Delamination of 2D coordination polymers: The role of solvent and ultrasound.

Two novel cadmium-based 2D coordination polymers have been synthesized and characterized. Experimental results evidence that the best delamination processes occurs when weak interactions dominate the cohesion between layers and solvent molecules are occluded within the crystalline network. In this case, the delamination of the crystals occurs spontaneously in water. On top of that, and thanks to the high stability of the resulting (flake) colloidal dispersions, we have completed a detailed study of the sonication assisted delamination impact by: I) comparison of two different sonication approaches (bath vs. tip sonication) and II) optimization of final flake morphology and yield by controlling solvent and sonication time. Our results definitely pave the way for the fabrication and implementation of 2D coordination polymers using ultrasound.

Reversible stimulus-responsive Cu(I) iodide pyridine coordination polymer.

We present a structurally flexible copper-iodide-pyridine-based coordination polymer showing drastic variations in its electrical conductivity driven by temperature and sorption of acetic acid molecules. The dramatic effect on the electrical conductivity enables the fabrication of a simple and robust device for gas detection. X-ray diffraction studies and DFT calculations allow the rationalisation of these observations.

Delayed pharmacological effects of antidepressants.

Although antidepressants may not be primary mood stabilizers, they are efficacious in the prophylaxis of recurrent depressive illnesses, as well as in the treatment of acute episodes. Pharmacological effects that may contribute to the prophylactic effects of these drugs are not understood. Studies have been carried out in which antidepressants have been given to laboratory animals, such as rats, for periods of up to 3-4 weeks. Data obtained in such studies are thought to be important for their beneficial effects in depressive episodes, but also may be relevant to their prophylactic effects. Results are presented showing that when selective inhibitors of serotonin or norepinephrine uptake are given for such time periods, they still produce selective effects on serotonergic or noradrenergic parameters. For example, long-term administration of selective norepinephrine reuptake inhibitors causes a down-regulation of beta(1) adrenoceptors. Selective serotonin reuptake inhibitors do not produce this effect. Long-term administration of selective serotonin reuptake inhibitors causes down-regulation of the serotonin transporter, but not the norepinephrine transporter. In contrast, selective norepinephrine reuptake inhibitors down-regulate the norepinephrine transporter but not the serotonin transporter. Substantial loss of serotonin transporter binding sites takes 15 days to occur and is accompanied by a marked reduction of serotonin transporter function in vivo.

Effects of chronic antidepressant treatments on serotonin transporter function, density, and mRNA level.

To investigate functional changes in the brain serotonin transporter (SERT) after chronic antidepressant treatment, several techniques were used to assess SERT activity, density, or its mRNA content. Rats were treated by osmotic minipump for 21 d with the selective serotonin reuptake inhibitors (SSRIs) paroxetine or sertraline, the selective norepinephrine reuptake inhibitor desipramine (DMI), or the monoamine oxidase inhibitor phenelzine. High-speed in vivo electrochemical recordings were used to assess the ability of the SSRI fluvoxamine to modulate the clearance of locally applied serotonin in the CA3 region of hippocampus in drug- or vehicle-treated rats. Fluvoxamine decreased the clearance of serotonin in rats treated with vehicle, DMI, or phenelzine but had no effect on the clearance of serotonin in SSRI-treated rats. SERT density in the CA3 region of the hippocampus of the same rats, assessed by quantitative autoradiography with tritiated cyanoimipramine ([(3)H]CN-IMI), was decreased by 80-90% in SSRI-treated rats but not in those treated with phenelzine or DMI. The serotonin content of the hippocampus was unaffected by paroxetine or sertraline treatment, ruling out neurotoxicity as a possible explanation for the SSRI-induced decrease in SERT binding and alteration in 5-HT clearance. Levels of mRNA for the SERT in the raphe nucleus were also unaltered by chronic paroxetine treatment. Based on these results, it appears that the SERT is downregulated by chronic administration of SSRIs but not other types of antidepressants; furthermore, the downregulation is not caused by decreases in SERT gene expression.

Ca2+ and pH modulate alternative splicing of exon 5 in NMDA receptor subunit 1.

RT-PCR and intracellular Ca2+ measurements were used to identify factors that modulate alternative splicing of exon 5 in the NMDA receptor transcript encoding NR1, in cultured cerebellar granule neurons. Although cells grown in media containing 5 mM KCl demonstrate compromised survival, they show the predicted developmental transition from NR1a (-exon 5) to NR1b (+exon 5) mRNA expression. This transition was blocked under culture conditions that promote survival; inclusion or exclusion of exon 5 is a reversible process that is sensitive to alterations in Ca2+ and pH. We conclude that alternative splicing of NR1 pre-mRNA transcripts may be regulated by developmental cues that modulate the degree of glutamate receptor activation.

Glia modulate NMDA-mediated signaling in primary cultures of cerebellar granule cells.

Excessive activation of N-methyl-D-aspartate (NMDA) receptor channels (NRs) is a major cause of neuronal death associated with stroke and ischemia. Cerebellar granule neurons in vivo, but not in culture, are relatively resistant to toxicity, possibly owing to protective effects of glia. To evaluate whether NR-mediated signaling is modulated when developing neurons are cocultured with glia, the neurotoxic responses of rat cerebellar granule cells to applied NMDA or glutamate were compared in astrocyte-rich and astrocyte-poor cultures. In astrocyte-poor cultures, significant neurotoxicity was observed in response to NMDA or glutamate and was inhibited by an NR antagonist. Astrocyte-rich neuronal cultures demonstrated three significant differences, compared with astrocyte-poor cultures: (a) Neuronal viability was increased; (b) glutamate-mediated neurotoxicity was decreased, consistent with the presence of a sodium-coupled glutamate transport system in astrocytes; and (c) NMDA- but not kainate-mediated neurotoxicity was decreased, in a manner that depended on the relative abundance of glia in the culture. Because glia do not express NRs or an NMDA transport system, the mechanism of protection is distinct from that observed in response to glutamate. No differences in NR subunit composition (evaluated using RT-PCR assays for NR1 and NR2 subunit mRNAs), NR sensitivity (evaluated by measuring NR-mediated changes in intracellular Ca2+ levels), or glycine availability as a coagonist (evaluated in the presence and absence of exogenous glycine) were observed between astrocyte-rich and astrocyte-poor cultures, suggesting that glia do not directly modulate NR composition or function. Nordihydroguaiaretic acid, a lipoxygenase inhibitor, blocked NMDA-mediated toxicity in astrocyte-poor cultures, raising the possibility that glia effectively reduce the accumulation of highly diffusible and toxic arachidonic acid metabolites in neurons. Alternatively, glia may alter neuronal development/phenotype in a manner that selectively reduces susceptibility to NR-mediated toxicity.

The MAO-B inhibitor deprenyl, but not the MAO-A inhibitor clorgyline, potentiates the neurotoxicity of p-chloroamphetamine.

The effect of co-administration of MAO inhibitors together with a low dose of the neurotoxic amphetamine p-chloroamphetamine (pCA) on neurotoxicity was examined. Neurotoxicity was assessed by measuring decreases in the binding of [3H]cyanoimipramine to serotonin uptake sites using quantitative autoradiography. By itself, a low dose of pCA (2 mg/kg) did not produce any alterations in radioligand binding, measured 7 days after drug administration. However, co-administration of the MAO-B selective inhibitor deprenyl (1 mg/kg) or the non-selective inhibitor pargyline (50 mg/kg) produced significant decreases in radioligand binding. Measurements of the effects of these drugs on body temperature ruled out the possibility that deprenyl and pargyline were increasing neurotoxicity by producing a drug-induced hyperthermia. In contrast to the effects of deprenyl and pargyline, co-administration of the MAO-A selective inhibitor clorgyline (1 mg/kg) did not alter binding. By themselves none of the MAO inhibitors produced neurotoxic effects. There are a number of possible explanations for these results. Administration of deprenyl or pargyline, together with pCA, itself a MAO-A inhibitor, will lead to inhibition of both MAO-A and MAO-B activities. This will likely lead to an enhanced release of dopamine and serotonin compared with the release following administration of pCA alone or pCA together with clorgyline. Elevation of the extracellular levels of either or both of these monoamines could lead to enhanced neurotoxicity. Whatever the mechanism involved, our results show that the co-administration of a type-B MAOI enhances the neurotoxic effects of pCA on serotonin neurons.

Effect of CH3HgCl and several transition metals on the dopamine neuronal carrier; peculiar behaviour of Zn2+.

CH3Hg+ and metal ions inhibited the specific binding of (1-[2-(diphenylmethoxy)ethyl]-4-(3-phenyl-2-[1-3H]propenyl) piperazine) ([3H]GBR 12783) to the dopamine neuronal carrier present in membranes from rat striatum with a general rank order of potency CH3Hg+ > Cu2+ > Cd2+ > Zn2+ > Ni2+ = Mn2+ = Co2+, suggesting that -SH groups are chiefly involved in this inhibition. Five millimolar dithiothreitol reversed the rather stable block of the specific binding produced by Cd2+ or Zn2+. An increase in the concentration of Na+, or addition of either K+ or Ca2+ reduced the inhibitory effects of metal cations, except Cu2+. Zn2+ (3 microM) reduced the inhibitory potency of Cd2+ on the binding but was ineffective against CH3Hg+ and Cu2+. Zn2+ at 0.3 to 10 microM significantly enhanced the specific binding of [3H]GBR 12783 and [3H]cocaine by 42 to 146%. Zn2+ (3 microM) increased the affinity of all pure uptake inhibitors tested and of the majority of the substrates for the [3H]GBR 12783 binding site. Dissociation experiments revealed that Zn2+ both inhibited and enhanced the [3H]GBR 12783 binding by recognizing amino acids located close to or in the radioligand binding site. Micromolar concentrations of Zn2+ noncompetitively blocked the [3H]dopamine uptake but they did not modify the block of the transport provoked by pure uptake inhibitors. These findings suggest that Na+, K+, Ca2+ and metal ions could recognize some -SH groups located in the [3H]GBR 12783 binding site; low concentrations of Zn2+ could allow a protection of these -SH groups.

Effects of several cations on the neuronal uptake of dopamine and the specific binding of [3H]GBR 12783: attempts to characterize the Na+ dependence of the neuronal transport of dopamine.

We have studied the effects of several cations on (1) the neuronal uptake of [3H]dopamine ([3H]DA) and (2) the specific binding of 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenyl-2-[1-3H]propenyl)piperazi ne ([3H]GBR 12783) to a site associated with the neuronal carrier of DA, in preparations obtained from rat striatum. When studied under the same experimental conditions, both the uptake of [3H]DA and the binding of [3H]GBR 12783 were similarly impaired by the gradual replacement of NaCl by sucrose. In both processes, no convenient substitute for Na+ was found. Furthermore, potential substitutes of Na+ acted as inhibitors of the uptake with a rank order of potency as follows: K+ = Li+ > or = Cs+ > or = Rb+ > choline+ > Tris+ > sucrose, which was somewhat different from that observed in binding studies, i.e., Cs+ > Rb+ > choline+ > or = K+ > Li+ > Tris+ > sucrose. In the presence of either 36 mM or 136 mM Na+, [3H]DA uptake was optimal with 2 mM Mg2+, 1 mM K+, or 1 mM Ca2+. In contrast, higher concentrations of divalent cations competitively blocked the uptake process. K+ concentrations > 50 mM impaired the specific binding, whereas in the millimolar range of concentrations, K+ noncompetitively inhibited the uptake. Decreasing the Na+ concentration increased the inhibitory effect of K+, Ca2+, and Mg2+ on the specific uptake. An increase in NaCl concentration from 0 to 120 mM elicited a significant decline in the affinity of some substrates for the [3H]GBR 12783 binding site. An uptake study performed using optimal experimental conditions defined in the present study revealed that decreasing Na+ concentration reduces the affinity of DA for the neuronal transport. We propose a hypothetical model for the neuronal transport of DA in which both Na+ and K+ membrane gradients are involved.

Effects of high-dose methamphetamine on monoamine uptake sites in rat brain measured by quantitative autoradiography.

The neurotoxicity of methamphetamine to monoaminergic neurons was examined. Neurotoxicity was assessed by quantitative autoradiography using radioligands specific for binding to norepinephrine, dopamine, and serotonin uptake sites. High-dose administration of methamphetamine led to decreases in binding to uptake sites for the three monoamines. Norepinephrine binding sites were decreased in certain amygdaloid nuclei and in the dorsomedial hypothalamic nucleus. Serotonin binding sites were reduced in widespread brain areas, while dopamine binding sites were reduced in the caudate putamen, olfactory tubercle, and nucleus accumbens. The decreases in binding site density for the three monoamines are limited to terminal field areas; cell body areas are not affected. Our results indicate that methamphetamine is neurotoxic to serotonin, dopamine, and norepinephrine neurons. The neurotoxicity to norepinephrine neurons is in selected brain areas.

Lack of effect of high-dose cocaine on monoamine uptake sites in rat brain measured by quantitative autoradiography.

There have been a number of claims that high-dose administration of cocaine to rats leads to neurotoxic effects on dopamine neurons. In this study possible neurotoxic effects on monoamine neurons were examined by measuring the effects of cocaine (35 mg/kg daily for 10 days) on the binding of radioligands to uptake sites for dopamine, serotonin and norepinephrine using qualitative autoradiography. No effects of cocaine on any of the binding sites were observed and therefore, it is concluded that cocaine, unlike amphetamine derivatives which have similar pharmacologic properties, does not produce neurotoxic effects on monoamine neurons.

Thermodynamic analyses of the binding of substrates and uptake inhibitors on the neuronal carrier of dopamine labeled with [3H]GBR 12783 or [3H]mazindol.

We have investigated the thermodynamic properties of the binding of substrates and uptake blockers to the specific sites labeled with a tritiated dopamine uptake inhibitor (i.e., 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenyl-2-propenyl)piperazine ([3H] GBR 12783) or [3H]mazindol) using striatal membrane preparations. Raising the incubation temperature from 0 degrees C to 25 degrees C or 37 degrees C resulted in an increase in the dissociation constant of both [3H]mazindol and [3H]GBR 12783 for their specific sites of binding present in membrane suspensions obtained from either rabbit or rat striatum. However, maximal concentrations of binding sites were not affected by temperature. At all tested temperatures, both substrates and carrier blockers competed with either [3H]mazindol or [3H]GBR 12783 in a monophasic fashion, with Hill coefficients close to unity. Raising the temperature induced little or no increase in inhibition constants (Ki) for substrates (Ki ratio 37/0 degrees C less than 2.5). This is consistent with the mild increase of the Michaelis constant of dopamine for the neuronal uptake system when the incubation temperature was raised from 12.5 to 37 degrees C (from 126 to 406 nM). In contrast, increasing the temperature resulted in a more important increase in the Ki of uptake inhibitors (33 greater than Ki ratio greater than 5). Thermodynamic calculations showed that the binding of substrates is generally characterized by a mild decrease in enthalpy (range, -2- -6 kcal/mol) associated with an increase in entropy, whereas binding of uptake inhibitors led to a decrease of both parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Ionic requirements for the specific binding of [3H]GBR 12783 to a site associated with the dopamine uptake carrier.

At 0 degrees C, when Na+ was the only cation present in the incubation medium, increasing the Na+ concentration from 3 to 10 mM enhanced the affinity of [3H]1-[2-(++di-phenylmethoxy)ethyl]-4-(3-phenyl-2-propenyl)piperaz ine [( 3H]GBR 12783) for the specific binding site present in rat striatal membranes without affecting the Bmax. For higher Na+ concentrations, specific binding values plateaued and then slightly decreased at 130 mM Na+. In a 10 mM Na+ medium, the KD and the Bmax were, respectively, 0.23 nM and 12.9 pmol/mg of protein. In the presence of 0.4 nM [3H]GBR 12783, the half-maximal specific binding occurred at 5 mM Na+. A similar Na+ dependence was observed at 20 degrees C. Scatchard plots indicated that K+, Ca2+, Mg2+, and Tris+ acted like competitive inhibitors of the specific binding of [3H]GBR 12783. The inhibitory potency of various cations (K+, Ca2+, Mg2+, Tris+, Li+, and choline) was enhanced when the Na+ concentration was decreased from 130 to 10 mM. In a 10 mM Na+ medium, the rank order of inhibitory potency was Ca2+ (0.13 mM) greater than Mg2+ greater than Tris+ greater than K+ (15 mM). The requirement for Na+ was rather specific, because none of the other cations acted as a substitute for Na+. No anionic requirement was found: Cl-, Br-, and F- were equipotent. These results suggest that low Na+ concentrations are required for maximal binding; higher Na+ concentrations protect the specific binding site against the inhibitory effect of other cations.

Sodium independence of the binding of [3H]GBR 12783 and other dopamine uptake inhibitors to the dopamine uptake complex.

When Na+ was the only cation present in the incubation medium used for the determination of the specific binding of [3H]GBR 12783 in rat striatal membranes, the Na+-dependence between 10 and 210 mM Na+ was not observed. In media with low (10 mM) or high (130 mM) Na+ concentration, mazindol and nomifensine competed with [3H]GBR 12783 for its specific binding site with the same affinities. With the exception of amineptine, all the tested catecholamine uptake inhibitors were equally potent to compete with [3H]GBR 12783 when Na+ concentration was decreased from 130 to 10 mM. These data suggest that the media previously used for the binding studies of tritiated inhibitors of dopamine uptake (Tris-ions buffer and Krebs-Ringer medium) contain ions which could exert inhibitory effects on the specific binding at low Na+ concentration.