Decrease of acetylcholine release from cortical slices in aged rats: investigations into its reversal by phosphatidylserine

The release of total acetylcholine (ACh) and [3H]ACh was investigated in electrically stimulated cortical slices prepared from 4- and 18-month-old male Wistar rats. The slices were prelabeled with [3H]choline ([3H]Ch) and perfused with Krebs solution containing physostigmine. Total ACh was measured and the nature of the tritium efflux identified by HPLC. The total tritium content in the slices at the end of the incubation period was half as great in the old as in young rats. A linear relationship was found between stimulation frequencies (2, 5, and 10 Hz) and fractional [3H]ACh release in both young and old rats. In the latter the release was significantly smaller. At 10 Hz stimulation frequency the ratio between the two 2-min stimulation periods, S2/S1, was higher in the 18-month-old rats than in the young rats. Specific activity of the evoked ACh release was significantly smaller in S2 than in S1 in 4-month-old rats only. These findings indicate that the young synthetize ACh from endogenous unlabeled Ch more than older rats. In 18-month-old rats both the evoked total ACh and [3H]ACh release, expressed as picograms per minute, showed an approximately 50% decrease in both S1 and S2 stimulation periods, with no significant difference in specific activity. Phosphatidylserine (PtdSer) administration (15 mg/kg, i.p. daily) for 1 week to 18-month-old rats prevented the reduction in total evoked ACh release but not the reduction in evoked [3H]ACh release. The specific activity of ACh release was therefore significantly smaller than that of the young and untreated old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the nootropic drug oxiracetam on field potentials of rat hippocampal slices

1. The effect of the nootropic drug oxiracetam on hippocampal neurotransmission was investigated in the CA1 region of the rat hippocampal slice in vitro by use of extracellular recordings. 2. Superfusion of oxiracetam (0.1-100 microM) produced a concentration-dependent, wash-resistant (greater than 90 min), increase in initial slope and amplitude of the dendritic field excitatory postsynaptic potential (e.p.s.p.). This increase was maximal at a concentration of 1 microM (70%). 3. Input-output curves relating the initial slope to the amplitude of the afferent volley were significantly (P less than 0.05) steeper and showed a greater maximal response in the presence of 1 microM oxiracetam than in control conditions. 4. Two trains of high frequency stimulation (100 Hz, 0.4 s, 5 min apart) delivered in the stratum radiatum 30 min after washout of oxiracetam (1 microM) still elicited a long-term potentiation (LTP) of the field e.p.s.p. However, the absolute magnitude of the LTP produced did not differ from that obtained in untreated slices. 5. After induction and establishment of LTP, oxiracetam (1 microM) had a smaller (27%) and reversible effect on the evoked field e.p.s.p. 6. D-2-Amino-5-phosphonopentanoic acid (AP-5), at the same concentration (50 microM) which in our conditions prevented the induction of LTP, blocked the action of 1 microM oxiracetam and strongly depressed the effect of higher concentrations of the nootropic drug. 7. It is concluded that oxiracetam provokes an enduring increase of neurotransmission in the CA1 rat hippocampal region. This action appears to share some features with LTP as indicated by its persistence, sensitivity to AP-5 and lack of additivity with electrically-induced LTP.

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.

The relationship between the behavioral effects of cognition-enhancing drugs and brain acetylcholine. Nootropic drugs and brain acetylcholine

The effect of different doses of the cognition-enhancing agent oxiracetam on the disruption of acquisition of a passive avoidance conditioned response (step-through) by scopolamine 0.6 mg/kg s.c., and on the impairment of performance by scopolamine 0.2 mg/kg s.c. in an eight-arm maze was investigated in adult male Wistar rats. At the end of the experiments, ACh levels were measured in the cerebral cortex and hippocampus by an HPLC method, in order to ascertain whether a relationship exists between the effects of the two drugs on behavior and cholinergic function. In the step-through test, oxiracetam at doses of 50 and 100 mg/kg s. c., given 30 min. before scopolamine, antagonized both scopolamine-induced behavioral disruption and decrease in ACh levels but was inactive at the dose of 300 mg/kg s. c. In the eight-arm maze test, oxiracetam prevented scopolamine-induced disruption of the performance and decrease in brain ACh at the dose of 30 mg/kg s. c. but was inactive at the dose of 100 mg/kg s. c. In conclusion, when scopolamininduced disruption of behavior is prevented or reduced, the scopolamininduced decrease in ACh level, particularly in the hippocampus, is also reduced. The present results therefore offer further confirmation of a relationship between the cognition-enhancing effects of oxiracetam and its effects on hippocampal and cortical cholinergic mechanisms.

Effects of nerve growth factor and GM1 ganglioside on the number and size of cholinergic neurons in rats with unilateral lesion of the nucleus basalis

Four groups of rats with a unilateral ibotenic acid lesion of the nucleus basalis were treated with saline, nerve growth factor (NGF) 10 micrograms administered intracerebroventricularly twice per week, sialoganglioside GM1 30 m/kg daily i.p. and NGF twice per week plus GM1 10 mg/kg i.p. daily, respectively, beginning immediately after lesioning. Twenty-one days later the rats treated with saline showed a marked impairment in negotiating a 'step through' passive avoidance conditioned response, a 32% decrease in the number of choline acetyltransferase (ChAT)-positive neurons in the lesioned nucleus basalis and a 12% decrease in their areas. The rats treated with NGF and NGF plus GM1 showed no difference from sham-operated rats. In the GM1-treated rats a 12% decrease only in the number of ChAT-positive neurons was detected while performance and neuronal areas were normal. These findings indicate that NGF and GM1 prevent the cholinergic deficit by protecting the cholinergic neurons of the nucleus basalis from ibotenic acid neurotoxicity.

Effect of age on K+-induced cytosolic Ca2+ changes in rat cortical synaptosomes

45Ca2+ uptake and cytosolic Ca2+ concentrations [( Ca2+]i) were measured in synaptosomes prepared from the cerebral cortex of 3-, 16-, and 24-month-old male Charles River Wistar rats. Electron-microscopic examination demonstrated no morphological differences between the synaptosomes prepared from 3- and 24-month-old rats. The fast phase of Ca2+ uptake was reduced in the 24-month-old animals as compared to the 3-month-old ones (-23%, p less than 0.001), whereas no difference was found between the 16- and the 3-month-old rats. Age did not modify [Ca2+]i, as measured by the quin 2 technique, both at rest and immediately after depolarization with 50 mM K+. The Ca2+ load following depolarization was cleared in about 13 min in the 3-month-old rats. The rate of clearance was significantly slower both in the 16- (p less than 0.01) and in the 24-month-old rats (p less than 0.0001). The addition of verapamil (60 microM) after depolarization restored [Ca2+]i to resting level in aged rats at the same rate as in young rats. A prolonged Ca2+ influx, therefore, may be responsible for the slower clearance of Ca2+ load in aged rats.

GM1 ganglioside counteracts cholinergic and behavioral deficits induced in the rat by intracerebral injection of vincristine

The intracerebroventricular injection of 0.5 mg of vincristine sulphate in adult male Wistar rats caused within 11 days the impairment of motor and reflexive behavior, evaluated by the elevated platform and hanging wire tests, a decrease in food consumption and loss of body weight, a 45% decrease in hippocampal choline acetyltransferase (ChAT) activity and a 35% decrease in the rate of high-affinity choline uptake (HACU) in the injected side. The latter effects are due to the death of neurons in the respective hemiseptum. Intrafimbrial injection of vincristine caused the same decrease in ChAT activity without behavioral alterations. Daily i.p. administration of GM1 ganglioside, beginning immediately after the vincristine injection, prevented dose dependently the decrease in ChAT activity and HACU rate. Prevention was complete with the 60 mg/kg dose. The same dose was equally active on ChAT activity when given s.c. but was inactive p.o. The ChAT decrease was also prevented when GM1 treatment began 5 days after vincristine. GM1 60 mg/kg i.p. also reduced the behavioral toxicity of vincristine. The possibility that GM1 might prevent vincristine toxicity by antagonizing its disruption of neurofilaments and axonal flow is discussed.

Interaction between nerve growth factor and GM1 monosialoganglioside in preventing cortical choline acetyltransferase and high affinity choline uptake decrease after lesion of the nucleus basalis

Monosialoganglioside GM1 and nerve growth factor (NGF) were administered alone or concomitantly to adult male rats with a unilateral ibotenic acid lesion of the nucleus basalis magnocellularis (NBM). High-affinity choline uptake (HACU) rate and choline acetyltransferase (ChAT) activity were measured, 4 and 21 days after surgery, respectively, in the frontal and parietal cortices of both hemispheres. A 33-34% decrease in HACU rate and a 43-39% decrease in ChAT activity was found in the ipsilateral cortices 4 and 21 days, respectively, after the lesion. If the lesioned rats received NGF (10 micrograms i.c.v.) twice a week or daily administrations of GM1 (30 mg/kg, i.p.), beginning immediately after surgery the decrease in HACU rate and ChAT activity was smaller. If NGF and GM1 were given concomitantly no decrease in HACU rate and ChAT activity was detected in the lesioned hemisphere and a slight increase occurred in the contralateral hemisphere. However, after the concurrent administration of NGF (10 micrograms i.c.v.) and the inactive dose of GM1 10 mg/kg i.p. no decrease in HACU and ChAT activity was also found in the lesioned rats. The latter finding indicates a potentiation by GM1 of NGF effects on the cholinergic neurons of the NBM. The two drugs may either antagonize the neurotoxic effects of ibotenic acid or stimulate a compensatory activity in the remaining neurons.

Cholinergic and noradrenergic denervations decrease labelled purine release from electrically stimulated rat cortical slices

The origin of cortical purine release was investigated by measuring [3H]purine release from electrically stimulated cortical slices of rats after neurotoxic lesions of cholinergic, noradrenergic and serotoninergic pathways innervating the cortex. Purines were labelled by incubating the cortical slices with [3H]adenine. The 3H efflux at rest and during stimulation, analysed by high performance liquid chromatography, consisted of adenosine, inosine, hypoxanthine and a small amount of nucleotides. Twenty days after unilateral or bilateral lesion of the nucleus basalis a marked decrease in choline acetyltransferase activity was associated with a decrease in [3H]purine release. A linear relationship was found between the decrease in choline acetyltransferase activity and [3H]purine release. A partial recovery in both choline acetyltransferase activity and [3H]purine release was observed eight months after the lesion. Twenty days after intra-cerebroventricular injection of 6-hydroxydopamine a 59% decrease in cortical noradrenaline content was associated with a 44% decrease in [3H]purine release. Conversely, no change in [3H]purine release was found in rats in which a 89% decrease in cortical serotonin content was induced by intra-cerebroventricular injection of 5,7-dihydroxytryptamine. The decrease in [3H]purine release after the lesion of the cholinergic and noradrenergic pathways may depend on metabolic changes, a loss of a stimulating influence of acetylcholine and noradrenaline or may indicate a release of [3H]purine from cholinergic and noradrenergic fibres.

Nootropic drugs and brain cholinergic mechanisms

1. This review has two aims: first, to marshal and discuss evidences demonstrating an interaction between nootropic drugs and brain cholinergic mechanisms; second, to define the relationship between the effects on cholinergic mechanisms and the cognitive process. 2. Direct or indirect evidences indicating an activation of cholinergic mechanisms exist for pyrrolidinone derivatives including piracetam, oxiracetam, aniracetam, pyroglutamic acid, tenilsetam and pramiracetam and for miscellaneous chemical structures such as vinpocetine, naloxone, ebiratide and phosphatidylserine. All these drugs prevent or revert scopolamine-induced disruption of several learning and memory paradigms in animal and man. 3. Some of the pyrrolidinone derivatives also prevent amnesia associated with inhibition of acetylcholine synthesis brought about by hemicholinium. Oxiracetam prevents the decrease in brain acetylcholine and amnesia caused by electroconvulsive shock. Oxiracetam, aniracetam and pyroglutamic acid prevent brain acetylcholine decrease and amnesia induced by scopolamine. Comparable bell-shaped dose-effect relationships result for both actions. Phosphatidylserine restores acetylcholine synthesis and conditioned responses in aging rats. 4. The mechanisms through which the action on cholinergic systems might take place, including stimulation of the high affinity choline uptake, are discussed. The information available are not yet sufficient to define at which steps of the cognitive process the action on cholinergic system plays a role and which are the influences of the changes in cholinergic function on other neurochemical mechanisms of learning and memory.

Decrease of brain acetylcholine release in aging freely-moving rats detected by microdialysis

In vivo extracellular acetylcholine release from brain hemispheric areas of 2-, 9-, and 18-month-old rats was measured by intracerebral microdialysis coupled with a radioenzymatic assay. Dialysis tubing was inserted transversally through both striata, frontal cortices and dorsal hippocampi 24 hours before the experiments. In the 2-month-old rats, the net average acetylcholine output, corrected for recovery and expressed in fmoles/min/single striatum, cortex and hippocampus, was 902.4 +/- 67, 303.9 +/- 14 and 334 +/- 32, respectively. In 18-month-old rats acetylcholine output was 53, 35 and 37% lower in striatum, cortex and hippocampus, respectively, than in young rats. The release from the striatum in the 9-month-old was intermediate between those of the 2- and 18-month-old rats. The intracerebroventricular injection of hemicholinium-3 caused a marked decrease in acetylcholine release from the striata of 2- and 18-month-old rats. If the decrease with hemicholinium was expressed as percent of the basal release there was no age-related difference between the young and old rats, indicating that the differences observed were due to the lower basal release found in the old rats. The possibility that the deficit in basal acetylcholine release with age may depend on a reduction of acetylcholine synthesis is discussed.

Muscarinic modulation of purine release from electrically stimulated rat cortical slices

The release of 3H-labeled purines at rest and during electrical stimulation was investigated in slices of rat cortex prelabeled with [3H]adenine and perfused with Krebs solution. A linear relationship was found between radioactivity efflux and stimulation frequency from 2.5 to 20 Hz. At frequencies of less than 2.5 Hz, no increase in radioactivity efflux was detected. The amount of tritium released per pulse increased with stimulation frequency up to 10 Hz and declined at 20 Hz. The tritium efflux from the slices at rest and at a stimulation frequency of 10 Hz, analyzed by HPLC with ultraviolet absorbance detection at 254 nm, consisted mostly of adenosine, inosine, and hypoxanthine. The 3H-labeled purine release evoked by 10-Hz stimulation increased with current intensity from 15 to 100 mA/cm2. At 20 mA/cm2, addition of 0.5 microM tetrodotoxin to the superfusing Krebs solution brought about a 98% decrease of 3H-labeled purine release. At higher current strength, the percentage of tetrodotoxin-sensitive-evoked tritium efflux was smaller. At 30 mA/cm2, 86% of the evoked release was tetrodotoxin sensitive. Under these stimulation conditions, tritium efflux showed a 69% decrease when the slices were superfused with calcium-free Krebs solution containing 0.5 mM EGTA. The muscarinic agonist oxotremorine (30 microM) significantly enhanced the 10-Hz-stimulated 3H-labeled purine release. The effect of oxotremorine was partially prevented by tetrodotoxin, was antagonized by atropine (1.5 microM), and was mimicked by addition of physostigmine (3.8 microM) to the superfusion fluid. Atropine alone did not affect the evoked release, and none of the drugs modified the basal tritium efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral and bilateral nucleus basalis lesions: differences in neurochemical and behavioural recovery

The neurochemical and behavioural recovery following unilateral and bilateral lesions of the nucleus basalis was investigated in adult male Wistar rats 20 days and 6 months after surgery. The lesions were made by stereotaxic injections of ibotenic acid. Twenty days after surgery there was a statistically significant choline acetyltransferase decrease in the frontal and parietal ipsilateral cortex of the unilaterally lesioned rats and in the cortex of both hemispheres after bilateral lesions. Cortical high affinity choline uptake rate was significantly decreased 4 days after lesions but showed a rapid recovery within 20 days post-lesion in unilaterally and bilaterally lesioned rats. However, at this time both groups of lesioned rats showed a marked impairment in the acquisition of passive and active (shuttle-box) avoidance conditioned responses. Six months after surgery the decrease in choline acetyltransferase activity was smaller and statistically significant in the ipsilateral frontal cortex only in the unilaterally lesioned rats and in the frontal and parietal cortex of both hemispheres in the bilaterally lesioned rats. High affinity choline uptake was increased in the contralateral hemispheres of the unilaterally lesioned rats and was significantly larger than in the bilaterally lesioned rats. There was no difference in the acquisition of both passive and active avoidance conditioned responses between the sham operated and unilaterally lesioned rats, while the bilaterally lesioned rats could only negotiate the active avoidance conditioned response. In conclusion, our experiments demonstrate a remarkable neurochemical and behavioural recovery within 6 months in rats with a unilateral lesion of the nucleus basalis and only a limited recovery in the bilateral lesioned rats.

Purinergic modulation of cortical acetylcholine release is decreased in aging rats

The effect of adenosine, N-ethylcarboxamide adenosine (NECA), and caffeine on acetylcholine (ACh) release was investigated in cortical slices prepared from 3 and 22-24-month-old rats. The slices were perfused with Krebs solution and electrically stimulated at 0.2, 1, and 5 Hz stimulation frequency. In old rats, ACh released by stimulation at 1 and 5 Hz was about half as large as in adult rats. In 22-24-month-old rats, the potency of adenosine was strongly reduced, and a similar significant inhibition of ACh release was obtained with concentrations of 1 microM adenosine in adult and 300 microM in old rats. Conversely, NECA, which has no effect on ACh release in adult rats, brought about a 40% decrease in old rats. Caffeine at 50 microM concentration enhanced, and at 500 microM inhibited, the evoked ACh release in adult rats, but was inactive in old rats. The possibility is envisaged that aging may modify purinergic modulation of ACh release by inducing conformational changes in purinergic receptors or changing adenosine metabolism.

Effect of pyroglutamic acid stereoisomers on ECS and scopolamine-induced memory disruption and brain acetylcholine levels in the rat

The acquisition of a passive avoidance conditioned response was disrupted in the rat by electroconvulsive shock (ECS) and scopolamine administration. D,L-pyroglutamic acid (D,L-PCA) 500 and 1000 mg/kg, administered as arginine salt 120 min before the retest, prevented both the ECS and scopolamine-induced amnesia. Arginine alone was ineffective. Scopolamine brought about a 52 and 39% decrease, respectively, in cortical and hippocampal acetylcholine (ACh) levels, measured by means of a gas-chromatographic method. D,L-PCA 500 and 1000 mg/kg also prevented the decrease in brain ACh level. When the two isomers were studied separately, D-PCA was more effective than L-PCA and antagonized scopolamine-induced amnesia at the doses of 250 and 500 mg/kg. In conclusion, D,L-PCA is active on cortical and hippocampal cholinergic mechanisms and, like other 2-oxopyrrolidone derivatives, shows cognition-enhancing properties.

Effect of phosphatidylserine on acetylcholine release and content in cortical slices from aging rats

Cortical slices were prepared from male rats 3 to 28 months old. The slices were superfused with choline-enriched Krebs solution containing physostigmine and electrically stimulated at frequencies of 1, 2 and 5 Hz for 5 min periods preceded and followed by rest periods. The amount of acetylcholine released during the stimulation periods was quantified by bioassay. In some experiments acetylcholine content was measured at the end of the superfusion period in stimulated and unstimulated slices. The evoked acetylcholine release was constant between 3 and 11 months of age at each frequency tested and showed a 50% decrease between 11 and 14 months of age with no further decrease up to 28 months. No difference in the evoked acetylcholine release was detected between 3 and 16 month old rats if the old rats were pretreated with phosphatidylserine 15 mg/kg IP for at least 7 days. The effect of phosphatidylserine lasted for 5 days after interruption of the treatment. There was no difference in acetylcholine content between the stimulated and unstimulated slices in 3 month old rats. In 16 month old rats stimulation brought about a 44% decrease in acetylcholine content. This decrease did not occur in rats pretreated with phosphatidylserine for 7 days. Phosphatidylserine appears to restore acetylcholine release in aging rats by maintaining an adequate acetylcholine supply in the slices.

An analysis of cholecystokinin-induced increase in acetylcholine output from cerebral cortex of the rat

The effect of colecystokinin (CCK-8) on the release of ACh from the cerebral cortex was studied in urethane-anaesthetized rats with the cortical cup technique. The increase in output of ACh brought about by the administration of CCK-8 1.5 micrograms/kg (i.p.) was prevented by pretreatment with haloperidol (1 mg/kg i.p.) and by lesions of the nucleus basalis magnocellularis and substantia nigra but it was reduced only slightly by bilateral vagotomy. Conversely, none of the treatments abolished the decrease in output of ACh brought about by CCK-8 at a dose of 10 micrograms/kg (i.p.). Local injection of CCK-8 into the nucleus basalis had no effect. Therefore, CCK-8 appears to increase cortical cholinergic activity by indirectly stimulating the cholinergic neurones of the nucleus basalis through dopaminergic neurones.

Interactions between oxiracetam, aniracetam and scopolamine on behavior and brain acetylcholine

The effect of cognition-enhancing agents oxiracetam and aniracetam on scopolamine-induced amnesia and brain acetylcholine decrease was investigated in the rat. Acetylcholine levels were measured by means of a gas-chromatographic method. Scopolamine (0.63 mg/kg IP 60 min before training) prevented the acquisition of a passive avoidance conditioned response ("step through": retest 30 min after training) and brought about a 64, 56 and 42% decrease in acetylcholine level in the cortex, hippocampus and striatum respectively. Oxiracetam (50 and 100 mg/kg IP) administered 30 min before scopolamine reduced the scopolamine-induced amnesic effect and decrease in acetylcholine level in the cortex and hippocampus, but not in the striatum. Lower and higher doses of oxiracetam were ineffective. Aniracetam (100 mg/kg PO) also prevented scopolamine-induced amnesia but attenuated acetylcholine decrease in the hippocampus only. Aniracetam (300 mg PO) reduced acetylcholine decrease in the hippocampus but did not prevent scopolamine-amnesia. In conclusion, oxiracetam and aniracetam exert a stimulatory effect on specific central cholinergic pathways. However, a direct relationship between cognition-enhancing properties and cholinergic activation needs further confirmation.