GABAergic regulation of striatal opioid gene expression

Peptides derived from prodynorphin and preproenkephalin are located in GABAergic striatal projection neurons. We have used nucleic acid hybridization techniques to investigate the role of GABA in the regulation of striatal opioid peptide gene expression. Rats were treated with the GABA-transaminase inhibitors aminooxy acetic acid, ethanolamine O-sulphate and gamma-vinyl-GABA for one week. The GABA levels in the striatum were significantly elevated after each treatment. The GABA-transaminase-inhibitors decreased the striatal levels of the opioid peptides met-enkephalin and dynorphin(1-8) and concomitantly decreased the concentrations of the mRNAs coding for proenkephalin and prodynorphin. These findings indicate that GABA exerts an inhibitory influence on prodynorphin and proenkephalin gene expression in the striatum. The mechanisms underlying these inhibitions are discussed.