Linomide induces apoptotic death of cortical CD4/CD8 double positive thymocytes and thymic atrophy by a corticosteroid-independent pathway.

Linomide is a synthetic immunomodulator which was shown to protect animals against a wide range of experimental autoimmune diseases. In this study we have investigated the effects of Linomide on the thymus in an effort to elucidate the mechanisms by which this immunomodulator suppresses autoimmune reactivity. Normal or adrenalectomized SJL/J mice were treated orally for 10 days with linomide (80 mg/kg/day). Thymocytes were tested by FACS for the analysis of the CD4 and CD8 markers and TCR expression on their surface. Thymuses from these animals were examined for size and cellularity and immunohistopathologically for the detection of apoptosis and for the expression of the markers CD4 and CD8. A significant reduction in the thymus size and cellularity was observed in mice treated with Linomide, starting from day 3 after treatment, accompanied by an enhanced apoptotic death of cortical thymocytes, which was first noted on day 1 of treatment and peaked on day 3. FACS analysis and immunohistochemistry revealed a significant depletion of the CD4(+)/CD8(+) (double positive) cells with a parallel relative increase of the more mature, medullar, single positive, lymphocytes. These effects on the thymus were not mediated through a corticosteroid-dependent pathway, and were also observed in adrenalectomized and Linomide-treated animals. These observations may be of importance for the clarification of the role of thymus in autoimmunity and the possible ways for immune intervention with immunomodulators like Linomide at this level.

The effects of long-term corticosterone administration on hippocampal morphology and cognitive performance of middle-aged rats.

The main objective of this research was to study the relationship between glucocorticoids, aging and the deterioration of cognitive functions. Towards this end, an attempt was made to develop an animal model which will enable the investigation of such interactions, using subcutaneously implanted sustained-release corticosterone pellets. The goal was to achieve moderately high concentrations of corticosterone in plasma, comparable to the peak basal levels or to those found under mild stress. Middle-aged (12 months old) Fischer-344 rats, used in this study, were divided before the prolonged hormonal treatment into cognitively 'impaired' and 'non-impaired' groups using the Morris water maze. The cognitive impairment, which was induced by the long-term corticosterone administration, was exhibited during acquisition of the 8-arm radial maze only in the 'non-impaired' group. Behavioral scores for drug-treated 'impaired' rats were not statistically different from those of the placebo-treated 'impaired' group. The morphological deterioration in hippocampal areas of the brain was quantified and revealed high correlation with the behavioral data. This animal model may become extremely useful in testing projected prophylactic therapy against the brain damage and cognitive deficits induced by the high corticosteroid-aging combination.

Aging, stress, and cognitive function.

Stress was implied as involved in "enhanced aging," and prolonged administration of corticosterone was claimed to lead to central neuronal lesions. This study describes an animal model that simulates the steroid elevation associated with stress by a continuous slow-release administration of corticosterone, in young (3 months old) and middle-aged (12 months old) Fischer 344 rats. Plasma concentrations of corticosterone were stable throughout the day, with no diurnal variation, within the range associated with mild stress. Corticosterone prolonged treatment resulted in morphological changes mainly in the CA1, CA4, and dentate gyrus areas of the hippocampus. Middle-aged rats showed higher vulnerability to the long-term COR treatment than young ones, even when COR treatment was prolonged in young rats from 63 to 90 days. Middle-aged rats were screened before the corticosterone treatment, using the Morris water maze, and divided between cognitively "impaired" and "nonimpaired" subpopulations. Severe cognitive damage during acquisition of the eight-arm radial maze was shown, after the continuous hormonal treatment, in rats initially defined as "nonimpaired" in the Morris water maze. This animal model might be useful for testing the protective effects of drugs against brain changes and cognitive damage, during either pathological or normal aging.

Morphological hippocampal changes during normal aging and their relation to cognitive deterioration.

Cognitive and memory capacities were assessed in two strains of rats of various age groups prior to histological evaluation of their brains. Male Wistar rats, at the age of 3, 12, 17 and 24 months, were tested using the 8-arm radial maze and male Fischer 344 rats, aged 3, 12 and 16 months, were tested in the Morris water maze. Significant memory impairments were found in both strains already at the age of 12 months in about 50% of the population. Morphological analysis of the brains revealed age-related structural changes in the hippocampal formation starting with the middle-age group. Degenerative CA1 and CA3 pyramidal cells characterized the hippocampus of cognitive-impaired rats, while non-impaired animals exhibited intact hippocampus irrespective of age. This characteristic was supported by quantitative morpho-analysis. The best correlation between the decrease of area or number of cells and working memory impairment was found for CA3 region in both strains. Age-related decline in the density of muscarinic receptors in Wistar rats' brain corresponded with the pattern of cognitive deficit. The results of the present study support the hypothesis which associates hippocampal integrity with normal memory function. It is concluded that chronological age by itself is not an adequate indicator of age-related brain alterations and individual evaluation of performance, based on behavioral scores, is recommended.