In vitro activity of LY393558, an inhibitor of the 5-hydroxytryptamine transporter with 5-HT(1B/1D/2) receptor antagonist properties.

1-[2-[4-(6-fluoro-1H-indol-3-yl)-3,6-dihydro-1(2H)-pyridinyl]ethyl]-3-isopropyl-6-(methylsulphonyl)-3,4-dihydro-1H-2,1,3-benzothiadiazine-2,2-dioxide (LY393558) is a potent inhibitor of [3H]5-hydroxytryptamine ([3H]5-HT) uptake into rat cortical synaptosomes (pIC(50)=8.48+/-0.12). It produces a dextral shift of the 5-HT dose-response curves for the binding of GTPgamma[35S] to human 5-HT(1B) (pK(b)=9.05+/-0.14) and 5-HT(1D) (pK(b)=8.98+/-0.07) receptors and inhibits the contractile response of the rabbit saphenous vein to the 5-HT(1B/D) receptor agonist, sumatriptan (pK(b)=8.4+/-0.2). In addition, it is an antagonist at the 5-HT(2A) (pK(i)=7.29+/-0.19) and 5-HT(2B) (pK(i)=7.35+/-0.11) receptors. Presynaptic autoreceptor antagonist activity was demonstrated by its ability to potentiate the K(+)-induced outflow of [3H]5-HT from guinea pig cortical slices (pEC(50)=7.74+/-0.05 nM) in which the 5-HT transporter had been inhibited by a maximally effective concentration of paroxetine. It is concluded that LY393558 should be an effective antidepressant with the potential to produce an earlier onset of efficacy than selective serotonin uptake inhibitors.

LY367265, an inhibitor of the 5-hydroxytryptamine transporter and 5-hydroxytryptamine(2A) receptor antagonist: a comparison with the antidepressant, nefazodone.

The potential antidepressant, LY367265 (1-[2-[4-(6-fluoro-1H-indol-3-yl)-3, 6-dihydro-1(2H)-pyridinyl]ethyl]-5,6-dihydro-1H,4H-[1,2, 5]thiadiazolo[4.3.2-ij]quinoline-2,2,-dioxide) has been shown to have a higher affinity for the 5-hydroxytryptamine (5-HT) transporter (K(i)=2.3 nM) and 5-HT(2A) (K(i)=0.81 nM) receptor than the clinically effective antidepressant, nefazodone. It is a potent inhibitor of [3H]5-HT uptake into rat cortical synaptosomes (IC(50)=3.1 nM) and shows selectivity over that for [3H]noradrenaline (IC(50)>1000 nM). It potentiates potassium-induced [3H]5-HT outflow from prelabelled guinea pig cortical slices both in the presence (EC(50)=950 nM) and absence (EC(50)=250 nM) of a saturating concentration of the 5-HT transport inhibitor, paroxetine, indicating a low level of activity at the 5-HT(1B/1D) autoreceptor. These studies indicate that LY367265 is a putative antidepressant which, because of its 5-HT(2A) receptor antagonist activity, has the potential to produce less sleep disturbance and sexual dysfunction than selective serotonin uptake inhibitors.

omega-Agatoxin IVA identifies a single calcium channel subtype which contributes to the potassium-induced release of acetylcholine, 5-hydroxytryptamine, dopamine, gamma-aminobutyric acid and glutamate from rat brain slices.

The voltage-dependent calcium channels (VDCCs) involved in K(+)-induced transmitter release have been studied. A maximally effective concentration of the N-type VDCC inhibitor, omega-conotoxin GVIA (GVIA) blocked the release of 5-HT (30%), DA (30%) and ACh (60%) but not that of GABA or glutamate. The O, P and Q-type VDCC inhibitor, omega-agatoxin IVA (Aga IVA, 1 microM), blocked 100% of GABA and glutamate, 70% of DA and about 50% of 5-HT and ACh release. The slopes of the inhibiton curves indicate that it acts on the same, single type of VDCC in all cases. omega-Conotoxin MVIIC (MVIIC) completely inhibited the release of all the transmitters. It is concluded that a single GVIA-insensitive type of VDCC is involved in the K(+)-induced release of all the transmitters and, in addition, N-type VDCCs, with a higher affinity for GVIA than MVIIC, are required for the release of 5-HT, DA and ACh. The non-N-type VDCC is not the O-type as it is not blocked by low (< 10 nM) concentrations of MVIIC. Further resolution of this VDCC into P or Q-type requires more selective antagonists.

Synthesis and dopamine antagonist activity of 2-thioether derivatives of the ergoline ring system.

A series of 2-thioether derivatives of a number of clavine alkaloid (ergoline) ring systems have been synthesized and tested for dopamine antagonist activity. Of the compounds tested 2-(methylthio)-agroclavine (8,9-didehydro-6,8-dimethyl-2-(methylthio)ergoline) (6) was the most potent and had a profile of activity in animal models indicative of potential antipsychotic activity. The synthesis and biological activity of a number of metabolites of 6, including the 13-hydroxy derivative, are also reported.

Actions of arginine polyamine on voltage and ligand-activated whole cell currents recorded from cultured neurones.

1. Toxins from invertebrates have proved useful tools for investigation of the properties of ion channels. In this study we describe the actions of arginine polyamine which is believed to be a close analogue of FTX, a polyamine isolated from the American funnel web spider, Agelenopsis aperta. 2. Voltage-activated Ca2+ currents and Ca(2+)-dependent Cl- currents recorded from rat cultured dorsal root ganglion neurones were reversibly inhibited by arginine polyamine (AP; 0.001 to 100 microM). Low voltage-activated T-type Ca2+ currents were significantly more sensitive to AP than high voltage-activated Ca2+ currents. The IC50 values for the actions of AP on low and high voltage-activated Ca2+ currents were 10 nM and 3 microM respectively. AP was equally effective in inhibiting high voltage-activated currents carried by Ba2+, Sr2+ or Ca2+. However, AP-induced inhibition of Ca2+ currents was attenuated by increasing the extracellular Ca2+ concentration from 2 mM to 10 mM. 3. The actions of AP on a Ca(2+)-independent K+ current were more complex, 1 microM AP enhanced this current but 10 microM AP had a dual action, initially enhancing but then inhibiting the K+ current. 4. gamma-Aminobutyric acid-activated Cl- currents were also reversibly inhibited by 1 to 10 microM AP. In contrast N-methyl-D-aspartate currents recorded from rat cultured cerebellar neurones were greatly enhanced by 10 microM AP. 5. We conclude that at a concentration of 10 nM, AP is a selective inhibitor of low threshold T-type voltage-activated Ca2+ currents. However, at higher concentrations 1-10 microM AP interacts with ion channels or other membrane constituents to produce a variety of actions on both voltage and ligand gated ion channels.

Effects of conformationally restricted 4-piperazinyl-10H-thienobenzodiazepine neuroleptics on central dopaminergic and cholinergic systems.

The levels of antidopaminergic and anticholinergic activities of neuroleptics, 4-piperazinyl-10H-thienobenzodiazepines, are modulated by imposing steric impedence to the piperazine ring. The optimum situation in favor of the anticholinergic action is reached in compound 5, 2,3-dimethyl-7-fluoro-4-(4-methyl-1-piperazinyl)-10H-thieno[2,3-b][1,5]benzodiazepine, where a maximum activity (equivalent to hyoscine), as measured by the [3H]QNB receptor binding assay, is obtained. The structure-activity relationships found highlight the importance of certain spatial dispositions of the distal piperazine nitrogen (electron lone pair) with respect to the tricyclic system. The evidence for molecular topography of these compounds is presented from X-ray, NMR, and other physical data. The conformational aspects for correspondence to the relevant receptors are discussed.