Deficits in attentional functions belong to the core cognitive symptoms in schizophrenic patients. Alertness is a nonselective attention component that refers to a state of general readiness that improves stimulus processing and response initiation. The main goal of the present study was to investigate cerebral correlates of alertness in the human <em>5HT</em>(2A) agonist and N-methyl-D-aspartic acid (NMDA) antagonist model of psychosis. Fourteen healthy volunteers participated in a randomized double-blind, cross-over event-related functional magnetic resonance imaging (fMRI) study with dimethyltryptamine (DMT) and S-ketamine. A target detection task with cued and uncued trials in both the visual and the auditory modality was used. Administration of DMT led to decreased blood oxygenation level-dependent response during performance of an alertness task, particularly in extrastriate regions during visual alerting and in temporal regions during auditory alerting. In general, the effects for the visual modality were more pronounced. In contrast, administration of S-ketamine led to increased cortical activation in the left insula and precentral gyrus in the auditory modality. The results of the present study might deliver more insight into potential differences and overlapping pathomechanisms in schizophrenia. These conclusions must remain preliminary and should be explored by further fMRI studies with schizophrenic patients performing modality-specific alertness tasks.

Development of serotonin (<em>5HT</em>(1B/1D)) agonists for the acute attack of migraine resulted in considerable interest in their action. The superior sagittal sinus (SSS) was isolated in alpha-chloralose (60 mg/kg, i.p. and 20 mg/kg i.v.i. supplementary 2 hourly) anaesthetised cats. The SSS was stimulated electrically (100 V, 250 micros duration, 0.3 Hz) and neurons of the trigeminocervical complex monitored using electrophysiological methods. To test 5-HT(1B) receptor-mediated activity common carotid blood flow (CCF) was monitored with a transonic flow probe placed around the vessel. Naratriptan (5-HT(1B/1D/1F) receptor agonist) and alniditan (5-HT(1B/1D) receptor agonist) produced reductions in carotid blood flow of 38+/-5% and 42+/-6%, respectively. These effects were attenuated by the 5-HT(1B) receptor antagonist SB224289 (P<0.05). LY344864 (5-HT(1F) receptor agonist) had no effect on CCF. Naratriptan inhibited SSS-evoked activity (61+/-7%), an effect partially inhibited by the 5-HT(1B) receptor antagonist SB224289 (30+/-5%), or by the 5-HT(1D) receptor antagonist BRL-15572 (37+/-6%). There remained an inhibitory effect of naratriptan after both 5-HT(1B) and 5-HT(1D) receptor blockade (22+/-5%). Alniditan inhibited SSS-evoked trigeminal activity (53+/-6%), an effect abolished after 5-HT(1B) and 5-HT(1D) receptor blockade. LY344864 (5-HT(1F) receptor agonist) inhibited SSS-evoked trigeminal activity (28+/-5%), an effect unaltered by either SB224289 or BRL-15572. It can be concluded that there are inhibitory 5-HT(1B), 5-HT(1D) and 5-HT(1F) receptors in the trigeminocervical complex of the cat. 5-HT(1B) receptor-mediated inhibition is the most potent of the three in terms of inhibition of trigeminovascular nociceptive traffic.

Antenatal maternal long-term hypoxia (LTH) can alter serotonin (5-HT) and calcium (Ca(2+)) signaling in fetal pulmonary arteries (PAs) and is associated with persistent pulmonary hypertension of the newborn (PPHN). In humans, the antenatal maternal hypoxia can be secondary to smoking, anemia, and chronic obstructive pulmonary disorders. However, the mechanisms of antenatal maternal hypoxia-related PPHN are unresolved. Because both LTH and 5-HT are associated with PPHN, we tested the hypothesis that antenatal maternal LTH can increase 5-HT-mediated PA contraction and associated extracellular Ca(2+) influx through L-type Ca(2+) channels (Ca(L)), nonselective cation channels (NSCCs), and reverse-mode sodium-calcium exchanger (NCX) in the near-term fetus. We performed wire myography and confocal-Ca(2+) imaging approaches on fetal lamb PA (∼ 140 days of gestation) from normoxic ewes or those acclimatized to high-altitude LTH (3801 m) for ∼110 days. Long-term hypoxia reduced the potency but not the efficacy of 5-HT-induced PA contraction. Ketanserin (100 nmol/L), a 5-HT(2A) antagonist, shifted 5-HT potency irrespective of LTH, while GR-55562 (1 µmol/L), a 5-HT(1B/D) inhibitor, antagonized 5-HT-induced contraction in normoxic fetuses only. Various inhibitors for Ca(L), NSCC, and reverse-mode NCX were used in contraction studies. Contraction was reliant on extracellular Ca(2+) regardless of maternal hypoxia, NSCC was more important to contraction than Ca(L), and reverse-mode NCX had little or no role in contraction. Long-term hypoxia also attenuated the effects of 2-APB and flufenamic acid and reduced Ca(2+) responses observed by imaging studies. Overall, LTH reduced <em>5HT</em>(1B/D) function and increased NSCC-related Ca(2+)-dependent contraction in ovine fetuses, which may compromise pulmonary vascular function in the newborn.

Nicergoline, a drug used for the treatment of Alzheimer's disease and other types of dementia, was tested for its ability to protect neurons against beta-amyloid toxicity. Pure cultures of rat cortical neurons were challenged with a toxic fragment of beta-amyloid peptide (betaAP(25-35)) and toxicity was assessed after 24 h. Micromolar concentrations of nicergoline or its metabolite, MDL, attenuated betaAP(25-35)-induced neuronal death, whereas MMDL (another metabolite of nicergoline), the alpha1-adrenergic receptor antagonist, prazosin, or the serotonin <em>5HT</em>-2 receptor antagonist, methysergide, were inactive. Nicergoline increased the basal levels of Bcl-2 and reduced the increase in Bax levels induced by beta-amyloid, indicating that the drug inhibits the execution of an apoptotic program in cortical neurons. In mixed cultures of rat cortical cells containing both neurons and astrocytes, nicergoline and MDL were more efficacious than in pure neuronal cultures in reducing beta-amyloid neurotoxicity. Experiments carried out in pure cultures of astrocytes showed that a component of neuroprotection was mediated by a mechanism of glial-neuronal interaction. The conditioned medium of cultured astrocytes treated with nicergoline or MDL for 72-96 h (collected 24 h after drug withdrawal) was neuroprotective when transferred to pure neuronal cultures challenged with beta-amyloid. In cultured astrocytes, nicergoline increased the intracellular levels of transforming-growth factor-beta and glial-derived neurotrophic factor, two trophic factors that are known to protect neurons against beta-amyloid toxicity. These results raise the possibility that nicergoline reduces neurodegeneration in the Alzheimer's brain.

Clinical trials indicate that inositol may be effective in the treatment of patients with depression, panic disorder and obsessive compulsive disorder (OCD), but not in the treatment of patients with schizophrenia, Alzheimer's disease, ADHD or autism. This spectrum of clinical action parallels that of serotonin selective reuptake inhibitors (SSRIs), but inositol is a precursor in the phosphatidylinositol cycle, a second messenger system distal to the receptor for <em>5HT</em>-2. To study its mechanism of therapeutic action there is a need to test inositol's activity in animal models of psychopathology. In rats, chronic inositol was demonstrated to increase activity levels, reduce immobility time in the forced swim test and in the reserpine-induced hypoactivity models of depression, and reduce anxiety-like behaviors in the elevated plus-maze. The reduction in anxiety-like behaviors appears to be related to baseline levels of activity. Inositol treatment was not observed to have any effect on amphetamine-induced hyperactivity, apomorphine-induced stereotypy, or on the performance of memory tasks by monkeys. Clinical controlled trials of inositol in patients with depression, panic disorder, and OCD were small, and positive psychoactive effects in animals clearly strengthen the case for further clinical trials and potential for general therapeutic use in humans.

BACKGROUND

Ficus religiosa (Moraceae) is reported to have numerous therapeutic utility in folk medicine. Among different biological activities on central nervous system, it has been reported to be used in ethnomedical treatment of epilepsy, which led us to further explore its anticonvulsant activity in various animal models of epilepsy.

OBJECTIVE

To investigate anticonvulsant activity of methanolic extract of figs of Ficus religiosa in animal models and to determine its possible anticonvulsant mechanism.

METHODS

Anticonvulsant activity of figs extract (25, 50 and 100 mg/kg, i.p.) was studied in seizures induced by maximum electroshock (MES), picrotoxin and pentylenetetrazol (PTZ). Cyproheptadine, a nonselective (<em>5HT</em>(1/2)) serotonin antagonist (4 mg/kg, i.p.) was used to study the reversal of protective effect of extract in the above mentioned models. Acute toxicity, neurotoxicity and potentiation of pentobarbitone induced sleep by extract was also studied.

RESULTS

Extract showed no toxicity, potentiated pentobarbitone induced sleep and inhibited seizures induced by MES and picrotoxin in a dose dependent manner. Anticonvulsant effect of extract was comparable to clinically used antiepileptic drugs (phenytoin and diazepam). However, PTZ induced seizures were not inhibited. Animals pretreated with cyproheptadine showed inhibition of the anticonvulsant effect of extract.

CONCLUSIONS

These findings suggested that the methanolic extract of figs of Ficus religiosa had anticonvulsant activity against MES and picrotoxin induced convulsions, with no neurotoxic effect, in a dose dependent manner. Inhibition of the anticonvulsant effect of extract by cyproheptadine substantiates the involvement of serotonergic pathways for the anticonvulsant activity of extract.

Triptans, acting as serotonin, 5-HT(1B/1D/1F), receptor agonists, provide an effective and established treatment option in migraine and cluster headache. Clinical observations suggest a relatively specific effect of these compounds on primary headache disorders, but not in other pain syndromes. The mechanism of this specificity, however, is not well understood. Hence, we systematically studied primary sensory ganglia in rat to determine if the peripheral distribution of <em>5HT</em>(1B/1D/1F) receptors showed any anatomical difference that would account for the specificity of clinical effect. Rat primary afferent and sensory ganglia neurons--trigeminal ganglia (Vg), and dorsal root ganglia (DRG): C(2), C(5), T(5), L(5)--were examined using paraffin-embedded, slide-bound tissue sections reacted with specific primary antibodies for rat 5-HT(1B, 1D) and (1F) receptors in a peroxidase-based immunohistochemical method. Immunoreactivity specific for all three serotonergic receptor subtypes was demonstrated in the five peripheral nervous system regions examined and quantitated. There was a good agreement for 5-HT(1B) and 5-HT(1D) receptors to that previously demonstrated in Vg and DRG L(5), while this was the first characterisation for 5-HT(1F) receptor in any of the five regions, as well as for 5-HT(1B) and <em>5HT</em>(1D) receptors in DRG C(2), C(5) and T(5). In summary, all three 5-HT receptors are equally represented in Vg and the DRGs examined. We conclude that the triptans are theoretically able to bind to receptors at each level of the peripheral neuraxis without any apparent anatomical preference for the head.

To create potentially superior aids to smoking cessation and/or antidepressants and to elucidate bupropion's possible mechanisms of action(s), 23 analogues based on its active hydroxymetabolite (2S,3S)-4a were synthesized and tested for their abilities to inhibit monoamine uptake and nAChR subtype activities in vitro and acute effects of nicotine in vivo. The 3',4'-dichlorophenyl [(+/-)-4n], naphthyl (4r), and 3-chlorophenyl or 3-propyl analogues 4s and 4t, respectively, had higher inhibitory potency and/or absolute selectivity than (2S,3S)-4a for inhibition of DA, NE, or <em>5HT</em> uptake. The 3'-fluorophenyl, 3'-bromophenyl, and 4-biphenyl analogues 4c, 4d, and 4l, respectively, had higher potency for antagonism of alpha4beta2-nAChR than (2S,3S)-4a. Several analogues also had higher potency than (2S,3S)-4a as antagonists of nicotine-mediated antinociception in the tail-flick assay. The results suggest that compounds acting via some combination of DA, NE, or <em>5HT</em> inhibition and/or antagonism of alpha4beta2-nAChR can potentially be new pharmacotherapeutics for treatment of nicotine dependence.

The 5-hydroxytryptamine (<em>5HT</em>) precursors tryptophan and 5-hydroxytryptophan had no significant effect on the behavior of rats in the formalin test when given by themselves. However, both compounds significantly attenuated the analgesic effect of morphine in the formalin test. The <em>5HT</em> antagonist methysergide enhanced the antinociceptive effect of morphine but systemic <em>5HT</em> had no effect. Assays of whole brain and spinal cord indoles revealed different patterns as a result of tryptophan or 5-hydroxytryptophan loading. The effect common to both treatments was an increase in brain <em>5HT</em>. There was no effect of morphine on any measure. Formalin injection by itself did not alter indole levels in the brain or spinal cord. Our results, taken in conjunction with previous work, suggest that 1) <em>5HT</em> in the spinal cord does not influence pain perception in the formalin test and 2) <em>5HT</em> in the brain can antagonize morphine analgesia in the formalin test. We conclude that there may be circumstances in which the use of <em>5HT</em> precursors for clinical pain management may be contraindicated.

The action of 5-hydroxytryptamine (<em>5HT</em>) on nicotinic acetylcholine receptor (nAChR) channels was investigated in mouse myotubes, human cloned TE671/RD cells, and Xenopus laevis oocytes. The decay of the ACh-activated whole-cell currents was reversibly accelerated in the presence of <em>5HT</em> (10(-5) to 10(-3) M), in a dose-dependent manner. <em>5HT</em> also reduced the size and accelerated the decay of currents elicited by ACh in Xenopus oocytes injected with mRNA extracted from C2 myotubes or Torpedo electroplaques, or oocytes injected with cloned mouse muscle AChR subunit mRNAs. The effect of <em>5HT</em> was promptly reversed after washout, or by depolarizing the oocyte beyond -10 mV. In patch-clamp recordings from myotubes, bath-application of <em>5HT</em> did not exert an indirect influence on the ACh-activated channels within the patch membrane. In contrast, when the patch membrane was exposed to <em>5HT</em> (10(-6) M), ACh unit responses appeared as bursts of short pulses. It is concluded that the regulation of ACh responses by <em>5HT</em> results from a fast noncompetitive blocking action of nAChR-channels. These results show that ligand-gated channels, activated by their specific neurotransmitter, may be regulated by a different neurotransmitter through a direct action on the receptor molecule.

An understanding of the basic anatomy and physiology of the cranial circulation facilitates the assessment and management of patients with headache, particularly vascular-type headaches, such as migraine. At the very least, all pain is perceived and processed in the brain. With migraine it is likely that the fundamental problem and its clinical expression are driven by the CNS; thus study of the brain regarding headache is warranted. As therapy evolves during the 1900s, such an understanding will be necessary, as new and highly specific receptor-targeted compounds allow treatment and improvement of headache in many patients. Since writing this article, the nomenclature for serotonin (<em>5HT</em>) receptors has changed so that any reference herein to <em>5HT</em>ID alpha is now <em>5HT</em>ID and <em>5HT</em>ID beta is now <em>5HT</em>I beta. This change in nomenclature is discussed in Martig PR, Hoyer D, Humphrey PPA, et al: Alignment of receptor nomenclature with the human genome: Classification of <em>5HT</em>-1 beta and <em>5HT</em>-1D receptor subtypes. Trends in the Pharmacological Sciences 17:103, 1996.

Medullary respiratory neurons are influenced by a variety of neuromodulators, but there is a lack of information about the specific intracellular signal pathways involved. In this report we describe the modulatory effects of the cyclic adenosine-triphosphate (cAMP)-dependent protein kinase and of protein kinase C pathways on voltage- and ligand-controlled ionic conductances and demonstrate their functional significance in regulating the excitability of medullary respiratory neurons of the vivo cat. Evidence is presented that PKA and PKC pathways are persistently activated. PKA regulates current flow through persistently activated and GABAB receptor-controlled potassium channels as well as GABAA receptor-controlled chloride channels. PKC also depresses persistent potassium currents but it potentiates excitatory and inhibitory synaptic currents. The clinical significance of these intracellular signal pathways is demonstrated in a case of a child suffering from apneustic breathing, who was successfully treated with a <em>5HT</em>-1A receptor agonist.

Hormonal responses to oral paroxetine were examined in a group of healthy subjects. The calcium response to serotonin (5-hydroxytryptamine, <em>5HT</em>), mediated by platelet <em>5HT</em>2A, was also measured. Paroxetine elicited a cortisol response that was directly correlated with the magnitude of platelet calcium response. The cortisol response was also correlated with the trait of impulsivity. These results suggest that paroxetine may be a useful probe in studies of serotonergic systems.

A gene for serotonin <em>5HT</em>-2 receptor (HTR2) is assigned to human chromosome 13 by somatic cell hybrids and to region 13q14-q21 by in situ hybridization. It is assigned to mouse chromosome 14 by somatic cell hybrid analysis.

The action of serotonin (<em>5HT</em>) was investigated on guinea-pig isolated ileum. Low concentrations of <em>5HT</em> (10(-8) - 2.5 x 10(-7) mol x 1(-1)) produced contractile responses which were abolished by atropine and by methionine enkephalin but not by methysergide. Higher concentrations of <em>5HT</em> (5 x 10(-7) - 5 x 10(-6) mol x 1(-1)) produced contractions which were inhibited by methysergide. The atropine-sensitive response was also abolished following desensitization of preparations to substance P and by the substance P antagonist [D-Pro2,D-Phe7,D-Trp9]SP. It was concluded that the atropine-sensitive response to <em>5HT</em> is mediated by substance P.

Impulsive individuals often display an aversion to waiting for rewards. Delay aversion can be quantified in rats in a delayed reward task, in which animals choose between an immediately available, small reward, and a large reward available after a delay. In previous research conducted at our laboratory and in literature, positive correlations between delay aversion and aggression, substance abuse and persistence during extinction of conditioned responses were found. The correlations suggest a possible shared pharmacology. Therefore, we tested drugs with known effects on these behaviors for possible effects on delay aversion: the dopamine D(3)-receptor agonist 7-OH-DPAT, the 5-HT(1A)-receptor agonist flesinoxan, the <em>5HT</em>(1A/1B)-receptor agonist eltoprazine, and the NMDA-receptor agonist d-cycloserine. The results show that 7-OH-DPAT slightly decreased choice for the large reward. Flesinoxan disrupted task execution by lowering choice for the large reward even at a delay of 0 s. Eltoprazine slightly increased choice for the large reward, but the 5-HT(1B)-antagonist GR127935 had no effect. Administration of D-cycloserine also had no effect on choice behavior. The data suggest the dopamine D(3)-receptor and the 5-HT(1B)-receptor are interesting targets for treating delay aversion impulsivity. These targets were correctly predicted by the positive correlation between delay aversion and aggressive behavior and the intimate links between delay aversion and substance abuse disorders.

BACKGROUND

Various studies have demonstrated a modulating role for serotonin in attention. Selective serotonin inhibitors have repeatedly been shown to impair performance in sustained attention tasks.

OBJECTIVE

To assess the contribution of serotonin reuptake inhibition and specific blockade of the pre-synaptic 5-HT(1a) receptor and the 5-HT(2a) receptor to deficits in attention.

METHODS

The study was conducted according to a randomized, double-blind, placebo controlled, four-way crossover design including 16 healthy volunteers. Treatments consisted of oral administration of the selective serotonin reuptake inhibitor (SSRI) escitalopram 20 mg + placebo; escitalopram 20 mg + ketanserin (5-HT(2a) antagonist), 50 mg; escitalopram 20 mg + pindolol (5-HT(1a) antagonist) 10 mg; and placebo + placebo on four separate days. A range of performance tasks were conducted to assess the subjects' attention and motor functions.

RESULTS

Escitalopram administered alone impaired tracking performance in a divided attention task. The combination of escitalopram and pindolol and escitalopram and ketanserin impaired divided attention as compared to placebo. In addition, escitalopram and ketanserin impaired sustained attention. Divided attention impairment observed after combined treatments did not significantly differ from impairments after escitalopram alone. Sustained attention impairment observed after combined escitalopram and ketanserin significantly differed from escitalopram alone.

CONCLUSIONS

<em>5HT</em>(1a) blockade hardly affected SSRI effects on attention. Additional <em>5HT</em>(2a) blockade, however, produced impairments of sustained attention and motor impulse control.

In Xenopus oocytes injected with rat brain RNA, serotonin (<em>5HT</em>) and acetylcholine (ACh) evoke membrane responses through a common biochemical cascade that includes activation of phospholipase C, production of inositol 1,4,5-trisphosphate (Ins1,4,5-P3), release of Ca2+ from intracellular stores, and opening of Ca-dependent Cl- channels. The response is a Cl- current composed of a transient component (<em>5HT</em>1 or ACh1) and a slow, long-lasting component (<em>5HT</em>2 or ACh2). Here we show that only the fast, but not the slow, component of the response is subject to desensitization that follows a previous application of the transmitter. The recovery of <em>5HT</em>1 from desensitization is biphasic, suggesting the existence of two types of desensitization: short-term desensitization (STD), which lasts for less than 0.5 h; and long-term desensitization (LTD) lasting for up to 4 h. The desensitization between <em>5HT</em> and ACh is heterologous and long-lasting. We searched for (a) the molecular target and (b) the cause of desensitization. (a) Pre-exposure to <em>5HT</em> does not reduce the response evoked by intracellular injection of Ca2+ and by Ca2+ influx. Cl- current evoked by intracellular injection of Ins1,4,5-P3 was reduced shortly after application of <em>5HT</em>, but fully recovered 30 min later. Thus, the Cl- channel is not a target for desensitization. Neither Ins1,4,5-P3 receptor nor the Ca2+ store is a target of LTD but they may be the targets of STD. (b) Ca2+ injection did not inhibit the <em>5HT</em> response, suggesting that Ca2+ is not a sole cause of STD or LTD.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of central serotonin <em>5HT</em>2 receptors is believed to be the primary mechanism whereby lysergic acid diethylamide (LSD) and other hallucinogens induce psychoactive effects. This hypothesis is based on extensive radioligand binding and electrophysiological and behavioral studies in laboratory animals. However, the pharmacological profiles of <em>5HT</em>2 and <em>5HT</em>1C receptors are similar, making it difficult to distinguish between effects due to activation of one or the other receptor. For this reason, it was of interest to investigate the interaction of LSD with <em>5HT</em>1C receptors. Agonist-stimulated phosphoinositide hydrolysis in rat choroid plexus was used as a direct measure of <em>5HT</em>1C receptor activation. (+)LSD potently stimulated phosphoinositide hydrolysis in intact choroid plexus and in cultures of choroid plexus epithelial cells, with EC50 values of 9 and 26 nM, respectively. The effect of (+)LSD in both systems was blocked by <em>5HT</em> receptor antagonists with an order of activity consistent with interaction at <em>5HT</em>1C receptors. Neither (+)-2-bromo-LSD nor lisuride, two nonhallucinogenic congeners of LSD, were able to stimulate <em>5HT</em>1C receptors in cultured cells or intact choroid plexus. In contrast, lisuride, like (+)LSD, is a partial agonist at <em>5HT</em>2 receptors in cerebral cortex slices and in NIH 3T3 cells transfected with <em>5HT</em>2 receptor cDNA. The present finding that (+)LSD, but not its nonhallucinogenic congeners, is a <em>5HT</em>1C receptor agonist suggests a possible role for these receptors in mediating the psychoactive effects of LSD.

The distribution of serotonin (<em>5HT</em>) neurons was investigated in the brainstem of 8 human fetuses ranging in age from 15 to 27 weeks of gestation. We conducted the peroxidase-antiperoxidase (PAP) immunohistochemical technique using antiserotonin serum to detect the cell bodies of <em>5HT</em>-containing neurons. Positively stained <em>5HT</em> neurons were clearly demonstrated in the brainstem of all fetuses examined. They varied in shape, showing round to oval cell bodies with unipolar, bipolar, or multipolar processes. A large number of <em>5HT</em> neurons were located in the midline raphe nuclei. In addition, numerous <em>5HT</em> neurons were observed widely in the other tegmental areas. The nuclei containing <em>5HT</em> neurons were listed according to the terminology by Olszewski and Baxter for human brainstem, and an atlas was given. The distribution of <em>5HT</em> neurons in the raphe nuclei of human fetuses was essentially similar to those of many mammals already reported. However, the lateral extension of <em>5HT</em> neurons to the other tegmental areas beyond the midline raphe nuclei was much greater in human fetuses compared to other mammals.

A recent report demonstrated that JC virus (JCV) employs serotonin receptor 2A (<em>5HT</em>(2A)R) to infect the glial cells. To assess the ability of a potent <em>5HT</em>(2A)R blocker, risperidone, to inhibit JCV infection, the authors treated primary human fetal glial (PHFG) cells in vitro with risperidone for 24 h and inoculated with JCV(Mad1). There was no significant difference in JCV genome copies or mRNA transcripts and protein expression in treatment-naive and risperidone-treated PHFG cells. These data indicate that risperidone does not inhibit JCV(Mad1) attachment, internalisation, and replication in PHFG cells, and <em>5HT</em>(2A)R blockers may not be effective in treating progressive multifocal leukoencephalopathy (PML).

BACKGROUND

We have recently reported dynamic circadian rhythms of serotonin (5-HT, 5-hydroxytryptamine) output in the pineal gland of rat, which precedes the onset of N-acetylserotonin (NAS) and melatonin secretion at night. The present study was aimed at investigating in detail the relationship between 5-HT onset (<em>5HT</em>-on) and melatonin onset (MT-on) in multiple strains of rats and comparing them with those of hamsters.

METHODS

Animals were maintained in chambers equipped with light (250 lux at cage levels) and ventilation in a temperature-controlled room. Following surgical implantation of a microdialysis probe in the pineal gland, animals were individually housed for on-line pineal microdialysis and for automated HPLC analysis of 5-HT and melatonin. Animals were under a light-dark cycle of 12:12 h for the duration of the experiments.

RESULTS

All animals displayed dynamic 5-HT and melatonin rhythms at night. In all cases, <em>5HT</em>-on (taken at 80% of the daily maximum levels) preceded MT-on (taken at 20% of the daily maximum levels). Within the same animals, <em>5HT</em>-on as well as MT-on across multiple circadian cycles exhibited minimum variations under entrained conditions. Large inter-individual variations of both <em>5HT</em>-on and MT-on were found in outbred rats and hamsters under entrained conditions. In comparison, inbred rats displayed very small individual variations of <em>5HT</em>-on and MT-on. Importantly, we have uncovered a species-specific relationship of <em>5HT</em>-on and MT-on. <em>5HT</em>-on of rats, regardless of the strain, preceded MT-on of the same rats by 50 min. In contrast, <em>5HT</em>-on of hamsters led MT-on by as much as 240 min. Thus, while a constant relationship of <em>5HT</em>-on and MT-on exists for animals of the same species, the relative timings of <em>5HT</em>-on and MT-on differ between animals of different species.

CONCLUSIONS

These results suggest that both 5-HT and melatonin could serve as reliable markers of the circadian clock because of their day-to-day precision of onset timings within the same animals or within individuals of the same strain or same species. The results also demonstrate that data for MT-on cannot be compared directly between different species, and that <em>5HT</em>-on may be a more reliable circadian marker when data from animals of different species are compared.

Efforts to define either a biomarker for irritable bowel syndrome (IBS) or a valid animal model have proven disappointing. The aims of this study were to determine if buspirone stimulates prolactin release through the 5-hydroxytryptamine (<em>5HT</em>)1a receptor and whether this response is altered in patients with IBS and in the rat maternal separation model. Buspirone (30 mg) was used to stimulate prolactin release in 40 patients with IBS and in 40 healthy controls. In study 1, 10 IBS patients and 10 controls underwent pretreatment with pindolol (<em>5HT</em>1a antagonist) or placebo followed by buspirone. In study 2, 30 patients with IBS and 30 healthy controls had prolactin release stimulated by buspirone. Maternally separated and nonseparated rats were also treated with buspirone and prolactin monitored. Serotonin metabolites were measured together with the expression of the <em>5HT</em>1a and serotonin transporter (SERT) gene. Pindolol produced a dose-dependent decrease in the buspirone prolactin response. Patients with IBS and maternally separated rats showed an exaggerated release of prolactin in response to buspirone. In the animal model, an increased turnover of <em>5HT</em> was found in the brainstem together with a trend toward increased activity of the SERT gene. In conclusion altered central serotonin responses are found in both IBS and in an animal model.

The effects of GBR 12783, an aryl 1,4-dialk(en)ylpiperazine derivative, were studied on the in vivo and ex vivo neuronal uptake of dopamine (DA), norepinephrine (NE) and serotonin (<em>5HT</em>). The drug inhibited potently (IC50 = 1.8 nM) and competitively the [3H]DA uptake by rat striatal synaptosomes. It produced significant [14C]DA release only at much higher concentrations (in the micromolar range). Depending on the animal species (rat or mouse) and the experimental conditions, GBR 12783 was 18-90 times and 85-300 times less effective against NE and <em>5HT</em> uptake respectively than against DA uptake. In synaptosomes preloaded with [3H]DA, GBR 12783 added to the superfusion medium prevented the (+)amphetamine-induced DA release. The total binding of [3H]GBR 12783 to a membranal fraction prepared from striatum was lower than the binding to a synaptosomal fraction, suggesting its entry in synaptosomes. In addition, the concentration-dependent release of [3H]DA produced by GBR 12783 from a striatal vesicular fraction may account for the synaptosomal DA release promoted by micromolar concentrations of the drug. In ex vivo experiments, the ID50 for DA uptake inhibition (30 min after i.p. administration) was 8.1 mg/kg. After a dose of 10 mg/kg i.p., the striatal DA uptake inhibition occurred quickly (less than 10 min) and was long-lasting (greater than 5 h). The specificity of the drug for the DA uptake relative to NE and <em>5HT</em> uptakes was also seen after i.p. administration of GBR 12783.