The effect of intrastriatal injection of fluorocitrate on amino acid pattern, cell enzyme markers, and ultrastructural appearance was investigated. A dose of 1 nmol of fluorocitrate resulted in temporarily decreased levels of glutamine, glutamate, and aspartate, whereas the level of alanine was increased. The glutamine level was severely reduced after 4 h but was reversed after 24 h. The activity of different cellular enzyme markers did not change markedly after this dose. Ultrastructural changes in glial cells were observed, concomitant with the biochemical changes. A dose of greater than or equal to 2 nmol of fluorocitrate resulted in more marked and irreversible changes in amino acid levels. By 24-72 h after the injection of this dose, several marker enzyme activities decreased markedly. The ultrastructural changes affected the neurons as well as the glial cells and were not reversible. The use of microinjection of 1 nmol of fluorocitrate into the neostriatum of the rat to provide a model for studying transmitter amino acid metabolism in brain devoid of glial cell activity is discussed.

Steroid-thyroid hormone receptors typically bind as dimers to DNA sequences that contain repeated elements termed half-sites. NGFI-B, an early response protein and orphan member of this receptor superfamily, binds to a DNA sequence that contains only one half-site (5'-AAAGGTCA-3'). A domain separate from the NGFI-B zinc fingers, termed the A box, was identified and is required for recognition of the two adenine-thymidine (A-T) base pairs at the 5' end of the NGFI-B DNA binding element. In addition, a domain downstream of the zinc fingers of the orphan receptor H-2 region II binding protein, termed the T box, determined binding to tandem repeats of the estrogen receptor half-site (5'-AGGTCA-3').

No abstract

This work was carried out to evaluate the importance of glial cells in providing precursors for the in vivo synthesis of gamma-aminobutyric acid (GABA). Fluorocitrate, which selectively inhibits the tricarboxylic acid cycle in glial cells, was administered locally in rat neostriatum. Inhibition of the glial cell tricarboxylic acid cycle led to a decrease both in glutamine level and in gamma-vinyl GABA (GVG)-induced GABA accumulation, an observation indicating reduced GABA synthesis. The role of glutamine, which is synthesized in glial cells as a precursor for GABA, was further investigated by inhibition of glutamine synthetase with intrastriatally administered methionine sulfoximine. In this case, the glutamine level was reduced to near zero values, and the GVG-induced GABA accumulation was only half that of normal. The results show that glutamine is an important precursor for GABA synthesis, but it cannot be the sole precursor because it was not possible to depress the GVG-induced GABA accumulation completely.

The role of glial cells for the inactivation and synthesis of precursors for amino acid transmitters was studied in the brains of anesthetized rats in vivo using the microdialysis technique. The dialysis probes were inserted stereotactically into each neostriatum. One neostriatum was treated with the gliotoxin fluorocitrate, whereas the contralateral side served as a control. The basal efflux of amino acids, reflecting the extracellular level, was measured as well as the efflux during depolarization with 100 mM K+ in the dialysis stream. The potassium-evoked efflux of transmitter amino acids was calcium dependent and thus considered to reflect release from the transmitter pool. gamma-Aminobutyric acid (GABA) and glutamate release from the treated side was higher than the control value during the first 2-3 h, a result indicating an important role of glial cells in the inactivation of released transmitter. After 6-7 h with fluorocitrate, the release of glutamate was lower than the control value, a result indicating an important role of glial cells in the synthesis of precursors for the releasable pool of glutamate. The role of glutamine for the production of transmitter glutamate and GABA in vivo was further investigated by inhibiting glutamine synthetase with intrastriatally administered methionine sulfoximine. The release of gluatamate into the dialysis probe decreased to 54% of the control value, whereas the release of GABA decreased to 22% of the control value, a result indicating that glutamine may be more important for transmitter GABA than for transmitter glutamate.