Acetyl-L-carnitine: behavioral, electrophysiological, and neurochemical effects

Reelin changes hippocampal learning in aging and Alzheimer's disease

The hippocampal formation (HF) is a neuroanatomical region essential for learning and memory. As one of the earliest regions to display the histopathological hallmarks of Alzheimer's disease (AD), determining the specific mechanisms of the HF's vulnerability is of capital importance. Reelin, a glycoprotein crucial in cortical lamination during embryonic neurogenesis, has an uncommon expression pattern within the HF and has been implicated in both learning and AD pathogenesis. We hypothesized that Reelin deficiency would expedite behavioral impairments which accompany normal aging. Additionally, we hypothesized that Reelin deficiency in the presence of mutated human microtubule associated protein tau (MAPT) would further impair hippocampal function. To test our hypothesis, we utilized cohorts of aged mice, aged mice with Reelin conditional knockout (RcKO), and adult mice with both RcKO and MAPT in the Barnes maze and Trace fear conditioning. Consistent with prior literature, increased age in wild-type mice was sufficient to reduce spatial searching in the Barnes maze. Increased age both exacerbated spatial impairments and altered context learning in RcKO mice. Lastly, adult mice with both RcKO and the MAPT transgene displayed both the lowest age-of-onset and most severe spatial learning deficits. In conclusion, Reelin deficiency when combined with AD risk-factors produced consistent impairments in spatial memory tasks. Furthermore, our results further implicate Reelin's importance in both HF homeostasis and AD pathogenesis.

Serum Metabolomics of Early Postoperative Cognitive Dysfunction in Elderly Patients Using Liquid Chromatography and Q-TOF Mass Spectrometry

Postoperative cognitive dysfunction (POCD) is a common postoperative complication observed in elderly patients. However, the diagnosis of POCD is not very satisfactory as no specific biomarkers have been classified. It is necessary to identify new diagnostic markers to better understand the pathogenesis of POCD. We performed liquid chromatography with a time-of-flight mass spectrometer- (LC/Q-TOF-MS-) based metabolomics study to investigate POCD. A total of 40 metabolites were differentially expressed between POCD and non-POCD patients. In this study, we investigated whether phosphatidylserine (PS) (17:2/0:0), with an area under the curve value of 0.966, was a potential sensitive and specific biomarker for the diagnosis and prognosis of POCD. Pathway analysis showed that fatty acid metabolism, lipid metabolism, and carnitine metabolism were significantly altered in POCD. Network analysis indicated that nitric oxide signaling, PI3K-AKT signaling, mTOR signaling, and mitochondrial dysfunction were related to the pathogenesis of POCD. This study showed that metabolic profiling was meaningful when studying the diagnosis and pathogenesis of POCD.

NMDA Receptor Function During Senescence: Implication on Cognitive Performance

N-methyl-D-aspartate (NMDA) receptors, a family of L-glutamate receptors, play an important role in learning and memory, and are critical for spatial memory. These receptors are tetrameric ion channels composed of a family of related subunits. One of the hallmarks of the aging human population is a decline in cognitive function; studies in the past couple of years have demonstrated deterioration in NMDA receptor subunit expression and function with advancing age. However, a direct relationship between impaired memory function and a decline in NMDA receptors is still ambiguous. Recent studies indicate a link between an age-associated NMDA receptor hypofunction and memory impairment and provide evidence that age-associated enhanced oxidative stress might be contributing to the alterations associated with senescence. However, clear evidence is still deficient in demonstrating the underlying mechanisms and a relationship between age-associated impaired cognitive faculties and NMDA receptor hypofunction. The current review intends to present an overview of the research findings regarding changes in expression of various NMDA receptor subunits and deficits in NMDA receptor function during senescence and its implication in age-associated impaired hippocampal-dependent memory function.

Memory in aged mice is rescued by enhanced expression of the GluN2B subunit of the NMDA receptor

The GluN2B subunit of the N-methyl-d-aspartate (NMDA) receptor shows age-related declines in expression across the frontal cortex and hippocampus. This decline is strongly correlated to age-related memory declines. This study was designed to determine if increasing GluN2B subunit expression in the frontal lobe or hippocampus would improve memory in aged mice. Mice were injected bilaterally with either the GluN2B vector, containing cDNA specific for the GluN2B subunit and enhanced green fluorescent protein (eGFP); a control vector or vehicle. Spatial memory, cognitive flexibility, and associative memory were assessed using the Morris water maze. Aged mice, with increased GluN2B subunit expression, exhibited improved long-term spatial memory, comparable to young mice. However, memory was rescued on different days in the Morris water maze; early for hippocampal GluN2B subunit enrichment and later for the frontal lobe. A higher concentration of the GluN2B antagonist, Ro 25-6981, was required to impair long-term spatial memory in aged mice with enhanced GluN2B expression, as compared to aged controls, suggesting there was an increase in the number of GluN2B-containing NMDA receptors. In addition, hippocampal slices from aged mice with increased GluN2B subunit expression exhibited enhanced NMDA receptor-mediated excitatory post-synaptic potentials (EPSP). Treatment with Ro 25-6981 showed that a greater proportion of the NMDA receptor-mediated EPSP was due to the GluN2B subunit in these animals, as compared to aged controls. These results suggest that increasing the production of the GluN2B subunit in aged animals enhances memory and synaptic transmission. Therapies that enhance GluN2B subunit expression within the aged brain may be useful for ameliorating age-related memory declines.

Acetyl-L-carnitine improves behavior and dendritic morphology in a mouse model of Rett syndrome

Rett syndrome (RTT) is a devastating neurodevelopmental disorder affecting 1 in 10,000 girls. Approximately 90% of cases are caused by spontaneous mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). Girls with RTT suffer from severe motor, respiratory, cognitive and social abnormalities attributed to early deficits in synaptic connectivity which manifest in the adult as a myriad of physiological and anatomical abnormalities including, but not limited to, dimished dendritic complexity. Supplementation with acetyl-L-carnitine (ALC), an acetyl group donor, ameliorates motor and cognitive deficits in other disease models through a variety of mechanisms including altering patterns of histone acetylation resulting in changes in gene expression, and stimulating biosynthetic pathways such as acetylcholine. We hypothesized ALC treatment during critical periods in cortical development would promote normal synaptic maturation, and continuing treatment would improve behavioral deficits in the Mecp2(1lox) mouse model of RTT. In this study, wildtype and Mecp2(1lox) mutant mice received daily injections of ALC from birth until death (postnatal day 47). General health, motor, respiratory, and cognitive functions were assessed at several time points during symptom progression. ALC improved weight gain, grip strength, activity levels, prevented metabolic abnormalities and modestly improved cognitive function in Mecp2 null mice early in the course of treatment, but did not significantly improve motor or cognitive functions assessed later in life. ALC treatment from birth was associated with an almost complete rescue of hippocampal dendritic morphology abnormalities with no discernable side effects in the mutant mice. Therefore, ALC appears to be a promising therapeutic approach to treating early RTT symptoms and may be useful in combination with other therapies.

Characterizing cognitive aging of spatial and contextual memory in animal models

Episodic memory, especially memory for contextual or spatial information, is particularly vulnerable to age-related decline in humans and animal models of aging. The continuing improvement of virtual environment technology for testing humans signifies that widely used procedures employed in the animal literature for examining spatial memory could be developed for examining age-related cognitive decline in humans. The current review examines cross species considerations for implementing these tasks and translating findings across different levels of analysis. The specificity of brain systems as well as gaps in linking human and animal laboratory models is discussed.

Dissecting the age-related decline on spatial learning and memory tasks in rodent models: N-methyl-D-aspartate receptors and voltage-dependent Ca2+ channels in senescent synaptic plasticity

In humans, heterogeneity in the decline of hippocampal-dependent episodic memory is observed during aging. Rodents have been employed as models of age-related cognitive decline and the spatial water maze has been used to show variability in the emergence and extent of impaired hippocampal-dependent memory. Impairment in the consolidation of intermediate-term memory for rapidly acquired and flexible spatial information emerges early, in middle-age. As aging proceeds, deficits may broaden to include impaired incremental learning of a spatial reference memory. The extent and time course of impairment has been be linked to senescence of calcium (Ca²⁺) regulation and Ca²⁺-dependent synaptic plasticity mechanisms in region CA1. Specifically, aging is associated with altered function of N-methyl-D-aspartate receptors (NMDARs), voltage-dependent Ca²⁺ channels (VDCCs), and ryanodine receptors (RyRs) linked to intracellular Ca²⁺ stores (ICS). In young animals, NMDAR activation induces long-term potentiation of synaptic transmission (NMDAR-LTP), which is thought to mediate the rapid consolidation of intermediate-term memory. Oxidative stress, starting in middle-age, reduces NMDAR function. In addition, VDCCs and ICS can actively inhibit NMDAR-dependent LTP and oxidative stress enhances the role of VDCC and RyR-ICS in regulating synaptic plasticity. Blockade of L-type VDCCs promotes NMDAR-LTP and memory in older animals. Interestingly, pharmacological or genetic manipulations to reduce hippocampal NMDAR function readily impair memory consolidation or rapid learning, generally leaving incremental learning intact. Finally, evidence is mounting to indicate a role for VDCC-dependent synaptic plasticity in associative learning and the consolidation of remote memories. Thus, VDCC-dependent synaptic plasticity and extrahippocampal systems may contribute to incremental learning deficits observed with advanced aging.

Aging impairs hippocampus-dependent long-term memory for object location in mice

The decline in cognitive function that accompanies normal aging has a negative impact on the quality of life of the elderly and their families. Studies in humans and rodents show that spatial navigation and other hippocampus-dependent functions are particularly vulnerable to the deleterious effects of aging. However, reduced motor activity and alterations in the stress response that accompany normal aging can hinder the ability to study certain cognitive behaviors in aged animals. In an attempt to circumvent these potential confounds, we used a hippocampus-dependent object-place recognition task to show that long-term spatial memory is impaired in aged mice. Aged animals performed similarly to young adult mice on an object recognition task that does not rely on hippocampal function.

The effects of aging and genotype on NMDA receptor expression in growth hormone receptor knockout (GHRKO) mice

Caloric restriction enhances N-methyl-D-aspartate (NMDA) receptor binding and upregulates messenger RNA expression of the GluN1 subunit during aging. Old growth hormone receptor knockout mice resemble old calorically restricted rodents in enhanced life span and brain function, as compared with aged controls. This study examined whether aged growth hormone receptor knockout mice also show enhanced expression of NMDA receptors. Six or 23- to 24-month-old male normal-sized control or dwarf growth hormone receptor knockout mice were assayed for NMDA-displaceable [(3)H]glutamate binding (autoradiography) and GluN1 subunit messenger RNA (in situ hybridization). There was slight sparing of NMDA receptor binding densities within aged medial prefrontal and motor cortices, similar to caloric restriction, but there were greater age-related declines in GluN1 messenger RNA in growth hormone receptor knockout versus control mice. These results suggest that some of the functional improvements in aged mice with altered growth hormone signaling may be due to enhancement of NMDA receptors, but not through the upregulation of messenger RNA for the GluN1 subunit.

Acetyl-L-carnitine improves aged brain function

The effects of acetyl-L-carnitine (ALCAR), an acetyl derivative of L-carnitine, on memory and learning capacity and on brain synaptic functions of aged rats were examined. Male Fischer 344 rats were given ALCAR (100 mg/kg bodyweight) per os for 3 months and were subjected to the Hebb-Williams tasks and AKON-1 task to assess their learning capacity. Cholinergic activities were determined with synaptosomes isolated from brain cortices of the rats. Choline parameters, the high-affinity choline uptake, acetylcholine (ACh) synthesis and depolarization-evoked ACh release were all enhanced in the ALCAR group. An increment of depolarization-induced calcium ion influx into synaptosomes was also evident in rats given ALCAR. Electrophysiological studies using hippocampus slices indicated that the excitatory postsynaptic potential slope and population spike size were both increased in ALCAR-treated rats. These results indicate that ALCAR increases synaptic neurotransmission in the brain and consequently improves learning capacity in aging rats.

Selective Vulnerabilities of N-methyl-D-aspartate (NMDA) Receptors During Brain Aging

N-methyl-D-aspartate (NMDA) receptors are present in high density within the cerebral cortex and hippocampus and play an important role in learning and memory. NMDA receptors are negatively affected by aging, but these effects are not uniform in many different ways. This review discusses the selective age-related vulnerabilities of different binding sites of the NMDA receptor complex, different subunits that comprise the complex, and the expression and functions of the receptor within different brain regions. Spatial reference, passive avoidance, and working memory, as well as place field stability and expansion all involve NMDA receptors. Aged animals show deficiencies in these functions, as compared to young, and some studies have identified an association between age-associated changes in the expression of NMDA receptors and poor memory performance. A number of diet and drug interventions have shown potential for reversing or slowing the effects of aging on the NMDA receptor. On the other hand, there is mounting evidence that the NMDA receptors that remain within aged individuals are not always associated with good cognitive functioning. This may be due to a compensatory response of neurons to the decline in NMDA receptor expression or a change in the subunit composition of the remaining receptors. These studies suggest that developing treatments that are aimed at preventing or reversing the effects of aging on the NMDA receptor may aid in ameliorating the memory declines that are associated with aging. However, we need to be mindful of the possibility that there may also be negative consequences in aged individuals.

The N-methyl-D-aspartate receptor modulator GLYX-13 enhances learning and memory, in young adult and learning impaired aging rats

NMDA receptor (NMDAR) activity has been strongly implicated in both in vitro and in vivo learning models and the decline in cognitive function associated with aging and is linked to a decrease in NMDAR functional expression. GLYX-13 is a tetrapeptide (Thr-Pro-Pro-Thr) which acts as a NMDAR receptor partial agonist at the glycine site. GLYX-13 was administered to young adult (3 months old) and aged (27-32 months old) Fischer 344 X Brown Norway F1 rats (FBNF1), and behavioral learning tested in trace eye blink conditioning (tEBC), a movable platform version of the Morris water maze (MWM), and alternating t-maze tasks. GLYX-13 (1mg/kg, i.v.) enhanced learning in both young adult and aging animals for MWM and alternating t-maze, and increased tEBC in aging rats. We previously showed optimal enhancement of tEBC in young adult rats given GLYX-13 at the same dose. Of these learning tasks, the MWM showed the most robust age related deficit in learning. In the MWM, GLYX-13 enhancement of learning was greater in the old compared to the young adult animals. Examination of the induction of long-term potentiation (LTP) and depression (LTD) at Schaffer collateral-CA1 synapses in hippocampal slices showed that aged rats showed marked, selective impairment in the magnitude of LTP evoked by a sub-maximal tetanus, and that GLYX-13 significantly enhanced the magnitude of LTP in slices from both young adult and aged rats without affecting LTD. These data, combined with the observation that the GLYX-13 enhancement of learning was greater in old than in young adult animals, suggest that GLYX-13 may be a promising treatment for deficits in cognitive function associated with aging.

Cerebral metabolic effects of acetyl-l-carnitine in rats during aging

The aim of the present study was to investigate the neuronal structures that mediate the antiaging properties of acetyl-l-carnitine (ALCAR). The regional cerebral metabolic rates for glucose (rCMRglc) have been determined with the quantitative autoradiographic [(14)C]2-deoxyglucose procedure at different times after i.v. administration of saline or ALCAR 500 mg/kg to naïve, non pretreated 3-, 12- and 24-month-old rats and to 24-month-old rats pretreated with ALCAR (100 mg/kg/day, for 3 months). rCMRglc increased maximally at 30 min after ALCAR in 3-, 12- and 24-month old rats (14, 15 and 15 areas affected, 19, 24 and 22% mean increments). Peak metabolic activations occurred with similar magnitude in motor, visual, limbic and thalamic areas in all age rats and with larger magnitude in hippocampal and thalamic areas in aged rats. Cerebral metabolic activations subsided by 60 min after ALCAR in 3-month rats (3 brain regions affected, 4% decrease) and persisted by that time in 12- and 24-month-old rats (14 and 12 regions affected, 15 and 20% increases). Cerebral activations were enhanced in aged rats after chronic treatment with ALCAR (24 brain regions affected, 20% mean increase). Hence, during aging, metabolic responsivity to ALCAR is maintained in most brain areas and increased in limbic and thalamic regions. Increased responsivity to ALCAR may result from undetermined pharmacokinetic factors and/or from a higher sensitivity and contribute to the aging reversal properties of ALCAR.

Acetyl-L-carnitine up-regulates expression of voltage-dependent anion channel in the rat brain

Acetyl-L-carnitine (ALC) exerts unique neuroprotective, neuromodulatory, and neurotrophic properties, which play an important role in counteracting various pathological processes, and have antioxidative properties, protecting cells against lipid peroxidation. In this study, suppression subtractive hybridization (SSH) method was applied for the generation of subtracted cDNA libraries and the subsequent identification of differentially expressed transcripts after treatment of rats with ALC. The technique generates an equalized representation of differentially expressed genes irrespective of their relative abundance and it is based on the construction of forward and reverse cDNA libraries that allow the identification of the genes that are regulated after ALC treatment. In the present paper, we report the identification of the gene of mitochondrial voltage-dependent anion channel (VDAC) protein which is positively modulated by the ALC treatment. VDAC is a small pore-forming protein of the mitochondrial outer membrane. It represents an interesting tool for Ca(2+) homeostasis, and it plays a central role in apoptosis. In addition, VDAC seems to have a relevant role in the synaptic plasticity.

Identification of differentially expressed genes induced in the rat brain by acetyl-L-carnitine as evidenced by suppression subtractive hybridisation

Acetyl-L-carnitine (ALC) is a molecule widely present in the central nervous system (CNS) formed by the reversible acetylation of carnitine. It acts by stimulating energy metabolism. Reported neurobiological effects of this substance include modulation of brain energy and phospholipid metabolism; cellular macromolecules (including neurotrophic factors and neurohormones); synaptic transmission of multiple neurotransmitters. ALC is of considerable interest for its clinical application in Alzheimer's disease and in the treatment of painful neuropathies. There are experimental data that it affects attention and antagonizes deterioration of ability to learn, improving long-term memory. Moreover, ALC influences nonassociative learning of sensitization type in Hirudo medicinalis. These findings are suggesting that ALC might exert its effects by means of new protein synthesis. ALC or saline solution was injected intraperitoneally each day for 21 days in rats. Poly(A)+ RNAs were isolated from control and treated rat brain. Suppression subtractive hybridisation (SSH) method was applied for the generation of subtracted cDNA libraries and the subsequent identification of differentially expressed transcripts after treatments. The technique generates an equalized representation of differentially expressed genes irrespective of their relative abundance, and it is based on the construction of forward and reverse cDNA libraries that allow the identification of the genes that are regulated or switched off/on after ALC treatment. We identified two modulated genes, the isoform gamma of 14-3-3 protein and a precursor of ATP synthase lipid-binding protein, and one gene switched on by the treatment, the heat shock protein hsp72.

A placebo-controlled screening trial of olanzapine, valproate, and coenzyme Q10/L-carnitine for the treatment of cocaine dependence

AIMS

To conduct a medication screening trial on the efficacy of olanzapine, valproate or coenzyme Q10/L-carnitine combination versus placebo for the treatment of cocaine dependence.

DESIGN

A four-arm, modified blinded, parallel group study in an out-patient setting using the Cocaine Rapid Efficacy and Safety Trials (CREST) study design.

SETTING

The study was performed at the New York Medications Development Research Unit (MDRU).

PARTICIPANTS

All participants met Diagnostic and Statistical Manual version IV (DSM-IV) criteria for cocaine dependence and provided at least two urine samples positive for benzoylecgonine (BE) during the 2-week screening period. Sixty-eight participants were enrolled with 39 completing the study.

INTERVENTION

After a 2-week screening period, 68 subjects were assigned randomly to receive either olanzapine (10 mg/day), valproate (1500 mg/day), coenzyme Q10 (200 mg/day) and L-carnitine (500 mg/day) combination or placebo for an 8-week treatment period. All subjects also received individual cognitive behavioral counseling during treatment.

MEASUREMENTS

Primary outcome measures included quantitative urine benzoylecgonine (BE) levels, self-report of drug use, and global impression scores. Secondary outcomes included cocaine craving, study retention and related psychosocial measures. Safety measures included adverse event monitoring, vital signs, and extrapyramidal side-effects tests.

RESULTS

Study retention was similar across all treatment groups, and all groups showed improvement across most measures of treatment efficacy over the duration of the study. None of the study medications, however, were superior to placebo on any of the primary or secondary outcome measures. Cocaine use, as measured by urine BE levels and self-report, was not significantly lower than placebo in any of the drug treatment groups. All study medications were equally well tolerated, and few medication side effects were observed.

CONCLUSION

This pilot study does not support the effectiveness of olanzapine, valproate or coenzyme Q10/L-carnitine combination for the treatment of cocaine dependence.

Long-term potentiation and memory

One of the most significant challenges in neuroscience is to identify the cellular and molecular processes that underlie learning and memory formation. The past decade has seen remarkable progress in understanding changes that accompany certain forms of acquisition and recall, particularly those forms which require activation of afferent pathways in the hippocampus. This progress can be attributed to a number of factors including well-characterized animal models, well-defined probes for analysis of cell signaling events and changes in gene transcription, and technology which has allowed gene knockout and overexpression in cells and animals. Of the several animal models used in identifying the changes which accompany plasticity in synaptic connections, long-term potentiation (LTP) has received most attention, and although it is not yet clear whether the changes that underlie maintenance of LTP also underlie memory consolidation, significant advances have been made in understanding cell signaling events that contribute to this form of synaptic plasticity. In this review, emphasis is focused on analysis of changes that occur after learning, especially spatial learning, and LTP and the value of assessing these changes in parallel is discussed. The effect of different stressors on spatial learning/memory and LTP is emphasized, and the review concludes with a brief analysis of the contribution of studies, in which transgenic animals were used, to the literature on memory/learning and LTP.

Effect of L-carnitine on carrageenan-induced inflammation in aged rats

BACKGROUND

It is known that L-carnitine is a cofactor in the transport of fatty acids across the inner mitochondrial membrane for beta-oxidation. However, L-carnitine is an antioxidant compound widely used for the treatment of deficits in functions due to the aging process.

OBJECTIVE

The purpose of the study was to investigate the effect of L-carnitine on carrageenan-induced inflammation in aged rats.

METHODS

L-carnitine (50 mg/kg/day) or control vehicle was given by gavage for 30 consecutive days to young (2-month-old) and aged (24-month old) rats. 6 ml of air was injected subcutaneously into the dorsum of each rat, followed 2 days later by 4 ml of 2% carrageenan. After 2 days, the exudate was collected from the inflamed site of each rat. The quantity of collected exudate and the number of cells which have migrated to the inflamed site were determined.

RESULTS

No differences were observed in quantity of exudate in all groups; a decrease in the number of exudate cells was established in aged rats. However, L-carnitine treatment significantly increased the number of exudate cells in both young and aged rats. The exudate cells from the aged rats exhibited a decline of both phagocytic and chemotactic activities as compared with those from the young rats, and the decreased functions were significantly enhanced by L-carnitine treatment. However, superoxide anion release was seen to be unchanged in exudate cells due to aging, and L-carnitine intake decreased the production of superoxide anion by these cells in young and aged rats.

CONCLUSIONS

These findings demonstrate that L-carnitine is capable of restoring the age-related changes in the functions of inflammatory cells. Moreover, L-carnitine may play a protective role in the tissue destruction in inflammation by decreasing the superoxide anion production.

Reduced synaptic plasticity in the lateral perforant path input to the dentate gyrus of aged C57BL/6 mice

Hippocampal slices obtained from C57BL/6 mice (3-25 mo) were used to investigate the effects of aging on excitatory postsynaptic potentials (EPSPs) elicited in dentate gyrus with lateral perforant path stimulation. The maximal amplitude of the EPSP, as well as the degree of paired-pulse facilitation, was significantly reduced in animals aged 12 mo or more compared with younger animals (<12 mo). Although all animals showed equivalent short-term potentiation (STP) in response to high-frequency stimulation, this did not translate into a long-lasting increase in synaptic efficacy in the older animals. A significant degree of long-term potentiation (LTP) of synaptic efficacy was only observed in animals <12 mo of age when measured 30 min after induction. Blocking GABAA-mediated inhibition significantly enhanced STP in younger and older animals; however, a significant degree of LTP was again only observed in slices taken from younger animals. These data indicate that the lateral perforant path input to the dentate gyrus is altered by the aging process, and that this results in a reduction in the capacity of this input to exhibit long-lasting synaptic plasticity.

Theta-frequency synaptic potentiation in CA1 in vitro distinguishes cognitively impaired from unimpaired aged Fischer 344 rats

Hippocampal-dependent learning and memory deficits have been well documented in aging rodents. The results of several recent studies have suggested that these deficits arise from weakened synaptic plasticity within the hippocampus. In the present study, we examined the relationship between hippocampal long-term potentiation (LTP) in vitro and spatial learning in aged (24-26 months) Fischer 344 rats. We found that LTP induced in the CA1 region using theta-frequency stimulation (5 Hz) is selectively impaired in slices from a subpopulation of aged rats that had shown poor spatial learning in the Morris water maze. LTP at 5 Hz in aged rats that did not show learning deficits was similar to that seen in young (4-6 months) controls. We also found that 5 Hz LTP amplitude strongly correlated with individual learning performance among aged rats. The difference in 5 Hz LTP magnitude among aged rats was not attributable to an altered response to 5 Hz stimulation or to differences in the NMDA receptor-mediated field EPSP. In addition, no performance-related differences in LTP were seen when LTP was induced with 30 or 70 Hz stimulation protocols. Finally, both 5 Hz LTP and spatial learning in learning-impaired rats were enhanced with the selective muscarinic M2 antagonist BIBN-99 (5,11-dihydro-8-chloro-11-[[4-[3-[(2,2-dimethyl-1-oxopentyl)ethylamino]propyl]-1-piperidinyl]acetyl]-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one). These findings reinforce the idea that distinct types of hippocampal LTP offer mechanistic insight into age-associated cognitive decline.

Long-term potentiation in aged rats is restored when the age-related decrease in polyunsaturated fatty acid concentration is reversed

Several age-related changes have been identified in rat hippocampus; among these are deficits in glutamate release and long-term potentiation in dentate gyrus. These deficits correlate with a decrease in the concentration of arachidonic acid in hippocampus. In this study, the effects of dietary supplementation for 8 weeks with omega -6 or omega -3 fatty acids were assessed in groups of aged and young rats. The data presented indicate that dietary supplementation in aged rats restored the concentrations of arachidonic acid and docosahexanoic acid in hippocampal preparations to those observed in tissue prepared from young rats. In parallel, aged rats which received the experimental diets sustained long-term potentiation in a manner indistinguishable from young rats. The evidence presented supports the view that an age-related increase in reactive oxygen species production is linked with the decrease in polyunsaturated fatty acids and that a diet enriched in eicosapentanoic acid has antioxidant properties which may play a key role in reversal of the observed age-related deficits.

Assessment of choline uptake for the synthesis and release of acetylcholine in brain slices by a dynamic autoradiographic technique using [11C]choline

The uptake of choline for the synthesis and release of acetylcholine was investigated in brain slices by dynamic positron autoradiography using [11C]choline. Brain slices (330 microm) were incubated with [11C]choline in oxygenated Krebs-Ringer medium at 34 degrees C and serial two-dimensional time-resolved images of the uptake and release of radioactivity were recorded on Storage Phosphor screens. [11C]choline uptake increased with the period of incubation and was 1.9 times higher in the striatum than cerebral cortex. The uptake in the striatum was significantly diminished by hemicholinium-3 (HC-3), an inhibitor of high-affinity choline uptake. Pretreatment of brain slices with 50 mM K(+) for 20 min enhanced the uptake in striatum. The uptake of [11C]choline in brain slices was saturable using nonlabeled choline. Two uptake systems, a high-affinity and a low-affinity system, were confirmed to exist by kinetic analysis using Lineweaver-Burk plots. The 11C radioactivity that had accumulated in the striatum disappeared on treatment with veratridine, a depolarization agent, in the presence of HC-3. This pattern of disappearance was consistent with that of the appearance of unlabeled and labeled acetylcholine in the medium. These results indicate that this method is useful for obtaining information regarding the uptake of choline for the synthesis and release of acetylcholine in live brain tissues.

Enhancement of learning capacity and cholinergic synaptic function by carnitine in aging rats

The effects of a carnitine derivative, acetyl-L-carnitine (ALCAR), on the cognitive and cholinergic activities of aging rats were examined. Rats were given ALCAR (100 mg/kg) per os for 3 months and were subjected to the Hebb-Williams tasks and a new maze task, AKON-1, to assess their learning capacity. The learning capacity of the ALCAR-treated group was superior to that of the control. Cholinergic activities were determined with synaptosomes isolated from the cortices. The high-affinity choline uptake by synaptosomes, acetylcholine synthesis in synaptosomes, and acetylcholine release from synaptosomes on membrane depolarization were all enhanced in the ALCAR group. This study indicates that chronic administration of ALCAR increases cholinergic synaptic transmission and consequently enhances learning capacity as a cognitive function in aging rats.

Acetyl-L-carnitine enhances Na(+), K(+)-ATPase glutathione-S-transferase and multiple unit activity and reduces lipid peroxidation and lipofuscin concentration in aged rat brain regions

This study investigated the effects of chronically administered acetyl-L-carnitine (ALC) on sodium potassium adenosine triphosphatase (Na(+), K(+)-ATPase), glutathione-S-transferase (GST), glutathione peroxidase (GPx), multiple unit activity (MUA) and lipid peroxidation (LP) and lipofuscin (LF) concentration in brain regions: cerebral cortex, hippocampus, striatum and thalamus, of 24-month-old rats. The activity of Na(+), K(+)-ATPase and GST was enhanced; that of GPx was unaffected. The MUA was increased while the levels of LP and LF were decreased. These novel data provide new additional evidence concerning the antiaging attributes of ALC.

Acetyl-L-carnitine physical-chemical, metabolic, and therapeutic properties: relevance for its mode of action in Alzheimer's disease and geriatric depression

Acetyl-L-carnitine (ALCAR) contains carnitine and acetyl moieties, both of which have neurobiological properties. Carnitine is important in the beta-oxidation of fatty acids and the acetyl moiety can be used to maintain acetyl-CoA levels. Other reported neurobiological effects of ALCAR include modulation of: (1) brain energy and phospholipid metabolism; (2) cellular macromolecules, including neurotrophic factors and neurohormones; (3) synaptic morphology; and (4) synaptic transmission of multiple neurotransmitters. Potential molecular mechanisms of ALCAR activity include: (1) acetylation of -NH2 and -OH functional groups in amino acids and N terminal amino acids in peptides and proteins resulting in modification of their structure, dynamics, function and turnover; and (2) acting as a molecular chaperone to larger molecules resulting in a change in the structure, molecular dynamics, and function of the larger molecule. ALCAR is reported in double-blind controlled studies to have beneficial effects in major depressive disorders and Alzheimer's disease (AD), both of which are highly prevalent in the geriatric population.

Age-related changes in LTP and antioxidant defenses are reversed by an alpha-lipoic acid-enriched diet

Among the age-related changes identified in rat hippocampus are impairments in LTP and glutamate release. These deficits have been coupled with decreased arachidonic acid concentration. In this study we compared LTP and glutamate release in groups of aged and young rats fed for 8 weeks on a control diet or on a diet enriched in alpha-lipoic acid. Dietary supplementation in aged rats restored hippocampal arachidonic acid concentration to levels observed in tissue prepared from young rats. We observed that aged rats that received the experimental diet sustained LTP in perforant path-granule cell synapses in a manner indistinguishable from young rats whereas the age-related impairment in glutamate release was reversed in synaptosomes prepared from dentate gyrus obtained from these rats. The evidence presented supports the hypothesis that the alpha-lipoic acid-enriched diet has antioxidant properties, because the age-related increase in superoxide dismutase activity and decrease in alpha-tocopherol concentration were reversed. The finding that the age-related increase in interleukin-1 (IL-1)beta concentration was also reversed suggests a possible role for this cytokine in ageing.

Age-related working memory deficits in the allocentric place discrimination task: possible involvement in cholinergic dysfunction

It is well known that learning and memory ability declines with aging. Age-related long-term changes in learning and memory ability in rats were investigated with the place navigation task and the allocentric place discrimination task (APDT) in a water maze using the same animals for each task. In a working memory place navigation task, aged animals could learn the location of the platform as well as when they were young, although strategy shifts were observed. In contrast, accuracy in the APDT significantly declined from 90% to 65% with aging. This impairment was ameliorated by an acetylcholine esterase inhibitor physostigmine at 22-23 months old. No amelioration was, however, detected in the same animals tested when they further aged to 26-27 months old. These results suggest that the APDT performance is sensitive to age-related memory deficits and that this may be due to the cholinergic dysfunction.

Age-related changes in oxidative mechanisms and LTP are reversed by dietary manipulation

Aged rats exhibit an impaired ability to sustain long-term potentiation in dentate gyrus which correlates with a decrease in arachidonic acid concentration. Here we confirm the previous finding that dietary supplementation with arachidonic acid and its precursor, gamma-linolenic acid, reversed the impairment in LTP in aged rats and report that there is a significant correlation between membrane arachidonic acid concentration and response to tetanic stimulation. We observed that age was associated with decreases in the concentration of vitamins C and E and increased activity of superoxide dismutase, indicative of a compromise in antioxidative defenses; these changes were paralleled by increases in interleukin-1beta (IL-1beta) concentration and lipid peroxidation. Dietary manipulation restored polyunsaturated fatty acid concentrations to values observed in tissue prepared from young rats and reversed the age-related changes in vitamins E and C, IL-1beta concentration and superoxide dismutase activity. We propose that these changes reverse the increase in lipid peroxidation and thereby the age-related change in polyunsaturated fatty acids.

Sex dimorphisms in the rate of age-related decline in spatial memory: relevance to alterations in the estrous cycle

The present experiments demonstrate the existence of sex differences in the rate of development and the magnitude of age-dependent impairments in cognitive and sensorimotor abilities. Although no sex differences were found in spatial reference memory at a young age, the mnemonic ability of female rats deteriorated more rapidly than that of male rats. A major drop in reference memory of the females occurred at the age of 12 months, whereas in the males the onset of impairments occurred later, at the age of 18 months. In spatial working memory, on the other hand, the magnitude of decline was greater in females than in males, although the onset of these impairments occurred at the age of 24 months in both sexes. A sexual dimorphism-aging interaction also was observed in sensorimotor performance. Up to the age of 18 months the females outperformed the males. Subsequently, by the age of 24 months, the performance of the females declined to a level similar to that of the males. The deficits observed in reference and working memory seem to be cognitive in origin and not attributable to alterations in sensory and motor abilities. In addition, the earlier onset of reference memory impairments in females generally coincides with the onset of alterations in the estrous cycle, suggesting that a decline in the estrogenic milieu of the females could be a factor in accelerating the rate of age-related cognitive impairments in the female rat.

Effects of age and sex on the water maze performance and hippocampal cholinergic fibers in rats

We have examined if age-related deterioration of spatial memory and cholinergic innervation of the dentate gyrus is gender-specific. Aging progressively affected the performance of male and female rats in place discrimination version of the water maze task. On repeated acquisition task, only old males, but not old females, were significantly impaired relative to young and adult animals of both sexes. In parallel, we found that the age-associated reduction of the density of cholinergic fibers in the dentate gyrus was significantly more profound in old males than in age-matched females. These results suggest that, although male and female rats have an identical pattern of reference memory decline, impairment of the working memory and deterioration of the hippocampal cholinergic system are slower to develop in females than in males.

Age-related changes of the nucleolar organizer regions without neuron loss in medial mamillary bodies (hypothalamus) in old rats

Age-related morphological and functional changes were studied in the medial mamillary nuclei of the hypothalamus (MMN). The number of nerve cells and the volume of MMN were estimated in both groups of Wistar rats, adult and old (3 and 22 months, respectively) using stereologic methods such as the optical fractionator and Cavalieri's method respectively. The number of neurons and glial cells remain inalterable with ageing but there was an age-dependent reduction in MMN volume. In the second experiment, functional changes in the MMN neurons were observed although there was no loss in neuron number. Several functional parameters of the Ag-NORs were quantified by a computer analysis system: area and number of Ag-NORs per neuron; number of neurons with one or several Ag-NORs and also surface of neuronal nucleus. The present study shows how ageing causes volumetric and functional changes in the MMN whereas the number of neurons and glial cells remain unchanged in the mamillary region. All these results confirm the effects of age on proteic synthesis activity in neurons of the MMN, showing a decreased neuronal activity in this region.

Reduction in the MK-801 binding sites of the NMDA sub-type of glutamate receptor in a mouse model of congenital hyperammonemia: prevention by acetyl-L-carnitine

Our earlier studies on the pharmacotherapeutic effects of acetyl-L-carnitine (ALCAR), in sparse-fur (spf) mutant mice with X linked ornithine transcarbamylase deficiency, have shown a restoration of cerebral ATP, depleted by congenital hyperammonemia and hyperglutaminemia. The reduced cortical glutamate and increased quinolinate may cause a down-regulation of the N-methyl-D-aspartate (NMDA) receptors, observed by us in adult spf mice. We have now studied the kinetics of [3H]-MK-801 binding to NMDA receptors in spf mice of different ages to see the effect of chronic hyperammonemia on the glutamate neurotransmission. We have also studied the Ca2+-dependent and independent (4-aminopyridine (AP) and veratridine-mediated) release of glutamate and the uptake of [3H]-glutamate in synaptosomes isolated from mutant spf mice and normal CD-1 controls. All these studies were done with and without ALCAR treatment (4 mmol/kg wt i.p. daily for 2 weeks), to see if its effect on ATP repletion could correct the glutamate neurotransmitter abnormalities. Our results indicate a normal MK-801 binding in 12-day-old spf mice but a significant reduction immediately after weaning (21 day), continuing into the adult stage. The Ca2+-independent release of endogenous glutamate from synaptosomes was significantly elevated at 35 days, while the uptake of glutamate into synaptosomes was significantly reduced in spf mice. ALCAR treatment significantly enhanced the MK-801 binding, neutralized the increased glutamate release and restored the glutamate uptake into synaptosomes of spf mice. These studies point out that: (a) the developmental abnormalities of the NMDA sub-type of glutamate receptor in spf mice could be due to the effect of sustained hyperammonemia, causing a persistent release of excess glutamate and inhibition of the ATP-dependent glutamate transport, (b) the modulatory effects of ALCAR on the NMDA binding sites could be through a repletion of ATP, required by the transporters to efficiently remove extracellular glutamate.

Life-long diet restriction failed to retard cognitive aging in Fischer-344 rats

Although the beneficial effects of diet restriction on longevity and the retardation of many somatic age-related processes are well established, the answer to the question of whether anti-aging effects of diet restriction extend to the brain and cognitive function remains unclear. In the present study, the effects of long-term dietary restriction (60% of ad-libitum calories) on an age-related alteration of memory and sensorimotor function have been investigated in Fischer 344 male rats at four different ages: 6 months, 12 months, 18 months, and 24 months. A major drop in reference memory of DR and AL rats occurred at the age of 18 months. The performance deficits in working memory tasks were observed in both diet groups at the age of 24 months. These results indicate that diet restriction failed to provide protection against age-related deficits in memory. Although DR rats outperformed AL rats in sensorimotor tasks throughout the life-span, the slope of the declining function in DR rats paralleled those of AL rats, suggesting that diet restriction failed to alter the rate of aging in sensorimotor performance, as well.

Acetyl-L-carnitine modulates glucose metabolism and stimulates glycogen synthesis in rat brain

The effects of acetyl-L-carnitine on cerebral glucose metabolism were investigated in rats injected with differently 14C- and 13C-labelled glucose and sacrificed after 15, 30, 45, and 60 min. Acetyl-L-carnitine was found to reduce total 14CO2 release from [U-14C]glucose along with the decrease in [1-13C]glucose incorporation into cerebral amino acids and tricarboxylic acid cycle intermediates. However the 13C labelling pattern within different carbon positions of glutamate, glutamine, GABA, and aspartate was unaffected by acetyl-L-carnitine administration. Furthermore, the cerebral levels of newly-synthesized proglycogen were higher in rats treated with acetyl-L-carnitine than in untreated ones. These results suggest that acetyl-L-carnitine was able to modulate cerebral glucose utilization and provide new insights on the mechanisms of action of this molecule in the central nervous system.

Dietary supplementation with vitamin E reverses the age-related deficit in long term potentiation in dentate gyrus

Long term potentiation (LTP) in dentate gyrus is impaired in aged rats, and this has been associated with an age-related decrease in membrane arachidonic acid concentration. In this study, we considered whether the trigger for this age-related decrease in arachidonic acid might be increased lipid peroxidation stimulated by the proinflammatory cytokine, interleukin-1beta. Groups of aged and young rats were fed on a control diet or a diet supplemented with alpha-tocopherol and assessed for their ability to sustain LTP. Aged rats fed on the control diet exhibited an impaired ability to sustain LTP and analysis of tissue prepared from these rats exhibited increased interleukin-1beta, increased lipid peroxidation, and decreased membrane arachidonic acid concentration compared with young rats fed on either diet. Aged rats fed on the supplemented diet sustained LTP in a manner indistinguishable from young rats, and the age-related increases in interleukin-1beta and lipid peroxidation and the decrease in membrane arachidonic acid concentration were all reversed. We propose that interleukin-1beta may be the trigger that induces these age-related changes and may therefore be responsible for the deficit in long term potentiation in aged rats. The observation that alpha-tocopherol reverses these changes is consistent with the hypothesis that some age-related changes in hippocampus might derive from oxidative stress.

Evidence that increased hippocampal expression of the cytokine interleukin-1 beta is a common trigger for age- and stress-induced impairments in long-term potentiation

Several cytokines and their receptors are identified in brain; one of these is the proinflammatory cytokine interleukin-1beta that is synthesized and released from neurons and glia in response to stress or insult. Among the actions of interleukin-1beta is its ability to inhibit long-term potentiation in the hippocampus in vitro, an action that mimics one of the consequences of stress and age. It has been shown that the concentration of interleukin-1beta in brain tissue is increased in neurodegenerative conditions, and recent evidence from our laboratory has indicated an increase in the concentration of interleukin-1beta in the hippocampus of aged rats. These observations led us to consider that the underlying common cause of impaired long-term potentiation in aged and stressed rats might be increased endogenous interleukin-1beta concentration in hippocampus. The data presented here indicate that there was an inverse relationship between concentration of interleukin-1beta in the dentate gyrus and long-term potentiation in perforant path-->granule cell synapses in aged rats, stressed rats, and rats pretreated with interleukin-1beta. The evidence suggested that the cytokine induces formation of reactive oxygen species that triggers lipid peroxidation in vivo, as well as in vitro, and that these changes lead to depletion of membrane arachidonic acid that correlates with impaired long-term potentiation. We propose that three theories of aging, the glucocorticoid theory, the membrane theory, and the free radical theory, constitute three facets of age with one underlying trigger: an increase in the endogenous concentration of interleukin-1beta in hippocampus.

Aging differentially alters forms of long-term potentiation in rat hippocampal area CA1

Long-term potentiation (LTP) of the Schaffer collateral/commissural inputs to CA1 in the hippocampus was shown to consist of N-methyl-D-aspartate receptor (NMDAR) and voltage-dependent calcium channel (VDCC) dependent forms. In this study, the relative contributions of these two forms of LTP in in vitro hippocampal slices from young (2 mo) and old (24 mo) Fischer 344 rats were examined. Excitatory postsynaptic potentials (EPSP) were recorded extracellularly from stratum radiatum before and after a tetanic stimulus consisting of four 200-Hz, 0.5-s trains given 5 s apart. Under control conditions, a compound LTP consisting of both forms was induced and was similar, in both time course and magnitude, in young and old animals. NMDAR-dependent LTP (nmdaLTP), isolated by the application of 10 microM nifedipine (a voltage-dependent calcium channel blocker), was significantly reduced in magnitude in aged animals. The VDCC dependent form (vdccLTP), isolated by the application of 50 microM D,L-2-amino-5-phosphonvalerate (APV), was significantly larger in aged animals. Although both LTP forms reached stable values 40-60 min posttetanus in young animals, in aged animals vdccLTP increased and nmdaLTP decreased during this time. In both young and old animals, the sum of the two isolated LTP forms approximated the magnitude of the compound LTP, and application of APV and nifedipine or genestein (a tyrosine kinase inhibitor) together blocked potentiation. These results suggest that aging causes a shift in synaptic plasticity from NMDAR-dependent mechanisms to VDCC-dependent mechanisms. The data are consistent with previous findings of increased L-type calcium current and decreased NMDAR number in aged CA1 cells and may help explain age-related deficits in learning and memory.

The ability of aged rats to sustain long-term potentiation is restored when the age-related decrease in membrane arachidonic acid concentration is reversed

The ability of aged rats to sustain long-term potentiation in the dentate gyrus of the hippocampus is impaired and this impairment correlates with decreased release of glutamate and a decrease in membrane arachidonic acid concentration. Twenty-two-month-old rats receiving a diet supplemented with arachidonic acid and its precursor, gamma-linolenic acid, sustained long-term potentiation in a manner indistinguishable from four-month-old controls. Dietary supplementation also restored arachidonic acid concentrations in membranes prepared from hippocampus of these aged animals to levels observed in hippocampus of four-month-old rats. Glutamate release stimulated by depolarization was similar in dentate gyrus prepared from young rats and aged rats which received the experimental diet, but was markedly reduced in aged animals which received the control diet. In addition, the synergism between arachidonic acid and the metabotropic glutamate receptor agonist, trans-1-amino-cyclopentyl-1,3-dicarboxylate, on glutamate release, which was observed in hippocampal synaptosomes prepared from four-month-old rats, was also observed in hippocampal preparations obtained from aged rats which had been fed with the experimental diet, but was absent in hippocampal preparations obtained from aged animals which were fed with control diet. Thus, reversing the age-related decrease in membrane arachidonic acid concentration restored ability of aged animals to sustain long-term potentiation and reversed age-related changes in glutamate release.

Age-related decrease in the N-methyl-D-aspartateR-mediated excitatory postsynaptic potential in hippocampal region CA1

Glutamatergic fast synaptic transmission is known to be altered with age in a region-specific manner in hippocampus of memory-impaired old rats. In the present experiment, presynaptic fiber potentials and non-N-methyl-D-aspartate (NMDAR) and NMDAR-mediated synaptic responses in CA1 were compared in three ages of behaviorally characterized male F-344 rats. In the CA1 region, old rats showed approximately equivalent reductions in non-NMDAR- and NMDAR-excitatory postsynaptic potential amplitudes for a given size of presynaptic fiber potential. There was no change in magnitude of the presynaptic response itself at any stimulus level. These results are consistent with the hypothesis that there is a reduction in the number of Schaffer collateral synapses per presynaptic axon. This pattern of results in CA1 is very different from what is known to occur at the perforant path-granule cell synapse. In fascia dentata the non-NMDAR-mediated excitatory postsynaptic potential is increased in amplitude, although the NMDAR-mediated excitatory postsynaptic potential is reduced for a given presynaptic input. These data suggest that age-related functional alterations in neurotransmitter receptor subtypes occur differentially between closely-related anatomical subregions.

Oxotremorine infusions into the medial septal area of middle-aged rats affect spatial reference memory and ChAT activity

Age-related spatial memory deficits are correlated with septohippocampal cholinergic system degeneration. The present study examined the effect of intraseptal infusions of the cholinergic agonist, oxotremorine, on spatial reference memory in middle-aged rats using place discrimination in the water maze, and on cholinergic activity using choline acetyltransferase (ChAT) activity. Oxotremorine mildly improved the rate of place discrimination acquisition of middle-aged rats during initial sessions only, but did not affect asymptotic levels of performance achieved. Of the brain regions assayed, ChAT activity increased with age in the temporal cortex and dorsal CA2/3 region of the hippocampus. Oxotremorine significantly decreased ChAT activity in the dorsal hippocampus. In contrast to our previous results in aged rats indicating a more robust effect of oxotremorine on spatial working memory, the present results suggest a modest effect of intraseptal oxotremorine on the acquisition of a spatial reference memory task.

The synergism between ACPD and arachidonic acid on glutamate release in hippocampus is age-dependent

Activation of the metabotropic glutamate receptor by the specific agonist trans-1-amino-cyclopentyl-1,3-dicarboxylate (ACPD) increases release of glutamate and activation of protein kinase C in the presence of a low concentration of arachidonic acid in hippocampal synaptosomes prepared from 4-month-old rats. The data presented indicate an age-related decrease in both [3H]glutamate release and protein kinase C activation and an age-related decrease in the release response to arachidonic acid and ACPD, with no corresponding change in protein kinase C activation. The finding that the interaction between arachidonic acid and ACPD on release was absent in synaptosomes prepared in the presence of heparin, an antagonist at inositol trisphosphate receptors, suggests that mobilization of intracellular calcium stores plays a role in the synergism between arachidonic acid and ACPD on [3H]glutamate release in hippocampal synaptosomes.

Nicotine enhances Morris water maze performance of young and aged rats

We have recently demonstrated that nicotine administration improves the acquisition and/or memory retention of aged rats in 17-arm radial maze, Lashley III maze, and one-way active avoidance testing. The present study extends our evaluation of nicotine's cognition-enhancing potential by determining the effect of nicotine on acquisition and retention of the Morris water maze in young adult (2 to 3 months old) and aged (25 to 26 months old) Sprague-Dawley rats. For 3 days prior to the onset of testing, and 15 min prior to daily testing, rats were treated IP with 0.2 mg/kg nicotine or saline vehicle. Compared to the performance of young adults, vehicle-treated aged rats were impaired in water maze acquisition. Nicotine substantially enhanced the acquisition of aged rats. Furthermore, nicotine significantly improved the memory retention of young adult rats. These cognitive improvements may involve a nicotine-receptor induced increase in generalized alertness and/or a facilitation of higher integrative function. The results suggest that nicotine and/or nicotinic agonists may be useful in treating age-associated memory impairment and/or Alzheimer's disease.