GR38032F is a highly selective <em>5HT</em>3-receptor antagonist which inhibits vomiting induced by cisplatin, cyclophosphamide or X-radiation in the ferret. Since cisplatin selectively increased the levels of <em>5HT</em> and 5HIAA in the intestinal mucosa, a possible site of the antiemetic action of GR38032F may be on <em>5HT</em>3-receptors on vagal afferents in the small intestine. The potent antiemetic action of GR38032F should be of clinical value in reducing the nausea and vomiting associated with radiotherapy or chemotherapy of cancer.

Despite the evidence for a significant contribution of brainstem serotonergic (<em>5HT</em>) systems to the control of spinal cord "pain" transmission neurons, attention has turned recently to the influence of nonserotonergic neurons, including the facilitatory and inhibitory controls that originate from so-called "on" and "off" cells of the rostroventral medulla (RVM). Unclear, however, is the extent to which these latter circuits interact with or are influenced by the serotonergic cell groups. To address this question we selectively targeted expression of a transneuronal tracer, wheat germ agglutinin (WGA), in the <em>5HT</em> neurons so as to study the interplay between the <em>5HT</em> and non-<em>5HT</em> systems. In addition to confirming the direct medullary <em>5HT</em> projection to the spinal cord we also observed large numbers of non-<em>5HT</em> neurons, in the medullary nucleus reticularis gigantocellularis and magnocellularis, that were WGA-immunoreactive, i.e., were transneuronally labeled from <em>5HT</em> neurons. FluoroGold injections into the spinal cord established that these reticular neurons are not only postsynaptic to the <em>5HT</em> neurons of the medulla, but that most are also at the origin of descending, bulbospinal pathways. By contrast, we found no evidence that neurons of the midbrain periaqueductal gray that project to the RVM are postsynaptic to midbrain or medullary <em>5HT</em> neurons. Finally, we found very few examples of WGA-immunoreactive noradrenergic neurons, which suggests that there is considerable independence of the monoaminergic bulbospinal pathways. Our results indicate that <em>5HT</em> neurons influence "pain" processing at the spinal cord level both directly and indirectly via feedforward connections with multiple non-<em>5HT</em> descending control pathways.

The physiological effects of <em>5HT</em> receptor coupling to TTX-resistant Na(+) current, and the signaling pathway involved, was studied in a nociceptor-like subpopulation of rat dorsal root ganglion (DRG) cells (type 2), which can be identified by expression of a low-threshold, slowly inactivating A-current. The <em>5HT</em>-mediated increase in TTX-resistant Na(+) current in type 2 DRG cells was mimicked and occluded by 10 microM forskolin. Superfusion of type 2 DRG cells on the outside with 1 mM 8-bromo-cAMP or chlorophenylthio-cAMP (CPT-cAMP) increased the Na(+) current, but less than <em>5HT</em> itself. However, perfusion of the cells inside with 2 mM CPT-cAMP strongly increased the amplitude of control Na(+) currents and completely occluded the effect of <em>5HT</em>. Thus it appears that the signaling pathway includes cAMP. The phosphodiesterase inhibitor 3-isobutyl-L-methylxanthine (200 microM) also mimicked the effect of <em>5HT</em> on Na(+) current, suggesting tonic adenylyl cyclase activity. <em>5HT</em> reduced the amount of current required to evoke action potentials in type 2 DRG cells, suggesting that <em>5HT</em> may lower the threshold for activation of nociceptor peripheral receptors. The above data suggest that serotonergic modulation of TTX-resistant Na(+) channels through a cAMP-dependent signaling pathway in nociceptors may participate in the generation of hyperalgesia.

The serotonin transporter (SERT) on the plasma membrane is the major mechanism for the clearance of plasma serotonin (5-hydroxytryptamine (<em>5HT</em>)). The uptake rates of cells depend on the density of SERT molecules on the plasma membrane. Interestingly, the number of SERT molecules on the platelet surface is down-regulated when plasma <em>5HT</em> ([<em>5HT</em>](ex)) is elevated. It is well reported that stimulation of cells with high [<em>5HT</em>](ex) induces transamidation of a small GTPase, Rab4. Modification with <em>5HT</em> stabilizes Rab4 in its active, GTP-bound form, Rab4-GTP. Although investigating the mechanism by which elevated plasma <em>5HT</em> level down-regulates the density of SERT molecules on the plasma membrane, we studied Rab4 and SERT in heterologous and platelet expression systems. Our data demonstrate that, in response to elevated [<em>5HT</em>](ex), Rab4-GTP co-localizes with and binds to SERT. The association of SERT with Rab4-GTP depends on: (i) <em>5HT</em> modification and (ii) the GTP-binding ability of Rab4. Their association retains transporter molecules intracellularly. Furthermore, we mapped the Rab4-SERT association domain to amino acids 616-624 in the cytoplasmic tail of SERT. This finding provides an explanation for the role of the C terminus in the localization and trafficking of SERT via Rab4 in a plasma <em>5HT</em>-dependent manner. Therefore, we propose that elevated [<em>5HT</em>](ex)"paralyzes" the translocation of SERT from intracellular locations to the plasma membrane by controlling transamidation and Rab4-GTP formation.

Serotonin transporters (SERTs) are targets for drugs such as Prozac that increase serotonin (<em>5HT</em>) levels by blocking <em>5HT</em> reuptake. Although SERTs saturate in the micromolar range, synaptic <em>5HT</em> may exceed 1 mM. To examine SERT's response to high <em>5HT</em> concentrations, we expressed Drosophila SERT (dSERT) in Xenopus oocytes and found that transport continued to increase with concentration up to 0.3 mM <em>5HT</em>. As <em>5HT</em> is a monovalent cation, its entry through an ion channel in SERT might explain uptake at high concentrations. We therefore investigated dSERT using traditional ion channel methods, including mole-fraction experiments under voltage clamp. We propose that SERTs may function as <em>5HT</em>-permeable channels, and that this mechanism may be important for clearance of the neurotransmitter at high concentrations.

Serotonin (5-HT) is a major neurotransmitter that influences various behaviors, neuronal plasticity, learning, and memory in molluscs. Although the physiology of 5-HT transmission in molluscs is well studied, little is known about the pharmacology and diversity of the 5-HT receptor system. Based on the high homology of genes coding for guanine nucleotide-binding protein (G protein)-coupled receptors, we have cloned a gene for the Lymnaea stagnalis 5-HT (<em>5HT</em>lym) receptor. The putative receptor protein, 509 amino acids long, has highest homology with the Drosophila 5-HT receptors and mammalian <em>5HT</em>1 receptors. As revealed by RNA blot-hybridization analysis, two mRNA species of 2.3 and 3.2 kb are detected in the central nervous system of Lymnaea. Transient expression of <em>5HT</em>lym in COS-7 cells showed saturable [3H]lysergic acid diethylamide binding with an estimated dissociation constant of 0.9 nM. The <em>5HT</em>lym receptor exhibited a mixed <em>5HT</em>-like pharmacology that cannot be precisely categorized with existing mammalian classification nomenclature. However, the <em>5HT</em>lym receptor does display some characteristics that have been attributed to the putative mammalian vascular <em>5HT</em>1-like receptor.

The techniques of extracellular single cell recording and microiontophoresis were used to study the effects of serotonin (5-HT) and of 5-HT(1A), 5-HT(2A/2C) and 5-HT(3) receptor agonists on the spontaneous activity of amygdaloid neurons in rats anesthetized with urethane. The background discharge rate was modified by 5-HT as well as by 5-HT agonists in about two-thirds of neurons tested in different nuclei of the amygdaloid complex. Whereas the 5-HT(2) and 5-HT(3) agonists significantly increased the neuronal discharge rate in nearly all subdivisions of the amygdala, the 5-HT(1A) agonist significantly inhibited the firing rate. Co-administration of bicuculline and 5-HT receptor agonists prevented the 8-OH-DPAT-induced increases in the firing rate in most cases tested, as well as the inhibitory effects of DOI or 2-methyl-<em>5HT</em>. Therefore, GABAergic interneurons seem to be involved in the mediation of serotonergic effects. The action of 5-HT agonists on the neuronal discharge rate was blocked by different receptor-specific antagonists. The results support the hypothesis that 5-HT exerts control throughout the amygdala by acting at least on 5-HT(1A), 5-HT(2A/2C) and 5-HT(3) receptors seemingly located both on projection and interneurons.

Human recombinant tissue-type plasminogen activator (rt-PA) has been shown to be an effective and safe agent for coronary thrombolysis in patients with acute myocardial infarction. However, thrombolysis is associated with a high rate of acute reocclusion after discontinuation of rt-PA. The goals of the present study were to assess whether reocclusion after thrombolysis is caused by intracoronary platelet aggregation and to determine the role of thromboxane A2 (TxA2) and serotonin (<em>5HT</em>) in mediating this phenomenon. Accordingly, coronary thrombosis was induced in anesthetized, open-chest dogs by insertion of a copper coil into the left anterior descending coronary artery (LAD). LAD blood flow was monitored throughout the experiment by means of a Doppler flow probe placed proximally to the coil. Thrombolysis was achieved with rt-PA (0.05 mg/kg bolus + micrograms/kg/min infusion) in 23 +/- 3 min. rt-PA was then discontinued and each animal received a bolus of heparin (150 U/kg) every hour. Reperfusion was followed by repeated cycles of gradual occlusions followed by spontaneous restorations of blood flow (cyclic flow variations, CFVs) before a persistent occlusion recurred. In control dogs (n = 6), heparin alone did not prevent CFVs and reocclusion time was 25 +/- 4 min. Administration of an intravenous bolus of 0.2 +/- 0.06 mg/kg SQ29548, a TxA2/prostaglandin H2-receptor antagonist, and an intravenous bolus of 0.2 +/- 0.04 mg/kg ketanserin, a <em>5HT</em>2-receptor antagonist, completely abolished CFVs in six of six dogs and reocclusion time was greater than 158 +/- 14 min (p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonin (<em>5HT</em>) systems play important roles in brain development, and early perturbations of <em>5HT</em> receptor expression produce permanent changes in <em>5HT</em> synaptic function and associated behaviors. We exposed pregnant Rhesus monkeys to environmental tobacco smoke (ETS) during gestation and for up to 3 months postnatally and examined the expression of <em>5HT</em>(1A) and <em>5HT</em>(2) receptors, and of the presynaptic <em>5HT</em> transporter in brain regions containing <em>5HT</em> projections (frontal, temporal and occipital cortex) and cell bodies (midbrain). Perinatal ETS exposure elicited upregulation of <em>5HT</em>(1A) receptor expression without parallel changes in the other two proteins, a pattern consistent with specific <em>5HT</em> receptor dysregulation, rather than universal disruption of <em>5HT</em> synaptic development. The effects seen here for ETS in a primate model are virtually identical in direction, magnitude and regional selectivity to those obtained previously for prenatal nicotine administration in rats. Specifically, early <em>5HT</em>(1A) overexpression alters the program for future synaptic and behavioral <em>5HT</em> responses, thus providing a mechanistic link for the shared effects of ETS and nicotine on a specific pathway responsible for behavioral anomalies associated with perinatal tobacco exposure. These results reinforce the need to reduce ETS exposure of pregnant women and young children.

Though initially conceptualized as resulting from peer imitation of child-onset or life-course-persistent youth [Moffitt, 1993], there is mounting evidence from twin studies that adolescent-onset or adolescent-limited antisocial behavior may also be genetically influenced. This study sought to provide preliminary molecular genetic evidence in support of these findings. We further evaluated whether genetic associations varied between behavioral subtypes of ASB (i.e., physical aggression and nonaggressive rule-breaking), given that only the latter has been found to characterize adolescent-onset ASB. The sample consisted of 211 undergraduate men of European-American ancestry. Three polymorphisms with theoretical and/or empirical ties to ASB or related traits (i.e., tryptophan hydroxylase-A218C, <em>5HT</em>(2A) His452Tyr, and the DAT1 variable nucleotide tandem repeat) were genotyped. Analyses revealed that two of the three polymorphisms (i.e., His452Tyr and DAT1) were associated with adolescent ASB. Moreover, these associations appeared to be specific to the nonaggressive, rule-breaking form of ASB, and did not extend to physical aggression, further supporting ties to adolescent ASB in particular. Such results thus constructively replicate earlier findings of genetic influence on adolescent ASB. They also offer preliminary evidence that the genetic processes underlying aggressive and nonaggressive antisocial behavior may be (at least partially) distinct.

The mechanism mediating the effects of cannabinoids on anxiety-related responses appear to involve cannabinoid CB1 and non-CB1 receptors. However, other neurotransmitters may play a role in such effect. This study shows evidence of an interaction between endocannabinoid system and serotonin (5-HT), 1A receptor subtype on anxiety-like behavior in Sprague-Dawley rats. The exogenous cannabinoid agonist, Delta9-tetrahydrocannabinol (THC), and N-(4-hydroxyphenyl)-arachidonylamide, the anandamide transporter inhibitor (AM 404) were evaluated in the elevated plus maze test. THC (0.075-0.75 mg/kg i.p.), given 30 min and AM 404 (0.75-1.25 mg/kg i. p.), given 60 min before the test, exhibited a dose-response anxiolytic effect evaluated in terms of increase in the percentage of total entries and time spent in the open and decrease of total entries and time spent in the closed arms. The anxiolytic effect obtained with the maximal active dose of both THC (0.75 mg/kg) and AM 404 (1.25 mg/kg) was blocked by the 5-HT1A receptor antagonist, N-[2-[4-(2-methoxyphenyl) piperazin-1-yl]ethyl]-N-pyridin-2-yl-cyclohexanecarboxamide dihydro chloride (WAY-100635 (300 microg/kg, s.c.), given 30 min before THC or 15 min before AM 404. The combination of an ineffective dose of THC (0.015 mg/kg) or AM 404 (0.015 mg/kg) on anxiety-related responses with an ineffective dose of the <em>5HT</em>(1A) receptor agonist, 8-Hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT) (7.5 microg/kg, i.p.), led to a synergistic effect. No interference with spontaneous motor activity, evaluated in an activity cage for 5 min, in rats given the drugs alone or in combination, was found. These data suggest that the anxiolytic effect produced by endo- and eso-cannabinoids is modulated by 5-HT1A receptors.

Recent major findings from studies of SLC6A4 and its corresponding protein, the serotonin (5-HT) transporter (SERT) in humans, rodents and non-human primates indicate that combinations of SLC6A4 non-coding 5', 3' UTRs and intronic regions plus coding variants acting together can change <em>5HT</em> transport as much as 40-fold in vitro. In vivo, SLC6A4 variants in humans and other species lead to marked physiological changes, despite mitigating neurodevelopmental adaptations in 5-HT receptors plus compensatory alterations in 5-HT synthesis and metabolism. Polymorphisms in SLC6A4 are associated with differences in emotional, endocrine, and personality characteristics as well as many diseases. This gene, in combinations with gene×gene (G×G) and gene×environment (G×E) interactions nonetheless remains incompletely understood, with some association findings remaining controversial. Considering its primary importance in the regulation and function of the entire serotonergic system (as evidenced by the consequences of SERT-mediated reuptake inhibition by SRIs like fluoxetine in humans and of genetically engineered changes in mice and rats), it seems likely that SLC6A4 and SERT will remain areas of high interest in our field's attempts to better understand and treat 5-HT-related disorders.

Brain tryptophan (TRP) concentrations and serotonin (<em>5HT</em>) synthesis and release increase during running. This increase in <em>5HT</em> function may promote central fatigue and contribute to suboptimal physical performance. The rise in brain TRP is reputed to result from exercise-induced elevations in serum nonesterified fatty acid (NEFA) concentrations, which dissociate TRP from albumin in blood and increase the serum free TRP pool. But, as discussed in this article, ample evidence exists that the serum free TRP pool does not control brain TRP uptake. The clearest data are dietary, but pharmacologic data in exercising rats also support this conclusion. Changes in the serum levels of amino acids that compete with TRP for brain uptake appear also not to explain the rise in brain TRP. The mechanism is therefore not presently known. The link between the rise in brain TRP and <em>5HT</em> synthesis/release is not simple: a rise in brain TRP stimulates <em>5HT</em> synthesis/release in actively firing neurons. Hence, during exercise, only <em>5HT</em> neurons that are firing should increase <em>5HT</em> production/release when brain TRP rises. It is not known which <em>5HT</em> neurons fire during exercise; the <em>5HT</em> neurons that respond to exercise-induced increases in brain TRP are therefore not known. Hence, it is not possible to conclude which <em>5HT</em> neurons contribute to the generation of central fatigue. Because some <em>5HT</em> neurons control specific functions important to physical performance (e.g., respiration), the current understanding of <em>5HT</em> neuronal function in central fatigue might benefit from the study of specific <em>5HT</em> pathways during exercise.

Physical exercise is a low-cost, safe, and efficient intervention for the reduction of neuropathic chronic pain in humans. However, the underlying mechanisms for how exercise reduces neuropathic pain are not yet well understood. Central monoaminergic systems play a critical role in endogenous analgesia leading us to hypothesize that the analgesic effect of low-intensity exercise occurs through activation of monoaminergic neurotransmission in descending inhibitory systems. To test this hypothesis, we induced peripheral nerve injury (PNI) by crushing the sciatic nerve. The exercise intervention consisted of low-intensity treadmill running for 2 weeks immediately after injury. Animals with PNI showed an increase in pain-like behaviors that were reduced by treadmill running. Reduction of serotonin (5-hydroxytryptamine) synthesis using the tryptophan hydroxylase inhibitor para-chlorophenylalanine methyl ester prevented the analgesic effect of exercise. However, blockade catecholamine synthesis with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine had no effect. In parallel, 2 weeks of exercise increased brainstem levels of the 5-HT and its metabolites (5-hydroxyindoleacetic acid), decreased expression of the serotonin transporter, and increased expression of 5-HT receptors (<em>5HT</em>-1B, 2A, 2C). Finally, PNI-induced increase in inflammatory cytokines, tumor necrosis factor-alpha, and interleukin-1 beta, in the brainstem, was reversed by 2 weeks of exercise. These findings provide new evidence indicating that low-intensity aerobic treadmill exercise suppresses pain-like behaviors in animals with neuropathic pain by enhancing brainstem 5-HT neurotransmission. These data provide a rationale for the analgesia produced by exercise to provide an alternative approach to the treatment of chronic neuropathic pain.

We compared the antiplatelet effects of clopidogrel and the intravenous platelet P2Y(12) receptor antagonist AR-C69931MX, which acts on the same receptor as clopidogrel by a different and reversible mechanism and, unlike clopidogrel, is active in vitro. Thirteen patients with acute coronary syndromes entered into a phase II study of intravenous AR-C69931MX (Group 1) and eight patients undergoing intracoronary stent implantation and treated with clopidogrel (Group 2) were studied using a whole blood single-platelet counting aggregation assay. Group 2 patients were also studied using turbidimetry with ADP and TRAP as agonists and whole blood [(14)C]<em>5HT</em> release to study dense granule secretion in response to ADP, collagen and TRAP. In Group 2 studies, a therapeutic concentration of AR-C69931MX was added in vitro before and after clopidogrel administration. AR-C69931MX in Group 1 achieved greater inhibition of ADP-induced platelet aggregation than clopidogrel in Group 2 and AR-C69931MX in vitro added to the effects of clopidogrel on ADP-induced aggregation. AR-C69931MX but not clopidogrel inhibited TRAP-induced aggregation and granule secretion and AR-C69931MX had a more consistent inhibitory effect on collagen-induced responses. In conclusion, therapeutic administration of clopidogrel moderately inhibits platelet P2Y(12) receptor activation and substantially greater P2Y(12) receptor blockade can be achieved with AR-C69931MX.

BACKGROUND

Tobacco smoking reduces appetite and body weight. Cessation of smoking leads to hyperphagia and weight gain. Food intake is a function of meal number (MN) and meal size (MZ) (i.e., Food intake = MN x MZ). The effect of nicotine on these feeding components and their relationships to dopamine and serotonin in the lateral hypothalamic area (LHA) were determined.

METHODS

In Fischer-344 rats the effect of 7 days of systemic nicotine infusion on the feeding patterns was measured by rat eater meter and changes in serotonin (<em>5HT</em>) and dopamine (DA) in the LHA were measured by in vivo microdialysis.

RESULTS

Nicotine infusion caused hypophagia through a significant decrease in MN with a smaller decrease in MZ, resulting in a body weight reduction. <em>5HT</em> and DA concomitantly increased in LHA. Stopping nicotine resulted in hyperphagia by a significant increase in MZ. Body weight normalized. <em>5HT</em> and DA in LHA decreased after nicotine was stopped.

CONCLUSIONS

Nicotine's hypophagic effect was associated with increased <em>5HT</em> and DA in LHA, whereas hyperphagia after nicotine cessation was accompanied by decreased concentrations of the neurotransmitters. These findings suggest that nicotine affects appetite regulation, in part by modulation of LHA-DA and <em>5HT</em>.

A series of bupropion (1a) analogues (1b-1ff) were synthesized, and their in vitro and in vivo pharmacological properties evaluated with the goal of developing a 1a analogue that had better properties for treating addictions. Their in vitro pharmacological properties were examined by [(3)H]dopamine ([(3)H]DA), [(3)H]serotonin ([(3)H]<em>5HT</em>), and [(3)H]norepinephrine ([(3)H]NE) uptake inhibition studies, and by binding studies at the dopamine, serotonin, and norepinephrine transporters using [(125)I]RTI-55 in cloned transporters. Several analogues showed increased [(3)H]DA uptake inhibition with reduced or little change in [(3)H]<em>5HT</em> and [(3)H]NE uptake inhibition relative to bupropion. Thirty-five analogues were evaluated in a 1 h locomotor activity observation test and 32 in an 8 h locomotor activity observation test and compared to the locomotor activity of cocaine. Twenty-four analogues were evaluated for generalization to cocaine drug discrimination after i.p. administration, and twelve analogues were tested in a time course cocaine discrimination study using oral administration. 2-(N-Cyclopropylamino)-3-chloropropiophenone (1x) had the most favorable in vitro efficacy and in vivo pharmacological profile for an indirect dopamine agonist pharmacotherapy for treating cocaine, methamphetamine, nicotine, and other drugs of abuse addiction.

Serotonin (5-hydroxytryptamine; <em>5HT</em>) a monoamine neurotransmitter mediates a wide range of physiological actions in the human body. For example <em>5HT</em> is implicated in psychiatric and neurological disorders and also plays a fundamental role in tumour growth, differentiation and gene expression. <em>5HT</em> acts as a growth factor for several types of tumoural and non-tumoural cells. This review considers the role of <em>5HT</em> and its receptors in the human body with particular reference to carcinogenesis. We conclude that <em>5HT</em> causes growth proliferation and <em>5HT</em> antagonists cause growth inhibition in a variety of tumour cells (e.g. prostate carcinoma, lung carcinoma and colonic carcinoma). Therefore, further studies should look into the potential use of <em>5HT</em> antagonists in the treatment of cancer.

Serotonergic (<em>5HT</em>) neurons exert diverse and widespread functions in the brain. Dysfunction of the serotonergic system gives rise to a variety of mental illnesses including depression, anxiety, obsessive compulsive disorder, autism and eating disorders. Here we show that human primary fibroblasts were directly converted to induced serotonergic (i<em>5HT</em>) neurons by the expression of Ascl1, Foxa2, Lmx1b and FEV. The transdifferentiation was enhanced by p53 knockdown and appropriate culture conditions including hypoxia. The i<em>5HT</em> neurons expressed markers for mature serotonergic neurons, had Ca(2+)-dependent <em>5HT</em> release and selective <em>5HT</em> uptake, exhibited spontaneous action potentials and spontaneous excitatory postsynaptic currents. Application of serotonin significantly increased the firing rate of spontaneous action potentials, demonstrating the functional utility of i<em>5HT</em> neurons for studying serotonergic neurotransmission. The availability of human i<em>5HT</em> neurons will be very useful for research and drug discovery on many serotonin-related mental disorders.

At the present time, the following summary statements can be made as to 24-hour changes in receptor binding. In all receptors studied in homogenates from whole rat forebrain (alpha 1, alpha 2, beta-adrenergic, muscarinic cholinergic, dopaminergic, <em>5HT</em>-1, <em>5HT</em>-2, adenosine, opiate, benzodiazepine, GABA, imipramine), significant variations over 24 hours have been documented. The receptor rhythms measured change in wave form, amplitude, and phase throughout the year, even though the animals have been kept on a defined and constant LD cycle. Whether these rhythms are truly seasonal requires further investigation. The rhythms are circadian: i.e. they persist in the absence of time cues, and the unimodal rhythms do not persist after lesion of the putative circadian pacemaker in the suprachiasmatic nuclei. The rhythms can be uni- or bimodal, and each brain region shows a particular pattern. The pattern can be different for the same ligand in different nuclei of a given brain region (e.g. hypothalamus). Nearly all studies of receptor rhythms have been carried out in rats; the results vary according to strain and even within the same strain from different breeding lines. Receptor rhythm characteristics are modified by age: e.g. the amplitude, phase, as well as the 24-hour mean of binding to a given ligand in a defined brain region. The changes in number of binding sites over 24 hours can be correlated with amine turnover, second messenger, or function of that brain region; however these relationships, although consistent within a region, do not hold for all regions. If gradual changes in CNS neurotransmitter receptor function are considered important in the pathogenesis of schizophrenia and affective disorders and the mode of action of psychopharmacological agents, then consideration of the short term rapid change over 24 hours is equally necessary. Chronic treatment with a number of psychoactive drugs known to induce up- or down-regulation of receptor number, also induces marked changes in circadian rhythm parameters of wave form, amplitude, phase and 24-hour mean. This is of methodological importance for single time-point studies, since the interpretation of the results will depend on time of day. Preliminary evidence supports the assumption that the significant variation in receptor binding throughout the day may underlie the well-known circadian rhythms of susceptibility to many CNS drugs. New findings of circadian rhythms in receptors on blood cells indicate the relevance of these changes also in human physiology.

ADP plays a major role in the amplification of platelet aggregation induced by other platelet agonists. ADP initiates platelet activation via the P2Y(1) receptor and amplifies platelet activation via the P2Y(12) receptor. Using the selective P2Y(1) receptor antagonist A2P5P and the selective P2Y(12) receptor antagonist AR-C69931MX, we assessed the relative contributions of P2Y(1) receptor and P2Y(12) receptor activation to platelet aggregation in hirudin-anticoagulated whole blood induced by PAF, <em>5HT</em>, epinephrine, TRAP, streptokinase, U46619 and collagen. The effects of aspirin were assessed concurrently. A2P5P and AR-C69931MX variably inhibited aggregation induced by most of the agonists studied, whereas aspirin only inhibited aggregation induced by streptokinase and collagen. In some experiments, A2P5P and AR-C69931MX yielded additive inhibition of aggregation. All three antagonists interacted synergistically to inhibit collagen-induced aggregation. These studies demonstrate that P2Y(1) receptor activation plays a significant role in amplifying aggregation induced by agonists other than ADP, in addition to the established roles of P2Y(12) receptor activation and thromboxane A(2) synthesis.

Despite the well-documented relation between estradiol (E2) and behavior, exposure to stressors may modify sensitivity to E2. The effects of E2 on behavior are, in part, likely related to their modulation of the serotonin (<em>5HT</em>) and oxytocin systems. The short allele (s-variant) polymorphism found in the promoter region of the SLC6A4 gene that encodes the <em>5HT</em> transporter (<em>5HT</em>T) modulates responsivity to stressors. The current study used ovariectomized adult female rhesus monkeys to evaluate how exposure to the psychosocial stressor of social subordination and polymorphisms in the gene encoding <em>5HT</em>T influence the behavioral effects of E2 and immunoreactive serum oxytocin. Dominant females had higher levels of oxytocin than subordinate animals even though E2 increased immunoreactive serum oxytocin in all females. E2 increased affiliative behaviors in all animals, with even more of these prosocial behaviors directed at dominant females. S-variant females, regardless of social status, were more aggressive toward more subordinate cage mates and these behaviors too were increased by E2. Subordinate s-variant females are most often involved in agonistic behavior, less affiliative behavior, and were less responsive to the anxiolytic action of E2. The results show that the short allele of the <em>5HT</em>T gene synergizes with psychosocial stress exposure to affect the behavioral efficacy of E2 while confirming the actions of E2 for producing generalized behavioral arousal in females. Whether differences in the central action of <em>5HT</em> and/or oxytocin are responsible for this effect requires further study.

Spinal cord injury (SCI) results in abnormal pain syndromes in humans. In a rodent model of SCI, T13 spinal hemisection results in allodynia and hyperalgesia due in part to interruption of descending pathways, including serotonergic (5-HT) systems, that leads to hyperexcitability of dorsal horn neurons. To characterize further the role of 5-HT and 5-HT receptor subtypes 5-HT(1A) and 5-HT(3) in neuronal activation after hemisection, we have examined the responsiveness of dorsal horn neurons to a variety of innocuous and noxious peripheral stimuli. Male Sprague-Dawley rats, 150-175 g, were spinally hemisected (n=40) at T13 and allowed 4 weeks for development of mechanical allodynia and thermal hyperalgesia. Animals then underwent electrophysiologic recording and the results were compared with those from sham controls (n=15). Evoked responses of convergent dorsal horn neurons (n=224 total) at L3-L5 to innocuous and noxious peripheral stimuli were characterized after administration of vehicle, 5-HT (25, 50, 100, and 200 microg), 5-HT (100 microg) in conjunction with the selective 5-HT(1A) antagonist WAY 100135 (100 microg), the 5-HT(3) antagonist MDL 72222 (100 microg), the selective 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 150 microg), or the 5-HT(3) agonist 2-Me-<em>5HT</em> (75 microg), with or without pretreatment with antagonists; all treatments were delivered topically onto the cord adjacent to the recording electrode. In hemisected animals, increased responsiveness of convergent cells to all peripheral stimuli was observed bilaterally when compared to controls. No changes in ongoing background activity were present. In control animals, only the highest dose of 5-HT (200 microg) was sufficient to reduce evoked activity, whereas in hemisected animals a concentration-dependent decrease in response was observed. In hemisected animals, both 5-HT(1A) and 5-HT(3) receptor antagonism reduced the effectiveness of 5-HT, restoring elevated evoked activity by up to 70% at the doses tested. Administration of 5-HT(1A) and 5-HT(3) receptor agonists also decreased hyperexcitability, effects prevented by pretreatment with corresponding antagonists. These results demonstrate the development of denervation supersensitivity to 5-HT following SCI, corroborate behavioral studies showing the effectiveness of 5-HT in reducing allodynia and hyperalgesia after SCI, and contribute to a mechanistic understanding of the role of 5-HT receptor subtypes in chronic central pain.

Evidence suggests that the serotonin <em>5HT</em>-1 receptor site is functionally linked to adenylate cyclase in the brain, but a biochemical effector system which is linked to the serotonin <em>5HT</em>-2 receptor site has not been found. In the present paper we report an investigation of <em>5HT</em> stimulated phosphatidylinositol (PI) hydrolysis in rat cerebral cortex and have found that selective <em>5HT</em>-2 antagonists (pizotifen and ketanserin) block <em>5HT</em>'s effect upon PI metabolism. These data suggest that <em>5HT</em> stimulated PI hydrolysis is mediated by the <em>5HT</em>-2 binding site.