Neuronal degeneration in aging and after experimental injury

Animal models of age-related dementia: neurobehavioral dysfunctions in autoimmune mice

The development of strategies for treatment of Alzheimer's disease and other age-associated dementias is an important goal of research in the neurosciences. It is suggested that advances in understanding of the etiology of those disorders would provide the most obvious avenues to development of preventative treatments. Research findings from both clinical investigations and studies of animal models are presented which suggest a neuroimmunologic component in age-associated dementia. Clinical studies suggest an association between dementia and brain-reactive autoantibodies in subsets of patients with Alzheimer's disease. Studies of mice suggest that: 1) when compared with normal genotypes, mutant mice with accelerated autoimmunity show learning and memory impairments at earlier chronological ages; 2) the learning and memory deficits of autoimmune and normal mice are qualitatively similar; 3) the behavioral deficits of normal aged and autoimmune mice are sensitive to similar pharmacologic interventions. Overall, these findings suggest that intervention strategies targeting the immune system might be useful in the treatment or prevention of aging-associated dementia. Autoimmune mice would be useful as models for the development and testing of such immune-based interventions.

Autoimmunity and age-associated cognitive decline

It is suggested that the immune system may play a role in the etiology of age-associated cognitive decline and/or Alzheimer's disease. The relationship between brain-reactive antibodies (BRA) and age-associated cognitive dysfunction is reviewed and discussed. A parallel relationship between BRA increases with age and decline of avoidance learning capacity is described in mouse models. Transfer of immunity from old to young mice was found to accelerate both age-related formation of brain-reactive antibodies and age-related decline of avoidance learning capacity. Short-lived mouse genotypes with accelerated autoimmunity were found to show accelerated age-related declines in their ability to acquire an avoidance response when compared with nonautoimmune mice. Overall, these findings suggest that the immune system could be an important target for development of intervention strategies aimed at extending the intellectually competent period of life. Mice in which autoimmunity is accelerated may be useful as models for the development of such interventions.

Learning deficits occur in young mice following transfer of immunity from senescent mice

The extent to which immune processes contribute to senescence-related neurological/behavioral impairment was examined using an adoptive transfer procedure. C57BL/6 mice aged 22 to 24 months showed impaired ability for acquisition of an active avoidance response when compared with younger mice aged 3 months. An immunofluorescence assay of the sera of these mice indicated that only sera from the senescent mice reacted with brain antigen. When tested three months following irradiation and receipt of bone marrow/spleen cell suspensions from senescent mice, young mice showed senescence-like serum-brain reactivity and declines in their abilities to acquire learning. Young control mice receiving cell suspensions from age-matched donors showed no evidence of serum-brain reactivity or learning deficits, suggesting that impaired learning was related to acquisition of aged immunity and not a nonspecific effect of the transfer procedure. These findings indicate that immune processes may be involved in the etiology of senescence-related neurological/behavioral dysfunctions.

Immune manipulations and brain-reactive antibody formation in aging mice

Previous studies have demonstrated an increase in brain-reactive antibodies (BRA) in sera of various mammals as a function of age. The present study attempts to obtain a better understanding of the mode of formation of BRA by using various immunologic manipulations in young and old C57BL/6 mice. The mean BRA levels were significantly higher in older mice than in the young ones. Mixtures of bone marrow cells and spleen cells from old donors were able to adoptively transfer high BRA levels in young irradiated mice and this was not altered by pretreatment of the cells with anti-Thy-1.2 or anti-Ig serum plus complement. Transfer of young cells to old irradiated hosts did not lower the high BRA levels in the hosts. However, when the old hosts were also thymectomized and grafted with neonatal thymuses, BRA levels were significantly lowered. The studies tend to indicate that thymic involution or loss of thymic function in aging plays an important role in BRA formation in sera of aged mice.

Effects of controlled dietary restriction on brain-reactive antibodies in sera of aging mice

Previous studies have demonstrated that underfeeding in both premature and young mature animals may extend the life span as well as preserve the functions of the immune system. The effects of caloric restriction for a period of 12 months on different organs as well as the formation of brain-reactive antibodies in young mature mice (3 months) were tested. These animals showed a significantly lower weight of the total body and various organs including the brain, spleen, adrenals and kidneys. The brain weight/body weight ratio, on the other hand, was significantly higher in these mice. Sera in the dietary animals were mostly negative while those of control animals of the same age and sex had high levels. The present study supports the earlier observations that controlled dietary restriction is able to slow down the age-related deterioration of the immune system. The inhibition of brain-reactive antibody formation in these animals might also be related to a delayed onset of autoimmune disorders.

A quantitative study of age-related changes in the vascular architecture of the rat cerebral cortex

A quantitative study of age related changes in the vascular architecture of the rat cerebral cortex is described. A special vessel-filling technique, which allowed the simultaneous fixation of the vasculature, aided the identification of the vessels in histological sections. Vascular parameters, which included the total number of vessel fragments, a blood volume and a vessel wall-surface area index were obtained using a Quantimet 720 shape-analysing computer. In animals aged 13-83 weeks, there was an increase in the above vascular parameters which could mainly be attributed to an increase in the number of vessels with a diameter greater than 8 micrometers. In very old rats, aged 124 weeks, the vascularity of the cerebral cortex was severely reduced. These changes, which are very similar to those reported in the ageing human cerebral cortex, may be explained by either direct or indirect effects on the cerebral vasculature. Possible mechanisms are discussed in relation to similar changes observed in the cerebral vasculature after several different insults.

Brain-reactive antibodies in sera of aging non-human primates

Previous studies in our laboratory demonstrated an age-related increase in the brain-reactive antibodies in sera of aging mice. The present paper deals with the study of brain-reactive antibodies in sera of non-human primates (Macaca nemestrina) of three age groups (4, 10 and 20 years) by an indirect immunofluorescence method. The results indicated a progressive increase in the serum levels of these antibodies with advancing age. Since all three age groups examined demonstrated brain-reactive antibodies in sera, the age of onset of these antibodies could not be determined in these animals. It has been suggested that the formation of these antibodies could be evidence of autoimmune reactions which might play a significant role in neuronal degeneration during aging.

Ultrastructure of 6-aminonicotinamide (6-AN)-induced lesions in the central nervous system of rats. III. Alterations of the spinal gray matter lesion with aging

Following a single i.p. injection of 6-AN (10 mg/kg), the anterior horn cells of 20- and 25-month-old rats increased more in size and recovered slower from chromatolytic changes than those of 3-month-old rats. Neurofilamentous hyperplasia of the perikarya was more prominent in aged rats; proliferated neurofilaments were arranged in thick parallel bundles. In the acute stage, reactive and degenerative changes of glial and mesenchymal elements were more conspicuous in 3-month-old rats; however, they disappeared by day 14 with prominent proliferation of hypertrophic astrocytes. The older rats showed less intensity and slower progression of these changes; sponginess and swelling of the astrocytic cytoplasm were still observed at day 14. Our results suggest that these age-dependent changes in the response to neurotoxins are not only induced on the neuron without mitotic phenomena after birth, but also on neuroglial cells. Furthermore, an alteration or reduction in the support of the neuron augments its intensified and delayed susceptibility to neurotoxins.

Serum immunoglobulins and cognitive status in the elderly: 2. An immunological-behavioral relationship?

In 42 patients with cognitive dysfunction (senile dementia) significant correlations between immunoglobulins and various tests of intelligence were observed. Serum IgG emerged as the single best predictor of behavioural status. There is need for further research in this field.

Aging and the central nervous system

This review of the literature on aging and the central nervous system attempts to cover the basic perameters investigated at both human and infrahuman levels for the better part of the last century. The results have indicated that there is a rather considerable lack of consistency in the data both within the frame of reference of a single species, and with regard to intraspecies comparisons. We have suggested that possible reasons for the contradictory findings would rest upon variability in techniques employed but, perhaps more importantly, on the failure of investigators in this area to standardize terminology. It is suggested that such a standardization might well be one of the more useful things to be accomplished in order to facilitate the interpretation of future work. The literature review first dealt with gross, i.e., macroscopic changes in brain morphology that could correlate with age, and then covered changes at the microscopic level. Finally, a brief review of the literature with regard to the biochemistry of aging was carried out. Implications of the data were noted where appropriate.