[3H]L-655,708, a novel ligand selective for the benzodiazepine site of GABAA receptors which contain the alpha 5 subunit

Neuropharmacology. 1996;35(9-10):1331-5. doi: 10.1016/s0028-3908(96)00061-5.


A compound (L-655,708) has been identified which has at least 50-fold selectivity for the benzodiazepine site on GABAA receptors containing an alpha 5 subunit over those containing an alpha 1, alpha 2, alpha 3 or alpha 6 subunit in combination with beta 3 and gamma 2. The compound was radiolabelled with tritium and investigated as a novel radioligand which recognizes the benzodiazepine site of GABAA receptors which contain the alpha 5 subunit. [3H]L-655,708 labels one saturable and specific population of binding sites in rat hippocampus with a Kd of 2.4 +/- 0.7 nM and a Bmax of 256 +/- 42 fmol/mg protein. The pharmacology of the binding site labelled was consistent with that of receptors present in cells transfected with alpha 5, beta 2 and gamma 2 and with receptors immunoprecipitated from rat brain with an alpha 5-selective antiserum. It is concluded that [3H]L-655,708 is the first radioligand to date which is selective for any BZ2 subtype of the GABAA receptor and should provide a valuable tool for elucidating the structure and function of the alpha 5-containing GABAA receptor subtype.

MeSH terms

  • Animals
  • Hippocampus / drug effects
  • Hippocampus / metabolism
  • Imidazoles / pharmacology*
  • In Vitro Techniques
  • Kinetics
  • Ligands
  • Male
  • Membranes / drug effects
  • Membranes / metabolism
  • Precipitin Tests
  • Radioligand Assay
  • Rats
  • Receptors, GABA-A / drug effects
  • Receptors, GABA-A / metabolism*


  • Imidazoles
  • L 655,708
  • Ligands
  • Receptors, GABA-A