Effects of vinconate on age-related alterations in [3H]MK-801, [3H]glycine, sodium-dependent D-[3H]aspartate, [3H]FK-506 and [3H]PN200-110 binding in rats

Calcium Signaling During Brain Aging and Its Influence on the Hippocampal Synaptic Plasticity

Calcium (Ca²⁺) ions are highly versatile intracellular signaling molecules and are universal second messenger for regulating a variety of cellular and physiological functions including synaptic plasticity. Ca²⁺ homeostasis in the central nervous system endures subtle dysregulation with advancing age. Research has provided abundant evidence that brain aging is associated with altered neuronal Ca²⁺ regulation and synaptic plasticity mechanisms. Much of the work has focused on the hippocampus, a brain region critically involved in learning and memory, which is particularly susceptible to dysfunction during aging. The current chapter takes a specific perspective, assessing various Ca²⁺ sources and the influence of aging on Ca²⁺ sources and synaptic plasticity in the hippocampus. Integrating the knowledge of the complexity of age-related alterations in neuronal Ca²⁺ signaling and synaptic plasticity mechanisms will positively shape the development of highly effective therapeutics to treat brain disorders including cognitive impairment associated with aging and neurodegenerative disease.

NMDA Receptor Function During Senescence: Implication on Cognitive Performance

N-methyl-D-aspartate (NMDA) receptors, a family of L-glutamate receptors, play an important role in learning and memory, and are critical for spatial memory. These receptors are tetrameric ion channels composed of a family of related subunits. One of the hallmarks of the aging human population is a decline in cognitive function; studies in the past couple of years have demonstrated deterioration in NMDA receptor subunit expression and function with advancing age. However, a direct relationship between impaired memory function and a decline in NMDA receptors is still ambiguous. Recent studies indicate a link between an age-associated NMDA receptor hypofunction and memory impairment and provide evidence that age-associated enhanced oxidative stress might be contributing to the alterations associated with senescence. However, clear evidence is still deficient in demonstrating the underlying mechanisms and a relationship between age-associated impaired cognitive faculties and NMDA receptor hypofunction. The current review intends to present an overview of the research findings regarding changes in expression of various NMDA receptor subunits and deficits in NMDA receptor function during senescence and its implication in age-associated impaired hippocampal-dependent memory function.

Susceptibility to Calcium Dysregulation during Brain Aging

Calcium (Ca(2+)) is a highly versatile intracellular signaling molecule that is essential for regulating a variety of cellular and physiological processes ranging from fertilization to programmed cell death. Research has provided ample evidence that brain aging is associated with altered Ca(2+) homeostasis. Much of the work has focused on the hippocampus, a brain region critically involved in learning and memory, which is particularly susceptible to dysfunction during senescence. The current review takes a broader perspective, assessing age-related changes in Ca(2+) sources, Ca(2+) sequestration, and Ca(2+) binding proteins throughout the nervous system. The nature of altered Ca(2+) homeostasis is cell specific and may represent a deficit or a compensatory mechanism, producing complex patterns of impaired cellular function. Incorporating the knowledge of the complexity of age-related alterations in Ca(2+) homeostasis will positively shape the development of highly effective therapeutics to treat brain disorders.

Effect of δ-aminolevulinic acid and vitamin E treatments on the N-methyl-d-aspartate receptor at different ages in the striatum of rat brain

We report the effects of the chronic treatments with the oxidant agent delta-aminolevulinic acid (ALA) and with the antioxidant vitamin E on the N-methyl-D-aspartate (NMDA) receptors in the striatum of 4-, 12- and 24-month-old male Wistar rats. ALA and vitamin E were administered daily for 15 days (40 mg/kg i.p. and 20 mg/kg i.p. respectively). NMDA receptors were labeled by membrane homogenate binding, using tritiated dizocilpine ([3H]MK-801). [3H]MK-801 binding in the striatum was significantly decreased at all ages in ALA-treated rats with respect to their controls, and in contrast, was significantly increased at all ages when rats received the treatment with vitamin E. Western blot assays were performed using antibodies against the NR2A subunit, a NMDA receptor subunit widely distributed in the brain. We did not find significant differences in the amounts of NR2A in rats treated with either ALA or vitamin E with respect to those rats not treated. We conclude that the NMDA receptor densities in the rat striatum are modified by the chronic treatment with oxidants and antioxidants in an age-independent way, at least until 24 months. Also, our results support the notion that NR2A is not involved in these modifications.

Effect of vitamin E treatment on N-methyl-D-aspartate receptor at different ages in the rat brain

A comparative study using membrane homogenate binding, autoradiography, and Western blot assays was carried out to determine the age-related changes in N-methyl-D-aspartate (NMDA) receptors in 4-, 12- and 24-month-old male Wistar rats, treated or not with vitamin E. Vitamin E treatment was 20 mg/kg i.p. daily for 15 days. [(3)H] 5-methyl-10,11-dihydro-5H-dibenzo (a,d) cycloheptan-5,10-imine maleate (MK-801) binding was significantly increased in all areas studied (cortex and hippocampus) at all ages when rats received this treatment. A Western blot study in vitamin-E-treated rats and their controls did not reveal significant differences in the amounts of NR2A, an NMDA receptor subunit widely distributed in the brain mainly in cortex and hippocampus. We conclude that the effect of vitamin E on NMDA receptors is largely age independent. Previous reports and our data have described the presence of age-dependent NMDA receptor changes. The effect of vitamin E in aging is considered to be mediated by free radical scavenging, but from our data, we conclude that this mechanism is not relevant for age-dependent NMDA receptor changes. Our results also support that age or vitamin E treatment have no relevant effects on NR2A subunit, at least until 24 months in rats.

Increases in [3H]FK-506 and [3H]L-N(G)-nitro-arginine binding in the rat brain after nigrostriatal dopaminergic denervation

Receptor autoradiographic technique was studied to investigate sequential changes in FK-506 binding proteins, nitric oxide synthase and dopamine uptake sites in the brain 1 week to 8 weeks after unilateral 6-hydroxydopamine injection of the medial forebrain bundle in rats. [3H]FK-506, [3H]L-N(G)-nitro-arginine and [3H]mazindol were used to label FK-506 binding proteins (immunophilin), nitric oxide synthase and dopamine uptake sites, respectively. [3H]FK-506 binding showed about 13-25% increase in the ipsilateral striatum from 2 to 8 weeks after degeneration of nigrostriatal pathway. However, no significant change in [3H]FK-506 binding was observed in the ipsilateral substantia nigra during the postlesion periods. In the contralateral side, [3H]FK-506 binding also showed about 13-25% increase in the striatum from 2 to 8 weeks postlesion. The substantia nigra showed a 21% increase in [3H]FK-506 binding only 2 weeks after the lesioning. On the other hand, [3H]L-N(G)-nitro-arginine binding showed about 21-31% increase in the parietal cortex and striatum 1 week or 2 weeks postlesion. In the contralateral side, a 21% increase in [3H]L-N(G)-nitro-arginine binding was found in the dorsolateral striatum only 1 week postlesion. In contrast, degeneration of nigrostriatal pathway caused a conspicuous loss of [3H]mazindol binding in the ipsilateral striatum (87-96%), substantia nigra (36-73%) and ventral tegmental area (91-100%) during the postlesion periods. In the contralateral side, no significant changes in [3H]mazindol binding were observed in these areas up to 8 weeks after the postlesion. The present study demonstrates that unilateral injection of 6-hydroxydopamine into the medial forebrain bundle of rats can cause a significant increase in [3H]FK-506 and [3H]L-N(G)-nitro-arginine bindings in the brains. In contrast, a marked reduction in [3H]mazindol binding is observed in the brains after the lesioning, indicating severe damage to nigrostriatal dopaminergic pathway. These results suggest that immunophilin and nitric oxide synthase may play some role in the pathogenesis of neurodegenerative disorders such as Parkinson's disease.

Regulation of intracellular Ca2+ concentration by interleukin-1beta in rat cortical synaptosomes: an age-related study

The pro-inflammatory cytokine interleukin-1beta (IL-1beta) is released by cells during injury and stress, and increased neuronal expression of IL-1beta is a feature of age-related neurodegeneration. We have recently reported that IL-1beta has a biphasic effect on the K+-induced rise in intracellular Ca2+ concentration ([Ca2+]i) in cortical synaptosomes, exerting an inhibitory effect on the K+-induced rise in [Ca2+]i at lower (3.5 ng/mL) concentrations and a stimulatory effect on the K+-induced rise in [Ca2+]i at higher (100 ng/mL) concentrations. In the present study, we observed that the K+-induced rise in [Ca2+]i was inhibited to a similar extent by the lower concentration of IL-1beta in cortical synaptosomes prepared from young (3-month-old), middle-aged (12-month-old) and aged (24-month-old) rats. In contrast, cortical synaptosomes prepared from the aged rats exhibited an increased susceptibility to the higher concentration of IL-1beta, resulting in a marked elevation in [Ca2+]i. We propose that the age-related increase in neuronal concentration of IL-1beta promotes a dramatic elevation in [Ca2+]i following membrane depolarization, thereby altering Ca2+ homeostasis and exacerbating neuronal vulnerability to excitotoxicity.

Post-ischemic alterations in [3H]FK506 binding in the gerbil and rat brains

We investigated post-ischemic changes in FK506 binding protein (FKBP) in the brain after transient global ischemia in gerbils or transient focal ischemia in rats. [3H]FK506 was used to label FKBP as a immunophilin. In transient global ischemia, [3H]FK506 binding showed a transient reduction in the frontal cortex only 1 h after recirculation. In the striatum, the dorsolateral part exhibited a significant increase in [3H]FK506 binding 5, 24 and 48 h after ischemia. However, the ventromedial part showed a transient elevation in [3H]FK506 binding 24 h after ischemia. Thereafter, the ventromedial part showed no conspicuous change in [3H]FK506 binding up to 7 days after ischemia. The dorsolateral part also showed no significant change in [3H]FK506 binding 7 days after ischemia. In the hippocampus and thalamus, [3H]FK506 binding was unchanged in the stratum radiatum of the hippocampal CA1 sector, hippocampal CA3 sector, dentate gyrus and thalamus up to 7 days after ischemia. However, the stratum oriens of the hippocampal CA1 sector showed a significant reduction in [3H]FK506 binding 48 h and 7 days after ischemia. A histological study showed that transient cerebral ischemia caused a severe damage in the striatum and hippocampal CA1 sector. In a model of transient focal ischemia, a marked increase in [3H]FK506 binding was also found in the striatum and cerebral cortex where severe infarctions were observed. These results demonstrate that post-ischemic change in [3H]FK506 binding between the striatum and hippocampus may be produced by different mechanisms. Furthermore, our findings suggest that immunophilins may play some role in the pathogenesis of ischemic diseases.