Flight initiation and maintenance deficits in flies with genetically altered biogenic amine levels.

Insect flight is one of the fastest, most intense and most energy-demanding motor behaviors. It is modulated on multiple levels by the biogenic amine octopamine. Within the CNS, octopamine acts directly on the flight central pattern generator, and it affects motivational states. In the periphery, octopamine sensitizes sensory receptors, alters muscle contraction kinetics, and enhances flight muscle glycolysis. This study addresses the roles for octopamine and its precursor tyramine in flight behavior by genetic and pharmacological manipulation in Drosophila. Octopamine is not the natural signal for flight initiation because flies lacking octopamine [tyramine-beta-hydroxylase (TbetaH) null mutants] can fly. However, they show profound differences with respect to flight initiation and flight maintenance compared with wild-type controls. The morphology, kinematics, and development of the flight machinery are not impaired in TbetaH mutants because wing-beat frequencies and amplitudes, flight muscle structure, and overall dendritic structure of flight motoneurons are unaffected in TbetaH mutants. Accordingly, the flight behavior phenotypes can be rescued acutely in adult flies. Flight deficits are rescued by substituting octopamine but also by blocking the receptors for tyramine, which is enriched in TbetaH mutants. Conversely, ablating all neurons containing octopamine or tyramine phenocopies TbetaH mutants. Therefore, both octopamine and tyramine systems are simultaneously involved in regulating flight initiation and maintenance. Different sets of rescue experiments indicate different sites of action for both amines. These findings are consistent with a complex system of multiple amines orchestrating the control of motor behaviors on multiple levels rather than single amines eliciting single behaviors.

Cardiac effects of trace amines: pharmacological characterization of trace amine-associated receptors.

Trace amine-associated receptors, a novel class of G-protein coupled receptors which respond to trace amines but not to classical biogenic amines, have been found to be expressed in heart. Therefore, we investigated the cardiac effects of the trace amines p-tyramine, beta-phenylethylamine, octopamine, and tryptamine. Isolated rat hearts were perfused in the presence of trace amines, monitoring the hemodynamic variables. In addition, radioligand binding experiments with [3H]-p-tyramine and [125I]-3-iodothyronamine were performed in rat ventricular tissue. Octopamine, beta-phenylethylamine, and tryptamine produced a dose-dependent negative inotropic effect as shown by reduced cardiac output (IC(50)=109 microM, 159 microM, and 242 microM, respectively). In the same preparation a similar effect was produced by thyronamine and 3-iodothyronamine, with IC(50)=94 microM and 27 microM, respectively. The negative inotropic effect of octopamine was confirmed in a papillary muscle preparation. All trace amines except tryptamine increased the heart rate, but this action could be attributed to their sympathomimetic properties, since it was abolished by propranolol. The negative inotropic effect of trace amines was significantly increased by the tyrosine kinase inhibitor genistein. Specific and saturable binding of [(3)H]-p-tyramine and [125I]-3-iodothyronamine was observed in ventricular tissue. While [3H]-p-tyramine was displaced by 3-iodothyronamine, [(125)I]-3-iodothyronamine was not displaced by p-tyramine. In conclusion, trace amines and thyronamines are negative inotropic agents. Their effect appears to be mediated by a subtype of trace amine-associated receptor which is characterized by the rank of potency: 3-iodothyronamine > thyronamine = octopamine = beta-phenylethylamine, while tryptamine and p-tyramine are significantly less active.

Trace amine receptors as targets for novel therapeutics: legend, myth and fact.

Trace amines are attracting attention as neurotransmitters because they are believed to play a role in human disorders such as schizophrenia, depression, attention deficit disorder and Parkinson's disease. Research to date is promising and confirms the need for continuing work to forge the way for new drug discovery.

Peptide and trace amine orphan receptors: prospects for new therapeutic targets.

Over 20 orphan receptors predicted to exist from the human genome have now been paired with their cognate peptide ligand. In human tissues, expression of mRNA encoding several of these peptides (including bovine adrenomedullary peptide, orexins, prolactin-releasing peptide, tuberoinfundibular peptide 39 and neuropeptide B and W) and their receptors is predominantly in the CNS, implying a central role. However, ligand-binding and functional studies suggest that urotensin II, apelin, ghrelin, relaxin and urocortins, together with the trace amine tyramine, may have a role in the human cardiovascular system, with the prospect of becoming new therapeutic targets.

Substituted (pyrroloamino)pyridines: potential agents for the treatment of Alzheimer's disease.

A novel series of substituted (pyrroloamino)pyridines was synthesized, and the compounds were evaluated for cholinomimetic-like properties in vitro (inhibition of [3H]quinuclidinyl benzilate binding) and in vivo (reversal of scopolamine-induced dementia) as potential agents for the treatment of Alzheimer's disease. Compounds displaying significant activity were more broadly evaluated, which revealed the presence of a desirable adrenergic component of activity. The synthesis and structure-activity relationships for this series is presented, along with the biological profiles of selected compounds.

Synthesis and structure-activity relationships of N-propyl-N-(4-pyridinyl)-1H-indol-1-amine (besipirdine) and related analogs as potential therapeutic agents for Alzheimer's disease.

A series of novel N-(4-pyridinyl)-1H-indol-1-amines and other heteroaryl analogs was synthesized and evaluated in tests to determine potential utility for the treatment of Alzheimer's disease. From these compounds, N-propyl-N-(4-pyridinyl)-1H-indol-1-amine (besipirdine, 4c) was selected for clinical development based on in-depth biological evaluation. In addition to cholinomimetic properties based initially on in vitro inhibition of [3H]quinuclidinyl benzilate binding, in vivo reversal of scopolamine-induced behavioral deficits, and subsequently on other results, 4c also displayed enhancement of adrenergic mechanisms as evidenced in vitro by inhibition of [3H] clonidine binding and synaptosomal biogenic amine uptake, and in vivo by reversal of tetrabenazine-induced ptosis. The synthesis, structure-activity relationships for this series, and the biological profile of 4c are reported.

Increased biogenic amine release in mouse hypothalamus following immunological challenge: antagonism by indomethacin.

Stimulation of the acute-phase response in mice by lipopolysaccharide, pokeweed mitogen, concanavalin A or interleukin-1 was associated with increased release of biogenic amines, serotonin and norepinephrine in the hypothalamus as indexed by their primary metabolites, 5-hydroxyindoleacetic acid and 3-methoxy-4-hydroxyphenylglycol, respectively. The increases in norepinephrine and serotonin turnover observed 4 h following systemic administration of interleukin-1 were antagonized by concurrent administration of indomethacin, a potent inhibitor of cyclooxygenase. These data suggest that the increase in norepinephrine and serotonin release in mouse hypothalamus during the acute-phase response to infection is partially mediated by the actions of arachidonic acid metabolites.

Somatostatin: peripheral venoconstrictive activity and interaction with monoamines in man.

The mechanism of somatostatin venoconstriction and tachyphylaxis in the human hand vein in vivo has been investigated. No cross-tachyphylaxis was observed between somatostatin and 5-hydroxytryptamine, noradrenaline, adrenaline, dopamine or tyramine-induced venoconstriction. Somatostatin potentiates the venoconstrictive activity of noradrenaline, adrenaline and dopamine, but not that of 5-hydroxytryptamine and tyramine. Phentolamine antagonizes the somatostatin-induced venoconstriction, whereas methysergide, haloperidol and morphine do not. It is suggested that somatostatin could act on specific receptors in the hand vein, but the mechanism of somatostatin venoconstriction and interaction with vasoactive monoamines remains to be defined.

Lamotrigine inhibits monoamine uptake in vitro and modulates 5-hydroxytryptamine uptake in rats.

Lamotrigine is a novel anticonvulsant drug which also stabilises mood in bipolar illness via an unknown mechanism. We report the concentration-dependent inhibition of 5-hydroxytryptamine (5-HT) uptake in both human platelets and rat brain synaptosomes (IC50s were 240 and 474 microM, respectively) by lamotrigine. Synaptosomal uptake of noradrenaline (IC50 239 microM) and dopamine (IC50 322 microM) was also inhibited. Tetrodotoxin failed to modulate 5-HT uptake suggesting that sodium channel blockade does not mediate the lamotrigine effect. Lithium, sodium valproate, zonisamide, and carbamazepine all possess anti-manic activity but only the latter inhibited 5-HT uptake. The inhibition of the p-chloroamphetamine-induced 5-HT syndrome in rats suggests that lamotrigine also inhibits 5-HT uptake in vivo. These effects probably reflect an affinity for biogenic amine transporters. However, at present, it remains uncertain whether, at clinically effective doses, these effects contribute significantly to the efficacy of lamotrigine in bipolar illness.

R-(-)-deprenyl (Selegiline, Movergan) facilitates the activity of the nigrostriatal dopaminergic neuron.

(-)Deprenyl, when administered continuously in small doses (0.25 mg/kg/day), facilitates the activity of the nigrostriatal dopaminergic neuron because of its highly characteristic complex spectrum of pharmacologic activity: it is a highly potent and selective inhibitor of B-type MAO; it inhibits the reuptake of dopamine; it inhibits dopamine autoreceptors; it enhances scavenger function. 1) (-)Deprenyl treatment decreased significantly the activity of the cholinergic interneurons. In a series of experiments the acetylcholine (ACh) content was found to be 0.69 nmole/mg protein in the striatum of untreated rats, whereas a significantly higher amount of ACh (0.86 nmol/mg protein) was found in the rat striatum after two week pretreatment with (-)deprenyl, and the fractional rate constant (kb) of ACh efflux from the cholinergic interneurons of the striatum decreased significantly in the (-)deprenyl-treated group from 9.1 +/- 0.8 to 6.2 +/- 0.55. 2) The (-)deprenyl-induced increase of the dopaminergic tone in the striatum was proved by measurements of the activity of the nigrostriatal dopaminergic neuron. Whereas the striatum of untreated rats contained 52.7 +/- 1.6 nmole/g dopamine (DA) and the turnover rate (TRDA) was found to be 13.7 +/- 1.3 nmole/g/hr, the striatum of rats pretreated with 0.25 mg/kg (-)deprenyl daily for 28 days contained significantly higher amount of DA (81.77 +/- 5.7 nmole) and the turnover rate increased significantly to 24.44 +/- 1.1. Using the Glowinski-Iversen preparation we found that from the striata of untreated rats 200.0 +/- 25.8 pmole/g/min DA was released to KCl stimulation, whereas the amount of DA released to stimulation from the striata of rats pretreated with (-)deprenyl for 3 weeks increased significantly to 1452.2 +/- 183.1 pmole/g/min. 3) (-)Deprenyl inhibits the uptake of dopamine into the nigrostriatal dopaminergic neuron. In a new series of experiments we found that 420 +/- 21 pmole/g protein 3H-DA was taken up within 5 minutes in the striatum slices of untreated rats. Pretreatment of the rats with 0.25 mg/kg (-)deprenyl daily for two weeks decreased significantly the uptake of DA to 284 +/- 28 pmole/mg. 4) In a new series of experiments we found that the striata of untreated rats emitted 404.2 +/- 36.2 pmole/g/min ACh to ouabain stimulation but the striata dissected from rats pretreated with 6-hydroxy-dopamine (6-OHDA) released 811.4 +/- 49.2 pmol/g/min (p less than or equal to 0.001).

Effects of cholinergic and monoaminergic antagonists and tranquilizers upon spatial memory in rats.

To explore the pharmacological mechanisms of the spatial memory, performance on the radial arm maze was tested in rats under the following drugs, using a within-subject design; scopolamine (0.25 and 0.5 mg/kg), methylscopolamine (0.5 and 1 mg/kg), phentolamine (5 and 10 mg/kg), propranolol (10 and 20 mg/kg), chlorpromazine (1 and 2 mg/kg), and chlordiazepoxide (5 and 10 mg/kg). The number of correct choices was significantly decreased by scopolamine, while the other drugs, including methylscopolamine, showed no effects on the correct choices. Almost all drugs affected the running time. These findings indicate that the brain cholinergic system is involved in the spatial memory.

Spatial working memory in rats: effects of monoaminergic antagonists.

To assess the possible involvement of the monoaminergic neurotransmitters norepinephrine, dopamine and serotonin in the maintenance of spatial working memory rats were treated with antagonists 0 or 2 hr after completing the first 4 choices in an 8 arm maze. Haloperidol (0.25-1 mg/kg), when administered 2 hr after Choice 4, produced a small but consistent impairment in performance on retention tests given 5 hr after the first 4 choices. This deficit closely resembled natural forgetting in terms of the type of errors committed. By contrast, haloperidol in the same doses given 0 hr after Choice 4 or 3 hr before the first 4 choices did not affect retention. Likewise treatment with propranolol (10-20 mg/kg), phentolamine (5-20 mg/kg) or methysergide (5-15 mg/kg) did not impair spatial memory, regardless of when these drugs were injected within the session. Evidently dopaminergic neuronal systems are important in the maintenance of normal spatial working memory.

Endotoxin- and interleukin-1-induced hypophagia are not affected by adrenergic, dopaminergic, histaminergic, or muscarinic antagonists.

Endotoxin (lipopolysaccharide, LPS) and interleukin-1 (IL-1) administration induce hypophagia in rodents. Both IL-1 and LPS are known to activate cerebral norepinephrine and serotonin metabolism, and IL-1 affects that of acetylcholine and histamine. Each of these neurotransmitters has been implicated in feeding behavior. Therefore, the ability of specific antagonists of the above neurotransmitter systems to counteract feeding responses to peripherally injected mIL-1beta and LPS was studied. Feeding was assessed in nondeprived mice by measuring the intake of sweetened milk in a 30-min period, as well as daily food pellet intake. LPS and mIL-1beta reliably reduced milk intake, and often reduced food pellet intake and body weight. Treatment of the mice with peripherally administered alpha-adrenergic (phentolamine or prazosin) or 3-adrenergic antagonists (propranolol), either alone or in combination, did not significantly alter the hypophagic responses to mIL-1beta or LPS. Mice in which cerebral norepinephrine was depleted with DSP-4 or 6-hydroxydopamine also displayed the usual hypophagia in response to mIL-1beta and LPS. The hypophagic responses to mIL-1beta and LPS were not affected by the histaminergic antagonists, pyrilamine (H1), cimetidine (H2), thioperamide (H3), or the histamine-depleting agent, alpha-fluoromethylhistidine, nor by the muscarinic cholinergic antagonist, scopolamine. The responses to mIL-l1 were also unaffected by the dopamine receptor antagonist, haloperidol, the opioid receptor antagonist, naloxone, and the NO synthase inhibitor, L-NAME. These results suggest that adrenergic, dopaminergic, histaminergic, cholinergic, opioid or nitric oxide systems are not essential for the hypophagia induced by IL-1, and that multiple redundant pathways may be involved in illness-related hypophagia.

REM-sleep deprivation-induced increase in ethanol intake: role of brain monoaminergic neurons.

The ethanol intake of Long-Evans male rats was recorded before, during and after deprivation of rapid eye movement (REM) sleep produced with the flowerpot technique modified by using a cuff pedestal and electrified grid floor instead of water. Ethanol intake increased significantly during REM-sleep deprivation. A rebound decrease in ethanol drinking was then observed during the REM-rebound phase immediately after the termination of REM-sleep deprivation. Because REM-sleep deprivation has been reported to impair the function of central monoamine neuronal systems and because some studies have implicated these systems in the control of voluntary ethanol intake, we studied whether different monoamine uptake blocking agents could antagonize the increase in ethanol intake caused by REM-sleep deprivation. After three days of REM-sleep deprivation, the rats were given uptake blocking agents for serotonin (citalopram, 5, 10 and 20 mg/kg/day, IP), dopamine (GBR 12909, 5 mg/kg/day, IP) and noradrenaline (talsupram, 1, 5 and 10 mg/kg/day, IP). Citalopram and GBR 12909 did not modify the increased level of ethanol intake, but talsupram decreased ethanol intake to the levels seen prior to deprivation, and during the REM-rebound phase amplified the decrease found. These effects of talsupram could be antagonized by blocking mg/kg/day, IP). Prazosin alone tended to increase ethanol consumption. These findings suggest that functional alterations in central noradrenergic neurons during REM-sleep deprivation may contribute to the concurrent increase in ethanol intake.

[Sensitivity of fragmented and stratified sea urchin embryos to cytotoxic neuropharmacological preparations]. / Chuvstvitel'nost' zarodyshei-fragmentov i stratifitsirovannykh zarodyshei moskikh ezhei k tsitotoksicheskim neirofarmakologicheskim preparatam.

The red half embryos and related quarter embryos (yolk and pigment) of Arbacia lixula, obtained by means of centrifugation of the eggs in sucrose gradient, retain the normal level of sensitivity and supersensitivity to cytotoxic neuropharmaca, antagonists of biogenic monoamines. The white half embryos and clear quarter embryos practically lack supersensitivity whereas the granular quarter embryos restore it to the initial level. The non-pigmented blastomers of stratified embryos are characterized by somewhat weakened supersensitivity. A suggestion is put forward that the supersensitive embryos of A. lixula possess a sensibilizing factor which couples the supersensitivity receptors with the processes of cell division and moves together with the yolk granules upon centrifugation. This factor is not observed in the Strongylocentrotus granularis embryos lacking evident supersensitivity.

Biogenic amines modulate pulse rate in the dorsal blood vessel of Lumbriculus variegatus.

The biogenic amines are widespread regulators of physiological processes, and play an important role in regulating heart rate in diverse organisms. Here, we present the first pharmacological evidence for a role of the biogenic amines in the regulation of dorsal blood vessel pulse rate in an aquatic oligochaete, Lumbriculus variegatus (Müller, 1774). Bath application of octopamine to intact worms resulted in an acceleration of pulse rate, but not when co-applied with the adenylyl cyclase inhibitor MDL-12,330a. The phosphodiesterase inhibitor theophylline mimicked the effects of OA, but the polar adenosine receptor antagonist 8(p-sulphophenyl)theophylline was significantly less potent than theophylline. Pharmacologically blocking synaptic reuptake of the biogenic amines using the selective 5-HT reuptake blocker fluoxetine or various tricyclic antidepressants also accelerated heart rate. Depletion of the biogenic amines by treatment with the monoamine vesicular transporter blocker reserpine dramatically depressed pulse rate. Pulse rate was partially restored in amine-depleted worms after treatment with octopamine or dopamine, but fully restored following treatment with serotonin. This effect of 5-HT was weakly mimicked by 5-methoxytryptamine, but not by alpha-methylserotonin; it was completely blocked by clozapine and partially blocked by cyproheptadine. Because they are known to orchestrate a variety of adaptive behaviors in invertebrates, the biogenic amines may coordinate blood flow with behavioral state in L.variegatus.