Irritable bowel syndrome (IBS) is common and can be disabling. Several drugs that modulate serotonin (<em>5HT</em>) and other neurotransmitters in the gut (neuroenteric modulators) have either become available or are in development, but progress has been slowed by toxicity. Blockade of <em>5HT</em>(3) receptors slows colonic transit, increases fluid absorption and increases left colon compliance. Alosetron, a potent <em>5HT</em>(3) receptor antagonist, has, in women but not in men, a clinically significant but modest therapeutic gain over placebo in the relief of abdominal pain and discomfort and bowel-habit disturbance (but not bloating) in diarrhoea-predominant IBS. However, the drug unexpectedly was associated with ischaemic colitis and, very rarely, severe constipation-induced complications, and alosetron has been withdrawn. Cilansetron may have similar efficacy in men and women. <em>5HT</em>(4) receptor stimulation results in accelerated colonic transit, and tegaserod, a partial <em>5HT</em>(4) receptor agonist, has modest but clinically significant advantage over placebo in constipation-predominant IBS; the benefit seems to be confined to females. Long-term published data are lacking and safety concerns have been raised. Prucalopride, a full <em>5HT</em>(4) agonist that has been promising in idiopathic chronic constipation, may also be limited by toxicity. Other <em>5HT</em> receptor antagonists and agonists are under development for IBS. However, for modulators of single receptors to achieve a substantial therapeutic gain, and to do so safely, drug targets based on the pathophysiology of IBS need to be better defined.

Using a strategy based on nucleotide sequence homology between genes encoding receptors that interact with guanine nucleotide-binding proteins, we have isolated Drosophila genomic and cDNA clones encoding a functional serotonin receptor (<em>5HT</em>-dro receptor). This protein is expressed predominantly in Drosophila heads and exhibits highest homology with the human <em>5HT</em>1A receptor. The predicted structure of the <em>5HT</em>-dro receptor reveals two unusual features: (i) eight putative transmembrane domains instead of the expected seven and (ii) a Gly-Ser repeat that is a potential glycosaminoglycan attachment site. When stably introduced into mouse NIH 3T3 cells, the <em>5HT</em>-dro receptor activates adenylate cyclase in response to serotonin and is inhibited by serotonin receptor antagonists such as dihydroergocryptine. The <em>5HT</em>-dro receptor or closely related receptors might be responsible for the serotonin-sensitive cyclase that has been suggested to play a role in learning and modulation of circadian rhythm in a number of invertebrate systems.

We have synthesized several derivative of dl-threo-methylphenidate (Ritalin) bearing substituents on the phenyl ring. IC50 values for binding these compounds to rat brain monoamine transporters were assessed using [3H]WIN 35,428 (striatal membranes, dopamine transporters, DAT), [3H]nisoxetine (frontal cortex membranes, norepinephrine transporters, NET) and [3H]paroxetine (brain stem membranes, <em>5HT</em> transporters, <em>5HT</em>T). Affinities (1/Ki) decreased in the order: DAT>> NET>>) <em>5HT</em>T. 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 IC50 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 o-bromomethylphenidate did not bind to the DAT (IC50>> 50,000 nM). Affinities at the dopamine and norepinephrine transporters for substituted methylphenidate derivatives were well correlated (r2=0.90). Abilities of several methylphenidate derivatives to inhibit [3H]dopamine uptake in striatal synaptosomes corresponded well with inhibition of [3H]WIN 35, 428 binding. None of the compounds examined exhibited significant affinity to dopamine D1 or D2 receptors (IC50>> 500 or 5,000 nM, respectively), as assessed by inhibition of binding of [3H]SCH 23390 or [123I]epidepride, respectively, to striatal membranes.

Fetal or neonatal chlorpyrifos (CPF) exposure affects serotonin (<em>5HT</em>) synaptic function and related behaviors in adulthood. We examined the critical period and dose threshold for effects on <em>5HT</em> and assessed their emergence in adolescence. Pregnant rats were given CPF (1 or 5mg/kg/day) from gestational days (GD)17-20 or GD9-12 and <em>5HT</em> levels and turnover were evaluated on postnatal day 30; the lower dose lies below the threshold for inhibition of fetal brain cholinesterase. GD17-20 exposure increased <em>5HT</em> turnover in brain regions containing either <em>5HT</em> projections or cell bodies, with a preferential effect in males. Shifting the exposure to GD9-12 also augmented <em>5HT</em> activity but only in the cerebral cortex and without sex preference. Similar, but lesser effects were seen for dopamine turnover in the same regions. These results indicate that, in a critical developmental period, apparently subtoxic exposures to CPF produce long-term activation of <em>5HT</em> systems.

We have recently developed antisera which recognize epitopes of the cloned delta-opioid receptor (DOR; Dado et al., 1993). In the present report we have further characterized these antisera, and raised additional antisera in rats. We used these antisera to determine the distribution of DOR-like immunoreactivity (-Ll) in rat spinal cord and brainstem in relation to serotoninergic, noradrenergic, and enkephalinergic neurons. We found DOR-Ll in fibers and varicosities distributed throughout the spinal cord gray matter, with highest densities in the superficial dorsal horn, in autonomic regions, around the central canal as well as in the ventral horn motor nuclei. In the brainstem a dense innervation of DOR-immunoreactive (-IR) fibers was found in several nuclei such as spinal trigeminal nuclei, midline raphe nuclei, parabrachial nuclei, periaqueductal gray matter (PAG), interpeduncular nucleus, ans substantia nigra. A group of DOR-positive cells was seen in the laterodorsal tegmental nucleus. In addition, a few DOR-IR cell bodies were demonstrated in the parabrachial nuclei, interpeduncular nucleus, PAG, and superior and inferior colliculi as well as around the central canal in the spinal cord. All DOR-positive cells showed a punctuate staining pattern within the cytoplasm of the cell body and in primary dendrites. No plasma membrane staining of cells or dendrites could be demonstrated using the DOR antisera. Double-labeling experiments for DOR and 5-hydroxytryptamine (<em>5HT</em>, serotonin) revealed that some <em>5HT</em>-IR neurons in the raphe complex were surrounded by DOR-IR fibers. In the spinal cord a high degree of coexistence was found between DOR and <em>5HT</em> in nerve fibers and varicosities in the neuropil around the motoneurons and in lamina V of the dorsal horn. In autonomic regions of the spinal cord, a low degree of colocalization was seen between DOR and <em>5HT</em>; in the superficial dorsal horn no coexistence was found. Tyrosine hydroxylase (TH)-positive neurons in the brainstem (in the A5 area, locus coeruleus, and A7 area) were apposed by DOR-positive fibers. However, no coexistence could be seen between DOR and TH in any part of the spinal cord. A close relation, but no coexistence, was observed between DOR- and enkephalin (ENK)-IR fibers in the spinal cord ventral horn; in the intermediolateral nucleus a low degree of colocalization was observed. Thus, a delta-opioid receptor may affect the activity of descending serotoninergic and noradrenergic neurons by means of modulating the release of neurotransmitters from afferents to these neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Constipation disproportionately affects older adults, with a prevalences of 50% in community-dwelling elderly and 74% in nursing-home residents. Loss of mobility, medications, underlying diseases, impaired anorectal sensation, and ignoring calls to defecate are as important as dyssynergic defecation or irritable bowel syndrome in causing constipation. Detailed medical history on medications and co-morbid problems, and meticulous digital rectal examination may help identify causes of constipation. Likewise, blood tests and colonoscopy may identify organic causes such as colon cancer. Physiological tests such as colonic transit study with radio-opaque markers or wireless motility capsule, anorectal manometry, and balloon expulsion tests can identify disorders of colonic and anorectal function. However, in the elderly, there is usually more than one mechanism, requiring an individualized but multifactorial treatment approach. The management of constipation continues to evolve. Although osmotic laxatives such as polyethylene glycol remain mainstay, several new agents that target different mechanisms appear promising such as chloride-channel activator (lubiprostone), guanylate cyclase agonist (linaclotide), <em>5HT</em>(4) agonist (prucalopride), and peripherally acting mu-opioid receptor antagonists (alvimopan and methylnaltrexone) for opioid-induced constipation. Biofeedback therapy is efficacious for treating dyssynergic defecation and fecal impaction with soiling. However, data on efficacy and safety of drugs in elderly are limited and urgently needed.

Palonosetron is the only 5-HT(3) receptor antagonist approved for the treatment of delayed chemotherapy-induced nausea and vomiting (CINV) in moderately emetogenic chemotherapy. Accumulating evidence suggests that substance P (SP), the endogenous ligand acting preferentially on neurokinin-1 (NK-1) receptors, not serotonin (5-HT), is the dominant mediator of delayed emesis. However, palonosetron does not bind to the NK-1 receptor. Recent data have revealed cross-talk between the NK-1 and <em>5HT</em>(3) receptor signaling pathways; we postulated that if palonosetron differentially inhibited NK-1/5-HT(3) cross-talk, it could help explain its efficacy profile in delayed emesis. Consequently, we evaluated the effect of palonosetron, granisetron, and ondansetron on SP-induced responses in vitro and in vivo. NG108-15 cells were preincubated with palonosetron, granisetron, or ondansetron; antagonists were removed and the effect on serotonin enhancement of SP-induced calcium release was measured. In the absence of antagonist, serotonin enhanced SP-induced calcium-ion release. After preincubation with palonosetron, but not ondansetron or granisetron, the serotonin enhancement of the SP response was inhibited. Rats were treated with cisplatin and either palonosetron, granisetron, or ondansetron. At various times after dosing, single neuronal recordings from nodose ganglia were collected after stimulation with SP; nodose ganglia neuronal responses to SP were enhanced when the animals were pretreated with cisplatin. Palonosetron, but not ondansetron or granisetron, dose-dependently inhibited the cisplatin-induced SP enhancement. The results are consistent with previous data showing that palonosetron exhibits distinct pharmacology versus the older 5-HT(3) receptor antagonists and provide a rationale for the efficacy observed with palonosetron in delayed CINV in the clinic.

Fetal or neonatal exposure to chlorpyrifos (CPF) or related organophosphate pesticides leads to abnormalities of brain cell development, synaptic function, and behavior. Recent studies in rats indicate profound effects on serotonin (<em>5HT</em>) systems that originate during CPF exposure and that are still present at 2 months posttreatment in the young adult. To determine if these changes are permanent, we administered 1 mg/kg of CPF daily to neonatal rats on postnatal days 1-4, a regimen devoid of systemic toxicity, and examined <em>5HT</em> synaptic markers at 5 months of age: radioligand binding to <em>5HT</em>1A and <em>5HT</em>2 receptors and to the <em>5HT</em> transporter. There were global elevations in all three synaptic proteins, with pronounced sex selectivity (effects on males>females) and a regional hierarchy of effects, viz. striatum>midbrain approximately brainstem>cerebral cortex. Because there is a normal sex disparity for <em>5HT</em> synaptic proteins, with females having higher values than males, the increase caused by CPF exposure in males completely eliminated this difference. Our findings at 5 months of age replicate those seen in young adulthood and strongly suggest that the effects of neonatal CPF exposure on <em>5HT</em> systems are permanent.

Pavlovian olfactory learning in Drosophila produces two genetically distinct forms of intermediate-term memories: anesthesia-sensitive memory, which requires the amnesiac gene, and anesthesia-resistant memory (ARM), which requires the radish gene. Here, we report that ARM is specifically enhanced or inhibited in flies with elevated or reduced serotonin (<em>5HT</em>) levels, respectively. The requirement for <em>5HT</em> was additive with the memory defect of the amnesiac mutation but was occluded by the radish mutation. This result suggests that <em>5HT</em> and Radish protein act on the same pathway for ARM formation. Three supporting lines of evidence indicate that ARM formation requires <em>5HT</em> released from only two dorsal paired medial (DPM) neurons onto the mushroom bodies (MBs), the olfactory learning and memory center in Drosophila: (i) DPM neurons were <em>5HT</em>-antibody immunopositive; (ii) temporal inhibition of <em>5HT</em> synthesis or release from DPM neurons, but not from other serotonergic neurons, impaired ARM formation; (iii) knocking down the expression of d<em>5HT</em>1A serotonin receptors in α/β MB neurons, which are innervated by DPM neurons, inhibited ARM formation. Thus, in addition to the Amnesiac peptide required for anesthesia-sensitive memory formation, the two DPM neurons also release <em>5HT</em> acting on MB neurons for ARM formation.

The glycine receptor (GlyR) Cl(-) channel belongs to the cysteine-loop family of ligand-gated ion channel receptors. It is best known for mediating inhibitory neurotransmission in motor and sensory reflex circuits of the spinal cord, although glycinergic synapses are also present in the brain stem, cerebellum and retina. Extrasynaptic GlyRs are widely distributed throughout the central nervous system and they are also found in sperm and macrophages. A total of 5 GlyR subunits (alpha1-4 and beta) have been identified. Embryonic receptors comprise alpha2 homomers whereas adult receptors comprise predominantly alpha beta heteromers in a 2:3 stoichiometry. Notably, the alpha3 subunit is present in synaptic GlyRs that mediate inhibitory neurotransmission onto spinal nociceptive neurons. These receptors are specifically inhibited by inflammatory mediators, implying a role for alpha3-containing GlyRs in inflammatory pain sensitisation. Because molecules that increase GlyR current may have clinical potential as muscle relaxant and peripheral analgesic drugs, this review focuses on the molecular pharmacology of GlyR potentiating substances. Of all GlyR potentiating substances identified to date, we conclude that <em>5HT</em>(3)R antagonists such as tropisetron offer the most promise as therapeutic lead compounds. However, one problem is that that virtually all known GlyR potentiating compounds, including tropisetron analogues, lack specificity for the GlyR. Another is that almost nothing is known about the pharmacological properties of alpha3-containing GlyRs, which is the subtype of choice for targeting by novel antinociceptive agents. These issues need to be addressed before GlyR-specific therapeutics can be developed.

Antibodies made against serotonin (<em>5HT</em>) were used to identify the serotonin neuronal system in the developing and adult nervous system of Drosophila melanogaster. The <em>5HT</em> neuronal pattern is composed of a small number of neurons, 84 in larvae and 106 in adults, distributed in clusters composed of one to five neurons in the CNS; <em>5HT</em> immunoreactive (<em>5HT</em>-IR) neurons appear to be predominantly intrasegmental interneurons; however, intersegmental <em>5HT</em>-IR fibers are observed and at least some neurons send peripheral fibers. Acquisition of <em>5HT</em> immunoreactivity in the CNS occurs late in embryogenesis, by 16-18 hours, and most if not all the <em>5HT</em> neurons appear to persist into adulthood. During early metamorphosis, the intensity of <em>5HT</em>-IR neuropil transiently decreases. Other changes in the CNS during this period are reflected in the appearance of two new <em>5HT</em> clusters and <em>5HT</em>-IR neuropil in the developing optic lobes. Comparison of the <em>5HT</em>-IR pattern with other transmitter systems in Drosophila as well as comparison of the <em>5HT</em>-IR pattern within different insect species is presented.

Methamphetamine (m-AMPH) administration injures both striatal dopaminergic terminals and certain nonmonoaminergic cortical neurons. Fluoro-Jade histochemistry was used to label cortical cells injured by m-AMPH in order to identify factors that contribute to the cortical cell body damage. Rats given four injections of m-AMPH (4 mg/kg) at 2-h intervals showed hyperthermia (mean = 40.0 +/- 0.10 degrees C) and increased behavioral activation relative to animals given saline (SAL). Three days later, m-AMPH-treated animals showed indices of injury to striatal DA terminals (depletion of tyrosine hydroxylase immunoreactivity) and parietal cortical cell bodies (appearance of Fluoro-Jade stained cells). Pretreatment with a dopamine (DA) D1, D2, or N-methyl-D-aspartate (NMDA) receptor antagonist, or administration of m-AMPH in a 4 degrees C environment, prevented or attenuated m-AMPH-induced hyperthermia, behavioral activation, and injury to striatal DA terminals and parietal cortical cell bodies. Animals pretreated with a DA transport inhibitor prior to m-AMPH showed hyperthermia, behavioral activation, and parietal cortical cell body injury, but they did not show striatal DA terminal injury. Pretreatment with a <em>5HT</em> transport inhibitor failed to prevent m-AMPH-induced damage to striatal DA terminals or parietal cortical cell bodies. Animals given four injections of SAL in a 37 degrees C environment became hyperthermic, but showed no injury to striatal DA terminals or cortical cell bodies. The ability of the DA transport inhibitor to block m-AMPH-induced striatal DA damage, but not cortical injury, and the inability of hyperthermia alone to cause the cortical cell body injury suggests that m-AMPH-induced behavioral activation and hyperthermia may both be necessary for the subsequent parietal cortical cell body damage.

Vesicular monoamine transporters (VMATs) mediate the transport of dopamine (DA), serotonin (<em>5HT</em>), and other monoamines into secretory vesicles. The regulation of mammalian VMAT and the related vesicular acetylcholine transporter (VAChT) has been proposed to involve membrane trafficking, but the mechanisms remain unclear. To facilitate a genetic analysis of vesicular transporter function and regulation, we have cloned the Drosophila homolog of the vesicular monoamine transporter (dVMAT). We identify two mRNA splice variants (DVMAT-A and B) that differ at their C-terminus, the domain responsible for endocytosis of mammalian VMAT and VAChT. DVMAT-A contains trafficking motifs conserved in mammals but not C. elegans, and internalization assays indicate that the DVMAT-A C-terminus is involved in endocytosis. DVMAT-B contains a divergent C-terminal domain and is less efficiently internalized from the cell surface. Using in vitro transport assays, we show that DVMAT-A recognizes DA, <em>5HT</em>, octopamine, tyramine, and histamine as substrates, and similar to mammalian VMAT homologs, is inhibited by the drug reserpine and the environmental toxins 2,2,4,5,6-pentachlorobiphenyl and heptachlor. We have developed a specific antiserum to DVMAT-A, and find that it localizes to dopaminergic and serotonergic neurons as well as octopaminergic, type II terminals at the neuromuscular junction. Surprisingly, DVMAT-A is co-expressed at type II terminals with the Drosophila vesicular glutamate transporter. Our data suggest that DVMAT-A functions as a vesicular transporter for DA, <em>5HT</em>, and octopamine in vivo, and will provide a powerful invertebrate model for the study of transporter trafficking and regulation.

OBJECTIVE

The NK1-receptor antagonist MK-869 (L-754,030) has demonstrated antiemetic activity in humans receiving chemotherapy. Objectives of the present trial included the first assessment of oral MK-869 plus dexamethasone compared with a <em>5HT</em>(3) antagonist plus dexamethasone for prevention of acute and delayed emesis after high-dose cisplatin. Furthermore, the study sought to confirm that addition of MK-869 to a <em>5HT</em>(3) antagonist plus dexamethasone was more effective than just the <em>5HT</em>(3) antagonist plus dexamethasone for prevention of acute and delayed emesis.

METHODS

This multicenter, double-blind, parallel-group trial in 351 cisplatin-naïve patients evaluated prevention of acute (0 to 24 hours) and delayed emesis (primary efficacy parameter; days 2 to 5) after cisplatin >> or =70 mg/m(2)). Patients were randomized to four groups (I to IV) (n = number randomized; number evaluable): granisetron (10 microg/kg intravenously) pre-cisplatin followed by placebo on days 2 to 5 (group I) (n = 90; 90); granisetron and MK-869 (400 mg PO [by mouth]) pre-cisplatin, followed by MK-869 (300 mg PO) on days 2 to 5 (group II) (n = 86; 84); MK-869 (400 mg PO) the evening before and pre-cisplatin, followed by MK-869 (300 mg PO) on days 2 to 5 (group III) (n = 89; 88); or MK-869 (400 mg PO) pre-cisplatin, followed by MK-869 (300 mg PO) on days 2 to 5 (group IV) (n = 86; 84). All patients also received dexamethasone (20 mg PO) before cisplatin. Additional medication was available to treat emesis or nausea at any time.

RESULTS

In the acute period, 57%, 80%, 46%, and 43% of patients were without emesis in groups I, II, III, and IV, respectively (P <.01 for group II v group I). In the delayed period, the proportion of patients without emesis in groups I, II, III, and IV was 29%, 63%, 51%, and 57%, respectively (P <.01 for groups II, III, and IV v group I). The distribution of nausea scores in the delayed period was lower when comparing group II with group I (P <.05 for days 1 to 5 and days 2 to 5). One serious adverse event (dizziness) was rated as possibly related to MK-869.

CONCLUSIONS

Once daily oral administration of MK-869 was effective in reducing delayed emesis and nausea after high-dose cisplatin. However, the combination of the <em>5HT</em>3 antagonist plus dexamethasone was numerically superior to MK-869 plus dexamethasone in reducing acute emesis. Confirming and extending previous findings, the triple combination of a <em>5HT</em>(3) antagonist, MK-869, and dexamethasone provided the best control of acute emesis.

Changes in the cholinergic, serotonergic, noradrenergic, dopaminergic, GABAergic and somatostatinergic neurons were investigated to determine their roles in Alzheimer's disease (AD). Markers for these systems were analyzed in postmortem brain samples from 20 patients with AD and 14 controls. In the CSF study, markers for the cholinergic neurons (choline esterase, ChE) and for the somatostatinergic neurons (somatostatin-like immunoreactivity, SLI) were assayed for 93 and 75 probable AD patients and 29 and 19 controls, respectively. Activity of choline acetyltransferase (CAT) was decreased by 50-85% in four cortical areas and hippocampus in patients with AD, but not in other areas of the brain, indicating a profound deficit in the function of cholinergic projections ascending from the nucleus basalis to the cerebral cortex and hippocampus in AD. Muscarinic receptor binding was reduced by 18% in the frontal cortex but not in other areas of the brain in AD. Serotonin (<em>5HT</em>) concentrations were reduced (by 21-37%) in hippocampal cortex, hippocampus and striatum; and <em>5HT</em> metabolite levels were lowered (by 39-54%) in three cortical areas, thalamus and putamen in AD patients. Concentrations of noradrenaline (NA) were reduced (18-36%) in frontal and temporal cortex and putamen. These data imply that serotonergic and noradrenergic projections are also affected in AD but less than the cholinergic neurons. Dopamine (DA) concentrations in AD patients were reduced by 18-27% in temporal and hippocampal cortex and hippocampus, while HVA, the metabolite of DA, was unaltered. Glutamic acid decarboxylase activity was not altered in AD. SLI was decreased (28-42%) in frontal, temporal and parietal cortex, but not in thalamus and putamen in patients with AD. Frontal tangle scores correlated most strongly with cortical CAT activity reduction and less so with decreases of <em>5HT</em>, NA and DA, indicating a closer correlation with the cholinergic changes and severity of AD than with other neurotransmitter deficiencies. ChE activity and SLI were reduced by 20% and 35%, respectively, in CSF of the whole group of AD patients as compared to the controls. Comparison of CSF findings between four subgroups of dementia severity indicated that the SLI was already reduced in the group of mildest AD (-31%), while ChE activity was not. Although ChE activity in CSF declined in relation to dementia severity, however, the maximal reduction was only modest (-30%). On the other hand, SLI in CSF showed only a slight further reduction (up to -41%) as the dementia become more severe.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic constipation is common among nursing home residents. The aim of this study was to evaluate safety, tolerability and pharmacokinetics of the selective <em>5HT</em>(4) receptor agonist prucalopride in elderly, chronically constipated patients in nursing homes. A multicentre, phase II, randomized, double-blind dose-escalation study in 89 elderly constipated nursing home residents treated with placebo, 0.5, 1 or 2 mg prucalopride once daily for 28 days was analysed. Adverse events, vital signs, ECG, Holter monitor and pharmacokinetics were assessed (Clinicaltrials.gov identifier: NCT00627692). Patients' mean age was 83 years; 88% had a history of cardiovascular diseases. Most frequent adverse events, at least possibly related to prucalopride, were diarrhoea and abdominal pain. Relative to placebo, there were no differences in vital signs, ECG corrected QT interval, ECG morphology parameters, or incidence of supraventricular or ventricular arrhythmias on Holter monitoring. Plasma prucalopride concentrations increased proportionally with administered dose. Prucalopride up to 2 mg once daily for 4 weeks was safe and well-tolerated by constipated elderly patients, with no differences vs placebo in ECG or a range of Holter-monitoring parameters.

The serotonin syndrome is the result of excess stimulation of central nervous 5-hydroxytryptamine (<em>5HT</em>)-1a and <em>5HT</em>-2 receptors. The diagnosis requires a history of exposure to agents active at serotonin receptors and the presence of alterations in mental status, autonomic instability, and neuromuscular abnormalities such as tremor, hyperreflexia, or myoclonus. In this descriptive case series, five cases of serotonin syndrome are reported. All patients gave a history of recent exposure to one or more serotonergic medications, including moclobemide, paroxetine, sertraline, and venlafaxine, with clinical evidence of serotonin syndrome. All patients were administered cyproheptadine (4-8 mg orally) for serotonergic signs. Three had complete resolution of signs within 2 h of administration. Another two had a residual tremor or hyperreflexia following the first dose, which resolved following a repeat dose. There were no adverse outcomes from cyproheptadine use. The role of specific serotonin receptor antagonists such as cyproheptadine in the treatment of the serotonin syndrome remains to be delineated. Its use should be considered an adjunct to supportive care. Currently, it is unknown whether cyproheptadine modifies patient outcome.

Glycogen synthase kinase 3 (GSK3) was recently suggested to be a potential target of psychotropics used in psychiatric illnesses such as schizophrenia and bipolar disorder. Relevant studies have found that antipsychotic drugs regulate GSK3 activity via an increase in either inhibitory serine phosphorylation or amount of GSK3 after acute or subchronic treatment. Recent evidence shows that GSK3 is regulated by dopaminergic or serotonergic systems implicated in the pathophysiology and treatment mechanisms of schizophrenia and bipolar disorder. Therefore, antipsychotics may regulate GSK3 via antagonizing dopaminergic or serotonergic activity. However, the signaling pathway that is involved in GSK3 regulation by dopaminergic or serotonergic systems has not been well established. Haloperidol is a typical antipsychotic with potent dopamine D(2) receptor antagonism. Clozapine is an atypical antipsychotic with potent serotonin <em>5HT</em>(2) receptor antagonism. We injected rats with haloperidol or clozapine and examined the phosphorylation and amount of GSK3alpha/beta and its well-known upstream regulators Akt and Dvl in the rat frontal cortex by Western blotting. Both haloperidol and clozapine induced Ser21/9 phosphorylation of GSK3GSK3alpha/beta. Haloperidol increased the Ser473 phosphorylation of Akt transiently, whereas clozapine maintained the increase for 1 h. Haloperidol did not affect the phosphorylation and amount of Dvl, whereas clozapine increased both phosphorylation and the amount of Dvl. Our results suggest that GSK3 activity may be regulated by both typical and atypical antipsychotics and that Akt or Dvl, depending on the D(2)- or <em>5HT</em>(2)- receptor antagonism properties of typical and atypical antipsychotics, mediate the regulation differently.

The divalent cation calcium potentiates the physiological response of neuronal nicotinic receptors to agonists by enhancing ionic current amplitudes, apparent agonist affinity and cooperativity. Here we show that mutations in several consensus Ca2+ binding sequences from the N-terminal domain of the neuronal alpha 7 nicotinic acetylcholine receptor alter Ca2+ potentiation of the alpha 7-V201-<em>5HT</em>3 chimera. Mutations E18Q or E44Q abolish calcium-enhanced agonist affinity but preserve the calcium increase of plateau current amplitudes and cooperativity. On the other hand, mutations of amino acids belonging to the 12 amino acid canonical domain (alpha 7 161-172) alter all features of potentiation by enhancing (D163, S169), reducing (E161, S165, Y167) or abolishing (E172) calcium effects on ionic current amplitudes and agonist affinity. Introduction of the alpha 7 161-172 domain in the calcium insensitive 5-hydroxytryptamine (<em>5HT</em>3) serotoninergic receptor results in a receptor activated by <em>5HT</em> and potentiated by calcium. In vitro terbium fluorescence studies with an alpha 7 160-174 peptide further show that mutation E172Q also alters in vitro calcium binding. Data are consistent with the occurrence of distinct categories of regulatory calcium binding sites, among which the highly conserved (alpha 7 161-172) domain may simultaneously contribute to calcium and agonist binding.

Allopregnanolone [3alpha-hydroxy-5alpha-pregnan-20-one] (ALLO), a potent neurosteroid that positively modulates gamma-aminobutyric acid (GABA) action at various GABA(A) receptor subtypes is synthesized in nanomolar concentrations and stored non uniformly in various brain structures of mammals. We have measured brain ALLO content and its precursors by negative ion chemical ionization-mass-spectrometry after purification and separation of the different steroids with HPLC and gas chromatography. Our procedure measures steroids in the femtomolar range with structural information and unsurpassed selectivity. We were able to establish an association between the decrease in content of ALLO in mouse brain cortex elicited by either long-lasting social isolation or by the administration of 17beta-17 [bis (1-methylethyl) amino carbonyl] androstane-3,5-dilene-3-carboxylic acid (SKF 105111). an inhibitor of Types I and II 5alpha reductases, and the shortening of the righting reflex loss elicited by pentobarbital (PBT). SKF 105111 added to cortical brain slices in concentrations up to 10(-5) M failed per se to alter GABAergic currents or their potentiation by PTB recorded from pyramidal neurons. Fluoxetine (1.45 or 2.9 micromol/kg i.p.) doses that fail to change the PTB-induced loss of righting reflex and the level of brain ALLO in group-housed mice normalized both parameters in socially-isolated mice. In addition, we could detect both fluoxetine actions in socially isolated mice pretreated with doses of p-chlorophenylalanine (1.2 mmol/kg i.p. at 72, 48, and 24 h) that substantially inhibit brain serotonin <em>5HT</em> synthesis as shown by an 80% drop of brain <em>5HT</em> content. These studies for the first time have provided evidence suggesting that the endogenous cortical stores of ALLO physiologically upregulate GABAergic tone and by such a mechanism play a permissive or facilitatory role on the PTB-induced loss of the righting reflex. In the absence of such a permissive physiological influence by endogenous ALLO, the righting reflex inhibition by PTB is down regulated.

Serotonin (<em>5HT</em>) transporters (SERTs) are responsible for clearance of synaptic and plasma <em>5HT</em> and are molecular targets for multiple therapeutic and addictive compounds. Recently brain and peripheral SERT cDNAs have been cloned and characterized functionally in transfected cells. Antipeptide (S365) and anti-fusion protein (CT-2) antibodies, directed at epitopes poorly conserved among other Na+/Cl- cotransporters, have been prepared to facilitate the identification and characterization of SERT proteins in native and transfected cells. Immunoprecipitations and immunoblots of rat/human SERT-transfected HeLa cells reveal specific SERT-immunoreactive glycoproteins absent from extracts of vector-transfected cells and absent when incubations were conducted using peptide- or fusion protein-absorbed antibody. In SDS-PAGE of membranes prepared from rat midbrain and cortex, SERTs migrate as single 76 kDa polypeptides with a relative abundance consistent with the known distribution of <em>5HT</em> neurons and axonal projections. SERT-immunoreactive proteins are also detectable in platelet and pulmonary membranes, sites of peripheral <em>5HT</em> uptake, but not in liver. Our studies also indicate that brain and platelet SERTs are formed from identical polypeptides differing significantly in their extent of N-linked glycosylation. Immunocytochemistry performed on rat brain sections with CT-2 antibody revealed SERT expression associated with brainstem raphe nuclei in a pattern virtually identical to that obtained by labeling adjacent sections with <em>5HT</em> antisera. SERT-immunoreactive fibers were found to be widely distributed throughout the rodent brain, with highest density in forebrain regions known to receive a dense serotonergic innervation. In a similar manner, CT-2 antibody also detects endogenous expression of human SERT proteins, providing an opportunity for future studies on the modulation of transporter protein expression in neurologic and psychiatric disorders.

Serotonin (<em>5HT</em>) is a powerful modulator of respiratory circuitry in vitro but its role in the development of breathing behavior in vivo is poorly understood. Here we show, using <em>5HT</em> neuron-deficient Pet-1 (Pet-1(-/-)) neonates, that serotonergic function is required for the normal timing of postnatal respiratory maturation. Plethysmographic recordings reveal that Pet-1(-/-) mice are born with a depressed breathing frequency and a higher incidence of spontaneous and prolonged respiratory pauses relative to wild type littermates. The wild type breathing pattern stabilizes by postnatal day 4.5, while breathing remains depressed, highly irregular and interrupted more frequently by respiratory pauses in Pet-1(-/-) mice. Analysis of in vitro hypoglossal nerve discharge indicates that instabilities in the central respiratory rhythm generator contribute to the abnormal Pet-1(-/-) breathing behavior. In addition, the breathing pattern in Pet-1(-/-) neonates is susceptible to environmental conditions, and can be further destabilized by brief exposure to hypoxia. By postnatal day 9.5, however, breathing frequency in Pet-1(-/-) animals is only slightly depressed compared to wild type, and prolonged respiratory pauses are rare, indicating that the abnormalities seen earlier in the Pet-1(-/-) mice are transient. Our findings provide unexpected insight into the development of breathing behavior by demonstrating that defects in <em>5HT</em> neuron development can extend and exacerbate the period of breathing instability that occurs immediately after birth during which respiratory homeostasis is vulnerable to environmental challenges.

Serotonin (<em>5HT</em>) levels in platelet-rich plasma were measured in 5 autistic subjects who had siblings with either autism or pervasive developmental disorder (PDD), 23 autistic subjects without affected siblings, and 10 normal controls. The <em>5HT</em> levels of autistic subjects with affected siblings were significantly higher than probands without affected siblings, and autistic subjects without affected siblings had <em>5HT</em> levels significantly higher than controls. Differences in <em>5HT</em> levels remained significant after adjustment for sex, age, and IQ. These results suggest that <em>5HT</em> level in autistic subjects may be associated with genetic liability to autism.

The important biogenic amine, serotonin (<em>5HT</em>), was determined in whole blood, platelet-rich plasma (PRP), platelet-poor plasma (PPP), and plasma ultrafiltrate after simple deproteinization. Following ion-pair chromatography on standard or narrow-bore reverse-phase columns, <em>5HT</em> and the internal standard (N-methylserotonin-NMS) were detected by fluorometry with absolute detection limits of 2-4 pg. Levels obtained for whole blood and PRP were in agreement with previous methods. However, mean (+/- SD) values obtained for platelet-poor plasma (PPP) of 578 +/- 277 pg/ml (N = 7) were approximately 3-fold lower than the lowest previous reports. We also report the first determination of <em>5HT</em> in plasma ultrafiltrate, having observed mean levels of 387 +/- 222 pg/ml (N = 7).