Thymus-induced recovery of age-related decrease of brain cortex alpha- and beta-adrenoceptors

Noninvasive neonatal thymus graft into the axillary cavity extends the lifespan of old mice

Neonatal thymus grafts exert a rejuvenating action on various immunological and nonimmunological functions found altered in old mice. Commonly, half of a thymus is grafted under the kidney capsule. The invasiveness of the surgical procedure and the use of limited thymus tissue may explain why precedent survival kinetics remain unaffected. In this trial, we grafted two neonatal thymi into the axillary cavity of old mice, thus reducing the invasiveness of the intervention and increasing the amount of grafted neonatal tissue. Using a Piantanelli parametric model of survivorship, we found a significant change in mortality rate between the two groups (thymus graft and controls).

Alterations of brain insulin receptor characteristics in aging mice

An interesting role of insulin and insulin receptors (InsRs) in the brain is neuromodulation of monoaminergic systems. Since our previous studies showed age-dependent alterations of alpha- and beta-adrenoceptors in mouse brain cortex, the intriguing role of brain InsRs per se and their involvement in adrenergic modulation prompted us to check their eventual changes with aging. Thus, brain InsR characteristics were studied in young (3 months) and old (27 months) Balb/c-nu mice by direct binding with (125)I-insulin. A two-sites model analysis of data shows a statistically significant age-related decrease of receptor density (39%) and k(d) (57%) in the high affinity population. The low affinity receptor subset also shows a decreasing trend of its characteristics; however, differences are not statistically significant and show a high degree of interindividual variability in both groups of mice.

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.

The effects of clonidine premedication on the blood pressure and tachycardiac responses to ephedrine in elderly and young patients during propofol anesthesia

We studied the pressor and tachycardiac responses to ephedrine in elderly and young patients given either clonidine or midazolam during propofol anesthesia. In the first experiment, elderly (>60 yr) and young (20-45 yr) patients were randomly allocated to one of four groups according to age and premedicated regimens (n = 16 each; elderly-clonidine [EC], elderly-midazolam [EM], young-clonidine [YC], and young-midazolam [YM]). Under propofol anesthesia, ephedrine was injected, and hemodynamic measurements were made. In the second experiment, with clonidine premedication, elderly patients (n = 16) were given a reduced dose of propofol (EC-LP) and young patients (n = 16) were given an increased dose of propofol (YC-HP). Ephedrine was injected, and he- modynamic measurements were performed. The in-creases in mean blood pressure and heart rate were larger in the EC group than in the EM, YM, and EC-LP groups (P < 0.05). In the YC-HP group, the pressor response to ephedrine tended to be augmented as compared with the YC group but was not statistically significant. These results suggest that clonidine premedication augmented the pressor and tachycardiac responses to ephedrine, especially in elderly patients during a standard dose of propofol anesthesia, and that clonidine, age, and propofol could be involved in the augmentation of the blood pressure and tachycardiac responses to ephedrine.

IMPLICATIONS

Clonidine premedication augments the pressor and tachycardiac responses to ephedrine in elderly patients during standard or large doses of propofol anesthesia but does not augment during small doses of propofol anesthesia. Clonidine, age, and propofol could be involved in the augmentation of the pressor and tachycardiac responses to ephedrine.

Influence of age on circadian rhythms of adrenoceptors in brain cortex, heart and submandibular glands of BALB/c mice: when circadian studies are not only useful but necessary

In the present paper we study circadian rhythm variation of alpha1-adrenoceptors (alpha(1)ARs) and beta-adrenoceptors (betaARs) characteristics during aging. Experiments have been performed on mice's whole brain cortex, heart and submandibular glands, which have physiologically relevant regulatory functions at different ages. We used 36 young (4 months) and 36 old (26 months) mice; six animals from each group were sacrificed every 4h, starting at 8.00 a.m. Both the alpha(1)ARs and betaARs density in heart and brain and the betaARs of submandibular glands are significantly lower in old mice with respect to the young ones. The difference, however, if the comparison is performed only at a particular time, for example 8.00 a.m., is not always significant. The alpha(1)ARs density in submandibular glands does not show significant difference with aging, but opposite phases are observed. This study demonstrates that in dynamical systems such as receptors, single point analysis is not so suitable for a correct estimate of adrenoceptors density variation between young and old mice.

Long-live euthymic BALB/c-nu mice. I. Survival study suggests body weight as a life span predictor

This paper is the first of a series aimed to show the main physiological and pathological characteristics of male euthymic BALB/c-nu mice, a long-live strain of BALB/c mice bred in our own Institute. In particular, the first two paired papers are respectively devoted to general survival information and disease characteristics, also taking into account very old animals that are of high interest for studies on successful aging. In this paper we report the analysis of survival kinetics, the time course of body weight and the correlation between body weight and time-at-death. The longitudinal study has been performed on 88 male mice, checking individually their body weight and date of death and analyzing survival data by a model built by our own. Survival analysis shows quite higher longevity (median age: about 29 months) in this population when compared with other BALB/c strains. The most relevant finding on body weight is its correlation with longevity until the age of 22 months: thinner subjects live longer and lose weight at a lower rate than their heavier mates. Results have formed the basis on which to plan the cross-sectional experiment to study pathologies and biological parameters at different ages, including a group of mice at very advanced ages (34 months).

Long-live euthymic BALB/c-nu mice. II: spontaneous tumors and other pathologies

This paper is the second of a series aimed to show the main physiological and pathological characteristics of male euthymic BALB/c-nu mice, a long-live strain of BALB/c mice bred in our own Institute. The previous paired paper Piantanelli (Mech. Ageing Dev. (2001)) has been devoted to a survival study up to advanced ages highly interesting for studies on successful aging. In the present paper we report first data of a cross-sectional study on 4,15,22,28 and 34 months-old mice, dealing with tumors and other relevant pathologies. Results have shown that tumors or other pathologies can hardly be detected up to the age of 22 months. At 34 months of age about 40% of mice revealed a variety of neoplasia and other diseases are clearly detectable. These results suggest that a significant increase in longevity could be a factor increasing the risk of tumor development; thus, caution has to be paid in studies on mice utilized for long term carcinogenicity assay, where animals are sacrificed at the age of 18 months, according to the International Program. Finally, animals of the same chronological age have been subdivided in clusters according to their presumptive longevity, estimated taking advantage of the relationship between body weight and age-at-death found in the paired longitudinal study. This subdivision will be helpful in interpreting inter-individual variability of the biological parameters checked in these animals.

Insulin receptors in mouse brain: Reversibility of age-related impairments by a thymic extract

Recently, we have shown that insulin receptors (InsRs) in the brain undergo impairments with aging. Interestingly, age-related alterations of brain InsRs, are not irreparable as thymus grafts are able to recover them. With the present study we verified the possibility that an aqueous extract from calf thymus (TME) can mimic the restoring action of age-related impairments induced by thymus graft. InsR characteristics were assayed in a group of 25 months old BALB/c-nu mice treated with TME: 2μg/g body weight every third day, for total five subcutaneous injections. The last dose was injected the day before animals were killed. Other two groups of young (4 months) and old (25 months) mice received saline solution with the same schedule. A two-sites model analysis of receptor data confirms the age-dependent decrease of InsR number and kd previously observed in the high affinity population. Furthermore, a statistically significant recovery of number impairment is shown in TME-treated animals. On the contrary, the characteristics of the low affinity receptor subset show no statistically significant differences among the three animal models studied. TME induced recovery of the age-related changes found in brain InsRs, together with previously observed regulatory action of the same thymic extract on the adrenergic system, suggest that thymic gland does not necessarily have to mutually interact with other controlling systems for maintaining or recoving homeostasis of the complex neuroendocrine network during development and aging.

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.

Insulin receptors in the brain cortex of aging mice

The aim of the present study was to analyze whether aging also affects central insulin receptors in brain cortex as it does in whole brain of BALB/c-nu mice. Results showed statistically significant decrease of number and increase of affinity of insulin high affinity binding sites in old animals. As a consequence, central insulin actions, among which neuromodulation of monoaminergic system, can result altered during aging.

A role of the thymus and thymosin-alpha1 in brain NGF levels and NGF receptor expression

Using neonatal rats we investigated the role of the thymus and thymosin-alpha1 (T-alpha1) in brain NGF levels, NGF receptor (p75NGFr) expression, as well as the activity of choline acetyl-transferase, a cholinergic enzyme regulated by NGF. It is shown that early postnatal thymectomy causes a decrease in NGF in the hippocampus and cortex and p75NGFr distribution in the basal forebrain cholinergic neurons (FBCN). Intracerebral T-alpha1 injection in thymectomized animals induces a recovery, albeit not complete, of both NGF and p75NGFr. These findings indicate that thymectomy affects both the brain NGF producing and responding cells and that T-alpha1 may be one of the thymic hormones involved in the regulation of cerebral NGF synthesis.

Insulin receptors in mouse brain: age-related modifications are corrected by thymus graft

Recently, we have shown that insulin receptors (InsRs) in the brain undergo impairment with aging, as happens for other receptors such as alpha- and beta-adrenoceptors. Age-related alterations of adrenoceptors, which are modulated by brain InsRs, are not definitive as they can be recovered by a thymus graft. In this study we verified the possibility that the thymus graft can also recover the age-dependent modifications of brain InsRs. InsR characteristics were assayed in a group of 27 months old Balb/c-nu mice grafted with a neonatal thymus, under renal capsule, one month before the animals were killed. Another two groups of young (3 months) and old (27 months) mice were used as controls. A two-sites model analysis of receptor data confirmed the age-dependent decrease of InsR density previously observed in the high affinity population. Furthermore, a statistically significant recovery of this impairment was shown in thymus grafted animals. The low affinity receptor subset also showed some differences among the three animal models; however, they were not statistically significant. Thymus graft induced recovery of the age-related changes found in brain InsRs, together with the similar one observed on the adrenergic system, calls for deeper studies of their interaction and the role they can play on aging processes.

Learning disorders in thymectomized mice: a new screening model for cognitive enhancer

Although the close relationship between the thymus and neuroendocrine system during the aging process has been well documented, influence of the thymus on the cognitive function of the central nervous system remains unknown. Male ddY mice were thymectomized 3-4 weeks after birth. Learning behavior, tested in a step-down test and in a spatial memory task, was significantly impaired in thymectomized mice at 10 months, but not before 5 months, after thymectomy. Reduced immune response was also not obvious before 10 months. These results suggested that thymectomy in young adult life in mice not only impaired the immune response, but also deteriorated the learning and memory ability, and that learning disorders in thymectomized mice could be utilized as a new screening model for cognitive enhancer.

Ageing as upregulation failure

This paper investigates similarities in physiological senescent changes in various mammalian organ systems and relates these to postulated mechanisms of age modulation. It proposes that the observed decline in homeostasis with age is due to an inability of target cells, of neural, endocrine and other forms of control, to upregulate after their downregulation. The well-documented flattening of circadian rhythms with age, particularly the loss of the sustained diurnal hypothermic phase, is described as integral to such change, and maintenance or induction of certain youthful circadian patterns is proposed as a means of restoring homeostasis in senescence and other conditions.

Thymectomy-induced deterioration of learning and memory in mice

Male ddY mice were thymectomized 4 weeks after birth. Learning behaviors, tested in passive and active avoidance performances and in a spatial memory task, were significantly impaired in thymectomized mice at 10 months after thymectomy, in addition to the reduced immune response. Contents of hypothalamic norepinephrine and hypothalamic choline acetyltransferase activity were significantly increased in thymectomized mice. These results suggested that thymectomy at young adult life in mice not only impaired the immune response, but also deteriorated the learning and memory ability.

The role of brain-immune interactions in immunotoxicology

Certain xenobiotics (or the metabolites) can damage immunocompetence by directly interacting with one or more of the cells of the immune system and adversely affecting its function. It has also been proposed that xenobiotics may indirectly affect immune function by affecting other organ systems that will in turn affect immunocompetence. This review surveys evidence that supports the existence of a functional link between the brain and the immune system. In addition, we review data that support the concept that a xenobiotic-induced dysfunction in the neuroendocrine system may be associated with an immune dysfunction as well. Such chemicals do not necessarily interact directly with immunocompetent cells but would instead act to disrupt regulatory brain-immune interactions. This class of indirectly acting immunotoxic xenobiotics would not be detected in the typical in vitro screening assays.