G. Rossolini

Neurochemical parameters of the main neurotransmission systems in aging mice

The present work was designed to study the effect of aging on some parameters of the glutamatergic, aminergic and cholinergic neurotransmission, in the main brain areas of mice of the long-surviving BALB/c-nu strain. We have assayed: (1) the density of three ionotropic receptors for excitatory aminoacids (EAA) which selectively bind kainic acid (KA), N-methyl-D-aspartate (NMDA) and 2-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA); (2) the content of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) and the levels of the DA metabolite dihydrophenylacetic acid (DOPAC) and the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA); (3) the level of the choline acetyltransferase (ChAT), the enzyme catalyzing the synthesis of acetylcholine. The parameters were measured in animals at the age of 6, 12, 18 and 24 months; the brain zones under test were the frontal cortex (FC), the corpus striatum (STR), the hippocampus (HIP), the medio-dorsal cortex (DC) and the cerebellum (CER). Significant age-related variations for the density of KA-type and NMDA-type receptors were found in STR and a decrease of the NMDA parameter was found in DC. Neither the monoamine and metabolite contents nor the ChAT levels showed any significant variation in all the tested areas. These findings suggest that an unbalance among different neurotransmission activities could take place with normal aging in rodents: it could be involved in the onset of the motor deficit which occurs in the elderly of these and other mammals.

Mathematical modeling of the aging processes and the mechanisms of mortality: paramount role of heterogeneity.

Main problems of modeling the link between aging processes and mechanisms of mortality are addressed. Various applications of Gompertzs law, which allowed to formulate some fruitful hypotheses on the field, are reviewed. Some pitfalls occurring in its applications are also discussed using a model built on purpose to overcome these difficulties. The role played by heterogeneity emerges as the common cause of some relevant failure in using Gompertzs law and the necessary key ingredient of any model aimed to interpret the link between aging and mortality correctly. Though a number of problems are related to inter-individual variability, the search for their solution can lead to an intriguing approach to the study of aging and mortality. Living beings can be considered as complex systems and their age-related changes can be described at the light of complex system theory.

Influence of L‐Deprenyl Treatment on Mouse Survival Kinetics

The study of the mechanisms of aging received an important momentum from the use of animal models whose life span can be modified by definite controlled interventions. These models present, however, their limits when the interpretation of the results is attempted. At present, in fact, there is no agreement about how to measure the aging rate of a population or the biological age of an individual.’ Even when the findings seem clear-cut as happens in caloric restricted rats, caution is necessary in extrapolating results to animals living in unrestricted conditions. Despite the limitation that any model may have, manipulations able to prolong life span, and maximal life span in particular, remain among the most powerful tools to gain insights into basic aging processes. Thus, any new way of extending life is welcome, as from a multifaceted view a more complete and understandable picture can stem. In this framework, the observations of some authors on the effects of the monoamine oxidase inhibitor L-deprenyl on aged animals sound very interesting.24 It has been observed that this drug can prolong the life span of treated rats and improve their sexual activity at the same time.5*6 Interestingly, the treatment was effective when started at the end of the second year of life?,’ It is also worth stressing that L-deprenyl can be considered a safe drug, thus very useful in long-term experiments.“.6 In addition to the interest due to these characteristics, our attention was drawn by the possible relationships of its mechanism of action with that at the basis of our previous findings in old mice: age-related alterations of the adrenergic system in different tissues of aging animals.a*l These changes were demonstrated to be not definitive, being corrected by endocrine manipulation exerted just a little before two years of age.I2-l4 Since our previous experimental work on aging was done on mice, first of all a survival experiment was planned with the strain of mice of our own laboratory. The drug was administered to 22-month-old mice, as one of the most interesting characteristic to verify was the efficacy of a treatment starting late in life.

Biomarkers of Aging and Survival Kinetics

The search for biomarkers of aging has been the focus of aging research for many years. Nevertheless, the need for a biomarker, and even the possibility of achieving the goal of finding it, have been questioned by some authors,l-’ arguing that the approaches to the problem are often incorrect or useless. Unfortunately, concerning the impact of several studies on the search for biomarkers, we must admit that part of the experimental work is no more useful than asking people their chronological age. Despite these considerations, the subject is so important that we should continue in this field of gerontologic r e ~ e a r c h . ~ A good biomarker of aging will help us to unveil the determinants of aging, to standardize the studies in gerontology, to determine the individual biological age, and to monitor the influence of various interventions such as dietary restriction. The search for biomarkers, however, certainly claims improvements of methodological aspects, and key questions have been excellently addressed by various In the present paper we focus attention on some aspects of experimental findings that deserve more consideration than they have at present-for instance, the changing distribution of biological parameters in a heterogeneous population. We shall show how the lack of consideration of this aspect can lead to misinterpretation of experimental findings, and to kinetics of putative aging biomarkers quantitatively and qualitatively different from what is expected on a purely biological basis. In doing so we shall make use of some results obtained in developing a mathematical model of survival kinetics.

Aging Reversibility: from Thymus Graft to Vegetable Extract Treatment – Application to Cure an Age-associated Pathology

Neonatal thymus graft and thymus calf extract (TME) in vivo treatment exert similar corrective actions on different mouse age-related alterations. The aim of the present paper is to investigate whether a vegetal extract, wheat sprout extract (WESPRE), could mimic the thymus action on recovering age-related alterations and if this extract can cure an age-associated pathology, the cataract in dogs. Present experiments were carried out by using WESPRE and TME in vivo in old mice to check their ability to recover the altered DNA synthesis in hepatocyte primary cultures. Old mice treated with WESPRE and TME showed a recovery of hepatocyte DNA synthesis levels when compared with the old untreated ones. The increase of DNA and protein contents observed in aged animals is reduced by WESPRE treatments to levels observed in young mice hepatocytes. We measured also WESPRE phosphorylation activity by endogenous kinase: it was from 10 to 40 times higher with respect to wheat seeds. Old dogs were orally treated for a month and the lens opacity analysed before and after the treatment. Results showed a reduction from 25 to 40% of lens opacity. The efficacy of wheat sprouts in the recovery of age-related alterations and in treating age-associated pathologies could be due to the contemporary presence of small regulatory acid peptides, a remarkable level of highly energetic phosphoric radicals and antioxidant molecules, peculiarities that may be, to some extent, related to the aging process regulation.

Modelling the Link between Aging Rate and Mortality Rate

A problem commonly found in gerontological studies is that of comparing different survival curves in order to get information about the influence of various treatments on aging rate. The first difficulty arises in the very analysis of the differences eventually observed among the curves. Once this step is adequately performed, one has to face the difficulty of interpreting the differences between the survival curves. It is clear from data in the literature that both problems are frequently met with and are far from being solved. Controversies about the interpretation of data on life extension experiments such as dietary restriction and antioxidant treatment are striking examples of the present state of the art. In the present paper these two gerontologically relevant issues are addressed and a new approach to a solution is presented, using a recently proposed mathematical model of survival kinetics. I

Neuroendocrine thymus and β-adrenergic responsiveness in aging mice

Summary It has previously been shown that thymus exerts a regulatory influence on the β-adrenergic system, controlling, in particular, DNA synthesis in submandibular glands following injection with isoproterenol (IPR). A decreased peak of response found in old mice can be corrected by grafting a neonatal thymus into old animals. In order to clear whether its restoring action needs mutual interrelationships with other control systems or, alternatively, whether even some thymic factor can be effective, the IPR response mentioned above was also assayed in old animals treated with a thymic extract (TME). Among thenumerous thymic factors, this extract was chosen due to the effect that it was prepared on the basis of non-immunological tests and had already been shown to be effective in correcting some alterations observed in old rats. Results show that TME is capable of partially restoring the impaired response found in old mice. The location of the peak of thymidine incorporation, however, is shifted towards the right with respect the peak time observed in young, old and thymus-grafted old mice. Without additional studies, it cannot be decided whether the shift and the only partial recovery is due to the particular dose and duration of the treatment or represents a weaker action of the extract with respect to that of thymic graft.

Excitatory amino acid receptors in the prefrontal cortex of aging mice

The zones of the prefrontal cortex of Balb/c mice were tested for age-related changes of the ionotropic excitatory amino acid receptors density, together with zones of the dorsal cortex. Kainate, N-methyl-D-aspartate, and amino-3-hydroxy-5-methyloxazole-4-propionate sites were measured by slice receptor binding techniques in cortical zones from animals at the age of 6, 12, 18, and 24 months. An increase of the N-methyl-D-aspartate sites was detected in the medial prefrontal zone of mid-aged animals and was followed by a decrease at old age; a decrease of the N-methyl-D-aspartate and kainate sites was found for the medial dorsal (cingulate) cortex at old age. The age-related changes of receptor densities in the different cortical areas seem unrelated in origin. The sites decrease in the cingulate cortex could affect the transfer of the prefrontal cortex activity toward limbic structures.

Functional interrelationships in aging processes: alterations and reversibility.

The problem of assessing the relevance of the reversibility of age-related functional alterations for aging studies has been presented. Transduction mechanisms of adrenergic stimulation have been chosen as the target of age-related changes and thymus as the effector of some corrective interventions performed at advanced age. Both alterations of adrenoceptor characteristics and their reversibility have been reviewed. beta-adrenoceptors have been studied in organs bearing only one subtype of receptors or both, revealing an age-related decrease in density only in the beta1-subtype. It has been shown that a similar age-related decrease is present in alpha1-adrenoceptor density. Such alterations are corrected by grafting a neonatal thymus into old mice. On the contrary, thymus fails to correct the alteration of T4-induced upregulation of beta-adrenoceptors indicating some limits to its corrective effect when the net of functional interrelationships becomes relatively complex. Both failures and successes of thymic grafts and thymic extracts in reversing age-related changes are discussed taking into account the effects induced on the life span of the animals. Different unsolved problems stemming from the previous considerations are also presented. Among them the controversial question about linearity and non-linearity of biological parameters presumed to be good indices of aging is discussed, with the aid of a simple model as a schematic example.

The human lymphocyte as a model of β-adrenoceptor reculation in aging and disease

Summary Extensive experimental evidence suggests that human lymphocytes may model the behavior of other tissues as far as β-adrenoceptor characteristics are concerned. In fact, although lymphocytes bear only β2-adrenoceptor subtype, they may mirror other tissues in various physiological and pathological conditions. In the present paper examples are given demonstrating receptor regulations after drug or surgical stimulus. Age-related changes have also been taken into account. Treatment with β1-selective β-blockers without or with intrinsic sympathomimetic activity induces, respectively, up- or down-regulation of β-adrenoceptors of lymphocytes in agreement with other tissues, as suggested by clinical findings. Data on the influence of thyroidectomy are also in agreement with clinical observations and animal experimental findings on other tissues. Preliminary results on old subjects also suggest a possible role of the human lymphocyte in modelling other tissues or organs in relation to aging processes. The clinical application could be of paramount importance due to the impossibility to directly monitor the receptor status in most of human tissues.