The serotonin (5-hydroxytryptamine; <em>5HT</em>) transporter (SERT) catalyzes the movement of <em>5HT</em> across cellular membranes. In the brain, SERT clears <em>5HT</em> from extracellular spaces, modulating the strength and duration of serotonergic signaling. SERT is also an important pharmacological target for antidepressants and drugs of abuse. We have studied the flux of radio-labeled <em>5HT</em> through the transporter stably expressed in HEK-293 cells. Analysis of the time course of net transport, the equilibrium <em>5HT</em> gradient sustained, and the ratio of the unidirectional influx to efflux of <em>5HT</em> indicate that mechanistically, human SERT functions as a <em>5HT</em> channel rather than a classical carrier. This is especially apparent at relatively high [<em>5HT</em>](out) >> or =10 microM), but is not restricted to this regime of external <em>5HT</em>.

After a brief review of epidemiology, the focus is on biochemistry of diabetes. Animal and human studies are reviewed in terms of the impact of alterations in catecholamines and serotonin (5-hydroxytryptamine, <em>5HT</em>) on glucose utilization. Then, the implications of these experimental results for the choice of antidepressant in comorbid diabetes mellitus and depression as well as in diabetic neuropathy are discussed. Results of clinical investigations are then reviewed in terms of the above hypotheses. An Index Medicus Search for the past 10 years was supplemented by references from previous related reviews of the topic as well as by pending results, where available, not previously published. The range of prevalence of depression in diabetic patients has been 8-27%, depending on study criteria and procedures. An increase of catecholamines appears to increase glucose while both reducing insulin release and reducing sensitivity to insulin that is available. In contrast, increases in serotonergic function by increased precursor, increased release, or blocked metabolism and blocked reuptake in contrast seem to increase sensitivity to insulin and reduce plasma glucose. There have been six studies of fluoxetine, a selective serotonin reuptake inhibitor (SSRI), at a dose of 60 mg/day pursued up to 12 months that have demonstrated that medication's usefulness in diabetic patients, with reductions in weight (to 9.3 kg), in FPG (to 45 mg%), and in HbA1c (to 2.5%). In studies in comorbid diabetes mellitus and depression, nortriptyline, a norepinephrine reuptake inhibitor that produces increased synaptic catechols, has led to worsening of indices of glucose control. However, fluoxetine and sertraline, both selective serotonin reuptake inhibitors, in the same patient group, have produced results consistent with reductions in glucose levels. In diabetic neuropathy, perhaps due to the fact that catecholamines and serotonin may both be implicated in pain pathways, dual-action antidepressants appear more effective at lower doses than do specific serotonergic agents. The tricyclic antidepressants (TCA) (66.7%) have had success in double-blind studies, particularly imipramine, with a 81% response rate. Yet, there are positive reports concerning the SSRIs (paroxetine, citalopram, sertraline), as well as nefazodone, that focus on serotonin selectivity.

CONCLUSIONS

In comorbid diabetes mellitus and depression, most evidence supports the use of fluoxetine in control of glucose handling. Other characteristics in terms dosing, drug interactions, cognition, and sleep make sertraline an attractive alternative agent. In diabetic neuropathy without depression, the best choices among non-TCAs may include sertraline, citalopram, and perhaps, venlafaxine, since the TCAs appear to increase cravings and increase FBG levels.

Dopaminomimetic agents, which were rationally designed to reverse dopamine deficits in the substantia nigra and ventral tegmental area of the parkinsonian midbrain, effectively attenuate deficits in motor and non-motor behavior thought to be elicited by dopamine deficiencies in the striatal and frontal limbic regions, respectively. On the other hand, dopaminomimetic medications may also induce perturbations in postsynaptic peptides, causing dopaminergic hypersensitivity. Drug-induced chronic dopaminomimetic psychosis afflicts about one-fifth of PD patients on dopaminergic regimens. Although the long-held mechanism for psychosis in PD is excessive stimulation of mesocorticolimbic dopamine receptors, interactions between dopamine and serotonin, as well as participation of serotonin-modulated GABAergic neurons may also contribute to the pathophysiology. Reduction or withdrawal of anticholinergic agents, amantadine, and dopamine precursors or agonists constitutes a first approach to the problem but is often insufficient. Unfortunately, typical antipsychotic agents such as haloperidol, which selectively antagonizes dopamine D-2 receptors, can induce extrapyramidal syndromes such as tardive parkinsonism. On the other hand, emerging atypical neuroleptics such as clozapine, quetiapine, and olanzapine, which antagonize <em>5HT</em>-2A receptors (among others), inhibit D-2 receptors to a lesser degree and exhibit selective binding to mesolimbic (vs. striatal) dopamine receptors. The limbic selectivity of these agents appears to be of greater magnitude than that typical of risperidone. In addition, the selective antiserotonergic agent ondansetron is a prospective therapeutic option. The pharmacologic properties of these agents are explored.

It is widely accepted that the platelet release reaction is mediated by heterotrimeric complexes of integral membrane proteins known as SNAREs (SNAP receptors). In an effort to define the precise molecular machinery required for platelet exocytosis, we have analyzed platelets from cellubrevin/VAMP-3 knockout mice. Cellubrevin/VAMP-3 has been proposed to be a critical v-SNARE for human platelet exocytosis; however, data reported here suggest that it is not required for platelet function. Upon stimulation with increasing concentrations of thrombin, collagen, or with thrombin for increasing time there were no differences in secretion of [3H]-<em>5HT</em> (dense core granules), platelet factor IV (alpha granules), or hexosaminidase (lysosomes) between null and wild-type platelets. There were no gross differences in bleeding times nor in agonist-induced aggregation measured in platelet-rich plasma or with washed platelets. Western blotting of wild-type, heterozygous, and null platelets confirmed the lack of cellubrevin/VAMP-3 in nulls and showed that most elements of the secretion machinery are expressed at similar levels. While the secretory machinery in mice was similar to humans, mice did express apparently higher levels of synaptobrevin/VAMP-2. These data show that the v-SNARE, cellubrevin/VAMP-3 is not a requirement for the platelet release reaction in mice.

Injection of rat atrial RNA into Xenopus oocytes resulted in the expression of guanine nucleotide binding (G) protein-activated K+ channel. Current through the channel could be activated by acetylcholine or, if RNA encoding a neuronal <em>5HT</em>1A receptor was coinjected with atrial RNA, by serotonin (<em>5HT</em>). A <em>5HT</em>-evoked current (I<em>5HT</em>) was observed in oocytes injected with ventricle RNA fractions (of 2.5-5.5 kb) and <em>5HT</em>1A receptor RNA. I<em>5HT</em> displayed strong inward rectification with very little conductance above the K+ equilibrium potential, was highly selective for K+ over Na+, and was blocked by 5-300 microM Ba2+. I<em>5HT</em> was suppressed by intracellular injection of the nonhydrolyzable analog of GDP, guanosine 5'-[beta-thio]diphosphate, but not by treatment with pertussis toxin (PTX), suggesting coupling of the receptor to the G-protein-activated K+ channel via a PTX-insensitive G protein, possibly endogenously present in the oocyte. Coexpression of the alpha subunit of a PTX-sensitive G protein, G(i2), rendered I<em>5HT</em> sensitive to PTX inhibition. Native oocytes displayed a constitutively active inwardly rectifying K+ current with a lower sensitivity to Ba2+ block; expression of a similar current was also directed by atrial or ventricle RNA of 1.5-3 kb. Xenopus oocytes may be employed for cloning of the G-protein-activated K+ channel cDNA and for studying the coupling between this channel and G proteins.

The fan and rays of the C. elegans male tail constitute a compound sensory organ essential for mating. Within this organ, the individual sensilla, known as rays, have unique identities. We show that ray identities are patterned by a selector gene mechanism in a manner similar to other serially homologous axial structures. One selector gene that promotes the identities of a subset of the rays is the Hox gene egl-5. Within EGL-5-expressing rays, further patterning is provided by a Pax-6 homolog and a signal of the TGFbeta family. These genes and pathway coordinately specify multiple ray properties affecting all three terminal ray cell types. These properties include complex patterns of FMRFamide-like (FaRP) neuropeptides, serotonin (<em>5HT</em>) and dopamine expression, and ray morphology. Differences in these differentiated characteristics give each sensillum a unique identity and potentially endow the compound ray organ with a higher-order information gathering capacity.

Nicotine is a neuroteratogen that targets synaptic function during critical developmental stages and recent studies indicate that CNS vulnerability extends into adolescence, the age at which smoking typically commences. We administered nicotine to adolescent rats via continuous minipump infusions from PN30 to PN47.5, using 6 mg/kg/day, a dose rate that replicates the plasma nicotine levels found in smokers, and examined <em>5HT</em> receptors and related cell signaling during nicotine administration (PN45) and in the post-treatment period (PN50, 60, 75). Adolescent nicotine decreased <em>5HT</em>(2) receptor binding in brain regions containing <em>5HT</em> projections (hippocampus and cerebral cortex), with selectivity for females in the cerebral cortex; regions containing <em>5HT</em> cell bodies showed either an increase (midbrain in males) or no change (brainstem). In contrast, there were no significant changes in <em>5HT</em>(1A) receptors; however, the ability of the receptors to signal through adenylyl cyclase (AC) showed a switch from stimulatory to inhibitory effects in females during the post-treatment period. There were also transient alterations in AC responses to beta-adrenergic receptor stimulation, as well as pronounced induction of the AC response to the non-receptor-mediated stimulant, forskolin. Our results indicate that adolescent nicotine exposure alters the concentrations and functions of postsynaptic <em>5HT</em> receptors in a manner commensurate with impaired <em>5HT</em> synaptic function. The direction of change, emergence of defects after the cessation of nicotine administration, and sex-preference for effects in females, all support a relationship of impaired <em>5HT</em> function to the higher incidence of depression seen in adolescent smokers.

We utilized 3H-8-hydroxy-N,N-dipropyl-2-aminotetralin (3H-DPAT) and 125I-iodocyanopindolol (125I-CYP) to label serotonin (<em>5HT</em>) 1A and <em>5HT</em>1B receptors, respectively, in sections of the rat brain after characterizing the pharmacologic specificity of these agents. We then used quantitative autoradiography to measure the concentrations of <em>5HT</em>1A and <em>5HT</em>1B receptors in individual subnuclei of the nucleus of the solitary tract (NTS) and adjacent structures of the dorsal vagal complex. The highest <em>5HT</em>1A receptor concentrations were observed within the central and intermediate subnuclei of the NTS, with low quantities of 3H-DPAT binding sites observed in the hypoglossal nucleus and dorsal motor nucleus of the vagus. In contrast, the density of <em>5HT</em>1B receptors was relatively homogeneous through all NTS subnuclei, with the highest concentrations localized within the ventrolateral subnucleus. The hypoglossal and dorsal motor nuclei had slightly higher <em>5HT</em>1B receptor densities than the NTS subnuclei, whereas the area postrema had a very low density. These data suggest that <em>5HT</em>1A receptors are organized in a manner consistent with the cytoarchitectural and hodological parcellation of the NTS into individual subnuclei. The high concentrations of <em>5HT</em>1A receptors in the central and intermediate subnuclei suggest a role for these receptors in medullary reflex pathways subserving deglutition. The relatively high density of <em>5HT</em>1B receptors in the ventrolateral subnucleus suggests that these receptors modulate respiratory neurons, whereas the diffuse organization of <em>5HT</em>1B receptors in the remaining subnuclei suggests that they are associated with central <em>5HT</em> afferent pathways to the NTS. Further studies will be required to understand the physiologic role of <em>5HT</em>1 receptors within the NTS.

Postnatal serotonin (<em>5HT</em>) innervation in the cerebral cortex of mice has been studied by <em>5HT</em> immunohistochemistry. <em>5HT</em>-like immunoreactive (<em>5HT</em>-LI) nerve fibers and terminals appeared to increase transiently, particularly in the somatosensory (Sm) cortex during early postnatal days. As pups grow, <em>5HT</em> afferent inputs decreased rapidly to reach a similar pattern of distribution to that in adult animals. Since the transient increase was seen at a critical period (seventh postnatal day) for the differentiation of layer IV, it is suggested that increased <em>5HT</em> concentrations might have an effect on thalamocortical inputs and/or cortical lamination of the developing brains.

BACKGROUND

Although development of visceral pain is an important defensive mechanism, hypersensitivity results in a significant clinical problem and is likely to be one of the major factors involved in the pathogenesis of abdominal and chest pain in functional bowel disorders (FBDs). Understanding of the molecular mechanisms involved in peripheral sensitization of visceral nociceptors has advanced as a result of the experimental studies, especially in animal models, which have led to knowledge and identification of key mediators and receptors.

OBJECTIVE

To provide a comprehensive review focused on the peripheral mechanisms believed to be responsible for sensitization and potential molecular targets for a disorder which is common, distressing and has sub-optimal treatment options.

METHODS

Literature review using Ovid and Pubmed from 1966.

RESULTS

There is substantial interest in the development of new drugs for treatment of FBDs in the background of advances in understanding the molecular and physiological mechanisms of visceral hypersensitivity. The potential drug targets include TPRV1, ASICs, voltage-gated sodium channels, ATP, PAR-2, cannabinoid, prostaglandin, tachykinin and <em>5HT</em>(3) receptors.

CONCLUSIONS

It is anticipated that with advancing molecular understanding of the basis of visceral hypersensitivity, the next decade will see accelerated development of new molecules for treatment of functional bowel diseases.

Antidepressant drugs are devoid of mood-elevating effects in normal (non-depressed) human subjects, thus, it is necessary to evaluate the antidepressant property of compounds (drugs) in animal models of depression. Several animal models of depression have been introduced, however, only a few have been extensively validated. In the present study we report the results of investigations into monoaminergic receptors in the brain of rats subjected to chronic unpredictable stress (CUS) procedure (one of the well validated animal models of depression). We have examined the dopaminergic (D-1, D-2), adrenergic (alpha-1, beta-1) and serotonergic (<em>5HT</em>-1A, <em>5HT</em>-2A) receptors in different brain regions by a saturation radioligand binding method in rats subjected to CUS paradigm and control animals. CUS procedure resulted in a significant 29% increase in the D-1 receptor density in the limbic system and 52% increase of the density of <em>5HT</em>-2A receptors in the cerebral cortex. The present data indicate that the increase of the density of brain D-1 and <em>5HT</em>-2A receptors of rats subjected to CUS might be involved in the pathophysiology of "animal depression" (since chronic antidepressant treatment produced opposite changes i.e. decrease in the density of these receptors) and thus in pathophysiology of human depression.

OBJECTIVE

This article describes the possible role of various peptides in producing pain and inflammation in the temporomandibular joint (TMJ).

METHODS

Current research findings on the spectrophotometric quantification of TMJ synovial fluid for neuropeptide Y (NPY), serotonin (<em>5HT</em>), and interleukin-1beta (IL-1beta) are presented.

RESULTS

NPY was found in high levels in the synovial fluid of arthritic TMJs with resting pain, and serotonin (5-HT) was found in patients with pain perceived on mandibular movement. These pain-related mediators were also associated with restricted mandibular mobility. Interleukin-1beta (IL-1beta) was found to be strongly associated with hyperalgesia over the TMJ as well as resting pain. Anterior open bite as a clinical sign of joint destruction was found to be associated with high levels of NPY and IL-1beta in the synovial fluid. IL-1beta was also related to the radiographic signs of joint destruction.

CONCLUSIONS

Interaction between the peripheral nervous system (sensory and sympathetic nerves) and the immune system is probably of importance for the modulation of pain and inflammation in the TMJ, but this subject has to be investigated further with experimental clinical studies.

HAT is the most frequent drug induced immune-thrombocytopenia. We recently identified multimolecular PF4/heparin complexes as the major antigen. In order to evaluate the structural requirements for formation of the antigenic complex, we chemically synthesized 13 glucan sulfates and used 5 heparin fractions (2.4-4.8 kD) and a synthesized pentasaccharide, representing the antithrombin III binding sequence of heparin, for further characterize the HAT antigen. In the presence of glucan sulfates and heparin, HAT antibodies caused platelet activation typically at low but not at high concentrations, as measured by 14C-<em>5HT</em> release. The concentration range giving the activation pattern depended on the degree of sulfation (DS) and molecular weight (MW) of the glucan sulfates but not on the type of glycosidic linkage of a polysaccharide. With linear glucan sulfates with a chain length of 35 monosaccharides, the critical DS to form the HAT antigen ranged between 0.60 and 1.20. Glycosidic branched glucan sulfates were able to form the HAT antigen at a lower DS and a lower MW than linear glucan sulfates. Platelet activation by HAT-antibodies in the presence of linear curdlan sulfate fractions was dependent on their MW. At a low concentration (0.01 microM) medium-size fractions (60 kD) caused platelet activation but neither small (12 kD) nor large fractions (>> 150 kD) did. At higher concentrations (2 microM) the opposite reaction pattern was observed. In the case of heparin, the optimal chain length for forming the HAT antigen is a hexadecasaccharide (4.8 kD). Antigen generation decreased with larger and smaller fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Migraine patients show a specific cognitive processing with a loss of habituation in the interval and a normal habituation in the attack as measured by event-related potentials (ERPs). It is unknown whether the loss of habituation changes during the migraine interval or is a stable state. Serotonin (<em>5HT</em>) metabolism is involved in the pathophysiology of migraine and also in the generation of ERPs. We enrolled 14 patients with regular migraine attacks in order to measure visually evoked ERPs repetitively during the migraine interval and in the migraine attack. Cognitive habituation was evaluated by analysis of P3 latency. Platelet serotonin content and free serotonin plasma level were measured at the same time points. The loss of habituation increased continuously during the migraine interval and abruptly normalized in the migraine attack (p < 0.05, time series analysis). The platelet <em>5HT</em> content decreased significantly in the migraine attack (p < 0.03) and was at its maximum in the middle of the interval. The P3 latency was significantly increased in the attack (p < 0.01) and was significantly inversely correlated with the platelet <em>5HT</em> content (r = -0.44, p < 0.001). Free <em>5HT</em> plasma levels did not show any significant change. Our findings suggest that loss of cognitive habituation continuously increases during the migraine interval until its normalization in the migraine attack. This phenomenon cannot be attributed to serotonergic transmission. In patients with regular changes of cognitive habituation before the migraine attack, it might be possible to predict the attack by analysing ERPs.

OBJECTIVE

Serotonergic pathways in the central nervous system (CNS) are activated in the regulation of food intake and body weight. We hypothesized that adipocytes, like other cells of mesenchymal origin, possess serotonin receptors and thus could be regulated by peripherally circulating serotonin.

METHODS

In vivo studies: four Sprague-Dawley rats were given daily serotonin (<em>5HT</em>) injections subcutaneously (s.c., 25 mg/kg) for 5 days; four controls received saline. In a long-term study, 12 rats were given serotonin s.c. for 4 months, 10 controls received saline. Body weight was registered throughout the studies, and visceral adipose tissue and plasma were collected and analysed. Adipocytes were isolated from normal rat visceral abdominal adipose tissue and analysed for the expression of serotonin receptors, the serotonin transporter (<em>5HT</em>T/SERT), activation of serotonin synthesis (tryptophan hydroxylase 1, Tph1) and secretion and serotonin-induced leptin regulation by RT-PCR and protein analyses.

RESULTS

Hyperserotoninergic rats had significantly lower body weight (-7.4 and -6.8%) and plasma leptin levels (-44 and -38%) than controls, after both short- and long-term serotonin treatment, respectively, whereas plasma ghrelin levels were unaffected. Compared to controls, serotonin induced a 40-fold upregulation of <em>5HT</em>T mRNA in visceral adipose tissue after 5 days of treatment. In vitro experiments showed that adipocytes express serotonin receptors, Tph1 and <em>5HT</em>T, synthesize and secrete serotonin and that serotonin regulates leptin in mature adipocytes.

CONCLUSIONS

These findings show that serotonin may regulate adipocyte function in a direct manner via the blood circulation and/or paracrine and autocrine mechanisms, and not only indirectly via the CNS as previously assumed.

In previous studies tryptophan loads have been administered to human subjects in order to raise central levels of 5-hydroxytryptamine (<em>5HT</em>) and assess the effects of <em>5HT</em> on behaviour and mood. However, tryptophan is metabolised primarily along the oxidative kynurenine pathway. In this study a 6 g oral tryptophan load was administered to 15 healthy volunteers and the levels of kynurenines and lipid peroxidation products (indicative of oxidative stress) were measured. The results demonstrate that tryptophan loading produces a highly significant increase in lipid peroxidation products in parallel with increased kynurenines. The oxidative stress may result from the generation of quinolinic acid, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid, all of which are known to have the ability to generate free radicals. The results may have implications for the use of tryptophan loading in psychiatric practice, and for the chronic use of diets high in tryptophan.

The most widely recognised consequence of normal age-related changes in biological timing is the sleep disruption that appears in old age and diminishes the quality of life. These sleep disorders are part of the normal ageing process and consist primarily of increased amounts of wakefulness and reduced amounts of deep sleep. Changes in the amplitude and timing of the sleep-wake cycle appear to represent, at least in part, a loss of effective circadian regulation of sleep. Understanding alterations in the characteristics of stimuli that help to consolidate internal rhythms will lead to recommendations to improve synchronisation in old age. Converging evidence from both human and animal studies indicate that senescence is associated with alterations in the neural structure thought to be primarily responsible for the generation of the circadian oscillation, the suprachiasmatic nuclei (SCN). Work has shown that there are changes in the anatomy, physiology and ability of the clock to reset in response to stimuli with age. Therefore it is possible that at least some of the observed age-related changes in sleep and circadian timing could be mediated at the level of the SCN. The SCN contain a circadian clock whose activity can be recorded in vitro for several days. We have tested the response of the circadian clock to a number of neurochemicals that reset the clock in a manner similar to light, including glutamate, N-methyl-D-aspartate (NMDA), gastrin-releasing peptide (GRP) and histamine (HA). In addition, we have also tested agents which phase shift in a pattern similar to behavioural 'non-photic' signals, including neuropeptide Y (NPY), serotonin (<em>5HT</em>) and gamma-aminobutyric acid (GABA). These were tested on the circadian clock in young and older mice (approximately 4 and 15 months old). We found deficits in the response to specific neurochemicals but not to others in our older mice. These results indicate that some changes seen in the responsiveness of the circadian clock to light with age may be mediated at the level of the SCN. Further, the responsiveness of the circadian clock with age is attenuated to some, but not all stimuli. This suggests that not all clock stimuli lose their effectiveness with age, and that it may be possible to compensate for deficits in clock performance by enhancing the strength of those stimulus pathways which are intact.

Occurring both peripherally and centrally, the kynurenine pathway (KP) - an alternative pathway to 5-HT synthesis from tryptophan (TRP) - could be of particular value to better understand the link between peripheral changes of circulating levels of glucocorticoids (GC)/proinflammatory cytokines and altered neurotransmission observed in depressed patients. Indeed, it is activated by these mediators of stress and can produce several neuroactive compounds like quinolinic acid (QUIN) and kynurenic acid (KYNA) that can respectively increase and decrease glutamate concentration in brain. In order to characterize the role of both the peripheral and cerebral KP in the pathophysiology of depressive disorders, we used the Unpredictable Chronic Mild Stress (UCMS) to induce a depressive-like syndrome and we then measured the level of relevant TRP-KYN pathway metabolites: KYN, 3-hydroxykynurenine (3HK; precursor of QUIN) and KYNA. We also measured TRP-<em>5HT</em> pathway metabolites: TRP, 5-HT, 5-HIAA. We showed that UCMS increased TRP catabolism along the KP in the periphery. 5-HT and KYN were found to be strongly negatively correlated in all brain structures of control mice and of UCMS mice except in the hippocampus. More importantly we found that KYN was preferentially metabolized along the QUIN pathway at the subcortical level (amygdala/striatum) whereas, at the cortical level (cingulate cortex), the QUIN pathway was reduced. Considering the role of these metabolites on the glutamatergic neurotransmission, we propose that such KP alterations could participate to the cortical/subcortical glutamatergic alterations reported in depressed patients.

OBJECTIVE

While selective, bitter tasting, TAS2R agonists can relax agonist-contracted airway smooth muscle (ASM), their mechanism of action is unclear. However, ASM contraction is regulated by Ca²⁺ signalling and Ca²⁺ sensitivity. We have therefore investigated how the TAS2R10 agonists chloroquine, quinine and denotonium regulate contractile agonist-induced Ca²⁺ signalling and sensitivity.

METHODS

Airways in mouse lung slices were contracted with either methacholine (MCh) or <em>5HT</em> and bronchodilation assessed using phase-contrast microscopy. Ca²⁺ signalling was measured with 2-photon fluorescence microscopy of ASM cells loaded with Oregon Green, a Ca²⁺-sensitive indicator (with or without caged-IP₃). Effects on Ca²⁺ sensitivity were assessed on lung slices treated with caffeine and ryanodine to permeabilize ASM cells to Ca²⁺ .

RESULTS

The TAS2R10 agonists dilated airways constricted by either MCh or <em>5HT</em>, accompanied by inhibition of agonist-induced Ca²⁺ oscillations. However, in non-contracted airways, TAS2R10 agonists, at concentrations that maximally dilated constricted airways, did not evoke Ca²⁺ signals in ASM cells. Ca²⁺ increases mediated by the photolysis of caged-IP₃ were also attenuated by chloroquine, quinine and denotonium. In Ca²⁺-permeabilized ASM cells, the TAS2R10 agonists dilated MCh- and <em>5HT</em>-constricted airways.

CONCLUSIONS

TAS2R10 agonists reversed bronchoconstriction by inhibiting agonist-induced Ca²⁺ oscillations while simultaneously reducing the Ca²⁺ sensitivity of ASM cells. Reduction of Ca²⁺ oscillations may be due to inhibition of Ca²⁺ release through IP₃ receptors. Further characterization of bronchodilatory TAS2R agonists may lead to the development of novel therapies for the treatment of bronchoconstrictive conditions.

Augmentation of selective serotonin reuptake inhibitors (SSRIs) therapy by the 5-HT(1A) receptor agent pindolol may reduce the delay between initiation of antidepressant treatment and clinical response. This hypothesis is based on the ability of pindolol to block 5-HT(1A) autoreceptors in the dorsal raphe nuclei (DRN) and to potentiate the increase in 5-HT transmission induced by SSRIs. However, placebo-controlled clinical studies of pindolol augmentation of antidepressant therapy have reported inconsistent results. Here, we evaluated the occupancy of 5-HT(1A) receptors during treatment with pindolol controlled release (CR) in nine healthy volunteers with Positron Emission Tomography and [11C]WAY 100635. Subjects were studied four times: at baseline, following one week of pindolol CR 7.5 mg/day (4 and 10 hrs post dose), and following one dose of pindolol CR 30 mg(4 hrs post dose). Occupancy of the DRN was 40 +/- 29% on scan 2, 38 +/- 26% on scan 3, and 64 +/- 15% on scan 4. The average occupancy in all other regions was significantly lower at each doses (18 +/- 5% on scan 2, 12 +/- 3% on scan 3, and 42 +/- 4% on scan 4). These results suggest that the blockade in the DRN reached in clinical studies (7.5 mg/day) might be too low and variable to consistently augment the therapeutic effect of SSRIs. However, these data indicate that pindolol exhibits in vivo selectivity for the DRN 5-HT(1A) autoreceptors. As DRN selectivity is desirable for potentiation of 5-HT function, this observation represents an important proof of concept for the development of 5-HT(1A) agents in this application.

BACKGROUND

Prucalopride is a selective and specific 5-hydroxytryptamine(4) receptor agonist that is known to increase stool frequency and to accelerate colonic transit.

OBJECTIVE

To investigate the effect of prucalopride on high-amplitude propagated contractions and segmental pressure waves in healthy volunteers.

METHODS

After 1 week of dosing (prucalopride or placebo in a double-blind, randomized, crossover fashion), colonic pressures were recorded in 10 healthy subjects using a solid-state pressure catheter with six sensors spaced 10 cm apart. Subjects kept diary records of their bowel habits (frequency, consistency and straining). High-amplitude propagated contractions were analysed visually, comparing their total numbers and using 10-min time windows. Segmental pressure waves were analysed using computer algorithms, quantifying the incidence, amplitude, duration and area under the curve of all detected peaks.

RESULTS

When taking prucalopride, stool frequency increased, consistency decreased and subjects strained less. Prucalopride just failed to increase the total number of high-amplitude propagated contractions (P=0.055). The number of 10-min time windows containing high-amplitude propagated contractions was increased by prucalopride (P=0.019). Prucalopride increased the area under the curve per 24 h (P=0.026).

CONCLUSIONS

The 5-hydroxytryptamine(4) receptor agonist prucalopride stimulates high-amplitude propagated contractions and increases segmental contractions, which is likely to be the underlying mechanism of its effect on bowel habits in healthy volunteers.

Extracellular single-unit recordings in mouse brain slices were used to determine the effect of exogenously applied 5-HT on STN neurones. Recordings were made from 74 STN cells which fired action potentials at a regular rate of 7.19+/-0.5 Hz. In 61 cells (82%), 5-HT application increased STN neurone firing rate (10 microM, 180+/-16.8%, n=35) with an estimated EC(50) of 5.4 microM. The non-specific 5-HT(2) receptor agonist alpha-methyl 5-HT (1-10 microM) mimicked 5-HT induced excitations (15 cells). These excitations were significantly reduced by pre-perfusion with the specific 5-HT(2C) receptor antagonist RS102221 (500 nM, 9 cells) and the <em>5HT</em>(4) antagonist GR113808 (500 nM, 7 cells). In 6 cells (8%) 5-HT induced biphasic responses where excitation was followed by inhibition, while in 7 cells (9%) inhibition of firing rate was observed alone. Inhibitory responses were reduced by the 5-HT(1A) antagonist WAY100135 (1 microM, 4 cells). No inhibitory responses were observed following alpha-methyl 5-HT applications. Both the excitations and inhibitions were unaffected by picrotoxin (50 microM, n=5) and CNQX (10 microM, n=5) indicative of direct postsynaptic effects. Thus, in STN neurones, 5-HT elicits two distinct effects, at times on the same neurone, the first being an excitation which is mediated by 5-HT(2C) and 5-HT(4) receptors and the second an inhibition which is mediated by 5-HT(1A) receptors.

It has been widely accepted that <em>5HT</em> neurones promote anxiety, in humans as well as in animal models. This could be termed the "classic" hypothesis and it has led to a determined search for drugs which reduce <em>5HT</em> function, especially agents which have selective actions at <em>5HT</em> receptor subtypes. However, these novel agents tend to have weak and/or variable effects in animal models and more detailed examination of their actions suggests that not all findings are accounted for by the classic hypothesis. There appear to be circumstances in which increased <em>5HT</em> activity can reduce anxious behaviour. There is increasing evidence for multiple anxiety mechanisms, which may be able to explain differential patterns of drug effects within and between models. Animal models of anxiety may also detect non-anxiety factors: effects on cognition or on impulsivity could be reflected in some models. This could be important in the light of recent evidence that <em>5HT</em>-selective reuptake inhibitors are effective in impulsivity disorders. The classic hypothesis of <em>5HT</em> function in anxiety may be only one part of an increasingly complex story. Unravelling the rest of this story is likely to lead to new insights in our understanding of anxiety and related disorders.

Methysergide is a semisynthetic ergot alkaloid ergometrine derivative, introduced in pharmacotherapy for migraine prophylaxis as a specific serotonin (<em>5HT</em>) receptor antagonist. Methysergide is not just a <em>5HT</em>2 antagonist, it is also a <em>5HT</em>1 agonist. Open and controlled studies attest to methysergide's efficacy. It may be more effective in resistant cases with a high attack frequency and may act synergistically with ergotamine and dihydroergotamine (DHE) for breakthrough attacks. Contraindications include pregnancy, peripheral vascular disorders, severe arteriosclerosis, coronary artery disease, severe hypertension, thrombophlebitis or cellulitis of the legs, peptic ulcer disease, fibrotic disorders, lung diseases, collagen disease, liver or renal function impairment, valvular heart disease, debilitation, or serious infection. Methysergide can induce retroperitoneal fibrosis and pleural and heart valve fibrosis with an estimated incidence of 1 in 5,000 treated patients. Therefore, it should be reserved for severe cases in which other migraine preventive drugs are not effective.