modulation of cortical ACh release in the rat.

Acetylcholine↗