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G Pepeu

Publications and source records attributed to G Pepeu.

At least 55 records · Page 3Linked to original sources
PubMed1997

Effect of metrifonate on extracellular brain acetylcholine and object recognition in aged rats.

The effects of metrifonate were investigated in 4-6- and 22-24-month-old rats. Extracellular acetylcholine levels were measured by transversal microdialysis in vivo. Baseline extracellular acetylcholine levels in the cerebral cortex and hippocampus were 42% and 60% lower, respectively, in old than in young rats. Old rats did not discriminate between familiar and novel objects. In old rats, metrifonate (80 mg/kg p.o.) brought about 85% inhibition of cholinesterase activity in the cortex and hippocampus, a 4-fold increase in extracellular acetylcholine levels in the cortex only, and restored object recognition. In young rats, metrifonate caused 75% cholinesterase inhibition in the cerebral cortex and hippocampus, a 2-fold increase in cortical and hippocampal extracellular acetylcholine levels, and no effect on object recognition. The slight cholinesterase inhibition following metrifonate (30 mg/kg) in aged rats had no effect on cortical acetylcholine levels and object recognition. In conclusion, metrifonate may improve the age-associated cholinergic hypofunction and cognitive impairment.

Acetylcholine↗
PubMed1997

Effects of novelty, pain and stress on hippocampal extracellular acetylcholine levels in male rats.

In vivo microdialysis was used to assess the effects of Novelty, persistent pain (Formalin test) and stress (Restraint) on hippocampal acetylcholine (ACh) release. Experiments were carried out during the dark phase, i.e. during the active period of the animal, and consisted of four experimental phases: Baseline (30 min), Novelty (30 min), Formalin test (90 min) and Restraint (30 min); each animal was consecutively exposed to all phases. The extracellular levels of ACh in the dorsal hippocampus were estimated by measurement of its concentration in the perfusion fluid by high-performance liquid chromatography with electrochemical detection. The introduction to a new environment (Novelty) induced in all rats higher ACh levels than Baseline. Formalin treatment decreased ACh release only in animals considered 'Inactive' during the Novelty phase while no modification in ACh release was observed in the 'Active' ones. Restraint did not produce any modification of ACh release but increased Corticosterone plasma levels both in sham- and formalin-treated animals. Results indicate that Novelty, but not Formalin or Restraint, increases ACh release in the hippocampus and that the type of behavioral state displayed by the animal at the time of formalin injection determines the response of the septo-hippocampal cholinergic pathway.

Acetylcholine↗
PubMed1997

Tacrine administration enhances extracellular acetylcholine in vivo and restores the cognitive impairment in aged rats.

The effect of oral tacrine administration on cortical and hippocampal extracellular acetylcholine (ACh) levels has been investigated by a microdialysis technique, coupled to a HPLC method, in 6- and 22-24-month-old rats. In order to assess whether the increase in extracellular ACh levels was associated with an improvement in the age-related cognitive impairment, the object recognition and step-trough passive avoidance tests were carried out in the treated rats. The extracellular ACh levels measured in the cortex and hippocampus of aged rats without cholinesterase inhibitor in the perfusion Ringer solution were 39 and 54% lower, respectively, than in the young rats. At the dose of 3 mg kg-1, tacrine brought about a three- to four-fold increase in extracellular ACh levels, both in young and aged rats, which peaked 60-80 min after administration and disappeared within the next 60 min. At the same dose, tacrine caused a twofold increase in extracellular ACh levels in the hippocampus of young rats and a sixfold increase in aged rats. The absolute ACh levels at the peak in aged rats were not significantly different from those of young rats. In the object recognition test, aging rats were unable to discriminate between the familiar and novel object. Discrimination was restored by the administration of tacrine at the dose of 1 and 3 mg kg-1, but not 0. 3 mg kg-1 given 30 min before the first trial. Tacrine (3 mg kg-1 p. o.) administered to aging rats before the training trial significantly improved the acquisition of the passive avoidance conditioned response. Our findings demonstrate that tacrine increased both cortical and hippocampal extracellular ACh levels and improved behavioural functions in aged rats.

Acetylcholine↗
PubMed1997

The contribution of different types of calcium channels to electrically-evoked adenosine release from rat hippocampal slices.

The role of L-, N- and P-type voltage-dependent calcium channels (VDCCs) in the release of adenosine from rat hippocampal slices was investigated by evaluating the effect of the L-channel activator 1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)-phenyl]-3-pyr idi ne carboxylic acid methyl ester (Bay K 8644) and of three calcium channel antagonists: the L-channel antagonist nifedipine, the N-channel blocker omega-conotoxin GVIA (omega-CgTx) and the P-channel blocker omega-agatoxin IVA (omega-Aga-IVA). Adenosine and inosine release, evoked by 5 min electrical stimulation at 10 Hz of hippocampal slices, was assayed by HPLC with ultraviolet absorbance or fluorimetric detection. Nifedipine (100 nM) did not affect adenosine and inosine release evoked by electrical stimulation. Bay K 8644 (100 nM) brought about a statistically significant increase in adenosine evoked release (70%). At a higher concentration (1 microM) Bay K 8644 had no significant effect either on adenosine or inosine release evoked by electrical stimulation. The increase in adenosine release elicited by 100 nM Bay K 8644 was abolished by nifedipine (100 nM). Both omega-CgTx (10 microM) and omega-Aga-IVA (200 nM) caused a statistically significant reduction (77-78%) in evoked release of adenosine. When the previously demonstrated glutamate-dependent component of the release of adenosine was suppressed in the presence of the NMDA and non-NMDA receptor antagonists, D(-)-2-amino-7-phosphonoheptanoic acid (D-AP7. 100 microM) and 6,7-dinitroquinoxaline-2,3-dione (DNQX, 10 microM), the remaining release of adenosine was again significantly reduced by omega-CgTx (10 microM) (60%) and omega-Aga-IVA (200 nM) (73%). These data suggest that, while L-type VDCCs are involved in the regulation of the evoked release of adenosine only when activated by Bay K 8644, both P- and N-channels play a direct role in the calcium entry involved in the coupling process between electrical stimulation and adenosine release.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1997

Stereoselective increase in cholinergic transmission by R-(+)-hyoscyamine.

R-(+)-hyoscyamine, the dextro enantiomer of atropine, has been shown to amplify cholinergic transmission. R-(+)-hyoscyamine, unlike S-(-)-hyoscyamine, was able to increase acetylcholine release both in vitro and in vivo at a range of concentrations (10(-14) to 10(-12) M) and doses (5 microg/kg i.p.) which were inadequate for blocking muscarinic receptors. The increase over control values in ACh release was 15.9 +/- 2.1% in in vitro experiments performed in rat phrenic nerve-hemidiaphragm preparations (n = 6), and 63.3 + 16.3% in cortical microdialysis performed in free-moving rats (n = 5). The maximum ACh release was reached 60 min after R-(+)-hyoscyamine administration in in vivo experiments. At the same doses and concentrations, R-(+)-hyoscyamine was also able to elicit: antinociception of a cholinergic type (55.6-112.7% depending on the test used); complete prevention of scopolamine- and dicyclomine-induced amnesia; potentiation of muscular contractions electrically evoked in isolated guinea-pig ileum (16.7 +/- 3.6%) and in rat phrenic nerve-hemidiaphragm (19.9 +/- 3.2%) preparations. Antinociception was performed using the hot-plate and acetic acid abdominal constriction tests in mice, and the paw pressure test in rats, while prevention of induced amnesia was evaluated in mice using the passive-avoidance test. The respective affinities (pA2) for R-(+)- and S-(-)-hyoscyamine vs M1 (rabbit vas deferens), M2 (rat atrium) and M3 (rat ileum) receptor subtypes were as follows: 7.05 +/- 0.05/9.33 +/- 0.03 for M1; 7.25 +/- 0.04/8.95 +/- 0.01 for M2; 6.88 +/- 0.05/9.04 +/- 0.03 for M3. The respective pKi values for R-(+)- and S-(-)-hyoscyamine vs the five human muscarinic receptor subtypes expressed in Chinese hamster oocytes (CHO-K1) were as follows: 8.21 +/- 0.07/9.48 +/- 0.18 for m1; 7.89 +/- 0.06/9.45 +/- 0.31 for m2; 8.06 +/- 0.18/9.30 +/- 0.19 for m3; 8.35 +/- 0.11/9.55 +/- 0.13 for m4; 8.17 +/- 0.08/9.24 +/- 0.30 for m5.

Animals↗
PubMed1997

Selective muscarinic antagonists differentially affect in vivo acetylcholine release and memory performances of young and aged rats.

Brain acetylcholine release and memory performance were investigated in young (three- to six-months) and old (20- to 24-months) rats. Acetylcholine release was measured in vivo in the cortex and hippocampus of freely-moving animals, under basal conditions and in the presence of the following muscarinic antagonists: scopolamine, (+/-)-5,11-dihydro-11-[[(2-[2-[(dipropylamino) methyl]-1-piperidinyl]ethyl) amino] carbonyl]-6H-pyrido(2,3-b)(1,4)-benzodiazepine-6-one (AFDX 384) and pirenzepine. The amount of acetylcholine released from the cortex and hippocampus of old rats was significantly reduced. In the presence of scopolamine and AFDX 384 but not of pirenzepine, the acetylcholine release was significantly higher in the old than the young rats, suggesting that changes in presynaptic M2/M4 muscarinic receptor function occur with ageing in the two brain regions. Cognitive capacities were evaluated using two different behavioural tasks: object recognition and passive avoidance response. Old rats were unable to discriminate between familiar and novel objects and had impaired performance in the passive avoidance test. AFDX 384 restored the performance in both tests. Furthermore, in young rats AFDX 384 reversed the impairment of both object recognition and passive avoidance response induced by scopolamine. The effect of AFDX 384 on acetylcholine release and behaviour in the old rats offers further support to a relationship between the age-related cholinergic hypofunction and cognitive impairment and indicates the blockade of presynaptic muscarinic receptors as a possible selective target for therapeutic strategies aimed at improving age-associated memory deficits.

Acetylcholine↗
PubMed1997

Glutamatergic modulation of cortical acetylcholine release in the rat: a combined in vivo microdialysis, retrograde tracing and immunohistochemical study.

The microdialysis technique with one or two probes was used to investigate the modulation of cortically projecting cholinergic neurons by glutamatergic input in the rat in vivo. Male albino Wistar rats (250-300 g) were used. Under chloral hydrate anaesthesia microdialysis membranes were positioned in the parietal cortex, nucleus basalis magnocellularis (NBM) or medial septum. Acetylcholine was assayed using high-performance liquid chromatography (HPLC) with electrochemical detection while GABA was detected using HPLC with fluorimetric detection after derivatization of the amino acid with o-phthalaldehyde. Septo-cortical neurons were retrogradely labelled with fluoro-gold. Double labelling with choline acetyltransferase (ChAT) immunoreactivity was performed to identify these neurons. Our main findings were that: (i) i.c.v. administration of the NMDA antagonist 3-((R)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP, 1-5 nmol) increased cortical acetylcholine outflow; (ii) local administration of CPP (100 microM) to the cortex had no effect on cortical acetylcholine outflow; (iii) local administration of CPP (100 microM) to the NBM decreased cortical acetylcholine outflow; (iv) local administration of CPP (100-200 microM) to the septum increased cortical GABA and acetylcholine outflow; (v) administration of muscimol to the septum prevented the effect of CPP on cortical acetylcholine outflow; (vi) retrograde tracing with fluoro-gold labelled cell bodies in the medial septum; (vii) septal fluoro-gold-positive neurons were not ChAT-immunoreactive. Our in vivo neurochemical results, in combination with retrograde tracing and immunohistochemistry, indicate that the cortically projecting cholinergic system is indirectly regulated by a glutamatergic input via a polysynaptic GABAergic circuitry located in the septum.

Acetylcholine↗
PubMed1996

Enhanced acetylcholine release in the hippocampus and cortex during acquisition of an operant behavior.

The activity of the septo-hippocampal and nucleus basalis-cortical cholinergic pathways was investigated by measuring changes in the extracellular acetylcholine levels in the hippocampus and parietal cortex, by means of transversal microdialysis, during the acquisition and recall of a positively reinforced operant behavior. Adult male Wistar rats were trained in a sound-isolated operant chamber equipped with a single lever. The positive reinforcement was represented by food pellets and the number of cumulative reinforced responses was recorded every 30 min. Five groups of rats were used. Unoperated animals were used as controls. In two groups of untrained animals, the microdialysis tubes were transversally implanted in the parietal cortex, and hippocampus and the training in the operant behavior chamber began 24 h after surgery. In two further groups the microdialysis tubes were implanted in the parietal cortex, and hippocampus after training for 15 days in the operant chamber. Food was removed 12 h before training. The time needed by the control rats to reach a stable baseline of reinforced responses was 83 +/- 12 min, while in the untrained rats implanted with dialysis probes in the cerebral cortex and in the hippocampus was 621 +/- 129 and 521 +/- 126 min, respectively, and in those pretrained and implanted in cerebral cortex and in the hippocampus was 116 +/- 38 and 217 +/- 59 min, respectively. In the untrained operated rats, both cortical and hippocampal extracellular acetylcholine levels remained constant until the number of reinforced responses was low but increased significantly (+156% in the cortex and +183% in the hippocampus) in the first 30 min period in which there was a sharp rise in the reinforced responses. In the pretrained operated rats, neither in the cortex nor in the hippocampus was the increase in response rate accompanied by a statistically significant increase in extracellular acetylcholine levels. Our findings demonstrate that activation of the forebrain cholinergic pathways occurs during the acquisition of a rewarded operant responses, while recall of the same behavior is not associated with the activation of the cholinergic system.

Acetylcholine↗
PubMed1996

Synthesis and enantioselectivity of the enantiomers of PG9 and SM21, new potent analgesic and cognition-enhancing drugs.

The enantiomers of two alpha-tropanyl esters, SM21 (1) and PG9 (2), derived from (+)-R-hyoscyamine, that act by increasing the central cholinergic tone, were obtained by esterification after resolution of the corresponding racemic acids [(-)-S-1, (-)-R-2 and (+)-S-2] and by stereospecific synthesis [(+)-R-1]. Their analgesic and cognition-enhancing activities were tested in mice and their ACh-releasing properties determined on rat parietal cortex. These compounds show enantioselectivity in analgesic and cognition-enhancing tests on mice, the eutomers being the isomers which possess the same spatial arrangement of the groups on the chiral atom as (+)-R hyoscyamine [(+)-R-SM21, (+)-S-PG9]. The ACh-releasing effect of the enantiomers of SM21 in rats is in agreement with the results in mice, while PG9 enantiomers do not show any appreciable enantioselectivity in this test. On the basis of the different effects of the 5-HT4 antagonist SDZ 205557 on analgesia induced by the enantiomers of 1 and 2 and by (+)-R-hyoscyamine and the alpha-tropanyl ester of 2-phenylpropionic acid 3, a mechanism of action is proposed for this class of compounds.

Acetylcholine↗
PubMed1996

Central cholinergic antinociception induced by 5HT4 agonists: BIMU 1 and BIMU 8.

The antinociceptive effect of two 5-HT4 agonists, BIMU 1 and BIMU 8, were examined in mice and rats by using the hot-plate, abdominal constriction and paw-pressure tests. In both species, BIMU 1 (10-20 mg kg-1 s.c. and 40-60 mg kg-1 p.o. in mice; 20 mg kg-1 i.p. in rats) and BIMU 8 (20-30 mg kg-1 s.c. and 60 mg kg-1 p.o. in mice; 20 mg kg-1 i.p. in rats), produced significant antinociception which was prevented by atropine (5 mg kg-1 i.p.), hemicholinium-3 (1 microgram per mouse i.c.v.), SDZ 205-557 (10 mg kg-1 i.p.), GR 125487 (20 mg kg-1 i.p.) but not by naloxone (1 mg kg-1 i.p.), CGP 35348 (100 mg kg-1 i.p.) and reserpine (2 mg kg-1 i.p.). Moreover, BIMU 1 and BIMU 8 increase of pain threshold, is abolished by nucleus basalis magnocellularis (NBM) lesions in rats. SDZ 205-557 and GR 125487 which totally antagonized BIMU 1 and BIMU 8 antinociception did not modify morphine (7 mg kg-1 s.c.) or baclofen (4 mg kg-1 s.c.) antinociception. Intracerebroventricular injection in mice of BIMU 1 (3 micrograms per mouse) and BIMU 8 (10 micrograms per mouse), doses which were largely ineffective by parenteral routes, induces an antinociception whose intensity equaled that obtainable s.c., i.p. or p.o. In the antinociceptive dose-range, neither 5HT4 agonist impaired mice motor coordination evaluated by rota-rod test. On the basis of the above data, it can be postulated that BIMU 1 and BIMU 8 exerted an antinociceptive effect mediated by a central amplification of cholinergic transmission.

4-Aminobenzoic Acid↗
PubMed1996

Aniracetam restores object recognition impaired by age, scopolamine, and nucleus basalis lesions.

Object recognition was investigated in adult and aging male rats in a two-trials, unrewarded, test that assessed a form of working-episodic memory. Exploration time in the first trial, in which two copies of the same object were presented, was recorded. In the second trial, in which one of the familiar objects and a new object were presented, the time spent exploring the two objects was separately recorded and a discrimination index was calculated. Adult rats explored the new object longer than the familiar object when the intertrial time ranged from 1 to 60 min. Rats older than 20 months of age did not discriminate between familiar and new objects. Object discrimination was lost in adult rats after scopolamine (0.2 mg/kg SC) administration and with lesions of the nucleus basalis, resulting in a 40% decrease in cortical ChAT activity. Both aniracetam (25, 50, 100 mg/kg os) and oxiracetam (50 mg/kg os) restored object recognition in aging rats, in rats treated with scopolamine, and with lesions of the nucleus basalis. In the rat, object discrimination appears to depend on the integrity of the cholinergic system, and nootropic drugs can correct its disruption.

Aging↗
PubMed1996

The source of brain adenosine outflow during ischemia and electrical stimulation.

Adenosine outflow and adenosine and adenine nucleotide content of hippocampal slices were evaluated under two different experimental conditions: ischemia-like conditions and electrical stimulation (10 Hz). Five minutes of ischemia-like conditions brought about an 8-fold increase in adenosine outflow in the following 5 min during reperfusion, and a 2-fold increase in adenosine content, a 43% decrease in ATP, a 72% increase in AMP and a 30% decrease in energy charge (E.C.) at the end of the ischemic period. After 10 min of reperfusion ATP, AMP and E.C. returned to control values, while the adenosine content was further increased. Five minutes of electrical stimulation brought about an 8-fold increase in adenosine outflow that peaked 5 min after the end of stimulation, a 4-fold increase in adenosine content and an 18% decrease in tissue E.C. at the end of stimulation. After 10 min of rest conditions the adenosine content and E.C. returned to basal values. The origin of extracellular adenosine from S-adenosylhomocysteine (SAH) was examined under the two different experimental conditions. The SAH hydrolase inhibitor, adenosine-2,3-dialdehyde (10 microM), does not significantly modify the adenosine outflow evoked by electrical stimulation or ischemia-like conditions. This finding excludes a significant contribution by the transmethylation pathway to adenosine extracellular accumulation evoked by an electrical or ischemic stimulus, and confirms that the most likely source of adenosine is from AMP dephosphorylation.

Adenine Nucleotides↗
PubMed1996

A2 adenosine receptors: their presence and neuromodulatory role in the central nervous system.

1. Adenosine is an endogenous neuromodulator that exerts its depressant effect on neurons by acting on the A1 adenosine receptor subtype. Excitatory actions of adenosine, mediated by the activation of the A2 adenosine receptor subtype, have also been shown in the central nervous system. 2. Adenosine A2a receptors are highly localized in the striatum, as demonstrated by the binding assay of the A2a selective agonist, CGS2680, and by analysis of the A2 receptor mRNA localization with in situ hybridization histochemistry. However, adenosine A2a, receptors, albeit at lower levels, are also localized in other brain regions, such as the cortex and the hippocampus. 3. In the striatum, adenosine A2a, receptors are implicated in the control of motor activity. Evidences exists of an antagonistic interaction between adenosine A2a and dopamine D2 receptors. 4. Utilizing selective agonists and antagonists for adenosine A2a receptors, their role in the modulation of the release of several neurotransmitters (acetylcholine, dopamine, glutamate, GABA) has been extensively studied in the brain (striatum, cortex, hippocampus). Controversial results have been obtained and, because the overall effect of endogenous adenosine in the brain is that of an inhibitory tonus, the physiological meaning of the excitatory A2 receptor remains to be clarified.

Animals↗
PubMed1996

Inhibition of cortical acetylcholine release and cognitive performance by histamine H3 receptor activation in rats.

1. The effects of histamine and agents at histamine receptors on spontaneous and 100 mM K(+)-evoked release of acetylcholine, measured by microdialysis from the cortex of freely moving, rats, and on cognitive tests are described. 2. Local administration of histamine (0.1-100 microM) failed to affect spontaneous but inhibited 100 mM K(+)-stimulated release of acetylcholine up to about 50%. The H3 receptor agonists (R)-alpha-methylhistamine (RAMH) (0.1-10 microM), imetit (0.01-10 microM) and immepip (0.01-10 microM) mimicked the effect of histamine. 3. Neither 2-thiazolylethylamine (TEA), an agonist showing some selectivity for H1 receptors, nor the H2 receptor agonist, dimaprit, modified 100 mM K(+)-evoked release of acetylcholine. 4. The inhibitory effect of 100 microM histamine was completely prevented by the highly selective histamine H3 receptor antagonist, clobenpropit but was resistant to antagonism by triprolidine and cimetidine, antagonists at histamine H1 and H2 but not H3 receptors. 5. The H3 receptor-induced inhibition of K(+)-evoked release of acetylcholine was fully sensitive to tetrodotoxin (TTX). 6. The effects of intraperitoneal (i.p.) injection of imetit (5 mg kg-1) and RAMH (5 mg kg-1) were tested on acetylcholine release and short term memory paradigms. Both drugs reduced 100 mM K(+)-evoked release of cortical acetylcholine, and impaired object recognition and a passive avoidance response. 7. These observations provide the first evidence of a regulatory role of histamine H3 receptors on cortical acetylcholine release in vivo. Moreover, they suggest a role for histamine in learning and memory and may have implications for the treatment of degenerative disorders associated with impaired cholinergic function.

Acetylcholine↗