Neuropathological studies on strains of senescence-accelerated mice (SAM) with age-related deficits in learning and memory.

In a series of inbred Senescence-Accelerated mice (SAM) strains, accelerated-senescence prone SAMP substrains show early onset and rapid advancement of senescence. SAMP8 and SAMP10, in particular, exhibit a significant age-related deterioration in memory and learning for passive and active avoidance tasks with, respectively, a low and high incidence of systemic senile amyloidosis. In the brains of both SAMP8 and SAMP10 strains, we have found numerous morphological alterations. Here we review the changes seen in both neuronal or glial components in SAMP8/P10 brains. They may serve as markers of the neuronal degeneration leading to the deficits in learning and memory.

Neurochemical and immunocytochemical studies of catecholamine system in the brindled mouse.

The distribution of immunoreactive catecholamine neurons and fibers was investigated in brindled mottled mouse, a murine model of Kinky hair syndrome (KHS), using antisera against tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH). In all mice, including normal littermate controls, a transient increase of TH-immunoreactive neurons (TH-IN) was observed in the cerebral cortex during the second postnatal week. The numbers of TH-IN were more pronounced in hemizygous brindled males (MObr/y). In addition, TH-IN appeared and rapidly increased in number in the striatum of MObr/y after postnatal day 11 (P11). Striatal TH-IN were rarely detected in controls. After cupric chloride (CuCl2) treatment, TH-IN in the striatum of some of the MObr/y mice became less conspicuous. In the substantia nigra and ventral tegmental area where TH-IN are normally present, no differences either in the immunostaining of TH-IN or the pattern of TH immunoreactive fibers were detected between MObr/y and controls. In MObr/y, a superficial plexus of DBH immunoreactive fibers was more pronounced than in controls but there were no DBH immunoreactive neurons in the cerebral cortex or striatum in any of the mice examined. Neurochemical analysis revealed a marked decrease in norepinephrine levels and increase of serotonin and its metabolites in the brain in MObr/y. Together, these data suggest that the unusual expression of TH-IN in MObr/y represents perturbations of normal development of catecholamine neurons in this copper deficient mutant mouse.

The female brindled mouse as a model of Menkes' disease: the relationship of fur pattern to behavioral and neurochemical abnormalities.

The brindled mottled mutant mouse, a model of Menkes' disease, has alterations in copper homeostasis which cause, among other sequelae, neuronal degeneration in selected areas of brain. This work examined the neurochemical changes at postnatal days (PND) 15, 30 and 60 in females heterozygous for the sex-linked brindled mutation. These data were compared to behavioral alterations and to fur coat color at these same time points. The brindled heterozygotic females had lower concentrations of norepinephrine (NE) in the cingulate cortex, and higher levels of dopamine or dopamine metabolites in the cingulate cortex, thalamus and hypothalamus across all ages, although the difference was greatest at PND 15. The brindled females were much less active than their normal littermates at PND 15, but the differences were no longer evident at PND 30 and 60. Mottling of the fur is believed to result from low tyrosinase activity caused by abnormalities in copper metabolism. The fur pattern and behavior of the brindled mice were highly correlated with NE levels in the cingulate cortex and thalamus. These data show that female brindled mice have neurochemical abnormalities similar to (if less severe than) the male hemizygotes, that these abnormalities are regionally specific, are most apparent prior to 30 days of age, and are linked to behavioral deficits. These data also show that the extent of such deficits can be predicted by a quantitative analysis of the fur pattern of these females.

Isolation and morphologic characterization in vitro of Schwann cells of the twitcher mouse.

Schwann cells were isolated and cultured from the twitcher mouse, an authentic model of human globoid cell leukodystrophy. We observed some difference in morphology and initial cell growth between the cells from suckling and adult mice. Initial growth was slower in homozygous and heterozygous twitcher (twi/twi; twi/+) cells than in normal cells (+/+) when cells were cultured from suckling mice. On the other hand, cell growth was initially accelerated in cells from adult twi/twi mice compared with adult twi/+ or +/+ animals. The yield of Schwann cells was much less from adults. In the cells from adult twi/twi, the perikaryon was swollen, and typical inclusions were easily recognized ultrastructurally, in particular after 14 days in vitro. However, only a few globoid cell leukodystrophy inclusions were detected in the cells from suckling twi/twi mice even after 28 days in vitro. The results indicate that Schwann cell pathology can be studied in twi/twi using an in vitro system and that twi/twi Schwann cells from suckling and adult mice have some differences in morphology as well as in the degree of initial growth.

Spontaneous spongy degeneration of the brain stem in SAM-P/8 mice, a newly developed memory-deficient strain.

A spontaneous spongy degeneration of the brain stem and spinal cord was discovered in a murine model of accelerated senescence (SAM), cared for under both conventional (SAM-P/8) and specific pathogen-free (SAM-P/8/Ta) conditions. SAM-P/8 and SAM-P/8/Ta showed no clinical neurological abnormalities, yet there was a deterioration in learning and memory abilities. Light microscopic examination revealed a spongy degeneration in the brain stem and spinal cord, in the reticular formation, and proliferation of hypertrophic astrocytes in the spongy area. The spongiform degeneration progressed with advancing age from four to eight months, after which the entire brain was involved. Astrocytosis increased with advancing degeneration. Ultrastructurally, mild dendritic swelling occurred at one month of age. At two months of age, moderate postsynaptic swelling and a widening of intracellular membrane structure were observed, and at age five months there were large vacuoles circumscribed by membranous lamellae, identifiable as myelin. Vacuoles in SAM-P/8 proved to be swollen neuronal processes and oligodendroglial processes. These SAM-P/8 and SAM-P/8/Ta strains of mice are new memory-deficient strains with spontaneous spongy degeneration associated with aging.

Chronic food restriction modulates the advance of senescence in the senescence accelerated mouse (SAM).

The effects of chronic food restriction on grading scores of senescence, deposition of senile amyloid (ASSAM), mean life span and 10th decile were investigated by using animal models for accelerated senescence (SAM-P/1) and for normal aging (SAM-R/1). The experimental groups consisted of control (ad libitum fed), 80% (fed 80% of control intake), and 60% (fed 60% of control intake) groups. The grading score of SAM-P/1 mice was significantly improved in the 60% group, but not in the 80% group, compared to the control group. The grading score of SAM-R/1 mice, however, was significantly less than that in the control group in both the 60 and 80% groups. In SAM-P/1 mice liver, skin and testis, the severity of senile amyloid deposition was significantly less with 40% food restriction (60% group) than in the control group. A restriction of 20% (80% group) had no influence on amyloid deposition. A definite tendency to prolong mean life span (24.3%) and 10th decile (65.9%, mean life span of the last 10th of survivors of a group) was observed in the 60% group of SAM-P/1 mice, but the changes were not statistically significant. In the 80% group of SAM-P/1 mice and also in either restriction group of SAM-R/1 mice, however, such a tendency was not evident. These results indicate that 40% food restriction modulates the advance of senescence in these mice.

Grading score system: a method for evaluation of the degree of senescence in senescence accelerated mouse (SAM).

For evaluation of the degree of senescence in SAM-P, accelerated senescence prone mouse, formerly called SAM or prone series or P-series, consisting of SAM-P/1, SAM-P/2, SAM-P/3 and SAM-P/4 corresponding to P-1, P-2, P-3 and P-4 series, respectively, in the previous reports, and in SAM-R, accelerated senescence resistant mouse, formerly called resistant series or R-series, consisting of SAM-R/1, SAM-R/2 and SAM-R/3 corresponding to R-1, R-2 and R-3 series, respectively, in the previous reports, the grading score system was adopted. The items to be examined in this system include 11 categories selected from the clinical signs and gross lesions considered to be associated with the aging process. The degree of the senescence in each category was graded from 0 to 4 according to the detailed criteria devised in our laboratory. After 8 months of age each mouse was examined every 4 months, and some of the mice were examined after 2 months of age. In almost all categories, the grading score and incidence began to increase from 4 or 6 months of age and continued to increase with advancing age in both SAM-P and SAM-R. The increase, however, was more marked in SAM-P than in SAM-R. The slow but steady increase in the SAM-R levelled out at 24 months of age and was comparable to that at 12 months of age in SAM-P. In both SAM-P/1 at 8 months of age and SAM-R/2 at 12 months of age, there was a significant reverse correlation between total score of this grading score system and length of residual life after examination. Systematic and extensive studies using the grading score system showed that if the validity of the system is, based on "irreversibility" and "universality" of the changes in each category with advancing age, most categories are valid for evaluation of the degree of senescence. This grading score system is a unique, useful and convenient method for evaluation of the degree of senescence in mice.

Cataract and other ophthalmic lesions in senescence accelerated mouse (SAM). Morphology and incidence of senescence associated ophthalmic changes in mice.

In a murine model of accelerated senescence (SAM), grading score and incidence in cataract, periophthalmic lesions, opacity and ulcer of the cornea were determined in mice from 4 to 24 months of age. From 4 to 6 months of age, incidence and grading score of these four categories began to increase in both the accelerated senescence prone (SAM) and resistant series with normal aging, and these increases continued with aging. As compared with the resistant series, there was a higher incidence and grading score of the four categories and a higher rate of increase in the prone series. The prone 3 series in particular showed a much higher incidence and grading score on cataract, the rate being 27.5% and 70.6% at 12 and 16 months, respectively. Histologically, the cataract was classified into two types. In one, degeneration of lens fibers, disintegration of lens cortex, and at an advanced stage, liquefaction of the lens cortex and proliferation of the anterior lens epithelial cells occurred. In the other type, lens fibers lost their distinct shapes and a homogenous mass formed at the anterior and posterior superficial cortex. The anterior lens epithelial cells had shrunk. There was an opacity and ulcer of the cornea with keratitis and the corneal epithelium was lost in case of the latter. Periophthalmic lesions included catarrhal changes of the skin of the eyelids and face and blepharitis. There were no lesions specific to each of the prone and resistant series. Thus, SAM should prove to be a suitable murine model for investigation of age-related ophthalmic lesions, including cataract in humans.

Spontaneous age-associated amyloidosis in senescence-accelerated mouse (SAM).

Morphological studies on spontaneous systemic amyloidosis were conducted on 222 senescence-accelerated mice (SAM) (P) and on 150 mice in the senescence-resistant series (R). Among the pathologic findings, amyloidosis showed the highest incidence in both SAM (79.7%) and R (32.7%). Although an extensive deposition of amyloid was evident in some aged mice in the R series, a more severe amyloidosis occurred with a higher incidence in the P series. There was a statistical significance between the incidence of amyloidosis and age, in both the P and R series. There were no differences in organ distribution and mode of amyloid deposition between the P and R series or between the sexes. In about 60% of the amyloid-positive cases in the 28 killed SAM and 7 mice in the R series, there were no signs of inflammation or neoplasm. The morphological features in SAM more closely resembled those seen in cases of murine spontaneous senile amyloidosis than the features seen in cases of experimentally induced amyloidosis. This model is expected to be a valuable tool with which to assess the relationship between amyloid deposition and the aging process or senescence, perhaps even cases of human senile amyloidosis.

A new murine model of accelerated senescence.

Five senescence-prone series of mice (P-1, P-2, P-3, P-4 and P-5) and three senescence-resistant series (R-1, R-2 and R-3) were obtained by continuous sister-brother breeding from five original litters of AKR mice with severe deterioration, and the three original litters of AKR mice with normal aging, respectively. A grading score system was adopted to evaluate the degree of senescence of these mice and a steady and irreversible increase in this grading score was seen with advancing age in both the R and P series. The high grading score in the P series was due to an earlier onset of loss of passivity and reactivity, loss of skin glossiness and increased coarseness, hair loss, periophthalmic lesions, increased lordokyphosis of the spine and a more marked increase in their severity with advancing age as compared to the R series. Among the P series, P-2 showed a 100% incidence of systemic amyloidosis after 6 months of age and P-3 a 70% incidence of cataract over 16 months of age. The life span in the P series was shortened by about 26% of that of the R series. In view of the evidence obtained from the survivors, the growth rate and Gompertz function, the aging pattern in the P series was considered to be an acceleration of senescence. The P series has been named "SAM" ("Senescence Accelerated Mouse").