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.

Discovery and structure-activity relationships of novel selective norepinephrine and dual serotonin/norepinephrine reuptake inhibitors

Novel arylthiomethyl morpholines are potent selective norepinephrine reuptake inhibitors (NERIs) and dual serotonin/norepinephrine reuptake inhibitors (SRI/NERIs). The target compounds were prepared using a stereochemically versatile synthesis featuring an aldol condensation as the key step. One enantiomer of the 2-methoxy-substituted analogue was found to be a potent and selective norepinephrine reuptake inhibitor, whereas the opposite enantiomer was a potent dual serotonin/norepinephrine reuptake inhibitor.

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.

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.

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.

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.

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.

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.

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.

Effects of cocaine on methamphetamine-induced neurochemical changes: characterization of cocaine as a monoamine uptake blocker

Many of the rewarding aspects of cocaine are thought to be due to the ability of this stimulant to block reuptake of monoamines. However, because of its ability also to cause transmitter release, it is difficult to examine the properties of cocaine as an uptake blocker using in vitro techniques such as tissue slices or synaptosomes. Thus, we have evaluated cocaine as a blocker of dopamine and 5-hydroxytryptamine uptake processes by determining the in vivo effect of concurrent administrations of cocaine on the neurochemical effects of methamphetamine treatments. These findings demonstrated that cocaine like 5-hydroxytryptamine uptake blockers such as citalopram, greatly attenuated or blocked decreases in striatal and cortical tryptophan hydroxylase activities and concentrations of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid induced by multiple and single methamphetamine administrations. In contrast to other dopamine uptake blockers, such as amfonelic acid, cocaine did not attenuate the methamphetamine effects on striatal tyrosine hydroxylase activity and the concentrations of dopamine, dihydroxyphenylacetic acid and homovanillic acid. The neurochemical findings were correlated with behavioral analyses.

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.

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.

Biogenic amines and beta-endorphin responses in the rat vas deferens

1. Recent studies have demonstrated that activation of opioid peptide receptor by beta-endorphin results in a change of bioamines in peripheral tissues. 2. The present results could be interpreted assuming that the action of beta-endorphin, on the smooth muscle of the isolated rat vas deferens, is independent of catecholaminergic, cholinergic and tryptaminergic neurotransmission. 3. There is evidence that it is through a specific opioid 'epsilon-receptor' which have been shown a high degree of affinity for beta-endorphin.

Competitive antagonism by phentolamine of responses to biogenic amines and the transmitter at a neuroglandular junction

1. A quantitative study has been made of phentolamine's inhibition of the electrical and secretory responses of the isolated salivary glands of Nauphoeta cinerea Olivier to nerve stimulation and bath applications of agonists. 2. The results suggested that phentolamine is a competitive antagonist having an affinity constant of about 1 micrometer-1 for the receptors for dopamine, noradrenaline, adrenaline and the neurotransmitter. 3. Phentolamine also inhibited responses to 5-hydroxytryptamine in a manner seemingly more complex than competitive antagonism. Attempts to estimate the affinity constant gave values of about 0.08 and 0.015 microgram-1 for inhibition of the secretory and electrical responses respectively. 4. This investigation showed that phentolamine discriminates between two kinds of receptor in this gland, one binding 5-hydroxytryptamine and the other combining with catecholamines and the neurotransmitter.

Antagonism of biogenic amine-induced depression of cerebral cortical neurones by Na+, K+-ATPase in inhibitors

The effects of iontophoretically applied Na+-, K+-dependent adenosinetriphosphatase (Na+,K+-ATPase) (EC 3.6.1.3) inhibitors (ouabain, digitoxin, digitoxigenin, strophanthin K, strophanthidin, thevetin A and B, ethacrynate, and harmaline) on the depression of rat cerebral cortical neurones by noradrenaline, 5-hydroxytryptamine, and histamine have been studied. The inhibitors antagonized depressions of spontaneously active neurones evoked by these amines, but not those evoked by gamma-aminobutyric acid, adenosine, adenosine 5'-monophosphate, or calcium. The antagonistic potencies of the various inhibitors appeared to be proportional to their known potencies as inhibitors of Na+, K+-ATPase. The data therefore support the hypothesis that amines depress central neurones by activating an electrogenic sodium pump.

Possible involvement of monoamines in the release of adipokinetic hormone in the locust Schistocerca gregaria

1. The adipokinetic hormone release, which can be induced by anticholinesterases, is reduced by depleting the content of monoamines in the nervous system. 2. The participation of monoamines in the pathway of release of adipokinetic hormone is studied in vivo and in vitro. 3. A possible mechanism for anticholinesterase-induced release of this hormone involving cholinergic and aminergic transmission is postulated.

Dopaminergic mediation of the interoceptive cue produced by d-amphetamine in rats

After rats were trained to differentiate between the effects of d-amphetamine and saline in a state-dependent task, pretreatment with the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine, significantly decreased amphetamine discrimination. Pretreatment with the dopamine-beta-hydroxylase inhibitor, disulfiram, or with the tryptophan hydroxylase inhibitor, p-chloro-phenylalanine, was observed to have no effect on the rats' ability to discriminate d-amphetamine. Administration of haloperidol, a selective dopamine receptor blocker, completely abolished the amphetamine discrimination, whereas alpha- and beta-adrenergic receptor blockade had no effect. Apomorphine, a dopamine receptor stimulant, produced amphetamine-like responses and this was, likewise, abolished by pretreatment with haloperidol. These data suggest that dopaminergic systems mediate the interoceptive cue produced by d-amphetamine in rats, and these results are discussed in relation to possible dopamine mediation of amphetamine psychosis and paranoid schizophrenia.