PERSISTENT ELEVATION OF TISSUE GABA AND SERUM GONADOTROPIN CONCENTRATIONS BY GABA TRANSAMINASE INHIBITION IN GOLDFISH (CARASSIUS-AURATUS)

The irreversible gamma-aminobutyric acid transaminase inhibitor gamma- vinyl gamma-aminobutyric acid was used to elevate gamma-aminobutyric a cid concentrations in the brain, pituitary and peripheral tissues of t he goldfish (Carassius auratus). Administration of gamma-vinyl gamma-a minobutyric acid (300 mu g/g) caused a rapid and robust elevation of g amma-aminobutyric acid concentrations in the brain, pituitary and peri pheral tissues of the goldfish. The concentrations of gamma-aminobutyr ic acid in the brain and pituitary were elevated fivefold after 24 h, 10-fold after 48 h and continued to be 10 times the normal level for a t least 3 weeks. Treatment with gamma-vinyl gamma-aminobutyric acid al so elevated gamma-aminobutyric acid concentrations in the liver, but i n contrast to the gamma-aminobutyric acid concentrations in the nervou s tissue, these levels returned to normal by 3 weeks. Treatment with g amma-vinyl gamma-aminobutyric acid also elevated gamma-aminobutyric ac id concentrations in the heart, gill, kidney and ovaries. Elevation of gamma-aminobutyric acid concentrations was accompanied by an elevatio n in serum gonadotropin-II concentrations and serum testosterone conce ntrations, whereas serum growth hormone concentrations were unaffected . The elevation in serum gonadotropin-II was transient and, although p ituitary and brain gamma-aminobutyric acid levels remained high, serum gonadotropin-II concentrations returned to normal within 2 weeks. Tre atment with gamma-vinyl gamma-aminobutyric acid did not affect the con centrations of aminergic neurotransmitters or their metabolites, or gl utamate in the goldfish brain, but did significantly reduce taurine co ncentrations. The concentrations of gonadotropin-II in the pituitary a nd salmon gonadotropin-releasing hormone in the hypothalmus were sligh tly reduced 1 week after treatment with gamma-vinyl gamma-aminobutyric acid but remained unaltered in other tissues examined. These studies further implicate gamma-aminobutyric acid in the control of gonadotrop in-II secretion in the goldfish.