Library

Notes: Summary Dopamine receptors subtypes were studied in homogenates from rat brain areas, mainly the corpus striatum, using the two highly selective ligands 3H-apomorphine and 3H-domperidone. The clearly biphasic inhibition of the specific binding of these two ligands by some agents allowed us to define four distinct classes of binding site. 3H-apomorphine labels two classes of site displaying a large difference in affinity for domperidone, i.e. class I sites well recognized (IC50=5 nM) and class II sites poorly recognized (IC50=10 μM). 3H-domperidone also labels two distinet classes of site displaying a large difference in affinity for apomorphine and dopamine, i.e. class III sites well recognized by these agents (IC50=5 and 35 nM, respectively) and class IV sites poorly recognized (IC50=790 nM and 14 μM, respectively). The two classes I and III represent a single pharmacological class of dopaminergic receptors (labelled by either 3H-apomorphine or 3H-domperidone) as indicated by 1) their almost identical pharmacological specificities (high correlation between K d or K i values for a variety of dopaminergic agonists and antagonists); 2) their similar capacity in striatum as well as in other brain regions; 3) the identical decrease in capacity following kainate lesions; 4) their similar sensitivity to GTP and thermal denaturation. Because the pharmacological specificity of these sites excludes the possibility that they represent the recognition sites of the dopamine-sensitive adenylate cyclase, i.e. D-1 receptors, we propose to term them D-2 receptors. Class II and IV sites also differ from D-1 receptors as shown by drug specificity and the effect of kainate. We propose to term class II sites D-3 receptors and class IV sites D-4 receptors. D-2 receptors are characterised by a high affinity for both dopamine receptor agonists and antagonists (K i and K d values in the nM range). They are localised post-synaptically to dopaminergic terminals in the striatum as indicated by 1) their decreased number (−60%) following kainate lesions of intrinsic neurones, and 2) their increased number (+40%) after 6-OHDA-induced degeneration of dopaminergic neurones. The capacity of D-2 receptors is decreased by 80% in the presence of 25 μM GTP. The binding of ligands to D-2 receptors preicubated at 45°C decreases with a half-life of 10 min. D-2 receptors may mediate behavioral actions of apomorphine in low dosage which are easily antagonised by neuroleptics. D-3 receptors appear to be, at least in part, autoreceptors: their number decreases in striatum after 6-OHDA lesions (−30%) and is not modified following kainate lesions. They are characterised by a high affinity (K i in the nM range) for dopaminergic agonists (except for bromocriptine) contrasting with a rather low affinity for antagonists. The pharmacologically homogeneous class of D-3 receptor appears heterogeneous regarding both localisation and regulation by GTP. D-4 receptors are partly localised on intrastriatal neurones (−17% after kainate lesions, +17% following 6-OHDA lesions). However, the small change after kainate-induced lesions suggests that a significant fraction of D-4 receptors is localised on terminals from extrinsic neurones. D-4 receptors are characterised by a high affinity for dopamine receptor antagonists (K i in the nM range) contrasting with a relatively low affinity for agonists. The number of D-4 receptors increases after either GTP or heat denaturation, a change which probably corresponds to the decrease in D-2 receptors. D-4 receptors may mediate typical behavioral actions of apomorphine in moderate dosage.

Notes: Summary The experimental conditions allowing to elicit by administration of dopamine agonists a climbing behavior in rats, apparently analogous to the stereotyped cage climbing behavior previously described in mice (Protais et al. 1976), have been established. Among the various strains of rats studied i.e. Sprague-Dawley, Long Evans and Wistar, the latters were selected as the most responsive to the dopamine agonist apomorphine. However, even in the Wistar strain, only about 60% of animals responded to a test-dose of 0.4 mg/kg apomorphine by adopting in a sustained manner the typical upright position against the walls of a suitable experimental cage. Hence responsive rats were preselected 4 days before the experimental sessions and finally rated during a 60-min observation period. Increasing the test-dose of apomorphine led to a biphasic effect, the spontaneous climbing behavior being decreased at low dosage and, then, both the percentage of climbing animals and the duration of the behavior were progressively increased at higher dosages. A scoring system based on an all-or-none evaluation of the frequency of stereotyped climbing episods over the 1 h observation period was finally adopted allowing to establish dose response curves to apomorphine and its more potent derivative N-propylnorapomorphine. Dexamphetamine (associated to L-Dopa) also produced the stereotyped climbing behavior. The latter was completely abolished in animals treated with the “atypical” antipsychotic sulpiride. The effects of lesioning various cerebral dopaminergic areas on the apomorphine-induced behavior were investigated. The response was not significantly altered following bilateral thermocoagulations of the striatum (restricted lesions), globus pallidus, nucleus interstitialis of the striae terminalis, amygdala, nucleus lateralis septi or nucleus accumbens. Intrastriatal injections of 6-hydroxydopamine were without significant effect while large striatal thermocoagulations abolished the stereotyped behavior but were accompanied by a profound motor deficiency. Bilateral lesioning of the substantia nigra by either thermocoagulation or 6-hydroxydopamine, the latter leading to a 60% decrease in 3H-dopamine uptake in striatum without significant modification in nucleus accumbens, resulted in a hypersensitive response to apomorphine. Hence, these experiments do not allow to identify a single brain area where dopamine receptors mediating the climbing behavior are located although they suggest that the receptors involved receive a dopaminergic input originating from the substantia nigra.

Notes: Summary Dopaminergic binding sites were studied in slices from rat striatum incubated in a physiological medium and using the two highly selective ligands 3H-apomorphine and 3H-domperidone. The clearly biphasic or stretched inhibition of the specific binding of these two ligands by domperidone or apomorphine, respectively allowed to define three distinct classes of binding site. It was demonstrated, by comparing the binding of the 3H-ligand added at the beginning of slice incubation or just before homogenisation of tissue and filtration, that the “specific” bindings only occurred during the incubation of slices. The inhibition constants (K i values) of dopaminergic agents for the three classes of binding site as also the dissociation constants (K d values) of 3H-ligands and the maximal capacity (B max) of the three classes of binding site were closely similar to those of binding sites previously demonstrated on rat striatal membranes, namely D-2, D-3 and D-4 sites (Sokoloff et al. 1980a, b). Their identification on a preparation in which the cellular organisation is largely preserved rules out the possibility that these sites represent an artifact due to membrane preparation. Unexpectedly the addition of guanyl nucleotides like GTP or GppNHp to the slice preparation decreased the binding of 3H-apomorphine to the high affinity sites (particularly to the D-2 sites) while D-4 site binding was correspondingly increased. The guanylnucleotide effect apparently took place before cell disruption and occurred at concentrations similar to those required in striatal membrane preparations. These observations, together with those indicating the presence of high affinity binding sites for dopaminergic agonists in intact striatal cells, suggest that a putative nucleotide regulatory unit of dopamine receptors, is not fully occupied by intracellular GTP but could be interacted with from the external face of the cell membrane.

Notes: Summary 3H-Domperidone, a potent antagonist of dopamine but less lipophilic than neuroleptic drugs, was studied as a potential ligand for cerebral dopamine receptors. It labeled with high affinity an apparently homogeneous population of non-interacting sites in a particulate fraction of mouse striatum. Association occurred rapidly and dissociation was relatively slow (t1/2≃4min); this allowed extensive washing of membranes which reduced the non-specific binding to values as low as 5% of the total binding. Consistent Kd values of 0.7 nM were obtained by analysing by various methods either the kinetics of binding or the saturation of binding sites at equilibrium. The relative potencies of various dopamine receptor agonists or antagonists to inhibit 3H-domperidone binding, paralleled their pharmacological activity. On the other hand, a variety of non-dopaminergic agents failed to inhibit 3H-domperidone binding. The findings indicate that striatal dopamine receptors are selectively labeled by this 3H-ligand. In various non-striatal regions of mouse brain the saturable binding of 3H-domperidone was almost entirely inhibited by apomorphine indicating its selectivity for dopamine receptors in spite of the low density of the latter. This was not the case for the binding of 3H-spiperone, evaluated on the same preparations, indicating that 3H-domperidone probably represents the most selective ligand presently available.

Notes: Summary In order to document the hypothesis that anti-psychotics may interact with more than one class of cerebral dopamine receptors, the relative potencies of a series of compounds were compared in three behavioral tests and in binding studies with two radioligands. Apomorphine (0.6 mg/kg) simultaneously clicited in rat two kinds of facial stereotypies (sniffing and licking) and a stereotyped climbing behavior, allowing to compare in the same animals the relative potencies of various antipsychotics against the three behaviors. Only some substituted benzamides (Sulpiride, LUR 2366 and DAN 2163) antagonised at significantly lower dosages climbing than sniffing (or licking). The possibility that this discriminant potency might be related to a distinct affinity for two classes of dopamine receptors was investigated by binding studies on striatal membranes with 3H-apomorphine and 3H-domperidone. From lesion and subcellular fractionation studies, two classes of binding sites both labeled with 3H-domperidone but distinguished by apomorphine i.e. D-2 sites with nM affinity and D-4 sites with μM affinity for the dopamine agonist (according to the nomenclature of Sokoloff et al. 1980b) appear to be differently localised in striatum. Thus D-2 sites, whose number decreases after kainate lesion, are not significantly modified following cortical lesions and preferentially sediment with heavy primary subcellular fractions. In contrast D-4 sites, less affected by kainate lesions, are significantly decreased following cortical lesions (−30%) and preferentially sediment with the light subcellular fractions. In addition the apparently heterogenous recognition of total 3H-domperidone binding sites (i.e. the sum of D-2 and D-4 sites) by dopamine and apomorphine persists in the presence of guanosine-5′-triphosphate (pseudo-Hill coefficient of 0.60 instead of 0.55). This suggests that D-2 and D-4 sites cannot be considered as two discrete states of the same receptor strictly convertible one into the other by guanylnucleotides. Whereas most dopamine antagonists inhibited D-2 and D-4 site binding with similar affinities, the three benzamide derivatives with the largest selectivity in behavioral tests displayed 2–3-fold higher affinity for D-4 than for D-2 sites and the ratios of ID50 values of the whole series of antagonists against sniffing (or licking) and climbing behaviors were correlated (P〈0.01) with the ratios of K i values regarding D-2 and D-4 site binding. Also, sulpiride and LUR 2366 unlike haloperidol and metoclopramide, inhibited the total specific 3H-domperidone binding in a biphasic manner. However, the distinction by sulpiride and LUR 2366 of low and high affinity sites did not superimpose that of D-2 and D-4 sites, as distinguished by agonists. In this test the relative proportion of low affinity sites was 2-fold higher than that of D-2 sites and K i values for high affinity sites were lower than that for D-4 sites. Also the heterogeneity of 3H-domperidone sites regarding affinity of LUR 2366 persisted in the presence of low concentrations of apomorphine. Hence low affinity sites for discriminant benzamide derivatives may exist in two forms, distinguished by agonists and possibly interconvertible by GTP. Thus the hypothesis that two classes of central dopamine receptor can be distinguished by some substituted benzamides, but perhaps display no great difference in affinity of agonists in their physiological state, fits partic-ularly well with behavioral data.

Notes: Summary The in vivo accumulation of 3H-N-propyl norapomorphine in mouse striatum and tuberculum olfactorium and its inhibition by a series of classical neuroleptics and discriminant benzamide derivatives previously identified in behavioural and radioligand experiments has been studied. The ID50 values in the two brain areas did not significantly differ with any studied compound. In addition the regional distribution of a discriminant compound related to sulpiride and administered in tritiated form to rats was rather homogeneous. These data do not indicate a preferential accumulation of these compounds in limbic as opposed to striatal areas.

Notes: Abstract Mice treated with low doses of apomorphine tend to adopt a vertical position along the walls of their cage. Optimal conditions have been defined to obtain a reliable dose-response relationship. This peculiar behavior appears to be elicited by stimulation of dopamine receptors in the striatum: it is suppressed after coagulation of this structure while it is facilitated when these receptors are made hypersensitive by previous treatments with 6-hydroxydopamine or haloperidol; on the other hand, it is not modified by coagulation of the nucleus accumbens. The relative efficacy of various agonists and antagonists of dopamine receptors have been determined on this test. It appears that this stereotyped behavior might represent a convenient mean to assess the stimulation of striatal dopamine receptors in mice.

Notes: Abstract Mice treated with apomorphine tend to adopt a vertical position in a stereotyped manner. A quantal evaluation of this behaviour, taking into account its frequency and duration, leads to a biphasic dose-response curve that reveals opposite actions of the dopamine agonist.

Notes: Abstract Phase pure samples of (HgBi0.2 )Ba2Ca2CU3.1Ox have been synthesized on gold foils. The gold superconductor interface was found to enhance grain growth and alignment as seen by XRD, SEM, and magnetization measurements.

Notes: Abstract Synthesis and processing parameters for (Hg1−xBix)Ba2Ca2Cu3.1Oy were optimized for growth at temperatures suitable for growth on Ag and Au substrates (〈850° C). Use of Bi2CuO4 as a Bi source combined with variations of BaCaCuO precursor phase assemblages allowed the formation of some liquid phase during the reaction and resulted in dense (Hg1−xBix)Ba2Ca2Cu3.1Oy samples with aligned colonies of grains. Magnetization measurements in fields up to 30 T indicated good intergrain coupling within the large grain colonies. The results of the Bi doped samples are compared with those of previously reported Re doped samples.