Aging and the passage of L-tyrosine, L-DOPA, and inulin into mouse brain slices in vitro

Dopamine, acetylcholine, and glutamate interactions in aging. Behavioral and neurochemical correlates

Aging, hypoxia, and thiamin deficiency diminish motor performance. Similar alterations of ACh, DA, and glutamate metabolism accompany hypoxia, thiamin deficiency, and aging. Both aging and hypoxia reduce ACh release and stimulate DA and glutamate release. Presynaptic enhancement of DA and glutamate release may be important in the production of cell damage that may contribute, in part, to age-related deficits in motor as well as cognitive function. The decline in ACh release may be important in the production of the cognitive deficits. An understanding of the interactions of neurotransmitters in hypoxia and thiamin deficiency aids our understanding of normal aging and increases the possibility of developing better treatments for the multiple neurotransmitter deficiencies that accompany many metabolic, age-related, and chronic degenerative disorders.

Effect of age on behavioral and enzymatic changes during thiamin deficiency

Open field behavior and whole brain enzymatic activities were determined during thiamin deficiency in two strains of young, as well as in aged mice. In young CD-1 mice, thiamin deficiency reduced total distance traveled and vertical movements after 7 days and the decline was more than 50% by day 9. The behavioral deficit was highly correlated to decreases in 2-oxoglutarate dehydrogenase activity (KGDH). The open field behavior of Balb/c mice was about 40% less than in CD-1 mice and responded in a qualitatively different manner to thiamin deficiency. The activity of the Balb/c mice increased and then decreased with thiamin deficiency. The activity of 3 month old mice peaked on day 6 (126% of initial score), whereas 10 and 30 month mice showed a much greater increase (about 175% of initial scores), but on day 7. Although the activity of the thiamin dependent enzyme transketolase (TK) was affected similarly at all ages, the activity of KGDH in the aged brain was more sensitive to thiamin deficiency than in the young; KGDH activity declined 41%, 57% or 74% at 3, 10, or 30 months, respectively. Thus, the current mouse model is an attractive one to study the interaction of thiamin deficiency with aging.

Influence of aging on catecholamine levels, accumulation, and release in F-344 rats

Neuronal function in selected brain areas has been evaluated in Fischer 344 rats aged 2-4 months, 11-14 months and 21-26 months. In vitro release of 3H-norepinephrine from hypothalamus and occipital cortex and 3H-dopamine from striatum has been evaluated using potassium, amphetamine, and field-stimulation. In vitro uptake of 3H-catecholamines has been evaluated in the same tissues. Catecholamine levels were measured in six brain areas: hypothalamus, striatum, cortex, cerebellum, brainstem and midbrain. Significant age-related decreases of NE levels, uptake, and release to high frequency stimulation were seen in the hypothalamus. The decreases in 3H-NE uptake and NE levels in the hypothalamus were apparent at 12 months, whereas the decrease in 3H-NE release after high frequency stimulation was seen in the senile rats.

Selective alteration of mouse brain neurotransmitter release with age

The release of acetylcholine (ACh), glutamate (GLU) and dopamine (DA) from various brain regions was investigated in young (3 month) and old (30 month) Balb/c mice. Aging increased the basal release of GLU (77%) and DA (29%) in striatum and GLU in hippocampus (94%); the concentrations of these neurotransmitters in the media after K+ stimulation were unaltered by aging. Although the basal release of ACh was not altered by age, K+-stimulated ACh release was reduced in striatum. The age-related increases in basal GLU and DA release may be important in the pathophysiology of cell death during aging.

Age-related decrease in apomorphine modulation of acetylcholine release from rat striatal slices

Release of [3H]acetylcholine ( [3H]ACh) was assessed in striatal slices from mature, middle-aged and senescent Wistar rats 8, 12 and 24 months of age, respectively. There was an age-related decline in basal release of [3H]ACh as a function of age which was correlated with a decline in accumulation of [3H]ACh. However, the most striking finding was the failure of apomorphine to inhibit KCl-induced [3H]ACh release in the senescent (24 months) animals. Striatal dopaminergic receptor losses in senescence apparently produce several subsequent changes in striatal function which ultimately result in the decline of motor-behavioral function.

The microenvironment of the spinal ganglion neuron in the rat during aging

The environment and particularly the glial sheath of the spinal ganglion neurons was systematically studied by light and electron microscopy in the young and senescent rat. Experiments using radioactive tracers tested the consequences of the functional perturbations associated with structural impairments. The results suggested the possibility that the glial sheath and the neuron aged differently. Whereas the glial sheath maintained its functional capacity relatively intact, neuronal performance was markedly and more rapidly impeded. The morphology and volume of the extracellular space were unchanged. Therefore, impairment of the glioneuronal units in the spinal ganglion during aging cannot be assigned to environmental and vascular phenomena.

[3H]Dopamine accumulation and release from striatal slices in young, mature and senescent rats

Examinations of [3H]dopamine ([3H]DA) release following KCl or amphetamine administration in striatal slices from young (7 month), and senescent (24 month) Wistar rats showed no age-related changes. Further, the amount of [3H]DA accumulated in the striatal slices showed no changes with age. Thus, previously reported age-related deficits in motor behavior (i.e. rotational) are not produced by changes in striatal DA accumulation or release.

Biogenic amine-stimulated adenylate cyclase and spiroperidol-binding sites in rabbit brain: evidence for selective loss of receptors with aging

Evidence for selective decreases in biogenic amine receptor function with age in the rabbit has been obtained. Dopamine-stimulated adenylate cyclase activity in the striatum (caudate-putamen) of rabbit brain declined by about 50 percent as rabbits aged from less than 1 to 4 to 5 years of age. Similar decreases in transmitter-stimulated adenylate cyclase activity were found for histamine as well as for dopamine and norepinephrine in hypothalamus, frontal cortex and anterior limbic cortex. Isoproterenol-stimulated activity was also decreased with age in frontal cortex. These changes appeared to represent decreases in maximal response and not alteration in affinity for amine. In contrast, dopamine-stimulated adenylate cyclase of retina and transmitter-independent (basal or Gpp(NH)p-stimulated) activity in each of the regions studied were not altered with age. Dopamine receptors in striatum directly assessed by measurement of [3H]-spiroperidol binding revealed a comparable decrease in the number of binding sites without change in ligand affinity. Preliminary data also indicated decreased spiroperidol binding sites in the cortical regions of older animals. These changes in striatum and cortex were evident in the absence of decreases in either dopamine content or choline acetylase activity, an activity presumed to be present in neurons containing dopamine receptors. It is proposed that selective age-dependent decreases in postsynaptic biogenic amine receptor content occur in the absence of, or independent from, neuronal cell loss, possibly by a mechanism involving receptor desensitization. These changes occur in the animal model in those brain regions which in man are thought to be of importance in the loss of cerebral function that is found with senscence.

Age related changes in the effect of electroconvulsive shock (ECS) on the in vivo hydroxylation of tyrosine and tryptophan in rat brain

A single electroconvulsive shock (ECS) was applied to 40 young (9 months) and 40 old (24 months) male rats. The effect on brain catecholamine synthesis was determined at intervals after ECS by measuring the accumulation of dihydroxyphenylalamine (DOPA) and 5-hydroxytryptophan (5-HTP) in rats pretreated with a central decarboxylase inhibitor (M-hydroxybenzyl hydrazine, NSD 1015). This accumulation permitted an estimation of the in vivo rates of hydroxylation of tyrosine and tryptophan. Control brain DOPA and 5-HTP concentrations were both lower in the older animals. Following ECS there was an increase in brain DOPA concentration (maximal at 60 min after ECS) in both young and old rats, but the increase was much smaller in the older animals. There were no changes in brain 5-HTP at any time after ECS, in either age group. It appears that aging selectively affects the response of the brain dopaminergic neurotransmitter system to stress, and we suggest that this may be a factor in the decreased resistance to stress in older subjects.

Effect of aging on cyclic AMP levels and adenylate cyclase and phosphodiesterase activities in the rat corpus striatum

Cyclic AMP levels and activities of adenylate cyclase and phosphodiesterase in the striatum were measured in 4, 12, 24 and 30 month-old rats. No age-related changes were observed either in cyclic AMP levels or basal adenylate cyclase activity. However, there was an age-related decline in dopamine sensitivity of adenylate cyclase without affecting NaF-induced stimulation. There was also an age-dependent decrease in phosphodiesterase activity at low substrate concentrations (3 X 10(-7) and 3 X 10(-6) M) but not at high substrate concentrations (3 X 10(-5) and 3 X 10(-4) M). These results suggest that the functions of dopaminergic neurons may have been altered by aging.

Ageing and dopamine uptake by subcellular fractions of the C57BL/6J male mouse brain

The uptake of dopamine (DA) by synaptosomes from the hypothalamus and striatum was reduced in healthy ageing mice at DA concentrations below 10(-7) M. Kinectic analysis indicates that ageing increases the Km of high affinity DA uptake processes by about 35%, but does not alter alter Vmax. l-Tyrosine and serotonin uptake at low concentrations was unaltered by ageing in the striatum and hypothalamus; no changes of L-norepinephrine uptake were found in the hypothalamus. We conclude that ageing may selectively affect DA uptake processes by neuronal membranes.