Changes in [3H]-PK 11195 and [3H]-8-OH-DPAT binding following forebrain ischaemia in the gerbil.
1. A high density of [3H]-PK 11195 binding sites was present in gerbil cortical membranes (Bmax [3H]-PK 11195 1360 +/- 71 fmol mg-1 protein) in comparison to rat cortical membranes (254 +/- 21 fmol mg-1 protein). This effect was species-specific as similar findings were obtained with hippocampal membranes (Bmax 1430 +/- 111 fmol mg-1 protein in gerbil, compared to 196 +/- 31 in rat). 2. RO 5-4864, also a peripheral type benzodiazepine compound, displayed low affinity for the [3H]-PK 11195 site in the gerbil (pKi 6.57 +/- 0.02 and 6.70 +/- 0.12 in hippocampus and cortex respectively) compared to rat (pKi 8.16 +/- 0.07 and 8.48 +/- 0.02). Central benzodiazepine compounds, diazepam and flunitrazepam, also displayed this trend. 3. RO 5-4864 displaced [3H]-PK 11195 binding from gerbil and rat cortical membranes through a competitive interaction with Hill slopes close to unity. In both tissues, saturation isotherms of [3H]-PK 11195 binding indicated that the presence of RO 5-4864 caused changes in Kd without any effect on Bmax. In kinetic experiments, the presence of RO 5-4864 failed to modify the rate of dissociation of [3H]-PK 11195 from equilibrium in both rat and gerbil cortical membranes. 4. Forebrain ischaemia in the Mongolian gerbil (5 min bilateral carotid artery occlusion) with 7 days recovery caused a significant (P<0.05) decrease in the density of hippocampal 5-HTlA binding sites labelled by [3H]-8-OH-DPAT (Bmax control, 393 +/- 33 fmol mg-1 protein; ischaemic, 289 +/- 21 fmol mg protein)and an increase (P<0.01) in [3H]-PK 11195 binding sites (Bmax control, 1430 +/- 111 fmol mg-1 protein; ischaemic, 2160 +/- 170 fmol mg-1 protein). Ischaemia and recovery had no effect on the affinity of either ligand.5. Autoradiography experiments in gerbil brain sections revealed that the ischaemia-induced increase in[3H]-PK 11195 binding was consistent and significant in the CA, subfield on the hippocampus (control,152 +/- 42 fmol mg-1 tissue; ischaemic, 314 +/- 43 fmol mg-1 tissue).
Department of Pharmacology, Syntex Research Centre, Heriot-Watt University Research Park, Riccarton, Edinburgh.
B A
BA
Kenny
A C
AC
MacKinnon
M
M
Spedding
C M
CM
Brown
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000493:pharmacokinetics*; D000818:Animals; D001345:Autoradiography; D001569:Benzodiazepines / Q000494:pharmacology; D001570:Benzodiazepinones / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D002545:Brain Ischemia / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D003292:Convulsants / Q000494:pharmacology; D005849:Gerbillinae; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000493:pharmacokinetics*; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D016548:Prosencephalon / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*
D001570:Benzodiazepinones; D003292:Convulsants; D007546:Isoquinolines; D011963:Receptors, GABA-A; D001569:Benzodiazepines; C028513:4'-chlorodiazepam; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C037850:PK 11195