Enzymatic studies in senescent rodent brains

Reduction of cerebral cortical [3H]ouabain binding site (Na+,K(+)-ATPase) density in dementia as evaluated in fresh human cerebral cortical biopsies

Na+,K(+)-ATPase density in human cerebral cortex was for the first time studied by vanadate facilitated [3H]ouabain binding to intact samples. Fresh human cerebral cortical biopsies were obtained as a result of diagnostic frontal lobe biopsy from patients with normal pressure hydrocephalus (NPH) syndrome and associated dementia. For control measurements post-mortem samples were obtained from patients without clinically observed dementia. [3H]ouabain binding kinetics were evaluated: when incubating samples in 1 microM [3H]ouabain binding equilibrium was obtained after 6 h of incubation, non-specific uptake and retention amounted to only 2.3% of total uptake and retention of [3H]ouabain and release of specifically bound [3H]ouabain during washout in the cold occurred only slowly (T1/2 = 37 h). Evaluation of receptor affinity for ouabain was in agreement with a heterogeneous population of [3H]ouabain binding sites. [3H]Ouabain binding was significantly reduced after frozen storage of samples before measurements. Post-mortem degradation of cerebral [3H]ouabain binding sites occurred only slowly (T1/2 = 75 h). No significant variation in [3H]ouabain binding site density was observed between the cerebral lobes with occipital, parietal and temporal values (means +/- S.E.M., n = 5) amounting to 10281 +/- 649, 11267 +/- 1011 and 9263 +/- 615 pmol/g wet wt., respectively. [3H]Ouabain binding measured in frontal cortical samples gave values of (means +/- S.E.M., n = 5) 4274 +/- 1020 and 11397 +/- 976 pmol/g wet wt. delta % = 62; P < 0.05) in patients with dementia and controls, respectively. Human cerebral cortical capacity for active K+ uptake was around 37- and 16-fold greater than in skeletal muscular and myocardial tissue, respectively.

Adenosine triphosphatases of rat cerebral microvessels. Effect of age and diabetes mellitus

To determine the effect of age and diabetes mellitus on the activity of various adenosine triphosphatases (ATPases) of cerebral microvessels, streptozotocin-induced diabetic rats, and aged rats (26 months old) were compared to young control rats (4 months old). The results indicate that diabetic rats have reduced ATPase inhibition by N-ethylmaleimide (NEM), a vacuolar proton (H+)-ATPase inhibitor (98.7 +/- 0.81% vs 78.9 +/- 4.3% of buffer, p < 0.05). Aged rat cerebral microvessels also had reduced NEM sensitive ATPase activity. Sodium-potassium (Na(+)-K(+)-) or magnesium ATPase activity of cerebral microvessels was not altered with diabetes or aging. The changes in cerebral microvessels were distinct from those found in synaptosomal membranes indicating cell specificity of the findings. The results indicate that the age-related and diabetes-related changes in the activity of ATPases in cerebral microvessels are similar but not identical. These changes may contribute to the altered blood-brain barrier functions found in diabetic and aged rats.

Combination treatment with noradrenalin and serotonin reuptake inhibitors in resistant depression

Eight cases of resistant recurrent depression were treated with a combination of nortriptyline and a new serotonin reuptake inhibitor, with or without concurrent lithium therapy. Significant improvement was seen in all patients where other drug regimes and ECT had been ineffective. No adverse reactions occurred in any of our patients, seven of whom were elderly. The combination treatment was more effective than individual therapies alone.

Age-related changes in galanin-immunoreactive cells of the rat medial septal area

Age-related changes in the cholinergic cells have been reported in the rat medial septal area. The neuropeptide galanin is colocalized with acetylcholine in the majority of the medial septal neurons. To assess possible age-related changes in the galanin-containing septal cells, we have examined, with immunohistochemical methods, the distribution pattern, density, and morphological features of galanin-containing cells in the rat medial septal nucleus (MS) and the nucleus of the diagonal band of Broca (DBB) in 1, 3-6, 9-12, 16-18, 24-27, and 28-30 month-old rats. A morphometric computerized analysis was also performed. In addition, the intensity of the immunolabelling was measured by densitometry. Galanin-like immunoreactivity (galanin-LI) was present in both the MS and the DBB. Our results clearly indicate a progressive age-related decrease in the number of galanin-positive cells throughout the MS-DBB complex. Our quantitative study revealed a significant loss of galanin-positive cells in the MS-DBB complex of 16-18 (50.4%), 24-27 (52.3%), and 28-30 (52.4%) month-old rats compared to 3-6 month-old animals. A non-significant reduction (28.6%) in galanin-LI cell number was observed in 3-6 month-old rats compared to 1 month-old animals. The morphometric analysis demonstrated a significant reduction (18%) in the surface of galanin-positive cells remaining in the 28-30 month-old group. Furthermore, a significant decrease in the immunolabelling intensity was consistently observed in animals of 16 month-old and older. To determine whether changes in galanin-positive cells were associated with cholinergic changes, the number of cells stained for acetylcholinesterase (AChE) was estimated in 3-6, 9-12, 16-18, and 24-27 month-old rats. There was a 43% decrease in the number of AChE-positive cells and a 71% loss of galanin-positive cells in 24-27 month-old rats compared to 3-6 month-old. The galanin-cell loss in the medial septal area was therefore associated with a parallel, although smaller, cholinergic septal cell loss.

5'-Nucleotidase activity increases in aging rat brain

The enzyme 5'-nucleotidase is present in glial and neuronal membranes, and catalyzes the formation of adenosine, which in turn can act as a neuromodulator or neurotransmitter. The present study found marked increases in histochemically demonstrated 5'-nucleotidase activity in most regions of rat brain from young adulthood (3-4 months) to middle age (12-18 months), with smaller or no changes between middle and old age (24-32 months). The aging adult cerebellum showed alterations in the histochemical pattern, with declines in the molecular layer and increases in the Purkinje layer. Both myelin and synaptic plasma membrane fractions from forebrain showed increases in enzyme activity. Assays of various other body tissues suggested that the increases are fairly specific to brain, and thus apparently do not represent a ubiquitous cellular mechanism of aging. Changes in brain 5'-nucleotidase activity during aging probably reflect the increasing number and size of glial cells, and perhaps also affect synaptic transmission through regulation of adenosine.

Age-related differences in soman toxicity and in blood and brain regional cholinesterase activity

The toxicity (lethality, acute toxic signs and body weight loss) of the irreversible ChE inhibitor soman was assessed in four groups of male rats differing in age: 30, 60, 120 and 240 days old. Plasma and brain regional ChE activity profiles were also studied in these groups. All measures of the toxicity of soman were found to increase with age. The calculated 24-hr LD50s were 110, 87, 66 and 59 micrograms/kg, IM, for 30-, 60-, 120- and 240-day-old rats, respectively. A significant and positive age-related effect on toxic sign rating scores was observed at one hr following soman injection. Furthermore, during a 14-day postsoman observation period, it was observed that young rats had less initial weight loss and more rapid, sustained recovery of growth than older animals. Survivors from the two oldest age groups did not recover to baseline body weights by the end of the 14-day observation period. Basal level of plasma ChE activity did not change significantly with age, while brain regional ChE showed two distinct age-dependent patterns: a linear decrease in the brainstem, midbrain and cerebellum and an inverted U-shaped change in the cortex, hippocampus and striatum. Our data suggest a relationship between soman toxicity and the aging process, but fails to demonstrate a definite relationship between soman toxicity and basal ChE activity in blood and brain of rats.

The effects of aging on hippocampal and cortical projections of the forebrain cholinergic system

It has been proposed that disruption of cholinergic input to the hippocampus and cortex contributes to the learning and memory deficits associated with aging. The data reviewed here, however, suggest that the oft-stated generalization that normal aging is characterized by disruption of cholinergic input to the hippocampus and cortex is not entirely correct. Instead it appears that age-related changes are not consistently found on measures such as the activity of ChAT or the content of ACh in these regions, basal levels of ACh release in cortex, and the number of cholinergic neurons in the basal forebrain (source of cholinergic input to the hippocampus and cortex). These observations suggest that unlike Alzheimer's disease, normal aging does not reliably produce a degeneration of the cholinergic innervation of the hippocampus and cortex. The responsivity of the cholinergic system, however, is altered during normal aging. ACh synthesis and stimulation-induced release of ACh are diminished in aged animals. Further, the electrophysiological response of postsynaptic neurons to ACh is reduced during aging. Although some regional differences in these age-related changes may be present, the generalization that the functioning of the cholinergic system is impaired during aging is probably accurate. Thus, investigation of these changes in the dynamic properties of cholinergic input to the hippocampus and cortex during aging may provide clarification of the relationship between cholinergic dysfunction and age-related decline in learning and memory and may also provide a more reasonable rationale for treatment approaches.

Absence of age differences in protein synthesis by rat brain, measured with an initiating cell-free system

A cell-free protein synthesis system was derived from brains of young (3 month) and old (greater than 23 month) male Fischer-344 rats in order to examine brain protein synthesis in relation to age. The system was shown to be capable of reinitiating protein synthesis in vitro, and of synthesizing protein from exogenously added mRNA. Optimal ionic conditions for amino acid incorporation were 200 mM potassium ion and 5 mM magnesium ion, and amino acid incorporation depended on addition of ATP, GTP, and an energy-generating system (creatine phosphate and creatine phosphokinase). Amino acid incorporation was sensitive to the initiation inhibitors aurintricarboxylic acid and sodium fluoride. Optimal conditions were independent of the age of the rat from which the brain was taken. There was no statistically significant relation (p greater than 0.05) between capacity of amino acid incorporation and age. The aggregation state of brain polyribosomes also did not differ between young (3 month) and old (30 month) rats. The results suggest that overall brain protein synthesis capacity is age-invariant in the rat.

An altered response in the induction of cell membrane (Na + K)ATPase by thyroid hormone is characteristic of senescence in cultured human fibroblasts

There have been numerous investigations of thyroid function during senescence in humans. However, very little information is available on thyroid hormone action at the cell level during senescence. Therefore, we have investigated thyroid hormone induction of cell membrane (Na + K)ATPase during human senescence using three experimental fibroblast cell culture systems: (1) cells from premature aging syndrome, progeria; (2) aging in vitro; and (3) early passage cells from aged patients. In all cases senescence is associated with a dramatic alteration from the normal dose-dependent thyroid hormone induction of (Na + K)ATPase. Senescent cells depleted of thyroid hormones demonstrated an elevated activity of (Na + K)ATPase, while non-senescing cells exhibit the characteristic basal enzyme activities in the hypothyroid state. These results indicate that human senescence is associated with extreme alterations in thyroid hormone regulation of (Na + K)ATPase; and may suggest a more general change in thyroid hormone action at senescence. These changes may be associated with important alterations in cell metabolism and intracellular ionic environment during senescence.

Neuritic plaque-like structures in the rat cerebellum following prolonged alcohol consumption

Primitive neuritic plaques were observed in the inner third of the molecular layer of the cerebellar cortex of rats following chronic alcohol consumption. Neurites were identified as dystrophic parallel fiber boutons. Amyloid material dispersed among neurites was not clearly recognized, dystrophic some fibrils were frequently seen among them. Astrocytic processes were noted in the periphery of the plaque. Microglial reaction, however, was non-existent. The rarity of these lesions in the rat cerebellum and their probable relation to long periods of alcohol consumption is discussed.

Stability of neuron number in cortical barrels of aging mice

The question of whether age-related neuron loss occurs in the cerebral cortex of rodents, as it apparently does in humans, has not been directly answered by previous studies. The barrel, a discrete morphological and functional unit in rodent somatosensory cortex, is a favorable system in which to address the problem of neuron loss during senescence. The numerical density and absolute number of neurons as well as barrel volume were determined from a computer-assisted three-dimensional reconstruction of thick (100 microns) and semithin (1 micron) sections through a single barrel, C3, from inbred mice (C57Bl/6NNia) at 4, 12, 22, 26, 30, and 33 months of age. The number and density of neuron and glial cells and the volume of the barrel did not change significantly with age. These data indicate that neuron loss is not a universal phenomenon in senescence and that there may be significant species differences in the aging of laboratory rodents and humans.

Lipid peroxides in brain during aging and vitamin E deficiency: possible relations to changes in neurotransmitter indices

Lipid peroxide levels, were found to be significantly higher in brains of 18 month old as compared to 4 month old rats, with particularly large increases occurring in the olfactory bulb, globus pallidus, cerebral cortex and caudate-putamen (CP). Eighteen month old rats fed a vitamin E deficient diet for 9 months before sacrifice had lipid peroxide levels significantly higher than age-matched controls in the cerebral cortex, hippocampus and hypothalamus. Age-related decreases were seen in choline acetyltransferase, acetylcholinesterase and 3H-QNB binding in some but not all brain regions, while GABA transaminase and MAO showed age-related increases. No age-related change was seen in tyrosine hydroxylase in the CP or in 3H-dihydroalprenolol (DHA) or 3H-spiroperidol binding in the cortex. As compared with controls, vitamin E deficient rats showed decreases of 38% in cortical 3H-DHA binding, of 33% in 3H-QNB binding in the CP and of 23% and 12% in choline acetyltransferase in the CP and cerebellum, respectively. There were no completely consistent regional correlations between significant changes in lipid peroxidase levels and any neurotransmitter indices studied except for MAO which was only measured in the caudate-putamen.

Energy-metabolizing enzymes in brain regions of adult and aging rats

The regional enzyme activities of glucose metabolism in the rat brain were investigated. Hexokinase (EC 2.7.1.1) and pyruvate dehydrogenase (EC 1.2.4.1), key enzymes for glucose metabolism, showed no changes in activity in all the regions studied of the aging brain as compared with the adult brain. However, the activity of D-3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) is low throughout the adult brain and, in contrast with hexokinase and pyruvate dehydrogenase, its activity decreases significantly during aging. Other enzymes that showed significant decreases during aging are aldolase (EC 4.1.2.13), lactate dehydrogenase (EC 1.1.1.27), citrate synthase (EC 4.1.3.7), and NAD+-linked isocitrate dehydrogenase (EC 1.1.1.41). The catabolic enzyme in cholinergic metabolism, acetylcholinesterase (EC 3.1.1.7), selected as an example of a non-energy-metabolising enzyme, also showed significant decreases in all regions of the brain in aging, although its highest activity remained in the striatum. These results are discussed with respect to the energy metabolism in various brain regions and their status with aging.

Neurotransmitter enzymes in telencephalon, brain stem and cerebellum during the entire life span of the mouse

Neurochemical analysis of neuronal function was undertaken by measuring the activities of cholinacetyltransferase (CAT), acetylcholinesterase (AChE), and glutamic acid decarboxylase (GAD), in the telencephalon, brain stem and cerebellum of the mouse. Cholinergic activity was first expressed in the 10-day embryonic brain stem, which showed a relatively high CAT activity at birth. Postnatal brain stem development was characterized by a rapid and parallel increase in CAT and AChE. Although AChE peaked at 1 month, CAT activity was no achieved until 1 year. Acetylcholine synthesis was initiated in the 12-day embryonic telencephalon and a steady age-related increase in CAT was maintained until birth. A lag in both CAT and AChE activities was recorded during the first week of postnatal telencephalon development. Cerebellar CAT was low at birth, and increased irregularly to reach a maximum by 1 month. In contrast, postnatal cerebellar AChE activity increased steadily over the same time period. The GABA-ergic neuronal system matured rapidly in each brain region, and was unaffected by aging. Although the brain stem precociously expressed cholinergic activity, it wa the region most susceptible to deterioration during aging. Telencephalon CAT activity was unaffected by aging and in the cerebellum, a significantly reduced level of CAT was only found in truly senescent animals. The decreased cholinergic function during senescence was not due to either increased proteolysis or to alteration in the molecular form of the cholinergic enzymes.

Glutamate metabolism in ageing rat brain

The metabolism of glutamate, taken as an index of the metabolic state of the brain, was studied in brains of 3-, 12- and 30-month-old rats. Following the injection of a mixture of [3H]acetate and d-[2-14C]glucose, the brain levels of glutamate and aspartate were decreased in 30-month-old rats when compared with those of 3-month-old rats. No significant age-related differences were found in glutamine levels. Neither the protein levels nor the incorporation of the radioactivity in brain proteins differed among the three age groups, suggesting that there are no age-related differences in protein synthesis. The incorporation of d-[2-14C]glucose into aspartate and glutamine, expressed as the respective relative specific activities (RSA: specific activity of amino acid/specific activity of glutamate), did not change with age. Since glucose is the precursor of the large glutamate pool in brain, it can be concluded that no age-related changes occur in the metabolism of glutamate in the large compartment. The incorporation of [3H]acetate into aspartate, expressed as the RSA, did not differ among the age groups. The RSA of 3H-labelled glutamine, however, was significantly decreased 10 minutes after injection of the precursor mixture in brains of 30-month-old rats when compared with those of 3-month-rats. This difference had disappeared 20 minutes after injection, suggesting a somewhat delayed metabolism of glutamate in the small compartment, for which acetate is a precursor. These results and all the other parameters measured indicate that no large age-related metabolic changes in rat brain occur.

Effects of age on brain oxidative metabolism in vivo

Non-invasive optical techniques were used to monitor the effects of increasing cerebral energy demand on metabolic capabilities and vascular reactivity in young and aged brain. Low level of electrical stimulation of the cortex, in both young (4--7 months) and aged (24--28 months) rat brain, were accompanied by transient oxidations of NADH and cytochrome oxidase (a,a3) as measured by microfluorometry and reflection spectrophotometry respectively. Stimulation sufficient to produce spreading cortical depression was accompanied by an oxidation of both NADH and cytochrome a,a3 in young brain together with an increase in local blood volume. There was either no change or a slight disoxygenation of hemoglobin. In aged brain, however, spreading depression was associated with an oxidation of NADH and a reduction of cytochrome a,a3 together with an increase in local blood volume and an oxygenation of hemoglobin. The present results indicate that the relationship between microcirculation and the terminal oxidase step of the respiratory chain is altered in aged brain when energy demand is high.

Biochemical changes in the central nervous system with age in the rat

Studies dealing with biochemistry of the central nervous system of rats have been reviewed. Data on the effects of age on enzyme activity and cellular substrates have been summarized in tabular form. In general, it can be concluded that biochemical functions dealing with anabolism decrease whereas those dealing with catabolism increase as aging progresses.