5HT2 receptor changes in rat cortex and platelets following chronic ritanserin and clorgyline administration

Flavins and flavoproteins: applications in medicine

The potential of flavoproteins as targets of pharmacological treatments is immense. In this review we present an overview of the current research progress on medical interventions based on flavoproteins with a special emphasis on cancer, infectious diseases, and neurological disorders.

Therapeutic Potentials of Sarpogrelate in Cardiovascular Disease*

In view of the pivotal role of serotonin (5-HT) in a wide variety of cardiovascular disorders, extensive effort has been made to develop different types of 5-HT receptor antagonists for therapeutic use. On the basis of experimental studies, this article is focused on the potentials of sarpogrelate, a specific 5-HT2A receptor antagonist as an antiplatelet, antithrombotic, antiatherosclerotic and antianginal agent. The major effects of sarpogrelate are due to the inhibition of 5-HT-induced platelet aggregation and smooth muscle cell proliferation. This agent was found to attenuate the 5-HT-mediated increase in intracellular Ca2+ and ischemia-reperfusion injury in the heart. Sarpogrelate has been found to have beneficial effects in peripheral vascular disease, restenosis after coronary stenting, pulmonary hypertension, acute and chronic myocardial infarction.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

The effect of a 5HT2 receptor antagonist sarpogrelate (MCI-9042) treatment on platelet function in Buerger's disease

The effect of a new, specific 5-HT2 receptor antagonist sarpogrelate (MCI-9042) treatment on platelet function and serotonin levels in both plasma and whole blood in Buerger's disease, was assessed in a pilot study. We investigated 10 patients suffering from Buerger's disease. Sarpogrelate in a dose of 3 x 100 mg a day was given p.o. for a period of 8 weeks. It was well tolerated and no major side effects were noted. It was judged to be effective in some patients as assessed by its effect on both subjective complaints and objective evaluation of ankle pressure index (API). Sarpogrelate induced a significant decrease in plasma serotonin (5-HT) concentration starting after the 4th week which lasted through to the 8th week of the study, whereas plasma tryptophan concentration increased significantly after 2 and 4 weeks. There were no changes in plasma 5-HIAA concentration. On the other hand whole blood 5-HT concentration increased significantly after 2 weeks, and there was also a tendency to increase in whole blood tryptophan concentration (p = 0.052). Platelet aggregation induced by ADP and collagen did not show any statistically significant changes. Surprisingly, platelet aggregation induced by serotonin increased significantly after 2 weeks and even more so after 4 weeks of treatment, and then it returned to baseline values after 8 weeks. There was no effect on platelet count, APTT, TT and fibrinogen concentration.

Interfacial activation-based molecular bioimprinting of lipolytic enzymes

Interfacial activation-based molecular (bio)-imprinting (IAMI) has been developed to rationally improve the performance of lipolytic enzymes in nonaqueous environments. The strategy combinedly exploits (i) the known dramatic enhancement of the protein conformational rigidity in a water-restricted milieu and (ii) the reported conformational changes associated with the activation of these enzymes at lipid-water interfaces, which basically involves an increased substrate accessibility to the active site and/or an induction of a more competent catalytic machinery. Six model enzymes have been assayed in several model reactions in nonaqueous media. The results, rationalized in light of the present biochemical and structural knowledge, show that the IAMI approach represents a straightforward, versatile method to generate manageable, activated (kinetically trapped) forms of lipolytic enzymes, providing under optimal conditions nonaqueous rate enhancements of up to two orders of magnitude. It is also shown that imprintability of lipolytic enzymes depends not only on the nature of the enzyme but also on the "quality" of the interface used as the template.

Human platelet 5-HT2 receptor binding sites re-evaluated: a criticism of current techniques [corrected]

The human platelet 5-HT2 receptor may resemble a peripheral model of central 5-HT2 binding sites and has been linked to changes in 5-HT2 receptor function in depression. Therefore, evaluation of the human platelet 5-HT2 binding characteristics is important. Comparing [3H]ketanserin and [3H]LSD as ligands clearly indicated [3H]LSD as ligand of choice for binding studies dealing with the human platelet 5-HT2 receptor. [3H]LSD binding was specific, saturable, and depended upon incubation time, protein concentration and previous handling of tissue, i.e., use of fresh or frozen tissue. In contrast, studies with [3H]ketanserin were unsatisfactory. Although mean receptor densities and affinities have been relatively constant between individuals and over time in healthy subjects with [3H]LSD, examination of the individual data showed considerable variations within single subjects. Thus, KD ranged between 0.50 and 0.68 nM, and Bmax was in the range of 64.9 to 97.1 fmol/mg protein in healthy individual subjects. Therefore, we recommend [3H]LSD as ligand of choice to study platelet 5-HT2 receptor binding in humans. Furthermore, repeated measurement of individual data over time should be interpreted cautiously, especially when data from depressed patients are under examination.

Mianserin-induced up-regulation of serotonin receptors on normal human platelets in vivo

The antidepressant, mianserin, is a serotonin receptor (5-HT2) antagonist and produces down-regulation of 5-HT2 and 5-HT1c receptors in the cerebral cortex of rats. In preparation for testing the validity of platelets as a model system for changes in 5-HT2 receptors during antidepressant drug treatment, mianserin (40 mg daily), was given to five human volunteers for five days, and platelets were collected on days 0, 1, 6, and 8. 5-HT2 receptor affinity and density were measured by specific binding of 125I-LSD, with and without an excess of spiperone. 5-HT uptake site affinity and density were determined by 3H-paroxetine binding, with and without an excess of fluoxetine. Platelet serotonin content was measured using high pressure liquid chromatography and electrochemical detention. Platelet 5-HT2 receptor density was increased and the ligand affinity was decreased during mianserin administration. In contrast, platelet 5-HT content was not altered significantly by mianserin administration, nor was platelet uptake site density and ligand affinity.

Further evidence for enigmas in adaptation mechanisms for the DOI-induced behaviors

The acute and chronic effects of the 5-hydroxytryptamine2/1C (5-HT2/1C) receptor agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and the antagonist ketanserin were evaluated on the DOI-induced 5-HT2 receptor-mediated ear-scratch response (ESR) in mice. A challenge dose of DOI (2.5 mg/kg) administered 24 h following its first injection reduced the ESR frequency by 80-97%. The ESR score attained first injection value when the time lag between the first and the second injection was greater than 72 h. On the other hand, a single administration of ketanserin (1.0 mg/kg) caused no significant effect at 24 or 48 h but significantly reduced (51%, p < 0.05) the DOI-induced ESR 120 h following its injection. Chronic once-daily DOI injections reduced the ESR score by 80-97% throughout the treatment regimen. Following cessation from chronic treatment, the DOI-induced ESR frequency returned to control levels in a time-dependent manner. Repeated ketanserin administration significantly reduced the DOI-induced ESR score by 46% when tested 24 or 48 h following cessation of antagonist administration but had no effect at 78 h. Recently, we reported that 48 h following either a single DOI injection or termination from repeated DOI or ketanserin administration the DOI-induced head-twitch response (HTR) in mice exhibited supersensitivity. Thus, it appears that the DOI-induced behaviors exhibit differential adaptation mechanisms following either agonist or antagonist exposure. These studies further support our hypothesis that serotonergic drugs may have the ability to change independently the 5-HT-receptor sensitivity (signal transduction) and receptor density in the same or opposite directions.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation of multiple behavioral effects between olfactory bulbectomized C57Bl/6J and DBA/2J mice

The behavioral effects of bulbectomy and subsequent antidepressant treatment in two mice strains were compared on measures of open field behavior and passive and active avoidance 2 and 4 weeks after surgery. After bulbectomy, both strains displayed elevated locomotion in open field, corrected by antidepressants. Enhanced rearing was decreased by antidepressants in C57Bl/6J, but not in DBA/2J mice. Passive avoidance, being intact 2 weeks after surgery in both strains, was strongly impaired 4 weeks after bulbectomy in C57Bl/6J mice, with antidepressants restoring the performance. Active avoidance acquisition and retention were also dramatically disturbed in C57Bl/6J mice 2 and 4 weeks after surgery, and antidepressants had recuperative effect. In contrast, bulbectomized DBA/2J mice didn't show any significant passive or active avoidance deficits, and antidepressant treatment seemed to have no effect on their learning ability. The observed strain differences suggest that bulbectomy may produce quite diverse neurophysiological and neurochemical alterations in two strains.

Repeated administration of low doses of cocaine enhances the sensitivity of 5-HT2 receptor function

The acute and chronic effects of cocaine were evaluated on the 5-hydroxytryptamine (5-HT)-receptor 5-HT2 mediated behavioral function, the head-twitch response (HTR), in mice. In a recent study, we reported that the (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI)-induced HTR was dose dependently reduced by cocaine via indirect stimulation of serotonergic 5-HT1A and adrenergic alpha 2 receptors. In the present investigation, the HTR was evoked by the nonselective 5-HT agonist 5-methoxy-N,N-dimethyltryptamine hydrogen oxolate (5-MeO-DMT). Cocaine by itself failed to produce HTR but dose dependently inhibited the 5-MeO-DMT-induced behavior. Cocaine's effects were not due to 5-HT3 antagonism since acute administration of the more potent 5-HT3 antagonist (ICS-205,930) failed to produce or modify the 5-MeO-DMT-induced behavior. During withdrawal from chronic cocaine treatment (5-20 mg/kg), 5-MeO-DMT-induced HTR was enhanced. Depending upon the cocaine dose used, the induced supersensitivity persisted up to 172 h following cessation of cocaine treatment. The mechanisms of cocaine-induced supersensitivity were further investigated using the more selective 5-HT2 agonist DOI. Withdrawal from a low-dose (0.03-1.25 mg/kg) chronic cocaine treatment caused the DOI-induced HTR to increase, whereas withdrawal from a 5- and 10-mg/kg cocaine regimen had no significant effect. The maximal effect persisted up to 36 h following termination of cocaine treatment. Relative to vehicle-exposed controls, withdrawal from cocaine treatment enhanced the inhibitory potency of the 5-HT1A agonist (+-)-8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT) on DOI-induced HTR.(ABSTRACT TRUNCATED AT 250 WORDS)

The Department of Neuroscience at the Institute of Psychiatry

During the 1988/89 academic year the Department of Neuroscience was formed at the Institute of Psychiatry from the former Departments of Biochemistry and Pharmacology. The University agreed to the establishment of a new Chair of Neuroscience to accompany this academic initiative and to which Professor Brian Anderton was appointed in 1989. In 1989, a new Lecturer in Molecular Biology, Dr John Powell, was appointed as well as a Clinical Senior Lecturer jointly with the Department of Psychiatry, Dr Robert Kerwin; this latter post was a new post under the UFC New Clinical Appointments Scheme. These changes have led to a strengthening of the molecular and cellular neurobiological interests of this new department and will influence the future academic aims of the Department of Neuroscience and Institute of Psychiatry as a whole.

Effects of repeated treatment with 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on the autoregulatory control of dorsal raphe 5-HT neuronal firing and cortical 5-HT release

These experiments were designed to examine the effects of repeated 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) treatment on the autoregulatory control of cortical 5-HT release and dorsal raphe nucleus (DRN) 5-HT neuronal cell firing. Repeated DOI treatment decreased the behavioural responsiveness (wet-dog shakes) of 5-HT2 receptors and attenuated the inhibitory effects of the 5-HT1A receptor agonist, 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), on both cortical 5-HT release and DRN 5-HT neuronal firing. In contrast, the inhibitory effect of acute DOI on cortical 5-HT release and DRN 5-HT neuronal firing was unaffected by repeated DOI treatment. The results demonstrate that changes in the responsiveness of 5-HT2 receptor function may influence the responsiveness of presynaptic 5-HT1A receptors regulating 5-HT neuronal function. The results also provide further evidence that the inhibition of cortical 5-HT release and DRN 5-HT neuronal firing produced by DOI is not mediated by 5-HT2 receptor activation.

Effect of chronic ritanserin or clorgyline on amine and metabolite levels in rat frontal cortex

As part of an investigation of ritanserin-induced receptor down-regulation, monoamine and metabolite levels in rat frontal cortex were measured following chronic ritanserin (2 mg/kg per day) or clorgyline (10 mg/kg per day) administration. Clorgyline increased 5-hydroxytryptamine (5-HT) by 83%, noradrenaline (NA) by 54%, and dopamine (DA) by 16% and decreased 5-hydroxyindoleacetic acid (5-HIAA) by 28%, homovanillic acid (HVA) by 57% and 3,4-dihydroxyphenylacetic acid (DOPAC) by 67%. All these changes were statistically significant (P less than 0.001) except for the increase in DA. Ritanserin increased 5-HT by 30%, NA by 33% and DA by 26% and decreased 5-HIAA by 22%, HVA by 23% and DOPAC by 40%; however, only the increases in 5-HT and NA reached statistical significance (P less than 0.05). Monoamine oxidase (MAO) activity in cortical homogenates was also measured following the chronic ritanserin and clorgyline regimens and also following ritanserin administration in vitro. Chronic clorgyline and ritanserin inhibited MAO activity by 60 and 39%, respectively. In vitro, ritanserin administration at concentrations of less than 10(-6) M had no effect on MAO activity but at doses higher than 10(-6) M, MAO activity was inhibited in a dose-dependent manner from 18 +/- 0.5% at 3 x 10(-6) M to 63 +/- 9% at 10(-4) M. Thus, ritanserin appears to act as an MAO inhibitor in addition to being a 5-HT2 antagonist and this may be related to its ability to induce 5-HT2 receptor down-regulation.

The effect of chronic ritanserin and clorgyline administration on 5-HT2 receptor linked inositol phospholipid hydrolysis

We have previously shown that chronic administration of the 5-hydroxytryptamine (5-HT) receptor antagonist, ritanserin (10 mg/kg/day) or the monoamine oxidase type A inhibitor (MAOI), clorgyline (2 mg/kg/day), results in a reduction in 5-HT2 receptor number in rat cerebral cortex. This study investigates the effects of acute and chronic ritanserin administration, on 5-HT2 receptor linked inositol phospholipid hydrolysis in rat cortical slices and compares it with the effect of a chronic clorgyline regimen. [3H]Myo-inositol (50 microCi) was used to label inositol phospholipids. Their subsequent hydrolysis in the presence or absence of 5-HT was determined by the accumulation of [3H]myoinositol monophosphate ([3H]InsP). Addition of 5 nM ritanserin to slices had no effect on basal or 5-HT stimulated [3H]InsP accumulation whereas 100 nM ritanserin blocked the stimulated response by 65%. Acutely, ritanserin (15 mg/kg i.p.) completely blocked 5-HT stimulated [3H]InsP accumulation. Chronic ritanserin or clorgyline treatment had no effect on basal levels of [3H]InsP accumulation compared to controls (mean value 3125 +/- 298 dpm/mg protein). Ritanserin increased 5-HT stimulated [3H]InsP accumulation at 1 microM, 100 microM and 1 mM 5-HT and this effect was significant at 100 microM 5-HT. Clorgyline had no significant or consistent effect on 5-HT stimulated [3H]InsP accumulation at 1 microM, 100 microM and 1 mM 5-HT. Thus the effects of both chronic clorgyline and ritanserin administration on 5-HT2 linked inositol phospholipid hydrolysis do not correlate with their effects on 5-HT2 receptor number (Bmax). The situation is further complicated since ritanserin significantly increases phosphatidylinositol (PtdIns), phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) labelling whereas clorgyline significantly increases PtdIns and PtdIns4P labelling. The implications of this are discussed.