Alterations in glutamate dehydrogenase of the brain of rats of various ages

Impaired motor learning attributed to altered AMPA receptor function in the cerebellum of rats with temporal lobe epilepsy: ameliorating effects of Withania somnifera and withanolide A

The aim of this study was to investigate the effect of Withania somnifera (WS) extract, withanolide A (WA), and carbamazepine (CBZ) on cerebellar AMPA receptor function in pilocarpine-induced temporal lobe epilepsy (TLE). In the present study, motor learning deficit was studied by rotarod test, grid walk test, and narrow beam test. Motor learning was significantly impaired in rats with epilepsy. The treatment with WS and WA significantly reversed the motor learning deficit in rats with epilepsy when compared with control rats. There was an increase in glutamate content and IP3 content observed in rats with epilepsy which was reversed in WS- and WA-treated rats with epilepsy. alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor dysfunction was analyzed using radiolabeled AMPA receptor binding assay, AMPA receptor mRNA expression, and immunohistochemistry using anti-AMPA receptor antibody. Our results suggest that there was a decrease in Bmax, mRNA expression, and AMPA receptor expression indicating AMPA receptor dysfunction, which is suggested to have contributed to the motor learning deficit observed in rats with epilepsy. Moreover, treatment with WS and WA resulted in physiological expression of AMPA receptors. There was also alteration in GAD and GLAST expression which supplemented the increase in extracellular glutamate. The treatment with WS and WA reversed the GAD and GLAST expression. These findings suggest that WS and WA regulate AMPA receptor function in the cerebellum of rats with TLE, which has therapeutic application in epilepsy.

Decreased glutamate receptor binding and NMDA R1 gene expression in hippocampus of pilocarpine-induced epileptic rats: neuroprotective role of Bacopa monnieri extract

The potential for antiepileptic drugs to negatively impact cognitive abilities has generated renewed interest in herbal drugs and formulations in the treatment of epilepsy. Bacopa monnieri is one such widely used revitalizing herb that purportedly strengthens nervous function and also possesses memory-enhancing, antioxidative, antiepileptic, and anti-inflammatory properties. We investigated the neuroprotective role of B. monnieri extract in alteration of glutamate receptor binding and gene expression of NMDA R1 in hippocampus of temporal lobe epileptic rats. In association with pilocarpine-induced epilepsy, there was significant downregulation of NMDA R1 gene expression and glutamate receptor binding without any change in its affinity. B. monnieri treatment of epileptic rats significantly reversed the expression of NMDA R1 and glutamate receptor binding alterations to near-control levels. Also, in the epileptic rats, we measured a significant increase in the activity of glutamate dehydrogenase, which neared the control level after B. monnieri treatment. The therapeutic effect of B. monnieri was also observed in the Morris water maze experiment. These data together indicate the neuroprotective role of B. monnieri extract in glutamate-mediated excitotoxicity during seizures and cognitive damage occurring in association with pilocarpine-induced epilepsy.

Age-dependent changes in some aspects of glutamate metabolism in the brain of the teleost, Channa punctatus. I. Ammonia and glutamine contents and glutamate dehydrogenase activity

Age related changes in some aspects of glutamate metabolism were followed in the brain of a short lived species of tropical murrel, Channa punctatus. Both ammonia and glutamine contents of brain increased with advancing age of the murrel. The glutamate dehydrogenase activity of brain increased during maturation phase (year classes 0(+)-3+) followed by a decline in senescence phase (year classes 3(+)-6+). The pattern of age changes in glutamate metabolism in this species of fish shows similarity with the observations made in a majority of mammalian species, thereby suggesting a commonality in a basic metabolic mechanism during aging process in the central nervous system of vertebrates.

Effect of thermal inactivation and ATP on age related changes in hepatic glutamate dehydrogenase activity of male garden lizard

The total glutamate dehydrogenase (GDH) activity of the liver of the male garden lizard did not change during maturation (young to middle-aged) but showed a decline in later phase of the life span (middle-aged to old). On the other hand, the heat stable GDH activity increase during maturation and declined thereafter. The degree of thermal inactivation of the total GDH activity at 45 degrees +/- 1 degree C was not age-dependent. ATP stimulation of total GDH activity was about three times higher in old than in middle-aged lizards.

The evoked release of endogenous amino acids from tissue prisms of human neocortex

The K+-evoked release of 13 amino acids has been determined from tissue prisms of neocortex from patients of various ages, and from rats. Prisms were prepared from various regions of human neocortex obtained at neurosurgery. Upon depolarization aspartate, glutamate and gamma-aminobutyrate (GABA) were shown to be preferentially released. The efflux of glutamate was calcium-dependent. Prisms prepared from human neocortex obtained shortly after death also exhibited preferential K+-induced release of putative amino acid transmitters. Absolute concentrations released into the media were similar to those found for neurosurgical samples. Comparison of the release data for rat and human samples revealed that the efflux of aspartate, glutamate and GABA occurred to a greater extent from rat brain preparations. The K+-evoked release of glutamate from human samples showed a significant linear increase from 12 to 68 years of age.

Age-dependent changes in glutamate oxidation by non-synaptic and synaptic mitochondria from rat brain

The oxidation of glutamate by non-synaptic and synaptic mitochondria from brains of 3-, 12- and 24-month-old rats was studied. With glutamate plus malate as substrates, non-synaptic mitochondria showed higher respiration rates than synaptic mitochondria in all the three age groups studied. The rate of oxidation of L-[1-14C]glutamate and the activities of NAD-glutamate dehydrogenase and aspartate aminotransferase were also higher in non-synaptic mitochondria compared with synaptic mitochondria in three age groups. With glutamate plus malate as substrates, a significant reduction in state 3 respiration was observed in both mitochondrial populations from 12- and 24-month-old rats compared with 3-month-old animals. Although an age-dependent decrease in the oxidation of L-[1-14C]glutamate was observed in both non-synaptic and synaptic mitochondria from aging rats, the oxidation of [1-14C]-2-oxoglutarate was unaltered in non-synaptic and synaptic mitochondria from senescent rats. The activity of NAD-glutamate dehydrogenase was decreased with age in both mitochondrial populations, whereas aspartate aminotransferase was not altered with age. The results indicate that the oxidation rate of glutamate in rat brain mitochondria is decreased during aging.

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.