The monoamines dopamine (DA), serotonin (<em>5HT</em>), and octopamine (Oct) can each sculpt a unique motor pattern from the pyloric network in the stomatogastric ganglion (STG) of the spiny lobster Panulirus interruptus. In this paper we investigate the contribution of individual network components in determining the specific amine-induced cycle frequency. We used photoinactivation of identified neurons and pharmacological blockade of synapses to isolate the anterior burster (AB) and pyloric dilator (PD) neurons. Bath application of DA, <em>5HT</em>, or Oct enhanced cycle frequency in an isolated AB neuron, with DA generating the most rapid oscillations and Oct the slowest. When an AB-PD or AB-2xPD subnetworks were tested, DA often reduced the ongoing cycle frequency, whereas <em>5HT</em> and Oct both evoked similar accelerations in cycle frequency. However, in the intact pyloric network, both DA and Oct either reduced or did not alter the cycle frequency, whereas <em>5HT</em> continued to enhance the cycle frequency as before. Our results show that the major target of <em>5HT</em> in altering the pyloric cycle frequency is the AB neuron, whereas DA's effects on the AB-2xPD subnetwork are critical in understanding its modulation of the cycle frequency. Octopamine's effects on cycle frequency require an understanding of its modulation of the feedback inhibition to the AB-PD group from the lateral pyloric neuron, which constrains the pacemaker group to oscillate more slowly than it would alone. We have thus demonstrated that the relative importance of the different network components in determining the final cycle frequency is not fixed but can vary under different modulatory conditions.

OBJECTIVE

Neuroimaging research continues apace and is being applied to further understanding of the epilepsies, and improve clinical management.

RESULTS

Structural imaging has become more sensitive with developments of MRI hardware, acquisition and postprocessing methods. Tractography is being used to define critical pathways prior to surgery. Functional MRI for language lateralization is now a clinical tool. PET studies with specific ligands reveal neurochemical changes associated with specific epilepsy syndromes.

CONCLUSIONS

MRI at 3T with FLAIR and multiple channel coils identifies and clarifies relevant abnormalities in 20% of patients with previously unremarkable scans. Voxel-based analysis of diffusion scans may identify abnormalities in group comparisons. Identification of relevant abnormalities using voxel-based methods in individual patients requires a careful balance of sensitivity and specificity, and has a 10-30% yield. The PROPELLER sequence improves the detail of hippocampal anatomy and correlation with histological slices shows the pathological basis of MRI signal changes. Tractography has shown the connections of the language cortex and visualizes specific tracts. Electroencephalograms with simultaneous functional MRI and perfusion have shown that perfusion changes are a major determinant of changes in blood-oxygen-level-dependent signal. Functional MRI of language and memory are becoming used as a predictor of deficits as a result of temporal lobe resection.Increased uptake of the PET tracer 11C-alpha-methyl tryptophan shows promise for localizing epileptogenic malformations of cortical development. Abnormalities of <em>5HT</em>-1A receptor ligands have been reported in temporal lobe epilepsy, with controversial association with depression. Dopamine uptake abnormalities have been noted in autosomal dominant nocturnal frontal lobe epilepsy.

The RN46A cell line was derived from Embryonic Day 13 rat medullary raphe cells by infection with a retrovirus encoding the temperature-sensitive mutant of SV40 large T antigen. This cell line is neuronally restricted and constitutively differentiates following a shift to nonpermissive temperature. Undifferentiated RN46A cells express low levels of tryptophan hydroxylase (TPH), low-affinity neurotrophin receptor (p75NTR), and trkB immunoreactivities, but no detectable levels of serotonin (<em>5HT</em>) immunoreactivity. TrkB, p75NTR, and TPH, but not <em>5HT</em>, expressions increase with differentiation and treatment with brain-derived neurotrophic factor (BDNF). <em>5HT</em> synthesis in RN46A cells requires initial treatment with BDNF, followed by growth under partial membrane depolarizing conditions. Embryonic raphe cultures treated similarly with BDNF and partial depolarizing conditions also demonstrate increased <em>5HT</em> synthesis. The sodium-dependent transporter for <em>5HT</em> reuptake is present in undifferentiated RN46A cells, and the apparent Km and Bmax are unchanged by differentiation or BDNF treatment and membrane depolarization. The high-affinity <em>5HT</em>1A receptor is present in both undifferentiated and differentiated RN46A cells, and while the Kd is unaffected by differentiation or BDNF/membrane depolarization, the Bmax increases 20-fold after differentiation and 3.5-fold further with BDNF under depolarizing conditions. The expression of the synaptic vesicular monoamine transporter, as determined by the binding of [125I]iodovinyltetrabenazine, also increases in RN46A cells with differentiation. However, <em>5HT</em> release is constitutive and is independent of acute membrane depolarization. Collectively these data indicate that distinct aspects of serotonin metabolism are differentially regulated during development and suggest that <em>5HT</em> may function as a developmental signal in an autocrine loop during early serotonergic differentiation.

To date, two structurally related RNA-editing enzymes with adenosine deaminase activity have been identified in mammalian tissue: ADAR1 and ADAR2 [Bass B. I. et al. (1997) RNA 3, 947-949]. In rodents, ADAR2 undergoes alternative RNA splicing, giving rise to two splice variants that differ by the presence or absence of a 10-amino-acid insert in the carboxy-terminal catalytic domain. However, the physiological significance of the splicing and its regional and developmental regulation are as yet unknown. The present study examined spatial and temporal patterns of ADAR2 gene transcripts within specific neuronal populations of rat brain. The two rodent ADAR2 isoforms were expressed at comparable levels at all ages examined. rADAR2 messenger RNA expression was first detectable in the thalamic nuclei formation at embryonic day E19. The rADAR2b insert and rADAR2a splice probes produced images similar to that of the rADAR2 pan probe. At birth, rADAR2a messenger RNA splice variants were abundantly expressed in the thalamic nuclei. No signal for any probe was detectable in other brain regions, including neocortex, hippocampus, striatum and cerebellum at this stage of development. During the first week of postnatal life, rADAR2 messenger RNA expression (detected with the pan probe) increased gradually in several brain regions, with low expression detected at postnatal day P7 in the olfactory bulb, inferior colliculus, and within the pyramidal and granule cell layers of the hippocampus. Hybridization patterns of the rADAR2a variant probe reached peak expression at about the second week of life, while peak expression of the rADAR2b probe was reached at about the third week of life. At the end of the first week of life (P7), expression of both splice variants was strongest in the thalamic nuclei. By P14, rADAR2 messenger RNA expression was more consolidated in the deeper structures, including the thalamic nuclei and the granule cell layer of the cerebellum. By P21, maximal levels of rADARb expression were observed in the thalamic nuclei, inferior colliculus, cerebellum and pontine nuclei. In the adult, rADAR2 messenger RNA expression was of highest intensity in the thalamic nuclei, with high levels of expression in the olfactory bulb, inferior colliculus, cerebellum and pontine nuclei. At the level of the hippocampus, positive labelling was restricted to the CA3 region of the Ammon's horn and the dentate gyrus, with weak signals in the CA1 subfield. rADAR2 pan expression was at near background levels throughout the neocortex and caudate putamen. In summary, our study shows that ADAR2 messenger RNA expression is regulated in a cell-specific manner throughout development. At early ages, ADAR2 messenger RNA is expressed only within (and restricted to) the thalamic nuclei. By the third postnatal week, expression of the editase enzyme is more widely distributed throughout the olfactory bulb, CA3 and dentate gyrus of the hippocampus, thalamus, inferior colliculus and the molecular cell layer of the cerebellum. ADAR2 is thought to act at specific nucleotide positions in primary transcripts encoding glutamate receptor subunits, thereby altering gating and ionic permeability properties of AMPA- and kainate-activated channels. ADAR2 also acts at pre-messenger RNA encoding the serotonin <em>5HT</em>-2C receptor to alter G-protein coupling. Thus, RNA editing may be an important mechanism for fine-tuning of the physiological and pharmacological properties of transmitter receptors of the central nervous system.

In situ hybridization histochemistry was used to investigate acute estrogen effects on serotonin <em>5HT</em>1A receptor mRNA levels in limbic-related brain areas in the female ovariectomized rat. Acute administration of 17 beta-estradiol (10 micrograms) decreased <em>5HT</em>1A receptor mRNA expression levels within the medial amygdala (after 2 and 24 h), piriform cortex (after 2 and 24 h), and perirhinal cortex (after 24 h). No changes in <em>5HT</em>1A mRNA levels were observed in hippocampus or retrosplenial cortex. The findings suggest specific regional effects of estrogen on <em>5HT</em> functions mediated through regulation of the <em>5HT</em>1A gene.

Idiopathic Parkinson's disease (PD) is a common neurodegenerative disorder with prominent motor symptoms. However, depression is common in PD, affecting about 40% of PD patients. Since there is extensive evidence of degeneration of serotonin (<em>5HT</em>) neurons and loss of the <em>5HT</em> transporter (<em>5HT</em>T) in PD, we assessed whether a functional polymorphism in the promoter of the <em>5HT</em>T gene (<em>5HT</em>T gene-linked polymorphic region, <em>5HT</em>TLPR), which determines high or low <em>5HT</em> uptake, is associated with depressive symptomatology in PD patients. We found that patients with the short allele of the <em>5HT</em>TLPR had significantly higher scores on the Hamilton Depression Scale. A functional promoter polymorphism of the monoamine oxidase A (MAOA) gene showed no association. Thus, the <em>5HT</em>TLPR but not the MAOA gene promoter-associated polymorphism may be a risk factor for depression in PD patients, while neither polymorphism increases the risk for development of Parkinson's disease itself.

Suicidal patients often report problems with their sleep. Although sleep-related complaints and EEG (electroencephalographic) changes have been seen widely across the spectrum of psychiatric disorders, sleep complaints such as insomnia, hypersomnia, nightmares, and sleep panic attacks are more common in suicidal patients. The subjective quality of sleep as measured by self-rated questionnaires also appears to be more disturbed in suicidal depressive patients. Sleep studies have reported various polysomnographic findings including increased REM (rapid eye movement) time and REM activity in suicidal patients with depression, schizoaffective disorder, and schizophrenia. One mechanism responsible for this possible association between suicide and sleep could be the role of serotonin (<em>5HT</em>). Serotonergic function has been found to be low in patients who attempted and/or completed suicide, particularly those who used violent methods. Aggression dyscontrol appears to be an intervening factor between serotonin and suicide. Additionally, agents that enhance serotonergic transmission decrease suicidal behavior. Serotonin has also been documented to play an important role in onset and maintenance of slow wave sleep and in REM sleep. CSF 5-HIAA levels have been correlated with slow wave sleep in patients with depression as well as schizophrenia. Moreover, <em>5HT</em>2 receptor antagonists have improved slow wave sleep. Further studies are needed to investigate the possible role of sleep disturbance in suicidal behavior.

The selective estrogen receptor modulator (SERM), tamoxifen, effectively slows the progression of estrogen-positive breast cancer and aids in the prevention of cancer in at-risk women. Tamoxifen is well characterized with regards to its effects on breast cancer, but its effects on other estrogen-related systems, particularly neural circuits regulating brain function and mood, are poorly understood. Using ovariectomized rhesus monkeys, we examined the effects of tamoxifen, with and without estrogen replacement therapy (ERT), on social behavior and central serotonin (<em>5HT</em>) systems thought to influence these behaviors. Relative to placebo treatments, estrogen treatment increased serotonergic tone, based on response in prolactin and cortisol to fenfluramine, a <em>5HT</em> releasing agent. Tamoxifen neither blocked nor enhanced this effect, indicating it to be neither an antagonist nor an agonist on serotonergic activity. In contrast, CSF measures of the <em>5HT</em> metabolite, 5HIAA, were not significantly affected by treatment. Tamoxifen-treated animals showed increases in measures of anxiety, compared with ERT-treated animals, suggesting that this SERM may be anxiogenic. Co-treatment with estrogen attenuated the anxiogenic properties of tamoxifen. These data show that tamoxifen administration increased anxiety levels, but the affect was not associated with differences in central levels of the serotonin tone.

Progesterone stimulates prolactin secretion in estrogen-primed women and monkeys. We hypothesize that this effect is neurally mediated since pituitary lactotropes do not contain progestin receptors (PR). In rodents, progesterone enhances hypothalamic serotonin (<em>5HT</em>) content, and both progesterone and <em>5HT</em> stimulate prolactin and LH secretion. However, it was not known whether progesterone acts directly on <em>5HT</em> neurons or through other neurons. Using a double immunocytochemical procedure, we show that <em>5HT</em> neurons in macaque contain PR and thus are a progestin target system. Midbrain tissue blocks were obtained from two female monkeys and immersion-fixed prior to freezing and sectioning. PR was detected with a monoclonal antibody against human PR (B39) bridged to horseradish peroxidase and developed in diaminobenzidine. PR immunoreactivity appeared as a brown reaction product which localized in the nuclei of individual neurons. <em>5HT</em> was detected with an antiserum generated against a conjugate of <em>5HT</em> and BSA bridged to alkaline phosphatase. <em>5HT</em> immunoreactivity appeared as a blue reaction product in the cytoplasm and axons of the pontine raphe nucleus. Neurons containing both nuclear reaction product for PR and cytoplasmic reaction product for <em>5HT</em> were observed in both the dorsal and ventral aspects of the midbrain raphe nucleus as well as the raphe magnus. In summary, progesterone can have a direct action on <em>5HT</em> neuronal function and thereby influence those endocrine and affective systems under serotonergic control.

Tolerance and physical dependence development to morphine in mice can be prevented by concomitant administration of cycloheximide. The fact that the rate of synthesis of brain 5-hydroxytryptamine (<em>5HT</em>) increases with tolerance to morphine suggests that the protein involved may be associated with <em>5HT</em> synthesis. Inhibition of this synthesis with p-chlorophenylalanine markedly decreases tolerance and physical dependence development to morphine.

Mechanical distortion of the human cranial venous sinuses is painful as is cranial venous sinus distension during migraine. Sumatriptan, the serotonin (<em>5HT</em>)IB/D-like receptor agonist, is highly effective in relieving migraine headache and part of its action may be due to constriction of cranial dural blood vessels. Using immunohistochemical detection of the immediate early gene Fos, we have mapped the spatial pattern of neural activation in the caudal medulla and the upper cervical spinal cord (C1, C2 and C3) in cats following either electrical or mechanical stimulation of the superior sagittal sinus. Fourteen cats were anaesthetized with alpha-chloralose and prepared for physiological monitoring of blood pressure, heart rate, rectal temperature and expired CO2. Electrical stimulation evoked significant increases in the (median) numbers of Fos-positive cells in laminae I and IIo of the superficial dorsal horn of C1, C2 and C3 cervical spinal cord (88, 92 and 18 cells, respectively) and of the trigeminal nucleus caudalis (TNC) (81 cells). Mechanical stimulation revealed a similar pattern of neural activation but with reduced intensity in laminae I and IIo of the TNC (38 cells) and of C1 and C2 (32 and 31 cells, respectively). The temporalis muscle was stimulated mechanically in the control group and the numbers and distribution of Fos-positive cells were no different from those in non-stimulated controls. Treatment with sumatriptan reduced the numbers of Fos-positive cells found in laminae I and IIo of the TNC and C2 (6, 13 cells and 9 cells, respectively) after mechanical stimulation. These data suggest that the neural effect of sumatriptan alone is sufficient for significant attenuation of transmission in the trigeminal system. The fact that sumatriptan can inhibit trigeminal activation without its vascular effects suggests that drugs without a significant activity on blood vessels may be effective in the treatment of migraine.

The effects of progesterone (P) on serotonin (<em>5HT</em>) overflow in the ventromedial hypothalamus (VMH), preoptic area (POA) and midbrain central grey (MCG) were studied using in vivo microdialysis. Ovariectomized rats, pretreated with 5 micrograms estradiol, were anesthetized with chloral hydrate and stereotaxically implanted with dialysis probes directed towards one of the respective brain sites. Extracellular <em>5HT</em> levels stabilized 3 to 5 h following probe implantation. Under stable baseline conditions, perfusion of 1 microM tetrodotoxin through the dialysis probe resulted in 60-65% reduction in <em>5HT</em> overflow in the brain areas studied. In experiments testing the effect of P on <em>5HT</em> overflow, rats were subcutaneously injected with 0.5 mg P or propylene glycol vehicle. Samples were analyzed for <em>5HT</em> at 20 min intervals for 4 h after treatment. Perfusate levels of <em>5HT</em> were not significantly changed in the VMH, POA or MCG in vehicle-treated rats. Similarly, P treatment failed to significantly alter <em>5HT</em> overflow in the POA. In the VMH, perfusate levels of <em>5HT</em> were significantly reduced 60 min after P treatment. Decreases in perfusate <em>5HT</em> levels were detected 20 min after P in the MCG. The decreases in <em>5HT</em> overflow measured in the VMH and MCG following P treatment persisted for the remainder of the sampling period with the exception of 1 time point in the VMH. The results provide in vivo evidence for P-influenced decreases in <em>5HT</em> release in the VMH and MCG. The rapid decrease in extracellular <em>5HT</em> in the MCG suggests that this effect may represent a non-genomic action of P. These results are discussed in relation to the role of <em>5HT</em> in the regulation of lordosis behavior.

Whole blood serotonin (<em>5HT</em>) and plasma norepinephrine (NE) levels were determined in 47 families of autistic probands to study relationships within families of these measures. Whole blood <em>5HT</em>, but not plasma NE, was significantly positively correlated between autistic children and their mothers, fathers, and siblings. Twenty-three of the 47 families studied had at least 1 hyperserotonemic member. Of these 23 families, 10 (43.5%) had 2 or more hyperserotonemic members; 5 families were identified in which each family member studied had hyperserotonemia (whole blood <em>5HT</em> greater than 270 ng/ml). If the autistic child of a family was hyperserotonemic, the first-degree relatives were 2.4 times more likely to be hypersertonemic than if the autistic child was not hyperserotonemic. Mean whole blood <em>5HT</em> levels were higher in autistic subjects than their parents or siblings. Siblings were found to have lower plasma NE than autistic probands. This study replicates a previous study showing familial relationships of hyperserotonemia within families with autistic children.

Neo-natal rats emit ultrasonic vocalizations (USVs) when isolated from their mothers and littermates. Clinically effective anxiolytics reliably reduce USVs, making this behavior a useful animal model of the anxiolytic potential of novel pharmacological approaches to the treatment of anxiety. Here, we assess the hypothesis that USV duration (total time spent vocalizing) is a more sensitive measure of anxiolytic and antidepressant efficacy than USV number by testing established and putative anxiolytics in this model. Negative geotaxis and righting reflex latency were measured to assess sedating properties. The benzodiazepines, CDP (1-10 mg/kg) and diazepam (0.3-3 mg/kg), the <em>5HT</em>(1A) partial agonist, buspirone (0.3-3 mg/kg), and the mGluR5 antagonist, MTEP (1-30 mg/kg), reduced USV duration at lower doses and to a greater magnitude than USV number. The benzodiazepines, unlike buspirone and MTEP, produced measurable sedation, but it was dissociable from reductions in USV duration. The SSRI antidepressants, fluoxetine (1-30 mg/kg) and citalopram (0.3-30 mg/kg), reduced USV duration more than number with no measurable effect on sedation. The tricyclic antidepressants, imipramine (1-10 mg/kg) and amitriptyline (1-30 mg/kg), had no effect dissociable from sedation. These data support USV duration as a more sensitive and useful measure than USV number in the isolated rat pup model.

The neuronal-specific toxin alpha-conotoxin ImI (CTx ImI) has the sequence Gly-Cys-Cys-Ser-Asp-Pro-Arg-Cys-Ala-Trp-Arg-Cys-NH2, in which each cysteine forms a disulfide bridge to produce a constrained two-loop structure. To investigate the structural basis for bioactivity we mutated individual residues in CTx ImI and determined bioactivity. Bioactivity of the toxins was determined by their competition against 125I-labeled alpha-bungarotoxin binding to homomeric receptors containing alpha7 sequence in the major extracellular domain and <em>5HT</em>-3 sequence elsewhere. The results reveal two regions in CTx ImI essential for binding to the alpha7/<em>5HT</em>-3 receptor. The first is the triad Asp-Pro-Arg in the first loop, where conservative mutations of each residue diminish affinity by 2-3 orders of magnitude. The second region is the lone Trp in the second loop, where an aromatic side chain is required. The overall results suggest that within the triad of the first loop, Pro positions the flanking Asp and Arg for optimal interaction with one portion of the binding site, while within the second loop, Trp stabilizes the complex through its aromatic ring.

The <em>5HT</em>-mediated contraction of rat thoracic aorta is competitively blocked by the specific receptor antagonist <em>5HT</em>2 ketanserin. In this tissue the addition of <em>5HT</em> activated the turnover of 3H-phosphatidylinositol in a ketanserin-reversible fashion. These <em>5HT</em>2 recognition sites appear to be coupled to a phospholipase C mediated cleavage of phosphatidylinositol.

BACKGROUND

Pulmonary first pass filtration of particles marginally exceeding ∼7 µm (the size of a red blood cell) is used routinely in diagnostics, and allows cellular aggregates forming or entering the circulation in the preceding cardiac cycle to lodge safely in pulmonary capillaries/arterioles. Pulmonary arteriovenous malformations compromise capillary bed filtration, and are commonly associated with ischaemic stroke. Cohorts with CT-scan evident malformations associated with the highest contrast echocardiographic shunt grades are known to be at higher stroke risk. Our goal was to identify within this broad grouping, which patients were at higher risk of stroke.

METHODS

497 consecutive patients with CT-proven pulmonary arteriovenous malformations due to hereditary haemorrhagic telangiectasia were studied. Relationships with radiologically-confirmed clinical ischaemic stroke were examined using logistic regression, receiver operating characteristic analyses, and platelet studies.

RESULTS

Sixty-one individuals (12.3%) had acute, non-iatrogenic ischaemic clinical strokes at a median age of 52 (IQR 41-63) years. In crude and age-adjusted logistic regression, stroke risk was associated not with venous thromboemboli or conventional neurovascular risk factors, but with low serum iron (adjusted odds ratio 0.96 [95% confidence intervals 0.92, 1.00]), and more weakly with low oxygen saturations reflecting a larger right-to-left shunt (adjusted OR 0.96 [0.92, 1.01]). For the same pulmonary arteriovenous malformations, the stroke risk would approximately double with serum iron 6 µmol/L compared to mid-normal range (7-27 µmol/L). Platelet studies confirmed overlooked data that iron deficiency is associated with exuberant platelet aggregation to serotonin (<em>5HT</em>), correcting following iron treatment. By MANOVA, adjusting for participant and <em>5HT</em>, iron or ferritin explained 14% of the variance in log-transformed aggregation-rate (p = 0.039/p = 0.021).

CONCLUSIONS

These data suggest that patients with compromised pulmonary capillary filtration due to pulmonary arteriovenous malformations are at increased risk of ischaemic stroke if they are iron deficient, and that mechanisms are likely to include enhanced aggregation of circulating platelets.

TRPA1 is an ion channel that detects specific chemicals in food and also transduces mechanical, cold and chemical stimulation. Its presence in sensory nerve endings is well known and recent evidence indicates that it is expressed by some gastrointestinal enteroendocrine cells (EEC). The purpose of the present work is to identify and quantify EEC that express TRPA1 in the mouse gastrointestinal tract. Combined in situ hybridisation histochemistry for TRPA1 and immunofluorescence for EEC hormones was used. TRPA1 expressing EEC were common in the duodenum and jejunum, were rare in the distal small intestine and were absent from the stomach and large intestine. In the duodenum and jejunum, TRPA1 occurred in EEC that contained both cholecystokinin (CCK) and 5-hydroxytryptamine (<em>5HT</em>) and in a small number of cells expressing <em>5HT</em> but not CCK. TRPA1 was absent from CCK cells that did not express <em>5HT</em> and from EEC containing glucagon-like insulinotropic peptide. Thus TRPA1 is contained in very specific EEC populations. It is suggested that foods such as garlic and cinnamon that contain TRPA1 stimulants may aid digestion by facilitating the release of CCK.

Several drugs have been linked to valvulopathy in humans, including therapeutic agents for obesity, Parkinson's disease and migraine. There is increasing evidence that the 5-hydroxytryptamine 2B receptor (<em>5HT</em>2BR) activation and/or increased circulating <em>5HT</em> (5-hydroxytryptamine) may play a significant role in the pathogenesis of drug-induced valvulopathy. In the present study, we investigated whether 7-day <em>5HT</em> subcutaneous injections led to structural and compositional abnormalities in conjunction with transcriptomic modulation of <em>5HT</em>2BR and <em>5HT</em> transporter (<em>5HT</em>T) genes in the aortic and mitral valves of Sprague-Dawley (SD) rats. Subcutaneous injections of <em>5HT</em> for 7 days resulted in thickening and compositional alteration of aortic and mitral valves in SD rats. More specifically, valve-leaflets from <em>5HT</em>-treated rats had greater valve thickness, a higher amount of glycosaminoglycans (GAGs) and a lower amount of collagen. The compositional alteration was associated with up-regulation and down-regulation of <em>5HT</em>2BR and <em>5HT</em>T genes, respectively. The present study strongly suggests that the activation of <em>5HT</em>2BR and inhibition of <em>5HT</em>T played a significant role in the pathogenesis of <em>5HT</em>-induced valvulopathy in SD rats. Thus, these findings further highlight the necessity and/or utilization of animal models to screen potential valvular effects of serotonergic compounds.

The NK(1) receptor antagonist aprepitant (EMEND(R)), developed for use in combination with a <em>5HT</em>(3) receptor antagonist and a corticosteroid to prevent highly emetogenic chemotherapy-induced nausea and vomiting (CINV), has been shown to have a moderate inhibitory effect as well as a possible inductive effect on cytochrome P450 (CYP) 3A4. Aprepitant has been noted to produce modest decreases in plasma S(-)-warfarin concentrations, suggesting potential induction of CYP2C9. Because metabolism of some chemotherapeutic agents may involve CYP3A4, the potential inductive effect of the CINV dosing regimen of aprepitant on this metabolic pathway was evaluated using intravenous midazolam, a sensitive probe substrate of CYP3A4. The time course of induction of CYP2C9 by aprepitant was also evaluated using oral tolbutamide, a probe substrate of CYP2C9. In this double-blind, randomized, placebo-controlled, single-center study, 24 healthy subjects were randomized (12 subjects per group) to receive either an aprepitant 3-day regimen (aprepitant 125 mg p.o. on day 1 and aprepitant 80 mg p.o. on days 2 and 3) or matching placebo. All subjects also received probe drugs (midazolam 2 mg i.v. and tolbutamide 500 mg p.o.) once prior to aprepitant dosing (baseline) and again on days 4, 8, and 15. The ratio (aprepitant/placebo) of the geometric mean area under the plasma concentration curve (AUC) fold-change from baseline for midazolam was 1.25 on day 4 (p < 0.01), 0.81 on day 8 (p < 0.01), and 0.96 on day 15 (p = 0.646). The ratio (aprepitant/placebo) of the geometric mean AUC fold-change from baseline for tolbutamide was 0.77 on day 4 (p < 0.01), 0.72 on day 8 (p < 0.001), and 0.85 on day 15 (p = 0.05). Assessed using intravenous midazolam as a probe, aprepitant 125/80 mg p.o. administered over days 1 to 3 produced clinically insignificant weak inhibition (day 4) and induction (day 8) of CYP3A4 activity and no effect on CYP3A4 activity on day 15. Assessed using oral tolbutamide as a probe, the aprepitant regimen also produced modest induction of CYP2C9 activity on days 4 and 8, which resolved nearly to baseline by day 15. Thus, the aprepitant regimen for CINV results in modest, transient induction of CYPs 3A4 and 2C9 in the 2 weeks following administration.

Gymnodimines (GYMs) are phycotoxins exhibiting unusual structural features including a spirocyclic imine ring system and a trisubstituted tetrahydrofuran embedded within a 16-membered macrocycle. The toxic potential and the mechanism of action of GYM-A, highly purified from contaminated clams, have been assessed. GYM-A in isolated mouse phrenic hemidiaphragm preparations produced a concentration- and time-dependent block of twitch responses evoked by nerve stimulation, without affecting directly elicited muscle twitches, suggesting that it may block the muscle nicotinic acetylcholine (ACh) receptor (nAChR). This was confirmed by the blockade of miniature endplate potentials and the recording of subthreshold endplate potentials in GYM-A paralyzed frog and mouse isolated neuromuscular preparations. Patch-clamp recordings in Xenopus skeletal myocytes revealed that nicotinic currents evoked by constant iontophoretical ACh pulses were blocked by GYM-A in a reversible manner. GYM-A also blocked, in a voltage-independent manner, homomeric human alpha7 nAChR expressed in Xenopus oocytes. Competition-binding assays confirmed that GYM-A is a powerful ligand interacting with muscle-type nAChR, heteropentameric alpha3beta2, alpha4beta2, and chimeric alpha7-<em>5HT</em>(3) neuronal nAChRs. Our data show for the first time that GYM-A broadly targets nAChRs with high affinity explaining the basis of its neurotoxicity, and also pave the way for designing specific tests for accurate GYM-A detection in shellfish samples.

The effect of oxygen (O2) exposure on the ability of the isolated, perfused rat lung to clear serotonin (5-hydroxytryptamine, 5-HT) from the perfusate was evaluated in normal or vitamin E-deficient Sprague-Dawley rats. Rats were exposed to 100% O2 at 1 ATA for 4-48 h. Lungs were subsequently isolated, artificially ventilated, and perfused in a recirculating system with Krebs-Ringer bicarbonate solution, pH 7.4 containing 3% bovine serum albumin and 0.25 muM [14C] 5-HT. <em>5HT</em> clearance was calculated from the disappearance rate of [ 14C] 5-HT from the perfusate. In normal rats exposed to 100% O2, there was a progressive reduction in the clearance of 5-HT with increasing duration of O2 exposure. Compared to lungs from air-exposed controls, clearance was depressed 20% (P less than 0.01) after 18 h, 22% (P less than 0.01) after 24 h, and 35% (P less than 0.001) after 48 h. With vitamin E-deficient rats, the reduction in 5-HT clearance occurred after a shorter exposure time and was of greater magnitude than in rats on a normal diet. Depression of <em>5HT</em> clearance by the lungs is an early alteration of lung function fue to hyperoxia and is potentiated by vitamin E deficiency. The most likely mechanism for the depression of 5-HT clearance is interference with the transport properties of lung endothelium.

The nervous system copes with variability in the external and internal environment by using neuromodulators to adjust the efficacy of neural circuits. The role of serotonin (<em>5HT</em>) as a neuromodulator of olfactory information processing in the antennal lobe (AL) of Manduca sexta was examined using multichannel extracellular electrodes to record the responses of ensembles of AL neurons to olfactory stimuli. In one experiment, the effects of <em>5HT</em> on the concentration-response functions for two essential plant oils across a range of stimulus intensities were examined. In a second experiment, the effect of <em>5HT</em> on the ability of ensembles to discriminate odorants from different chemical classes was examined. Bath application of <em>5HT</em> enhanced AL unit responses by increasing response duration and firing rate, which in turn increased the amount of spike time cross-correlation and -covariance between pairs of units. <em>5HT</em> had the greatest effect on overall ensemble activation at higher odorant concentrations, resulting in an increase in the gain of the dose-response function of individual units. Additionally, response thresholds shifted to lower odorant concentrations for some units, suggesting that <em>5HT</em> increased their sensitivity. Serotonin enhanced ensemble discrimination of different concentrations of individual odorants as well as discrimination of structurally dissimilar odors at the same concentration. Given the known circadian fluctuations of <em>5HT</em> in the AL of this species, these findings support the hypothesis that <em>5HT</em> periodically enhances sensitivity and responsiveness in the AL of Manduca to maximize efficiency when the requirement for olfactory acuity is the greatest.

Normal controls (NC) (n = 15), patients with panic disorder (PD) (n = 13) and patients with major depression (MD) (n = 17) were challenged with a single, oral dose (0.25 mg/kg) of the selective <em>5HT</em> agonist m-chlorophenyl-piperazine (MCPP) or placebo. Blood samples were assayed for cortisol and MCPP levels every 30 min. The PD group had an augmented cortisol release when compared to the other two groups. Finally, a significant correlation was found across all subjects between clinical anxiety level and cortisol release on MCPP. These data support the hypothesis of <em>5HT</em> receptor hypersensitivity in PD.