Age-related changes in hippocampal drug facilitation of memory processing in SAMP8 mice

Neuroprotective and restorative properties of the GLP-1/GIP dual agonist DA-JC1 compared with a GLP-1 single agonist in Alzheimer's disease

The sister incretins glucagon-like peptide-1 (GLP-1) and glucagon dependent insulinotropic polypeptide (GIP) are growth factors responsible for re-sensitizing insulin signalling. Interestingly, their analogues, originally developed to treat type 2 diabetes (T2D), have demonstrated a range of neuroprotective and neurorestorative properties. Novel peptide GLP-1/GIP dual agonist (DA) shows good effects in diabetic patients, superior to the effects demonstrated by single GIP or GLP-1 mimetics. Furthermore, novel DAs have shown considerable neuroprotection in neurodegenerative models. Here, we investigated the neuroprotective and restorative involvement of the DA DA-JC1 and liraglutide (Lg), a single GLP-1 receptor analogue, in vitro using human neuroblastoma (SH-SY5Y) against oxidative stress induced by oxygen peroxide (H₂O₂), and in vivo, in a mouse model of Alzheimer's disease (AD), APP/PS1. First, we determined the ideal concentration of the peptides and demonstrated that DA-JC1 protects cells against oxidative stress more than Lg, improving cell viability, normalizing reactive oxygen species (ROS) and attenuating DNA damage generated by H₂O₂. Moreover, in 10-to-12-months-old APP/PS1 animals treated for 4 weeks, both Lg and DA-JC1 were very efficient in stimulating neurogenesis and reducing some important hallmarks of AD, but DA-JC1 was better than Lg in attenuating crucial neuroinflammatory markers, especially reactive astrocyte, in both wild-type (WT) and APP/PS1 hippocampal regions. Altogether, this study suggests an interactive role of GLP-1 and GIP receptors, enhancing the efficiency of single GLP-1 analogues, especially in attenuating oxidative stress and neuroinflammation. We confirm that combining GLP-1 and GIP results in a variety of beneficial effects, providing key evidences for the development of a promising therapeutic strategy for AD.

Highly water pressurized brown rice improves cognitive dysfunction in senescence-accelerated mouse prone 8 and reduces amyloid beta in the brain

Background

Alzheimer’s disease (AD) is the most common form of dementia and the number of AD patients continues to increase worldwide. Components of the germ layer and bran of Brown rice (BR) help maintain good health and prevent AD. Because the germ layer and bran absorb little water and are very hard and difficult to cook, they are often removed during processing. To solve these problems, in this study, we tried to use a high-pressure (HP) technique.

Methods

We produced the highly water pressurized brown rice (HPBR) by pressurizing BR at 600 MPa, and then we fed it to an AD mouse model, senescence-accelerated mouse prone 8, to investigate the therapeutic effects of HPBR on cognitive dysfunction by Y-maze spatial memory test.

Results

HP treatment increased the water absorbency of BR without nutrient loss. HPBR ameliorated cognitive dysfunction and reduced the levels of amyloid-β, which is a major protein responsible for AD, in the brain.

Conclusions

These results suggest that HPBR is effective for preventing AD.

The Chinese herbal formula Fuzheng Quxie Decoction attenuates cognitive impairment and protects cerebrovascular function in SAMP8 mice

PURPOSE

This study was designed to explore the underlying mechanism of action for a Fuzheng Quxie Decoction (FQD) in Alzheimer's disease (AD), to validate its neuroprotective effects, and to provide experimental support for its predicted mechanism of action.

METHODS

An integrative approach to network pharmacology was performed to predict the mechanism of action for treatment of AD with FQD. The predicted mechanism was validated in SAMP8 mice.

RESULTS

With predicted putative FQD targets and a collection of AD-related genes, 245 possible regulatory targets of FQD were identified for the treatment of AD. Pathway-enrichment analysis for the possible regulatory targets indicated that vascular endothelial growth factor (VEGF) and VEGF-receptor signaling were pivotal in the treatment of AD with FQD. In vivo experiments confirmed the neuroprotective effect and the predicted mechanism of action for treatment of AD with FQD.

CONCLUSION

This study contributes to an understanding of the neuroprotective effect of FQD and its potential mechanism of action for the treatment of AD.

LW-AFC Effects on N-glycan Profile in Senescence-Accelerated Mouse Prone 8 Strain, a Mouse Model of Alzheimer's Disease

Glycosylation is one of the most common eukaryotic post-translational modifications, and aberrant glycosylation has been linked to many diseases. However, glycosylation and glycome analysis is a significantly challenging task. Although several lines of evidence have indicated that protein glycosylation is defective in Alzheimer’s disease (AD), only a few studies have focused on AD glycomics. The etiology of AD is unclear and there are no effective disease-modifying treatments for AD. In this study, we found that the object recognition memory, passive avoidance, and spatial learning and memory of senescence-accelerated mouse prone 8 (SAMP8) strain, an AD animal model, were deficient, and LW-AFC, which was prepared from the traditional Chinese medicine prescription Liuwei Dihuang decoction, showed beneficial effects on the deterioration of cognitive capability in SAMP8 mice. Forty-three and 56 N-glycan were identified in the cerebral cortex and serum of SAMP8 mice, respectively. The N-glycan profile in SAMP8 mice was significantly different from that of senescence accelerated mouse resistant 1 (SAMR1) strains, the control of SAMP8 mice. Treatment with LW-AFC modulated the abundance of 21 and 6 N-glycan in the cerebral cortex and serum of SAMP8 mice, respectively. The abundance of (Hex)3(HexNAc)5(Fuc)1(Neu5Ac)1 and (Hex)2(HexNAc)4 decreased in the cerebral cortex and serum of SAMP8 mice compared with SAMR1 mice, decreases that were significantly correlated with learning and memory measures. The administration of LW-AFC could reverse or increase these levels in SAMP8 mice. These results indicated that the effects of LW-AFC on cognitive impairments in SAMP8 mice might be through modulation of N-glycan patterns, and LW-AFC may be a potential anti-AD agent.

Long-Term Treatment with Liraglutide, a Glucagon-Like Peptide-1 (GLP-1) Receptor Agonist, Has No Effect on β-Amyloid Plaque Load in Two Transgenic APP/PS1 Mouse Models of Alzheimer's Disease

One of the major histopathological hallmarks of Alzheimer’s disease (AD) is cerebral deposits of extracellular β-amyloid peptides. Preclinical studies have pointed to glucagon-like peptide 1 (GLP-1) receptors as a potential novel target in the treatment of AD. GLP-1 receptor agonists, including exendin-4 and liraglutide, have been shown to promote plaque-lowering and mnemonic effects of in a number of experimental models of AD. Transgenic mouse models carrying genetic mutations of amyloid protein precursor (APP) and presenilin-1 (PS1) are commonly used to assess the pharmacodynamics of potential amyloidosis-lowering and pro-cognitive compounds. In this study, effects of long-term liraglutide treatment were therefore determined in two double APP/PS1 transgenic mouse models of Alzheimer’s disease carrying different clinical APP/PS1 mutations, i.e. the ‘London’ (hAPP_Lon/PS1_A246E) and ‘Swedish’ mutation variant (hAPP_Swe/PS1_ΔE9) of APP, with co-expression of distinct PS1 variants. Liraglutide was administered in 5 month-old hAPP_Lon/PS1_A246E mice for 3 months (100 or 500 ng/kg/day, s.c.), or 7 month-old hAPP_Swe/PS1_ΔE9 mice for 5 months (500 ng/kg/day, s.c.). In both models, regional plaque load was quantified throughout the brain using stereological methods. Vehicle-dosed hAPP_Swe/PS1_ΔE9 mice exhibited considerably higher cerebral plaque load than hAPP_Lon/PS1_A246E control mice. Compared to vehicle-dosed transgenic controls, liraglutide treatment had no effect on the plaque levels in hAPP_Lon/PS1_A246E and hAPP_Swe/PS1_ΔE9 mice. In conclusion, long-term liraglutide treatment exhibited no effect on cerebral plaque load in two transgenic mouse models of low- and high-grade amyloidosis, which suggests differential sensitivity to long-term liraglutide treatment in various transgenic mouse models mimicking distinct pathological hallmarks of AD.

The GLP-1 Receptor Agonist Liraglutide Improves Memory Function and Increases Hippocampal CA1 Neuronal Numbers in a Senescence-Accelerated Mouse Model of Alzheimer's Disease

Recent studies indicate that glucagon-like peptide 1 (GLP-1) receptor agonists, currently used in the management of type 2 diabetes, exhibit neurotrophic and neuroprotective effects in amyloid-β (Aβ) toxicity models of Alzheimer’s disease (AD). We investigated the potential pro-cognitive and neuroprotective effects of the once-daily GLP-1 receptor agonist liraglutide in senescence-accelerated mouse prone 8 (SAMP8) mice, a model of age-related sporadic AD not dominated by amyloid plaques. Six-month-old SAMP8 mice received liraglutide (100 or 500 μg/kg/day, s.c.) or vehicle once daily for 4 months. Vehicle-dosed age-matched 50% back-crossed as well as untreated young (4-month-old) SAMP8 mice were used as control groups for normal memory function. Vehicle-dosed 10-month-old SAMP8 mice showed significant learning and memory retention deficits in an active-avoidance T-maze, as compared to both control groups. Also, 10-month-old SAMP8 mice displayed no immunohistological signatures of amyloid-β plaques or hyperphosphorylated tau, indicating the onset of cognitive deficits prior to deposition of amyloid plaques and neurofibrillary tangles in this AD model. Liraglutide significantly increased memory retention and total hippocampal CA1 pyramidal neuron numbers in SAMP8 mice, as compared to age-matched vehicle-dosed SAMP8 mice. In conclusion, liraglutide delayed or partially halted the progressive decline in memory function associated with hippocampal neuronal loss in a mouse model of pathological aging with characteristics of neurobehavioral and neuropathological impairments observed in early-stage sporadic AD.

Alzheimer's Disease and Hippocampal Adult Neurogenesis; Exploring Shared Mechanisms

New neurons incorporate into the granular cell layer of the dentate gyrus throughout life. Neurogenesis is modulated by behavior and plays a major role in hippocampal plasticity. Along with older mature neurons, new neurons structure the dentate gyrus, and determine its function. Recent data suggest that the level of hippocampal neurogenesis is substantial in the human brain, suggesting that neurogenesis may have important implications for human cognition. In support of that, impaired neurogenesis compromises hippocampal function and plays a role in cognitive deficits in Alzheimer's disease mouse models. We review current work suggesting that neuronal differentiation is defective in Alzheimer's disease, leading to dysfunction of the dentate gyrus. Additionally, alterations in critical signals regulating neurogenesis, such as presenilin-1, Notch 1, soluble amyloid precursor protein, CREB, and β-catenin underlie dysfunctional neurogenesis in Alzheimer's disease. Lastly, we discuss the detectability of neurogenesis in the live mouse and human brain, as well as the therapeutic implications of enhancing neurogenesis for the treatment of cognitive deficits and Alzheimer's disease.

The behavioral, pathological and therapeutic features of the senescence-accelerated mouse prone 8 strain as an Alzheimer's disease animal model

Alzheimer's disease (AD) is a widespread and devastating progressive neurodegenerative disease. Disease-modifying treatments remain beyond reach, and the etiology of the disease is uncertain. Animal model are essential for identifying disease mechanisms and developing effective therapeutic strategies. Research on AD is currently being carried out in rodent models. The most common transgenic mouse model mimics familial AD, which accounts for a small percentage of cases. The senescence-accelerated mouse prone 8 (SAMP8) strain is a spontaneous animal model of accelerated aging. Many studies indicate that SAMP8 mice harbor the behavioral and histopathological signatures of AD, namely AD-like cognitive and behavioral alterations, neuropathological phenotypes (neuron and dendrite spine loss, spongiosis, gliosis and cholinergic deficits in the forebrain), β-amyloid deposits resembling senile plaques, and aberrant hyperphosphorylation of Tau-like neurofibrillary tangles. SAMP8 mice are useful in the development of novel therapies, and many pharmacological agents and approaches are effective in SAMP8 mice. SAMP8 mice are considered a robust model for exploring the etiopathogenesis of sporadic AD and a plausible experimental model for developing preventative and therapeutic treatments for late-onset/age-related AD, which accounts for the vast majority of cases.

Limited impairments of associative learning in a mouse model of accelerated senescence

Research concerning impairment of associative learning during aging remains limited. The senescence-accelerated mice (SAM) prone/8 (P8) has been proposed as a useful model for the study of aging, and SAM resistant/1(SAMR1) is its control as a normal aging strain. Classical eyeblink conditioning has long been served as a model of associative learning. In order to explore the effects of aging on associative learning in SAM, the present study successively tested three paradigms of eyeblink conditioning in SAMP8 and SAMR1: classical single cue trace eyeblink conditioning (TEC), discriminative trace eyeblink conditioning and reversal learning of TEC. Behavioral performance indicated that SAMP8 could acquire limited single-cue trace eyeblink conditioning task and two-tone discrimination trace eyeblink conditioning with a relative lower acquisition rate compared to SAMR1. Both SAMP8 and SAMR1 failed to acquire reversal learning of discriminative TEC, and SAMP8' startle reflex to tone CS was lower than SAMR1. These results indicated that the impairments of aging on associative learning were incomplete in SAMP8.

Preparation and characterization of a monoclonal antibody with high affinity for soluble Abeta oligomers

Amyloid beta-protein (Abeta) has been causally implicated in the neurodegenerative processes that accompany Alzheimer's disease. Soluble oligomers of the Abeta(1-42) fragment are thought to be significantly more neurotoxic than higher molecular weight aggregates. We report the isolation and characterization of a mouse monoclonal antibody (MAb) directed against soluble Abeta(1-42) oligomers. Synthetic Abeta(1-42) oligomers were assembled in vitro; these were used to immunize mice, and hybridomas were isolated following myeloma fusion of splenocytes from immunized animals. Screening for reactivity against Abeta(1-42) resulted in the identification of MAb A8 with high affinity for soluble oligomers. The isotype of A8 was found to be IgG(2b). Experiments using sub-peptides of Abeta(1-42) revealed that the epitope identified by A8 lies within the 1-6 region of Abeta. The antibody displays high affinity for soluble Abeta(1-42) oligomers in the molecular weight range of 16.5-25 kDa, and detected target antigen in brain sections from senescence-accelerated SAMP 8 mice. The sensitivity and optimal titers for the detection of soluble Abeta(1-42) oligomers were determined to be 0.625 microg/mL in indirect ELISA, and 1:10(6), 1:4000, and 1:150 for ELISA, Western blotting, and immunohistochemistry, respectively. The A8 antibody specific for soluble Abeta(1-42) oligomers will provide a valuable tool for Alzheimer's disease research.

Nitric oxide activity and isoenzyme expression in the senescence-accelerated mouse p8 model of Alzheimer's disease: effects of anti-amyloid antibody and antisense treatments

Amyloid beta protein (Abeta) in Alzheimer's disease induces oxidative stress through several mechanisms, including stimulation of nitric oxide synthase (NOS) activity. We examined NOS activity and expression in the senescence-accelerated mouse P8 (SAMP8) line. The SAMP8 strain develops with aging cognitive impairments, increases in Abeta, and oxidative stress, all reversed by amyloid precursor protein antisense or Abeta antibody treatment. We found here that hippocampal NOS activity in 12-month-old SAMP8 mice was nearly double that of 2-month-old SAMP8 or CD-1 mice, but with no change in NOS isoenzyme mRNA and protein levels. Antisense or antibody treatment further increased NOS activity in aged SAMP8 mice. Antisense treatment increased inducible NOS (iNOS) mRNA levels, decreased neuronal NOS mRNA and protein levels, but did not affect endothelial NOS (eNOS) or iNOS protein or eNOS mRNA levels. These results suggest a complex relation between Abeta and NOS in the SAMP8 that is largely mediated through posttranslational mechanisms.

Increased permeability of blood-brain barrier on the hippocampus of a murine model of senescence

SAMP8 mice show several indicative characteristics of accelerated aging and have been used to study the physiological and physiopathological processes that take place during senescence. There is some controversy about the presence of a functional blood-brain barrier (BBB) disturbance on these animals, which could be related to the oxidative stress or the amyloidosis present in their brain. In order to elucidate BBB status in the hippocampus of SAMP8 mice, in this study we have determined the extravasation from brain microvessels of endogenous IgG in SAMP8 mice aged 3, 7 and 12 months and in age-matched control SAMR1 mice. Immunohistochemistry, confocal microscopy and an imaging methodology specially designed to quantify IgG extravasation have been used. The choroid plexus was analyzed as a control for positive extravasation in SAMP8 and SAMR1 mice and, as expected, in all studied ages high IgG immunoreactivity was observed in both strains. We have found significantly higher levels of IgG extravasation in the hippocampus of 12-month-old SAMP8 mice compared to SAMR1 mice, indicating an increased permeability of BBB in aged senescence-accelerated mice.

Sleep wake profile and EEG spectral power in young or old senescence accelerated mice

Changes occurring with age in cortical EEG and sleep-wake states architecture were examined in senescence accelerated prone (SAMP8) or senescence resistant (SAMR1) mice (age: 2 and 12 months) under baseline conditions or after a 4 h sleep deprivation (SD). In baseline conditions, an increase in slow wave sleep (SWS) amount (21-24%) occurs at the expense of the wakefulness (W) in old SAMP8 and SAMR1 mice versus young animals. In these conditions, SWS latency is reduced (67-72%). Moreover, in SAMP8 and SAMR1 mice, aging deteriorates paradoxical sleep (PS) architecture with more pronounced changes in SAMP8 (amount: -63%; episode duration: -44%; latency: +286%; circadian component loss; and EEG theta (theta) peak frequency (TPF): -1 Hz). During the 4 h recovery subsequent to a 4 h sleep deprivation, old SAMP8 mice exhibit an enhanced sensitivity resulting in SWS (+62%) and PS (+120%) rebounds, a characteristic of this inbred strain. Results obtained are discussed in line with the age-related learning and memory impairments existing in SAMP8 animals. In particular, the reduced cognitive performances described in old SAMP8 might be linked to the TPF deterioration during PS.

Age-related expression of ?1 receptors and antidepressant efficacy of a selective agonist in the senescence-accelerated (SAM) mouse

The sigma1 receptor is a unique intracellular receptor whose activation results in an efficient modulation of several neurotransmitter responses. Its role as a target for the rapid nongenomic effects of neuro(active)steroids and the age-related diminutions in steroid levels suggested that targeting the sigma1 receptor might allow alleviation of age-related neuronal dysfunctions. We examined here the expression and behavioral efficacy of sigma1 receptors in the senescence-accelerated (SAM) mouse model. The sigma1 receptor mRNA expression was measured by using comparative RT-PCR in the olfactory bulb, hippocampus, hypothalamus, cortex, or cerebellum of senescence-prone SAMP/8 and senescence-resistant SAMR/1 control animals. No difference was observed between substrains in 6-, 9-, and 12-month-old (m.o.) mice. The sigma1 protein expression was analyzed by using immunohistochemical techniques. Labeling was intense in the olfactory bulb, hippocampus, hypothalamus, and midbrain of both SAMR/1 and SAMP/8 mice, and the distribution appeared unchanged in 6-, 9-, and 12-m.o. animals. The receptor's in vivo availability was examined by using in vivo [3H](+)-SKF-10,047 binding. No age-related difference was observed in the olfactory bulb, hippocampus, hypothalamus, cortex, cerebellum, and brainstem of 6- or 12-m.o. SAMR/1 or SAMP/8 mice. The antidepressant efficacy of the selective agonist igmesine was examined in the forced-swimming test. The compound decreased significantly the immobility duration at 60 mg/kg in 6- and 12-m.o. SAMR/1 and in 6-m.o. SAMP/8 mice. In 12-m.o. SAMP/8 mice, the drug efficacy was facilitated; a significant effect was measured at 30 mg/kg. Decreased neurosteroid levels, particularly of progesterone, were seen in 12-m.o. SAMP/8 mice that might explain the enhanced efficacy of igmesine. Preserved sigma1 receptor expression and enhanced behavioral efficacy of sigma1 agonists were measured in SAM animals, confirming the therapeutic opportunities for selective ligands against age-related mood disorders.

Quantitative proteomics analysis of specific protein expression and oxidative modification in aged senescence-accelerated-prone 8 mice brain

The senescence-accelerated mouse (SAM) is a murine model of accelerated senescence that was established using phenotypic selection. The SAMP series includes nine substrains, each of which exhibits characteristic disorders. SAMP8 is known to exhibit age-dependent learning and memory deficits. In our previous study, we reported that brains from 12-month-old SAMP8 have greater protein oxidation, as well as lipid peroxidation, compared with brains from 4-month-old SAMP8 mice. In order to investigate the relation between age-associated oxidative stress on specific protein oxidation and age-related learning and memory deficits in SAMP8, we used proteomics to identify proteins that are expressed differently and/or modified oxidatively in aged SAMP8 brains. We report here that in 12 month SAMP8 mice brains the expressions of neurofilament triplet L protein, lactate dehydrogenase 2 (LDH-2), heat shock protein 86, and alpha-spectrin are significantly decreased, while the expression of triosephosphate isomerase (TPI) is increased compared with 4-month-old SAMP8 brains. We also report that the specific protein carbonyl levels of LDH-2, dihydropyrimidinase-like protein 2, alpha-spectrin and creatine kinase, are significantly increased in the brain of 12-month-old SAMP8 mice when compared with the 4-month-old SAMP8 brain. These findings are discussed in reference to the effect of specific protein oxidation and changes of expression on potential mechanisms of abnormal alterations in metabolism and neurochemicals, as well as to the learning and memory deficits in aged SAMP8 mice.

Antiaging methods and medicines for the memory

The interaction of bedside and basic science has led to the identification ofa short list of pathological proteins as causal in Alzheimer's disease. AI3P has received the most attention, and work with animal models has reinforced the evidence that overproduction of ABP causes cognitive impairments. Animal models are now being used to discover and develop unique therapeutics directed at reversing the deleterious effects of ABP. These models strongly suggest that established Alzheimer's disease might be reversible, not just preventable. Animal models are also demonstrating that other peptides and proteins can enhance or impair cognitive function. These peptides and proteins add further to the list of possible therapeutic candidates. Approaches such as these, and not the commercial antiaging remedies that have no scientific basis, will eventually provide medicine for memory enhancement.

Antibody to beta-amyloid protein increases acetylcholine in the hippocampus of 12 month SAMP8 male mice

Amyloid beta protein (Abeta) is the primary constituent of plaque seen in Alzheimer's disease. Abeta is proposed to play an etiological role in Alzheimer's disease and to be a cause of the decrease in the level of acetylcholine in the hippocampus. The SAMP8 strain of mouse develops age-related increases in Abeta and deficits in learning and memory by 12 months of age. We examined in 12 month old SAMP8 mice the effects of giving antibody to Abeta by septal or intracerebroventricular (ICV) injection on acetylcholine levels in the hippocampus. Antibody to Abeta increased acetylcholine in the hippocampus over 100% after ICV injection and over 200% after septal injection. Injection of rabbit serum, antibody directed towards mouse IgG, or a blocking antibody directed towards human interleukin-1beta were without effect. These results suggest that antagonism of Abeta increases acetylcholine concentrations in the hippocampus, an area important for learning and memory.

Deterioration in learning and memory of inferential tasks for evaluation of transitivity and symmetry in aged SAMP8 mice

This study examined age-dependent deficits in the learning and memory of inferential tasks, using an established senescence-accelerated mouse model in age-related brain dysfunction (SAMP8) and its genetically related inbred strain (SAMR1). The mice learned two sets of nonspatial odor-odor pairs by association learning successively (i.e., A-->B, X-->Y, then B-->C, Y-->Z). They were tested in transitive inference (i.e., A-->C, X-->Z) and symmetrical inference (i.e., C-->B, Z-->Y). In the probe test of A-->C, X-->Z transitive inference, 1-month-old SAMP8 and control SAMR1 at the same age significantly chose the alternative based on transitive inference, but 4- and 7-month-old SAMP8 performed at a random chance level, in comparison with unambiguous inference by control SAMR1 at the same ages. During the test of C-->B, Z-->Y symmetrical inference, SAMP8 at 1 month of age made errors as frequently as control SAMR1 at the same age, but SAMP8 at 4 and 7 months of age made more errors than SAMR1 at the same ages. At 4 and 7 months of age, SAMP8 made more errors than 1-month-old SAMP8. Control SAMR1 did not show such an age-related deficient. These results indicate that SAMP8 mice have age-related learning and memory deficits in the ability to perform inferential tasks. Age-related hippocampal dysfunction is suggested to be the cause of these age-related deficits in old SAMP8 mice during the performance of inferential tasks mediated by declarative memory.

Cholinergic deficits in the septal-hippocampal pathway of the SAM-P/8 senescence accelerated mouse

Senescence accelerated prone mouse strains (SAM-P) and resistant strains (SAM-R) have proven useful in elucidating aspects of the aging process. The senescence accelerated mouse SAM-P/8 strain exhibits severe age-related learning and memory impairments well before the median age of survival. Disruption of the brain cholinergic system produces learning and memory impairments as severe as those seen in aging SAM-P/8 mice. Therefore, we compared the effects of aging on cholinergic parameters in the septal-hippocampal pathway, a region known to play a role in learning and memory, in SAM-P/8 mice and mice of the senescence resistant SAM-R/1 strain. Between 4 and 12 months of age we observed a 40-50% decrease in choline acetyltransferase (ChAT) activity in two of three subregions of the hippocampus in the SAM-P/8, but not the SAM-R/1 strain. Between 4 and 12 months, SAM-P/8 mice also showed a 40-50% decrease in ChAT activity in the septal region that was maximal by 8 months of age. By contrast, these age-related changes were not observed in the control SAM-R/1 mouse strain. The changes in ChAT in the SAMP/8 mouse strain were limited to the septal-hippocampal cholinergic pathway. There were no differences in ChAT activity in the nucleus basalis of Meynert, nor any of several neocortical areas to which it projects. To determine the neurochemical specificity of these alterations, the activity of glutamic acid decarboxylase (GAD), was also measured in the septum and hippocampus of SAM-P/8 mice. There were no age-related alterations in the hippocampus, but a significant 50% increase in GAD activity in the septal nucleus at 12 months of age. There were no age-related alterations in either nicotinic (3H-cytisine) or muscarinic (3H-QNB) cholinergic receptor binding in the cortex or hippocampus of SAM-P/8 mice. However, there were significant strain differences. At 2 months of age, 3H-QNB binding was higher in hippocampus of the SAM-R/1 than in SAM-P/8 mice. Similarly, 3H-cytisine binding in cortex of SAM-R/1 mice was higher at both 2 and 13 months than in SAM-P/8 mice. The results suggest that a compromised septal-hippocampal cholinergic pathway may contribute to the previously reported early onset of impaired learning and memory in the SAM-P/8 mouse strain.

Effects of orexin-A on memory processing

Orexin-A is an endogenous peptide with receptors present throughout the brain. Here, we examined the effect of post-training administration of orexin-A on retention in active and passive avoidance. Orexin-A administered by intracerebroventricular (i.c.v.) injection to CD-1 mice post-training improved retention in both T-maze footshock avoidance and one trial step-down passive avoidance. SAMP8 mice have age-related deficits in learning and memory, which correlate with an increase in brain levels of beta amyloid (Abeta) and an impaired response to memory-enhancing compounds. Orexin-A at 3nmol improved retention in young and old SAMP8 mice. These findings show that orexin-A can improve memory even with overproduction of Abeta.

Antibody to amyloid beta protein alleviates impaired acquisition, retention, and memory processing in SAMP8 mice

SAMP8 (senescence-accelerated mouse, P8 strain) mice overproduce amyloid precursor protein and beta-amyloid and have learning and memory deficits. Preliminary data have indicated that overproduction of beta-amyloid plays a role in the pathogenesis of acquisition and retention deficits in SAMP8 mice. In the studies reported here, the authors examined the effects of polyclonal and monoclonal antibodies to beta-amyloid on acquisition and retention in an aversive T-maze testing paradigm when injected intracerebroventricularly (ICV) into 12-month SAMP8/TaJF mice. Both the polyclonal and monoclonal antibodies improved acquisition and retention when injected ICV 1 to 14 days prior to acquisition testing. Injection of all three antibodies intrahippocampally immediately following training improved retention on the T-maze when mice were tested 7 days later. The authors next studied the effect of monoclonal beta-amyloid antibody injected 48 h prior to training on the effect on retention in the T-maze of drugs modulating classical neurotransmitters. Arecoline and glutamate were injected directly into the hippocampus, and ketanserin, methiothepen, bicuculline, and OH-saclofen were injected into the septum. Previously, the authors have found that the doses of these drugs required to improve retention are markedly altered in 12-month SAMP8/TkJF mice compared to 4-month P8 mice. In these studies, it was demonstrated that antibody to beta-amyloid resulted in these drugs improving retention at doses that improved memory in 4-month SAMP8/TaJF mice. Based on these findings, we conclude that beta-amyloid overproduction is at least in part responsible for the acquisition and memory deficits in 12-month-old SAMP8/TaJF mice. Antibody to beta-amyloid restores the retention response to neurotransmitter manipulation to that seen in 4-month-old mice. beta-amyloid appears to play a key role in the loss of acquisition and retention seen in SAMP8/TaJF mice.

Alzheimer's disease through the eye of a mouse. Acceptance lecture for the 2001 Gayle A. Olson and Richard D. Olson prize

There is now ample evidence that beta-amyloid proteins decrease memory. The SAMP8 mouse (P8) develops an early decline in the ability to learn and to retain new information. The studies reviewed here suggest that this is due to overproduction of beta-amyloid. Both antibodies to beta-amyloid and specific antisense to the amyloid precursor protein reverse these deficits in the P8 mouse. This antisense can cross the blood brain barrier. It is hypothesized that the overproduction of beta-amyloid leads to a decline in Delta(9) desaturase activity with an alteration in membrane fatty acids. This results in altered membrane mobility leading to a decline in neurotransmitter activity and a decreased release of acetylcholine. This decreased cholinergic activity results in a decreased ability of the P8 mouse to learn and retain new information.

Passive avoidance and complex maze learning in the senescence accelerated mouse (SAM): age and strain comparisons of SAM P8 and R1

Two strains of the senescence accelerated mouse, P8 and R1,were tested in footshock-motivated passive avoidance (PA; P8, 3-21 months; R1, 3-24 months) and 14-unit T-maze (P8 and R1, 9, and 15 months) tasks. For PA, entry to a dark chamber from a lighted chamber was followed by a brief shock. Latency to enter the dark chamber 24 hours later served as a measure of retention. Two days of active avoidance training in a straight runway preceded 2 days (8 trials/day) of testing in the 14-unit T-maze. For PA retention, older P8 mice entered the dark chamber more quickly than older R1 mice, whereas no differences were observed between young P8 or R1 mice. In the 14-unit T-maze, age-related learning performance deficits were reflected in higher error scores for older mice. P8 mice were actually superior learners; that is, they had lower error scores compared with those of age-matched R1 counterparts. Although PA learning results were in agreement with other reports, results obtained in the 14-unit T-maze were not consistent with previous reports of learning impairments in the P8 senescence accelerated mouse.

Deterioration in learning and memory of fear conditioning in response to context in aged SAMP8 mice 1 1Abbreviations: SAM, senescence-accelerated mouse; SAMP, senescence-accelerated mouse prone; SAMR, senescence-accelerated mouse resistant; GABA, gamma-aminobutyric acid; MGRF, magnocelluar reticular formation; RSA, hippocampal rhythmic slow activity; CS, conditioned stimulus

This study examined age-dependent deficits in the learning and memory of fear conditioning, using a newly developed senescence-accelerated mouse (SAMP8) model of age-related brain dysfunction and its genetically related inbred strain (SAMR1). The mice were classically conditioned to tone by giving aversive foot shocks in a distinct experimental box (context). After conditioning, fear in response to the original context without the tone and to the tone in a different context were tested with no shocks. Freezing behavior was used as a reliable index of fear. At 4 and 8 months, contextual fear was weaker in the accelerated senescence-prone SAMP8 mice than in the accelerated senescence-resistant SAMR1 mice. However, at 1 and 2 months, both SAMP8 and SAMR1 mice showed significant contextual fear to equivalent levels. Aging did not affect the fear response to tone. These results indicate that SAMP8 mice have age-related learning and memory deficits in their fear response evoked by contextual but not explicit tone stimuli. Age-related hippocampal dysfunction is suggested to be the cause of these age-related deficits in contextual fear conditioning in SAMP8 mice.

Beta-amyloid precursor polypeptide in SAMP8 mice affects learning and memory

Senescence accelerated (SAMP8 [P8]) mice develop age-related deficits in memory and learning. We show that increased expression of amyloid precursor protein (APP) and its mRNA in the hippocampus are also age-related. Immunocytochemical data suggest that a critical amount of APP expression may be needed to generate amyloid (Abeta) protein plaques in the hippocampus. Deficits in acquisition and retention test performance were alleviated by administration of antibody to Abeta protein into the cerebral ventricles. This reversal of cognitive deficits provides a link between increased expression of both APP and Abeta protein and learning and memory loss in these mice.

Permanent and temporary inactivation of the hippocampus impairs T-maze footshock avoidance acquisition and retention

The hippocampus is widely recognized as playing an important role in learning and memory. Lesions of the hippocampus can disrupt spatial navigational learning and memory and injection of drugs into the hippocampus can affect both spatial navigational and nonspatial tasks. In the current studies we tested the effects of bilateral of electrolytic lesions and reversible inactivation of the hippocampus on acquisition and retention of T-maze footshock avoidance conditioning. Electrolytic lesions, which destroyed 31+/-0.04% of the hippocampus, significantly impaired acquisition and retention for T-maze footshock avoidance. No differences were found in motivation to avoid shock, open field activity, or foot shock sensitivity between lesion and control groups. Temporary inactivation of the hippocampus with lidocaine administered immediately before training disrupted acquisition and retention for T-maze footshock avoidance. Temporary hippocampal inactivation performed just prior to retention testing and post-training inactivation in mice trained to first avoidance had no effect on retention. However, temporary post-training inactivation in 'undertrained' (enough trials to remember 1 week later if treated with saline, but not allowed to make the avoidance response) mice impaired retention. The current findings indicate that the hippocampus plays an important role in learning and memory processing in the aversive T-maze paradigm.

Estradiol potentiates acetylcholine and glutamate-mediated post-trial memory processing in the hippocampus

There is increasing evidence that estrogen is involved in CNS activity, particularly memory. Several studies have suggested that estrogen improves memory by enhancing cholinergic and glutamatergic activity. In the present studies, we examined the effects of administration into the hippocampus of 17 beta-estradiol and estrone on retention of T-maze footshock avoidance in female ovariectomized mice. Both 17 beta-estradiol and estrone improved retention on an equimolar basis in a dose-dependent fashion. We then used the T-maze footshock paradigm to test whether a dose of 17 beta-estradiol ineffective as a single injection (subthreshold) could potentiate the effects of arecoline, a cholinergic agonist, or L-glutamate, a glutamatergic agonist, on retention. The dose of either arecoline or L-glutamate needed to improve retention was reduced at least ten-fold by the low dose of 17 beta-estradiol. These findings support the concept that estrogen improves memory by potentiating the activity of the cholinergic and glutamatergic systems.

The effect of cholinergic, GABAergic, serotonergic, and glutamatergic receptor modulation on posttrial memory processing in the hippocampus

Though the hippocampus is widely recognized as important in learning and memory, most of the evidence for this comes from animal lesion and human pathological studies. Due to the relatively small number of drugs that have been tested in the hippocampus for their ability to alter posttrial memory processing, there is a general impression that memory processing involves only a few neurotransmitters. We have evaluated the effects of cholinergic, GABAergic, serotonergic, and glutamatergic receptor agonists and antagonists for their ability to facilitate or impair retention. CD-1 mice received acute intrahippocampal drug infusion following footshock avoidance training in a T-maze. Retention was tested 1 week after training and drug administration. The results indicate that receptor agonists of acetylcholine and glutamate improved retention, while antagonists impaired retention. However, scopolamine did not impair retention, but M1 and M2 antagonists did. Receptor agonists of serotonin and GABA impaired retention, while antagonists improved retention. Drugs acting on 5-HT-1 and 5-HT-2 as well as GABA(A) and GABA(B) receptor subtypes did not differentially effect retention.

Modulation of memory processing in the cingulate cortex of mice

To evaluate the possible role of the cingulate cortex in memory processing for training using a noxious stimulus, we trained mice on foot shock avoidance in a T-maze. Cholinergic, GABAergic, serotonergic, and glutamatergic agonists and antagonists were administered into the cingulate cortex immediately after training. Retention for the foot shock avoidance training was tested 1 week later. The results indicate that muscarinic and nicotinic agonists improved retention, while antagonists impaired it. GABA and serotonin agonists impaired retention, while antagonists improved it. Drugs acting on GABA(A) and GABA(B) receptors had similar effects on retention, as did drugs acting on serotonin 1 and 2 receptor subtypes. Glutamate improved retention, and AP5, an antagonist of the excitatory amino acid site of the NMDA receptor, impaired retention. The cingulate cortex, like other parts of the limbic system, is involved in memory processing that occurs shortly after training.

Septo-hippocampal drug interactions in post-trial memory processing

To determine if serotonin and GABA regulate post-trial memory processing of the cholinergic projection from the septum to the hippocampus, mice were trained on footshock avoidance in a T-maze. Immediately after training, drugs were injected into the septum, hippocampus or both. Retention was tested 1 week after training and drug administration. Ketanserin, a serotonin type 2 receptor antagonist at a dose of 0.5 ng, had no measurable effect on retention, but it reduced the dose of bicuculline, in the septum, or arecoline in the hippocampus that was needed to improve retention. DOI, a serotonin type 2 receptor agonist at a dose of 2.5 ng, had the opposite effect of increasing the doses of bicuculline and arecoline needed to improve retention. Bicuculline, a GABA(A) receptor antagonist at a dose of 0.1 pg, did not affect retention when injected alone into the septum, but it reduced the dose of arecoline needed to improve retention in the hippocampus. Muscimol, a GABA(A) receptor agonist at a dose of 5 ng, injected into the septum, increased the dose of arecoline needed to improve retention. The results of this study are compatible with models that propose that serotonin innervation from the median raphe drives GABA interneurons in the medial septum that synapse on cholinergic neurons projecting to the hippocampus.

Peripheral steroid sulfatase inhibition potentiates improvement of memory retention for hippocampally administered dehydroepiandrosterone sulfate but not pregnenolone sulfate

Dehydroepiandrosterone sulfate (DHEAS) improves memory retention when administered peripherally. Estrone-3-O-sulfamate (EMATE), a steroid sulfatase inhibitor, potentiates the effect of DHEAS on memory retention such that lower doses of DHEAS improve memory retention. It is not clear if this effect is mediated by both compounds entering the central nervous system. In the current studies, mice were trained to avoid footshock in a T-maze and memory retention was tested 1 week later. DHEAS, injected into the hippocampus after training, improved memory retention in a dose-dependent manner. In previous studies, pregnenolone sulfate (PREGS) improved memory retention when injected into the hippocampus. EMATE, administered peripherally, potentiated the effect of centrally administered DHEAS on memory retention. However, EMATE did not potentiate the effect of centrally administered PREGS. It was concluded that EMATE, acting peripherally, increased plasma levels of DHEAS which entered the brain and added to the effect of centrally administered DHEAS. The failure of EMATE to potentiate PREGS is discussed.

Effect of age on calcium-dependent proteins in hippocampus of senescence-accelerated mice

The senescence-accelerated P8 mouse (SAMP8) is a well-characterized model for the age-related decline in acquisition and retention. Calcium-dependent protein kinase C (PKC) and calcium-calmodulin-dependent protein kinase (CAM K) have been implicated in these processes in the hippocampus. Therefore, the expression of hippocampal PKC and CAM K was determined in SAMP8 mice aged 4, 8, and 12 months. As measured by Western blotting, total hippocampal PKC-gamma protein declined linearly with age. In addition, the distribution of the PKC-gamma also changed with age. The amount of PKC in the particulate fraction declined linearly with age relative to the soluble PKC. The decline in total PKC and particulate PKC correlated with the previously reported decline in retention but not with the decline in acquisition. Western blotting revealed no consistent change in CAM KII protein levels. In addition to protein levels, Ca-dependent protein kinase activity may also be affected by changes in intracellular Ca concentration. Therefore, the levels of calbindin and the plasma membrane Ca pump, two proteins involved in maintaining low levels of intracellular Ca, were measured in the hippocampus. Calbindin protein declined progressively with age, but there was no significant change in total plasma membrane Ca pump expression. These studies demonstrate a decrease in the amount and distribution of hippocampal PKC-gamma in the SAMP8 between 4 and 12 months that is associated with decreased retention.

Senescence-accelerated mouse (SAM) as an animal model of senile dementia: pharmacological, neurochemical and molecular biological approach

To elucidate the fundamental mechanism of age-related deficiencies of learning and to develop effective drugs for intervention in age-related diseases such as learning dysfunctions, pertinent animal models that have characteristics closely similar to human dysfunctions should be established. SAM (senescence-accelerated mouse) has been established as a murine model of the SAM strains, groups of related inbred strains including nine strains of accelerated senescence-prone, short-lived mice (SAMP) and three strains of accelerated senescence-resistant, long-lived mice (SAMR). SAMP-strain mice show relatively strain-specific age-associated phenotypic pathologies such as shortened life span and early manifestation of senescence. Among the SAMP-strain mice, SAMP8 mice show an age-related deterioration in learning ability. Here, the neuropathological, neurochemical and pharmacological features of SAM are reported, especially for SAMP8. Moreover, the effects of several drugs on the biochemical and behavioral alterations in SAMP8 and the etiologic manifestation of accelerated senescence are also discussed.

Functional relationship between age-related immunodeficiency and learning deterioration

Disordered immune responses are supposed to alter the function of the central nervous system through the neuroendocrine immunomodulation network. In this paper, we studied the influence of the immune function on learning performances from the angle of pharmacology using aged garlic extract (AGE), an immunomodulator. Splenocyte proliferation, induced by concanavalin A or lipopolysaccharide, and the antibody production response were declined in senescence accelerated mouse-prone 8 (SAMP8) aged 12 months compared with age-matched SAMR1 (SAM-resistant 1). Chronic oral administration of AGE-containing food (2%, w/w) significantly enhanced the immune responses of both SAMP8 and SAMR1. Male ddY mice were thymectomized 4 weeks after birth and fed AGE-containing food after the operation until the experiments were finished. Learning performances, brain monoamine content and choline acetyltransferase (ChAT) activity, as well as the immune response were evaluated 10 months after the operation. Thymectomy resulted in not only immunodeficiency, but also deteriorated learning ability. AGE treatment prevented the reduction of the antibody production response induced by thymectomy and improved the thymectomy-induced deterioration of learning behaviours in passive avoidance performance and in a spatial memory task. The contents of hypothalamic noradrenaline, 3,4-dihydroxyphenylacetic acid and homovanillic acid, and the hypothalamic ChAT activity were increased in thymectomized mice compared to those of sham-operated control, while AGE treatment restored them to the control levels. These results suggest that the improvement of immune function is closely related to the amelioration of age-associated deterioration of learning and memory.

Age-related changes in septal serotonergic, GABAergic and glutamatergic facilitation of retention in SAMP8 mice

SAMP8/TaJf(P8) mouse strain has an inherited age-related impairment of learning and memory with its onset relatively early in its lifespan. Previously, it was reported that cholinergic and glutamatergic drugs injected into the hippocampus after behavioral training showed considerable shifts in the dose that improved retention in mice at 12 compared to 4 months of age. Cholinergic neurons in the septum supply most of the acetylcholine released in the hippocampus. In the present study, we determined if altered functional status of neurotransmission in the septum might account for the decrease in cholinergic and glutamatergic activity in the hippocampus of older SAMP8 mice. After training on footshock avoidance, P8 mice received a drug injection into the septum. Retention was tested 1 week later. The results indicate that bicuculline, GABA-A, and saclofen, GABA-B, receptor antagonist had to be injected at a higher dose in 12- than in 4-month-old mice to improve retention. The serotonergic antagonists, ketanserin and methiothepin, both showed dose response shifts such that less drug was needed to improve retention in 12- as compared to 4-month-old mice. It required four times more L-glutamate to improve retention in 12- than in 4-month-old mice. Agonists for acetylcholine, dopamine and norepinephrine receptors or an opiate antagonist required little or no change in the dose needed to improve retention in older P8 mice. SAMP8 mice may show an age-related impairment of septohippocampal functioning.

The pharmacology of post-trial memory processing in septum

The septum is recognized as important in learning and memory, but relatively little is known about the role of specific neurotransmitter receptors in memory processing in the septum. We evaluated the role of the classical neurotransmitters in mice that were prepared for intraseptal microinfusion of drug solution after footshock avoidance training in T-maze. Retention for the footshock training was determined 1 week after training and drug administration. The results indicated that receptor agonists of dopamine, norepinephrine, glutamate and acetylcholine improved retention, while the antagonists impaired retention. Receptor agonists of serotonin, gamma-amino butyric acid (GABA) and opioids impaired retention, while antagonists improved retention.

Learning and memory in the SAMP8 mouse

The SAMP8 (P8) mouse strain develops deficits in learning and memory relatively early in its lifespan. This review provides an overview of the age-related changes that occur in P8 mice. Behavioral studies with P8 mice show impaired acquisition and retention as early as 4 months of age. Deficits in acquisition and retention occur with both aversive and appetitive training tasks. Anatomical studies have detected a number of age-related changes that occur in the central nervous system of P8 mice. The age-related increase in amyloid beta protein is well correlated with the age-related decline in learning and memory. Antibody to amyloid beta protein injected prior to training alleviated impaired acquisition and retention, whereas post-training injections alleviated retention deficits in older P8 mice. Biochemical studies have detected numerous age-related changes with reduced NMDA receptor activity most closely related to impaired learning and memory in P8 mice. Pharmacological studies have found age-related functional changes in the ability of drugs to improve memory processing in P8 mice in the septum and the hippocampus. The specific pattern of pharmacological changes and the inferred change in neurotransmitter activity suggest that age-related impairment in memory processing may be due to impaired septohippocampal interactions. The proposal that P8 mice may be a useful model for studying the early phases of age-related dementia of the Alzheimer type, while still requiring considerable study, seems reasonable.

The cortical neuropeptide, cortistatin-14, impairs post-training memory processing

Cortistatin-14, a neuropeptide, is present primarily in the cortex and hippocampus. In the hippocampus, cortistatin-14 inhibits pyramidal cell firing and co-exists with GABA. To determine if cortistatin-14 would impair retention, saline or cortistatin-14 were injected intracerebroventricularly after footshock avoidance training in CD-1 mice. After 1 week, training was resumed to determine the effect of cortistatin-14 on retention. Cortistatin-14 was found to impair retention relative to the control group at doses of 0.5-5.0 micrograms.

Age-related changes in the expression of Alzheimer's beta APP in the brain of senescence accelerated mouse (SAM)-P/10

Patients with Alzheimer's disease (AD) show loss of memory and cognitive deficits the molecular mechanisms of which are not completely known. We examined age-related changes in the expression levels of beta-amyloid precursor protein (beta APP) in the brain of the senescence accelerated mouse (SAM) P/10, which shows age-dependent brain atrophy and impairment in learning and memory, and in the senescence resistant mouse (SAM)-R/1 using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. Levels of both beta APP mRNA and protein increased with age, reaching a peak at 8 months of age in the hippocampus of SAM-P/10. In contrast, beta APP protein level decreased with age in the hippocampus of SAM-R/1 while beta APP mRNA level did not change significantly. Levels of beta APP mRNA and protein showed no change with ageing in other brain regions, including cerebral cortex, thalamus/midbrain and cerebellum brain stem. These results suggest that the beta APP over-expression in the hippocampus might be related to the characteristic memory loss in SAM-P/10.