Serotonin 5-HT7 receptor is a biomarker poor prognostic factor and induces proliferation of triple-negative breast cancer cells through FOXM1.

BACKGROUND: Triple-negative breast cancer (TNBC) is an aggressive type of breast cancer and associated with poor prognosis and shorter survival due to significant genetic heterogeneity, drug resistance and lack of effective targeted therapeutics. Therefore, novel molecular targets and therapeutic strategies are needed to improve patient survival. Serotonin (5-hydroxytryptamine, 5-HT) has been shown to induce growth stimulatory effects in breast cancer. However, the molecular mechanisms by which 5-HT exerts its oncogenic effects in TNBC still are not well understood. METHODS: Normal breast epithelium (MCF10A) and two TNBC cells (MDA-MB-231, BT-546) and MCF-7 cells (ER +) were used to investigate effects of 5-HT7 receptor. Small interfering RNA (siRNA)-based knockdown and metergoline (5-HT7 antagonist) were used to inhibit the activity of 5-HT7. Cell proliferation and colony formation were evaluated using MTS cell viability and colony formation assays, respectively. Western blotting was used to investigate 5-HT7, FOXM1 and its downstream targets protein expressions. RESULTS: We demonstrated that 5-HT induces cell proliferation of TNBC cells and expression of 5-HT7 receptor and FOXM1 oncogenic transcription factor. We found that expression of 5-HT7 receptor is up-regulated in TNBC cells and higher 5-HT7 receptor expression is associated with poor patient prognosis and shorter patient survival. Genetic and pharmacological inhibition of 5-HT7 receptor by siRNA and metergoline, respectively, suppressed TNBC cell proliferation and FOXM1 and its downstream mediators, including eEF2-Kinase (eEF2K) and cyclin-D1. CONCLUSION: Our findings suggest for the first time that the 5-HT7 receptor promotes FOXM1, eEF2K and cyclin D1 signaling to support TNBC cell proliferation; thus, inhibition of 5-HT7 receptor/FOXM1 signaling may be used as a potential therapeutic strategy for targeting TNBC. 5-HT induces cell proliferation of TNBC cells through 5-HT7 receptor signaling. Also, genetic and pharmacological inhibition of 5-HT7 by RNAi (siRNA) and metergoline HTR7 antagonist, respectively inhibits FOXM1 oncogenic transcription factor and suppresses TNBC cell proliferation.

Conditional approach as cooperation in predator inspection: A role for serotonin?

In guppies (Poecilia reticulata), a small number of individuals break away from a shoal and approach a potential predator, a behavior termed "predator inspection". These animals often employ a "conditional approach" strategy, in which an individual approaches the predator in the first move and subsequently approaches it only if a second individual swims even with it during inspection. This strategy is analogous to the "tit-for-tat" strategy of the Prisoner's Dilemma, suggesting that it could be used to study cooperation. Serotonin is thought to mediate cooperative behavior in other fish species. Exposure to the animated image of a predator in a tank that contained a parallel mirror - mimicking an equally cooperating conspecific - promoted inspection and decreased refuge use, but increased freezing, suggesting that conditional approach is also associated with fear. To understand whether serotonin participates in conditional approach in guppies, we treated animals with either vehicle (Cortland's salt solution), fluoxetine (2.5 mg/kg) or metergoline (1 mg/kg), and tested then in a predator inspection paradigm. Fluoxetine increased the time the animal spent inspecting the predator image, while metergoline decreased it. Fluoxetine also decreased time spent avoiding the predator and increased freezing, while metergoline decreased freezing. These results suggest that phasic increases in serotonin levels promote conditional approach, suggesting a role for this neurotransmitter in cooperation. Preprint: https://doi.org/10.1101/436345; Data and scripts: https://github.com/lanec-unifesspa/TFT.

A macrophage-based screen identifies antibacterial compounds selective for intracellular Salmonella Typhimurium.

Salmonella Typhimurium (S. Tm) establishes systemic infection in susceptible hosts by evading the innate immune response and replicating within host phagocytes. Here, we sought to identify inhibitors of intracellular S. Tm replication by conducting parallel chemical screens against S. Tm growing in macrophage-mimicking media and within macrophages. We identify several compounds that inhibit Salmonella growth in the intracellular environment and in acidic, ion-limited media. We report on the antimicrobial activity of the psychoactive drug metergoline, which is specific against intracellular S. Tm. Screening an S. Tm deletion library in the presence of metergoline reveals hypersensitization of outer membrane mutants to metergoline activity. Metergoline disrupts the proton motive force at the bacterial cytoplasmic membrane and extends animal survival during a systemic S. Tm infection. This work highlights the predictive nature of intracellular screens for in vivo efficacy, and identifies metergoline as a novel antimicrobial active against Salmonella.

Investigation of Antidepressant, Anxiolytic and Sedative Activities of the Aqueous Leaf Extract of Musa sapientum Linn. (Banana; Musaceae).

BACKGROUND: Musa sapientum Linn. (Musaceae) is used in traditional African medicine in the management of mental disorders. This study was conducted to evaluate the central nervous system activities of the aqueous leaf extract of M. sapientum (MS). MATERIALS AND METHODS: MS (50, 100 and 200 mg/kg, p.o.) was administered to separate groups of mice 1 h before behavioural studies. The antidepressant effect was studied using the forced swimming test (FST) and tail suspension test (TST) while the elevated plus maze (EPM) and the hole-board tests were used to evaluate the anxiolytic effect. The probable mechanism of antidepressant-like effect was also investigated. RESULTS: MS (50, 100 and 200 mg/kg) produced significant (P<0.0001) reduction in the duration of immobility with peak effect at 200 mg/kg (79.6%) in FST and 66.9 % in TST respectively when compared with control. The pre-treatment of mice with prazosin (α1-adrenoceptor antagonist, 62.5 µg/kg, i.p.) and sulpiride (dopamine D2 receptor antagonist, 50 mg/kg, i.p.) significantly prevented the antidepressant effect produced by MS in FST. However, pre-treatment of mice with metergoline (5-HT2 receptor antagonist, 4 mg/kg, i.p.) and yohimbine (α2-adrenoceptor antagonist, 1 mg/kg, i.p.) did not prevent the antidepressant effect of MS. In the EPM test, MS did not significantly increase open arm exploration. It also did not significantly increase the number of head dips in the hole-board test. CONCLUSIONS: Results showed that MS had antidepressant activity possibly mediated through α1-adrenergic and D2 dopaminergic receptors, without significant anxiolytic effect.

Molecular basis involved in the blocking effect of antidepressant metergoline on C-type inactivation of Kv1.4 channel.

Voltage-gated potassium channels (VGKCs) are transmembrane ion channels specific for potassium. Currently there are nine kinds of VGKCs. Kv1.4 is one of shaker-related potassium channels. It is a representative alpha subunit of potassium channels that can inactivate A type-currents, leading to N pattern inactivation. Inactivation of Kv channels plays an important role in shaping electrical signaling properties of neuronal and muscular cells. The shape of N pattern inactivation can be modified by removing the N-terminal (NT) domain which results in non-inactivated currents and C pattern inactivation. In a previous work, we have reported the regulatory effect of metergoline on Kv1.4 and Nav1.2 channel activity. In the present study, we constructed a mutant of deleted 61 residues from NT of Kv1.4 channels (Kv1.4 Δ2-61) and found that it induced an outward peak and steady-state currents We also studied the modulation effect of metergoline on the activity of this Kv1.4 Δ2-61 mutant channel without having the N-terminal quick inactivation domain. Our results revealed that treatment with metergoline inhibited NT deleted Kv1.4 mutant channel activity in a concentration-dependent manner which was reversible. Interestingly, metergoline treatment induced little effects on the outward peak current in the deleted Kv1.4 mutant channel. However, metergoline treatment conspicuously inhibited steady state currents of Kv1.4 Δ2-61 channels with acceleration current mode. The acceleration of steady-state current of deleted Kv1.4 mutant channel occurred in a concentration-dependent manner. This means that metergoline can accelerate C pattern inactivation of Kv1.4 Δ2-61 channel by acting as an open state dependent channel blocker. We also performed site-directed mutations in V561A and K532Y, also known as C-type inactivation sites. V561A, K532Y, and V561A + K532Y substitution mutants significantly attenuated the acceleration effect of metergoline on C pattern inactivation of hKv1.4 channel currents. In docking modeling study, predicted binding residues for metergoline were analyzed for six amino acids. Among them, the K532 residue known as the C-type inactivation site was analyzed to be a major site of action. Then various mutants were constructed. K532 substitution mutant significantly abolished the effect of metergoline on Kv1.4 currents among various mutants whereas other changes had slight inhibitory effects. Furthermore, we found that metergoline had specificity for Kv1.4, but not for Kv1.5 currents. In addition, the A type current in rat neuronal cell was inhibited and accelerated of inactivation. This result further shows that metergoline might interact with Lys532 residue and then accelerate C pattern inactivation of Kv1.4 channels with channel type specificity. Taken together, these results demonstrate the molecular basis involved in the effect of metergoline, an ergot alkaloid, on human Kv1.4 channel, providing a novel interaction ligand.

Cortical Circuit Activity Evokes Rapid Astrocyte Calcium Signals on a Similar Timescale to Neurons.

Sensory stimulation evokes intracellular calcium signals in astrocytes; however, the timing of these signals is disputed. Here, we used novel combinations of genetically encoded calcium indicators for concurrent two-photon imaging of cortical astrocytes and neurons in awake mice during whisker deflection. We identified calcium responses in both astrocyte processes and endfeet that rapidly followed neuronal events (∼120 ms after). These fast astrocyte responses were largely independent of IP3R2-mediated signaling and known neuromodulator activity (acetylcholine, serotonin, and norepinephrine), suggesting that they are evoked by local synaptic activity. The existence of such rapid signals implies that astrocytes are fast enough to play a role in synaptic modulation and neurovascular coupling. VIDEO ABSTRACT.

Potentials of Mangifera indica in the treatment of depressive-anxiety disorders: possible mechanisms of action.

BACKGROUND: Mangifera indica (Anacardiaceae) is an important herb in the traditional African and Ayurvedic medicines. The stem barks are used in the treatment of hypertension, insomnia, tumour, depression, rheumatism and as a tonic. This study was carried out to investigate antidepressant- and anxiolytic-like effect of the hydroethanol stem bark extract of M. indica (HeMI) in mice. METHODS: HeMI (12.5-100 mg/kg, p.o.) was administered 1 h before subjecting the animal to the forced swim test (FST), tail suspension test (TST) and elevated plus maze tests (EPM). RESULTS: HeMI (12.5-100 mg/kg, p.o.) treatment produced significant reduction in immobility time [F(6.56)=8.35, p<0.001], [F(6,56)=7.55, p<0.001] in the FST and TST, respectively. Moreover, co-administration of sub-therapeutic doses of imipramine or fluoxetine with HeMI (3.125 mg/kg) elicited significant reduction in time spent immobile in the FST. However, pretreatment of mice with parachlorophenylalanine, metergoline, yohimbine or sulpiride abolished the antidepressant-like effect elicited by HeMI. In the EPM, HeMI produced significant [F(5,42)=8.91, p<0.001] increase in open arms exploration by 75.55 % and this effect was blocked by pretreatment of mice with flumazenil or metergoline. CONCLUSIONS: Findings from this study showed antidepressant-like effect of M. indica through interaction with 5-HT2 receptor, α2-adrenoceptor and dopamine D2-receptors. Also, an anxiolytic-like effect through its affinity for 5-HT2 and benzodiazepine receptors. Hence, M. indica could be a potential phytotherapeutic agent in the treatment of mixed anxiety-depressive illness.

Regulation of Human Kv1.4 Channel Activity by the Antidepressant Metergoline.

Metergoline is an ergot-derived psychoactive drug that is a ligand for various serotonin and dopamine receptors. Little is known about the effect of metergoline on different types of receptors and ion channels. Potassium channels are the most diverse group of ion channels. Kv1.4, a shaker family K channel alpha subunit, is one of a family of voltage gated K channels that mediates transient and rapid inactivating A-type currents and N-type inactivation. We demonstrated previously that metergoline inhibited the activity of neuronal voltage-dependent Na(+) channels in Xenopus laevis oocytes (Acta Pharmacol. Sin., 35, 2014, Lee et al.). In this study, we sought to elucidate the regulatory effects underlying metergoline-induced human Kv1.4 channel inhibition. We used the two electrode voltage-clamp (TEVC) technique to investigate the effect of metergoline on human Kv1.4 channel currents in Xenopus laevis oocytes expressing human Kv1.4 alpha subunits. Interestingly, metergoline treatment also induced inhibition of peak currents in human Kv1.4 channels in a concentration-dependent manner. The IC50 of peak currents of hKv1.4 currents was 3.6±0.6 µM. These results indicate that metergoline might regulate the human Kv1.4 channel activity that is expressed in X. laevis oocytes. Further, this regulation of potassium currents by metergoline might be one of the pharmacological actions of metergoline-mediated psychoactivity.

Development of a screening method to identify regulators of MICA shedding.

Immune cells, such as natural killer (NK) cells, recognize virally infected and transformed cells, and eliminate them through the interaction between NKG2D receptors on NK cells and NKG2D ligands on pathogenic cells. Shedding of NKG2D ligands is thought to be a type of counter-mechanism employed by pathogenic cells to evade from NKG2D-mediated immune surveillance. MHC class I polypeptide-related sequence A (MICA) is a prototypical NKG2D ligand. We previously reported that, in soluble form, MICA expression levels are significantly associated with hepatitis virus-induced hepatocellular carcinoma. Here, we report a MICA shedding assay that utilizes membrane-bound MICA tagged at its N-terminus with a nano-luciferase reporter to quantify MICA shedding into culture media. Using this method, we screened a compound library and identified putative regulators of MICA shedding that have the potential to enhance the immune reaction by simultaneously increasing cell surface MICA levels and decreasing soluble MICA levels. This shedding assay may be useful for screening regulators of cell surface molecule shedding.

Antidepressant and anxiolytic effects of the methanol root extract of Capparis thonningii: involvement of monoaminergic, cholinergic and GABAergic systems.

BACKGROUND: Capparis thonningii Schum. (Capparaceae) is used in traditional African Medicine for the treatment of mood disorders. OBJECTIVE: The study investigates antidepressant and anxiolytic activities of methanol root extract of C. thonningii (CT). METHODS: CT (25-100 mg/kg, p. o.) was administered 1 h before behavioral studies were carried out in mice. Antidepressant effect was investigated using the forced swimming test (FST) and tail suspension test (TST). The anxiolytic effect was evaluated using the elevated-plus maze test (EPM), hole-board test (HBT), and light-dark test. RESULTS: CT (25 and 50 mg/kg) increased swimming activity (P<0.05) by 92.73% and attenuated immobility time by 35.72%, similar to anti-immobility effect of imipramine (33.87%) in FST. In addition, CT (50 mg/kg) significantly (P<0.01) reduced immobility time by 30.24% in TST. -However, the antidepressant-like effect elicited by CT was reversed by metergoline, cyproheptadine, and sulpiride (40.81, 45.93, and 48.52%, respectively) pretreatment but prazosin, and yohimbine failed to reverse this antidepressant-like effect. Similar to diazepam, CT (25 mg/kg) increased duration of open arms exploration (P<0.05) by 43.73% in EPM, number of head-dips (HBT) (90.32%), and time spent in the light compartment by 45.77% in light/dark test indicating anxiolytic-like effect. The anxiolytic-like effect of CT was reversed by flumazenil pretreatment. CONCLUSION: The findings from this study suggest antidepressant-like effect of C. thonningii involving interaction with serotonergic (5-HT2), dopaminergic (D2), noradrenergic (α1 and α2), and muscarinic cholinergic systems; and anxiolytic effect through an interaction with GABAA benzodiazepine receptor.

Metergoline inhibits the neuronal Nav1.2 voltage-dependent Na(+) channels expressed in Xenopus oocytes.

AIM: Metergoline is an ergot-derived psychoactive drug that acts as a ligand for serotonin and dopamine receptors. The aim of this study was to investigate the regulatory effects of metergoline on the neuronal Nav1.2 voltage-dependent Na(+) channels in vitro. METHODS: Xenopus oocytes were injected with cRNAs encoding rat brain Nav1.2 α and ß1 subunits. Voltage-activated Na(+) currents were recorded using two-electrode voltage clamp technique. Drugs were applied though perfusion. RESULTS: Both metergoline and lidocaine reversibly and concentration-dependently inhibited the peak of Na(+) currents with IC50 values of 3.6 ± 4.2 and 916.9 ± 98.8 µmol/L, respectively. Metergoline (3 µmol/L) caused a 6.8 ± 1.2 mV depolarizing shift of the steady-state activation curve of the Na(+) currents, and did not alter the inactivation curve. In contrast, lidocaine (3 µmol/L) caused a 12.7 ± 1.2 mV hyperpolarizing shift of the inactivation curve of the Na(+) currents without changing the steady-state activation curve. Both metergoline and lidocaine produced tonic and use-dependent inhibition on the peak of Na(+) currents. CONCLUSION: Metergoline exerts potent inhibition on the activity of neuronal Nav1.2 channels, which may contribute to its actions on the central nervous system.

5-HT receptor subtypes as key targets in mediating pigment dispersion within melanophores of teleost, Oreochromis mossambicus.

The presence of distinct class of 5-HT receptors in the melanophores of tilapia (Oreochromis mossambicus) is reported. The cellular responses to 5-HT (5-hydroxytryptamine), 5-HT(1), and 5-HT(2), agonists on isolated scale melanophores were observed with regard to pigment translocation within the cells. It was found that 5-HT exerted rapid and strong concentration dependent pigment granule dispersion within the melanophores. The threshold pharmacological dose of 5-HT that could elicit a measurable response was as low as 4.7×10(-12) M/L. Selective 5-HT(1) and 5-HT(2) agonists, sumatriptan and myristicin were investigated and resulted in dose-dependent pigment dispersion. The dispersing effects were effectively antagonized by receptor specific antagonists. It is suggested that 5-HT-induced physiological effects are mediated via distinct classes of receptors that possibly participate in modulation of pigmentary responses of the fish.

Cocaine modulates pathways for photic and nonphotic entrainment of the mammalian SCN circadian clock.

Cocaine abuse is highly disruptive to circadian physiological and behavioral rhythms. The present study was undertaken to determine whether such effects are manifest through actions on critical photic and nonphotic regulatory pathways in the master circadian clock of the mouse suprachiasmatic nucleus (SCN). Impairment of SCN photic signaling by systemic (intraperitoneal) cocaine injection was evidenced by strong (60%) attenuation of light-induced phase-delay shifts of circadian locomotor activity during the early night. A nonphotic action of cocaine was apparent from its induction of 1-h circadian phase-advance shifts at midday. The serotonin receptor antagonist, metergoline, blocked shifting by 80%, implicating a serotonergic mechanism. Reverse microdialysis perfusion of the SCN with cocaine at midday induced 3.7 h phase-advance shifts. Control perfusions with lidocaine and artificial cerebrospinal fluid had little shifting effect. In complementary in vitro experiments, photic-like phase-delay shifts of the SCN circadian neuronal activity rhythm induced by glutamate application to the SCN were completely blocked by cocaine. Cocaine treatment of SCN slices alone at subjective midday, but not the subjective night, induced 3-h phase-advance shifts. Lidocaine had no shifting effect. Cocaine-induced phase shifts were completely blocked by metergoline, but not by the dopamine receptor antagonist, fluphenazine. Finally, pretreatment of SCN slices for 2 h with a low concentration of serotonin agonist (to block subsequent serotonergic phase resetting) abolished cocaine-induced phase shifts at subjective midday. These results reveal multiple effects of cocaine on adult circadian clock regulation that are registered within the SCN and involve enhanced serotonergic transmission.

Serotonin mediated changes in corticotropin releasing factor mRNA expression and feeding behavior isolated to the hypothalamic paraventricular nuclei.

Fenfluramine reduces hunger and promotes body weight loss by increasing central serotonin (5-HT) signaling. More recently, neuropeptides have been linked to the regulation of feeding behavior, metabolism and body weight. To examine possible interactions between 5-HT and neuropeptides in appetite control, fenfluramine (200 nmol/0.5 µl/side) was administered directly into the hypothalamic paraventricular nuclei (PVN) of male rats. Bilateral fenfluramine produced significant hypophagia and increased expression of PVN corticotropin releasing factor (CRF) mRNA and neuropeptide Y (NPY) mRNA in the arcuate nucleus within the first hour after drug administration. Fenfluramine's effects on feeding behavior and mRNA expression were blocked by PVN injections of a 5-HT(1-2) receptor antagonist, metergoline (15 nmol/0.5 µl/side). These data suggest that 5-HT neurons targeting hypothalamic paraventricular CRF neurons may participate in an appetite control circuit for reducing food intake.

Inverse agonism at α2A adrenoceptors augments the hypophagic effect of sibutramine in rats.

Because the use of monoamine reuptake inhibitors as weight-reducing agents is limited by adverse effects, novel antiobesity drugs are needed. We studied acute effects of the noradrenaline (NA) and serotonin (5-HT) reuptake inhibitor sibutramine (SIB), alone and after pretreatment with α1- and α2-adrenoceptor (AR), and 5-HT1/2/7, 5-HT1B and 5-HT2C receptor antagonists in order to determine which ARs and 5-HT receptors act downstream of SIB on feeding and locomotion. Acute effects on caloric and water intake, meal microstructure and locomotion were assessed, using an automated weighing system and telemetry in male rats with restricted 18-h access to Western style diet. SIB 3 mg/kg reduced meal size and frequency, which suggests enhanced within- and postmeal satiety. Imiloxan (α2B-AR), WB4101 (α1-AR), SB-224289 (5-HT1B), and modestly BRL 44408 (α2A/D-AR) attenuated SIB's effect on meal size, suggesting that α2B- and α1-ARs and 5-HT1B receptors mediate within-meal satiety, with a modest role for α2A/D-ARs. Only prazosin (α1/2B/2C-AR) counteracted SIB's effect on meal frequency. At 3 mg/kg, SIB modestly increased locomotion. This effect was blocked by metergoline (5-HT1/2/7), WB4101 (α1-AR), and RX821002 (α2-AR). Interestingly, the α2-AR antagonists atipamezole and RX821002 enhanced SIB's effect on caloric intake, probably due to inverse agonistic actions at α2A-autoreceptors that further enhanced release of NA that regulates caloric intake. Thus, an inverse agonist of presynaptic α2A-ARs might beneficially enhance SIB's weight-reducing effect and offer novel treatment for obesity. All in all, the present data supports the ARs and 5-HT receptors involved in the effects of SIB on different aspects of caloric intake and locomotion.

Metergoline-induced cell death in Candida krusei.

Metergoline possesses potent antifungal activity against Candida krusei, a notorious yeast species that is inherently resistant to the common antifungal agents. In an attempt to elucidate the action mechanisms of metergoline, the present study was designed to investigate its effects on a number of classical markers of apoptosis in C. krusei. The results showed that transient exposure (2h) to metergoline led to a massive intracellular accumulation of reactive oxygen species (ROS) and depolarization of mitochondrial membrane potential in a concentration-dependent fashion. Analyses of the treated fungal cells after prolonged incubation (12h) with metergoline by flow cytometry and fluorescence microscopy clearly demonstrated phosphatidylserine externalization, the presence of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling-positive cells and fungal cells undergoing necrosis. Taken together, our data provide evidence that metergoline elicited cell death process in C. krusei through elevation of the intracellular ROS level and perturbation of mitochondrial homeostasis, followed by damage of nucleus and eventual cell demise.

Anxiolytic effects of a semipurified constituent of guaraná seeds on rats in the elevated T-maze test.

The objective of this study was to investigate the effects of chronic administration of a semi-purified extract (Purified Extract A--PEA; 4, 8, or 16 mg/kg) of PAULLINIA CUPANA (guaraná) seeds on rats submitted to the elevated T-maze (ETM) model of generalized anxiety and panic disorders. The selective serotonin (5-HT) reuptake inhibitor (SSRI) paroxetine (PAR; 3 mg/kg), was used as a positive control. To evaluate possible serotonergic and dopaminergic neurotransmission involvement in the action of PEA during the ETM test, ineffective doses of metergoline (MET; 5-HT (2A/2C) antagonist receptor) or sulpiride (SUL; dopaminergic receptor antagonist) were acutely administered together with the PEA. The locomotion of the rats was assessed in a circular arena following each drug treatment. Both PEA (8 and 16 mg/kg) and PAR (3 mg/kg) increased one-way escape latencies from the open arm of the ETM, indicating a panicolytic effect compared to the control group. MET, in higher doses (1, 2 or 3 mg/kg), produced a panicolytic effect in the ETM test, whereas SUL did not (10, 20 or 40 mg/kg). The panicolytic effect produced by PEA (8 mg/kg) was blocked by both MET (2 mg/kg) and SUL (20 mg/kg), whereas the panicolytic effect produced by PAR (3 mg/kg) was blocked only by MET (2 mg/kg). These results show that chronic treatment with PEA produces a panicolytic effect during the ETM test, and that the dopaminergic and the serotonergic neurotransmission systems are involved in this effect.

On the intrinsic regulation of neuropeptide Y release in the mammalian suprachiasmatic nucleus circadian clock.

Timing of the circadian clock of the suprachiasmatic nucleus (SCN) is regulated by photic and non-photic inputs. Of these, neuropeptide Y (NPY) signaling from the intergeniculate leaflet (IGL) to the SCN plays a prominent role. Although NPY is critical to clock regulation, neither the mechanisms modulating IGL NPY neuronal activity nor the nature of regulatory NPY signaling in the SCN clock are understood, as NPY release in the SCN has never been measured. Here, microdialysis procedures for in vivo measurement of NPY were used in complementary experiments to address these questions. First, neuronal release of NPY in the hamster SCN was rhythmic under a 14L : 10D photocycle, with the acrophase soon after lights-on and the nadir at midday. No rhythmic fluctuation in NPY occurred under constant darkness. Second, a behavioral phase-resetting stimulus (wheel-running at midday that induces IGL serotonin release) acutely stimulated SCN NPY release. Third, bilateral IGL microinjection of the serotonin agonist, (+/-)-2-dipropyl-amino-8-hydroxyl-1,2,3,4-tetrahydronapthalene (8-OH-DPAT) (another non-photic phase-resetting stimulant), at midday enhanced SCN NPY release. Conversely, similar application of the serotonin antagonist, metergoline, abolished wheel-running-induced SCN NPY release. IGL microinjection of the GABA agonist, muscimol, suppressed SCN NPY release. These results support an intra-IGL mechanism whereby behavior-induced serotonergic activity suppresses inhibitory GABAergic transmission, promoting NPY activity and subsequent phase resetting. Collectively, these results confirm IGL-mediated NPY release in the SCN and verify that its daily rhythm of release is dependent upon the 14L : 10D photocycle, and that it is modulated by appropriately-timed phase-resetting behavior, probably mediated by serotonergic activation of NPY units in the IGL.

A role for serotonin in the antidepressant activity of NG-Nitro-L-arginine, in the rat forced swimming test.

The present study determined regional serotonin (5-HT) synthesis and metabolism changes associated with the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NA) and the influence of 5-HT receptor blockade in the antidepressant-like actions of L-NA in the forced swimming test (FST). Regional effects of L-NA (5,10 and 20mg/kg i.p.) on tryptophan hydroxylase (TPH) activity, the rate limiting enzyme for 5-HT synthesis, were determined by measuring accumulation of the transient intermediate 5-hydoxytryptophan (5-HTP) following in vivo administration of the amino acid decarboxylase inhibitor, NSD 1015 (100mg/kg). L-NA (5-20mg/kg) dose dependently increased 5-HTP accumulation, particularly in the amygdaloid cortex, following exposure to the FST. L-NA also provoked an increase in regional brain 5-HIAA concentrations and in the 5-HIAA:5-HT metabolism ratio. Co-treatment with NSD-1015 failed to consistently modify the antidepressant-like effects of L-NA in the FST. Sub-active doses of L-NA (1mg/kg) and the 5-HT re-uptake inhibitor fluoxetine (2.5mg/kg) acted synergistically to increase swimming in the test. Co-treatment with the non-selective 5-HT receptor antagonist metergoline (1, 2 and 4mg/kg), attenuated the L-NA (20mg/kg)-induced reduction in immobility and increase in swimming behaviours. Metergoline alone however provoked an increase in immobility and reduction in swimming behaviours in the test. A similar response was obtained following co-treatment with the preferential 5-HT(2A) receptor antagonist ketanserin (5mg/kg) and the 5-HT(2C) receptor antagonist RO-430440 (5mg/kg). Co-treatment with the 5-HT(1A) receptor antagonist WAY 100635 (0.3mg/kg) or the 5-HT(1B) receptor antagonist GR 127935 (4mg/kg) failed to influence the antidepressant-like activity of L-NA. Taken together these data provide further support for a role for 5-HT in the antidepressant-like properties of NOS inhibitors.

In vitro synergistic effects of metergoline and antifungal agents against Candida krusei.

Metergoline, a serotonin receptor antagonist, was evaluated for its antifungal activity against the opportunistic human fungal pathogen Candida krusei by a broth microdilution assay. The minimal inhibitory concentration and minimal fungicidal concentration of metergoline against C. krusei were 4 and 8 µg ml(-1) respectively. Significant synergism was found in combination of metergoline with amphotericin B (fractional inhibitory concentration index: 0.375-0.5) by a chequerboard assay. Metergoline also inhibited extracellular phospholipase secretion in a dose-dependent manner, which may be a possible action mechanism of metergoline on C. krusei.