Autoradiographic localization of peripheral benzodiazepine binding sites in the cat brain with [3H]PK 11195

The triakontatetraneuropeptide (TTN) stimulates thymidine incorporation in rat astrocytes through peripheral-type benzodiazepine receptors

Astrocytes and astrocytoma cells actively express the diazepam-binding inhibitor (DBI) gene, suggesting that DBI-processing products may regulate glial cell activity. In the present study, we have investigated the possible effect of one of the DBI-derived peptides, the triakontatetraneuropeptide (TTN), on [(3)H]thymidine incorporation in cultured rat astrocytes. Reversed-phase HPLC analysis of incubation media indicated that TTN is the major form of DBI-derived peptides released by cultured astrocytes. At very low concentrations (10(-14)-10(-11) M), TTN induced a dose-dependent increase in [(3)H]thymidine incorporation, whereas at higher concentrations (10(-10)-10(-5) M) the effect of TTN gradually declined. In the same range of concentrations, the specific peripheral-type benzodiazepine receptor (PBR) agonist Ro 5-4864 mimicked the bell-shaped stimulatory effect of TTN on [(3)H]thymidine incorporation. The PBR antagonist PK11195 (10(-6) M) suppressed the stimulatory action of both TTN and Ro 5-4864 on [(3)H]thymidine incorporation, whereas the central-type benzodiazepine receptor antagonist flumazenil (10(-6) M) had no effect. The present study demonstrates that the endozepine TTN stimulates DNA synthesis in rat glial cells through activation of PBRs. These data strongly suggest that TTN exerts an autocrine/paracrine stimulatory effect on glial cell proliferation.

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.

Expression of 10 GABA(A) receptor subunit messenger RNAs in the motor-related thalamic nuclei and basal ganglia of Macaca mulatta studied with in situ hybridization histochemistry

In situ hybridization histochemistry technique with [35S]UTP-labelled riboprobes was used to study the expression pattern of 10 GABA(A) receptor subunit messenger RNAs in the basal ganglia and motor thalamic nuclei of rhesus monkey. Human transcripts were used for the synthesis of alpha2, alpha4, beta2, beta3, gamma1 and delta subunit messenger RNA probes. Rat complementary DNAs were used for generating alpha1, alpha3, beta1 and gamma2 subunit messenger RNA probes. Nigral, pallidal and cerebellar afferent territories in the ventral tier thalamic nuclei all expressed alpha1, alpha2, alpha3, alpha4, beta1, beta2, beta3, delta and gamma2 subunit messenger RNAs but at different levels. Each intralaminar nucleus displayed its own unique expression pattern. In the thalamus, gamma1 subunit messenger RNA was detected only in the parafascicular nucleus. Comparison of the expression patterns with the known organization of GABA(A) connections in thalamic nuclei suggests that (i) the composition of the receptor associated with reticulothalamic synapses, except for those in the intralaminar nuclei, may be alpha1alpha4beta2delta, (ii) receptors of various other subunit compositions may operate in the local GABAergic circuits, and (iii) the composition of receptors at nigro- and pallidothalamic synapses may differ, with those at nigrothalamic probably containing beta1 and gamma2 subunits. In the medial and lateral parts of the globus pallidus, the subthalamic nucleus and the substantia nigra pars reticularis, the alpha1, beta2 and gamma2 messenger RNAs were co-expressed at a high level suggesting that this subunit composition was associated with all GABAergic synapses in the direct and indirect striatal output pathways. Various other subunit messenger RNAs were also expressed but at a lower level. In the substantia nigra pars compacta the most highly expressed messenger RNAs were alpha3, alpha4 and beta3; all other subunit messenger RNAs studied, except for gamma1, alpha1 and alpha2, were expressed at a moderate to high level. In the striatum, the following subunit messenger RNAs were expressed (listed in order of decreasing signal intensity): alpha4, beta3, alpha2, alpha3, beta2, delta, gamma2, alpha1. The expression patterns found in the monkey were similar to those described in comparable nuclei in the rat by Wisden et al. [J. Neurosci. (1992), 12, p. 1040]; however, the monkey nuclei displayed a much greater variety of GABA(A) receptor subunit messenger RNAs.

Hemodynamic effects of 5-aminolevulinic acid in humans

Endogenous protoporphyrin IX (PpIX), which results from the oral administration of 5-aminolevulinic acid (ALA), is being investigated for its efficacy as a photosensitizing agent for photodynamic therapy (PDT). Clinical use of ALA has been associated with only mild gastrointestinal side effects. The hemodynamic effects of orally administered ALA in doses used for PDT are unknown. Six patients with a significant history of cardiac disease underwent Swan-Ganz catheterization prior to ALA administration and abdominal operation for PDT. Hemodynamic data collection began at least 1 h prior to ALA, and continued for at least 4 h subsequently, during which time no other medications were administered. When compared to measurements made prior to ALA administration, all patients displayed a significant decrease in systolic and diastolic blood pressures, pulmonary artery systolic and diastolic pressures as well as pulmonary vascular resistance. Five of the six patients also developed a decrease in systemic vascular resistance. No significant changes in pulmonary capillary wedge pressure, cardiac output or cardiac index was observed, but the mean pulse rate rose significantly. These findings cannot be explained on the basis of other cardiovascular depressants or to poor central volume status. Although no adverse sequela were appreciated as a result of the observed hemodynamic changes, this potential should be recognized in patients undergoing PDT using ALA.

Cords, channels, corridors and conduits: critical architectural elements facilitating cell interactions in the lymph node cortex

The lymph node cortex is a critical site for encounter between recirculating T cells and their specific antigens. Due to its extreme plasticity, little is understood of the underlying functional unit of the lymph node cortex, the paracortical cord. The idealized paracortical cord (approximately 100 microns by 1000 microns) stretches from a medullary cord to the base of a B-cell follicle. In cross-section, a cord can be visualized as a set of nested cylinders consisting of spaces bounded by cells. The spaces are: i) the lumen of the high endothelial venule (HEV), ii) perivenular channels-narrow potential spaces (0.1 micron) tightly encircling the HEV, iii) corridors-broad spaces (10-15 microns) constituting the majority of the parenchyma, and iv) the cortical sinus. In addition to these spaces for cell traffic, the conduit (fifth space) is a special delivery system for the transit of soluble factors to the HEV and emigrating lymphocytes. The cellular barriers between these spaces are high endothelium, fibroblastic reticular cells, or sinus-lining cells. This review describes the spaces of the paracortical cord and their cellular boundaries, outlines the movement of cells and fluids through these spaces, and discusses how this anatomy affects the efficiency of surveillance by T cells.

Characterization of the peripheral-type benzodiazepine receptors in cultured astrocytes: evidence for multiplicity

In mammalian brain peripheral benzodiazepine (PBZD) receptors are predominantly localized on astroglial cells. Previous studies utilizing whole membrane preparations from brain and peripheral organs of various species have indicated several distinctions between the drug-receptor interactions of the two prototypic PBZD receptor ligands, PK 11195 and Ro5-4864. The present study was undertaken to determine whether putative differences in the binding of PBZD receptor ligands in homogenates of primary astrocyte cultures can be interpreted as the labeling of PBZD receptor subtypes. Equilibrium competition and saturation binding experiments in homogenate preparations of primary astrocytes from cerebral cortex of new born rats revealed that [3H]PK 11195 labels twice the number of [3H]Ro5-4864 binding sites. Unlabeled Ro5-4864 competes for [3H]PK 11195 binding in a manner suggesting the existence of multiple PK 11195 binding sites. The competition binding experiments, using various benzodiazepines, indicate that one binding component of PK 11195 corresponds to Ro5-4864 binding sites, whereas the second is different. The latter binding site does not correspond to the central BZD receptor but displays the pharmacological properties of the PBZD receptor. Further differences between the binding of PK 11195 and Ro5-4864 in astrocytes were detected in the presence of ethanol which was more effective in inhibiting the binding of the latter. Subcellular distribution studies indicated, however, that the binding of both [3H]PK 11195 and [3H]Ro5-4864 is associated primarily with the mitochondrial fraction of astrocytes. Taken together, the present study indicates the existence of non-overlapping PBZD binding sites in astrocytes and thus suggests the existence of PBZD receptor subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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).

In vitro quantitative autoradiography of [3H]-L-deprenyl and [3H]-PK 11195 binding sites in human epileptic hippocampus

Distribution of the enzyme monoamine oxidase B (MAO-B) and the peripheral benzodiazepine binding site (omega 3 site) was studied by quantitative autoradiography using [3H]L-deprenyl and [3H]PK 11195, two tentative glial markers, as ligands. Sclerotic hippocampus from seven patients who had had anterotemporal lobe resection because of intractable complex partial epilepsy were investigated and compared with postmortem hippocampus from three nonepileptic controls. A significantly higher degree of L-deprenyl and PK 11195 binding was observed in the epileptic cases. The increased binding of both ligands correlated to extent of neuronal loss, but only PK 11195 showed correlation to degree of gliosis. We concluded that both ligands could provide useful markers for quantitating the degree of gliosis in pathologic states such as epilepsy. They may be applicable in future in vivo studies with positron emission tomography (PET).

Biochemical, physiological, and pathological aspects of the peripheral benzodiazepine receptor

The PBR is a mitochondrial protein composed of at least two subunits, an approximately 30-kDa subunit that contains the site for BZs and an approximately 18-kDa subunit that binds isoquinoline carboxamide derivatives. Porphyrins and diazepam binding inhibitor are putative endogenous ligands for these receptors, which are under neural and hormonal control. Alterations in the density of PBR seem to be a sensitive indicator of stress: up-regulation after acute stress and down-regulation induced by repeated stress. PBR-specific ligands are involved in the control of cell proliferation and differentiation, and their binding is increased in some cancer tumors. Numerous studies in various endocrine organs have revealed that PBR are located in specific regions or tissues in the organs. Furthermore, PBR densities in various organs subject to hormonal control are regulated by organotropic hormones. At least in some cases, BZ ligands do not exert a specific effect in an organ, but rather modulate the well-documented effects of that particular hormone. To the best of our knowledge, BZ ligand action in peripheral tissues is dependent on recognition of PBR, which may suggest a receptor-mediated action.

[3H]PK 11195 and the localisation of secondary thalamic lesions following focal ischaemia in rat motor cortex

The peripheral-type benzodiazepine binding site (PTBBS) ligand, PK 11195, is known to be a marker of damage in the central nervous system, the binding being predominantly to macrophages. Using photochemically induced focal cortical ischaemia as a lesion model in the rat, we have investigated the detection of secondary lesions using [3H]PK 11195 and ex vivo autoradiography. Secondary lesions in the thalamus became apparent during the second week post-lesioning, at a time when [3H]PK 11195 binding around the primary lesion was beginning to subside. Using Brain Browser software, the identity of the labelled thalamic nucleus was confirmed, objectively, as the ventrolateral nucleus, known to have reciprocal connections with the lesioned cortical area. As with the primary lesion, high densities of PTBBS correlated with infiltration of macrophages. Three-dimensional reconstruction of [3H]PK 11195 autoradiograph images showed binding along white matter tracts between the primary and secondary lesions. We conclude that radiolabelled PK 11195 given in vivo can be used in the visualisation of secondary lesions and their associated degenerating tracts.

Brain kinetics and specific binding of [11C]PK 11195 to omega 3 sites in baboons: positron emission tomography study

We characterized, in vivo, using positron emission tomography in baboons, the kinetics and specific binding of i.v. injected [11C]PK 11195 to omega 3 sites in the brain. Following immediate access to brain tissue, the brain kinetics of [11C] K 11195 showed a slow elimination for the 60 min of study. Both coinjection and pulse-chase (at t = 8 min) with saturating amounts of cold PK 11195 immediately enhanced the availability of radiotracer to brain tissue, but also markedly increased the rate of washout. These effects presumably reflect displacement or inhibition of specifically bound [11C]PK 11195 to both peripheral and central omega 3 sites, respectively. These results indicate that [11C]PK 11195 has easy access and binds with moderate specificity to the normal primate brain in vivo.

Peripheral benzodiazepine binding sites in Alzheimer's disease frontal and temporal cortex

Much evidence has accumulated to suggest that the peripheral type benzodiazepine (PBZ) binding site has a predominantly glial localization. Elevated PBZ binding densities have been reported in various models of brain damage, apparently reflecting glial proliferation in response to neurodegeneration. In the present study, PBZ receptor densities were examined in frontal and temporal cortex of Alzheimer's disease (AD) patients using the ligand [3H]PK 11195. There was a highly significant (p less than 0.01) increase in PBZ binding sites in the temporal cortex from AD patients. In the frontal cortex, a moderate increase was observed that approached statistical significance (p = 0.07). Decreased choline acetyltransferase activity was observed in both regions. These findings offer support for the potential use of the PBZ binding site as a marker for gliosis associated with neuronal cell death.

Macrophage and astrocyte populations in relation to [3H]PK 11195 binding in rat cerebral cortex following a local ischaemic lesion

PK 11195 is a selective and specific ligand for the peripheral-type benzodiazepine binding site. Its potential for in vivo visualisation of lesioned human brain using positron emission tomography (PET) is currently being assessed. The present study examines the relationship between the temporal development of a local ischaemic lesion with its associated cell populations and the binding of [3H]PK 11195 in rat brain. Unilateral cortical infarcts were induced using the photosensitive dye Rose Bengal. At time intervals from 1 to 7 days after lesioning, the localisation of [3H]PK 11195 binding was determined using in vivo and in vitro autoradiography. Sections adjacent to those used for autoradiography were processed for immunohistochemistry using glial fibrillary acidic protein for astrocytes and ED-1 for macrophages. The results show that the binding of [3H]PK 11195 correlates in both time and spatial localisation with the appearance of macrophages around the lesion. Reactive astrocytes, although present, occupy a separate region in the tissue surrounding the lesion and lie outside the region defined by the [3H]PK 11195 binding. We conclude that the [3H]PK 11195 signal associated with this ischaemic lesion originates primarily from binding to macrophages and that [11C]PK 11195 could be used for imaging acute inflammatory response in human brain using PET.

Peripheral-type benzodiazepine receptors in human cerebral cortex, kidney, and colon

The specific binding of [3H]PK 11195 and [3H]Ro 5-4864 to human cerebral cortex, kidney, and colon membranes was studied in order to determine whether peripheral type benzodiazepine receptors (PBR) characteristics located in human tissues are similar to those located in calf or rat tissues. While [3H]PK 11195 (0.05-10 nM, final concentration) bound with high affinity (KD about 2 nM) to human cerebral cortex, kidney, and colon membranes, yielding maximal numbers of binding sites of 255 +/- 23, 1908 +/- 28, and 1633 +/- 98 fmol/mg protein, respectively, the specific binding of [3H]Ro 5-4864 (1.25-40 nM, final concentration), was barely detectable (nonspecific binding about 90% of the total binding). Furthermore, unlabeled PK 11195 was two orders of magnitude more potent than unlabeled Ro 5-4864 in displacing [3H]PK 11195 specific binding from human cerebral cortex and kidney membranes. These results indicate that PBR binding characteristics located in human tissues are similar (but not identical) to those located in calf tissues, but not to those located in rat tissues.

Benzodiazepine receptors and cerebrospinal fluid formation

There is autoradiographic evidence that peripheral-type benzodiazepine ligands bind with high affinity to the membranes of choroid plexus tissue. In this study, the binding of a 4'-chloro analog of diazepam (Ro 5-4864) to rabbit choroid plexus and cerebral cortex was accomplished utilizing an in vitro radioactive assay method. A kinetic analysis of this binding revealed a relatively high affinity of this ligand (KD) for peripheral binding sites in plexus tissue (KD = 16.1 nM/mg protein). There was a 4.6-fold greater density of binding sites (total receptor density (Bmax) = 2.3 pmol/mg) in choroidal membrane as compared to cortical tissue (Bmax = 0.5 pmol/mg). In 40 rabbits in which a ventricular perfusion system was used, the rate of cerebrospinal fluid (CSF) formation was observed to decrease some 48% in the presence of 10(-4) M Ro 5-4864, although some inhibition of secretory activity was still noted at a CSF concentration of 10(-8) M. The choroid plexus tissue levels of adenosine 3',5'cyclic monophosphate (cAMP) and adenosine triphosphatase (ATPase) were not affected by 10(-4) M Ro 5-4864. The results of this study support the notion that the specific benzodiazepine peripheral binding sites in choroid plexus serve to modulate CSF formation. The mechanism of action is poorly understood but does not involve the transport ATPase system or the second messenger cAMP.

Receptor binding characterization of the benzodiazepine radioligand 125I-Ro16-0154: potential probe for SPECT brain imaging

The binding of an iodinated benzodiazepine (BZ) radioligand has been characterized, particularly in regard to its potential use as a neuroreceptor brain imaging agent with SPECT (Single Photon Emission Computed Tomography). Ro16-0154 is an iodine-containing BZ antagonist and a close analog of Ro15-1788. In tissue homogenates prepared from human and monkey brain, the binding of 125I-labeled Ro16-0154 was saturable, of high affinity (Kd = 0.5 nM at 37 degrees C), and had high ratios of specific to non-specific binding (approximately 40:1). Physiological concentrations of NaCl (150 mM) enhanced specific binding approximately 15% compared to buffer without this salt. Kinetic studies of association and dissociation demonstrated a temperature dependent decrease in affinity with increasing temperature. Drug displacement studies confirmed that 125I-Ro16-0154 binds to the "central" type BZ receptor: binding is virtually identical to that of 3H-Ro15-1788 except that 125I-Ro16-0154 shows an almost 10 fold higher affinity at 37 degrees C. These in vitro results suggest that 123I-labeled Ro16-0154 shows promise as a selective, high affinity SPECT probe of the brain's BZ receptor.

Species differences and heterogeneity of solubilized peripheral-type benzodiazepine binding sites

The pharmacological characteristics of digitonin-solubilized peripheral-type benzodiazepine binding sites (PBS) from kidney membranes of various species were investigated to determine whether the species differences and heterogeneity observed in membrane-bound binding sites would be maintained after solubilization. [3H]PK 11195 (0.05 to 10 nM) bound with high affinity to rat, guinea pig, calf, and cat kidney solubilized preparations yielding maximal numbers of binding sites (Bmax) of 3,593 +/- 381, 25,645 +/- 1,795, 1,327 +/- 141, and 2,446 +/- 148 fmol/mg protein, respectively, and equilibrium dissociation constant (KD) values of 1.74 +/- 0.18, 2.15 +/- 0.15, 0.85 +/- 0.09, and 1.02 +/- 0.06 nM, respectively. On the other hand, the respective Bmax and KD values for [3H]Ro 5-4864 (1.25 to 40 nM) were 2,688 +/- 275, 14,182 +/- 1,134, 144 +/- 23 and 205 +/- 17 fmol/mg protein (about 75, 55, 11, and 8%, respectively, of that of [3H]PK 11195) and 13.8 +/- 1.5, 14.6 +/- 1.1, 10.6 +/- 1.7, and 19.9 +/- 1.2 nM. Unlabeled Ro 5-4864 was two orders of magnitude more potent in displacing [3H]PK 11195 binding from rat kidney solubilized preparations than from calf kidney solubilized preparations, whereas the potency of unlabeled PK 11195 in displacing [3H]PK 11195 binding from both rat and calf kidney solubilized preparations was almost identical. Analysis of these displacement data revealed that PK 11195 bound to a single population of binding sites (nH approximately equal to 1.0), whereas Ro 5-4864 bound to two populations of binding sites (nH less than 1.0) in both rat and calf kidney solubilized preparations. These results indicate that PBS species differences and heterogeneity observed in membrane-bound binding sites are retained in the soluble state and are probably attributable to variations in the molecular structure of PBS rather than to differences in membrane environment.

Synthesis and evaluation of 11C-PK 11195 for in vivo study of peripheral-type benzodiazepine receptors using positron emission tomography

The biodistribution of 3H-PK 11195, an antagonist of the peripheral-type benzodiazepine receptors, was studied in mice. High accumulations of radioactivity in the heart, lung, spleen, kidney and adrenal were observed after intravenous injection of tracer amounts of 3H-PK 11195 into the mice. The radioactivity in the heart, lung, spleen, kidney and adrenal was significantly decreased by the coadministration of carrier PK 11195, which indicated that PK 11195 specifically binds to the receptors. No radioactive metabolites were observed in the heart, lung and brain 20 min after intravenous administration of 3H-PK 11195. The accumulation of 3H-PK 11195 in the lung was not affected by pretreatment with either alpha-methyl benzylamine or imipramine, suggesting that 3H-PK 11195 specifically binds to the receptors. The ratios of radioactivity of the kidney, adrenal and spleen to blood increased as a function of time, whereas that of the lung and heart rapidly reached to a steady state. 11C-PK 11195 was synthesized by the N-methylation of desmethyl precursor yielding more than 100 mCi with high specific activity (more than 1.4 Ci/mumol). The labeling and purification procedure was completed within 23 min after the end of bombardment (EOB). The 11C-PK 11195 solution for injection seems to have a high potential for the in vivo study of the peripheral-type benzodiazepine receptors in the living human by means of positron emission tomography (PET).

Solubilization of peripheral-type benzodiazepine binding sites from cat cerebral cortex

The present study demonstrates for the first time the solubilization of peripheral-type benzodiazepine binding sites (PBS) from cat cerebral cortex. Of all detergents tested [digitonin, 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonate (CHAPS), Tween 20, deoxycholate, and Triton X-100] in the presence of NaCl, the best solubilization (15% of initial activity) was obtained using 0.5% of the zwitterionic detergent CHAPS plus 2 M NaCl. Specific binding of [3H]PK 11195 to membrane-bound and solubilized PBS was saturable, yielding equilibrium dissociation constants (KD) of 1.3 +/- 0.2 and 1.9 +/- 0.3 nM, respectively, and maximal numbers of binding sites of 1,435 +/- 150 and 980 +/- 126 fmol/mg protein, respectively. The KD value of PK 11195 binding to solubilized PBS obtained from experimental kinetic analysis was 0.95 +/- 0.09 nM. The relative potencies of various compounds (PK 11195, Ro 5-4864, diazepam, flunitrazepam, clonazepam, methyl-beta-carboline-3-carboxylate, and Ro 15-1788) in displacing [3H]PK 11195 specific binding from membrane-bound and solubilized PBS were similar. Most of the solubilized binding activity was destroyed by heating at 60 degrees C for 30 min or by treatment with 2 M guanidinium chloride, which indicates the presence of a protein-binding site in the solubilized preparation. Over 85% of the solubilized binding activity was retained after 1 week at 4 degrees C, which will enable future application of purification procedures without major concern for stability of the material.

Imaging of primary and remote ischaemic and excitotoxic brain lesions. An autoradiographic study of peripheral type benzodiazepine binding sites in the rat and cat

Seven days after unilateral middle cerebral artery occlusion in rats, peripheral type benzodiazepine binding sites (PTBBS), using [3H]PK 11195 as a specific radioligand, were greatly increased in the cortical and striatal regions surrounding the focus of infarction with smaller increases in the ventrolateral and posterior thalamic complexes and in the substantia nigra, all ipsilateral to the occlusion. Similarly, PTBBS increases were observed in the caudate nucleus and entorhinal cortex of cats likewise subjected to prior unilateral occlusion of the middle cerebral artery. Intrastriatal administration of N-methyl-D-aspartate (250 nmol) in the rat resulted in a dramatic ipsilateral increase in PTBBS levels in the striatum and in the deeper laminae of the ipsilateral frontoparietal cortex. Intrastriatal kainic acid administration (12 nmol) also elicited PTBBS increases ipsilaterally in rat striatum and cortex; a bilateral elevation of PTBBS levels was observed in the hippocampus. With all these interventions there existed a good spatial correlation between the PTBBS increase and neuronal loss as assessed either histologically or by the autoradiographic detection of the putative neuronal marker [3H]SCH 23390 (a D1 dopamine receptor ligand). Moreover, a glial proliferation of non-neuronal cells (macrophage and glial cells) was observed in brain regions noted to have increased PTBBS levels. PTBBS autoradiography thus constitutes a suitable technique for the localization of damaged areas in several experimental models of brain injury. PTBBS label not only the primary lesions but also functionally related areas and could further our understanding of phenomena such as partial neuronal loss and diaschisis. The study of PTBBS could be envisaged for the detection, localization and quantification of all neuropathological situations which engender a glial reaction or macrophage invasion and is potentially applicable to both experimental and human subjects, in which both autoradiographic and tomographic approaches could be undertaken.

Binding of [3H]Ro 5-4864 and [3H]PK 11195 to cerebral cortex and peripheral tissues of various species: species differences and heterogeneity in peripheral benzodiazepine binding sites

The binding of [3H]PK 11195 and [3H]Ro 5-4864 to membrane preparations from cerebral cortex and peripheral tissues of various species was studied. [3H]PK 11195 (0.05-10 nM) bound with high affinity to rat and calf cerebral cortical and kidney membranes. [3H]Ro 5-4864 (0.05-30 nM) also successfully labeled rat cerebral cortical and kidney membranes, but in calf cerebral cortical and kidney membranes, its binding capacity was only 3 and 4%, respectively, of that of [3H]PK 11195. Displacement studies showed that unlabeled Ro 5-4864, diazepam, and flunitrazepam were much more potent in displacing [3H]PK 11195 from rat cerebral cortex and kidney membranes than from calf tissues. The potency of unlabeled Ro 5-4864 in displacing [3H]PK 11195 from the cerebral cortex of various other species was also tested, and the rank order of potency was rat = guinea pig greater than cat = dog greater than rabbit greater than calf. Analysis of these displacement curves revealed that Ro 5-4864 bound to two populations of binding sites from rat and calf kidney and from rat, guinea pig, rabbit, and calf cerebral cortex but to a single population of binding sites from cat and dog cerebral cortex. Using [3H]PK 11195 as a ligand, the rank order of binding capacity in cerebral cortex of various species was cat greater than calf greater than guinea pig greater than rabbit greater than dog greater than rat, whereas when [3H]Ro 5-4864 was used, the rank order of binding capacity was cat greater than guinea pig greater than rat greater than rabbit greater than calf greater than dog.

Maximal electroshock increases the density of [3H]Ro 5-4864 binding to mouse cerebral cortex

The effects of chemically and electrically-induced convulsions on the binding of [3H]Ro 5-4864 to peripheral benzodiazepine receptors (PBR) was studied in both peripheral tissues and the central nervous system (CNS). Acute, maximal electroshock (MES) increased the density of PBR in mouse cerebral cortex as evidenced by a 30% increase in the Bmax of this archetypic ligand. These values returned to control levels by 60 minutes after MES treatment. In contrast, thirty and sixty minutes after convulsions induced by Ro 5-4864, strychnine, or pentylenetetrazol, neither the Bmax nor Kd of [3H]Ro 5-4864 binding to mouse cerebral cortical membranes was altered. The increase in [3H]Ro 5-4864 binding to cortex observed 30 minutes after MES was blocked by anticonvulsant doses of phenobarbital, phenytoin and clonazepam. No changes in the characteristics of [3H]Ro 5-4864 binding was observed in cerebellar or hippocampal membranes 30 minutes following acute MES. Further, after long-term MES administration (1 treatment/day, 5 days), no change in PBR density could be detected 30 minutes after the last MES. Finally, while no change in PBR density was noted in the kidneys 30 minutes after the MES, a significant increase in PBR density was seen in the cardiac ventricles. These results demonstrate a selective modulation of PBR density by MES, suggesting that the PBR could be involved in either the generation of seizures or in postictal compensatory processes.

Binding sites for a peripheral type benzodiazepine antagonist ([3H]PK 11195) in human iris

Peripheral-type benzodiazepine binding sites have been characterized on sections of 8 normal human iris/ciliary-body preparations. Saturability was determined at 25 degrees C with [3H] PK 11195 (1 nM) a specific ligand of peripheral type sites. The studies revealed a single class of binding sites for PK 11195 with a nanomolar range affinity (KD = 1.45 nM) and a maximal capacity (Bmax) of 35.5 fmol/mg protein. The displacement potency order of the benzodiazepines tested suggest that these sites belong to the peripheral type: PK 11211 (IC50 = 12 nM) greater than Ro 5-4864 (IC50 = 770 nM) greater than clonazepam (IC50 = 20,000 nM). The present data demonstrate that high affinity binding sites for peripheral type benzodiazepines are present in human iris/ciliary-body. This tissue is therefore a suitable tool for evaluation of the putative functional role of these binding sites.

Labelling of peripheral-type benzodiazepine binding sites in human brain with [3H]PK 11195: anatomical and subcellular distribution

The peripheral-type benzodiazepine binding site, erstwhile characterized in the rodent and feline brain, has now been characterized in post-mortem human brain using [3H]PK 11195. The kinetics and pharmacological properties of the binding of this ligand are similar to peripheral-type benzodiazepine binding sites elsewhere. The potency of RO5-4864 for this site in human brain is close to that seen in ruminant and carnivore tissues but considerably lower than in rodent tissues. The regional distribution of these binding sites would suggest a neuronal rather than a glial localization. [3H]PK 11195 bound in a similar fashion to slide-mounted sections of human brain, thus allowing quantitative studies of the regional distribution of peripheral-type benzodiazepine binding sites to be made. The binding sites were distributed heterogeneously, but were restricted to the grey matter. Highest densities of binding sites were found in forebrain structures. The localization was not limited to any functional system, nor did it resemble any previously described transmitter system. The similarities between peripheral-type benzodiazepine binding sites in human and in feline brain in terms of their pharmacological characteristics and their regional and subcellular distribution suggest that the cat, rather than the rat, may be the better model for studying a possible role for this site in human cerebral function.

Characterization of benzodiazepine receptors in the bovine pineal gland: evidence for the presence of an atypical binding site

Bovine and rat pineal benzodiazepine receptors were characterized using ligands with high affinities for either 'central-type' (CBR) or 'peripheral-type' (PBR) benzodiazepine receptors. The characteristics (Bmax = 83 +/- 10 fmol/mg protein, Kd = 3.88 +/- 0.46 nM) of benzodiazepine receptors in bovine pineal membranes measured with [3H]flunitrazepam (using flunitrazepam to define non-specific binding) were consistent with previously reported values. However, if non-specific binding was defined using Ro 15-1788 (a selective CBR ligand), the Bmax and Kd of [3H]flunitrazepam decreased 51 and 58%, respectively. In addition, when using PK 11195 to determine non-specific binding, the Bmax of [3H]flunitrazepam binding to bovine pineal decreased further (approximately 80%, Kd decreased approximately 39%). Together, these observations strongly suggested the presence of PBR in the bovine pineal. Bovine pineal PBR characterized with [3H]PK 11195 revealed a high density (relative to CBR) of high affinity binding sites (Kd = 1.08 +/- 0.30, Bmax = 776 +/- 33.0 fmol/mg protein). In contrast, when [3H]Ro 5-4864 (1-20 nM) was used to define PBR, no binding was detectable. These observations are in sharp contrast to the rat pineal gland, in which both [3H]Ro 5-4864 and [3H]PK 11195 bind to a large number of PBR with high affinity (Kd approximately equal to 1.9 nM, Bmax approximately equal to 26 pmol/mg protein). Bovine pineal PBR were further characterized with compounds structurally related to either Ro 5-4864 or PK 11195.(ABSTRACT TRUNCATED AT 250 WORDS)

3H-nicotine and 125I-alpha-bungarotoxin-labeled nicotinic receptors in the interpeduncular nucleus of rats. I. Subnuclear distribution

The distribution of nicotinic receptors within the interpeduncular nucleus (IPN) was determined in male rats following in vitro labeling with the cholinergic ligands 3H-nicotine and 125I-alpha-bungarotoxin (BTX). Autoradiographic images of two rostrocaudal levels of IPN were analyzed by computer-assisted densitometry and the optical density contributed by displaceable labeling was determined in the rostral, central, intermediate, and lateral subnuclei. 3H-nicotine labeling density within the four subnuclei differs significantly at both levels of IPN. The greatest density of labeling is localized in the rostral subnucleus, followed in order of diminishing density by the central, intermediate, and lateral subnuclei. Labeling within the rostral subnucleus is prominently localized within its central zone. In the central subnucleus, a dense concentration of binding sites is apparent in the middle region, adjacent to less dense vertically oriented columns; 3H-nicotine binding sites in the lateral subnuclei appear to be most concentrated medially, adjacent to the intermediate subnuclei. 125I-BTX labeling density within the four subnuclei also differs significantly at both levels of IPN. The greatest density of labeling is found in the rostral subnucleus, followed in order of decreasing density by the lateral, central, and intermediate subnuclei. The ovoid regions of the rostral subnucleus contain dense 125I-BTX labeling. In the lateral subnuclei, 125I-BTX binding appears to be predominantly along the lateral margins of the subnucleus. The present data indicate that the IPN contains two distinct populations of putative cholinergic nicotinic receptors identified, respectively, by 3H-nicotine and 125I-BTX labeling. Each population of labeled receptors is uniquely localized in patterns that suggest differences in density within and across subnuclei.

'Peripheral' benzodiazepine binding sites in human brain and kidney: autoradiographic studies

Benzodiazepine (BZ) recognition sites of the 'peripheral' type were localized autoradiographically in human postmortem brain and kidney using [3H]Ro 5-4864. These sites presented a relatively homogeneous distribution. Areas such as the ependyma, choroid plexus and olfactory bulb, which in the rat are very rich in these binding sites, presented densities in the human brain which were about 1/10 of those seen in the rat. Human tissues presenting gliosis, such as the hippocampi from senile dementia patients, did not show a clear increase in the number of [3H]Ro 5-4864 sites, in contrast with the high densities found in rat brain areas presenting neurotoxin-induced gliosis. Intermediate densities of binding were seen in a human glioblastoma tumor. The human kidney also showed lower densities of peripheral BZ binding sites, when compared to the rat kidney. These results indicate that marked species differences exist in the densities of peripheral BZ sites and that caution has to be exerted when extrapolating data from the experimental animal to human.

Evidence for species differences in 'peripheral' benzodiazepine receptors: an autoradiographic study

The presence, density and distribution of 'peripheral' benzodiazepine (BZ)-binding sites was investigated by autoradiography in the brains of rats, mice, guinea pigs and cats and in some areas of the dog and monkey brains, using [3H]Ro 5-4864 as a ligand. Marked interspecies differences were found in the distribution and densities of these sites. Rats and mice presented a low density of binding uniformly distributed throughout the brain with high densities concentrated in the ependyma, choroid plexus and olfactory nerve layer of the olfactory bulb. In contrast, guinea pig and cat brains presented relatively high concentrations of peripheral BZ binding sites throughout the grey matter ependyma and choroid plexus, but low in the olfactory bulb. Monkey and dog brains presented low densities of peripheral BZ binding sites, including the choroid plexus.

Differential sensitivity of "central" and "peripheral" type benzodiazepine receptors to phospholipase A2

The effects of preincubating cerebral cortical membranes with phospholipase A2 (PLA2) were examined on radioligand binding to benzodiazepine receptors of the "central" and "peripheral" types. PLA2 (0.005-0.1 U/ml) increased [3H]flunitrazepam and [3H]3-carboethoxy-beta-carboline binding by increasing the apparent affinities of these ligands with no concomitant change in the maximum number of binding sites. In contrast, neither gamma-aminobutyric acid (GABA)-enhanced [3H]flunitrazepam binding nor [3H]Ro 15-1788 binding was altered by preincubation with PLA2 at concentrations as high as 2 U/ml. Both pyrazolopyridine (SQ 65,396)- and barbiturate (pentobarbital)-enhanced [3H]flunitrazepam binding and [35S]t-butylbicyclophosphorothionate (TBPS) binding were markedly reduced by as little as 0.0025-0.005 U/ml of PLA2. These findings suggest that PLA2 inactivates the TBPS binding site on the benzodiazepine-GABA receptor chloride ionophore complex, which results in a selective loss of allosteric "regulation" between the components of this complex. PLA2 also reduced the apparent affinity of [3H]Ro 5-4864 to peripheral-type benzodiazepine receptors in cerebral cortical, heart, and kidney membranes, but increased the number of [3H]PK 11195 binding sites with no change in apparent affinity. These data demonstrate that PLA2 can differentially affect the lipid microenvironment of "central" and "peripheral" types of benzodiazepine receptors.

Subcellular localization of "peripheral-type" binding sites for benzodiazepines in rat brain

The binding of [3H]Ro 5-4864, a specific ligand for "peripheral-type" benzodiazepine binding sites and [3H]Ro 15-1788, a specific ligand for the central benzodiazepine receptors, was determined in subcellular fractions of rat brain. As previously reported, the highest levels of "peripheral-type" benzodiazepine binding sites and benzodiazepine receptors were found in the crude P1 and P2 fractions, respectively. Purification of these crude fractions revealed that high levels of both [3H]Ro 5-4864 and [3H]Ro 15-1788 binding were present in the mitochondrial and synaptosomal fractions. In contrast, the purified nuclei and myelin contained low levels of both [3H]Ro 5-4864 and [3H]Ro 15-1788 binding.