Postnatal development and kinetics of [3H]gaboxadol binding in rat brain: in vitro homogenate binding and quantitative autoradiography.
The postnatal development of the binding of the GABA(A) receptor agonist [(3)H]gaboxadol in rat brain was investigated. Using brain tissue from rats obtained at postnatal days 1, 10, 25, and >25 (adult), the binding of [(3)H]gaboxadol and the benzodiazepine [(3)H]flunitrazepam to GABA(A) receptors was compared in homogenate binding assays and quantitative receptor autoradiography. Kinetic and equilibrium data obtained in homogenate binding studies revealed two different [(3)H]gaboxadol affinities. A kinetically derived K(D) of 3.7 nM in adult cerebellum, calculated from the association and dissociation rate constants k(on) (1.45 x 10(8) M(-1) min(-1)) and k(off) (0.54 min(-1)) was contrasted by an equilibrium K(D) of 38.6 nM, obtained by homologous competition experiments. Quantitative analysis of autoradiographic data revealed an increase in specific [(3)H]gaboxadol binding sites during brain development, which resembles the anatomical and temporal pattern of the postnatal expression of the extrasynaptic delta subunit of GABA(A) receptors. In conclusion, by the radioligand binding data obtained on native tissue, binding of gaboxadol to GABA(A) receptors located outside the synaptic junctions could be postulated.
Friemel
Anne
A
Department of Radiopharmacy, Institute of Interdisciplinary Isotope Research, Permoserstr. 15, 04318 Leipzig, Germany.
Ebert
Bjarke
B
Hutson
Pete H
PH
Brust
Peter
P
Nieber
Karen
K
Deuther-Conrad
Winnie
W
D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001345:Autoradiography / Q000379:methods; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism; D001923:Brain Chemistry / Q000502:physiology*; D005445:Flunitrazepam / Q000378:metabolism / Q000493:pharmacokinetics; D018755:GABA Agonists / Q000378:metabolism / Q000493:pharmacokinetics; D018757:GABA Modulators / Q000378:metabolism / Q000493:pharmacokinetics; D007555:Isoxazoles / Q000378:metabolism* / Q000493:pharmacokinetics*; D007700:Kinetics; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism; D013347:Subcellular Fractions; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018755:GABA Agonists; D018757:GABA Modulators; D007555:Isoxazoles; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; C015542:gaboxadol