The serotonin transporter (SERT) regulates extracellular levels of serotonin (5-hydroxytryptamine, <em>5HT</em>) in the brain by transporting <em>5HT</em> into neurons and glial cells. The human SERT (hSERT) is the primary target for drugs used in the treatment of emotional disorders, including depression. hSERT belongs to the solute carrier 6 family that includes a bacterial leucine transporter (LeuT), for which a high resolution crystal structure has become available. LeuT has proved to be an excellent model for human transporters and has advanced the understanding of solute carrier 6 transporter structure-function relationships. However, the precise structural mechanism by which antidepressants inhibit hSERT and the location of their binding pockets are still elusive. We have identified a residue (Ser-438) located within the <em>5HT</em>-binding pocket in hSERT to be a critical determinant for the potency of several antidepressants, including the selective serotonin reuptake inhibitor citalopram and the tricyclic antidepressants imipramine, clomipramine, and amitriptyline. A conservative mutation of Ser-438 to threonine (S438T) selectively increased the K(i) values for these antidepressants up to 175-fold. The effects of introducing a protein methyl group into the <em>5HT</em>-binding pocket by S438T were absent or reduced for analogs of these antidepressants lacking a single methyl group. This suggests that these antidepressants interact directly with Ser-438 during binding to hSERT, implying an overlapping localization of substrate- and inhibitor-binding sites in hSERT suggesting that antidepressants function by a mechanism that involves direct occlusion of the <em>5HT</em>-binding site.

Acute effects of estrogens on mnemonic processes were examined at the behavioral and neurochemical levels. 17beta-estradiol and 17alpha-estradiol influences on memory consolidation were assessed using object placement (OP) and object recognition (OR) tasks. Subjects received treatment immediately after a sample trial (exploring two novel objects), and memory of objects (OR memory) or location of objects (OP memory) was tested 4h later. Both isomers of estradiol enhanced memory. For spatial memory, 15 and 20 microg/kg of 17beta-estradiol facilitated OP, while lower and higher doses were ineffective. 17alpha-estradiol had a similar pattern, but a lower dose was effective. When treatment was delayed until 45 min after a sample trial, memory was not enhanced. For non-spatial memory, OR was facilitated at 5 microg/kg of 17beta-estradiol and at 1 and 2 microg/kg of 17alpha-estradiol and, similar to OP, lower and higher doses were ineffective. These data demonstrate that beneficial effects of estrogens are dose, time and task dependent, and the dose-response pattern is an inverted U. Because monoamines are known to have contributions to memory, brains were removed 30 min after treatment for measurements of dopamine (DA), norepinephrine (NE), serotonin (5-HT), and metabolites. Estrogen elevated <em>5HT</em>, NE metabolite MHPG, turnover ratio of NE to MHPG, and DA metabolite DOPAC levels in the prefrontal cortex, while NE and MHPG were decreased in the hippocampus. Thus, acute estrogens exert rapid effects on memory consolidation and neural function, which suggests that its mnemonic effects may involve activation of membrane associated estrogen receptors and subsequent signaling cascades, and that monoamines may contribute to this process.

The development of central serotonergic neurons has been examined immunocytochemically utilizing an antiserum to serotonin (5-HT). Cells of the B4-B9 complex are first detected early on embryonic day 13 (E13; 7 mm crown rump length, CRL) and increase rapidly in number through E15 when they appear as bilateral columns situated from just caudal to the mesencephalic flexure to the pontine flexure. Aggregation of cells into subgroups is apparent soon after 5-HT neurons leave the ventricular zone, allowing the identification of certain subdivisions of the B4-B9 complex long before they assume their adult locations. The initial detection of 5-HT immunoreactive cells in the medulla occurs 1-2 days after the appearance of cells in the B4-B9 complex, although it has been reported that the time of origin of medullary raphe neurons (B1-B3) occurs before that of raphe neurons in the midbrain and pons (B4-B9). The first medullary 5-HT neurons, comprising the B3 subdivision occur ventro-laterally on E14 (10-11 mm CRL) at least 1-2 days before midline 5-HT neurons are visualized in the B1 and B2 groups. Thus, in contrast to cells in the B4-B9 complex, medullary 5-HT neurons complete much of their migration before they can be detected immunocytochemically, indicating that the time of onset of transmitter synthesis and storage may differ during differentiation of cells sharing a common neurotransmitter phenotype. The formation of ascending 5-HT fiber projections occurs rapidly from cells of the B4-B9 complex. Within 24 hours after the initial detection of 5-HT fiber immunoreactivity in such cells at E13, their axons are seen entering the caudal diencephalon (E14). These fibers have traversed the diencephalon and floor of the telencephalon by E15-E16 and reach the frontal neocortical pole by E17. The main ascending bundle of 5-HT axons courses through the diencephalon in the vicinity of the medial forebrain bundle, although some fibers also diverge and travel along certain pre-existing non-<em>5HT</em> pathways. However, examples are also found of acute directional changes in 5-HT fiber growth which do not appear to be associated with pre-formed non-<em>5HT</em> pathways. The pattern of ascending fiber outgrowth suggests a priority routing system which provides certain regions with 5-HT axons in a preferential sequence irrespective of the distance of these areas from 5-HT cell groups or from major bundles of ascending 5-HT fibers.

Benzodiazepine sedative-hypnotic drugs are widely used for the treatment of insomnia. Nevertheless, their adverse effects, such as next-day hangover, dependence and impairment of memory, make them unsuitable for long-term treatment. Melatonin has been used for improving sleep in patients with insomnia mainly because it does not cause hangover or show any addictive potential. However, there is a lack of consistency on its therapeutic value (partly because of its short half-life and the small quantities of melatonin employed). Thus, attention has been focused either on the development of more potent melatonin analogs with prolonged effects or on the design of slow release melatonin preparations. The MT(1) and MT(2) melatonergic receptor ramelteon was effective in increasing total sleep time and sleep efficiency, as well as in reducing sleep latency, in insomnia patients. The melatonergic antidepressant agomelatine, displaying potent MT(1) and MT(2) melatonergic agonism and relatively weak serotonin <em>5HT</em>(2C) receptor antagonism, was found effective in the treatment of depressed patients. However, long-term safety studies are lacking for both melatonin agonists, particularly considering the pharmacological activity of their metabolites. In view of the higher binding affinities, longest half-life and relative higher potencies of the different melatonin agonists, studies using 2 or 3mg/day of melatonin are probably unsuitable to give appropriate comparison of the effects of the natural compound. Hence, clinical trials employing melatonin doses in the range of 50-100mg/day are warranted before the relative merits of the melatonin analogs versus melatonin can be settled.

The molecular architecture of developing serotonin (<em>5HT</em>) neurons is poorly understood, yet its determination is likely to be essential for elucidating functional heterogeneity of these cells and the contribution of serotonergic dysfunction to disease pathogenesis. Here, we describe the purification of postmitotic embryonic <em>5HT</em> neurons by flow cytometry for whole-genome microarray expression profiling of this unitary monoaminergic neuron type. Our studies identified significantly enriched expression of hundreds of unique genes in <em>5HT</em> neurons, thus providing an abundance of new serotonergic markers. Furthermore, we identified several hundred transcripts encoding homeodomain, axon guidance, cell adhesion, intracellular signaling, ion transport, and imprinted genes associated with various neurodevelopmental disorders that were differentially enriched in developing rostral and caudal <em>5HT</em> neurons. These findings suggested a homeodomain code that distinguishes rostral and caudal <em>5HT</em> neurons. Indeed, verification studies demonstrated that Hmx homeodomain and Hox gene expression defined an Hmx(+) rostral subtype and Hox(+) caudal subtype. Expression of engrailed genes in a subset of <em>5HT</em> neurons in the rostral domain further distinguished two subtypes defined as Hmx(+)En(+) and Hmx(+)En(-). The differential enrichment of gene sets for different canonical pathways and gene ontology categories provided additional evidence for heterogeneity between rostral and caudal <em>5HT</em> neurons. These findings demonstrate a deep transcriptome and biological pathway duality for neurons that give rise to the ascending and descending serotonergic subsystems. Our databases provide a rich, clinically relevant resource for definition of <em>5HT</em> neuron subtypes and elucidation of the genetic networks required for serotonergic function.

Nicotine is a neuroteratogen that disrupts neurodevelopment and synaptic function, with vulnerability extending into adolescence. We assessed the permanence of effects in rats on indices of neural cell number and size, and on acetylcholine and serotonin (<em>5HT</em>) systems, conducting assessments at 6 months of age, after prenatal nicotine exposure, adolescent exposure, or sequential exposure in both periods. For prenatal nicotine, indices of cell number and size showed few abnormalities by 6 months, but there were persistent deficits in cerebrocortical choline acetyltransferase activity and hemicholinium-3 binding to the presynaptic choline transporter, a pattern consistent with cholinergic hypoactivity; these effects were more prominent in males than females. The expression of <em>5HT</em> receptors also showed permanent effects in males, with suppression of the <em>5HT</em>(1A) subtype and upregulation of <em>5HT</em>(2) receptors. In addition, cell signaling through adenylyl cyclase showed heterologous uncoupling of neurotransmitter responses. Nicotine exposure in adolescence produced lasting effects that were similar to those of prenatal nicotine. However, when animals were exposed to prenatal nicotine and received nicotine subsequently in adolescence, the adverse effects then extended to females, whereas the net effect in males was similar to that of prenatal nicotine by itself. Our results indicate that prenatal or adolescent nicotine exposure evoke permanent changes in synaptic function that transcend the recovery of less-sensitive indices of structural damage; further, prenatal exposure sensitizes females to the subsequent adverse effects of adolescent nicotine, thus creating a population that may be especially vulnerable to the lasting behavioral consequences of nicotine intake in adolescence.

BACKGROUND

In the developing brain, serotonin (<em>5HT</em>) systems are among the most sensitive to disruption by organophosphates.

OBJECTIVE

We exposed neonatal rats to daily doses of diazinon or parathion on postnatal days (PND)1-4 and evaluated <em>5HT</em> receptors and the <em>5HT</em> transporter in brainstem and forebrain on PND5, focusing on doses of each agent below the maximum tolerated dose and spanning the threshold for cholinesterase inhibition: 0.5, 1, or 2 mg/kg for diazinon, and 0.02, 0.05, and 0.1 mg/kg for parathion.

RESULTS

Diazinon evoked up-regulation of <em>5HT</em>1A and <em>5HT</em>2 receptor expression even at doses devoid of effects on cholinesterase activity, a pattern similar to that seen earlier for another organophosphate, chlorpyrifos. In contrast, parathion decreased <em>5HT</em>1A receptors, again at doses below those required for effects on cholinesterase. The two agents also differed in their effects on the <em>5HT</em> transporter. Diazinon evoked a decrease in the brainstem and an increase in the forebrain, again similar to that seen for chlorpyrifos; this pattern is typical of damage of nerve terminals and reactive sprouting. Parathion had smaller, nonsignificant effects.

CONCLUSIONS

Our results buttress the idea that, in the developing brain, the various organophosphates target specific neurotransmitter systems differently from each other and without the requirement for cholinesterase inhibition, their supposed common mechanism of action.

BACKGROUND

Emergence agitation (EA) in children is increased after sevoflurane anaesthesia. The efficacy of prophylactic treatment is controversial. The aim of this study was to provide a meta-analysis of the studies of the pharmacological prevention of EA in children.

METHODS

A comprehensive literature search was conducted to identify clinical trials that focused on the prevention of EA in children anaesthetized with sevoflurane, desflurane, or both. The data from each trial were combined using the Mantel-Haenszel model to calculate the pooled odds ratio (OR) and 95% confidence interval. I(2) statistics were used to assess statistics heterogeneity and the funnel plot and the Begg-Mazumdar test to assess bias.

RESULTS

Thirty-seven articles were found which included a total of 1695 patients in the intervention groups and 1477 in the control ones. Midazolam and <em>5HT</em>(3) inhibitors were not found to have a protective effect against EA [OR=0.88 (0.44, 1.76); OR=0.39 (0.12, 1.31), respectively], whereas propofol [OR=0.21 (0.16, 0.28)], ketamine [OR=0.28 (0.13, 0.60)], alpha(2)-adrenoceptors [OR=0.23 (0.17, 0.33)], fentanyl [OR=0.31 (0.18, 0.56)], and peroperative analgesia [OR=0.15 (0.07, 0.34)] were all found to have a preventive effect. Subgroup analysis according to the peroperative analgesia given does not affect the results.

CONCLUSIONS

This meta-analysis found that propofol, ketamine, fentanyl, and preoperative analgesia had a prophylactic effect in preventing EA. The analgesic properties of these drugs do not seem to have a role in this effect.

Although it is well established that hallucinogens act as 5-HT(2A) and 5-HT(2C) receptor agonists, little is known about the relative contributions of 5-HT(2A) and 5-HT(2C) receptors to the acute behavioral effects of these drugs. The behavioral pattern monitor was used to characterize the effects of the hallucinogen 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on locomotor and investigatory behavior in mice. Studies were also conducted to assess the contributions of 5-HT(2A) and 5-HT(2C) receptors to the behavioral effects of DOI. DOI produced an inverted U-shaped dose-response function, with lower doses (0.625-5.0 mg/kg) increasing and higher doses >> or =10 mg/kg) decreasing locomotor activity. The increase in locomotor activity induced by 1.0 mg/kg DOI was absent in 5-HT(2A) receptor KO mice, suggesting the involvement of 5-HT(2A) receptors. The reduction in locomotor activity produced by 10 mg/kg DOI was potentiated in 5-HT(2A) KO mice and attenuated by pretreatment with the selective 5-HT(2C/2B) antagonist SER-082. These data indicate that the decrease in locomotor activity induced by 10 mg/kg DOI is mediated by 5-HT(2C) receptors, an interpretation that is supported by the finding that the selective 5-HT(2C) agonist WAY 161,503 produces reductions in the locomotor activity that are potentiated in <em>5HT</em>(2A) KO mice. These results show for the first time that 5-HT(2A) and 5-HT(2C) receptors both contribute to the effects of DOI on locomotor activity in mice. Furthermore, these data also suggest that 5-HT(2A) and 5-HT(2C) receptors exert opposing effects on locomotor activity.

There are several lines of evidence, the majority indirect, suggesting that changes in serotonergic or dopaminergic neurotransmission may contribute to the pathogenesis of obsessive-compulsive disorder (OCD). We evaluated the co-occurrence of serotonergic and dopaminergic dysfunctions in OCD subjects, all drug-naive, with no co-morbidity and homogeneous for symptoms. Each subject underwent two positron emission tomography (PET) scans to measure in vivo both serotonin (5-HT(2A)) and dopamine (D(2)) receptor distribution. For this, we used [11C]MDL and [11C]Raclopride, highly selective antagonists of 5-HT(2A) and D(2) receptors, respectively. The comparison with a control group was carried out using both voxel-wise (SPM2) and regions of interest (ROI) approaches. There was a significant reduction of 5-HT(2A) receptor availability in frontal polar, dorsolateral, and medial frontal cortex, as well as in parietal and temporal associative cortex of OCD patients. We also found a significant correlation between 5-HT(2A) receptor availability in orbitofrontal and dorsolateral frontal cortex and clinical severity, suggesting a specific role for serotonin in determining the OCD symptoms. There was also a significant reduction of [11C]Raclopride uptake in the whole striatum, particularly in the ventral portion, possibly reflecting endogenous dopaminergic hyperactivity. The co-existence of serotonergic and dopaminergic dysfunction in the same homogeneous group of drug-naive OCD patients provides in vivo evidence for the complex molecular mechanisms of OCD, and represents the basis for further studies on the effect of therapeutic agents with specific modulatory effects on these neurotransmission systems.

During brain development, serotonin (<em>5HT</em>) provides essential neurotrophic signals. In the present study, we evaluated whether the developmental neurotoxicity of chlorpyrifos (CPF) involves effects on <em>5HT</em> signaling, as a potential mechanism underlying noncholinergic neuroteratogenic events. We evaluated four different treatment windows ranging from the neural tube stage [gestational days (GD) 9-12] and the late gestational period (GD17-20) through postnatal phases of terminal neuronal differentiation and synaptogenesis [postnatal days (PN) 1-4, PN11-14]. Exposure to CPF on GD9-12 elicited initial suppression, immediately followed by rebound elevation, of <em>5HT</em>1A and <em>5HT</em>2 receptors as well as the <em>5HT</em> transporter, all at doses below the threshold for cholinergic hyperstimulation and the resultant systemic toxicity. In contrast, with GD17-20 exposure, the initial effect was augmentation of all three components by low doses of CPF. Sensitivity of these effects declined substantially when exposure was shifted to the postnatal period. We also identified major alterations in <em>5HT</em>-mediated responses, assessed for the adenylyl cyclase signaling cascade. Although GD9-12 exposure had only minor effects, treatment on GD17-20 elicited supersensitivity to both stimulatory and inhibitory responses mediated by <em>5HT</em>. Our results indicate that CPF affects <em>5HT</em> receptors, the presynaptic <em>5HT</em> transporter, and <em>5HT</em>-mediated signal transduction during a discrete critical gestational window. These effects are likely to contribute to the noncholinergic component of CPF's developmental neurotoxicity.

Serotonin (<em>5HT</em>)-induced facilitation of synaptic transmission from tail sensory neurons (SNs) to motor neurons (MNs) in the marine mollusc Aplysia provides a cellular model of short- and long-term memory for behavioral sensitization of the tail withdrawal reflex. Synaptic facilitation at these synapses occurs in three temporal phases: short-term (STF, lasting minutes), intermediate-term (ITF, lasting more than an hour), and long-term (LTF, lasting >24 hr). STF, ITF, and LTF differ in their induction requirements: A single brief exposure of <em>5HT</em> induces STF, whereas five applications are required for ITF and LTF. Moreover, STF and LTF can be induced independently. Different forms of memory often show differential sensitivity to the pattern of training trials. To begin to explore this effect at a cellular level, we examined ITF and LTF induced by one of two patterns of <em>5HT</em> application: a spaced pattern (five 5-min exposures with an interval of 15 min) or a massed pattern (one continuous 25-min application). The spaced and massed patterns both induced ITF; however, spaced <em>5HT</em> application was significantly more reliable at inducing LTF than was massed application. Thus, whereas induction of ITF and LTF require similar amounts of <em>5HT</em>, the cellular mechanisms underlying the induction of LTF are more sensitive to the pattern of the induction trials. In the massed group, further analysis revealed a relationship between the expression of ITF and the subsequent expression of LTF, suggesting that these two processes may be mechanistically related.

5-HT(2C) receptor (<em>5HT</em>(2C)R, serotonin-2C) RNA undergoes editing to produce several receptor variants, some with pharmacological differences. This investigation comprised two parts: the characterisation of 5-HT(2C)R RNA editing in a larger human control sample than previously examined, and a comparative study in subjects with schizophrenia. Secondary structure analysis of the putative edited region of the human 5-HT(2C)R gene predicted the existence of a double stranded (ds) RNA loop, essential for RNA editing in this receptor. RNA was then extracted from frontal cortex of five controls and five subjects with schizophrenia. RT-PCR products of the edited region were cloned and sequenced (n = 100). Reduced RNA editing, increased expression of the unedited 5-HT(2C-INI) isoform in schizophrenia (P = 0.001) and decreased expression of the 5-HT(2C-VSV) and 5-HT(2C-VNV) isoforms were detected in the schizophrenia group. In addition, two novel mRNA edited variants were identified: 5-HT(2C-MNI) and 5-HT(2C-VDI). Screening of the 5-HT(2C)R gene did not reveal any mutations likely to disrupt the dsRNA loop, suggesting that the reduced RNA editing in schizophrenia may instead be caused by altered activity of the editing enzyme(s). Since the unedited 5-HT(2C-INI) is more efficiently coupled to G proteins than the other isoforms, its increased expression in schizophrenia may lead to enhanced 5-HT(2C)R-mediated effects. The results also illustrate that potentially important receptor alterations may occur in schizophrenia which are not detectable merely in terms of receptor abundance.

The possible involvement of the ascending 5-hydroxytryptaminergic (<em>5HT</em>ergic) pathways in determining the effectiveness of delayed positive reinforcers was investigated using Mazur's (1984) adjusting-delay paradigm. Fourteen rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei; 12 rats received sham lesions. The rats made repeated choices in a two-lever operant conditioning chamber between a smaller reinforcer delivered after a 2-s delay and a larger reinforcer delivered after a variable delay, the length of which was determined by the subject's previous choices. When the two reinforcers consisted of one and two food pellets, the "indifference point" (the delay to the larger reinforcer that rendered the two reinforcers equally effective) was shorter in the lesioned group than in the control group. Increasing the sizes of the reinforcers to three and six pellets reduced the indifference point in both groups and abolished the between-group difference. The levels of <em>5HT</em> and 5-hydroxyindoleacetic acid (5HIAA) in the parietal cortex, hippocampus, amygdala, nucleus accumbens and hypothalamus were greatly reduced in the lesioned group, but the levels of noradrenaline and dopamine were not significantly affected. The results are consistent with the suggestion that the <em>5HT</em>ergic pathways play a role in maintaining the effectiveness of delayed reinforcers.

It is no longer tenable to attribute all the antipsychotic action of antipsychotic drugs to dopamine (DA) D2 receptor blockade and subsequent development of depolarization inactivation of the mesolimbic or mesocortical DA neurons. The chief evidence for this position is that clozapine (CLOZ) does not differ from typical antipsychotic drugs in these regards but is more effective than typical neuroleptic drugs. The mechanism of action of atypical antipsychotic drugs related to CLOZ may involve reduction of dopaminergic activity in the mesolimbic system by a variety of mechanisms, including D1 and D2 receptor blockade. Relatively higher affinity for the serotonin (<em>5HT</em>)2 receptor than for the D2 receptor may also be important to the action of CLOZ-like compounds. Enhanced DA release in the mesocortical system may be relevant to the effectiveness of these agents in treating negative symptoms. Several other classes of new agents alter the dopaminergic system by means of alternative mechanisms. Partial DA agonists may modulate DA neurotransmission more adequately than pure antagonists by producing a mix of direct agonist and antagonistic effects. DA autoreceptor agonists and <em>5HT</em>3 antagonists appear to act by diminishing the release of DA from some, but not all, DA neurons. Substituted benzamides are "pure" D2 antagonists with some in vivo selectivity for limbic D2 over striatal D2 receptors. Highly selective D1 antagonists have been proposed to produce equivalent antipsychotic activity and fewer extrapyramidal symptoms than D2 antagonists. Antagonists of the recently identified D3 receptors are being sought. Excessive stimulation of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor, leading to neurotoxicity or diminished activation of this receptor, is the target of novel approaches to treating schizophrenia. Phencyclidine (PCP) antagonists that would activate the NMDA receptor and sigma receptor antagonists are of interest as antipsychotic agents. Therapeutic strategies for treating schizophrenia, schizophrenia-related disorders, and other psychoses will likely be genuinely diverse in the next decade.

Although numerous stress-related molecules have been implicated in vulnerability to psychiatric illness, especially major depression and anxiety disorders, the role of the brain mineralocorticoid receptor (MR) in stress, depression, and affective function is not well defined. MR is a steroid hormone receptor that detects circulating glucocorticoids with high affinity and has been primarily implicated in controlling their basal level and circadian rhythm. To specifically address the role of MR in hypothalamic-pituitary-adrenal axis activity and anxiety-related behaviors, we generated transgenic mice with increased levels of MR in the forebrain (MRov mice) by using the forebrain-specific calcium/calmodulin-dependent protein kinase II alpha promoter to direct expression of MR cDNA. A mild but chronic elevation in forebrain MR results in decreased anxiety-like behavior in both male and female transgenic mice. Female MRov mice also exhibit a moderate suppression of the corticosterone response to restraint stress. Increased forebrain MR expression alters the expression of two genes associated with stress and anxiety, leading to a decrease in the hippocampal glucocorticoid receptor (GR) and an increase in serotonin receptor <em>5HT</em>-1a, consistent with the decreased anxiety phenotype. These data suggest that the functions of forebrain MR may overlap with GR in hypothalamic-pituitary-adrenal axis regulation, but they dissociate significantly from GR in the modulation of affective responses, with GR overexpression increasing anxiety-like behavior and MR overexpression dampening it. These findings point to the importance of the MR:GR ratio in the control of emotional reactivity.

That serotonin (<em>5HT</em>) is involved in regulating hypothalamic-pituitary- adrenal axis (HPA) function has long been recognized. A variety of drugs including precursors of <em>5HT</em> such as <em>5HT</em>P, drugs which release <em>5HT</em> such as fenfluramine and drugs which act directly on <em>5HT</em> receptors such as ipsapirone increase cortisol and ACTH concentrations. There is a general assumption that such stimulation occurs at a hypothalamic level. However, our increasing understanding of the complex interplay between <em>5HT</em> and the HPA raises questions as to the validity of this simple model. An increasing volume of experimental research indicates that <em>5HT</em> can act directly on the adrenal gland and possibly on the anterior pituitary as well. These findings have major implications for the interpretation of neuroendocrine studies of <em>5HT</em> conducted in psychiatric conditions, such as depression.

Chemical and biological labeling is fundamental for the elucidation of the function of proteins within biochemical cellular networks. In particular, fluorescent probes allow detection of molecular interactions, mobility and conformational changes of proteins in live cells with high temporal and spatial resolution. We present a generic method to label proteins in vivo selectively, rapidly (seconds) and reversibly, with small molecular probes that can have a wide variety of properties. These probes comprise a chromophore and a metal-ion-chelating nitrilotriacetate (NTA) moiety, which binds reversibly and specifically to engineered oligohistidine sequences in proteins of interest. We demonstrate the feasibility of the approach by binding NTA-chromophore conjugates to a representative ligand-gated ion channel and G protein-coupled receptor, each containing a polyhistidine sequence. We investigated the ionotropic <em>5HT</em>(3) serotonin receptor by fluorescence measurements to characterize in vivo the probe-receptor interactions, yielding information on structure and plasma membrane distribution of the receptor.

Neurocognitive research has focused on monoaminergic influences over broad behavior patterns. For example, dopamine (DA) generally facilitates informational transfer within limbic and cortical networks to promote reward-seeking behavior. Specifically, DA activity in prefrontal cortex modulates the ability for nonhuman primates and humans to perform spatial working memory tasks. Serotonin (<em>5HT</em>) constrains the activity of DA, resulting in an opposing relationship between DA and <em>5HT</em> with respect to emotional and motor behaviors. A role for <em>5HT</em> in constraining prefrontally guided spatial working memory (WM) processes in humans has not been empirically demonstrated but is a logical avenue for study if these principles of neurotransmitter activity hold within cortical networks. In this study, normal humans completed a visuospatial WM task under pharmacological challenge with (i) bromocriptine, a DA agonist and (ii) fenfluramine, a serotonin agonist, in a double-blind, repeated-measures, placebo-controlled design. Findings indicate that bromocriptine facilitated spatial delayed, but not immediate, memory performance. Fenfluramine resulted in impaired delayed spatial memory. These effects were not due to nonspecific arousal, attentional, sensorimotor or perceptual changes. These findings suggest that monoaminergic neurotransmitters (DA and <em>5HT</em>) may interact within cortical networks to modulate the expression of specific cognitive behaviors, particularly effortful processes associated with goal-directed activity.

The lifetimes of activated postsynaptic receptor channels contribute to the efficiency of synaptic transmission. Here we show that structural differences within the interface dividing extracellular and transmembrane domains of homomeric alpha7 and 5-HT(3A) receptors account for the large differences in open-channel lifetime and time of desensitization onset between these contrasting members of the Cys-loop receptor superfamily. For alpha7 receptors, agonist-evoked single-channel currents appear mainly as isolated brief openings (tau(o) = 0.35 ms), whereas macroscopic currents after a step pulse of agonist desensitize rapidly (tau(d) = 0.4 ms). In contrast for 5-HT(3A) receptors, agonist-evoked single-channel currents appear as clusters of many long openings in quick succession (tau(cluster) = 1.2 s), whereas macroscopic currents desensitize slowly (tau(d) = 1.1 s). A chimeric alpha7-<em>5HT</em>(3A) receptor exhibits functional properties intermediate between those of the parent receptors, but the functional signatures of each parent are reconstituted after substituting the major loops within the interface of the extracellular and transmembrane domains from the corresponding parent receptor. Furthermore, these structural loops contribute to open-channel lifetime and time of desensitization onset in a nonadditive manner. The results suggest that desensitization is the major determinant of the lifetimes of activated alpha7 and 5-HT(3A) receptors and that functional differences between the two receptors arise primarily through structural differences at the interface between extracellular and transmembrane domains.

Serotonin (<em>5HT</em>) is a platelet-stored vasoconstrictor. Altered concentrations of circulating <em>5HT</em> are implicated in several pathologic conditions, including hypertension. The actions of <em>5HT</em> are mediated by different types of receptors and terminated by a single <em>5HT</em> transporter (SERT). Therefore, SERT is a major mechanism that regulates plasma <em>5HT</em> levels to prevent vasoconstriction and thereby secure a stable blood flow. In this study, the response of platelet SERT to the plasma <em>5HT</em> levels was examined within two models: (i) in subjects with chronic hypertension or normotension; (ii) on platelets isolated from normotensive subjects and pretreated with <em>5HT</em> at various concentrations. The platelet <em>5HT</em> uptake rates were lower during hypertension due to a decrease in Vmax with a similar Km; also, the decrease in Vmax was primarily due to a decrease in the density of SERT on the platelet membrane, with no change in whole cell expression. Additionally, while the platelet <em>5HT</em> content decreased 33%, the plasma <em>5HT</em> content increased 33%. Furthermore, exogenous <em>5HT</em> altered the <em>5HT</em> uptake rates by changing the density of SERT molecules on the plasma membrane in a biphasic manner. Therefore, we hypothesize that in a hypertensive state, the elevated plasma <em>5HT</em> levels induces a loss in <em>5HT</em> uptake function in platelets via a decrease in the density of SERT molecules on the plasma membrane. Through the feedback effect of this proposed mechanism, plasma <em>5HT</em> controls its own concentration levels by modulating the uptake properties of platelet SERT.

Drugs differing in their primary mechanism of action but having in common the ability to act as antidepressants such as fluoxetine (10 mg/kg SC), clomipramine (10 mg/kg IP), imipramine (10 mg/kg IP), desipramine (10 mg/kg IP) and (+/-) 8-OHDPAT (0.03 mg/kg SC) increase extracellular concentrations of dopamine in the rat prefrontal cortex but not in the medial nucleus accumbens. Buspirone (1 mg/kg SC) increased dopamine both in the prefrontal cortex and in the nucleus accumbens. Extracellular <em>5HT</em> was increased by fluoxetine, clomipramine and imipramine but not by desipramine while 8-OHDPAT and buspirone decreased it. These results raise the possibility that the property of stimulating dopamine transmission in the prefrontal cortex has a role in the antidepressant properties of these drugs.

Biogenic amines such as serotonin elicit or modulate a wide range of behaviours by interacting with multiple receptor subtypes. We have isolated cDNA clones encoding three distinct Drosophila serotonin receptors which belong to the G protein-coupled receptor family. When expressed in mammalian cells, these receptors activate different intracellular effector systems. The <em>5HT</em>-dro1 receptor stimulates adenylate cyclase while the <em>5HT</em>-dro2A and the <em>5HT</em>-dro2B receptors inhibit adenylate cyclase and activate phospholipase C. Expression of all three receptors starts in late embryos and is restricted to distinct populations of cells in the central nervous system. The <em>5HT</em>-dro2A receptor is predominantly expressed in midline motor neurons (VUM neurons) that innervate larval muscles thus suggesting a role for this receptor in motor control.

Fatigue is often related to cancer, and that related to its treatment is the most commonly reported side effect of cancer treatment. It differs from that induced by other causes, such as sleep disturbance and exertion, as the latter are typically alleviated by a period of rest. In contrast to exercise-induced fatigue, the fatigue reported by cancer patients is usually described as an unusual, excessive, whole-body experience that is disproportionate or unrelated to activity or exertion and is not relieved by rest or sleep. Cancer-related fatigue is a subjective experience that has a clear detrimental effect on a cancer patient's quality of life and ability to sustain the usual personal, professional, and social relationships. The fatigue can be pervasive: cancer patients frequently report that fatigue begins with treatment, continues during the course of chemotherapy or radiation treatment, and declines somewhat - but frequently sustains at a higher-than-baseline rate - after treatment is over. It may also persist for several years even in patients with no apparent disease. While a number of researchers have speculated about the nature of cancer-related fatigue, there has been little systematic research on its etiology or treatment. In many aspects our knowledge of the fatigue mechanisms in cancer patients is at a similar stage to that reached in our understanding of anti-cancer therapy-induced nausea and vomiting about 20 years ago. This paper introduces four plausible hypotheses for the development of fatigue. Evidence available to support a role for anemia, adenosine triphosphate, vagal afferents, and the interaction of the HPA/cytokines and <em>5HT</em> is discussed.