A new murine model of accelerated senescence

Age-associated DNA damage is accelerated in the senescence-accelerated mice

We investigated how the DNA status correlates with the aging process in organisms, in different organs and in tissues using two inbred strains of mice, which are genetically related but have different senescence patterns. The SAMP1 mice belong to an accelerated senescence-prone and short lived strain, the other, SAMR1 mice are from an accelerated senescence-resistant and long lived strain. Using the alkaline filter elution technique, pieces of tissues from six organs: lung, intestine, liver, brain, muscle, and heart have been examined for DNA damage, mainly DNA single strand breaks. It was shown that in newborns the DNA damage is minimal, and it was increased significantly with calendric age in all organs in both strains. Although the correlation of DNA damage with aging differed in the different six organs, damage was significantly higher in SAMP1 mice than SAMR1 mice at later life in all organs. This is another remarkable example for the strong correlation of DNA damage and aging process, especially with senescence acceleration.

Animal models for the effect of age on susceptibility to inhaled particulate matter

Epidemiological findings of associations between ambient particulate matter (PM) and respiratory and cardiovascular mortality and morbidity have fostered increased laboratory research aimed at understanding the key PM components, mechanisms, and dose-response relationships responsible for the effects. Because the health impacts are largely observed in subpopulations having characteristics known or presumed to confer increased susceptibility to PM, there is a need for identifying, developing, and using animal models of these susceptibility factors. Age, during both development and senescence of the cardiorespiratory system and its defenses, is one of the PM susceptibility factors cited frequently. This review is intended as a summary of current knowledge regarding age-related differences in the structure and function of the respiratory and pulmonary vascular systems of humans and animals. Its purpose is to facilitate the selection of appropriate animal models for research on the various facets of potential age-related susceptibility of the human respiratory tract to the effects of inhaled PM. The selection of models is a difficult challenge because no single animal species adequately models the full range of human respiratory anatomy, physiology, and age-related changes. With careful selection among the many species, strains, and comparative ages, however, animals can be selected to model most, if not all, of the individual factors hypothesized to confer increased susceptibility of humans to inhaled PM. The existing information does not provide an adequate basis for selecting models to test all of the current age-related susceptibility hypotheses. However, the information summarized in this report should facilitate the investigator's review of potential models.

Wild type ApoA-II gene does not rescue senescence-accelerated mouse (SAMP1) from short life span and accelerated mortality

Biochemical and genetic data suggest that the Apoa2c allele of the apolipoprotein A-II gene causes severe senile amyloidosis (AApoAII) in SAMP1, a mouse model for accelerated senescence. We analyzed the effects of replacement of Apoa2c in SAMP1 mice with non-amyloidogenic Apoa2b on amyloidosis, lipoprotein metabolism, and progression of senescence using a congenic strain, P1.R1-Apoa2b, which has the Apoa2b chromosome region of SAMR1 in the genome of SAMP1. Age-associated amyloid deposition was not observed, but plasma concentrations of apoA-II protein and HDL-cholesterol decreased with age in P1.R1-Apoa2b. P1.R1-Apoa2b showed lower scores of senescence than did SAMP1. However, the life span and mortality rate doubling time were similar in P1.R1-Apoa2b and SAMP1. These results suggest that replacement of Apoa2c with non-amyloidogenic Apoa2b does not rescue SAMP1 mice from a short life span and accelerated mortality.

Sensitivity of the olfactory sense declines with the aging in senescence-accelerated mouse (SAM-P1)

The decline in olfaction with age is well documented in histological, psychological, and electroencephalographical studies. However, there are few electrophysiological studies on changes in the sensitivity of the peripheral olfactory cells with age. We evaluated the behavior, the amplitude of electro-olfactogram (EOG), and the thickness of the olfactory epithelium in the Senescence-Accelerated Mouse (SAM-P1). This strain of mouse exhibits accelerated senescence and age-related pathologies, and it is commonly used as a model for research on aging. Its median survival time is 55 weeks. To ensure our results would be restricted to the olfactory system, we chose vanillin as a stimulus, because this stimulus has no definitive chorda tympani (VII) response, and we verified that it is tasteless. The data demonstrate that olfactory sensitivity to vanillin decreases dramatically with age in these mice, and that this is due to loss in the number of olfactory receptor cells.

In vivo specific binding characteristics and pharmacokinetics of a 1,4-dihydropyridine calcium channel antagonist in the senescent mouse brain

PURPOSE

To characterize the in vivo specific binding and pharmacokinetics of a 1,4-dihydropyridine (DHP) calcium channel antagonist, PN 200-110, in the senescent brain, using senescence-accelerated prone mice (SAMP8) and senescence-resistant mice (SAMR1).

METHODS

Blood, brain, and heart samples were taken periodically from SAMR1 and SAMP8 following intravenous injection of (+)-[3H]PN 200-110, and the concentration of (+)-[3H]PN 200-110 in the plasma and tissues was determined. In addition, the in vivo specific binding of (+)-[3H]PN 200-110 in the brains of SAMRI and SAMP8 was measured periodically after intravenous injection of the radioligand.

RESULTS

There was very little significant difference between SAMR1 and SAMP8 in terms of the half-life (t(1/2)), total body clearance (CL(tot)), steady-state volume of distribution (Vd(ss)). and AUC for the plasma concentration of (+)-[3H]PN 200-110 after intravenous injection of the radioligand. The brain concentration (AUCbrain) for (+)-[3H]PN 200-110 and the brain/plasma AUC ratio (AUCbrain/AUCplasma) were significantly lower in SAMP8 than in SAMR1, and the heart concentration (AUCheart) and the heart/plasma AUC ratio (AUCheart/AUCplasma) were similar in both strains. Also, the brain/plasma unbound AUC ratio (AUCbrain/AUCplasma-free) for (+)-[3H]PN 200-110 was significantly lower in SAMP8 than in SAMRI. The in vivo specific binding (AUCspecific binding, maximal number of binding sites: Bmax) of (+)-[3H]PN 200-110 was significantly lower in brain particulate fractions of SAMP8 than SAMR1.

CONCLUSIONS

The concentration and in vivo specific binding of (+)-[3H]PN 200-110 was significantly reduced in the senescent brain. The simultaneous analysis of the concentrations of centrally acting drugs and the in vivo specific binding in the brain in relation to their pharmacokinetics may be valuable in evaluating their CNS effects.

Effects of an in vivo 60 Hz magnetic field on monoamine levels in mouse brain

We studied the effects of electromagnetic fields (EMF) on mouse brain monoamine levels in models of (1) chronic exposure (7 days) of EMF (60 Hz, 10 Gauss) to mice in a vertical orientation, (2) prolonged chronic exposure (84 days) of EMF (60 Hz, 10 Gauss) to mice in a horizontal mode, (3) acute exposure (6 h) of EMF (60 Hz, 10 Gauss) to senescence accelerated mice (SAM-P8) at ages 1, 3, 6, 9 and 12 months in the horizontal mode, and (4) acute exposure (1 h) of EMF (60 Hz, 1, 3.3 and 10 Gauss) to restrained mice in the horizontal mode. No model except the restrained one changed their monoamine or metabolite levels by exposure to EMF. In the restrained group, dihydroxyphenylacetic acid (DOPAC) was significantly increased in the hippocampus (HP) and hypothalamus (HY), homovanillic acid (HVA) was significantly increased in HY, and 5-hydroxyindolacetic acid (5-HIAA) was significantly increased in HP and thalamus-midbrain (TM). None of these monoamine metabolite levels were changed when the mouse was restrained without EMF exposure. These results suggest that monoamine metabolism is influenced by EMF only when the exposure is in the same direction as the mouse position. Another possibility is that EMF enhances the restraint stress since stress is known to increase monoamine metabolism.

Learning deficiency and alterations in acetylcholine receptors and protein kinase C in the brain of senescence-accelerated mouse (SAM)-P10

The senescence-accelerated mouse (SAM) is known to be a murine model for accelerated aging. A novel inbred SAMP10 has shown age-related brain atrophy and learning deficiency. In the present study, we investigated the changes in learning ability and in ligand binding with muscarinic acetylcholine (mACh) receptors, alpha adrenoceptors and protein kinase C in SAMP10. In Morris's water maze task, in a control strain of SAMR1 at 9 months, the escape latency and path length decreased with increasing trial days, in contrast, escape latency and path length did not decrease in SAMP10. These results indicate that SAMP10 exhibits learning deficiency. The ligand binding activity of mACh receptors decreased in the hippocampus of SAMP10 and the protein kinase C level in the hippocampus of SAMP10 was lower than that of SAMR1. On the other hand, there was no significant difference between SAMR1 and SAMP10 regarding ligand binding activity of alpha(1) and alpha(2) adrenoceptors. Thus, a reduction of mACh receptors and protein kinase C in the brain seems to underlie dysfunction of learning and memory in SAMP10.

Vitamin E and immunity

Vitamin E is a potent antioxidant and has an ability to modulate host immune functions. This chapter consists of five parts: (1) vitamin E deficiency and immunity, (2) vitamin E supplementation and immunity, (3) vitamin E and the decreased cellular immunity with aging, (4) vitamin E and T-cell differentiation in the thymus, and (5) vitamin E and acquired immune deficiency syndrome (AIDS). In vitamin E deficiency most of the immune parameters show a downward trend, which is associated with increased infectious diseases and the incidence of tumors. In contrast, vitamin E supplementation has various beneficial effects on the host immune system. The decreased cellular immunity with aging or during the development of AIDS is markedly improved by the intake of a high vitamin E diet. In addition, vitamin E plays an important role in the differentiation of immature T cells in thymus. Vitamin E deficiency induces the decreased differentiation of immature T cells, which results in the early decrease of cellular immunity with aging in spontaneously hypertensive rats. Conversely, vitamin E supplementation induces a higher differentiation of immature T cells via increased positive selection by thymic epithelial cells, which results in the improvement of decreased cellular immunity in the aged. Furthermore, vitamin E supplementation induces the early recovery of thymic atrophy following X-ray irradiation. Taken together, these results suggest that vitamin E is an important nutrient for maintaining the immune system, especially in the aged.

Altered aging-related thymic involution in T cell receptor transgenic, MHC-deficient, and CD4-deficient mice

During aging in mice and humans, a gradual decline in thymus integrity and function occurs (thymic involution). To determine whether T cell reactivity or development affects thymic involution, we compared the thymic phenotype in old (12 months) and young (2 months) mice transgenic for rearranged alphabeta or beta 2B4 T cell receptor (TCR) genes, mice made deficient for CD4 by gene targetting (CD4(-/-)), mice made deficient for major histocompatibility complex (MHC) class I (beta2M-/-) or class II genes (A(beta)(b-/-) on C57Bl/6 background) or both. The expected aging-related reductions in thymic weights were observed for all strains except those bearing disruption of both class I and class II MHC genes. Therefore, disruption of MHC class I and class II appeared to reverse or delay aging-related thymic atrophy at 12 months. Immunohistochemical analysis of aging-associated alterations in thymic morphology revealed that TCR alphabeta transgenes, CD4 disruption, and MHC class II disruption all reduced or eliminated these changes. All strains examined at 12 months showed alterations in the distribution of immature thymocyte populations relative to young controls. These results show that aging-associated thymic structural alterations, size reductions, and thymocyte developmental delays can be separated and are therefore causally unrelated. Furthermore, these results suggest that the T cell repertoire and/or its development play a role in aging-related thymic involution.

Age-related changes in myelopoietic response to lipopolysaccharide in senescence-accelerated (SAM) mice

The effects of in vivo lipopolysaccharide (LPS) administration on myelopoiesis were examined in senescence-accelerated (SAM) mice. Young mice injected with LPS exhibited: (a) increased femoral proliferative pool size; (b) transient reduction in femoral non-proliferative pool size and number of femoral colony forming unit-granulocyte macrophages (CFU-GMs); (c) marked increase in splenic CFU-GMs; and (d) transient increase in S-phase of femoral CFU-GMs. The responses of old mice after LPS administration differed from those of young mice in the following points: (a) no recovery of the femoral non-proliferative pool or femoral CFU-GMs, (b) less significant augmentation of the femoral proliferative pool and splenic CFU-GMs, and (c) prolonged reduction in S-phase of femoral CFU-GM. Injection of LPS into mice resulted in a hyperproduction of colony-stimulating activity (CSA) in bone followed by production of colony-inhibitory activity (CIA) in young mice and in contrast, an excessive CIA secretion from bone without an increase in CSA levels in old mice. These imbalances in the regulatory factors derived from non-hemopoietic cells in the bones may lead to an inappropriate response of myelopoiesis in aged SAM mice after LPS administration, which may play a key role in infections.

Hippocampal cholinergic neurostimulating peptides (HCNP)

Neuronal development and differentiation require a variety of cell interactions. Diffusible molecules from target neurons play an important part in mediating such interactions. Our early studies used explant culture technique to examine the factors that enhance the differentiation of septo-hippocampal cholinergic neurons, and they revealed that several components resident in the hippocampus are involved in the differentiation of presynaptic cholinergic neurons in the medial septal nucleus. One of these components, originally purified from young rat hippocampus, is a novel undecapeptide (hippocampal cholinergic neurostimulating peptide; HCNP); this enhances the production of ChAT, but not of AchE. Later experiments revealed that: (1) a specific receptor appears to mediate this effect; (2) NGF and HCNP act cooperatively to regulate cholinergic phenotype development in the medial septal nucleus in culture; and (3) these two molecules differ both in their mechanism of release from the hippocampus and their mechanism of action on cholinergic neurons. The amino acid sequence deduced from base sequence analysis of cloned HCNP-precursor protein cDNA shows that HCNP is located at the N-terminal domain of its precursor protein. The 21 kDa HCNP precursor protein shows homology with other proteins, and it functions not only as an HCNP precursor, but also as a binding protein for ATP, opioids and phosphatidylethanolamine. The distribution and localization of HCNP-related components and the expression of their mRNAs support the notion that the precursor protein is multifunctional. In keeping with its multiple functions, the multiple enhancers and promoters found in the genomic DNA for HCNP precursor protein may be involved in the regulation of its gene in a variety of cells and at different stages of development. Furthermore, several lines of evidence obtained from studies of humans and animal models suggest that certain types of memory and learning disorders are associated with abnormal accumulation and expression of HCNP analogue peptide and/or its precursor protein mRNA in the hippocampus.

Age-related changes in the D-aspartic acid content of the teeth of the senescence-accelerated mouse

It is known that D-aspartic acid increases with age in dentine. Here, age-related changes in the D to L-aspartic acid (D/L) ratios of the lower teeth of two different sublines of the senescence-accelerated mouse (SAM), SAMP2/Iw (SAM, prone 2/Iwate) and SAMR1/Iw (SAM, resistant 1/Iwate) were measured by gas chromatography. The D/L ratio of the molars increased with advancing age, whereas that of the incisors did not. In mice younger than 6 months of age the D/L ratio of the molars from SAMP2/Iw tended to be higher than that from SAMR1/Iw, whereas the converse applied to older mice. Racemization in the molars occurred significantly faster in SAMR1/Iw than SAMP2/Iw (p = 0.01-0.001). Analysis according to the kind of tooth showed that the D/L ratio increased gradually in the order incisors < third molars < second molars < first molars, indicating that the ratio was higher the earlier the molars formed. As racemization depends upon the environmental temperature, the rectal temperatures of the mice were also examined. The rectal temperature of SAMP2/Iw was highest when they were 2 months old, but declined rapidly thereafter, whereas the rectal temperature of SAMRI/Iw was highest when they were 6 months old, after which it declined gradually. These results indicate that the D-aspartic acid contents of the molars of SAMR1/Iw and SAMP2/Iw increase with age in a different fashion and suggest that the fashion was determined by the body temperature, but not by the senescence-accelerated age.

Ultrastructural changes in microvessel with age in the hippocampus of senescence-accelerated mouse (SAM)-P/10

Microvessels in the hippocampus of aged SAM-P/10 (14 months old) showed the following ultrastructural changes compared with those of young-mature controls (3 months old): (1) the majority of capillaries had lost the smooth contours typical of young cases; (2) the luminal surface of capillaries showed irregularity; (3) the endothelial cytoplasm was thicker; (4) vesicles appeared more frequently in the endothelium; (5) interendothelial tight junctions and basement membranes, however, seemed to show no significant abnormalities; (6) pericytes, especially those of arterioles and venules, contained many enlarged cytoplasmic inclusions with honeycomb-like vacuoles; (7) the area of glial perivascular end feet was greater. These morphological findings raise the possibility of impaired blood-brain barrier function and microhemodynamic disturbances in aged SAM-P/10 hippocampus.

Age-associated changes in the dopamine synthesis as determined by GTP cyclohydrolase I inhibitor in the brain of senescence-accelerated mouse-prone inbred strains (SAMP8)

Our objective in this study was to elucidate the mechanism underlying the decrease in dopamine (DA) levels in the brain with ageing We administered 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of GTP cyclohydrolase I to senescence-accelerated mouse-prones (SAMP8), to inhibit DA and serotonin syntheses, and following immunohistochemical staining, analyzed the immunoreactive intensities (IR-Is) for DA in the nigrostriatal dopaminergic neurons by microphotometry. The DA-IR-Is in the substantia nigra pars compacta and neostriatum of young mice (2 months old) reached a minimal value 3 h after DAHP administration and returned to the control value 12 h after the administration. However, in aged mice (10 months old), the minimal value was reached 6 h after the administration and the value remained at approximately 70 and 80% of the control value at 24 and 72 h, respectively, after DAHP administration. The results suggest that DA turnover is lower in aged mice than in young mice.

Comparison of erythropoietic response to androgen in young and old senescence accelerated mice

In this study, to clarify whether the functional capacity of hemopoietic progenitor cells and the micro-environment of aged mice are identical with those of the young, we investigated the changes in the number of hemopoietic progenitor cells and the production of regulatory cytokines from splenic cells as well as changes in the serum levels of cytokine in senescence-accelerated mice (SAM) after administration of 19-nandrolone decanoate (19-ND), a synthetic androgenic anabolic steroid. 19-ND induced an increase in erythroid colony-forming units (CFU-E), erythroid burst-forming units (BFU-E), and granulocytic-macrophage committed progenitor cells (CFU-GM) in bone marrow and spleen; especially remarkable increases were observed in the splenic CFU-E in both young and old mice. Antigen expression analysis of hemopoietic organs revealed that total TER-119+ cells per spleen of young and old mice with androgen treatment rose 2.6- and 3.2-fold over their respective control values. The responsiveness of hemopoietic progenitor cells to androgen did not change with age. Injection of 19-ND into young and old mice markedly enhanced the erythropoietin levels but not IL3 and GM-CSF levels in the serum of both groups. Cytokine production assessed by pokeweed mitogen-stimulated spleen condition medium showed an age-related decline. Androgen treatment could not influence IL-3 and GM-CSF production of spleen. These findings suggest that the spleen of both old and young mice served as the major site of regenerative repopulation of hemopoietic progenitors, especially the late erythroid progenitors in 19-ND-treated mice. The proliferative reserve of erythropoiesis with androgen treatment in aged mice was not reduced more than that in treated-young mice.

Different changes in concentrations of monoamines and their metabolites and amino acids in various brain regions by the herbal medicine/Toki-Shakuyaku-San between female and male senescence-accelerated mice (SAMP8)

Due to it's estrogen-secreting qualities, a Japanese herbal medicine, Toki-Shakuyaku-San may have a potential role for Alzheimer's disease in women. The effect of treatment with Toki-Shakuyaku-San testing on concentrations of monoamines, their metabolites and amino acids in the cortex, hippocampus and striatum of senescence accelerated mice (SAMP8) was examined and sex differences of SAMP8 and ddY mice was studied. In the female SAMP8, concentrations of gamma-aminobutyric acid, alanine, and glycine were elevated in three regions after treatment. The concentration of glutamate was decreased in the cortex, hippocampus, and striatum of female and male SAMP8 and not in female and male ddY mice. These results suggest that different effects of Toki-Shakuyaku-San treatment on concentrations of monoamines, their metabolites and amino acids in the brain tissue may be due to its stimulation of secreted estrogen on neurons.

Assessment of DNA-protein crosslinks in the course of aging in two mouse strains by use of a modified alkaline filter elution applied to whole tissue samples

Two different mouse strains have been used for determination of age dependence of DNA-protein crosslinks by alkaline filter elution: a long lived laboratory strain, NMRI and an accelerated senescence-prone, short lived strain, SAMP1. Five organs were selected: Brain, kidney, lung, heart and liver. Remarkably in all five organs of short lived SAMPI mice crosslinks increased significantly with age. In NMRI however only in brain and heart a significant rise in old age has been observed, while in the other organs there was no increase in DNA-protein crosslinking. Appreciable mitotic activity which is lacking in brain and heart could be the reason for this difference. Poor repair in all five organs could be an important component for the multiple ailments and shortened life span in SAMP1 mice.

Age-related defects in lifespan and learning ability in SAMP8 mice

Pertinent animal models of age-related learning deficiencies are required to elucidate the mechanism of age-related learning deficiencies and to develop novel therapeutic drugs for age-related diseases such as learning defects. Among many strains of accelerated senescence prone, senescence-accelerated mouse (SAM), SAMP8 mice have age-related defects in learning and cognitive abilities. We review recent findings on alterations in SAMP8 brain in neurochemical parameters related to neurotransmission and synaptic plasticity compared to those in SAMR1 brain as the control. In addition, we report the preventive effects of drugs on learning deficiencies in SAMP8 and discuss the usefulness of SAMP8 as an animal model of age-related learning deficiencies.

Senescence-accelerated mouse (SAM): a biogerontological resource in aging research

The senescence-accelerated mouse (SAM), consisting of 14 senescence-prone inbred strains (SAMP) and 4 senescence-resistant inbred strains (SAMR) has been under development since 1970 through the selective inbreeding of AKR/J strain mice donated by the Jackson laboratory in 1968, based on the data of the grading score of senescence, life span, and pathologic phenotypes. The characteristic feature of aging common to all SAMP and SAMR mice is accelerated senescence and normal aging, respectively. Furthermore, SAMP and SAMR strains manifest various pathobiological phenotypes which include such neurobiological phenotypes as deficits in learning and memory, emotional disorders, abnormal circadian rhythms, brain atrophy, hearing impairment, etc., and are often characteristic enough to differentiate the strains. Various efforts are currently being made using the SAM model to clarify the underlying mechanisms in accelerated senescence as well as the etiopathogenic mechanisms in age-associated pathobiologies. Genetic background and significance of SAM development are discussed.

High-linoleate and high-alpha-linolenate diets affect learning ability and natural behavior in SAMR1 mice

Semipurified diets incorporating either perilla oil [high in alpha-linolenate, 18:3(n-3)] or safflower oil [high in linoleate, 18:2(n-6)] were fed to senescence-resistant SAMR1 mouse dams and their pups. Male offspring at 15 mo were examined using behavioral tests. In the open field test, locomotor activity during a 5-min period was significantly higher in the safflower oil group than in the perilla oil group. Observations of the circadian rhythm (48 h) of spontaneous motor activity indicated that the safflower oil group was more active than the perilla oil group during the first and second dark periods. The total number of responses to positive and negative stimuli was higher in the safflower oil group than in the perilla oil group in the light and dark discrimination learning test, but the correct response ratio was lower in the safflower oil group. The difference in the (n-6)/(n-3) ratios of the diets reflected the proportions of (n-6) polyunsaturated fatty acids, rather than those of (n-3) polyunsaturated fatty acids in the brain total fatty acids, and in the proportions of (n-6) and (n-3) polyunsaturated fatty acids in the total polyunsaturated fatty acids of the brain phospholipids. These results suggest that in SAMR1 mice, the dietary alpha-linolenate/linoleate balance affects the (n-6)/(n-3) ratio of brain phospholipids, and this may modify emotional reactivity and learning ability.

Increased expression of hippocampal cholinergic neurostimulating peptide-related components and their messenger RNAs in the hippocampus of aged senescence-accelerated mice

Hippocampal cholinergic neurostimulating peptide stimulates cholinergic phenotype development by inducing choline acetyltransferase in the rat medial septal nucleus in vitro. Adult senescence-accelerated-prone mice/8, a substrain of the senescence-accelerated-prone mouse, show a remarkable age-accelerated deterioration in learning and memory. We cloned mouse hippocampal cholinergic neurostimulating peptide precursor protein complementary DNA. The deduced amino acid sequence showed that the neurostimulating peptide itself is the same as that found in the rat. In situ hybridization revealed that the highest expression of the precursor protein messenger RNA was in hippocampal pyramidal neurons. Compared with a strain of senescence-accelerated-resistant mouse (control mouse), adult senescence-accelerated-prone mice/8 showed increased expression of both the precursor messenger RNA and the neurostimulating peptide-related immunodeposits in the hippocampal CA1 field. The deposits were intensely and diffusely precipitated in neuropils throughout the strata oriens and radiatum in senescence-accelerated-prone mice/8, but not in control mice. The neurostimulating peptide content in the hippocampus was higher in senescence-accelerated-prone mice/8 than in control mice, while its precursor protein itself was not different between the two strains. Furthermore, our previous and present data show that the medial septal and hippocampal choline acetyltransferase activity was significantly lower in senescence-accelerated-prone mice/8 than in control mice. The data suggest that, in hippocampal neurons in adult senescence-accelerated-prone mice/8, the production of hippocampal cholinergic neurostimulating peptide precursor protein in neuronal somata, which is associated with an increased expression of its messenger RNA in the CA1 field, occurs as a consequence of low activity in their presynaptic cholinergic neurons. This is followed by accelerated processing to generate bioactive peptide and transport to its functional fields. However, certain mechanisms reduce the release of the peptide and lead to its accumulation in the neuropil. These disturbances of the septohippocampal cholinergic system might be the biochemical mechanism underlying the characteristic deterioration of senescence-accelerated-prone mice/8.

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.

Hyperexcitability of amygdala neurons of senescence-accelerated mouse revealed by electrical and optical recordings in an in vitro slice preparation

In the amygdala (AMG) slices obtained from both the young (4-7 months old) and aged (17-20 months old) groups of Senescence-Accelerated Mouse (SAM) P10, spontaneous bursts were recorded in the medial, central and basolateral nuclei. The spontaneous bursts were also observed in the slices from the young group of SAMR1, whereas the mean frequency was significantly lower than that from the young group of SAMP10. The spontaneous burst was barely detectable in slices from the aged group of SAMR1 during perfusing with the standard solution, while bicuculline methiodide (10 microM), a GABAA receptor antagonist, or Mg2+-free solution induced a similar bursting activity observed in the young group. The burst response was also evoked in the medial, central and basolateral AMG following stimulation of the stria terminalis (ST). Both spontaneous and evoked bursts were completely suppressed by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 4 microM), an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptor antagonist, but not by (+)-5-methyl-10, 11-dihydro-5H-dibenzo-[a,d]-cyclohepten-5,10-imine hydrogen maleate (MK-801, 30 microM), an N-methyl-d-aspartate receptor antagonist. The hyperexcitability of the AMG neurons was further substantiated by optical recordings. Following stimulation of the ST, the optical signals reflected postsynaptic responses spread into the medial and central AMG areas at 2-5 ms and faded out at 20-30 ms after stimulation. The intensity of the optical signal recorded in the slice from the young SAMP10 was significantly higher than that from SAMR1 or ddY mice. These observations indicate that bursts mediated by AMPA/kainate receptors were transiently generated in the AMG of SAMR1 at the young age, while the bursts with higher frequency were continuously generated in the AMG of SAMP10. The chronic neuronal hyperactivity in the AMG may be partially responsible for the age-related deterioration of memory and learning abilities observed in SAMP10.

Structural and functional changes in proteins induced by free radical-mediated oxidative stress and protective action of the antioxidants N-tert-butyl-alpha-phenylnitrone and vitamin E

The free radical theory of aging proposes that reactive oxygen species (ROS) cause oxidative damage over the lifetime of the subject. It is the cumulative and potentially increasing amount of accumulated damage that accounts for the dysfunctions and pathologies seen in normal aging. We have previously demonstrated that both normal rodent brain aging and normal human brain aging are associated with an increase in oxidative modification of proteins and in changes in plasma membrane lipids. Several lines of investigation indicate that one of the likely sources of ROS is the mitochondria. There is an increase in oxidative damage to the mitochondrial genome in aging and a decreased expression of mitochondrial mRNA in aging. We have used a multidisciplinary approach to the characterization of the changes that occur in aging and in the modeling of brain aging, both in vitro and in vivo. Exposure of rodents to acute normobaric hyperoxia for up to 24 h results in oxidative modifications in cytosolic proteins and loss of activity for the oxidation-sensitive enzymes glutamine synthetase and creatine kinase. Cytoskeletal protein spin labeling also reveals synaptosomal membrane protein oxidation following hyperoxia. These changes are similar to the changes seen in senescent brains, compared to young adult controls. The antioxidant spin-trapping compound N-tert-butyl-alpha-phenylnitrone (PBN) was effective in preventing all of these changes. In a related study, we characterized the changes in brain protein spin labeling and cytosolic enzyme activity in a series of phenotypically selected senescence-accelerated mice (SAMP), compared to a resistant line (SAMR1) that was derived from the same original parents. In general, the SAM mice demonstrated greater oxidative changes in brain proteins. In a sequel study, a group of mice from the SAMP8-sensitive line were compared to the SAMR1-resistant mice following 14 days of daily PBN treatment at a dose of 30 mg/kg. PBN treatment resulted in an improvement in the cytoskeletal protein labeling toward that of the normal control line (SAMR1). The results of these and related studies indicate that the changes in brain function seen in several different studies may be related to the progressive oxidation of critical brain proteins and lipids. These components may be critical targets for the beneficial effects of gerontotherapeutics both in normal aging and in disease of aging.

Somatic mutation and aging

A key prediction of the somatic mutation theory of aging is that there is an invariant relationship between life span and the number of random mutations. A number of studies at a number of gene loci have shown that somatic mutations of a variety of types accumulate with age. Dietary restriction, which prolongs life span, results in slowed accumulation of HPRT mutants in mice. Conversely, senescence-accelerated mice, which have been bred to have a shortened life span, show accelerated accumulation of somatic mutations.

Age-related changes in the brains of senescence-accelerated mice (SAM): association with glial and endothelial reactions

Twelve substrains of inbred senescence-accelerated mice (SAM) have been developed, among which the SAMP8 and SAMP10 strains show a significant age-related deterioration in learning and memory for passive and active avoidance tasks. These strains have, respectively, a low and high incidence of systemic senile amyloidosis. Although we found no amyloid deposits in their brain parenchyma, a variety of age-related alterations were identified, involving neurons, glia, and vessels in the brain tissues. Here we review the degenerative changes in aged SAMP8 and SAMP10 brains. These changes are generally similar to the pathology of aging human brain and may be characterized by their association with some specific glial reactions.

An early stage mechanism of the age-associated mitochondrial dysfunction in the brain of SAMP8 mice; an age-associated neurodegeneration animal model

In order to characterize the early stage of mitochondrial dysfunction, we investigated the redox state and oxidative phosphorylation of the brain mitochondria from 2-month-old Senescence-accelerated mouse (SAM)P8 and SAMR1 mice; SAMP8 mice exhibit various signs of age-associated neurodegeneration and rapid mitochondrial dysfunction, although SAMR1 mice do not. The redox state was estimated as the reduction rate of Cu-pyruvaldehyde-bis (N4-methylthiosemicarbazone) (Cu-PTSM), the reduction of which is closely related to the electron leakage from the mitochondrial electron transport system in the brain, using electron spin resonance spectrometry (ESRS). The oxidative phosphorylation was measured polarographically. The SAMP8 mouse brain mitochondria demonstrated higher redox state and a higher activity of mitochondrial respiration with lower respiration control ratio than the mitochondria of SAMR1 mouse brains. This indicates that an inefficient hyperactive state can exist in the mitochondrial electron transport system before the age-associated mitochondrial dysfunction develops.

Neurochemical and behavioral characterization of potential antidepressant properties of indeloxazine hydrochloride

The potential antidepressant properties of indeloxazine hydrochloride were examined in vitro and in vivo. Indeloxazine showed preferential affinity for both [3H] citalopram (Ki: 22.1 nM) and [3H]nisoxetine binding sites (Ki: 18.9 nM) in membranes of the rat cerebral cortex. In microdialysis studies, intraperitoneal injection of indeloxazine (3 and 10 mg/kg) dose-dependently increased the extracellular level of both serotonin and norepinephrine in rat frontal cortex of freely moving rats. Amitriptyline was almost equivalent to indeloxazine in these two assays with the exception of a much weaker effect on extracellular serotonin levels. Spontaneous [3H]serotonin release from rat cortical synaptosomes was significantly enhanced by indeloxazine (10-1000 nM). In behavioral studies, indeloxazine increased the number of wheel rotations in forced swimming tests in both ICR mice (50 mg/kg, p.o.) and SAMP8//YAN, a substrain of senescence-accelerated mouse (20 and 30 mg/kg, p.o.). Indeloxazine (3-10 mg/kg p.o.) also inhibited the incidence of muricide in raphe-lesioned rats. These results suggest that indeloxazine is an inhibitor of serotonin and norepinephrine uptake and has potential antidepressant properties. In addition, the drug-induced enhancement of serotonin release may contribute to its potent effects on the serotonergic system in vivo.

Reduced expression of interleukin-11 in bone marrow stromal cells of senescence-accelerated mice (SAMP6): relationship to osteopenia with enhanced adipogenesis

Aging is associated with an increase in bone marrow adipose tissue and a reduction in bone turnover. The P6 strain of senescence-accelerated mice (SAM) exhibit an early decrease in bone mass with a reduction in bone remodeling. In the bone marrow, suppressed osteoblastogenesis and osteoclastogenesis with enhanced adipogenesis are observed. The present study was undertaken to clarify the mechanism of age-related changes in bone turnover using bone marrow cells from SAMP6 mice. Because interleukin (IL)-11 has been shown to potently inhibit adipogenesis and to stimulate osteoclast formation, the effect of IL-11 on the differentiation of bone marrow cells was examined. The impaired formation of both osteoblasts and osteoclasts was restored and the enhanced formation of adipocytes was suppressed by the addition of 10 pM recombinant human IL-11. Other cytokines that activate gp130 as a common signal transducer, IL-6 and leukemia inhibitory factor, did not have such effects. Sequence analysis of the entire coding region of IL-11 cDNA obtained from SAMP6 stromal cells revealed no mutations. Constitutively secreted IL-11 protein into culture media, and its mRNA expression stimulated by transforming growth factor beta were reduced in stromal cells from SAMP6 compared with those in control mice. These results demonstrate that the expression of IL-11 is reduced in bone marrow cells of SAMP6 and suggest that the reduction in IL-11 actions is involved in the impairment of both osteoblastogenesis and osteoclastogenesis in these mice. There is a possibility that alterations in IL-11 actions may be associated with the age-related impairment in bone metabolism.

D-serine content and D-[3H]serine binding in the brain regions of the senescence-accelerated mouse

An established senescence-accelerated model mouse strain, SAMP8, shows the deterioration of learning and memory compared with a normal control strain, SAMR1. D-Serine binds to strychnine-insensitive glycine binding sites of the N-methyl-D-aspartate (NMDA) receptor complex, and enhances glutamate binding to the receptor complex. To investigate the relationship of endogenous brain D-serine and the brain dysfunction caused by aging, the level of brain free D-serine and the D-[3H]serine binding to the brain samples were examined using the SAMP8 and SAMR1 mice. The free D-serine level was highest in the cerebral frontal and occipital cortices in both the SAMP8 and SAMR1; no difference in the D-serine level was shown between the two strains. A receptor autoradiographical analysis showed that the D-[3H]serine binding to the brain section was highest in the hippocampus, and the binding in the SAMP8 brains was lower than that of the SAMR1. The D-[3H]serine binding to the crude cerebral membranes indicated that the value of the total binding sites for the SAMP8 was lower than that for the SAMR1, whereas the value of the dissociation constant Kd for the SAMP8 was similar to that of the SAMR1. These results suggest that the number of D-[3H]serine binding sites was decreased in the SAMP8 compared to the SAMR1, but the affinity of D-[3H]serine to the binding sites was not altered. These results support the view that a decrease of NMDA receptor complex is involved in the age-related neural dysfunction of SAMP8 mice.

Age-related changes in levels of brain-derived neurotrophic factor in selected brain regions of rats, normal mice and senescence-accelerated mice: a comparison to those of nerve growth factor and neurotrophin-3

Age-related changes in the levels of brain-derived neurotrophic factor (BDNF) in selected regions of brains from rats, normal mice and senescence-accelerated mice were compared to those of nerve growth factor (NGF) and neurotrophin-3 (NT-3). The concentration of BDNF increased with age in the rat hippocampus while it decreased in the rat cerebral cortex. The level of BDNF in the hippocampus from aged rats was about 260%, of that in the same region from young adult rats. A strong staining with antibodies specific for BDNF was observed in the hilus of the dentate gyrus in the hippocampus from aged rats. By contrast, BDNF levels were significantly lower in four brain regions from aged rats as compared to young adult rats (30, 56, 52 and 52%, lower in the septum, cerebral cortex, cerebellum and striatum, respectively). Patterns of age-related changes in the level of BDNF in the mouse hippocampus. cerebral cortex, cerebellum and olfactory bulb were similar to those in the respective regions from rats. In rats, the concentration of NGF decreased with age in the cerebral cortex but remained unchanged in the hippocampus, cerebellum and olfactory bulb. In mice, levels of NGF increased in all four brain regions from 1 to 18 months after birth. The concentrations of NT-3 increased and decreased with age in the rat cerebral cortex and cerebellum, respectively, while minimal changes were observed in the rat hippocampus and olfactory bulb as was also true in mice. In senescence-accelerated mice with memory disturbances, no marked increases in levels of NGF and BDNF in the hippocampus and in the level of NT-3 in the cerebral cortex were found. Thus, increases in levels of BDNF and NT-3 occurred in the murine hippocampus and cerebral cortex, respectively, during normal aging, but not during aging of mice with pathological changes.

Difference between senescence-accelerated prone and resistant mice in response to insulin in the heart

The effect of insulin on the translocation of GLUT4 (glucose transporter isoform 4) from the intracellular membranes to the plasma membranes was compared in the hearts of 4-8 week old SAMP8, a substrain of senescence-accelerated prone mouse and those of SAMR1, a substrain of senescence-accelerated resistant mouse. After 20 min of the intravenous injection of insulin, the blood glucose levels in SAMR1 and SAMP8 were decreased by 50 and 68%, respectively. Under this condition, the concentrations of GLUT4 protein in the plasma membranes in the hearts of SAMR1 and SAMP8 were increased 1.8- and 2.1-fold, respectively. Concomitantly, the concentrations of the GLUT4 protein in the intracellular membranes in the hearts of SAMR1 and SAMP8 were decreased by about 70 and 50%, respectively. These results suggest that the heart of 4-8 week old SAMP8 is more sensitive to insulin than that of age-matched SAMR1.

Spontaneous and artificial lesions of magnocellular reticular formation of brainstem deteriorate avoidance learning in senescence-accelerated mouse SAM

The role of the magnocellular reticular formation (MGRF) of the brainstem on learning and memory was examined in memory-deficient mice with spontaneous spongy degeneration in the brainstem (senescence-accelerated mouse, SAMP8) and control mice (accelerated-senescence resistant mouse, SAMR 1). SAMP8 showed spontaneous age-related impairment of learning and memory, as determined by passive and active avoidance responses. The deficits of learning and memory function in passive avoidance performances began at two months of age and increased with ageing. In the brains of SAMP8 at one month of age and older, spongy degeneration was mainly observed in the brainstem, while no vacuoles were evident in SAMR1 control (normal ageing mouse) brains in the age range tested (up to 12 months). The vacuolization in SAMP8 was marked in the MGRF, especially in the dorsomedial MGRF. Quantitative analysis of the vacuolization showed that the total area and number of vacuoles in the MGRF increased with age, and they were affected by the degree of deficits in learning and memory. The latency 24 h after footshock in passive avoidance tests decreased with the increase in total area and number of vacuoles in MGRF. The number of shocks in active avoidance tests increased with the increase in total number and area of vacuoles. Thus, learning and memory ability in passive and active avoidance responses deteriorated with enlargement in the vacuolated area in MGRF, and it was assumed that MGRF (especially, the dorsomedial part) possesses functions related to learning and memory. To confirm this notion, behavior and memory tests (passive avoidance and active avoidance tests, open field tests and shock sensitivity measurements) were carried out in SAMR1 mice, whose bilateral dorsomedial MGRF was destroyed electrolytically (MGRF-lesioned mice). The MGRF-lesioned mice showed no difference from sham mice in sensory threshold or open field activity; however, there was severe deterioration in passive avoidance behavior and impairment in the active avoidance performances. From the results in SAMP8 and MGRF-lesioned mice, it was confirmed that MGRF (especially the dorsomedial part) has functions related to learning and memory, and is one part in the learning and memory system of the brain. Thus, SAMP8 can serve as a model of RF-lesioned mice with impaired learning and memory functions.

Behavioral assessment of the senescence-accelerated mouse (SAM P8 and R1)

Senescence-accelerated mice (SAM P8 and R1) were behaviorally assessed in a cross-sectional study at 4 and 15 months of age. Behavioral measures included memory (place discrimination and repeated acquisition in a water maze), sensorimotor performance (turning in an alley, traversing bridges, wire rod hanging, and falls from a wire screen), psychomotor performance (open-field exploration), and emotionality (entries in a plus maze, grooming, and defecation in a plus maze and in an open field). In the water maze, aged P8 mice were impaired in place discrimination and in repeated acquisition tasks, demonstrating evidence of an age-related decline in spatial memory processing abilities. The demonstration of this impairment, however, was complicated by noncognitive factors, such as the tendency of many older P8 mice to float. Sensorimotor skill impairment was accelerated with age in P8 mice, but not in R1 mice, and this impairment was present despite the lack of age-related changes in body weight in P8 mice. Although P8 and R1 mice were not different in general activity at old age, P8 mice were substantially more hyperactive in an open field and in the plus maze than R1 mice when compared at young age. Independent of age, P8 mice demonstrated a reduction of anxiety-like behavior in the plus maze. Taken as a whole, the data suggest that although age-related behavioral alterations occur in the P8 mice, some of these changes are evident at 4 months of age. Thus, the behavioral abnormalities that exist not only represent an accelerated aging phenomenon but may also be considered a developmental pathology.

A spin trap, N-tert-butyl-alpha-phenylnitrone extends the life span of mice

To characterize the pharmacological effects of N-tert-butyl-alpha-phenylnitrone (PBN) on life span, we administered PBN in drinking water to 24.5-month-old mice, and the survivors were counted. Their water consumption and body weights were measured as biological markers. PBN-treated animals as compared with control animals had prolonged mean and maximum life spans. Their water consumption decreased but no significant change was found in their body weights, indicating that the metabolism was improved. Results showed that PBN indeed affects physiological functions and extends life span. We propose that nitric oxide release from PBN may be involved in altering the aging process.

Immunocytochemical study of catecholaminergic neurons in the senescence-accelerated mouse (SAM-P8) brain

The catecholaminergic neurons of senescence-accelerated mice (SAM-P8) were analyzed by immunohistochemical microphotometry in terms of immunoreactivities to aromatic L-amino acid decarboxylase (AADC), dopamine (DA), or noradrenaline (NA). Accelerated senescence-resistant mice (SAM-R1) were used as control mice. The immunoreactivities to AADC, DA, and NA of the catecholaminergic neurons of the SAM-P8 mice were weaker than those of the SAM-R1 mice in all the brain regions. Immunoelectron microscopy revealed progressive degeneration of dopaminergic neurons and their terminal fibers in the substantia nigra as well as in noradrenergic neurons and their proximal dendrites in the locus coeruleus of the SAM-P8 mice. In contrast, there was no difference between the SAM-P8 and SAM-R1 mice in the distribution of AADC-only positive neurons (designated as D neurons in the rat brain by Jaeger et al.) nor in their immunoreactivities. These results may indicate that DA neurons in the substantia nigra and NA neurons in the locus coeruleus degenarate more rapidly during aging in SAM-P8 mice than in control SAM-R1 mice and that D neurons may function as a part of a compensatory system for the decreases in catecholaminergic neurons during aging.

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.

Senescence-accelerated overexpression of S100beta in brain of SAMP6 mice

S100beta is an astrocyte-derived protein with paracrine and autocrine effects on neurons and glia. Brain S100beta expression increases progressively with age, and this increased expression has been implicated as a factor underlying the increasing risk of Alzheimer's disease that accompanies aging. Senescence acceleration-prone (SAMP) mice are a group of inbred strains that provide animal models of aging and of various age-related disease processes in the brain and peripheral tissues. One of these strains, the osteopenic SAMP6, has not been previously associated with central nervous system alterations. We used Northern and Western immunoblot analysis and immunohistochemical labeling to examine S100beta expression in brains of SAMP6 mice. Cerebral tissue levels of S100beta and of S100beta mRNA were 2.2-fold and 1.6-fold those of senescence-resistant (control) mice at 4 months of age (p < 0.05 in each case), and were 3.7-fold and 1.9-fold those of control mice at 6 months of age (p < 0.01 in each case). In contrast, levels of glial fibrillary acidic protein (GFAP) in cerebral hemispheres were not different from those of controls. Image analysis of immunohistochemical preparations showed increased numbers and immunoreactive intensity of S100beta-immunoreactive astrocytes in both the hippocampus and cerebral cortex of SAMP6 mice at 4 months of age (p < 0.05 or better in each case). These increases were greater in the hippocampus than in the cerebral cortex. In contrast, increases in numbers of GFAP immunoreactive astrocytes were noted only in the hippocampus. Our finding of increased S100beta gene expression in brains of SAMP6 mice mirror age-associated increases in S100beta expression in human brain and suggest that SAMP6 may provide insights into age-associated brain alterations and diseases.

Mitochondrial dysfunction in the senescence accelerated mouse (SAM)

Oxidative damage to DNA, proteins, and lipids in mitochondria caused by free radicals may be one factor in aging. Oxidative phosphorylation was estimated in liver mitochondria from senescence accelerated mice (SAMP8) and a senescence resistant substrain (SAMR1). The respiratory control ratio decreased in liver mitochondria of SAMP8 during aging, and it was estimated that at 18 months of age this respiratory control value suggested that it might be insufficient to provide ATP synthesis necessary for normal cell metabolism. In addition, the ADP/O, an index of efficiency of ATP synthesis, was depressed at 18 months of age. Dinitrophenol-dependent uncoupled respiration in liver mitochondria of SAMP8 mice was markedly decreased with aging, suggesting a dysfunctional energy transfer mechanism in mitochondria of aged SAMP8 mice. Active uptake of calcium in liver mitochondria was markedly dysfunctional in SAMP8 mice with aging, and uncoupling of respiration was induced more easily in aged mitochondria. Milder effects on these functional parameters were observed in SAMR1 mice. A similar dysfunction was also observed in heart mitochondria of SAMP8 mice at 12 months of age. The amount of Bcl-x in liver mitochondria was slightly decreased in SAMP8. We suggest that these changes in mitochondrial function may be related to the shorter life span of the senescence accelerated mouse.

Age-related decline in humoral immunity caused by the selective loss of TH cells and decline in cellular immunity caused by the impaired migration of inflammatory cells without a loss of TDTH cells in SAMP1 mice

We investigated the cellular basis of the age-related decline in antibody (Ab) and delayed-type hypersensitivity (DTH) responses to sheep red blood cells (SRBC) in vivo in short-lived senescence-accelerated mouse (SAM) P1. In SAMP1 mice, age-related decreases in CD4+ T cells in the peripheral blood occurred earlier than in control mice and occurred in parallel with the age-related decline in Ab and DTH responses. In addition, the involution of the thymus was faster. The injection of thymic T cells from young mice before sensitization completely restored the Ab responses in aged SAMP1 mice. These data suggest that the age-related decline in Ab response is due to the age-related early loss of helper-T (TH) cells. On the other hand, the local transfer of spleen cells from sensitized aged donors into the footpads of naive syngeneic recipients evoked strong DTH responses, demonstrating the existence of DTH-mediating T (TDTH) cells in the spleens of aged SAMP1 mice. Moreover, the local injection of naive spleen cells from young donors, together with the antigen, into the footpads caused DTH responses in sensitized aged recipients. These findings indicate that TDTH cells were induced and were able to migrate and function as effector cells in aged mice. When naive spleen cells from aged donors were injected locally into the footpad, they restored the DTH response in aged mice, but this effect did not work if the cells were injected intravenously. This demonstrates that the inflammatory cells of the aged mice were able to work at the local site, but could not migrate there. The intravenous injection of naive spleen cells from young donors restored the DTH response in aged mice, suggesting that the endothelial cells of aged mice were not impaired and permitted the inflammatory cells to migrate into the extravascular tissues. Thus, although the age-related decline of the Ab and DTH responses occur in parallel, we found different effects of aging on TH and TDTH cells in SAMP1 mice. Furthermore, our data suggest that the reason for the low DTH response in aged SAMP1 mice is not the loss of TDTH cells, but rather the impaired migration of inflammatory cells into the local site.

Senescence-related change in autologous mixed-lymphocyte reaction in senescence-accelerated mice

Using the senescence-accelerated mouse (SAM) strains, we examined the senescence-related changes of autologous mixed-lymphocyte reaction (AMLR) as well as the phenotypic alteration of the T cell subsets. Splenic T cells from senescence-prone (SAM-P) and resistant (SAM-R) strains of mice were incubated with autologous non-T cells, and AMLR was measured on day 1-5. The kinetics of AMLR responses revealed a marked alteration in senescent SAM-P but not in non-senescent SAM-R mice, in which the peak response occurred at day 1, the response decreasing thereafter up to day 5. Similar senescence-related change was observed in aged (24-month-old) SAM-R and BALB/c mice. Furthermore, the T cells from the aged SAM-R mice cultured with non-senescent syngeneic non-T cells showed a very similar pattern to that cultured with autologous non-T cells. Flow cytometric analysis of T cell phenotype indicated that the percentage of CD4+ CD45RBhi T cells correlated with the peak AMLR responses in both SAM-P and SAM-R mice, and that the percentage of the T cell subset with extrathymic properties was significantly higher in SAM-P mice. These findings suggest that the alteration in kinetics of AMLR is related to senescence but not to the strain of mice, and may reflect a senescence-related dysfunction of the autoregulatory immune mechanisms of T cells.

Differences between the circadian system of two strains of senescence-accelerated mice (SAM)

The aim of this study was to look for morphological or functional differences between the circadian system of two substrains of Senescence Accelerated Mice (SAM): senescence-prone (SAMP8; average median survival time = 10.0 months) and senescence-resistant (SAMR1; average median survival time = 18.9 months). Neither the general structure nor the quantitative analysis of the number of VP-positive neurons in matched sections revealed differences between SAMP8 and SAMR1 mice. Under LD 12/12 photoperiod, all animals showed the typical pattern of wheel running activity with maximum activity in the first half of darkness period. The period of the locomotor activity in free running as well as the time course for synchronization after a 6 h phase delay of LD cycle were similar in both strains of SAM mice. However, SAMP8 animals reentrained significantly earlier (3.4 +/- 0.4 days) than SAMR1 (6.3 +/- 0.9 days) after a 6 h phase advance of LD cycle. We conclude that the circadian system of SAMP8 mice presents some functional differences with that of SAMR1, which could help to explain their different rate of ageing.