Mitochondrial enzymes related to glutamate and GABA metabolism in the hippocampus of young and aged rats: A quantitative histochemical study

Abstract

Quantitative histochemistry (scanning microphotometry) was used to determine the activities of the mitochondrial enzymes NAD-linked isocitrate dehydrogenase (EC 1.1.1.41), L-glutamate dehydrogenase (EC 1.4.1.3) and GABA transaminase (EC 2.6.1.19) in various layers of the hippocampus (middle one third) of young (3-4 months old) and memory-impaired aged rats (28-30 months old). For comparison, determinations of cytochrome c oxidase (EC 1.9.3.1) as a marker for mitochondria and energy metabolism were also performed. The study showed that there was a layered reaction pattern in the hippocampus and that the cellular distribution and the levels of enzyme activity were different. However, the activities of the different enzymes (excepting GABA transaminase and cytochrome c oxidase) were significantly correlated in the hippocampus in both age groups. Age-dependent changes were only observed for NAD-linked isocitrate dehydrogenase and GABA transaminase (significant increases of activities in some layers of the hippocampus, preferentially in the terminal field of the perforant path). From the present study it is concluded that, 1. the enzymatic complement of mitochondria in neurons and glia depends upon layer specific metabolic processes of the hippocampus (also with respect to glutamatergic and GABAergic terminal fields) indicating a layer specific interaction of the enzymes studied to produce or catabolize glutamate and GABA, and 2. the age dependent changes of the studied enzymes are very restricted.

In situ measurements of enzyme activities in the brain

“…This suggestion is supported by quantitative enzyme histochemistry which shows that the activities of GABAT and GDH are significantly correlated in the rat hippocampus ( Fig. 7; Kugler & Baier, 1992).…”

“…Pronounced ICDH activities are present in the lacunosum-molecular layer of the hippocampus proper (CA1 and CA3) and intermediate activities in the dentate gyrus molecular layer (Figs 3, 4, 5;Kugler & Baier, 1992). Both layers contain the terminations of the glutamatergic tractus perforans (cf.…”

“…10; see above). A moderate to high level of GDH activity in these layers was also determined by microphotometric measurements (Figs 3, 4;Kugler & Baier, 1992).…”

“…2; see above). Microphotometric measurements in the rat hippocampus showed that the activities of ICDH and GDH are significantly correlated (Kugler & Baier, 1992). Glutamate is converted by glutamine synthetase to glutamine.…”

“…Kugler, 1988a;King et al, 1989;Kugler & Baier, 1992). The aim of catalytic enzyme histochemistry is, in principle, to apply biochemical methods to tissue sections (van Duijn & van der Ploeg, 1980) and to obtain and visualize a product of an enzymatic reaction at the site of occurrence of the enzyme in a brain section.…”