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Notes: Abstract To determine whether field-selected resistance of diamondback moth (Plutella xylostella L.) (Lepidoptera: Plutellidae) to Bacillus thuringiensis is based on behavioral or physiological adaptation, we measured mortality, consumption, and movement of larvae from a susceptible and a resistant colony when placed on untreated and B. thuringiensis treated cabbage. Colonies did not differ in mortality, consumption, or movement on untreated cabbage. However, for a given amount of consumption of treated cabbage, resistant larvae had lower mortality than susceptible larvae, demonstrating that resistance had a physiological basis. The movement patterns could not account for the differences between colonies in survival. Resistant larvae did not avoid B. thuringiensis more than did susceptible larvae. Thus, we found no evidence for behavioral resistance.

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: 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 labelling of rat cerebral cortex α2-adrenoceptors with [3H]-yohimbine ([3H]-YOH) was investigated. At 25° C, binding equilibrium was reached in about 10 min and dissociation occurred with a half time of about 1 min. Saturation experiments gave an equilibrium K D value of 10.13±1.95 nM and a maximum number of sites of 254±22 fmol/mg protein. The [3H]-YOH binding sites exhibited α2-adrenergic receptor specificity; the order of potency for the antagonists was rauwolscine 〉 yohimbine ≫ prazosin 〉 corynanthine. For the agonists, the order was: oxymetazoline 〉 clonidine 〉 (−)-adrenaline 〉 (−)-noradrenaline ≫ (−)-phenylephrine. Agonists exhibited shallow curves in inhibiting [3H]-YOH binding, with pseudo-Hill coefficients (nH) of less than 1.0. These curves were shifted to lower overall affinity and steepened in the presence of 100 μM GTP. Antagonist competition curves were also shallow but GTP had no significant effect. Divalent cations at millimolar concentrations decreased the [3H]-YOH binding: IC50 values were about 6.0, 6.8 and 0.3 mM for Ca2+, Mg2+ and Mn2+ respectively. The maximal number of [3H]-YOH binding sites in the cortex was close to that labelled by the agonist [3H]-paraaminoclonidine ([3H]-PAC). The regional distribution of these sites in the brain, examined at a single concentration of [3H]-YOH and [3H]-PAC, showed a similar pattern except in the striatum. Taken together, the results indicate that like [3H]-PAC, [3H]-YOH labels α2-adrenoceptors in rat brain cortex. They also show that [3H]-YOH is a useful tool for the study of the high and low affinity sites.

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 The effect of Bacillus thuringiensis insecticidal toxins on the monovalent cation content and intracellular pH (pH i ) of individual Sf9 cells of the lepidopteran species Spodoptera frugiperda (fall armyworm) was monitored with the fluorescent indicators potassium-binding benzofuran isophthalate (PBFI) and 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). The sequential removal of K+ and Na+ from the medium, in the presence of CryIC, a toxin which is highly active against Sf9 cells, caused sharp shifts in the fluorescence ratio of PBFI, demonstrating a rapid efflux of these ions. In Sf9 cells, pH i depends strongly on the activity of a K+/H+ exchanger. In the absence of toxin, removal of K+ from the external medium resulted in a reversible acidification of the cells. In the presence of CryIC, pH i equilibrated rapidly with that of the bathing solution. This effect was both time- and concentration-dependent. In contrast with CryIC, CryIIIA, a coleopteran-specific toxin, and CryIA(a), CryIA(b) and CryIA(c), toxins which are either inactive or poorly active against Sf9 cells, had no detectable effect on pH i . B. thuringiensis endotoxins thus appear to act specifically by increasing the permeability of the cytoplasmic membrane of susceptible cells to at least H+, K+ and Na+.

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 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.