Glutamate and gamma-aminobutyric acid (GABA), act as excitatory and inhibitory neurotransmitters in CNS respectively. An increase in glutamate and a decrease in GABA concentration were observed in aged brain. However, the mechanism of these changes has not been very well elucidated. Glutamate decarboxylase (GAD) catalyzes the conversion of glutamate to GABA. Since the vitamin B6 is essential for the activities of GAD, this study was undertaken to investigate the effects of vitamin B6 administration on age related changes in rat brain. The animals were injected intraperitoneally with 1, 10 and 100 mg vitamin B6 /kg body weight /day for 30 days, and specific activity of GAD was assayed in the brain supernatant. The activity of the enzyme in aged rats was significantly lower as compared to that of young animals. Vitamin B6 induced activation of the brain enzyme in both ages, but the rate of the activation was markedly pronounced in aged animals. Significant activation rate of GAD by vitamin B6 in aged rat brain may be resulted from either lower availability of vitamin B6 in aged animals, or lower affinity of the enzyme for pyridoxal -5-phosphate, which is likely to be related to conformational changes of the enzyme during aging. It is suggested that vitamin B6 may restore the activity of the brain glutamate decarboxylase in aged rat.

Nuclear poly(ADP-ribose) polymerase levels as well as the DNA strand break levels of whole-brain neuronal and astroglial cells were investigated . Three-and 30month-old rats were used . Low-molecular-weight neurofilaments and glutamine synthetase served as neuronal and astroglial markers, respectively . A large increase in the poly(ADP-ribose] polymerase activity was observed in the neurons (threefold) and astrocytes (3 .7-fold) derived from 30-month-old rats . Similarly, the amount of poly(ADP-ribose) polymerase, evaluated per milligram of DNA, in-creased~3 .5-fold in neurons and 3 .9-fold in astrocytes prepared from 30-month-old rats . Whether the increase in the poly(ADP-ribose) polymerase activity was due to an enhanced rate of DNA strand break was investigated by determining the rate of DNA unwinding . A significant increase in DNA unwinding rate was detected in the neurons {2 .7-fold}, although a lower increase was observed in the astroglia (1 .3-fold) of aged animals .

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By use of high performance liquid chromatography with electrochemical detection to measure dopamine production, tyrosine hydroxylase (EC 1.14.16.2) activity has been measured in rat brain synaptosomes from striatum and forebrain. Normal specific activities three- to fivefold higher than previously reported in the literature for radiochemical methods of assay were found. It is suggested that synaptosomes contain a significant amount of endogenous substrate for tyrosine hydroxylase, which causes dilution of the added labelled tyrosine and hence underestimation of the activity of this enzyme when radiochemical methods are used.