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Aims Methylphenidate (MPD) widely prescribed for the treatment of attention deficit hyperactivity disorder (ADHD), is a psychostimulant and can produce addiction in patients treated with it. In view of growing increase in the use of drug by general population as a cognitive enhancer, the present study is designed to investigate reinforcing and cognition enhancing effects of MPD in rats. Associated changes in serotonin-1A receptor expression are investigated as a potential molecular mechanism involved. Methods Learning acquisition and memory retention in Morris water-maze test were used to assess cognitive effects of MPD. Reinforcing effects were evaluated in conditioned place-preference (CPP) paradigm. The expression of 5-hydroxytryptamine (5-HT; serotonin)-1A receptor in the nucleus accumbens and prefrontal cortex of repeated MPD treated animals was determined by qRT-PCR. Findings Lower doses (0.5 and 2.5 mg/kg) of MPD enhanced learning acquisition and memory retention but higher doses (5 mg/kg) impaired these. The drug administered repeatedly at a dose of 2.5 mg/kg was reinforcing in CPP test, but sensitization like effects of this dose were only transient. These animals tested in water-maze test exhibited improved memory retention but no effect occurred on learning acquisition. The expression of 5-HT-1A receptor was markedly attenuated in the nucleus accumbens; attenuation in the prefrontal cortex was not significant. Significance The findings suggest that clinically relevant doses of MPD can produce drug addiction, but effects of the drug on memory retention are retained. A downregulation of 5-HT-1A receptor in the nucleus accumbens seems important in the reinforcing effects of MPD.

This review analyses the knowledge about the incidence of transient apnoeic spells, induced by substances which activate vagal chemically sensitive afferents. It considers the specificity and expression of appropriate receptors, and relevant research on pontomedullary circuits contributing to a cessation of respiration. Insight is gained into an excitatory drive of 5-HT1A serotonin receptors in overcoming opioid-induced respiratory inhibition.

This study was to investigate the sleep promoting effects of combined γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP), by examining neuronal processes governing mRNA level alterations, as well as assessing neuromodulator concentrations, in a fruit fly model.Behavioral assays were applied to investigate subjective nighttime activity, sleep episodes, and total duration of subjective nighttime sleep of two amino acids and GABA/5-HTP mixture with caffeine treated flies. Also, real-time PCR and HPLC analysis were applied to analyze the signaling pathway.Subjective nighttime activity and sleep patterns of individual flies significantly decreased with 1% GABA treatment in conjunction with 0.1% 5-HTP treatment (p0.001). Furthermore, GABA/5-HTP mixture resulted in significant differences between groups related to sleep patterns (40%, p0.017) and significantly induced subjective nighttime sleep in the awake model (p0.003). These results related to transcript levels of the GABAB receptor (GABAB-R1) and serotonin receptor (5-HT1A), compared to the control group. In addition, GABA/5-HTP mixture significantly increased GABA levels 1h and 12h following treatment (2.1 fold and 1.2 fold higher than the control, respectively) and also increased 5-HTP levels (0 h: 1.01 μg/protein, 12h: 3.45 μg/protein).In this regard, we successfully demonstrated that using a GABA/5-HTP mixture modulates subjective nighttime activity, sleep episodes, and total duration of subjective nighttime sleep to a greater extent than single administration of each amino acid, and that this modulation occurs via GABAergic and serotonergic signaling.

Aims Ambroxol is a muco-active agent with multiple, clinically relevant effects in the airway. Despite its widespread use and well documented clinical efficacy, there are few data on its mechanism of action and receptor pharmacology beyond sodium channel blockade and inhibition of guanylate cyclase. Accordingly, in vitro studies were conducted to determine its overall receptor pharmacology and possible sites of action. Materials and methods In vitro radioligand binding/enzyme inhibition studies were conducted at 62 receptors, ion channels and enzymes using standard techniques. Additional in vitro studies were conducted to establish the potency of ambroxol at selected sites. Key findings These studies indicate that ambroxol has affinity for the 5-HT3 serotonin receptor, as well as affinity for the 5-HT serotonin transporter (SERT), with IC50 values of 17,600 nM and 19,500 nM respectively. In vitro functional studies in isolated guinea pig colon indicate that ambroxol is a 5-HT3 serotonin receptor antagonist with an IC50 value of 36,000 nM. Significance Together, these studies indicate that ambroxol may exert its beneficial properties via antagonism of the 5-HT3 serotonin receptor and/or inhibition of serotonin uptake (5-HT transport: SERT), in addition to its reported effects at the sodium channel and guanylate cyclase.

A growing body of evidence suggests that our diet is an important contributing factor in the development, management and prevention of a number of psychiatric illnesses. Tryptophan, an essential amino acid, is the sole precursor of neurotransmitter 5-hydroxytryptamine (5-HT; serotonin). Administration of tryptophan can boost serotonin neurotransmission to produce therapeutically important effects in serotonin deficiency disorders. Anorexia nervosa (AN) an eating disorder associated with high levels of psychiatric comorbidity including psychosis, hyperactivity, depression and anxiety has highest lethality of all psychiatric illnesses. Evidence suggests that excessive dieting and food restriction can decrease brain tryptophan and serotonin in AN patients to precipitate depression, psychosis and hyperactivity. There are currently no FDA approved pharmacological treatments available for AN patients; antidepressants and antipsychotics, largely used to treat associated psychiatric comorbidities are also not very effective. The aim of this non-systematic review article is to evaluate and document a potential importance of tryptophan supplementation in improving therapeutics in AN patients.

Aims The purpose of this study was to investigate the antinociceptive effect of epicatechin as well as the possible mechanisms of action in diabetic rats. Main methods Rats were injected with streptozotocin to produce hyperglycemia. The formalin test was used to assess the nociceptive activity. Key findings Acute pre-treatment with epicatechin (0.03–30 mg/kg, i.p.) prevented formalin-induced nociception in diabetic rats. Furthermore, daily or every other day treatment for 2 weeks with epicatechin (0.03–30 mg/kg, i.p.) also prevented formalin-induced nociception in diabetic rats. Acute epicatechin-induced antinociception was prevented by l -NAME ( N ω -nitro- l -arginine methyl ester hydrochloride, 1–10 mg/kg, non-selective nitric oxide synthesis inhibitor), 7-nitroindazole (0.1–1 mg/kg, selective neuronal nitric oxide synthesis inhibitor), ODQ (1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one, 0.2–2 mg/kg, guanylyl cyclase inhibitor) or glibenclamide (1–10 mg/kg, ATP-sensitive K + channel blocker). Moreover, epicatechin (3 mg/kg)-induced antinociception was fully prevented by methiothepin (0.1–1 mg/kg, serotonergic receptor antagonist), WAY-100635 (0.03–0.3 mg/kg, selective 5-HT 1A receptor antagonist) or SB-224289 (0.03–0.3 mg/kg, selective 5-HT 1B receptor antagonist). In contrast, BRL-15572 (0.03–0.3 mg/kg, selective 5-HT 1D receptor antagonist) only slightly prevented the antinociceptive effect of epicatechin. Naloxone (0.1–1 mg/kg, opioid antagonist) did not modify epicatechin's effect. Significance Data suggest the involvement of the nitric oxide–cyclic GMP–K + channel pathway as well as activation of 5-HT 1A and 5HT 1B , and at a lesser extent, 5-HT 1D , but not opioid, receptors in the antinociceptive effect of epicatechin in diabetic rats. Our data suggest that acute or chronic treatment with epicatechin may prove to be effective to treat nociceptive hypersensitivity in diabetic patients.

Aims The present study analyzed the potential antinociceptive effect of the antimigraine drugs sumatriptan, dihydroergotamine or methysergide in rats submitted to the formalin test. Moreover, by using selective antagonists, the role of 5-HT1B/1D serotonergic receptors was investigated in the antinociception induced by these antimigraine drugs. Main methods The formalin test was used to assess the nociceptive activity. Overt pain-like behavior (flinching, 1 h) and evoked nociception (long-lasting secondary mechanical allodynia and hyperalgesia, 6 days) were determined in the same rat. Key findings Ipsilateral, but not contralateral, pre-treatment (in μg/paw) with sumatriptan (10–300), methysergide (1–30) or dihydroergotamine (1–30) significantly prevented flinching behavior (at 1 h) as well as secondary allodynia and hyperalgesia (at day 6) induced by formalin. Interestingly, the antinociceptive (flinching), antiallodynic and antihyperalgesic effects of sumatriptan were completely prevented by peripheral pre-treatment with selective antagonists at the 5-HT1B (SB 224289; 100) or 5-HT1D (BRL 15572; 100) receptors. In contrast, the acute antinociceptive effects of methysergide and dihydroergotamine were partially prevented by SB 224289 and BRL 15572. The antiallodynic and antihyperalgesic effects of both drugs were completely prevented by BRL 15572 and partially prevented by SB 224289. Given alone, SB 224289 or BRL 15572 did not modify per se the long-lasting secondary allodynia and hyperalgesia. Significance The above findings suggest that: (i) the antimigraine drugs sumatriptan, methysergide and dihydroergotamine reduce the acute and chronic nociception induced by formalin; and (ii) this antinociceptive effect results from activation of peripheral 5-HT1B/1D serotonergic receptors.

Aims Olfactory bulbectomy (OBX) in rodents represents a valuable experimental model of depression. This study was designed to shed further light on the impact of putative serotonergic neuronal degeneration in OBX mice and to assess the effect of a widely used antidepressant on serotonergic related behavioral changes induced by OBX. Main methods Adult male ddY mice were subject to bilateral OBX or sham surgery. The serotonin (5-HT) 2A/2C receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) enhanced a head-twitch response (HTR) in OBX mice. Effects of 5-HT 2A , 5-HT 2C antagonists and fluvoxamine were observed in OBX mice following DOI administration. Key findings The HTR elicited by the administration of DOI (0.5 mg/kg and 1 mg/kg, i.p.) was increased about twofold in OBX mice when compared with controls on the 14th day after the surgery. The injection of ketanserin (0.025 mg/kg, i.p.), a 5-HT 2A receptor antagonist, inhibited the enhancement of the DOI-induced HTR after OBX. Likewise, the administration of SB 242084 (1 mg/kg, s.c.), a 5-HT 2C receptor antagonist, also inhibited the DOI-induced HTR in OBX mice. Chronic but not acute treatment with the antidepressant fluvoxamine, a selective serotonin reuptake inhibitor (SSRI), suppressed the enhancement of DOI-induced HTR after OBX. Significance These findings indicate that OBX, and the subsequent degeneration of neurons projecting from the olfactory bulb, caused a supersensitivity of 5-HT 2A/2C receptors which may be involved in symptoms of depression.

Aims The hypothalamic suprachiasmatic nucleus (SCN), which functions as a circadian pacemaker in mammals, is influenced by melatonin and serotonin. Agomelatine, which acts as an antidepressant and can synchronize disturbed circadian rhythms, displays a unique mechanism of action involving both melatonergic agonist and 5-HT 2C antagonist properties. This study investigated the dose-dependent effects of agomelatine, melatonin and a selective 5-HT 2C receptor antagonist, S32006, on SCN neurons in an in vitro slice preparation. Main methods Brain slices containing the SCN were prepared from male Wistar rats and maintained in a recording chamber. Changes in firing rates of SCN neurons were recorded after perfusion of drugs. Key findings SCN firing rates were dose-dependently suppressed by 19.2–80.9% following perfusion of 0.04–0.32 mM agomelatine (p 50 = 0.14 mM). Perfusion with melatonin (0.4–3.2 mM) resulted in 16.6–62.5% dose-dependent reductions in firing rates (at least p 50 = 1.59 mM) and of the duration of suppression. A selective melatonin receptor antagonist (S22153 at 0.32 mM) and a 5-HT 2c receptor agonist (Ro60-0175) reduced the suppressive effects of 0.16 mM agomelatine by 35% and 50.2%, respectively. A 5-HT 2C receptor antagonist (S32006; 0.03–0.12 mM) significantly decreased SCN firing rates (19.6–91.8%; at least p 50 = 0.05 mM). Co-perfusion of S32006 (0.06 mM) with a 5-HT 2C agonist (Ro60-0175; 0.003 mM) reduced suppressions evoked by S32006 alone by ~ 72.1%. Significance These results are consistent with the hypothesis that agomelatine acts directly on the SCN via both agonist effects at melatonergic receptors and antagonist effects at 5-HT 2C receptors, which parallel its mechanisms of action as an antidepressant.

Aims Combinations of non-steroidal anti-inflammatory drugs (NSAIDs) and cannabinoids are promising because of their potential synergistic effects in analgesia, resulting in a reduction in dosage and minimizing adverse reactions. The analgesic effect of acetylsalicylic acid (ASA), probably due to a central mechanism, also implicates changes in the central monoaminergic system. Therefore, we decided to evaluate the antinociceptive interaction between the CB 1 receptor agonist, HU210, and ASA in tests involving central pain in rats as well as the implication of the central serotonergic system thereon. Main methods The selective CB 1 antagonist SR141716A and the potent cannabinoid agonist HU210 were evaluated alone and in combination with ASA in both algesimetric tests (hot-plate and formalin tests) and for 5-HT activity and 5-HT 2 receptor density and affinity. Key findings ASA or HU210 alone showed a dose-dependent effect in both tests. HU210, at an inactive dose, significantly increased the antinociceptive effect of the sub-active dose of ASA. SR141716A (1.5 mg/kg i.p.) was ineffective per se and failed to modify antinociception induced by the HU210 plus ASA combination in either test. HU210 plus ASA significantly decreased the 5-HIAA/5-HT ratio and the 5-HT 2 receptor density in the frontal cortex, changes not antagonized by SR141716A. Significance The present study provides evidence that mutual potentiation of the antinociceptive effects of HU210 and ASA may, at least partly, depend on serotonergic mechanisms, with an indirect participation of cannabinodiergic mechanism. In conclusion, combinations of low doses of cannabinoids and NSAIDs may be of interest from the therapeutic point of view.

Aims Serotonin (5-HT) is capable of reducing the oxidative burst of professional phagocytes. In this study, we investigated whether 5-HT mediates this modulation via 5-HT receptors (5-HTR) or whether this is due instead to 5-HT antioxidative properties. Main methods The leukocytes or polymorphonuclear leukocytes (PMNL) were isolated from human blood, and their ability to produce reactive oxygen species (ROS) after 5-HT or its agonist treatment was tested by luminol-enhanced chemiluminescence (CL) analysis. Key findings It was found that 5-HTR 2 agonist DOI hydrochloride does not have any antioxidative properties, despite its ability to inhibit the CL response of activated human total leukocytes. On the other hand, DOI hydrochloride was unable to inhibit the CL response of activated human PMNL. It seems that the reduction of the oxidative burst of professional phagocytes was evoked by the activation of 5-HTR not on the neutrophil surface but on the surface of different leukocytes, which produced anti-inflammatory cytokines with NADPH oxidase activity modulating properties. Significance Platelets and activated PMNL are in tight contact at sites of inflammation. 5-HT released from platelets might have a protective function against PMNL-derived oxidative stress and oxidative damages.

The present study evaluated the effect of 5-hydroxytryptamine (5-HT) on intestinal Na(+)/H(+) exchanger (NHE) activity and the cellular signaling pathways involved in T84 cells. T84 cells express endogenous NHE1 and NHE2 proteins, detected by immunoblotting, but not NHE3. The rank order for inhibition of NHE activity in acid-loaded T84 cells was 5-(N-ethyl-N-isopropyl)-amiloride (EIPA; IC(50)=519 [465, 579] nM)cariporide (IC(50)=630 [484, 819] nM)amiloride (IC(50)=19 [16, 24] microM); the NHE3 inhibitor S3226 was found to be devoid of effect. This different inhibitory sensitivity indicates that both NHE1 and NHE2 isoforms may play an active role in Na(+)-dependent intracellular pH (pH(i)) recovery in T84 cells. Short-term exposure (0.5 h) of T84 cells to 5-HT increased NHE activity in a concentration-dependent manner. The stimulation induced by 5-HT (30 microM) was partially inhibited by both WAY 100135 (300 nM) and ketanserin (300 nM), antagonists of 5-HT(1A) and 5-HT(2) receptors, respectively. NHE activity was significantly increased by 8-OH-DPAT and alpha-methyl-5-HT, agonists of, respectively, 5-HT(1A) and 5-HT(2) receptors. An incubation of T84 cells with anti-G(s) and anti-G(beta) antibodies complexed with lipofectin did not prevent the 5-HT-induced stimulation of NHE activity. Overnight treatment with anti-G(ialpha1,2) and anti-G(q/11) antibodies complexed with lipofectin blocked the stimulatory effect induced by 8-OH-DPAT and alpha-methyl-5-HT, respectively. It is concluded that in T84 cells 5-HT enhances intestinal NHE activity through stimulation of G(ialpha1,2)-coupled 5-HT(1A) and G(q/11)-coupled 5-HT(2) receptors.

Acute treatment with fluvoxamine reduces responding for ethanol more than responding for food. However, pharmacotherapy for alcoholism is likely to require chronic treatment. These experiments were performed to assess the effects of chronic fluvoxamine on ethanol- and food-maintained behaviors. Effects of chronic fluvoxamine (10 and 17.8 mg/kg/day × 30 days) on ethanol- and food-maintained responding were compared to responding during saline treatment in four Sprague–Dawley rats responding for ethanol and food under a multiple fixed-ratio 5, fixed-ratio 5 schedule. In two subjects, chronic fluvoxamine reduced ethanol-maintained responding more than food-maintained responding; however this effect was transient. In another subject, treatment persistently decreased food-maintained responding relative to ethanol-maintained responding. Finally, in one subject, fluvoxamine nonspecifically disrupted responding for food and ethanol. Similar to results in humans, outbred Sprague–Dawley rats had differential responses to chronic fluvoxamine. The effect was transient in rats that responded favorably (greater reduction of ethanol relative to food responding), while response reductions persisted throughout treatment in rats that responded unfavorably (greater reduction of food relative to ethanol or nonspecific reductions).

Phosphodiesterase-4 (PDE4) is one of the main enzymes that specifically terminate the action of cAMP, thereby contributing to intracellular signaling following stimulation of various G protein-coupled receptors. PDE4 expression and activity are modulated by agents affecting cAMP levels. The selective PDE4 inhibitor (R)-rolipram labeled with C-11 was tested in vivo in rats to analyze changes in PDE4 levels following drug treatments that increase synaptic noradrenaline (NA), serotonin (5HT), histamine (HA) and dopamine (DA) levels. We hypothesized that increasing synaptic neurotransmitter levels and subsequent cAMP-mediated signaling would significantly enhance (R)-[(11)C]rolipram retention and specific binding to PDE4 in vivo. Pre-treatments were performed 3 h prior to tracer injection, and rats were sacrificed 45 min later. Biodistribution studies revealed a dose-dependent increase in (R)-[(11)C]rolipram uptake following administration of the monoamine oxidase (MAO) inhibitor tranylcypromine, NA and 5HT reuptake inhibitors (desipramine [DMI], maprotiline; and fluoxetine, sertraline, respectively), and the HA H(3) receptor antagonist (thioperamide), but not with DA transporter blockers GBR 12909, cocaine or DA D(1) agonist SKF81297. Significant increases in rat brain and heart reflect changes in PDE4 specific binding (total-non-specific binding [coinjection with saturating dose of (R)-rolipram]). These results demonstrate that acute treatments elevating synaptic NA, 5HT and HA, but not DA levels, significantly enhance (R)-[(11)C]rolipram binding. Use of (R)-[(11)C]rolipram and positron emission tomography as an index of PDE4 activity could provide insight into understanding disease states with altered NA, 5HT and HA concentrations.

Cholestasis contributes to the genesis of fatigue through several mechanisms. Among these mechanisms, affected serotonergic neurotransmission is important in the pathogenesis of central fatigue. Previously, elevated levels of 5-hydroxyindole acetic acid (5-HIAA), the metabolite of 5-hydroxytryptamine (5-HT) and increased 5-HT(2) receptor density were demonstrated in the anterior hypothalamus and in the hippocampus of bile duct resected rats (BDR), respectively. The aim of this paper is to demonstrate evoked 5-HT release in selected brain regions like anterior hypothalamus and hippocampal CA1 regions of cholestatic rats using BDR rats as an experimental model for cholestasis. In this study, we analyzed the K+ evoked 5-HT and its metabolite 5-HIAA levels by using HPLC with electrochemical detection in the microdialysis samples collected from anterior hypothalamic and hippocampal CA1 regions of sham-operated and BDR rats (n = 6). The ratios of [5-HIAA] to [5-HT] following perfusion with 100 mM K+ artificial cerebrospinal fluid was used for the comparison of the evoked release of 5-HT. Locomotor activity was used to assess the signs of cholestasis associated fatigue in the BDR rats. The vertical and horizontal activity counts within 15 min were found to be decreased in the BDR rats compared to sham-operated rats (p < 0.05). Besides, the number of fecal boli (an index of emotionality) was also significantly fewer in the cholestatic rats (p < 0.05). No significant difference between the sham-operated and the BDR rats was detected in the basal 5-HT and 5-HIAA levels of anterior hypothalamus. K+ stimulation yielded a more profound increase in the [5-HIAA]/[5-HT] in the BDR rats (p < 0.05). The basal levels of 5-HT in CA1 region of the BDR rats was found to be lower than that of sham-operated group (p < 0.05), but no significant difference was observed in terms of evoked 5-HT release in both sham-operated and BDR rats. These findings imply the presence of affected serotonergic system in cholestasis.

The present study was performed to examine the neuroprotective effects of 5-hydroxytryptamine (5-HT)(3) receptor antagonists against hydrogen peroxide (H(2)O(2))-induced neurotoxicity using cultured rat cortical neurons. Pretreatment of 5-HT(3) receptor antagonists, tropanyl-3,5-dichlorobenzoate (MDL72222, 0.1 and 1 microM) and N-(1-azabicyclo[2.2.2.]oct-3-yl)-6-chloro-4-ethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxamide hydrochloride (Y25130, 0.5 and 5 microM), significantly inhibited the H(2)O(2) (100 microM)-induced neuronal cell death as assessed by a MTT assay and the number of apoptotic nuclei, evidenced by Hoechst 33342 staining. The protective effects of MDL72222 (1 microM) and Y25130 (5 microM) were completely blocked by the simultaneous treatment with 100 microM 1-phenylbiguanide, a 5-HT(3) receptor agonist, indicating that the protective effects of these compounds were due to 5-HT(3) receptor blockade. In addition, MDL72222 (1 microM) and Y25130 (5 microM) inhibited the H(2)O(2) (100 microM)-induced elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)) and glutamate release, generation of reactive oxygen species (ROS), and caspase-3 activity. These results suggest that the activation of the 5-HT(3) receptor may be partially involved in H(2)O(2)-induced neurotoxicity, by membrane depolarization for Ca(2+) influx. Therefore, the blockade of 5-HT(3) receptor with MDL72222 and Y25130 may ameliorate the H(2)O(2)-induced neurotoxicity by interfering with the increase of [Ca(2+)](c), and then by inhibiting glutamate release, generation of ROS and caspase-3 activity.

Cardio-respiratory reflex effects of an exogenous serotonin challenge are suggested to be modulated by activation of the peripheral 5HT2 and 5HT3 receptors. In the present experiments the blocking effects of serotoninergic active drugs: ketanserin and tropanserin (MDL 72222) were studied in six pentobarbitone-chloralose anaesthetized cats. Bolus injection of serotonin (0.05 mg·kg−1) into the right femoral vein evoked prompt apnea, hypotension followed by tachypnoeic breathing. Pre-treatment with ketanserin (0.1 mg·kg−1), 5HT2 receptor antagonist, shortened the duration of post-serotonin apnea (P < 0.05), but had no effect on the pattern of post-apnoeic breathing. 5HT3 receptor blockade with the selective antagonist MDL 72222 (0.2 mg·kg−1) totally eliminated respiratory response to serotonin. In breaths that followed post-serotonin apnea, peak amplitude of the integrated phrenic signal was reduced (P < 0.001), unbiased by ketanserin blockade, and remained at the baseline level in MDL treated rats. Serotonin-induced hypotension was unaffected by the blockade of 5HT2 receptors. Inactivation of 5HT3 receptors with MDL attenuated the fall in blood pressure (P < 0.05). This data suggests that the squeal of serotonin-induced pulmonary chemoreflex, i.e. respiratory arrest, post-apnoeic pattern of breathing, bradycardia, and partially hypotension are mediated by 5HT3 receptors.

Four weeks old (weanling) female rats were treated with the tricyclic antidepressant and histamine/serotonin receptor blocker mianserin for studying its faulty hormonal imprinting effect. Measurements were done four months later. Brain serotonin levels significantly decreased in four regions (hippocampus, hypothalamus, striatum and brainstem), without any change in the cortex. Sexual activity of the treated and control rats was similar. Cerebrospinal fluid nocistatin level was one magnitude higher in the treated rats, than in the controls. The density of uterine estrogen receptors was significantly reduced, while binding capacity of glucocorticoid receptors of liver and thymus remained at control level. The results call attention to the possibility of 1. a broad spectrum imprinting at the time of weaning by a receptor level acting non-hormone molecule 2. imprinting of the brain in a non-neonatal period of life and 3. a very durable (lifelong?) effect of the late imprinting with an antidepressant.

Hormonal imprinting takes place perinatally at the first encounter between the developing receptor and its target hormone. As a consequence of imprinting the receptor accomplishes its maturation and reaches the binding capacity characteristic to the adult age. In the excess of target hormone or presence of molecules similar to the target hormone, which are able to bind to the unmatured receptors, faulty imprinting develops with life-long consequences. At present, serotonin was given to neonatal rats and their sexual activity, brain serotonin level and steroid receptor's binding capacity was measured in adult age. Brain serotonin level was significantly reduced in male's striatum and parallel with this, male's sexual activity significantly increased. In other regions of the male brain (prefrontal cortex, hypothalamus, hippocampus) there was a statistically non-significant tendency for a decrease in serotonin level. No significant differences were detected in female brain values, and there was only slight change in female's sexual activity. There was also no change in the binding capacity of thymic glucocorticoid and uterine estrogen receptors. The experiments call attention to the possibility of perinatal imprinting by a neurotransmitter causing changes in brain neurotransmitter level for life, which is manifested in altered sexual activity.

The purpose of the present study was to study the effect of an acute dose of the serotonin (5-HT) – noradrenaline (NA) reuptake inhibitor venlafaxine on extracellular concentrations of 5-HT, NA and dopamine (DA) in the hippocampus and on the peripheral hormone concentrations in freely moving rats. Blood obtained from a catheter placed in the vena femoralis was analyzed for adrenocorticotropin (ACTH), beta-endorphins, prolactin (PRL), growth hormone (GH) and cortisol. Collections are referred to pre and post injection of 20 mg/kg of venlafaxine. Extracellular hippocampal NA and 5-HT as determined with in vivo microdialysis increased significantly after drug injection. PRL and ACTH were significantly affected by the drug. At the selected dose venlafaxine is able to increase the release of 5-HT but also of NA in rat hippocampus. Due to the dual reuptake properties of the drug and the functional interconnection of the NA and the 5-HT systems, the observed effects on peripheral hormones are possibly mediated by a combined action of these 2 systems.

Mechanisms for hyperleptinemia elicited by a serotonin (5-hydroxytryptamine, 5-HT) precursor, 5-hydroxytryptophan (5-HTP), were investigated. 5-HTP elicited apparent increases in serum leptin levels of mice. Administration of 5-HTP did not alter expression of leptin mRNA in white adipose tissues. Furthermore, neither 5-HTP nor 5-HT increased leptin secretion from isolated fat pads of mice. Since insulin is known to enhance leptin release, involvement of insulin in 5-HTP-induced hyperleptinemia was examined. 5-HTP significantly elevated serum insulin levels. In mice treated with streptozotocin, which depletes insulin, 5-HTP did not increase serum leptin levels. These results suggest that hyperinsulinemia participates the elevation of serum leptin levels elicited by 5-HTP.

Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.

Systemic administration ( i.v .) of serotonin (5-HT) evoked a transient vagal afferent nerve discharge, bradycardia, and hypotension in the rat. The half-effective dose of 5-HT for nerve discharge was 13 μg/kg. The time- and dose-dependent kinetics of the nerve discharge rate were similar to the change of heart rate. The afferent neuronal discharge was mimicked by a selective 5-HT 3 receptor agonist, 1-phenylbiguanide hydrochloride (PBA), and inhibited by a selective 5-HT 3 antagonist, granisetron. The 5-HT 3/4 agonist, cisapride partially activated the vagus nerve, but the 5-HT 4 agonist, RS6733 had no effect on the vagal afferent activity. Intra-gastric perfusion of lidocaine, moreover, abolished the 5-HT-induced vagal activation. These results indicate that the 5-HT transmission signal in the gastric mucosa inputs to the brain stem via 5-HT 3 receptor-mediated vagal nerve afferent.

The purpose of this study was to determine whether the 5-hydroxytryptamine7 (5-HT7) receptor is expressed by nociceptor-like neurons in the rat PNS and whether 5-HT activates these nociceptors via the 5-HT7 receptor subtype. Using a polyclonal antibody and the method of immunofluorescence staining, we demonstrated that the 5-HT7 receptor appears predominately on “nociceptor-like” neurons of the rat lumbar dorsal root ganglia. Using immunocytochemical methods, we showed that the immunoreactivity of the 5-HT7 receptor antibody complex is localized in the superficial layers of the spinal cord dorsal horn, which corresponds with laminae I, IIouter and IIinner. Furthermore, we demonstrated that noxious stimulation produced by knee injection of 5-HT or a 5-HT7 agonist dose-dependently increases c-Fos production of the rat spinal cord dorsal horn. This effect was significantly inhibited by the preinjection of a 5-HT7 antagonist. We conclude that the 5-HT7 receptor is expressed by rat primary afferent nociceptors which terminate in the superficial layers of the spinal cord dorsal horn and that the 5-HT7 receptor subtype is involved in nociceptor activation by 5-HT.

The purpose of this study was to examine the gastrin-releasing peptide (GRP) mediated regulation of 5-HT neuronal activity in the paraventricular nucleus of the hypothalamus under basal and restraint stress conditions. Intracerebroventricular (icv) administration of GRP (1, 10, 100 ng/rat) increased 5-HIAA concentrations in the paraventricular nucleus (PVN) of the hypothalamus, but was without effect in the accumbens, suprachiasmatic and arcuate nuclei. Administration of (Leu 13 -ψ-CH 2 NH-Leu 14 ) Bombesin (10, 100 and 1000 ng/rat; icv), a GRP antagonist, had no effect by itself on PVN serotonergic activity; however, a dose of 1 μg/rat of this compound, completely blocked the increase of 5-HIAA concentrations induced by GRP (10 ng). Restraint stress increased serotonergic activity -as shown by an elevation of 5-HIAA in the PVN- as well as plasma ACTH and corticosterone. This stress-induced activation of both the serotonergic neurons and the hypothalamus–pituitary–adrenal axis was blocked by CRF and GRP antagonists. Interestingly, when the activation of hypothalamic 5-HT neurons was induced by GRP administration, α-helical (9-41) CRF was ineffective. These data suggest that GRP, by acting on GRP receptors but not via CRF receptors, increases 5-HT neuronal activity in the PVN. In turn, it appears that endogenous GRP and CRF receptor ligands are both simultaneously involved in the regulation of the increase in 5-HT neuronal activity, ACTH and corticosterone secretion, under stress conditions.

Recent studies show that angiotensin II (AngII) can act from within the cell, possibly via intracellular receptors pharmacologically different from typical plasma membrane AngII receptors. The role of this intracellular AngII (AngII(i)) is unclear. Besides direct effects of AngII(i) on cellular processes one could hypothesise a possible role of AngII(i) in modulation of cellular responses induced after heterologous receptor stimulation. We therefore examined if AngIIi influences [Ca2+](i) in A7r5 smooth muscle cells after serotonin (5HT) or UTP receptor stimulation. Application of AngIIi using liposomes, markedly inhibited Ca-45(2+) influx after receptor stimulation with 5HT or UTP. This inhibition was reversible by intracellular administration of the AT(1)-antagonist losartan and not influenced by the AT(2)-antagonist PD123319. Similar results were obtained in single cell [Ca2+](i) measurements, showing that AngII(i) predominantly influences Ca2+ influx and not Ca2+ release via AT(1)-like receptors. It is concluded that AngII(i) modulates signal transduction activated by heterologous receptor stimulation. (C) 2001 Elsevier Science Inc. All rights reserved.

The urinary excretion products of serotonin (5-hydroxytryptamine, 5HT) are 5-hydroxyindole-3-acetic acid (5HIAA) and 5-hydroxytryptophol (5HTOL), and the ratio of 5HTOL to 5HIAA is normally very low (< 0.01 ) in man. Intake of foods rich in 5HT (high amounts in banana, pineapple, and walnuts) induces a general increase in the output of 5HT metabolites, without affecting the 5HTOL/5HIAA ratio. In contrast, during metabolism of ethanol there is a shift in the catabolic pattern of 5HT, and the formation of 5HTOL increases appreciably at the expense of 5HIAA. Accordingly, the urinary 5HTOL/ 5HIAA ratio increases and does not recover to baseline levels until several hours after ethanol has been cleared from the body. When 10 healthy subjects ingested a moderate dose of ethanol (0.5 g/kg), the urinary 5HTOL/SHIAA ratio was increased approximately 70-fold on average at 4 h after intake. When the same amount of ethanol was ingested together with 3 bananas (approximately 10 mg 5HT), this ratio was increased approximately 100-fold at 4 h and still significantly higher than baseline levels at 24 h. Starting at 3-4 h after the combined intake of ethanol and banana, 7 subjects experienced one or more unpleasant symptoms (diarrhea, headache, and fatigue) which are associated with the 5HT system. The events were transient but typically lasted for several hours, and the duration correlated with the time period during which 5HTOL levels were raised. Intake of ethanol and banana separately produced much lower increases in 5HTOL output and caused no corresponding effects. This observation indicate that dietary 5HT intake together with even a moderate dose of ethanol can provoke unpleasant physiological symptoms. The symptoms may be attributed to the high concentration of 5HTOL.

The dependence of platelet-5HT content on apparent kinetic parameters of 5HT uptake was analyzed in 56 healthy subjects and 47 depressed patients, who had not been taking psychotropic medication for several months. There were no significant relationships between apparent Vmax or Km and platelet-5HT content in both groups. However, the ratio of Vmax to Km, as a measure of apparent 5HT uptake efficiency, significantly correlated with the platelet-5HT concentration in healthy subjects (r=0.627 p

Using positron emission tomography (PET) and [11C]N-methylspiperone (NMSP), we examined 5-HT2 receptors in the cortex of schizophrenic patients in whom we previously observed decereased prefrontal D1 receptor binding. The subjects were 10 neuroleptic-naive schizophrenic patients, 7 schizophrenic patients who were drug-free but had previously been treated with neuroleptics, and 12 normal controls. A non-significant trend towards decreased prefrontal [11C]NMSP binding was observed in the neuroleptic-treated patients, suggesting a possible effect of previous neuroleptic treatment on the alteration in cortical 5-HT2 function. However, the neuroleptic-naive patients showed no noticeable difference in cortical [11C]NMSP binding compared to controls. Our results do not rule out the role of 5-HT2 function as a crucial site of therapeutic activity of schizophrenia, but they do suggest that cortical 5-HT2 receptors might not be primarily involved in the pathophysiology of schizophrenia.

The effects of serotonin (5-HT) 1A drugs on the development and expression of sensitization to the locomotor effect of amphetamine (AMPH) were studied in mice. 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT 1A agonist, dose-dependently reduced the expression of AMPH (2.5 mg/kg)-induced sensitization. The latter inhibitory effect of 8-OH-DPAT was reversed by (S)-N-tert-butyl-3-(4-(2-methoxyphenyl)piperazin-1-yl)-2-phenylpropamine (WAY 100135), a 5-HT 1A antagonist. WAY 100135 given alone did not affect expression of AMPH sensitization. Combined injections of 8-OH-DPAT, but not WAY 100135, with AMPH (2.5 mg/kg) during the development of sensitization, protected against the expression of sensitization to a challenge dose of AMPH (2.5 mg/kg) 3 days after withdrawal. The above inhibitory effect of 8-OH-DPAT on the development of AMPH sensitization was blocked by pretreatment with WAY 100135. The AMPH-induced conditioned locomotion was unaffected by pretreatment with 8-OH-DPAT. These results indicate that 5-HT 1A receptors are not involved in AMPH-induced sensitization per-se, whereas their pharmacological activation leads to the inhibition of both the development and the expression of AMPH-induced sensitization.

Recent findings indicate that elevations in body temperature during acute d-fenfluramine (Fen) exposure enhance long-term 5-HT depletion. Therefore, we hypothesized that when repeated exposure to d-Fen produced repeated elevations in body temperature, 5-HT reductions would be greater in comparison to a single d-Fen exposure. Groups of animals were exposed to d-Fen for 1 or 4 days in a 28 degrees C environment. Exposure to d-Fen in the 28 degrees C environment induced an increase in body temperature and resulted in a long-term decrease in brain 5-HT. However, brain 5-HT was not different between the two groups. An additional experiment revealed that if the initial exposure to d-Fen does not induce elevations in body temperature, then long-term 5-HT depletion can be prevented. We conclude that the central nervous system rapidly adapts to the 5-HT depleting action of d-Fen thereby preventing further decreases in 5-HT concentrations from d-Fen exposure. In addition, this rapid adaptation circumvented the hyperthermia-enhanced 5-HT depletion that results from d-Fen exposure in a warm environment.

The brain stems (BS) of streptozotocin (STZ)-diabetic rats were studied to see the changes in neurotransmitter content and their receptor regulation. The norepinephrine (NE) content determined in the diabetic brain stems did not show an increase, while epinephrine (EPI) content increased significantly compared with control. The NE to EPI turnover showed a significant increase. The alpha2 adrenergic receptor kinetics revealed that the receptor affinity was significantly reduced during diabetes. In insulin treated rats the NE content decreased while EPI content remained increased as in the diabetic state. Insulin treatment increased the Bmax for alpha2 adrenergic receptors significantly while the increase in Kd reversed to normal. Unlabelled clonidine inhibited [3H]NE binding in BS of control diabetic and insulin treated diabetic rats showed that alpha2 adrenergic receptors consisted of two populations of binding sites with Hill slopes significantly away from unity. In diabetic animals the ligand bound weaker to the low affinity site than in controls. Insulin treatment reversed this alteration to control levels. The displacement analysis using (-)-epinephrine against [3H]yohimbine in control and diabetic animals revealed two populations of receptor affinity states. In control animals, when GTP analogue added with epinephrine, the curve fitted for a single affinity model; but in the diabetic BS this effect was not observed. In both the diabetic and control BS the effects of monovalent cations on affinity alterations were intact. Our data thus show that alpha2 adrenergic receptors have a reduced affinity due to an altered post receptor affinity regulation The serotonin (5-HT) content in the brain stem increased. Its precursor (5-hydroxy) tryptophan (5-HTP) showed an increase and its breakdown metabolite (5-hydroxy) indoleacetic acid (5-HIAA) showed a significant decrease. This showed that in serotonergic nerves there is a disturbance in both synthetic and breakdown pathways which lead to an increased 5-HT. The high affinity serotonin receptor numbers remained unaltered with a decrease in the receptor affinity. The insulin treatment reversed these altered serotonergic receptor kinetic parameters to control level. Thus our study shows a decreased serotonergic receptor function. These changes in adrenergic and serotonergic receptor function were suggested to be important in insulin function during STZ diabetes.

The effect of the selective 5-HT3 receptor antagonist ondansetron on the ethanol-induced place preference in rats exposed to conditioned fear stress, which stimulates the release of endogenous opioid peptides (beta-endorphin and enkephalins), was investigated using the conditioned place preference paradigm. In addition, we also examined the effect of ondansetron on the ethanol-induced place preference enhanced by the administration of mu- and delta-opioid receptor agonists (exogenous opioids). The administration of ethanol (300 mg/kg, i.p.) induced a significant place preference in rats exposed to conditioned fear stress. Pretreatment with ondansetron (0.01 and 0.1 mg/kg, s.c.) effectively attenuated this ethanol-induced place preference. When the mu-opioid receptor agonist morphine (0.1 mg/kg, s.c.) or the selective delta-opioid receptor agonist 2-methyl-4a(alpha)-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a(alpha)-octah ydroquinolino [2,3,3-g] isoquinoline (TAN-67; 20 mg/kg, s.c.) was administered in combination with 75 mg/kg ethanol (which tended to produce a place preference), the ethanol-induced place preference was significantly enhanced. The selective mu-opioid receptor antagonist beta-funaltrexamine at a dose of 10 mg/kg significantly attenuated the enhancement of the ethanol-induced place preference produced by morphine. Ondansetron (0.1 mg/kg, s.c.) also significantly attenuated the enhancement of the ethanol-induced place preference produced by morphine. Furthermore, the selective delta-opioid receptor antagonist naltrindole at a dose of 3 mg/kg significantly attenuated the enhancement of the ethanol-induced place preference produced by TAN-67. Ondansetron (0.1 mg/kg, s.c.) slightly, but significantly, attenuated the enhancement of the ethanol-induced place preference produced by TAN-67. These results suggest that 5-HT3 receptors may be involved in the rewarding mechanism of ethanol under psychological stress, and may play an important role in the rewarding effect of ethanol through the activation of mu- and delta-opioid receptors.

The effect of the 5-HT4 antagonists GR113808A and GR125487D on cocaine-induced cardiac arrhythmia was examined in the rat. Cocaine alone, given i.v. at a rate of 2 mg/kg every 5 min, produced an initial increase in blood pressure followed by a severe drop in pressure and bradycardia. Sustained ventricular fibrillation was noted after 6-12 mg/kg cocaine and quickly progressed to asystole. Pretreatment with both GR113808A and GR125487D antagonized these effects in a dose-dependent manner. When given after the onset of arrhythmia, both drugs reversed the cocaine-induced arrhythmia's. Thus, the 5-HT4 antagonists may be useful in the treatment of cocaine toxicity.

The purpose of the present study was to elucidate the distribution of 5-HT6 receptor mRNA and possible physiological functions of the 5-HT6 receptor subtype using antisense oligonucleotides (AOs) in rats. Continuous intracerebroventricular injection of AOs caused a 30% reduction in the number of [3H]-lysergic acid diethylamide binding sites. Conditioned fear stress-induced increase in 5-HT release from the prefrontal cortex was significantly inhibited by treatment with AOs. The present study suggests that 5-HT6 receptors may be functionally expressed in the brain, where one of the functions appears to be in the mediation of certain anxiety disorders.

The effects of intrathecally (i.t.) administered GABA(A)-receptor antagonist picrotoxin or bicuculline on the antinociception produced by i.t. serotonin (5-HT), gamma-aminobutyric acid (GABA), muscimol--the GABA(A) agonist or baclofen--the GABA(B) agonist were investigated and compared using the tail-flick assay in rats. The results showed that 1) both i.t. picrotoxin (1.5 nmol) and i.t. bicuculline (0.5 nmol) exhibited a partial and later-emerged blockade on the antinociception produced by 5-HT (120 nmol) or GABA (1.5 nmol); 2) both i.t. picrotoxin and i.t. bicuculline, with the same dosages, completely blocked the antinociception produced by muscimol (1.0 nmol), but showed no effects on that produced by baclofen (0.3 nmol). The results suggest that GABA may mediate the 5-HT-induced antinociception at the spinal level, with the GABA(B)-receptors exhibiting the effect at the early-stage and the GABA(A)-receptors at the later stage of the 5-HT-induced antinociception.

Recent head-twitch response (HTR) studies in mice have indicated that withdrawal from chronic cocaine exposure produces deficits in CNS conversion of L-tryptophan to 5-HT. In the present study, the ability of 5-HT releaser, d-fenfluramine, was utilized to induce the HTR in mice following abstinence from chronic cocaine exposure. d-Fenfluramine-induced HTR, is a 5-HT 2A receptor-mediated phenomenon and its induction frequency can be regarded as an indirect but in vivo measure of basal brain 5-HT concentration. Thus, different groups of mice were injected with cocaine twice daily (0, 0.1, 0.5, 2.5, 5 or 10 mg/kg, i.p.) for either 7 or 13 days. At 24 h after last cocaine injection, the treated mice received d-fenfluramine (5 mg/kg, i.p.) and the induced HTR (mean±SEM) was recorded for the next 30 min. Cocaine attenuated the d-fenfluramine-induced HTR frequency by 30–37% in the 13-day regimen and significant effects were observed from 0.5 mg/kg dose. At 24 h withdrawal in the 7-day cocaine exposure group, the mean HTR frequencies were attenuated, however, they did not achieve statistical significance. Extended abstinence studies (i.e. 24, 48, 72 and 96 h postwithdrawal) from chronic cocaine exposure (0, 0.5 and 5 mg/kg/day for either 7 or 13 days) indicated that in the 7-day exposure group, significant reductions (26, 39 and 22%) in HTR frequency occurred at 48, 72 and 96 h following withdrawal from 0.5 mg/kg cocaine, whereas its 5 mg/kg dose failed to induce a significant effect. In the 13-day exposure group significant reductions in HTR frequency were observed at 24 h abstinence (27%) for the 0.5 mg/kg cocaine dose and at 24 and 48 h for the 5 mg/kg. Overall, these results indicate that abstinence from chronic exposure to cocaine produces enduring deficits in basal 5-HT concentration. Lastly, serotonergic function appears to be uniquely sensitive to chronic administration of low doses of cocaine.

C6-glioma cells endogenously express both 5HT2A receptors and inducible nitric oxide synthase (iNOS). iNOS can be induced by transcriptional activation to produce nitric oxide (NO) in response to a challenge with lipopolysaccharide (LPS). Experiments were conducted to determine whether 5HT2A receptor activation could modify the production of NO in response to LPS. Incubation of 10 microg/ml LPS with C6-glioma cells for a period of 24 hours resulted in a 2.6 fold increase in nitrite levels, as a measure of NO levels, over vehicle treated controls. Co-incubation with the selective 5HT2A receptor partial agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) produced a dose-dependent inhibition of the LPS-induced nitrite levels of 22% with an IC50 of 16 nM. The full agonists serotonin (5HT) and alpha-methyl-5HT produced an inhibition of approximately 30% at a concentration of 1 microM. The inhibitory effect of 1 microM DOI was blocked by the 5HT2A receptor antagonists spiperone and ritanserin (10 nM). Inhibition of protein kinase C (PKC) using 100 nM chelerythrine prevented the DOI-mediated decrease in LPS-induced nitrite levels. Addition of DOI to the cells after 1 hr following the LPS addition did not produce a decrease in nitrite levels indicating iNOS was not modified post-translationally. The data demonstrate that iNOS activity can be modulated by serotonin 5HT2A receptor activation, most likely at the initiation of the induction process, via PKC. We therefore suggest that there may be a link between the serotonergic system and NO-mediated immune responses in the brain.

Rats were trained to discriminate eltoprazine (1-(2,3-dihydro-1,4-benzodioxin-5-yl)-piperazine) (1.0 mg/kg p.o.) from demineralized water in a two lever operant procedure. Eltoprazine generalized to the 5-HT1B receptor agonist anpirtoline (6-chloro-2-[piperidyl-4-thiol]-pyridine hydrochloride), the 5-HT(1A,1B) receptor agonists batoprazine (8-(1-piperazinyl)-2H-1-benzopyran-2-one) and 1-NP (1-(1-naphthyl)piperazine hydrochloride), and to the 5-HT(1B/2C) receptor agonist mCPP (1-(3-chlorophenyl)piperazine dihydrochloride). The 5-HT1A receptor agonist flesinoxan (R(+)-N-[2[4-(2,3-dihydro-2-2-hydroxy-methyl-1,4-benzodioxin-5-yl) -1-piperazinyl]ethyl]-4-fluorobenzoamide) generalized partially and the 5-HT1A receptor antagonist WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride) failed to antagonize the eltoprazine cue, suggesting that 5-HT1A receptors are of limited importance in the discriminative stimulus properties of eltoprazine. Methiothepin, mCPP, mianserin and alprazolam did not antagonize the eltoprazine cue. The 5-HT(1A,1B,1D) receptor agonist GR46611X (3-[3-(2-dimethylamino-ethyl)-1H-indol-6-yl]-N-(4-methoxy-benzyl)acrylam ide) and the 5-HT(1B,1D) receptor antagonist GR127935T (N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1,-biphenyl]-4-carboxamide) did neither generalize to nor antagonize the eltoprazine cue, whereas (-)-alprenolol showed partial antagonism and substitution. These results show that the eltoprazine discriminative stimulus is mediated by the 5-HT1B receptor, although the lack of good 5-HT1B receptor antagonists weakens this conclusion.

Since reduced levels of brain serotonin are known to cause behavioural abnormalities, to which diabetics are also prone, we investigated the effect, in rats, of chronic diabetes on brain serotonin concentration and on the numbers of 5-HT(1A) and 5-HT2 receptors in cerebral cortex and brainstem. Our data show that streptozotocin induces a longlasting hyperglicemia that is associated with a decrease in cerebral concentration of serotonin and with an accompanying increase in the maximum number of 5-HT(1A) and 5-HT2 receptors in the brain areas studied. Our results may suggest that changes in serotonergic transmission in the CNS play a role in diabetes-related behavioural abnormalities.

The present investigation examined the interaction between fluoxetine enantiomers and LSD in rats trained with LSD as a discriminative stimulus. The dose response relationships for LSD alone and in combination with either (+)- or (-)-fluoxetine were determined. In both instances, the LSD dose response relationship was shifted to the left. However, statistical significance was observed only for the (+)- enantiomer. It is concluded that the effects of LSD as a discriminative stimulus are potentiated by the acute administration of fluoxetine. These results are consistent with anecdotal reports of interactions between LSD and acutely administered SSRIs in humans.

Antroduodenal myoelectric activity was recorded in conscious sheep by electrodes chronically implanted in the muscular wall. Furthermore, plasma immunoreactive (i.r.) motilin, somatostatin and bombesin concentrations were determined by RIA. The intravenous infusion of somatostatin (20 ng/kg/min), bombesin (10 ng/kg/min) or serotonin (5-HT, 4 μg/kg/min) for 5 min, induced a duodenal myoelectric activity front followed by a period of quiescence. These duodenal events were concomitant with an antral inhibition. This pattern resembled that observed in a spontaneous migrating myoelectric complex (MMC) in sheep. Bombesin and 5-HT evoked an additional and transient increase in antral activity simultaneously with the duodenal activity front. On the other hand, plasma i.r. motilin levels did not show any fluctuations during spontaneous MMC cycles or after somatostatin, bombesin or 5-HT infusions. Likewise, plasma i.r. bombesin levels remained unchanged during spontaneous MMC or after administration of somatostatin. However, 5-HT-induced duodenal activity fronts were closely associated with a sharp peak in plasma i.r. bombesin. Finally, plasma i.r. somatostatin concentrations rose at the end of spontaneous phase III and peaked in phase I. A similar pattern of somatostatin release in plasma was found while the duodenal activity front and quiescence period developed after either 5-HT or bombesin infusions. These results do not indicate a role for motilin in the control of MMCs in sheep, although a definitive conclusion cannot be drawn until synthetic sheep motilin is available. However, our data suggest that somatostatin and bombesin-like peptides as well as 5-HT, acting in a coordinated manner, could be involved in the regulation of cyclical antroduodenal motor events in sheep.

That serotonin (5HT) is involved in regulating hypothalamic-pituitary- adrenal axis (HPA) function has long been recognized. A variety of drugs including precursors of 5HT such as 5HTP, drugs which release 5HT such as fenfluramine and drugs which act directly on 5HT 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 5HT and the HPA raises questions as to the validity of this simple model. An increasing volume of experimental research indicates that 5HT 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 5HT conducted in psychiatric conditions, such as depression.

The effects of central administration of two serotonin receptor agonists, 8-OH-DPAT and mCPP, on tuberoinfundibular dopaminergic (TIDA) neuron activity and serum prolactin (PRL) levels in ovariectomized, estrogen-treated rats were determined. 8-OH-DPAT dose-dependently (0.1-10 microgram/rat, icv) stimulated serum PRL levels, and depressed serotonergic neuron activity in 30 min. However, the TIDA neuron activity was not affected at all. Similar treatment of mCPP was less effective than 8-OH-DPAT: only the highest dose of mCPP (10 microgram) stimulated PRL secretion and inhibited serotonergic neuron activity. No change in TIDA neuron activity was observed either. We conclude that central serotonin acts on 5-HT1 receptors to stimulate the PRL secretion, which may not involve the TIDA neurons.

High affinity [3H] dihydroergocryptine binding sites different from alpha1/alpha2-adreno, dopamine or serotonin receptors were detected in a crude membrane fraction from hamster liver by radioligand binding filtration assay. The binding was saturable and reversible, as well as time and protein dependent. Scatchard analysis revealed a single population of binding sites with Kd 3.8 +/- 0.9 nM and Bmax = 675 +/- 130 pmol/g tissue (mean +/- S.E.M., n=6) in the male hamster crude liver membrane fraction. In the female liver membranes the Kd value was 4.4 + 1.2 nM and Bmax = 1025 +/- 190 pmol/g tissue (mean + S.E.M., n = 6). Differences between males and females in Bmax values were significant (P0.01). The most potent inhibitors of [3H] dihydroergocryptine binding were bromocriptineergotaminedihydroergocryptinedihydroergocristinealpha ergocristinedihidroergotamineergocornineergocristinenicardipine(+) butaclamolPK 11195nitrendipinedomperidone(-)butaclamol (in order of decreasing affinity). The described type of dihydroergocryptine binding sites was not detected in hamster brain, kidney, spleen or lungs. Obtained data support the concept that some ergot-derivatives may induce metabolic effects in the liver through peripheral mechanisms other than those, mediated by alpha-adrenoreceptors.

We have synthesized several derivatives of dl-threo -methylphenidate (Ritalin) bearing substituents on the phenyl ring. IC 50 values for binding of these compounds to rat brain monoamine transporters were assessed using [ 3 H]WIN 35,428 (striatal membranes, dopamine transporters, DAT), [ 3 H]nisoxetine (frontal cortex membranes, norepinephrine transporters, NET) and [ 3 H]paroxetine (brain stem membranes, 5HT transporters, 5HTT). Affinities (1/Ki) decreased in the order: DAT > NET ⪢ 5HTT. Substitution at the para position of dl-threo -methylphenidate generally led to retained or increased affinity for the dopamine transporter (bromo > iodo > methoxy > hydroxy). Substitution at the meta position also increased affinity for the DAT (m-bromo > methylphenidate; m-iodo-p-hydroxy > p-hydroxy). Substitution at the ortho position with bromine considerably decreased affinity. Similar IC 50 values for binding of o-bromomethylphenidate to the dopamine transporter were measured at 0, 22 and 37 degrees. N-Methylation of the piperidine ring of methylphenidate also considerably reduced affinity. The dl-erythro isomer of obromomethylphenidate did not bind to the DAT (IC 50 > 50,000 nM). Affinities at the dopamine and norepinephrine transporters for substituted methylphenidate derivatives were well correlated (r 2 = 0.90). Abilities of several methylphenidate derivatives to inhibit [ 3 H]dopamine uptake in striatal synaptosomes corresponded well with inhibition of [ 3 H]WIN 35, 428 binding. None of the compounds examined exhibited significant affinity to dopamine D1 or D2 receptors (IC 50 > 500 or 5,000 nM, respectively), as assessed by inhibition of binding of [ 3 H]SCH 23390 or [ 123 I]epidepride, respectively, to striatal membranes.

The mechanism of the hyperglycemic response to intraperitoneally administered serotonin (5-HT) was studied in rats. 5-HT i.p.-induced hyperglycemia was strongly antagonized by the 5-HT2A receptor antagonist ketanserin. 5-HT did not affect the serum insulin levels and increased plasma glucagon levels only at the high dose of 10 mg/kg. 5-HT dose-dependently induced a remarkable increase in plasma adrenaline levels and these effects were antagonized by ketanserin. 5-HT-induced hyperglycemia was abolished by adrenodemedullation. These results suggest that the hyperglycemic effects of 5-HT are closely related to the release of adrenaline from the adrenal gland, mediated by 5-HT2A receptors.

The dopamine (DA) uptake inhibitor, GBR 12909 (GBR) and a neonatal dopaminergic denervated rat model were used as tools to study the influence of DA on the serotonin (5HT) system in the striatum. The striatal levels of the amines and their acid metabolites (dihydroxyphenylacetic acid, DOPAC; 5-hydroxyindoleacetic acid, 5HIAA) were determined by HPLC. The administration of a single dose (20 mg/kg) of GBR failed to affect the steady-state levels of the amines or metabolites. Repeated administration of GBR (20 mg/kg/day) for 2 or 4 days decreased DA and DOPAC; only the 4-day regimen decreased 5HT and increased 5HIAA levels. The neonatal dopaminergic lesion with 6-hydroxydopamine (6OHDA) depleted (> 95%) DA and DOPAC and increased 5HT and 5HIAA levels in the striatum. Administration of GBR (20 mg/kg/day for 4 days) to lesioned animals failed to influence the lesion-induced increases in 5HT and 5HIAA levels. The results suggest GBR decreases the steady-state levels of DA, resulting in a compensatory increase in the turnover of 5HT that is dependent on the presence of intact dopaminergic terminals. Thus, the effect of GBR on 5HT turnover is indirect. The studies provide further support for a prominent dopaminergic influence on striatal 5HT metabolism.

The effects of the new 5-HT2A receptor antagonist sarpogrelate on the cellular action of serotonin were examined in cultured rat mesangial cells by measuring cytosolic free calcium concentration ([Ca2+]i). Sarpogrelate inhibited serotonin-induced increases in [Ca2+]i in a concentration-dependent manner. M1, a major metabolite of sarpogrelate, also exhibited an inhibitory effect exceeding that of sarpogrelate. The inhibitory effects of sarpogrelate and M1 were abolished by washing out these compounds. In contrast, the increase in [Ca2+]i induced by angiotensin II or arginine vasopressin was not affected by pretreatment of the cells with sarpogrelate or M1. These results suggest that sarpogrelate and its major metabolite (M1) act as reversible and specific 5-HT2A receptor antagonists against the contractile action of platelet-derived serotonin in mesangial cells.