Conformationally restricted analogues of remoxipride as potential antipsychotic agents.

Several conformationally restricted derivatives of (S)-3-bromo-N-((1-ethyl-2-pyrrolidinyl)methyl)-2,6-dimethoxybenzamide (remoxipride) were synthesized and evaluated in vitro for their ability to inhibit [3H]raclopride binding at the dopamine D-2 receptor. The cyclic benzamides designed to mimic the intramolecular hydrogen bonding of desmethylremoxipride (4, FLA-797) included 2,3-dihydro-4H-1,3-benzoxazin-4-ones, 2,3-dihydro-4H-1,3-benzthiazin-4-ones, phthalimides, 1-isoindolinones, 1,2-benzisothiazol-3(2H)-ones, and 1,2-benzisothiazol-3(2H)-one 1,1-dioxides. In this series, enhanced affinities to the dopamine D-2 receptor were not observed. The phthalimidine analogue 24b ((S)-6-chloro-2-(1-ethylpyrrolidinyl)-1-isoindolinone) exhibited the highest affinity to the dopamine D-2 receptor with an IC50 of 1.3 microM, which was equipotent to remoxipride.

Synthesis and evaluation of the antidepressant activity of the enantiomers of bupropion.

The synthesis of the enantiomers of bupropion, (rac)-2-tert-butylamino-3'-chloropropiophenone 1 (Wellbutrin) is described. The enantiomers were compared with the racemate in both the tetrabenazine-induced sedation model and the inhibition of uptake of biogenic amine assay. No significant differences were found in their potencies to reverse tetrabenazine-induced sedation in mice or in their IC50 values as inhibitors of biogenic amine uptake into nerve endings obtained from mouse brain.

Alterations in extracellular and tissue levels of biogenic amines in rat brain induced by the serotonin2 receptor antagonist, ritanserin.

Systemic administration of ritanserin elicited rapid changes in dopamine (DA) and serotonin (5-HT) levels in both dialysate and neuronal tissue extracts. These effects occurred in both a site-selective and a dose-related manner. Increases in extracellular levels of DA and 5-HT in the nucleus accumbens were maximal at 120-140 min after treatment. A dose of 0.63 mg/kg of ritanserin elicited larger and more prolonged increases in extracellular DA and 5-HT levels than did the 0.3 mg/kg dose. By contrast, 0.63 mg/kg of ritanserin elicited no changes in either DA or 5-HT levels with dialysate collected from the striatum. Ritanserin also induced dose-related decreases in tissue levels of DA and 5-HT from the nucleus accumbens. The site specificity of action was again noted in that there were no dose-dependent decreases in tissue levels of DA or 5-HT measured from the striatum. Ritanserin exerted little effect on metabolite levels from either dialysate or tissue extracts. Taken together, these findings show that selective 5-HT2 receptor antagonism modulates DA and 5-HT neurotransmission in a specific manner. These actions appear to involve increased release of DA and 5-HT rather than significant changes in metabolism. These findings add further weight to the importance of 5-HT2 receptor interactions as an important component of antipsychotic activity.

Effects of the 5-HT2 receptor antagonist, ritanserin, on biogenic amines in the rat nucleus accumbens.

The effects of acute ritanserin treatment on dopamine (DA) and serotonin (5-HT) release and metabolism were studied in tissue and microdialysis samples of the nucleus accumbens in rats. Administration of a moderate dose of ritanserin elicited decreases in DA and 5-HT in tissue with concomitant increases in extracellular fluid. These data show that selective 5-HT2 receptor antagonism modulates DA as well as 5-HT neurotransmission and adds support to the suggestion that 5-HT/DA interactions may be important in the treatment of psychoses.

Analysis of rat brain microdialysate by gas chromatography-high-resolution selected-ion monitoring mass spectrometry.

Gas chromatography-high-resolution selected-ion monitoring mass spectrometry was used to analyze catecholamine metabolites in rat brain microdialysate. Dialysate samples were collected in vials containing stable isotope analogues of homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 5-hydroxyindoleacetic acid (5HIAA) and analyzed as their trimethylsilyl derivatives. The metabolite levels were monitored at 20-min intervals throughout the time course of the experiment, beginning immediately after surgery and implantation of the dialysis probe and ending 4 h after amphetamine treatment. The levels of HVA were observed to decrease after amphetamine treatment, while those of MHPG and 5HIAA did not change significantly.

Gastrin-releasing peptide receptor in rat brain membranes: specific binding and stimulation of phosphoinositide breakdown.

The binding of gastrin-releasing peptide (GRP) to rat brain membranes was characterized. GRP binds specifically to a high affinity site in rat brain membranes, with a Kd equal to 2 nM and Bmax equal to 5 pmol/g wet weight of tissue. The specific binding is saturable, reversible, and dependent on tissue concentration, time of incubation, and the pH of the buffer. Hippocampus, cortex, and striatum contained the highest concentration of high affinity binding sites and the thalamus the lowest. The affinities of GRP, bombesin, and their analogues for the GRP receptor were determined. GRP(14-27) and [Tyr4]bombesin had the greatest affinity, whereas GRP(1-16), which lacks the COOH terminal region, had no affinity for the receptor. GRP, bombesin, and analogues stimulate the breakdown of phosphatidylinositol in rat brain hippocampal minces and potencies correspond to their affinities for the GRP receptor.

Inhibition of receptor-mediated stimulation of cyclic AMP accumulation in neuroblastoma-hybrid NCB-20 cells by a phorbol ester.

Activation of protein kinase C by phorbol esters such as phorbol 12-myristate 13-acetate (PMA), modulates responsiveness of the cyclase system in many cell types. In the neuroblastoma-hybrid cell line NCB-20, PMA causes a reduction in receptor-mediated accumulation of cyclic AMP. The reduction in receptor responses by PMA occurs within 3 min and is still apparent at 40 min. This occurs in a concentration-dependent manner with an EC50 for PMA of approx. 30 nM. Accumulations of cyclic AMP that are elicited by prostaglandin E2, vasoactive intestinal peptide or 2-chloroadenosine are decreased in the presence of PMA. Accumulations of cyclic AMP that are elicited by forskolin in the absence of a receptor agonist are unaffected by the presence of PMA. Inhibition of cyclic AMP generation by dopamine is not diminished by PMA suggesting the receptor input through the inhibitory Ni-guanyl nucleotide binding protein is still functional after PMA treatment. The generalized inhibition of receptor-mediated responses by PMA could be due to a protein kinase C-mediated phosphorylation of the stimulatory Ns-guanyl nucleotide binding protein, but other mechanisms are possible.

Accumulations of cyclic AMP and inositol phosphates in guinea pig cerebral cortical synaptoneurosomes: enhancement by agents acting at sodium channels.

Activation of alpha 1-adrenergic receptors by norepinephrine in guinea pig cortical synaptoneurosomes augments accumulations of cyclic AMP elicited by 2-chloroadenosine and concomitantly increases formation of inositol phosphates. Various agents that affect calcium channels or sites of action of calcium have little or no effect on cyclic AMP accumulation elicited either with 2-chloroadenosine, or with a 2-chloroadenosine/norepinephrine combination, nor did they markedly affect formation of inositol phosphates elicited by norepinephrine. However, EGTA reduces both cyclic AMP accumulation and inositol phosphate formation. Agents such as batrachotoxin, scorpion (Leiurus) venom and pumiliotoxin B that are active at voltage-dependent sodium channels enhance accumulations of cyclic AMP and inositol phosphates. These effects are blocked by tetrodotoxin. It is proposed that enhanced influx of sodium ions increases phosphatidylinositol metabolism, resulting in formation of diacylglycerols and inositol phosphates, and that the former, through activation of protein kinase, causes an enhancement of cyclic AMP accumulations in brain tissue.

Anticonvulsant activity of piperidinol and (dialkylamino)alkanol esters.

Aromatic and heterocyclic esters of 1-methyl-4-piperidinol and 1,4-dimethyl-4-piperidinol and aromatic esters of (dialkylamino)alkanols were prepared and evaluated for antiepileptic activity by the maximal electroshock seizure (MES) and subcutaneous pentylenetetrazole seizure threshold (scMet) assays and for minimal central neurotoxicity by the rotorod ataxia test. The most potent compound, namely the 2-phenylbenzoate (57) of 3-(diethylamino)propanol, was slightly more potent than diphenylhydantoin in the MES assay, while the 2-phenylbenzoate (24) of 1-methyl-4-piperidinol and the 2-phenylbenzoate (56) of (diethylamino)ethanol displayed activity comparable to that of diphenylhydantoin. The 2-phenethylbenzoate ester (6) of 1-methyl-4-piperidinol exhibited one-third the activity of diphenylhydantoin. The 2,4,5-trimethylbenzoate 40 and 2,4,6-trimethylbenzoate 41 of 1-methyl-4-pieridinol were even less potent, but did display activity in the phenobarbital-methsuximide range. Certain compounds interact with sites associated with the GABA receptor-chloride channel complex, but their potencies as anticonvulsant agents do not correlate with interaction at sites on the channel complex. Certain analogues antagonize binding of a batrachotoxin analogue to sodium channel sites, a property indicative of local anesthetic activity. There are structural similarities between 2-phenylbenzoates 57, 56, and 24 and diphenylhydantoin, and the latter anticonvulsant also antagonizes binding of the batrachotoxin analogue.

Regulation of phosphatidylinositol turnover in brain synaptoneurosomes: stimulatory effects of agents that enhance influx of sodium ions.

Norepinephrine and carbamoylcholine stimulate accumulation of [3H]inositol phosphates from [3H]inositol-labeled guinea pig cerebral cortical synaptoneurosomes through interaction with alpha 1-adrenergic and muscarinic receptors, respectively. In addition to such agonist, a variety of natural products that affect voltage-dependent sodium channels can markedly stimulate accumulation of [3H]inositol phosphates. These include alkaloids that activate sodium channels, such as batrachotoxin, veratridine, and aconitine; peptide toxins that alter activation or slow inactivation of sodium channels, such as various scorpion toxins from Leiurus, Centruroides, and Tityus species; and agents that cause repetitive firing of sodium channel-dependent action potentials, such as pyrethroids and pumiliotoxin B. Ouabain, and agent that will increase accumulation of internal sodium by inhibition of Na+, K+-ATPase, also stimulates formation of [3H]inositol phosphates, as does monensin, a sodium ionophore. Tetrodotoxin and saxitoxin, specific blockers of voltage-dependent sodium channels, prevent or reduce the stimulatory effects of sodium channel agents and ouabain on phosphatidylinositol turnover, while having lesser or no effect, respectively, on receptor-mediated or monensin-mediated stimulation. Removal of extracellular sodium ions markedly reduces stimulatory effects of sodium channel agents, while removal of extracellular calcium ions with EGTA blocks both receptor-mediated and sodium channel agent-mediated phosphatidylinositol turnover. The results provide evidence for a hitherto unsuspected messenger role for sodium ions in excitable tissue, whereby neuronal activity and the resultant influx of sodium will cause activation of phospholipase systems involved in hydrolysis of phosphatidylinositols, thereby generating two second messengers, the inositol phosphates, which mobilize calcium from internal stores, and the diacylglycerols, which activate protein kinase C.

Accumulations of inositol phosphates and cyclic AMP in brain slices: synergistic interactions of histamine and 2-chloroadenosine.

2-Chloroadenosine, 5'-N-ethylcarboxamidoadenosine, N6-cyclohexyladenosine and other adenosine analogs enhance histamine-elicited, but not norepinephrine- or carbamylcholine-elicited accumulations of inositol phosphates in [3H]inositol-labeled guinea-pig cerebral cortical slices. The adenosine analogs alone have no effect on accumulations of inositol phosphates. The effect of 2-chloroadenosine is blocked by the adenosine receptor antagonists theophylline and 1,3-dialkyl-8-p-sulfophenylxanthines. The rank order of activity of the six adenosine analogs with respect to augmentation of histamine-elicited accumulation of inositol phosphates in guinea-pig cerebral cortical slices is different from the rank order at an A2-adenosine receptor that mediates synergistic accumulations of cyclic AMP by adenosine analogs and histamine in guinea-pig cerebral cortical slices.

The protein kinase C activator phorbol-12-myristate-13-acetate enhances cyclic AMP accumulation in pheochromocytoma cells.

The protein kinase C activator, phorbol-12-myristate-13-acetate (PMA), augments the cyclic AMP accumulation induced by forskolin in pheochromocytoma (PC 12) cells with an EC50 value of 14 nM, while having no effect on basal values. At a concentration of 100 nM PMA markedly augmented the magnitude of the forskolin response and, in addition, caused a slight increase in the potency of forskolin. PMA also enhanced the maximal cyclic AMP accumulation produced by 2-chloroadenosine, and caused a slight increase in potency of the adenosine analog. Since PMA mimics the effect of diacylglycerols that form during the turnover of the membrane lipid, phosphatidylinositol, the results suggest an interrelationship between the systems involved in phosphatidylinositol turnover and cyclic AMP generation in PC 12 cells.

Accumulation of inositol phosphates and cyclic AMP in guinea-pig cerebral cortical preparations. Effects of norepinephrine, histamine, carbamylcholine and 2-chloroadenosine.

Norepinephrine and serotonin augment by about 2-fold the accumulation of cyclic [3H]AMP elicited by 2-chloroadenosine in [3H]adenine-labeled guinea-pig cerebral cortical slices. Histamine causes a 3-fold augmentation. The first two agents have no effect on cyclic AMP alone, while histamine has only a small effect alone. The augmentation of the 2-chloroadenosine response appears to be mediated by alpha 1-adrenergic, 5HT2-serotonergic and H2-histaminergic receptors. VIP-elicited accumulations of cyclic AMP are also augmented through stimulation of alpha 1-adrenergic, 5HT2-serotonergic and H1-histaminergic receptors. Activation of these amine receptors also increases the turnover of phosphatidylinositols in [3H]inositol-labeled guinea pig cerebral cortical slices. Norepinephrine causes a 5-fold, serotonin a 1.2-fold, and histamine a 2.5-fold increase in accumulations of [3H]inositol phosphates. 2-Chloroadenosine, vasoactive intestinal peptide, baclofen, and somatostatin have no effect on phosphatidylinositol turnover, nor do the last two agents augment accumulations of cyclic AMP elicited by 2-chloroadenosine. The data suggest a possible relationship between turnover of phosphatidylinositol and the augmentations of the cyclic AMP accumulations elicited by biogenic amines in brain slices.

Biochemical characterization of a filtered synaptoneurosome preparation from guinea pig cerebral cortex: cyclic adenosine 3':5'-monophosphate-generating systems, receptors, and enzymes.

A particulate preparation was obtained by low speed centrifugation of guinea pig cerebral cortical homogenates prepared with a Krebs-Henseleit buffer. Light microscopic examination, using a reflected light differential interference contrast system, reveals the presence of intact neurons, axonal fragments, glial cells, and erythrocytes along with an abundance of small spherical entities (diameter about 1.1 micron) and snowman-shaped entities (diameter of larger sphere about 1.1 micron, diameter of attached smaller sphere about 0.6 micron). Many unattached smaller spherical entities are also present (diameter about 0.6 micron). Pressure filtration through 5- or 10-micron Millipore filters, followed by low speed centrifugation and resuspension, removes most of the larger entities to afford a suspension composed mainly of the small spherical and snowman-shaped entities. Electron microscopic examination reveals the presence of many synaptosomes with attached resealed postsynaptic entities. It is proposed that these correspond to the snowman-shaped entities to be termed synaptoneurosomes. Accumulations of cyclic AMP elicited by 2-chloroadenosine and histamine, and by combinations of 2-chloroadenosine, histamine, norepinephrine, and forskolin, are lower in filtered than in unfiltered preparations, whereas accumulations elicited by forskolin are unchanged. Levels of adenylate cyclase are reduced by filtration, whereas levels of phosphodiesterase are unchanged. Filtration reduces levels of markers for whole cells and endothelial cells, whereas neuronal markers such as acetylcholinesterase activity and norepinephrine uptake are increased. Levels of S-100 protein, a marker for glial cells, are not significantly decreased. There is no apparent change in the density of many receptors or ion channels. Levels of A1-adenosine and H1-histamine receptors are increased, whereas levels of so-called peripheral benzodiazepine-binding sites are decreased.

An activator of protein kinase C (phorbol-12-myristate-13-acetate) augments 2-chloroadenosine-elicited accumulation of cyclic AMP in guinea pig cerebral cortical particulate preparations.

Norepinephrine and histamine markedly augment accumulations of cyclic AMP elicited by 2-chloroadenosine in a guinea pig cerebral cortical vesicular preparation. In addition, these biogenic amines stimulate phosphatidylinositol turnover. Phosphatidylinositol turnover is associated with mobilization of internal calcium and with stimulation of protein kinase C. Phorbol-12-myristate-13-acetate (PMA), a known activator of protein kinase C, has no effect on cyclic AMP levels alone, but in a concentration-dependent manner enhances accumulations of cyclic AMP elicited by 2-chloroadenosine. PMA, like norepinephrine, also enhances accumulations of cyclic AMP elicited by histamine. PMA has no effect on the synergistic accumulations of cyclic AMP elicited by combinations of amines and 2-chloroadenosine. PMA also augments accumulations of cyclic AMP elicited by forskolin. The results suggest that activation of phosphatidylinositol turnover by biogenic amines may lead via stimulation of protein kinase C to enhanced responsiveness of cyclic AMP-generating systems.

The effects produced by prostaglandin D2 on serotonin turnover and release and tryptophan uptake.

In earlier studies, it was proposed that there was a serotonergic involvement in the ability of prostaglandin D2 (PGD2) to potentiate pentobarbital sleeping time. The actions of PGD2 on neuronal turnover and release of serotonin and uptake of tryptophan were examined in mice. The effect of PGD2 administration on serum tryptophan levels was also investigated. PGD2 (1 and 4 mg/kg) increased the concentrations in whole brain of endogenous tryptophan (TRYP) and of 3H-tryptophan (3H-TRYP) following an intravenous (IV) injection of 3H-tryptophan. Formation of 3H-5-hydroxyindoleacetic acid (3H-5HIAA) was doubled after PGD2 administration (1 and 4 mg/kg). Whole brain concentrations of endogenous serotonin (5HT) and 3H-serotonin (3H-5HT) were unchanged after the administration of the prostaglandin. PGD2 (10(-4) to 10(-10)M) in vitro had no effect on spontaneous or K+-evoked release of 3H-5HT from whole brain synaptosomes. Uptake of 3H-tryptophan in synaptosomes was neither stimulated nor depressed by (10(-4) to 10(-12)M) PGD2. There was also no change in serum tryptophan levels after administration of this prostaglandin. Thus, PGD2 administration does affect the serotonergic system but no direct neurochemical correlate of sedation can be shown.

Involvement of the serotonergic system in the prolongation of pentobarbital sleeping time produced by prostaglandin D2.

In the present study, the depressant and sedative actions of prostaglandin D2 (PGD2) were investigated. Intravenous (IV) administration of PGD2 produced a significant decrease in the spontaneous locomotor activity of mice from 1 to 15 minutes following injection. Prostaglandin D2 was also able to potentiate pentobarbital sleeping time at doses of 0.4 and 4.0 mg/kg when administered intravenously. Distribution studies with 3H-PGD2 (6 microCi, 4 mg/kg) showed that only 0.04% of the tritium administered could be found in brain at 5 min after the injection, and that only 50% of this was parent 3H-PGD2. The role of the serotonergic neurotransmitter system in the depressant action of PGD2 was investigated with drugs which modulate this system. The ability of PGD2 to potentiate pentobarbital sleeping time was diminished by pretreatment with agents that reduce brain level or synthesis rate of serotonin. Such agents include para-chlorophenylalanine (PCPA), a tryptophan hydroxylase inhibitor, 5,7-dihydroxytryptamine (5,7-DHT), a neurotoxin with selectivity for serotonergic neurons, and quipazine, a serotonergic autoreceptor stimulant. On the other hand, pretreatment with 5-hydroxytryptophan (5-HTP), the precursor of serotonin, further enhanced the potentiation of pentobarbital sleeping time by PGD2. These data suggest that the depressant actions of PGD2 are linked to the serotonergic neurotransmitter system.

Barbiturate and picrotoxin-sensitive chloride efflux in rat cerebral cortical synaptoneurosomes.

The effects of various barbiturates and picrotoxin in modifying the efflux of chloride (36Cl-) was studied in a novel subcellular preparation from rat cerebral cortex, the 'synaptoneurosome'. Dilution of synaptoneurosomes pre-loaded with 36Cl- resulted in rapid efflux of 36Cl- that could be measured as early as 10 s following dilution. In the presence of barbiturates such as pentobarbital and hexobarbital there was a significant increase in 36Cl- efflux which was not observed with the pharmacologically-inactive barbiturate, barbital. The effect of barbiturates in enhancing 36Cl- efflux was also stereospecific [(-)-DMBB greater than (+)-DMBB] and reversed by picrotoxin. By contrast, picrotoxin alone significantly inhibited 36Cl- efflux. These data demonstrate pharmacologically relevant Cl- transport for the first time in a subcellular brain preparation.