Gonadal regulation of GABAA receptors in the different brain areas of the male Japanese quail

Summary Quantitative autoradiography was used to investigate the distribution and effects of gonadal hormones on [³H] muscimol (specific GABA_A receptor ligand) binding in the male Japanese quail brain. In gonadally intact Japanese quail brains, [³H] muscimol revealed a heterogeneous distribution with high GABA_A receptor levels in the cerebellum pars granularis (656 fmol/mg wet weight of tissue) and in the pars molecularis (405 fmol/mg wet weight of tissue). Low receptor levels were found in the nucleus preopticus anterior and the nucleus lateralis of the hypothalamic regions (<220 fmol/mg wet weight of tissue) as well as thalamic nuclei such as rotundus and pretectalis (220–261 fmol/ mg wet weight of tissue). Castration resulted in [³H] muscimol binding changes in both brain areas that contain steroid receptors and brain areas devoid of steroid receptors. In fact, castration led to high binding levels in the preopticus anterior nucleus and in the anterior neostriatum area, brain areas that are known to contain gonadal steroid receptors. Castration also elevated [³H] muscimol binding in the hyperstriatum ventrale and reduced binding levels in the paleostriatum augmentatum and the stratum griseum centrale area; all of these areas are known to be devoid of gonadal steroid receptors. At this point it was also important to know whether the gonadal steroid effect is due to alterations in the number of binding sites (B_max) and/or the affinity binding state (K_D). The saturation binding study, dealing with some of the areas described above in brains of male quails castrated or castrated and treated with testosterone or estradiol, demonstrated that the steroid replacement therapy was responsible for the changes of the B_max. Diminishing B_max values were displayed in the hypothalamic preoptic area and the hyperstriatum ventrale of the male quail treated with testosterone and estradiol while a reduced B_max was obtained in the anterior neostriatum of the quail treated with the former steroid. Our findings suggest that these steroids might control some centrally mediated behavior activities through effects on the maximum number of GABA_A binding sites in the male Japanese quail.     

Evidence for GABAB-receptors on cultured astrocytes of rat CNS: autoradiographic binding studies

Summary The cellular localization of GABA-binding sites was studied in explant cultures of rat cerebellum, brain stem and spinal cord by means of autoradiography. Labelling of GABA_B-sites was done with ³H(-)baclofen or ³H-GABA in presence of unlabelled bicuculline. Binding sites for these radio-ligands were found on many neurones and on a large number of astrocytes. Labelling of glial cells was usually weaker than that of neurones. Combining autoradiography with staining with anti-glial fibrillary acidic protein (GFAP) revealed that the glial cells labelled with ³H-baclofen or ³H-GABA were GFAP-positive. In contrast, when GABA_A-sites were localized using ³H-GABA in presence of unlabelled baclofen, the GABA_A-agonists ³H-muscimol and ³H-THIP, or the antagonist ³H-(+)-bicuculline, binding only occurred to neurones but not to astrocytes. Immunohistochemical investigations with the monoclonal antibody (bd-17) against the GABA_A/benzodiazepine/chloride channel complex revealed that neurones were specifically stained whereas glial cells were immunonegative. From our observations it is suggested that astrocytes possess GABA_B-receptors but there is little evidence for the existence of GABA_A-sites on glial elements.     

Characterization of coexistent histamine H1- and H2-receptor binding sites in the purified guinea pig myocardial membranes from ventricles

In the present work, we identified and characterised histamine H1-and H2-receptors in highly purified myocardial membranes isolated from female guinea pig ventricles. We determined the binding parameters for the interactions of³H-mepyramine with the histamine H1-receptor binding site and³H-tiotidine with the histamine H2-receptor binding site. Binding of both ligands in our study was saturable, reversible and of high affinity. Scatchard's analysis of the specific³H-mepyramine binding revealed the existence of high and low affinity binding sites with apparent K_D values of 0.4 nM and 4.5 nM, respectively. The density of binding sites (B_max) was 100 fmol/mg protein for the high and 466 fmol/mg protein for the low affinity binding site.³H-tiotidine binds to a single population of binding sites with a K_D of 1.0 nM and a B_max of 27 fmol/mg protein. These data suggest that both histamine H1-and H2-receptors coexist in the guinea pig myocardium with a significantly higher prevalence of the histamine H1-receptor population.     

3H-Mepyramine binding and histamine-stimulated cAMP accumulation in mammalian retina

The specific binding of different amounts of³H-mepyramine to the bovine retina revealed a quasi-hyperbolic curve which approached saturation at³H-ligand concentration over 9–12 nM. Scatchard analysis of the binding data showed two binding sites with K_D values of 0.76 nM and 7.3 nM and B_max of 49.3 and 194.6 fmole/mg protein, respectively. In the guinea-pig brain³H-mepyramine bound to a single population of binding sites with K_D value of 1.6 nM and B_max of 291 fmole/mg protein. Various H₁-antihistamines were potent competitors of the³H-mepyramine binding: there was a big difference in potency of d- and 1-chlorpheniramine in both membrane preparations.In the rabbit retina slices histamine, in contrast to dopamine, weakly stimulated cAMP accumulation.The data suggest that the mammalian retina may possess histamine receptors.     

Localisation of dopamine D3 receptor in the rat cerebellar cortex: a light microscope autoradiographic study

The pharmacological properties and the anatomical localisation of dopamine D₃ receptor were assessed in the rat cerebellar cortex using radioligand binding techniques associated with light microscope autoradiography and 7-[³H]hydroxy-N,N-di-n-propyl-2-aminotetralin (7-[³H]OH-DPAT) as a ligand. 7-[³H]OH-DPAT was specifically bound to sections of rat cerebellar cortex with a dissociation constant (K_d) of 0.5 nM and a maximum density of binding sites (B_max) of 97 ± 4 fmol/mg tissue. The rank order of potency of competitors of 7-[³H]OH-DPAT binding and the observation that guanosine triphosphate did not affect radioligand binding suggest the labelling of a dopamine D₃ receptor. 7-[³H]OH-DPAT binding sites are located mainly in the molecular layer and in lesser amounts in the Purkinje neuron layer, primarily within the cell body of Purkinje neurons. No specific accumulation of silver grains was observed in the granule neuron layer or in the white matter of the cerebellar cortex. The localisation of a putative dopamine D₃ receptor within Purkinje neurons suggests that this site may have functional relevance in the cerebellar cortex.     

Characterisation of histamine-H1 receptor binding sites in bovine, rat and guinea pig thoracic aorta

Radioligand binding studies elucidating the localization of vascular histaminergic-H₁ receptors using³H-mepyramine demonstrate that, in addition to histaminergic-H₁ receptors associated with the vascular smooth muscle membranes of bovine thoracic aorta, these receptor binding sites are also present on the endothelial layer of bovine aorta. The receptor number in the vascular smooth muscle membranes was diminished when the aorta was rubbed of endothelium prior to the membrane preparation (B_max=58.5 vs 53.7 fmol/mg protein). As shown in a further study, vascular smooth muscle histamine receptors are homogeneous (high affinity sites only — K_D=3.11 nM), whereas high and low affinity sites exist in the endothelium (K_D=2.19 nM and 32.0 nM respectively).There are species differences in the binding characteristics between bovine, rat and guinea pig vascular smooth muscle histaminergic-H₁ receptors: bovine and guinea pig vascular histamine receptors are homogeneous (high affinity sites) whereas two affinity sites for³H-mepyramine binding exist in the rat.     

Localization and quantification of [125I]-endothelin binding sites in human fetal and adult kidneys — Relevance to renal ontogeny and pathophysiology

Summary Endothelins, 21 amino acid peptides, produced by endothelial cells are potent vasoconstrictors and mitogens. According to experimental studies in animals, endothelins seem to be involved in the regulation of renal hemodynamics. In order to gain insight into its potential effects in man, a quantitative analysis of its binding sites was performed in human kidneys. Because of the proliferative action of endothelin in cell culture we also compared binding sites in fetal and adult kidneys. Binding sites for [¹²⁵I]-endothelin-1,2,3 were visualized by in-vitro autoradiography and quantified by densitometry. In both adult and fetal tissue, specific binding sites occurred in the cortex, medulla, and renal vessels. Unlabeled endothelins and sarafotoxin, a peptide with a high sequence homology to endothelins, inhibited [¹²⁵I]-endothelin-1 binding with IC₅₀ in the 9.8 to 0.023 nM range, whereas unrelated peptides (angiotensin II, atrial natriuretic peptide) and the calcium antagonist nitrendipine failed to compete for [¹²⁵I]-endothelin-1 binding sites. Linear Scatchard analysis revealed that the number of binding sites (expressed per tissue equivalent: TE) were consistently higher in fetal than in adult kidneys, while affinities did not differ significantly in cortex, medulla, and vessels (fetal/adult: cortex K_D 43.4±19.6/55.9±16.7 nM; B_Max13.5±7.8/2.7±1.3 fmol/mg TE; medulla K_D 26.3±10.9/34.6±7.4 nM; B_Max 10.1±0.9/ 3.7±1.1 fmol/mg TE; vessels K_D 41.1±22.9/ 23.7±8.1 nM; B_Max 12.9±3.9/4.1±1.2 fmol/mg TE). Medullary capillaries and veins showed strong binding in human and rat kidneys which may be important for the pathophysiology of acute renal failure. Human adult and fetal glomeruli had only a few binding sites. This contrasts to findings in the rat kidney in which glomeruli have a high concentration of endothelin binding sites; although this does not role out an influence per se, it does point out the need to subject the assumption of a relevant glomerular effect of endothelin in man to closer scrutiny. The diffuse and strong binding in fetal kidney may indicate a role for endothelin in the process of renal maturation.Abbreviations ET Endothelin - TE Tissue equivalent This work is dedicated to Prof. Dr. med. F. Scheler, head of the Department of Nephrology, University Hospitals, Göttingen on the occasion of his 65th birthday.     

Taurine-transporter gene knockout-induced changes in GABA(A), kainate and AMPA but not NMDA receptor binding in mouse brain

The aim of this study was to determine whether the knockout of the taurine-transporter gene in the mouse affects the densities of GABA_A, kainate, AMPA and NMDA receptors in the brain. The caudate-putamen, the hippocampus and its subregions, and the cerebellum of six homozygous taurine-transporter gene knockout mice and six wild-type (WT) animals were examined by means of quantitative receptor autoradiography. Saturation studies were carried out for all four receptor types in order to find possible intergroup differences in B _max and K _D values. Taurine-transporter gene knockout animals showed significantly higher GABA_A receptor densities in the molecular layer of the hippocampal dentate gyrus and in the cerebellum than did WT animals. The densities of kainate receptors were significantly higher in the caudate-putamen, the CA1 and hilus regions of the hippocampus and in the cerebellum of knockout animals. The caudate-putamen and cerebellum of these mice also contained significantly higher AMPA receptor densities. However, there were no significant differences between knockout and WT animals concerning the densities of NMDA receptors. Reduced brain taurine levels are associated with increased GABA_A, kainate and AMPA receptor densities in some of the regions we examined.     

Retinal [I]iodomelatonin binding sites in the tree shrew (Tupaiidae)

The characteristics of melatonin-binding sites labelled by [¹²⁵I]iodomelatonin in membrane preparations from the tree shrew retina were determined. Specific binding of [¹²⁵I]iodomelatonin to the membrane preparations of tree shrew retina was rapid, stable, saturable, and reversible. Among the indoles tested only 6-chloromelatonin, melatonin and N-acetylserotonin had significant affinities to the [¹²⁵I]iodomelatonin binding site. Scatchard analysis of the membrane preparations revealed a dissociation constant (K_d) of 51.0 ± 16 pM and total number of binding sites (B_max) of 1.97 ± 0.6 fmol/mg protein.     

Differential localization of GABA-dependent and GABA-independent benzodiazepine binding sites within synapses of rat cerebral cortex

Fractions containing non-junctional membranes (fraction 1) could be separated from those enriched in junctional complexes (fraction 2) by sucrose gradient centrifugation of osmotically disrupted rat cerebral cortex synaptosomes. [³H]flunitrazepam binding sites were found to be homogeneous characterized by K_d = 0.65 nM, B_max = 13 pM for fraction 1; and K_d = 2 nM, B_max = 45 pM for fraction 2. GABA-dependent benzodiazepine receptor sites were found to be localized to the junctional complex fraction, while non-junctional membranes showed GABA-independent receptor and acceptor binding sites.     

Alterations in platelet alpha2-adrenoceptors by aspirin

Epinephrine-induced platelet aggregation (mediated through interaction with alpha₂-adrenoceptors) is inhibited by aspirin. To determine if aspirin modulates alpha₂-adrenoceptors, we quantitated dissociation constant (K_D) and maximum number of binding sites (B_max) on isolated platelet membranes using alpha₂-antagonist³H-yohimbine in normal subjects given 650 mg of aspirin orally. Alpha₂-receptor K_D increased from 3.20±1.80 to 7.32±3.32 nM (p<0.02) and B_max from 115±77 to 190±140 fmol/mg protein. To determine if these alterations in alpha₂-receptors by aspirin were mediated through circulatory or intracellular effects, intact platelets or isolated platelet membranes were incubated with aspirin for 30 minutesin vitro. In thesein vitro experiments, alpha₂-receptor K_D increased from 2.92±1.76 to 9.83±8.55 nM and B_max from 140±81 to 191±129 fmol/mg protein (p<0.05). Oral ingestion of aspirin or incubation of aspirin with intact platelets or lysates increased (3 to 10 fold) the concentration of 1-epinephrine required for inhibition, of³H-yohimbine binding by 50% (p<0.05). Basal platelet cyclic AMP as well as its elevation with PGE₁ or PGI₂ and decrease with catecholamines were not influenced by aspirin treatment of platelets. These data indicate that aspirin decreases platelet alpha₂-receptor affinity for agonist as well as antagonist. These effects of aspirin are independent of circulatory or dynamic intraplatelet changes.     

Laminar distribution of neurotransmitter receptors in different reeler mouse brain regions

Mapping of multiple receptors of neurotransmitters provides insight into the spatial distribution of neurotransmission-relevant molecules in the cerebral cortex. During development, lack of reelin leads to impaired migration, disturbed lamination of the hippocampus and inverted neocortical layering. In the adult, reelin may regulate synaptic plasticity by modulating neurotransmitter receptor function. Using quantitative in vitro receptor autoradiography, different receptors, in particular, the binding site densities and laminar distribution of various glutamate, GABA, muscarinic and nicotinic acetylcholine, serotonin, dopamine and adenosine receptors, were analyzed in cortical and subcortical structures of reeler and wild-type brains. Differential changes in the laminar distribution, maximum binding capacity (B _max) and regional density of neurotransmitter receptors were found in the reeler brain. A decrease of whole brain B _max was found for adenosine A₁ and GABA_A receptors. In the forebrain, several binding sites were differentially up- or down-regulated (kainate, A₁, benzodiazepine, 5-HT₁, M₂, α₁ and α₂). In the hippocampus, a significant decrease of GABA_B, 5-HT₁ and \textA₁^￠ {\text{A}}_1^{\prime} receptors were observed. The density of M₂ receptors increased, while other receptors remained unchanged. In the neocortex, some receptors demonstrated an obviously inverted laminar distribution (AMPA, kainate, NMDA, GABA_B, 5-HT₁, M₁, M₃, nAch), while the distribution of others (A₁, GABA_A, benzodiazepine, 5-HT₂, muscarinic M₂, adrenergic α₁, α₂) seemed to be less affected. Thus, the laminar receptor distribution is modulated by the developmental impairment and suggests and reflects partially the laminar inversion in reeler mice.     

Oocytes from Xenopus laevis contain an intrinsic σ2-like binding site

In preparation for expression studies for rat brain σ-binding sites, Xenopus oocytes were tested for the presence of [³H]di-o-tolylguanidine (DTG)-binding sites. Native oocytes were found to contain two intrinsic [³H]DTG-binding sites, a high-affinity site (K_d = 32 ± 6 nM, B_max of 45.7 ± 19 pmol/mg protein) and a low-affinity binding site (K_d = 1.3 ± 0.7 μM, B_max of 3.2 ± 0.7 nmol/mg protein). In a series of radioligand-binding-displacement studies, the high-affinity binding sites were found to have a binding profile which has a similar K_d to that of the mammalian σ₂-binding site (32 vs. 38 nM). Comparison of the IC₅₀ values for inhibition of [³H]DTG binding in rat liver and oocytes for DTG, haloperidol (HAL), (−)-pentazocine, (+)-3-(3-hydroxyphenyl)-N-propylpiperidine hydrochloride ((+)-3-PPP), (+(-pentazocine and Zn²⁺, showed similarity in rank (r² = 0.913) but a 7-fold lower potency in oocytes. These results suggest that the high-affinity [³H]DTG-binding site in oocytes represents a σ₂-like binding site.     

Taurine-transporter gene knockout-induced changes in GABAA, kainate and AMPA but not NMDA receptor binding in mouse brain

The aim of this study was to determine whether the knockout of the taurine-transporter gene in the mouse affects the densities of GABA_A, kainate, AMPA and NMDA receptors in the brain. The caudate-putamen, the hippocampus and its subregions, and the cerebellum of six homozygous taurine-transporter gene knockout mice and six wild-type (WT) animals were examined by means of quantitative receptor autoradiography. Saturation studies were carried out for all four receptor types in order to find possible intergroup differences in B _max and K _D values. Taurine-transporter gene knockout animals showed significantly higher GABA_A receptor densities in the molecular layer of the hippocampal dentate gyrus and in the cerebellum than did WT animals. The densities of kainate receptors were significantly higher in the caudate-putamen, the CA1 and hilus regions of the hippocampus and in the cerebellum of knockout animals. The caudate-putamen and cerebellum of these mice also contained significantly higher AMPA receptor densities. However, there were no significant differences between knockout and WT animals concerning the densities of NMDA receptors. Reduced brain taurine levels are associated with increased GABA_A, kainate and AMPA receptor densities in some of the regions we examined.     

Characterization of subtypes of gamma-aminobutyric acid receptors in an Ascaris muscle preparation by binding assay and binding of PF1022A,a new anthelmintic,on the receptors

 We examined the effect of PF1022A, one of the gabergic anthelmintics newly developed in Japan, on gamma-aminobutyric acid (GABA) receptors using a radioligand binding technique in isolated membrane preparations of the nematode Ascaris suum. Membrane protein was prepared from the homogenate of somatic muscle cells after ultracentrifugation. In addition to the basic binding of [2,3-³H-(N)]-GABA, the radioligand [methyl-³H]-bicuculline is used to identify the GABA_A receptor, whereas [butyl-4-³H]-baclofen is employed for GABA_B receptor sites. The dissociation constants (K _d values) and the maximal numbers of binding sites (B_max values) from Scatchard plotting for GABA receptors are close to those obtained in mammalian brain. PF1022A displaced in a concentration-dependent way the binding of [2,3-³H(N)]-GABA and [methyl-³H]-bicuculline as did other specific gabergic agents. In addition, PF1022A decreased the binding of [butyl-4-³H]-baclofen at a higher concentration, although this binding did not represent GABA_B sites. In a comparison of the inhibition constants (K_i values) of PF1022A with those of other agents, it is conclusive that PF1022A bound with GABA receptors. A direct effect of PF1022A on GABA receptors can thus be postulated. Received: 10 March 1995 / Accepted: 27 June 1995     

Galanin receptors and their second messengers in the lumbar dorsal spinal cord

The ligand binding properties of galanin receptors were examined in crude synaptosomal fraction preparations of lumbar dorsal spinal cord, using chloramin-T mono-iodinated porcine Tyr²⁶ galanin as ligand. The equilibrium binding of [¹²⁵I]galanin showed the presence of a single population of high-affinity binding sites with K_D= 0.6±0.2 nM in a concentration of 55±15 fmol mg^-1 protein (B_max. The N-terminal fragments galanin (1–16) and galanin (1–12) fully displaced specific [¹²⁵1]galanin binding from membranes with IC₅₀ values 6 nM and 4 μM, respectively. The C-terminal fragment galanin (17–29) did not displace [¹²⁵I]galanin when applied in the concentration range 10^-11–10^-4 M. GTP inhibited the specific binding of [¹²⁵I] galanin in a concentration dependent manner, with 54% inhibition at 1 mM, suggesting that the galanin receptor found in lumbar dorsal spinal cord is G-protein coupled. Second messenger systems, through which the galanin receptor in lumbar dorsal spinal cord may exert its effect, were also studied. A galanin (10,μm) produced inhibition (58%) of the depolarization induced cGMP increase was found, whereas galanin (10 μM) did not inhibit the noradrenalin (100 μM) activated CAMP synthesis or phosphoinositide turnover in tissue slices of the spinal cord. Bilateral transection of the sciatic nerve at midthigh level 14 days prior to the binding experiment was performed, a treatment which is known to cause a dramatic increase of galanin-like immunoreactivity in the superficial layers of the dorsal spinal cord, dorsal root ganglion and in galanin mRNA levels, but no significant effect on B_max or K_D of the galanin receptor was found.     

3H-Ouabain binding sites in porcine skeletal muscle as influenced by environmental temperature and energy intake

The influence of environmental temperature and energy intake on³H-ouabain binding sites in skeletal muscle has been investigated in young growing pigs at 8 weeks of age. Animals lived for several weeks at 35 or 10°C on a high (H) or low (L) level of energy intake. The four treatment groups were thus: 35H, 35L, 10H and 10L. The total number of³H-ouabain binding sites (B _max) in longissimus dorsi muscle (mean values ± SEM) were 221±66, 214±61, 350±76 and 486±114 pmol/g wet weight for the 35H, 35L, 10H and 10L groups respectively.B _max was significantly greater in those living in the cold than the warm (P<0.001). Moreover, at 10°C energy intake had a significant effect, withB _max being greater in the 10L than the 10H group (P<0.005). Level of energy intake had no influence onB _max at 35°C. The apparent dissociation constant was not affected by either temperature or intake. The elevatedB _max and hence the increase in number of Na⁺, K⁺-pumping sites in the cold is probably related to increased muscular activity associated with shivering. However, thyroid status also influences the number of Na⁺, K⁺-pumping sites and this may have been a contributory factor in the present study. In addition, the elevatedB _max suggests a greater potential for non-shivering thermogenesis associated with increased Na⁺, K⁺-ATPase concentration in the cold. Differences in relative stage of development between the four groups may help to explain the results forB _max in relation to level of energy intake.     

Increases of kinin B1 and B2 receptors binding sites after brain infusion of amyloid-beta 1-40 peptide in rats

Although numerous inflammation pathways have been implicated in Alzheimer's disease, the involvement of the kallikrein–kinin system is still under investigation. We anatomically localized and quantified the density of kinin B₁ and B₂ receptors binding sites in the rat brain after the infusion of amyloid-β (Aβ) peptide in the right lateral brain ventricle for 5 weeks. The conditioned avoidance test showed a significant reduction of memory consolidation in rats infused with Aβ (68.6 ± 20.9%, P < 0.05) when compared to control group (90.8 ± 4.1%; infused with vehicle). Autoradiographic studies performed in brain samples of both groups using [¹²⁵I]HPP-[des-Arg¹⁰]-Hoe-140 (150 pM, 90 min, 25 °C) showed a significant increase in density of B₁ receptor binding sites in the ventral hippocampal commissure (1.23 ± 0.07 fmol/mg), fimbria (1.31 ± 0.05 fmol/mg), CA1 and CA3 hippocampal areas (1.05 ± 0.03 and 1.24 ± 0.02 fmol/mg, respectively), habenular nuclei (1.30 ± 0.04 fmol/mg), optical tract (1.30 ± 0.05 fmol/mg) and internal capsule (1.26 ± 0.05 fmol/mg) in Aβ group. For B₂ receptors ([¹²⁵I]HPP-Hoe-140, 200 pM, 90 min, 25 °C), a significant increase in density of binding sites was observed in optical tract (2.04 ± 0.08 fmol/mg), basal nucleus of Meynert (1.84 ± 0.18 fmol/mg), lateral septal nucleus – dorsal and intermediary portions (1.66 ± 0.29 fmol/mg), internal capsule (1.74 ± 0.19 fmol/mg) and habenular nuclei (1.68 ± 0.11 fmol/mg). In control group, none of these nuclei showed [¹²⁵I]HPP-Hoe-140 labeling. This significant increase in densities of kinin B₁ and B₂ receptors in animals submitted to Aβ infusion was observed mainly in brain regions related to cognitive behavior, suggesting the involvement of the kallikrein–kinin system in Alzheimer's disease in vivo.     

Glucose and Cyclic Adenosine Monophosphate Stimulate Activities of Adenylate Cyclase and Guanylate Cyclase of Tetrahymena Pyriformis Infusoria

The sensitivities of cyclase enzymes adenylate cyclase and guanylate cyclase to glucose and extracellular cAMP were studied in Tetrahymena pyriformis infusoria. Glucose effectively stimulated activities of both cyclase enzymes, while cAMP more effectively stimulated adenylate cyclase. It was shown that [6-¹⁴C]glucose specifically bound to Tetrahymena pyriformis infusoria at dissociation constant (KD) and number of binding sites (B_max) 43 nM and 7.53 fmol glucose per 100,000 cells and [8-³H]cAMP bound at 19 nM and 4.46 fmol cAMP per 100,000 cells, respectively. Hence, glucose and cAMP specifically bound to Tetrahymena pyriformis cells and stimulated activities of cyclases in these infusoria.     

The effect of phencyclidine on [3H]GABA and [3H]fulnitrazepam binding in the brain of naive and handling-habituated rats

The effects of handling and handling combined with phencyclidine (PCP) treatment on GABAergic neurotransmission were studied in Sprague-Dawley rats. The animal material consisted of handling-habituated (HH, for 11 d), acutely handled (naive, N), handling-habituated and PCP-treated (10 mg kg^-1 i. p., HH+PCP) and acutely handled (naive) PCP-treated (N+PCP) and unhandled ‘control’ rats. The binding of [³]GANA and [³H]flunitrazepam (FLU) was studied with membrances and the release of [³H]GABA with slices prepared from the striatum and frontal cortex. In the striatum the maximal binding capacity (B_max) and the binding constant (K_D was lower in N rats. K_D constants of [³H]FLU were significantly lower in both brain areas in N rats than in HH rats. After PCP treatment both B_max and K_D for [³H]GAGA diminished. Neither handlign nor PCP had any effect on [³H]GABA release from striatal and frontal cortical slices. Handling prior to killing thus affects differently the GABAergic parameters studied and modulates the PCP-induced effects