SAMR1 Control Research Articles

Ameliorative effects of dietary carotenoids on memory deficits in senescence-accelerated mice (SAMP8)

We previously reported that the dietary ingestion of the red-bell pepper ( Capsicum annuum L.) or tomato ( Lycopersicon esculentum Mill.) ameliorated the age-related alteration of SAMP8. These vegetable abounds in antioxidative carotenoids, capsanthin and lycopene. We examined the effects of feeding red-bell pepper or capsanthin on the age-related disorders in the senescence-accelerated mouse (SAMP8), a murine model of the accelerated decline in learning ability, and the control SAMR1 mouse. SAMP8 mice that received a diet containing 0.1% (w/w) capsanthin showed a much better memory acquisition in passive avoidance tasks compared to those given the control diet. The ingestion of capsanthin showed no effect on the learning ability of the SAMR1 mice. The activity of choline acetyltransferase (ChAT) in the parietal cortex of SAMP8 mice fed the diet containing capsanthin was potentiated compared to that in those fed the common diet. These observations indicate that the amelioratory effect of the red-bell pepper on the learning impairment in SAMP8 mice is mainly due to capsanthin. The ingestion of lycopene (0.02% (w/w) in the diet) also ameliorated the memory deficits in the SAMP8 mice analogous to the feeding of capsanthin.

Physiological characteristics in SAMP1 and SAMP2 mice

We examined the physiological and behavioral characteristics of senescence-accelerated mice, SAMP1 and SAMP2 strains. In SAMP1 (P1) mice, we examined the diurnal rhythms of food and water intake, spontaneous motor activity (SMA), and spontaneous wheel running (SWR). Without a SWR exercise, food and water intake and SMA in the P1 mice were significantly higher during the light (L)-phase of the light/dark (LD) cycle than for the control SAMR1 (R1) mice. Additionally, the SWR and SMA activity split into two peaks. SWR exercise significantly increased the percentage of nocturnal food intake and SMA in P1 mice. Thus disordered diurnal rhythms in P1 mice can be normalized partially by the SWR exercise. In SAMP2 (P2) mice, we examined the physiological characteristics throughout the life span. The food and water intake, oxygen uptake ( V O 2), and SWR were higher than those of the control R1 mice, whereas the body weight, colonic temperature (Tco) and pelt weight were significantly lower. These results suggest that: (1) lower Tco in P2 mice is caused by morphological or insulated characteristics, and (2) and the short life span in P2 mice is caused by excessive food intake and higher V O 2 and SWR activity.

Diurnal rhythm disorder of behavioral activity in SAMP1 mice is partially normalized by spontaneous wheel running

We examined the diurnal rhythms of food and water intake, spontaneous wheel running (SWR), and spontaneous motor activity (SMA) in the SAMP1 strain, a mouse model of accelerated senescence. Without SWR exercise, food, and water intake in the SAMP1 mice was significantly higher during the light (L)-phase of the light–darkness (LD) cycle than in the control SAMR1 strain. Additionally, SWR and SMA activity rhythms were split in SAMP1 mice, as demonstrated by the appearance of a secondary peak starting from the end of the dark (D)-phase. SWR exercise significantly increased the percentages of nocturnal food and water intake and SMA in the SAMP1 mice, although food and water intake did not reach the level of control SAMR1 mice. Thus, the disordered diurnal rhythms in SAMP1 mice can be normalized, even if only partially, by SWR exercise.

Differential expression of the liver proteome in senescence accelerated mice.

The senescence-accelerated mouse (SAM) is a useful animal model to study aging or age-associated disorders due to its inherited aging phenotype. To investigate proteins involved in the aging process in liver, we compared the young (4- or 20-week old) and the aged group (50-week-old) of SAMP8 (short life span) and SAMR1 (control) mice, and identified 85 differentially expressed distinct proteins comprising antioxidation, glucose/amino acid metabolism, signal transduction and cell cycle systems using proteomics tools. For the antioxidation system, the aged SAMP8 mice showed a large increase in glutathione peroxidase and decreases in glutathione-S-transferase and peroxiredoxin, ranging from 2.5- to 5-fold, suggesting lower detoxification potentials for oxidants in the aged SAMP8 liver. Similarly, levels of key glycolytic enzymes decreased greatly in the aged SAMP8 compared to SAMR1, indicating a disturbance in glucose homeostasis that may be closely related to the typical deficits in learning and memory of the aged SAMP8. Protein profiles of amino acid metabolic enzymes suggest that accumulation of glutamine and glutamate in tissues of the aged SAMP8 may be due to hyperexpression of ornithine aminotransferase and/or glutamate dehydrogenase. Decreases in levels of proteins involved in signal transduction/apoptosis (e.g., cathepsin B) in the aged SAMP8 may support the previously proposed negative relationship between apoptosis and aging. However, the changes described above were not markedly seen in the young group of both strains. For cell cycle systems, levels of selenium binding protein increased about four-fold with age in SAMP8. Yet, almost no change occurred in either the young or the aged SAMR1, which may explain problems associated with cell proliferation and tissue regeneration in the aged SAMP8. In conclusion, composite profiles of key proteins involved in age-related processes enable assessment of accelerated senescence and the appearance of senescence-related pathologies in the aged SAMP8.

Impaired osteoblastic differentiation, reduced bone formation, and severe osteoporosis in noggin-overexpressing mice.

We describe the effects of the overexpression of noggin, a bone morphogenetic protein (BMP) inhibitor, on osteoblast differentiation and bone formation. Cells of the osteoblast and chondrocyte lineages, as well as bone marrow macrophages, showed intense beta-gal histo- or cytostaining in adult noggin+/- mice that had a LacZ transgene inserted at the site of noggin deletion. Despite identical BMP levels, however, osteoblasts of 20-month-old C57BL/6J and 4-month-old senescence-accelerated mice (SAM-P6 mice) had noggin expression levels that were approximately fourfold higher than those of 4-month-old C57BL/6J and SAM-R1 (control) mice, respectively. U-33 preosteoblastic cells overexpressing the noggin gene showed defective maturation and, in parallel, a decreased expression of Runx-2, bone sialoprotein, osteocalcin, and RANK-L. Noggin did not inhibit the ligandless signaling and pro-differentiation action of the constitutively activated BMP receptor type 1A, ca-ALK-3. Transgenic mice overexpressing noggin in mature osteocalcin-positive osteoblasts showed dramatic decreases in bone mineral density and bone formation rates with histological evidence of decreased trabecular bone and CFU-osteoblast colonies at 4 and 8 months. Together, the results provide compelling evidence that noggin, expressed in mature osteoblasts, inhibits osteoblast differentiation and bone formation. Thus, the overproduction of noggin during biological aging may result in impaired osteoblast formation and function and hence, net bone loss.

Age‐related loss of synapses in the frontal cortex of SAMP10 mouse: A model of cerebral degeneration

SAMP10 mouse is a model of brain aging in which senescence is characterized by cerebral atrophy most prominent in the frontal cortex, deterioration in performance of learning and memory tasks, and alterations of the central dopaminergic system. The present study investigates age-related changes in the expression of synapse-related proteins to determine whether the number of synapses is decreased in SAMP10 mice. We quantified expression levels of synaptophysin, a presynaptic protein, and of PSD-95, a postsynaptic protein in various brain regions by immunoblotting. Both synapse-related proteins (52% of synaptophysin and 55% of PSD-95) were lost from the anterior cerebral cortex in SAMP10 mice at age 10-12 months compared with those in mice at age 3 months. Synaptophysin was lost by 30% from the posterior cerebral cortex of SAMP10 mice at age 15-16 months. The level of synaptophysin, but not of PSD-95 decreased by about 25% in the brain stem of SAMP10 mice aged 7 and 10-12 months. A loss of synapse-related proteins was not significant in other brain regions. Age-related loss of synaptophysin or PSD-95 was not evident in normal aging control SAMR1 mice that do not develop brain atrophy. In summary, synapses were lost with aging in SAMP10 mice and the synaptic loss was most prominent in the anterior cerebral neocortex. Since a loss of neocortical synapses is the primary correlate with the intellectual decline in human neurodegenerative diseases, SAMP10 mouse is a useful model with which to study the mechanisms underlying synaptic loss in human neurodegenerative dementias.

Abstracts from Other Presentations at the International Symposium on Toxins and Natural Products in Honor of Professor Anthony T. Tu

Abstracts from Other Presentations at the International Symposium on Toxins and Natural Products in Honor of Professor Anthony T. Tu

Long bones from the senescence accelerated mouse SAMP6 have increased size but reduced whole-bone strength and resistance to fracture.

The senescence accelerated mouse strain P6 (SAMP6) has emerged as a useful model of senile osteoporosis because it has many features of the disease, including low trabecular bone formation and low areal bone density. We further characterized the SAMP6 model of senile osteoporosis by comparing morphological, mechanical, and densitometric properties of femurs and tibias from SAMP6 mice to those of the control strain (SAMR1) at 4 months and 12 months of age. SAMP6 long bones had increased periosteal width and endosteal area (p < 0.05), resulting in an average increase of 30% in moments of inertia (p < 0.05), but no difference in bone area (p > 0.05) compared with control. Despite their increased moments of inertia, long bones from SAMP6 mice were relatively weak and brittle. Ultimate bending moment was reduced by 25%, and both postyield displacement and energy-to-fracture were reduced by 60% compared with SAMR1 controls (p < 0.001). Average cortical ash fraction was increased slightly from 0.74 in SAMR1 to 0.76 in SAMP6 bones (p < 0.05), indicating that increased mineralization may have contributed to the brittleness of SAMP6 bones. The relative differences we observed--increased endosteal and periosteal dimensions, reduced bending strength, increased brittleness, and increased mineralization--are analogous to changes that occur in the aging human skeleton. Moreover, these features were consistently observed in young (4-month) and old (12-month) animals. These findings extend the previous descriptions of the SAMP6 mouse and identify key mechanical features that further validate its relevance as a unique and functionally relevant model of senile osteoporosis.

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.

Amelioratory Effect of Dietary Ingestion of Lycopene and Tomato Rich in Lycopene on Learning Impairment in Senescence-Accelerated Mice (SAMP8).

We previously reported that the dietary ingestion of red bell pepper (Capsicum annuum L.) which contained a large amount of antioxidative carotenoids ameliorated the age-related phenomena of learning disorder and degradation of hair glossiness in the senescence-accelerated mouse (SAM). As lycopene is one of the most popular carotenoids in human serum and exists in abundance in tomato, we examined the effects of dietary lycopene and tomato rich in lycopene on the age-related disorders in SAMP8//Kgm, a mouse model of accelerated decline in learning and memory, and control SAMR1//Kgm mice. SAMP8 mice that received a diet containing 0.02% (w/w) lycopene or 20% (w/w) tomato powder showed much better acquisition in passive avoidance tasks than those given the control diet. Dietary lycopene and tomato had no effect on the ability of learning and memory in SAMR1 mice. Those observations indicated that the dietary ingestion of lycopene in tomato ameliorated the learning impairment in SAMP8.

Ultrastructural and permeability features of microvessels in the hippocampus, cerebellum and pons of senescence-accelerated mice (SAM).

We previously reported that the accumulation of blood-borne radiolabelled serum albumin in brain parenchyma increased with aging, especially in senescence-accelerated mice (SAMP8), which showed age-related deficits in learning and memory. In this study, in order to examine morphological events related to the age-related increase of the brain accumulation of serum albumin, the transvascular passage of blood-borne horseradish peroxidase (HRP) and ultrastructural features of microvessels were examined in the hippocampus, cerebellum and pons of SAMP8 and SAMR1 (control) mice. Ultrastructural examination of the hippocampus showed that the staining for HRP was occasionally spreading throughout the parajunctional cytoplasm of the endothelial cell of aged SAMP8 mice, but not in young SAMP8 mice nor in SAMR1 mice. The number of vessels showing the staining reaction for HRP in the parajunctional cytoplasm of the endothelial cells in aged SAMP8 mice increased significantly compared with that in the others. Electron microscopic morphometry showed that there were no significant differences among the number of HRP-positive vesicles per unit area of the endothelial cell cytoplasm in young and old mice of both strains. The staining reaction for HRP was not seen in the basal lamina of microvessels and the perivascular neuropil in all mice examined. Perivascular lipofuscin-like granules and collagen deposits, swelling of astroglial perivascular endfeet and perivascular cells containing foamy, lipid-like droplets were frequently found in several brain regions of aged SAMP8 mice. The perivascular cells with a few lipid-like droplets and more electron-homogeneous lysosomes were occasionally seen in SAMR1 and young SAMP8, while the other findings were scarcely observed in SAMR1 and young SAMP8 mice. These findings suggest that the blood-brain barrier to HRP was preserved in microvessels in three brain regions of SAM mice but the blood microvessels showed some age-related ultrastructural alterations in SAMP8 brains. Uncontrolled passage of HRP through the parajunctional cytoplasm of the endothelial cells may partly contribute to the age-related increase of accumulation of serum albumin in SAMP8 brains.

Depressive Behavior and Alterations in Receptors for Dopamine and 5-Hydroxytryptamine in the Brain of the Senescence Accelerated Mouse (SAM)-P10

The senescence accelerated mouse (SAM) is known as a murine model of aging. SAM consists of senescence accelerated-prone mouse (SAMP) and senescence accelerated-resistant mouse (SAMR). Previous studies reported that SAMP 10 exhibits age-related learning impairments and behavioral depression in a tail suspension test after 7 months. We investigated the changes in emotional behavior in a forced swimming test and in receptors for dopamine and 5-hydroxytryptamine (5-HT) in SAMP10. SAMP10 at 8 months showed an increase of immobility in the test compared with SAMR1. Treatment with desipramine (25 mg/kg, i.p., 3 days) in SAMP10 caused a decrease in immobility. In the cortex from SAMP10, [3H]quinpirole binding to D2/D3 dopamine receptors increased significantly compared with control SAMR1. In the hippocampus from SAMP10, [3H]8-hydroxy DPAT binding to 5-HT1A receptor increased. In midbrains from SAMP10, bindings of [3H]quinpirole and [3H]8-hydroxy DPAT increased. [3H]SCH23390 binding to D1/D5 receptors and [3H]ketanserin binding to 5-HT2 receptor in brain regions examined in SAMP10 were similar to those in SAMR1. The present findings represent the first neurochemical evidence of an increase of D2/D3 and 5-HT1A receptors in SAMP10. SAMP10 may be a useful model of aging associated depressive behavior.

Depressive behavior and alterations in receptors for dopamine and 5-hydroxytryptamine in the brain of the senescence accelerated mouse (SAM)-P10.

The senescence accelerated mouse (SAM) is known as a murine model of aging. SAM consists of senescence accelerated-prone mouse (SAMP) and senescence accelerated-resistant mouse (SAMR). Previous studies reported that SAMP10 exhibits age-related learning impairments and behavioral depression in a tail suspension test after 7 months. We investigated the changes in emotional behavior in a forced swimming test and in receptors for dopamine and 5-hydroxytryptamine (5-HT) in SAMP10. SAMP10 at 8 months showed an increase of immobility in the test compared with SAMR1. Treatment with desipramine (25 mg/kg, i.p., 3 days) in SAMP10 caused a decrease in immobility. In the cortex from SAMP10, [3H]quinpirole binding to D2/D3 dopamine receptors increased significantly compared with control SAMR1. In the hippocampus from SAMP10, [3H]8-hydroxy DPAT binding to 5-HT1A receptor increased. In midbrains from SAMP10, bindings of [3H]quinpirole and [3H]8-hydroxy DPAT increased. [3H]SCH23390 binding to D1/D5 receptors and [3H]ketanserin binding to 5-HT2 receptor in brain regions examined in SAMP10 were similar to those in SAMR1. The present findings represent the first neurochemical evidence of an increase of D2/D3 and 5-HT1A receptors in SAMP10. SAMP10 may be a useful model of aging associated depressive behavior.

Age-dependent cerebral atrophy and cognitive dysfunction in SAMP10 mice

Findings obtained from a series of studies to characterize age-dependent changes in brain morphology and behavior of inbred SAMP10 mice are reviewed. Following apparently normal development, SAMP10 mice developed brain atrophy with advancing age. The neocortex was diffusely atrophic in aged SAMP10 mice, with the frontal cortex being most affected. The entorhinal cortex, amygdala, and nucleus accumbens were also atrophic. Other subcortical structures were mildly atrophic, but the hippocampus was not atrophic. Mild to moderate hypertrophic astrocytosis was seen in the atrophied regions. Alzheimer’s type pathology was not seen. The cortical atrophy was due to both loss and shrinkage of neurons. Brain atrophy was not remarkable in normal aging control SAMR1 mice. In accordance with above morphological changes, SAMP10 mice developed cognitive impairments with advancing age that were demonstrated by poor performance in passive avoidance and conditional avoidance tasks. All of these features of SAMP10 mice were inherited. SAMP10, therefore, is a unique model of age-dependent, inherited cerebral atrophy with cognitive dysfunction.

Increased mitochondrial DNA deletion in the brain of SAMP8, a mouse model for spontaneous oxidative stress brain

Oxidative stress is considered to be closely correlated with degenerative brain abnormalities. In this study, the plausibility of a SAMP8 strain mouse showing memory deterioration and short life span as an oxidative stress brain model was evaluated. Mitochondrial DNA deletions were detected using polymerase chain reaction (PCR) as cumulative spontaneous oxidative stress. In the 4–8-week-old SAMP8 brain, multiple mitochondrial DNA (mtDNA) deletions were already found and the contents were significantly higher than those of SAMR1 or ddY controls. Enzyme activity studies indicated that electron transport was disturbed at the lower site of the chain and the electronegativity of the upper site might be increased, a result of radical production and therefore oxidative stress.

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.

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.

Alterations in acetylcholine, NMDA, benzodiazepine receptors and protein kinase C in the brain of the senescence-accelerated mouse: an animal model useful for studies on cognitive enhancers

The senescence-accelerated mouse (SAMP8) is a useful murine model of accelerated aging and learning deficiency. We examined bindings of [3H]pirenzepine, [3H]dizocilpine (MK-801), [3H]flunitrazepam, [3H]8-hydroxy-2-(di-n-propylamino)-tetralin (8-OHDPAT) and [3H]phorbol 12,13-dibutylate (PDBu) in SAMP8 brains, and compared them to those of SAMR1 (control). In the hippocampus of SAMP8 at 12 months, bindings of [3H]pirenzepine, [3H]MK-801, [3H]flunitrazepam, [3H]8-OH-DPAT and [3H]PDBu were significantly lower than those in SAMR1. In the cerebral cortex, bindings of [3H]pirenzepine, [3H]flunitrazepam and [3H]8-OH-DPAT were higher to SAMP8 than to SAMR1 at 12 months. [3H]PDBu binding was decreased in both the fractions of the membrane and cytosol in the hippocampus of SAMP8. The neurochemical findings presented here support behavioral and pharmacological findings that SAMP8 is a useful model of learning dysfunction and anxiety-deficiency. The usefulness of SAMP8 in studies on cognitive enhancers is also discussed.

Increased Expression of Cathepsins E and D in Reactive Microglial Cells Associated with Spongiform Degeneration in the Brain Stem of Senescence-Accelerated Mouse

Senescence-accelerated mouse (SAM) P8 and P10 exhibit a spongy degeneration, especially in the brain stem, and a brain atrophy mainly in the frontal portion of the cerebral cortex, respectively, with advancing age. In an attempt to clarify the role of two distinct intracellular aspartic proteinases, cathepsins E (CE) and D (CD), in these age-related pathological changes, accumulation and localization of these enzymes were investigated in the brain stem and the cerebral cortex of SAMP8 and P10 and in the senescence-resistant control SAMR1 with four different age groups (1 week and 2, 6, and 12 months). In the brain stem of SAMP8, a marked spongy degeneration was observed at more than 2 months of age. The same degree of spongy degeneration was also observed in the brain stem of age-matched SAMP10 but not SAMR1. The nonlysosomal enzyme CE was barely detectable in the brain stem of all three strains at 1 week of age, but it was markedly accumulated in the brain stem of SAMP8 and P10 at 2 months of age. The lysosomal enzyme CD was found in relatively high concentration in the brain stem of all three strains at 1 week of age. At 2 months of age, CD contents were significantly increased in the brain stem of SAMP8 and P10 compared with those of age-matched SAMR1. At the light-microscopic level, increased immunoreactivities for CE in the brain stem of 2-month-old SAMP8 and P10 were found in reactive microglial cells clustered at the spongy areas but not in microglial cells with resting or ramified morphology and astrocytes. The increased immunoreactivity for CD was observed mainly in reactive astrocytes and partially in reactive microglial cells. Immunoblotting analyses revealed that CE in the brain stem of 2-month-old SAMP10 consisted of only the mature form of 42 kDa, whereas CD in this tissue is composed of mainly the mature form of 44 kDa and partially its degradation products. On the other hand, there was a marked brain atrophy mainly in the frontal portion of the cerebral cortex of 6-month-old SAMP10 but not in age-matched SAMP8 or SAMR1. Although CE was not detectable even in the atrophied cortical area of SAMP10, CD contents in the cerebral cortex slightly increased with senescence in all three strains. These results strongly suggest that CE and CD are upregulated in reactive glial cells and are closely linked with the progression of the spongiform degeneration in the brain stem of SAMP8 and P10, but not in the atrophy developed in the cerebral cortex of SAMP10.

Expression of neurotrophin genes in the brain of senescence-accelerated mouse (SAM) during postnatal development

We compared the expression patterns of neurotrophin genes in the brain of senescence-accelerated mouse (SAMP8) which shows age-related impairment of learning behavior, with SAMR1 control which shows normal aging. By Northern blot analysis, NT-3 mRNA levels in the cortex were higher in SAMP8 than in SAMR1 mice during development, whereas in the midbrain, hippocampus and forebrain, NT-3 expression levels in SAMP8 were lower than those in SAMR1. At early stages, although NGF mRNA levels in SAMP8 were lower than those in SAMR1, BDNF mRNA levels were almost equivalent in both strains. By in situ hybridization analysis, NT-3 mRNA signals in the CA1 and CA2 regions in SAMP8 were shown to be reduced at early stages. However, BDNF mRNA signals were almost equivalent in both SAMR1 and SAMP8.