Cannabidiol Exerts Sedative and Hypnotic Effects in Normal and Insomnia Model Mice Through Activation of 5-HT1A Receptor

Cannabis sativa has been used for improving sleep for long history. Cannabidiol (CBD) has drown much attention as a non-addictive psychoactive component in Cannabis sativa extract. However, the effects of CBD on sleep architecture and it's acting mechanism remains unclear. In the present study, we evaluated the sedative-hypnotic effect of cannabidiol (CBD), assessed the effects of CBD on sleep using a wireless physiological telemetry system. We further explored the therapeutic effects of CBD using 4-chloro-dl-phenylalanine (PCPA) induced insomnia model and changes in sleep latency, sleep duration and intestinal flora were evaluated. CBD shortened sleep latency and increases sleep duration in both normal and insomnia mice, and those effects were blocked by 5-HT1A receptor antagonist WAY100635. We determined that CBD increases 5-HT1A receptors expression and 5-HT content in the hypothalamus of PCPA-pretreated mice and affects tryptophan metabolism in the intestinal flora. These results showed that activation of 5-HT1A receptors is one of the potential mechanisms underlying the sedative-hypnotic effect of CBD. This study validated the effects of CBD on sleep and evaluated its potential therapeutic effects on insomnia.

Structure activity relationships of 5-HT2B and 5-HT2C serotonin receptor antagonists: N6, C2 and 5'-Modified (N)-methanocarba-adenosine derivatives

(N)-Methanocarba adenosine derivatives were structurally modified to target 5-HT2B serotonin receptors as antagonists, predominantly containing branched N6-alkyl groups. N6-Dicycloalkyl-methyl groups, including their asymmetric variations, as well as 2-iodo, were found to generally favor 5-HT2Rs, while only N6-dicyclohexyl-methyl derivative 35 showed weak 5-HT2AR affinity (Ki 3.6 μM). The highest 5-HT2BR affinities were Ki 11-23 nM (N6-dicyclopropyl-methyl-2-iodo 11, 2-chloro-5'-deoxy-5'-methylthio 15 and N6-((R)-cyclobuty-cyclopropyl-methyl)-2-iodo 43), and Ki 73 nM at 5-HT2CR for 36. Direct comparison of adenine ribosides and their corresponding rigid (N)-methanocarba derivatives (cf. 51 and MRS8099 45) indicated a multifold affinity enhancement with the bicyclic ring system. Compounds 43, 45 and 48 were functional 5-HT2BR (KB 2-3 nM) and 5-HT2CR (KB 79-328 nM) antagonists in a Gq-mediated calcium flux assay, with 5-HT2BR functional selectivity ranging from 45- (48) to 113-fold (43). Substantial adenosine receptor (AR) affinity (Ki, A1AR < Ki, A3AR < Ki, A2AAR) was still present in this series, suggestive of dual acting compounds: 5-HT2B antagonist and A1AR agonist, potentially useful for treating chronic conditions (fibrosis; pain). Given its affinity (17 nM) and moderate 5-HT2BR binding selectivity (32-fold vs. 5-HT2CR, 4-fold vs. A1AR), 43 (MRS7925) could potentially be useful for anti-fibrotic therapy.

The Serotonin Neurotransmitter Modulates Virulence of Enteric Pathogens

The gut-brain axis is crucial to microbial-host interactions. The neurotransmitter serotonin is primarily synthesized in the gastrointestinal (GI) tract, where it is secreted into the lumen and subsequently removed by the serotonin transporter, SERT. Here, we show that serotonin decreases virulence gene expression by enterohemorrhagic E. coli (EHEC) and Citrobacter rodentium, a murine model for EHEC. The membrane-bound histidine sensor kinase, CpxA, is a bacterial serotonin receptor. Serotonin induces dephosphorylation of CpxA, which inactivates the transcriptional factor CpxR controlling expression of virulence genes, notably those within the locus of enterocyte effacement (LEE). Increasing intestinal serotonin by genetically or pharmacologically inhibiting SERT decreases LEE expression and reduces C. rodentium loads. Conversely, inhibiting serotonin synthesis increases pathogenesis and decreases host survival. As other enteric bacteria contain CpxA, this signal exploitation may be engaged by other pathogens. Additionally, repurposing serotonin agonists to inhibit CpxA may represent a potential therapeutic intervention for enteric bacteria.

Chemosensitivity of Phox2b-expressing retrotrapezoid neurons is mediated in part by input from 5-HT neurons

KEY POINTS

Neurons of the retrotrapezoid nucleus (RTN) and medullary serotonin (5-HT) neurons are both candidates for central CO2 /pH chemoreceptors, but it is not known how interactions between them influence their responses to pH. We found that RTN neurons in brain slices were stimulated by exogenous 5-HT and by heteroexchange release of endogenous 5-HT, and these responses were blocked by antagonists of 5-HT7 receptors. The pH response of RTN neurons in brain slices was markedly reduced by the same antagonists of 5-HT7 receptors. Similar results were obtained in dissociated, primary cell cultures prepared from the ventral medulla, where it was also found that the pH response of RTN neurons was blocked by preventing 5-HT synthesis and enhanced by blocking 5-HT reuptake. Exogenous 5-HT did not enable latent intrinsic RTN chemosensitivity. RTN neurons may play more of a role as relays from other central and peripheral chemoreceptors than as CO2 sensors.

ABSTRACT

Phox2b-expressing neurons in the retrotrapezoid nucleus (RTN) and serotonin (5-HT) neurons in the medullary raphe have both been proposed to be central respiratory chemoreceptors. How interactions between these two sets of neurons influence their responses to acidosis is not known. Here we recorded from mouse Phox2b+ RTN neurons in brain slices, and found that their response to moderate hypercapnic acidosis (pH 7.4 to ∼7.2) was markedly reduced by antagonists of 5-HT7 receptors. RTN neurons were stimulated in response to heteroexchange release of 5-HT, indicating that RTN neurons are sensitive to endogenous 5-HT. This electrophysiological behaviour was replicated in primary, dissociated cell cultures containing 5-HT and RTN neurons grown together. In addition, pharmacological inhibition of 5-HT synthesis in culture reduced RTN neuron chemosensitivity, and blocking 5-HT reuptake enhanced chemosensitivity. The effect of 5-HT on RTN neuron chemosensitivity was not explained by a mechanism whereby activation of 5-HT7 receptors enables or potentiates intrinsic chemosensitivity of RTN neurons, as exogenous 5-HT did not enhance the pH response. The ventilatory response to inhaled CO2 of mice was markedly decreased in vivo after systemic treatment with ketanserin, an antagonist of 5-HT2 and 5-HT7 receptors. These data indicate that 5-HT and RTN neurons may interact synergistically in a way that enhances the respiratory chemoreceptor response. The primary role of RTN neurons may be as relays and amplifiers of the pH response from 5-HT neurons and other chemoreceptors rather than as pH sensors themselves.

Observations on the Psychotogenic Effect of N-N Diethyltryptamine, a New Tryptamine Derivative

Since Evarts, Fabing and Marrazzi reported on bufotenine and Szára on N-N dimethyltryptamine (DMT) the tryptamine derivatives have been arousing increased interest. A team of the above Institute was the first to test DMT and N-N diethyltryptamine (DET) in man. These compounds were synthesized by Szára, by the method of Speeter and Anthony. DET was then synthesized again and analysed pharmacologically by Borsi and Lénárt.

Recent developments in the prevention of chemotherapy-induced nausea and vomiting (CINV): a comprehensive review

The prevention of chemotherapy-induced nausea and vomiting (CINV) has been revolutionized over the past 25 years. Guideline-based treatment means that vomiting can be prevented in the majority, but not in all patients. Therefore, antiemetic research continues with the goal of optimizing CINV control for all patients. This comprehensive review summarizes the research efforts in this field over the past few years. Emerging from this research are two new antiemetic agents, netupitant/palonosetron, the first antiemetic combination agent and rolapitant, a new NK1RA. In addition, studies have evaluated the benefits of olanzapine and ginger, explored optimal combinations of agents for delayed CINV prevention, confirmed that dexamethasone-sparing regimens are effective, and demonstrated the value of NK1RAs in high-dose chemotherapy settings as well as with certain moderately emetogenic chemotherapies such as carboplatin. Research has also validated the correlation between antiemetic guideline adherence and improved CINV control. Finally, regulatory authorities have utilized extreme caution in retiring some 5-HT3RAs or decreasing their maximum dose.

Clinical and animal pharmacology of migraine: new perspectives

Animal and clinical pharmacological studies show in certain vascular beds a biphasic action [potentiation and inhibition of serotonin (5-HT) responses] of some anti-migraine drugs, such as ergotamine, methysergide and more recently Org GC 94. Potentiation occurs at therapeutic drug concentrations. The present investigations seem to support the 5-HT theory of migraine and other essential headaches. In this theory, anti-migraine drugs, such as ergotamine, methysergide, pizotifen, and Org GC 94 could reduce the occurrence of pain in migraine and other esscutial headaches by acting as partial agonists tending to correct a deficiency of central 5-HT concentrations or turnover.

Acetyl-l-carnitine prevents serotonin-induced behavioural sensitization and dishabituation in Hirudo medicinalis

Several studies suggest that acetyl-l-carnitine (ALC) might influence learning processes. Along this line of investigation, we have previously shown that ALC impaired sensitization and dishabituation induced by nociceptive stimulation of the dorsal skin of the leech Hirudo medicinalis, in the behavioural paradigm of the swim induction (SI). In previous works we showed that 5HT was involved in both sensitization and dishabituation of SI acting through the second messenger cAMP. In this work, we have reported that for given doses and temporal ranges ALC was able to block sensitization and to impair dishabituation mimicked by the injection of 5-HT or 8Br-cAMP, a membrane permeable analogue of cAMP. Our results show that a single treatment with 2mM ALC was the most effective concentration to block the onset of sensitization induced by 5-HT injection and its major effects occurred 11 days after ALC treatment. 2mM ALC also blocked sensitization induced by 8Br-cAMP injection, whereas, ALC did not completely abolish dishabituation induced by 5-HT or 8Br-cAMP injection at the tested concentrations and at every time point.

Effect of serotonin and calcium on the supercontractile muscles of the adult blowfly crop

Bioassays and electrophysiological recordings were conducted to determine the role of serotonin and calcium on the supercontractile pump muscles of the diverticulated crop of adult blowflies. Using in situ crop preparations, serotonin was found to significantly increase the rates of contractions of a specific pump in the crop wall, pump P4. The addition of the serotonin antagonist, mianserin, or calcium free saline, both significantly reduced the contraction rates of this pump. Recordings, using suction electrodes from pump P4, confirm the in situ bioassay data and show that serotonin promotes muscle activity in empty crops in which no pump activity is normally observed. Moreover, our data indicate the crucial role of extracellular calcium ions in crop pump contractile activity. These results provide new information on how the crop of adult dipterans is modulated and suggest that serotonin, possibly supplied by neurons in the thoracico-abdominal neural plexus, may be involved in modulating the pumping of crop contents into the midgut for digestion or triggering antiperistalsis from the foregut in the process known as regurgitation or 'bubbling'.

Vasorelaxing effect of levosimendan against 5-hydroxytryptamine-induced contractions in isolated human conduit bypass grafts

Levosimendan is a novel inodilator drug developed for the treatment of heart failure. The possible vasodilating property of the drug in human coronary artery bypass grafts was investigated. Isometric tensions of the left internal thoracic artery (LITA, n = 8) as well as the proximal and distal segments of the radial artery (RA, n = 8 and 8) were measured in isolated organ baths. Concentration-relaxation curves for levosimendan (0.009-1.14 μmol L−1) were obtained against 5-hydroxytryptamine (5-HT; serotonin, 0.002–9.3 μmol L 1)-induced contractions. 5-HT-induced contraction of LITA was considerably smaller than that of the proximal and distal RAs. Levosimendan relaxed the grafts in the following order of calculated maximum efficacies (Emax): LITA &gt; proximal RA &gt; distal RA (LITA 100.3 ±16.2% of 5-HT-induced maximum tension, proximal RA 86.9 ±8.6%, distal RA 59.4 ± 17.5%, P &lt; 0.05 LITA vs distal RA). The potency values of levosimendan, expressed as the negative logarithm of 50% effective concentrations (pD2), were comparable in the three bypass grafts (LITA −6.52 ± 0.44 log mol L−1, proximal RA −6.60 ± 0.49 log mol L−1, distal RA −6.85 ± 0.45 log mol L−1). The results suggest that levosimendan is an effective vasorelaxant of conduit bypass grafts and may serve as a new therapeutic tool, especially in the case of LITA and proximal RA grafts, for relieving perioperative spasm and subsequent graft failure.

The bovine mammary gland expresses multiple functional isoforms of serotonin receptors

Recent studies in dairy cows have demonstrated that serotonergic ligands affect milk yield and composition. Correspondingly, serotonin (5-HT) has been demonstrated to be an important local regulator of lactational homeostasis and involution in mouse and human mammary cells. We determined the mRNA expression of bovine 5-HT receptor (HTR) subtypes in bovine mammary tissue (BMT) and used pharmacological agents to evaluate functional activities of 5-HT receptors. The mRNAs for five receptor isoforms (HTR1B, 2A, 2B, 4, and 7) were identified by conventional real-time (RT)-PCR, RT quantitative PCR, and in situ hybridization in BMT. In addition to luminal mammary epithelial cell expression, HTR4 was expressed in myoepithelium, and HTR1B, 2A, and 2B were expressed in small mammary blood vessels. Serotonin suppressed milk protein mRNA expression (alpha-lactalbumin and beta-casein mRNA) in lactogen-treated primary bovine mammary epithelial cell (BMEC) cultures. To probe the functional activities of individual receptors, caspase-3 activity and expression of alpha-lactalbumin and beta-casein were measured. Both SB22489 (1B antagonist) and ritanserin (2A antagonist) increased caspase-3 activity. Expression of alpha-lactalbumin and beta-casein mRNA levels in BMEC were stimulated by low concentrations of SB224289, ritanserin, or pimozide. These results demonstrate that there are multiple 5-HT receptor isoforms in the bovine mammary gland, and point to profound differences between serotonergic systems of the bovine mammary gland and the human and mouse mammary glands. Whereas human and mouse mammary epithelial cells express predominately the protein for the 5-HT(7) receptor, cow mammary epithelium expresses multiple receptors that have overlapping, but not identical, functional activities.

Effect of 8-hydroxy-2-(N,N-di-n-propylamino)tetralin and MDMA on the discriminative stimulus effects of the classical hallucinogen DOM in rats

Co-administration of the 5-HT1A serotonin receptor agonist (+/-)8-hydroxy-2-(N,N-di-n-propylamino)tetralin [(+/-)8-OH DPAT] enhances the discriminative stimulus effects of the classical hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) in rats. In the present investigation, using Sprague-Dawley rats trained to discriminate DOM (1.0 mg/kg) from saline vehicle under a VI-15 s schedule of reinforcement, it was shown that the stimulus-enhancing actions of 8-OH DPAT are related more to its R(+)-isomer than to its S(-)-enantiomer, and that the (+/-)- and R(+)8-OH DPAT-induced effects are antagonized by the 5-HT1A receptor antagonist NAN-190. (+/-)8-OH DPAT and its isomers substitute in rats trained to discriminate the designer drug N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA; methylenedioxymethamphetamine) from vehicle indicating some similarity of effect. On this basis, it was hypothesized that MDMA might be capable of enhancing the DOM stimulus. Co-administration of MDMA with low (i.e., 0.1 and 0.3 mg/kg) doses of DOM resulted in greater DOM-appropriate responding than engendered by administration of DOM alone. As such, the present findings are the first to demonstrate an MDMA-induced enhancing effect on the discriminative stimulus actions of a classical hallucinogen. The results also suggest that a 5-HT1A serotonin receptor mechanism might contribute to this phenomenon.

Correlation of human cold pressor pain responses with 5-HT(1A) receptor binding in the brain

We determined whether serotonin 5-HT(1A) receptor availability in the brain is associated with cold pressor pain (CPP) or sympathetic reflex responses. Psychophysical testing was performed in eleven healthy males who had participated in a positron emission tomography study with [carbonyl-(11)C]WAY-100635 ligand for the assessment of 5-HT(1A) receptor binding potential (BP). Psychophysical testing consisted of determining CPP threshold, tolerance, intensity, unpleasantness and CPP threshold modulation by conditioning CPP. Autonomic control was assessed by determining the cutaneous vasoconstriction responses in the finger induced by CPP and Valsalva maneuver. CPP intensity was inversely correlated with 5-HT(1A) BP in multiple cortical and subcortical areas, including the prefrontal and cingulate cortices, insula, amygdala and the dorsal raphe. CPP unpleasantness was not significantly correlated with 5-HT(1A) BP in any of the regions of interest. Increase of CPP threshold by conditioning CPP was directly correlated with 5-HT(1A) BP in the amygdala and medial prefrontal cortex. Vasoconstriction induced by Valsalva but not CPP was directly correlated with 5-HT(1A) BP in the ventral part of the anterior cingulate cortex and the anterior insula. The results suggest that 5-HT(1A) receptors in the brain influence pain and Valsalva-induced sympathetic vasoconstriction reflex. In general, subjects with high availability of 5-HT(1A) receptors have low CPP intensity accompanied by a high capacity for central suppression of pain or a sympathetic vasoconstriction response by a Valsalva maneuver.

Putting evidence into practice: evidence-based interventions to prevent, manage, and treat chemotherapy-induced nausea and vomiting

Chemotherapy-induced nausea and vomiting (CINV) continues to have a considerable effect on the physical and psychological well-being of patients with cancer, despite significant advances in antiemetic drugs since the 1990s. This article reviews and summarizes past and current empirical evidence related to interventions for CINV. A resource that summarizes evidence-based interventions for CINV is critical for effective management of this distressing symptom. Pharmacologic and nonpharmacologic interventions are appraised. Finally, gaps in the literature and opportunities for research, education, and practice changes are discussed.

The antimalarial drugs quinine, chloroquine and mefloquine are antagonists at 5-HT3 receptors

BACKGROUND AND PURPOSE

The antimalarial compounds quinine, chloroquine and mefloquine affect the electrophysiological properties of Cys-loop receptors and have structural similarities to 5-HT(3) receptor antagonists. They may therefore act at 5-HT(3) receptors.

EXPERIMENTAL APPROACH

The effects of quinine, chloroquine and mefloquine on electrophysiological and ligand binding properties of 5-HT(3A) receptors expressed in HEK 293 cells and Xenopus oocytes were examined. The compounds were also docked into models of the binding site.

KEY RESULTS

5-HT(3) responses were blocked with IC (50) values of 13.4 microM, 11.8 microM and 9.36 microM for quinine, chloroquine and mefloquine. Schild plots indicated quinine and chloroquine behaved competitively with pA (2) values of 4.92 (K (B)=12.0 microM) and 4.97 (K (B)=16.4 microM). Mefloquine displayed weakly voltage-dependent, non-competitive inhibition consistent with channel block. On and off rates for quinine and chloroquine indicated a simple bimolecular reaction scheme. Quinine, chloroquine and mefloquine displaced [(3)H]granisetron with K (i) values of 15.0, 24.2 and 35.7 microM. Docking of quinine into a homology model of the 5-HT(3) receptor binding site located the tertiary ammonium between W183 and Y234, and the quinoline ring towards the membrane, stabilised by a hydrogen bond with E129. For chloroquine, the quinoline ring was positioned between W183 and Y234 and the tertiary ammonium stabilised by interactions with F226.

CONCLUSIONS AND IMPLICATIONS

This study shows that quinine and chloroquine competitively inhibit 5-HT(3) receptors, while mefloquine inhibits predominantly non-competitively. Both quinine and chloroquine can be docked into a receptor binding site model, consistent with their structural homology to 5-HT(3) receptor antagonists.

Exaggerated 5-HT1A but normal 5-HT2A receptor activity in individuals ill with anorexia nervosa

BACKGROUND

Many studies have found disturbances of serotonin (5-HT) activity in anorexia nervosa (AN). Because little is known about 5-HT receptor function in AN, positron emission tomography (PET) imaging with 5-HT receptor-specific radioligands was used to characterize 5-HT1A and 5-HT2A receptors.

METHODS

Fifteen women ill with AN (ILL AN) were compared with 29 healthy control women (CW); PET and [11C]WAY100635 were used to assess binding potential (BP) of the 5-HT1A receptor, and [18F]altanserin was used to assess postsynaptic 5-HT2A receptor BP. [15O] water and PET were used to assess cerebral blood flow.

RESULTS

The ILL AN women had a highly significant (30%-70%) increase in [11C]WAY100635 BP in prefrontal and lateral orbital frontal regions, mesial and lateral temporal lobes, parietal cortex, and dorsal raphe nuclei compared with CW. The [18F]altanserin BP was normal in ILL AN but was positively and significantly related to harm avoidance in suprapragenual cingulate, frontal, and parietal regions. Cerebral blood flow was normal in ILL AN women.

CONCLUSIONS

Increased activity of 5-HT1A receptor activity may help explain poor response to 5-HT medication in ILL AN. This study extends data suggesting that 5-HT function, and, specifically, the 5-HT2A receptor, is related to anxiety in AN.

Reduced serotonin-1A receptor binding in social anxiety disorder

BACKGROUND

Results from studies in serotonin-1A (5-HT1A) knockout mice and previous positron emission tomography (PET) studies in humans imply a role for 5-HT1A receptors in normal state anxiety as well as in certain anxiety disorders. The objective of this study was to investigate 5-HT1A receptor binding potential (BP) in social anxiety disorder (SAD).

METHODS

Using PET and [carbonyl-11C]WAY-100635, we compared a homogeneous group of 12 unmedicated, male SAD patients with 18 healthy control subjects (HC). A multivariate ANOVA with all regional BP values as dependent variables, age and four radiochemical variables as covariates was performed.

RESULTS

We found a significantly lower 5-HT1A BP in several limbic and paralimbic areas but not in the hippocampus (p = .234) of SAD patients. The difference in 5-HT1A binding was most significant in the amygdala (-21.4%; p = .003). There was also a more than 20% lower 5-HT(1A) BP of SAD patients in the anterior cingulate cortex (p = .004), insula (p = .003), and dorsal raphe nuclei (p = .030).

CONCLUSIONS

The lower 5-HT1A binding in the amygdala and mesiofrontal areas of SAD patients is consistent with 1) preclinical findings of elevated anxiety in 5-HT1A knockout mice, 2) a previous PET study in healthy volunteers showing an inverse correlation between 5-HT1A BP and state anxiety, and 3) another human PET study in patients with panic disorder showing reduced 5-HT1A binding, thus corroborating the potential validity of 5-HT1A receptors as targets in the treatment of human anxiety disorders.

Effects of the reference tissue setting on the parametric image of 11C-WAY 100635

OBJECTIVES

C-WAY 100635 has been used widely in the PET research field to measure 5-HT1A receptors in the living human brain. Reference tissue model analysis, in which the cerebellum was used as the reference tissue, was employed in clinical studies. However, the reported binding potentials varied greatly among the reports. In this study, regions of interest (ROIs) of the cerebellum for C-WAY 100635 were determined in five different approaches for six healthy male volunteers, and the effects on binding potential parametric images were compared.

METHODS

First, ROIs on the cerebellar cortex were decided based on information from magnetic resonance imaging (MRI), and then divided into upper and lower parts. They were then refined according to coregistered positron emission tomography (PET) image information, generating upper-refined and lower-refined parts. In a different approach, circular ROIs were decided upon, based on the PET images, and the areas under the curve (AUCs) of five ROIs were compared. Parametric images of binding potentials were calculated with the five ROIs as the reference, and compared with each other.

RESULTS

The AUCs of the lower-refined parts were the lowest among the first four ROIs. The ratio of the AUCs between the upper part and lower-refined part was 1.54+/-0.17, that between the upper-refined part and lower-refined part was 1.27+/-0.21, that between the lower part and lower-refined part was 1.04+/-0.02, and that between the circular ROIs and lower-refined part was 1.01+/-0.04. The differences in AUCs among the five cerebellar parts led to significant differences in the binding potential parametric images.

CONCLUSION

The binding potential parametric images of C-WAY100635 could vary significantly according to the different methods of establishing ROIs, using the cerebellum as the reference tissue, because radioactivity in the cerebellum for C-WAY100635 is very low.

The role of 5-HT7 receptors in the control of seizures

Serotonin exerts its effects via at least 14 different receptor subtypes, but the role of only a few of them has been studied in relation to the control of seizures. A negative role of 5-HT(7) receptors has recently been proposed. To evaluate further in unstressed and stressed animals the possible role of this receptor subtype in the control of brain excitability, we treated mice with antagonists and agonists of these receptors prior to exposure to swim stress and the intravenous infusion of picrotoxin, a non-competitive GABA(A) receptor antagonist. In accordance with the previous studies, swim stress increased the doses of picrotoxin producing two convulsant signs (running/bouncing clonus, tonic hindlimb extension) and death, i.e., swim stress increased the seizure threshold for picrotoxin. SB-269970 (10-30 mg/kg ip), a selective antagonist of 5-HT(7) receptors, and ritanserin (1 mg/kg ip), a nonselective 5-HT (2/7) antagonist, failed to affect, while 5-carboxamidotryptamine (5-CT), a potent 5-HT (1/7) receptor agonist, increased in unstressed and swim-stressed mice the doses of picrotoxin producing convulsions and death. The anticonvulsant effect obtained with 5-CT 0.5 mg/kg was not greater than that obtained with 0.1 mg/kg. The 5-CT (0.1 mg/kg ip)-induced increase of the seizure threshold for picrotoxin in stressed mice was abolished with SB-269970 (10 mg/kg), but not with WAY-100635 (0.3 mg/kg), a selective antagonist of 5-HT(1A) receptors, suggesting that the anticonvulsant effect of 5-CT against convulsions produced by picrotoxin was achieved via 5-HT(7) receptors. The results suggest a positive role of 5-HT(7) receptors in the control of seizures.

Control of shivering during regional anaesthesia: prophylactic ketamine and granisetron

BACKGROUND

The aim of the present study was to compare placebo, ketamine, granisetron and a combination of ketamine and granisetron in the prevention of shivering caused by regional anaesthesia.

METHODS

In this prospective, randomized, double-blind study, 160 ASA I and II patients undergoing urological surgery were included. Subarachnoid anaesthesia was performed in all patients with bupivacaine 15 mg. The patients were randomly allocated to receive saline (group P, n= 40), ketamine 0.5 mg (group K, n= 40), granisetron 3 mg (group G, n= 40) or ketamine 0.25 mg + granisetron 1.5 mg (group KG, n= 40). Shivering was graded as 0 = no shivering, 1 = piloerection or peripheral vasoconstriction but no visible shivering, 2 = muscular activity in only one muscle group, 3 = muscular activity in more than one muscle group but not generalized, and 4 = shivering involving the whole body. If 15 min after spinal anaesthesia and concomitant administration of a prophylactic dose of one of the study drugs, the patients shivered according to at least grade 3, the prophylaxis was regarded as ineffective and intravenous (i.v.) pethidine 25 mg was administered.

RESULTS

After 15 min, the number of patients with observed shivering was 22 in group P, 6 in group G, 7 in group GK and 0 in group K. The difference between group K and all the other groups was statistically significant (P < 0.0001). The number of patients with a shivering score of 3 was statistically significantly higher in group P compared with the other groups.

CONCLUSION

The prophylactic use of 0.5 mg/kg i.v. ketamine was effective in preventing shivering developed during regional anaesthesia.

A comparison of recent parametric neuroreceptor mapping approaches based on measurements with the high affinity PET radioligands [11C]FLB 457 and [11C]WAY 100635

In positron emission tomography (PET) studies, the detailed mapping of neuroreceptor binding is a trade-off between parametric accuracy and spatial precision. Logan's graphical approach is a straightforward way to quickly obtain binding potential values at the voxel level but it has been shown to have a noise-dependent negative bias. More recently suggested approaches claim to improve parametric accuracy with retained spatial resolution. In the present study, we used PET measurements on regional D2 dopamine and 5-HT1A serotonin receptor binding in man to compare binding potential (BP) estimates of six different parametric imaging approaches to the traditional Logan ROI-based approach which was used as a "gold standard". The parametric imaging approaches included Logan's reference tissue graphical analysis (PILogan), its version recently modified by Varga and Szabo (PIVarga), two versions of the wavelet-based approach, Gunn's basis function method (BFM) and Gunn et al.'s recent compartmental theory-based approach employing basis pursuit strategy for kinetic modeling (called DEPICT). Applicability for practical purposes in basic and clinical research was also considered. The results indicate that the PILogan and PIVarga approaches fail to recover the correct values, the wavelet-based approaches overcome the noise susceptibility of the Logan fit with generally good recovery of BP values, and BFM and DEPICT seem to produce values with a bias dependent on receptor density. Further investigations on this bias and other phenomena revealed fundamental issues regarding the use of BFM and DEPICT on noisy voxel-wise data. In conclusion, the wavelet-based approaches seem to provide the most valid and reliable estimates across regions with a wide range of receptor densities. Furthermore, the results support the use of receptor parametric imaging in applied studies in basic or clinical research.

Serotonin-induced in vitro long-term facilitation exhibits differential pattern sensitivity in cervical and thoracic inspiratory motor output

Intermittent hypoxia induces 5-HT-dependent, pattern-sensitive long-term facilitation (LTF) of spinal respiratory motor output. We used a split-bath in vitro neonatal rat brainstem-spinal cord preparation to test whether: 1) intermittent spinal 5-HT exposure (without hypoxia) is sufficient to induce LTF in phrenic and intercostal inspiratory motor outputs; 2) LTF magnitude is greater in intercostal versus phrenic activity; and 3) phrenic and intercostal motor output exhibits differential pattern sensitivity to 5-HT application. With a barrier at spinal segment C1, 5-HT (5 muM) was applied episodically (3 min 5-HT, 5 min wash, x3) to the spinal cord (C2-L1) while recording inspiratory bursts in cervical (C4 or C5) and thoracic (T5 or T6) ventral roots. Episodic 5-HT application increased cervical and thoracic burst amplitudes to 136+/-22% and 150+/-22% of baseline, respectively, at 120 min post-drug (P<0.01). Continuous 5-HT application (5 muM, 9 min) had no effect on cervical burst amplitude at 120 min post-drug, but increased thoracic burst amplitude to 142+/-11% of baseline at 120 min post-drug (P<0.001). Methysergide pretreatment abolished both cervical and thoracic 5-HT-induced LTF. Quantitative reverse transcriptase-polymerase chain reaction and immunocytochemistry revealed that 5-HT(2A) and 5-HT(7) receptor subtypes (receptors known to influence LTF expression in adult rats) are expressed in ventral cervical and thoracic spinal cord with no differences in expression levels due to spinal segment or age. Thus, 5-HT is sufficient to induce spinal LTF in neonatal rats and differences in pattern sensitivity suggest heterogeneity in underlying mechanisms.

Antidepressant-like activity of n-hexane extract of nutmeg (Myristica fragrans) seeds in mice

The present study was undertaken to investigate the effect of an n-hexane extract of Myristica fragrans seeds on depression in mice by using the forced swim test (FST) and the tail suspension test (TST). M. fragrans extract (5, 10, and 20 mg/kg) was administered orally for 3 successive days to different groups of Swiss male young albino mice. M. fragrans extract significantly decreased immobility periods of mice in both the FST and the TST. The 10 mg/kg dose was found to be most potent, as indicated by the greatest decrease in the immobility period compared with the control. Furthermore, this dose of the extract was found to have comparable potency to imipramine (15 mg/kg i.p.) and fluoxetine (20 mg/kg i.p.). The extract did not have a significant effect on locomotor activity of mice. Prazosin (62.5 microg/kg i.p.; an alpha (1)-adrenoceptor antagonist), sulpiride (50 mg/kg i.p.; a selective D(2) receptor antagonist), and p-chlorophenylalanine (100 mg/kg i.p.; an inhibitor of serotonin synthesis) significantly attenuated the M. fragrans extract-induced antidepressant-like effect in the TST. Thus, extract of M. fragrans elicited a significant antidepressant-like effect in mice, when assessed in both the TST and the FST. The antidepressant-like effect of the extract seems to be mediated by interaction with the adrenergic, dopaminergic, and serotonergic systems.

A comparison of in vivo and in vitro neuroimaging of 5-HT1A receptor binding sites in the cat brain

To validate the cat as a suitable model for positron emission tomography imaging (PET) and to gain further knowledge on the anatomical distribution of the serotonin-1A receptor (5-HT 1A) in the feline brain, we used PET with [18F]MPPF and in vitro autoradiography with [3H]MPPF, [3H]8-OH-DPAT and [3H]paroxetine. PET radioactivity curves with [18F]MPPF were very reproducible in anaesthetized cats, with the highest radioactivity uptakes recorded in the hippocampus, cingulate cortex, septum, infralimbic cortex and raphe nucleus, whereas the lowest were found in the cerebellum. [3H]8-OH-DPAT binding displayed a comparable, albeit lower, regional distribution than with [3H]MPPF. Autoradiography also revealed the presence of 5-HT 1A receptor binding sites in the cortex and in the interpeduncular nucleus, due to its greater sensitivity and spatial resolution compared with PET imaging. The cat constitutes an interesting experimental model for PET imaging, as many physiological concepts have been well established with this animal. Our study also shows the advantages of combining complementary neuroimaging techniques such as in vivo PET imaging and in vitro autoradiography to visualize the distribution of the 5-HT 1A receptors.

Brain serotonin transporter density and aggression in abstinent methamphetamine abusers

CONTEXT

In animals, methamphetamine is known to have a neurotoxic effect on serotonin neurons, which have been implicated in the regulation of mood, anxiety, and aggression. It remains unknown whether methamphetamine damages serotonin neurons in humans.

OBJECTIVE

To investigate the status of brain serotonin neurons and their possible relationship with clinical characteristics in currently abstinent methamphetamine abusers.

DESIGN

Case-control analysis.

SETTING

A hospital research center.

PARTICIPANTS

Twelve currently abstinent former methamphetamine abusers (5 women and 7 men) and 12 age-, sex-, and education-matched control subjects recruited from the community.

INTERVENTIONS

The brain regional density of the serotonin transporter, a structural component of serotonin neurons, was estimated using positron emission tomography and trans-1,2,3,5,6,10-beta-hexahydro-6-[4-(methylthio)phenyl]pyrrolo-[2,1-a]isoquinoline ([(11)C](+)McN-5652). Estimates were derived from region-of-interest and statistical parametric mapping methods, followed by within-case analysis using the measures of clinical variables.

MAIN OUTCOME MEASURES

The duration of methamphetamine use, the magnitude of aggression and depressive symptoms, and changes in serotonin transporter density represented by the [(11)C](+)McN-5652 distribution volume.

RESULTS

Methamphetamine abusers showed increased levels of aggression compared with controls. Region-of-interest and statistical parametric mapping analyses revealed that the serotonin transporter density in global brain regions (eg, the midbrain, thalamus, caudate, putamen, cerebral cortex, and cerebellum) was significantly lower in methamphetamine abusers than in control subjects, and this reduction was significantly inversely correlated with the duration of methamphetamine use. Furthermore, statistical parametric mapping analyses indicated that the density in the orbitofrontal, temporal, and anterior cingulate areas was closely associated with the magnitude of aggression in methamphetamine abusers.

CONCLUSIONS

Protracted abuse of methamphetamine may reduce the density of the serotonin transporter in the brain, leading to elevated aggression, even in currently abstinent abusers.

Placental Transfer of Ondansetron during Early Human Pregnancy

BACKGROUND AND OBJECTIVE

Nausea and vomiting are common conditions that occur during early pregnancy and can be disabling. Ondansetron had been used in pregnant women when treatment with conventional antiemetics has failed; however, the safety and tolerability of this relatively new antiemetic drug during pregnancy is still uncertain. The objective of this study was to quantify the placental transfer of ondansetron in the first trimester of human pregnancy.

PATIENTS AND METHODS

This was a prospective, observational study. Forty-one patients who requested surgical termination of pregnancy at the first trimester were administered three doses of ondansetron 8 mg before surgery. Maternal venous blood, coelomic fluid, amniotic fluid and fetal tissue were collected from each patient for analysis of ondansetron by liquid chromatography-mass spectometry.

RESULTS

Ondansetron was found in all samples. Drug concentration in fetal tissue was significantly higher than that in the amniotic fluid and similar to that in the coelomic fluid. The median (interquartile range) fetal/maternal ratio was 0.41 (0.31-0.52) and there were no significant correlations between ondansetron concentrations in each compartment and gestational age.

CONCLUSIONS

A significant amount of ondansetron was present in all embryonic compartments. The developmental significance of this drug exposure requires further investigation, i.e. whole embryo culture.

Brain serotonin1A receptor binding in major depression is related to psychic and somatic anxiety

BACKGROUND

The anxious phenotype of the 5-HT1A receptor knockout mouse and the anxiolytic properties of 5-HT1A agonists suggest that the 5-HT1A receptor modulates anxiety. We investigated the relationship of anxiety expressed in major depressive disorder (MDD) to regional 5-HT1A binding.

METHODS

Positron emission tomography with [carbonyl-11C]WAY-100635 was used to estimate regional 5-HT1A binding potential (BP) in 28 medication-free MDD subjects. Stepwise linear regression assessed the predictive capacity of three anxiety components, derived from a larger MDD sample and termed psychic, somatic, and motoric anxiety, on regional 5-HT1A BP.

RESULTS

Higher psychic (beta >or= .63) and lower somatic (beta <or= -.70) anxiety predicted over 50% of the variance in 5-HT1A BP in multiple cortical regions, but not in amygdala, hippocampus, or autoreceptors of the raphe nuclei. The psychic and somatic anxiety components were not related to depression severity. Comorbid panic disorder was associated with lower cortical and subcortical 5-HT1A BP.

CONCLUSIONS

The 5-HT1A receptor in the same brain regions has different relationships to psychic anxiety versus somatic anxiety. Lower 5-HT1A BP in panic disorder may be accounted for by higher somatic and lower psychic anxiety. Further study of the pathobiology of these anxiety components may identify distinct therapeutic targets or mechanisms.

Occupancy of striatal and extrastriatal dopamine D2/D3 receptors by olanzapine and haloperidol

There have been conflicting reports as to whether olanzapine produces lower occupancy of striatal dopamine D(2)/D(3) receptor than typical antipsychotic drugs and preferential occupancy of extrastriatal dopamine D(2)/D(3) receptors. We performed [(18)F] fallypride PET studies in six schizophrenic subjects treated with olanzapine and six schizophrenic subjects treated with haloperidol to examine the occupancy of striatal and extrastriatal dopamine receptors by these antipsychotic drugs. [(18)F] setoperone PET studies were performed in seven olanzapine-treated subjects to determine 5-HT(2A) receptor occupancy. Occupancy of dopamine D(2)/D(3) receptors by olanzapine was not significantly different from that seen with haloperidol in the putamen, ventral striatum, medial thalamus, amygdala, or temporal cortex, that is, 67.5-78.2% occupancy; olanzapine produced no preferential occupancy of dopamine D(2)/D(3) receptors in the ventral striatum, medial thalamus, amygdala, or temporal cortex. There was, however, significantly lower occupancy of substantia nigra/VTA dopamine D(2)/D(3) receptors in olanzapine-treated compared to haloperidol-treated subjects, that is, 40.2 vs 59.3% (p=0.0014, corrected for multiple comparisons); in olanzapine-treated subjects, the substantia nigra/VTA was the only region with significantly lower dopamine D(2)/D(3) receptor occupancy than the putamen, that is, 40.2 vs 69.2% (p<0.001, corrected for multiple comparison). Occupancy of 5-HT(2A) receptors was 85-93% in the olanzapine- treated subjects. The results of this study demonstrated that olanzapine does not produce preferential occupancy of extrastriatal dopamine D(2)/D(3) receptors but does spare substantia nigra/VTA receptors. Sparing of substantia nigra/VTA dopamine D(2)/D(3) receptor occupancy may contribute to the low incidence of extrapyramidal side effects in olanzapine-treated patients.

Hypothalamic 5-HT functional regulation through 5-HT1A and 5-HT2C receptors during pancreatic regeneration

5-HT receptors are predominantly located in the brain and are involved in pancreatic function and cell proliferation through sympathetic nervous system. The objective of this study was to investigate the role of hypothalamic 5-HT, 5-HT1A and 5-HT2C receptor binding and gene expression in rat model of pancreatic regeneration using 60% pancreatectomy. The pancreatic regeneration was evaluated by 5-HT content, 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus of sham operated, 72 h and 7 days pancreatectomised rats. 5-HT content was quantified by HPLC. 5-HT1A receptor assay was done by using specific agonist [3H]8-OH DPAT. 5-HT2C receptor assay was done by using specific antagonist [3H]mesulergine. The expression of 5-HT1A and 5-HT2C receptor gene was analyzed by RT-PCR. 5-HT content was higher in the hypothalamus of 72 h pancreatectomised rats. 5-HT1A and 5-HT2C receptors were down-regulated in the hypothalamus. RT-PCR analysis revealed decreased 5-HT1A and 5-HT2C receptor mRNA expression. The 5-HT1A and 5-HT2C receptors gene expression in the 7 days pancreatectomised rats reversed to near sham level. This study is the first to identify 5-HT1A and 5-HT2C receptor gene expression in the hypothalamus during pancreatic regeneration in rats. Our results suggest the hypothalamic serotonergic receptor functional regulation during pancreatic regeneration.

Sustained pharmacological blockade of NK1 substance P receptors causes functional desensitization of dorsal raphe 5-HT 1A autoreceptors in mice

Antagonists at NK1 substance P receptors have demonstrated similar antidepressant properties in both animal paradigms and in human as selective serotonin reuptake inhibitors (SSRIs) that induce desensitization of 5-HT 1A autoreceptors within the dorsal raphe nucleus (DRN). We investigated whether this receptor adaptation also occurs upon NK1 receptor blockade. C57B/L6J mice were treated for 21 days with the selective NK1 receptor antagonist GR 205171 (10 mg/kg daily) through subcutaneously implanted osmotic mini pumps, and DRN 5-HT 1A autoreceptor functioning was assessed using various approaches. Recording of DRN serotonergic neurons in brainstem slices showed that GR 205171 treatment reduced (by approximately 1.5 fold) the potency of the 5-HT 1A receptor agonist, ipsapirone, to inhibit cell firing. In parallel, the 5-HT 1A autoreceptor-mediated [35S]GTP-gamma-S binding induced by 5-carboxamidotryptamine onto the DRN in brainstem sections was significantly decreased in GR 205171-treated mice. In vivo microdialysis showed that the cortical 5-HT overflow caused by acute injection of the SSRI paroxetine (1 mg/kg) was twice as high in GR 205171-treated as in vehicle-treated controls. In the DRN, basal 5-HT outflow was significantly enhanced by GR 205171 treatment. These data supported the hypothesis that chronic NK1 receptor blockade induces a functional desensitization of 5-HT 1A autoreceptors similar to that observed with SSRIs.

Brain serotonin transporter distribution in subjects with impulsive aggressivity: a positron emission study with [11C]McN 5652

OBJECTIVE

The serotonin system is believed to play a role in modulating impulsivity and violence. Previous imaging studies have implicated the anterior cingulate and orbitofrontal cortex in impulsive aggression. This study evaluated regional serotonin transporter distribution in the brain of individuals with impulsive aggression by using positron emission tomography (PET) with the serotonin transporter PET radiotracer [(11)C]McN 5652.

METHOD

Ten individuals with impulsive aggression and 10 age- and sex-matched healthy comparison subjects underwent [(11)C]McN 5652 PET. All individuals were medication free at the time of scanning. Regional total distribution volumes were derived by using a one-tissue compartment kinetic model with arterial input function. Outcome measures of serotonin transporter availability included the binding potential and the specific-to-nonspecific partition coefficient (V(3)'').

RESULTS

Serotonin transporter availability was significantly reduced in the anterior cingulate cortex of individuals with impulsive aggression compared with healthy subjects, as noted by differences in both binding potential (mean=3.1 ml/g [SD=1.9] versus 5.0 ml/g [SD=2.0], respectively) and V(3)'' (mean=0.15 [SD=0.09] versus 0.26 [SD=0.09]). In other regions examined, serotonin transporter density was nonsignificantly lower in individuals with impulsive aggression compared with healthy subjects.

CONCLUSIONS

Pathological impulsive aggressivity might be associated with lower serotonergic innervation in the anterior cingulate cortex, a region that plays an important role in affective regulation.

Molecular Determinants of Picrotoxin Inhibition of 5-Hydroxytryptamine Type 3 Receptors

Previously, we reported that the GABA(A) receptor antagonist picrotoxin also antagonizes serotonin (5-HT)3 receptors and that its effects are subunit-dependent. Here, we sought to identify amino acids involved in picrotoxin inhibition of 5-HT3 receptors. Mutation of serine to alanine at the transmembrane domain 2 (TM2) 2' position did not affect picrotoxin (PTX) sensitivity in murine 5-HT3A receptors. However, mutation of the 6' TM2 threonine to phenylalanine dramatically reduced PTX sensitivity. Mutation of 6' asparagine to threonine in the 5-HT3B subunit enhanced PTX sensitivity in heteromeric 5-HT3A/3B receptors. Introduction of serine (native to the human 3B subunit) at the 6' position also increased PTX sensitivity, suggesting a species-specific effect. Mutation of the 7' leucine to threonine in 5-HT3A receptors increased PTX sensitivity roughly 10-fold, comparable with that observed in GABA(A) receptors, and also conferred distinct gating kinetics. The equivalent mutation in the 3B subunit (i.e., 7' valine to threonine) had no impact on PTX sensitivity in 5-HT3A/3B receptors. Interestingly, [3H]ethynylbicycloorthobenzoate ([3H]EBOB), a high-affinity ligand to the convulsant site in GABA(A) receptors, did not exhibit specific binding in 5-HT3A receptors. The structurally related compound, tert-butylbicyclophosphorothionate (TBPS), which potently inhibits GABA(A) receptors, did not inhibit 5-HT3 currents. Our results indicate that the TM2 6' residue is a common determinant of PTX inhibition of both 5-HT3 and GABA(A) receptors and demonstrate a role of the 7' residue in PTX inhibition. However, lack of effects of EBOB and TBPS in 5-HT3A receptors suggests that the functional domains in the two receptors are not equivalent and underscores the complexity of PTX modulation of LGICs.

Risperidone Withdrawal-Related Respiratory Dyskinesia

Risperidone is a frequently used member of a new class of atypical antipsychotics-the serotonin-dopamine antagonists (SDAs)-due to its comparatively high efficacy and low D2/5HT2 binding ratio, which results in a low incidence of extrapyramidal side effects including tardive dyskinesia (TD). The authors present an elderly patient with mixed dementia who developed TD at multiple sites, (including respiratory dyskinesia [RD], limb dyskinesia, and orofacial dyskinesia) following abrupt withdrawal of risperidone therapy. RD is not a rare condition, but is often misdiagnosed and is potentially lethal. Therefore, clinicians should pay close attention to possible onset of RD in patients with multiple risk factors for TD, even when SDA therapy is used. If RD is suspected, assessment should include spirography combined with fibroscopy for examination of irregularities in the rate, rhythm, and depth of respiration.

[11C]-WAY100635 PET demonstrates marked 5-HT1A receptor changes in sporadic ALS

The pathogenesis of amyotrophic lateral sclerosis (ALS) remains obscure, but it is now clear that neuronal loss is not confined to the motor cortex, even in cases without dementia. A reliable method of assessing cortical involvement in vivo remains elusive. WAY100635 binds selectively to the 5-hydroxytryptamine (5-HT1A) receptor, which is expressed on pyramidal neurones present throughout the cortex. [11C]-WAY100635 PET is, therefore, a potential marker of cerebral neuronal loss or dysfunction in ALS. Twenty-one ALS subjects and 19 healthy volunteers underwent [11C]-WAY100635 PET of the brain. A cortical template consisting of multiple volumes of interest (VOI) was applied to each individual's [11C]-WAY100635 binding potential (BP) image to determine the regional reduction in binding in ALS patients compared to controls. There was a marked reduction (21%) in both the global cortical and raphe BP of [11C]-WAY100635 in ALS patients (P < 0.001), with regional variations in the VOI analysis that ranged from 16% to 29% decrease compared with the control group, and trends to greater reductions in those with bulbar involvement. To clarify the significance of the global cortical reductions, statistical parametric mapping was used as an alternative method to identify the cortical regions with the most significant decreases in [11C]-WAY100635 binding. SPM analysis revealed the greatest differences between ALS cases and controls in frontotemporal regions, cingulate and lateral precentral gyri. The reductions in cortical [11C]-WAY100635 binding were not related to depression, riluzole or other drug use. We postulate that the reduction of 5-HT1A binding represents loss of, or damage to, neurones bearing these receptors although we cannot exclude the possibility that these reductions reflect alterations in receptor expression or function. Further investigation into the role of the 5-HT1A receptor and the potential of [11C]-WAY100635 PET as a marker of cortical dysfunction in ALS is warranted.

Ondansetron and Delta-9-Tetrahydrocannabinol Interfere With the Establishment of Lithium-Induced Conditioned Taste Avoidance in the House Musk Shrew (Suncus murinus)

Considerable evidence suggests that rats can learn to avoid a taste in the absence of nausea. The current experiments evaluated the potential of the antiemetic agents, ondansetron (OND) and delta-9-tetrahydrocannabinol (THC), to interfere with lithium chloride (LiCl)-induced taste avoidance in the house musk shrew, Suncus murinus, an insectivore that, unlike rats, is capable of vomiting. At a dose that did not modify saccharin (Experiment 1) or sucrose (Experiment 2) intake, OND prevented the establishment of LiCl-induced taste avoidance in the shrew. A low dose of THC (1 mg/kg), which did not modify sucrose intake during conditioning, also prevented the establishment of LiCl-induced taste avoidance in the shrew. Higher doses of THC were also effective, but they also suppressed sucrose consumption during conditioning. These results suggest that nausea is a necessary component of the unconditioned stimulus for the establishment of conditioned taste avoidance in the shrew, unlike the rat, which does not vomit when injected with a toxin.

Anxiolytic-like effects of extracts from Albizzia julibrissin bark in the elevated plus-maze in rats

The purpose of the this study was to characterize the putative anxiolytic-like effects of the aqueous extract of Albizzia julibrissin stem bark using the elevated plus maze (EPM) in rats. The water extract of Albizzia julibrissin was orally administered at 10, 50, 100 or 200 mg/kg to adult male SD rats, 1 h before behavioral evaluation in an EPM, respectively. Control rats were treated with an equal volume of saline, and positive control rats buspirone (1 mg/kg). Single or repeated treatment (for 7 days) of the water extract of Albizzia julibrissin (at 100 or 200 mg/kg) significantly increased time-spent and arm entries into the open arms of the EPM, and decreased time-spent and arm entries in the closed arms of the EPM versus saline controls (P < 0.05). However, no changes in the locomotor activity and myorelaxant effect were seen in any group versus the saline control. In addition, the anxiolytic-like effects of Albizzia julibrissin extract were abolished by pindolol (10 mg/kg, i.p), a 5-HT(1A/1B) receptor antagonist. These results suggest that Albizzia julibrissin might proved to be an effective anxiolytic agent, and that it acts via the serotonergic nervous system.

A novel antipsychotic, perospirone, has antiserotonergic and antidopaminergic effects in human brain: findings from neuroendocrine challenge tests

RATIONALE

Perospirone is a new antipsychotic drug in which dopamine D(2) antagonist and serotonin 5-HT(2) antagonist effects have been found in animal studies. It was developed by a Japanese pharmaceutical company and launched in 2001. Perospirone's receptor binding profile may resemble that of atypical antipsychotic drugs, but to date there has been no evidence relating to its receptor binding affinity in the human brain.

OBJECTIVE

The purpose of this study was to investigate the receptor binding profile of perospirone via neuroendocrine challenge tests.

METHODS

Twenty subjects (ten females and ten males) were tested on four occasions in a double-blind, cross-over design receiving: (a) placebo, (b) perospirone 4 mg, (c) paroxetine 20 mg, and (d) paroxetine 20 mg plus perospirone 4 mg, administered orally at 8.00 a.m. Plasma cortisol and prolactin levels were measured prior to administration and every hour for 6 h thereafter. In addition, psychological responses rated by visual analog scales and vital signs such as body temperature, pulse, and blood pressure were assessed in combination with blood sampling.

RESULTS

Perospirone 4 mg increased prolactin levels significantly higher than placebo, whereas paroxetine 20 mg plus perospirone 4 mg significantly attenuated cortisol responses induced by paroxetine 20 mg.

CONCLUSIONS

The present findings suggest that perospirone has the characteristics of both D(2) and 5-HT(2) antagonist in the human brain. Further PET studies in the human brain are required in order to directly investigate these effects.

Inhibitory Effect of Glucocorticoids on Human-cloned 5-hydroxytryptamine3AReceptor Expressed in Xenopus Oocytes

Background

Methylprednisolone, dexamethasone, and other glucocorticoids have been found effective against nausea and vomiting induced by chemotherapy and surgery. Although the specific 5-hydroxytriptamine3 (5-HT3) receptor antagonists such as ondansetron and ramosetron are used as antiemetics, reports show that the use of 5-HT3 receptor antagonists with some glucocorticoids brings additional effects. Glucocorticoids are reported to be antiemetic. The effect of glucocorticoids on 5-HT3 receptor, however, has not been well characterized. This study was designed to examine whether dexamethasone and methylprednisolone had direct effects on human-cloned 5-HT3A receptor expressed in Xenopus oocytes.

Methods

Homomeric human-cloned 5-HT3A receptor was expressed in Xenopus oocytes. The authors used the two-electrode voltage-clamping technique to study the effect of methylprednisolone and dexamethasone on 5-HT-induced current.

Results

Both dexamethasone and methylprednisolone concentration-dependently attenuated 5-HT-induced current. Dexamethasone inhibited 2 microm 5-HT-induced current, which was equivalent to EC30 concentration for 5-HT3A receptor, with an inhibitory concentration 50% of 5.29 +/- 1.02 microm. Methylprednisolone inhibited 2 microm 5-HT-induced current with an inhibitory concentration 50% of 1.07 +/- 0.15 mm. The mode of inhibition with either dexamethasone or methylprednisolone was noncompetitive and voltage-independent. When administered together with the 5-HT3 receptor antagonists, ramosetron or metoclopramide, both glucocorticoids showed an additive effect on 5-HT3 receptor.

Conclusion

The glucocorticoids had a direct inhibitory effect on 5-HT3 receptors. The combined effect of glucocorticoids and the 5-HT3 receptor antagonists seems additive.

Preferential 5-HT1A autoreceptor occupancy by pindolol is attenuated in depressed patients: effect of treatment or an endophenotype of depression?

Using positron emission tomography and the selective 5-HT1A receptor radioligand [11C]WAY100635, we previously demonstrated a preferential occupancy of 5-HT1A autoreceptors, compared to postsynaptic receptors by pindolol in healthy volunteers. We have speculated that preferential occupancy may be clinically important for the purported actions of pindolol in accelerating the antidepressant effects of selective serotonin re-uptake inhibitors (SSRIs). In this study, we have examined the preferential occupancy by pindolol of 5-HT1A autoreceptors, following three different pindolol regimes (10 mg single dose, 2.5 mg t.i.d., and 5 mg t.i.d., in 15 depressed patients on SSRIs. In addition, seven healthy volunteers were examined following a single 10 mg dose of pindolol. We found a preferential occupancy of 22.6+/-7.7% following a single dose of 10 mg of pindolol, in the healthy volunteers, which was attenuated in depressed patients on the same dose of pindolol to 2.9+/-10.8% (Student's t=3.94, df=12, p=0.002). In addition, we found a significant negative correlation between the degree of preferential occupancy and the severity of depression as assessed by the Hamilton depression rating score (HAM-D), Spearman's rho=-0.728, N=14, p=0.003, in the depressed sample. A possible mechanism underlying preferential occupancy and the attenuation of this phenomenon in depressed patients on SSRIs may include changes in the proportion of high affinity 5-HT1A sites in the autoreceptor region of the midbrain raphe. Speculatively, the degree of preferential occupancy may serve as a surrogate marker for depression, or the pharmacological effects of antidepressants.