Binding of the benzodiazepine ligand [3H]-RO 15-1788 to membrane preparations of the rabbit and turtle retina

Identification of anxiolytic/nonsedative agents among indol-3-ylglyoxylamides acting as functionally selective agonists at the gamma-aminobutyric acid-A (GABAA) alpha2 benzodiazepine receptor

Anxioselective agents may be identified among compounds binding selectively to the alpha(2)beta(x)gamma(2) subtype of the gamma-aminobutyric acid-A (GABA(A))/central benzodiazepine receptor (BzR) complex and behaving as agonists or among compounds binding with comparable potency to various BzR subtypes but eliciting agonism only at the alpha(2)beta(x)gamma(2) receptor. Because of subtle steric differences among BzR subtypes, the latter approach has proved much more successful. A biological screening within the class of indol-3-ylglyoxylamides 1-3 allowed us to identify compounds 1c and 2b as potential anxiolytic/nonsedative agents showing alpha(2) selective efficacy in vitro and anxioselective effects in vivo. According to molecular modeling studies, and consistently with SARs accumulated in the past decade, 5-NO(2)- and 5-H-indole derivatives would preferentially bind to BzR by placing the indole ring in the L(Di) and the L(2) receptor binding sites, respectively.

Effects of benzodiazepines on frog ERG

Effect of flurazepam (water-soluble benzodiazepine) on the amplitude and time course of ERG waves was investigated in superfused frog eyecups (Rana ridibunda). Flurazepam (50 and 100 microM) had inhibitory effect on the b- and d-wave amplitude, which was not accompanied with significant changes in their implicit time. Flurazepam potentiated the depressant effect of GABA (2.5 and 5 mM) on the b- and d-wave amplitude. The inhibitory effect of flurazepam was not blocked by 50 microM bicuculline (BCC), (GABA(A) antagonist), although the blocker markedly potentiated the b- and d-wave amplitude. The suppressive effect of flurazepam on the b- but not d-wave amplitude was blocked by 100 microM BCC. Our results indicate existence of functional benzodiazepine regulatory sites on GABA(A) receptors in distal frog retina.

[(3)H]Flumazenil binding in the human hippocampal formation, frontal cortex and cerebellum detected by high-resolution phosphorimaging

The pharmacological characterisation of the benzodiazepine binding site associated with the gamma-aminobutyric acid (GABA(A)) receptor in human brain has been demonstrated using in situ radioligand binding and autoradiography. The use of high-resolution phosphorimaging has allowed both the affinity (K(d)) and density (B(max)) of [(3)H]flumazenil binding to be measured within regions of the hippocampal formation as well as the cerebellum and frontal cortex. The Scatchard plots of data from all brain regions were linear with Hill coefficients close to unity consistent with the presence of a single binding site for [(3)H]flumazenil. The affinities of [(3)H]flumazenil binding within all the brain regions were similar (K(d) 1.57+/-0.20-3.08+/-0.01 nM), while the density of [(3)H]flumazenil binding varied significantly between the brain regions analysed (B(max) 182.7+/-7.3-596.7+/-34.0 fmol/mg ETE; P<0.0001). In conclusion, the present results indicate that in situ radioligand binding and high-resolution phosphorimaging techniques can be utilized to measure the distribution, density and affinity of [(3)H]flumazenil to the GABA(A) receptor within the human frontal cortex, cerebellum and hippocampal formation.

Autoradiographic distribution of peripheral benzodiazepine receptors in the retina of the albino rabbit, Lepus cunicula

The distribution of peripheral benzodiazepine receptors (PBRs) in the retina of the albino rabbit, Lepus cunicula, was studied by autoradiography using [3H]-PK11195, a isoquinoline carboxamide, as a tracer. Autoradiograms obtained by directly placing the slides containing the retina sections on tritium-sensitive film provide evidence for the presence of PBRs in rabbit retina. Furthermore, the dark field examination of photomicrographs taken from autoradiograms showed two dense horizontal bands corresponding to the outer and inner photoreceptor segments, and to the inner plexiform layer. The retinal regions where [3H]-PK11195 binding was more dense are rich in mitochondria, suggesting that as in other neuronal tissues, retinal PBRs are involved in the mitochondrial activity.

The peripheral-type benzodiazepine receptor ligands [3H]Ro 5-4864 and [3H]PK 11195 bind to the retina of rabbit, but not of turtle

The binding of [3H]flunitrazepam, [3H]Ro 5-4864, and [3H]PK 11195 to membrane preparations of the retina was studied in the turtle and rabbit. Only a single population of [3H]flunitrazepam binding sites was detected in the turtle, whereas two populations appeared to be present in the rabbit. No specific binding for [3H]Ro 5-4864 and [3H]PK 11195 could be detected in the turtle. In rabbit, both ligands bound with high affinity, revealing a significant population of binding sites (KD values of 24 +/- 2.3 and 2.2 +/- 0.8 nM, and Bmax values of 440 +/- 35 and 1,482 +/- 110 fmol/mg of protein, respectively). The binding was temperature- and protein-dependent. Displacement studies showed a similar rank order of potency of various unlabeled ligands against both [3H]Ro 5-4864 and [3H]PK 11195 (PK 11195 > Ro 5-4864 > flunitrazepam > flumazenil). These results suggest that peripheral-type benzodiazepine receptors are present in the retina of the rabbit, but not of the turtle.