Gamma-aminobutyric acid (GABA) receptor mediates suanzaorentang, a traditional Chinese herb remedy, -induced sleep alteration

Summary The sedative-hypnotic medications, including benzodiazepines and non-benzodiazepines, are the most common treatments for insomnia. However, concerns regarding patterns of inappropriate use, dependence and adverse effects have led to caution in prescribing those sedative-hypnotic medications. On the other hand, a traditional Chinese herb remedy, suanzaorentang, has been efficiently and widely used in clinic for insomnia relief without severe side effects in Asia. Although suanzaorentang has been reported to improve sleep disruption in insomniac patients, its mechanism is still unclear. The present study was designed to elucidate the effects of oral administration of suanzaorentang on physiological sleep-wake architectures and its underlying mechanism in rats. We found that oral administration of suanzaorentang at the beginning of the dark onset dose-dependently increased non-rapid eye movement sleep (NREMS) during the dark period, but had no significant effect on rapid eye movement sleep (REMS). Our results also indicated that intracerebroventricular (ICV) administration of γ-aminobutyric acid (GABA) receptor type A antagonist, bicuculline, significantly blocked suanzaorentang-induced enhancement in NREMS during the dark period, but GABA_B receptor antagonist, 2-hydroxysaclofen had no effect. These results implicated that this traditional Chinese herb remedy, suanzaorentang increases spontaneous sleep activity and its effects may be mediated through the GABA_A receptors, but not GABA_B receptors.     

Regulation of GABAergic inhibition by serotonin signaling in prefrontal cortex: molecular mechanisms and functional implications

Serotonergic neurotransmission in prefrontal cortex (PFC) plays a key role in regulating emotion and cognition under normal and pathological conditios. Increasing evidence suggests that serotonin receptors are involved in the complex regulation of GABAergic inhibitory transmission in PFC. Activation of postsynaptic 5-HT₂ receptors in PFC pyramidal neurons inhibits GABA_A-receptor currents via phosphorylation of GABA_A receptor γ2 subunits by RACK1-anchored PKC. In contrast, activation of postsynaptic 5-HT₄ receptors produces an activity-dependent bi-directional regulation of GABA-evoked currents in PFC pyramidal neurons, which is mediated through phosphorylation of GABA_A-receptor β subunits by anchored PKA. On the presynaptic side, GABAergic inhibition is regulated by 5-HT through the activation of 5-HT₂, 5-HT₁, and 5-HT₃ receptors on GABAergic intereneurons. These data provide a molecular and cellular mechanism for serotonin to dynamically regulate synaptic transmission and neuronal excitability in the PFC network, which may underlie the actions of many antidepressant and antipsychotic drugs.     

Synthesis, structure–affinity relationships, and modeling of AMDA analogs at 5-HT2A and H1 receptors: Structural factors contributing to selectivity

Histamine H₁ and serotonin 5-HT_2A receptors present in the CNS have been implicated in various neuropsychiatric disorders. 9-Aminomethyl-9,10-dihydroanthracene (AMDA), a conformationally constrained diarylalkyl amine derivative, has affinity for both of these receptors. A structure–affinity relationship (SAFIR) study was carried out studying the effects of N-methylation, varying the linker chain length and constraint of the aromatic rings on the binding affinities of the compounds with the 5-HT_2A and H₁ receptors. Homology modeling of the 5-HT_2A and H₁ receptors suggests that AMDA and its analogs, the parent of which is a 5-HT_2A antagonist, can bind in a fashion analogous to that of classical H₁ antagonists whose ring systems are oriented toward the fifth and sixth transmembrane helices. The modeled orientation of the ligands are consistent with the reported site-directed mutagenesis data for 5-HT_2A and H₁ receptors and provide a potential explanation for the selectivity of ligands acting at both receptors.     

Clozapine's Antipsychotic Effects do not Depend on Blockade of 5-HT3 Receptors

Sixteen known 5-HT₃ receptor blockers, including clozapine, fully or partially reverse the inhibitory effect of 1 M GABA on [³⁵S]TBPS binding, indicating that they are also GABA_A antagonists, some of them selective for subsets of GABA_A receptors. The 5-HT₃ receptor blocker, ondansetron, has been reported to produce some antipsychotic and anxiolytic effects. However, no antipsychotic effects have been reported for a large number of highly potent 5-HT₃ receptor blockers. Like clozapine, ondansetron partially reverses the inhibitory effect of GABA on [³⁵S]TBPS binding. Additivity experiments suggest that ten 5-HT₃ receptor blockers tested at low concentrations preferentially block subtypes of GABA_A receptors that are among those blocked by clozapine. Wiley and Porter (29) reported that MDL-72222, the most potent GABA_A antagonist decribed here, partially generalizes (71%) with clozapine in rats trained to discriminate an interoceptive clozapine stimulus, but only at a dose that severly decreases responding. Tropisetron (ICS-205,930) exhibits both GABA-positive and GABA-negative effects. R-(+)-zacopride is 6-fold more potent than S-(–)-zacopride as a GABA_A antagonist. We conclude that the observed antipsychotic and, possibly, anxiolytic effects of some 5-HT₃ receptor blockers are due to selective antagonism of certain GABA_A receptors, and not to blockade of 5-HT₃ receptors. We speculate that the anxiolytic and sedative effects of clozapine and several other antipsychotic drugs may be due to selective blockade of 122 GABA_A receptors which are preferentially located on certain types of GABAergic interneurons (probably parvalbumin positive). Blockade of these receptors will increase the inhibitory output of these interneurons. So far, no highly potent GABA_A antagonists with clozapine-like selectivity have been identified. Such compounds may exhibit improved clozapine-like antipsychotic activity.     

Dipeptide Tyr-Leu (YL) exhibits anxiolytic-like activity after oral administration via activating serotonin 5-HT1A, dopamine D1 and GABAA receptors in mice

We found that Tyr-Leu (YL) dose-dependently exhibits potent anxiolytic-like activity (0.1-1 mg/kg, i.p.) comparable to diazepam in the elevated plus-maze test in mice. YL was orally active (0.3-3 mg/kg). A retro-sequence peptide or a mixture of Tyr and Leu was inactive. The anxiolytic-like activity of YL was inhibited by antagonists for serotonin 5-HT_1A, dopamine D₁ and GABA_A receptors; however, YL had no affinity for them. We also determined the order of their activation is 5-HT_1A, D₁ and GABA_A receptors using selective agonists and antagonists. Taken together, YL may exhibit anxiolytic-like activity via activation of 5-HT_1A, D₁ and GABA_A receptors.     

DHA prevents altered 5-HT1A, 5-HT2A,CB1 and GABAA receptor binding densities in the brain of male rats fed a high-saturated-fat diet

Low levels of docosahexaenoic acid (DHA) have been linked to a number of mental illnesses such as memory loss, depression and schizophrenia. While supplementation of DHA is beneficial in improving memory and cognition, the influence of dietary fats on the neurotransmitters and receptors involved in cognitive function is still not known. The aim of this study was to investigate serotonin receptor (5-HT_1A and 5-HT_2A), cannabinoid receptor (CB1) and gamma-aminobutyric acid type A (GABA_A) receptor binding densities in the brain of male rats fed a high-saturated-fat (HF) diet, as well as the effect of DHA supplementation on HF diet. Alterations of these receptors in the post-mortem rat brain were detected by [³H]-WAY-100635, [³H]-ketanserin, [³H]-CP-55,940 and [³H]-muscimol binding autoradiography, respectively. In the hippocampus, the 5-HT_1A, CB1 and GABA_A receptor binding densities significantly increased in response to an HF diet, while in the hypothalamus, 5-HT_1A and CB1 binding densities significantly increased in HF-fed rats. Importantly, DHA supplementation prevented the HF-induced increase of receptors binding density in the hippocampus and hypothalamus. Furthermore, DHA supplementation attenuated 5-HT_2A receptor binding density in the caudate putamen, anterior cingulate cortex and medial mammillary nucleus, which was also increased in HF group. This study showed that an HF diet increased 5-HT_1A, 5-HT_2A, CB1 and GABA_A receptor binding densities in the brain regions involved in cognitive function and that dietary DHA can attenuate such alterations. These findings provide insight into the mechanism by which DHA supplementation ameliorates reduced cognitive function associated with an HF diet.     

MPPF et imagerie des récepteurs 5-HT1A de la sérotonine

[¹⁸F]MPPF is a 5-HT_1A antagonist of serotonin receptors, with interesting pharmacological properties. Its labelling is obtained with fluorine 18 and PET studies achieve molecular and functional neuroimaging of 5-HT_1A serotonin receptors.     

Time- and Behavioral State-Dependent Changes in Posterior Hypothalamic GABAA Receptors Contribute to the Regulation of Sleep

Sleep-wake behavior is regulated by a circadian rhythm, homeostatically and by additional mechanisms that determine the timing of slow-wave sleep and rapid eye movement sleep (REMS) episodes. The posterior hypothalamus coordinates the neural and humoral signals with the rest-activity cycle. It contains wake-active neurons, and is a site where stimulation of inhibitory GABA_A receptors promotes sleep, whereas their antagonism enhances wakefulness. We explored whether GABAergic mechanisms present in the posterior hypothalamus contribute to the homeostatic and other aspects of sleep-wake regulation. Using micropunches of tissue extracted from either the perifornical (PF) or dorsomedial (DM) regions of the posterior hypothalamus of rats, we determined that mRNA levels for selected subunits of GABA_A receptors (β1, β3 and ε) were higher at the end of the active period or following sleep deprivation, when the need for sleep is high, than after several hours of sleep, when sleep need is partially fulfilled. Such a pattern was present in the PF region only, and was consistent with changes in β1 subunit and GABA synthesizing enzyme (GAD) protein levels. In contrast, in the DM region, the levels of GABA_A receptor subunit mRNAs and proteins (α1, α2, β1) and GAD varied with circadian time, but were not responsive to sleep deprivation. Separate experiments with sleep-wake monitoring and local perfusion of the PF region with the GABA_A receptor antagonist bicuculline revealed that the antagonist had a weaker sleep-reducing effect when sleep need was enhanced by sleep deprivation and that the increased amount of REMS characteristic of the late sleep period was dependent on endogenous GABAergic inhibition. These results support the concept that a varying magnitude of GABAergic inhibition exerted within the PF region contributes to the homeostatic regulation of sleep and shapes its temporal pattern, whereas GABAergic mechanisms in the DM region contribute to circadian regulation.     

Relationship between 5-HT2A receptor mRNA density and contractility in trachea and aorta from guinea pig and rat

The present studies document marked differences in contractile responsiveness to serotonin in trachea and aorta between guinea pig and rat. For example, the guinea pig trachea and rat aorta markedly contract in response to serotonin via activation of 5-HT_2A receptors. In contrast, the rat and guinea pig aorta only modestly contract to serotonin. The availability of 5-HT_2A receptor selective cDNA clones from brain of both guinea pig and rat permitted molecular probes to be designed and PCR amplification studies initiated to identify and quantify 5-HT_2A receptor specific mRNA in these tissues. For trachea, 3-fold higher concentrations of 5-HT_2A receptor specific mRNA were found in guinea pig relative to rat trachea. These data are consistent with the more profound contractile response to serotonin in guinea pig versus rat trachea and suggest that differences in tracheal contractility to serotonin correlate with the density of 5-HT_2A receptor mRNA. In contrast, although rat aorta contracted more dramatically to serotonin than guinea pig aorta, rat aorta possessed a similar concentration of 5-HT_2A receptor specific mRNA as compared to guinea pig aorta. Thus, for the aorta, differences in the concentration of 5-HT_2A receptor mRNA are not sufficient to explain the observed differences in contractility between tissues from guinea pig and rat. These studies documenting 5-HT_2A receptor mRNA in rat trachea and guinea pig aorta, two tissues that do not markedly contract in response to serotonin indicate that 5-HT_2A receptor mRNA although present, has not resulted in a receptor capable of mediating a contractile response in these tissues.     

The Human Serotonin 1A Receptor Expressed in Neuronal Cells: Toward a Native Environment for Neuronal Receptors

1. The serotonin_1A (5-HT_1A) receptor is an important representative of G-protein coupled family of receptors. It is the most extensively studied among the serotonin receptors, and appears to be involved in various behavioral and cognitive functions.2. We report here the pharmacological and functional characterization of the human serotonin_1A receptor stably expressed in HN2 cell line, which is a hybrid cell line between hippocampal cells and mouse neuroblastoma.3. Our results show that serotonin_1A receptors in HN2-5-HT_1AR cells display ligand-binding properties that closely mimic binding properties observed with native receptors. We further demonstrate that the differential discrimination of G-protein coupling by the specific agonist and antagonist, a hallmark of the native receptor, is maintained for the receptor in HN2-5-HT_1AR cells. Importantly, the serotonin_1A receptor in HN2-5-HT_1AR cells shows efficient downstream signalling by reducing cellular cyclic AMP levels.4. We conclude that serotonin_1A receptors expressed in HN2-5-HT_1AR cells represent a useful model system to study serotonin_1A receptor biology, and is a potential system for solubilization and purification of the receptor in native-like membrane environment.     

Role of 5-HT1A receptors in fluoxetine-induced lordosis inhibition

The selective serotonin reuptake inhibitor (SSRI), fluoxetine (Prozac®), is an effective antidepressant that is also prescribed for other disorders (e.g. anorexia, bulimia, and premenstrual dysphoria) that are prevalent in females. However, fluoxetine also produces sexual side effects that may lead patients to discontinue treatment. The current studies were designed to evaluate several predictions arising from the hypothesis that serotonin 1A (5-HT_1A) receptors contribute to fluoxetine-induced sexual dysfunction. In rodent models, 5-HT_1A receptors are potent negative modulators of female rat sexual behavior. Three distinct experiments were designed to evaluate the contribution of 5-HT_1A receptors to the effects of fluoxetine. In the first experiment, the ability of the 5-HT_1A receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY100635), to prevent fluoxetine-induced lordosis inhibition was examined. In the second experiment, the effects of prior treatment with fluoxetine on the lordosis inhibitory effect of the 5-HT_1A receptor agonist, (±)-8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), were studied. In the third experiment, the ability of progesterone to reduce the acute response to fluoxetine was evaluated. WAY100635 attenuated the effect of fluoxetine; prior treatment with fluoxetine decreased 8-OH-DPAT's potency in reducing lordosis behavior; and progesterone shifted fluoxetine's dose-response curve to the right. These findings are consistent with the hypothesis that 5-HT_1A receptors contribute to fluoxetine-induced sexual side effects.     

Brainstem 5-Hydroxytrytamine1A Binding Sites are not Down-Regulated by Agonists which Induce Tolerance in the Rat: Myoclonus and other Serotonergic Behaviors

Abstract

To study the regulation of 5-HT_1A receptors in the brainstem, the region most relevant to the serotonin syndrome and to serotonin-responsive human myoclonic disorders, we chronically treated rats with various 5-HT_1A agonists and labeled 5-HT_1A sites with [³H]8-OH-DPAT. Daily injection for 30 consecutive days of 10 mg/kg ip 8-OH-DPAT (pre- and post-synaptic 5-HT_1A agonist) significantly decreased 8-OH-DPAT-evoked flat body posture, forelimb myoclonus, and hypothermia compared to chronic vehicle injection. There was no cross tolerance to 8-OH-DPAT in rats chronically injected with ipsapirone or buspirone (presynaptic 5-HT_1A agonists). However, none of the 5HT_1A agonists significantly altered B_max of brainstem 5-HT_1A binding sites. Chronic injection with other drugs such as 1-propranolol, (±) pindolol and spiperone (5-HT_1A and 5-HT₂ antagonists), methysergide (5-HT₁ and 5-HT₂ antagonist), and agonists and antagonists at various other 5-HT receptors also had no effect on binding parameters. These data demonstrate lack of cross-tolerance between pre- and post-synaptically acting 5-HT_1A agonists and absence of down-regulation of presynaptic 5-HT_1A sites at doses which induced tolerance of 5-HT_1A-mediated behaviors of the serotonin syndrome. They suggest changes in the post-synaptic cell rather than the receptor recognition site as the mechanism of tolerance.     

NONLINEAR BEHAVIOR OF HUMAN RESPIRATORY MOVEMENT DURING DIFFERENT SLEEP STAGES

To investigate the nonlinear properties of respiratory movement during different sleep stages, we applied an algorithm proposed by Grassberger and Procaccia to calculate the correlation dimension in rapid eye movement and non-rapid eye movement sleep. We also tested for nonlinearity in respiratory movement by comparing the correlation dimension for the original data with that for surrogate data. The study population included eight healthy volunteers. We recorded respiratory movement and the sleep electroencephalogram for 8 h. The correlation dimension for respiratory movement was 3.28 ± 0.19 (mean ± SD) during rapid eye movement sleep, 2.31 ± 0.21 during light sleep (stage I) and 1.64 ± 0.25 during deep slow-wave sleep (stage IV). Thus, the correlation dimension differed significantly by sleep stage (p < 0.001): it was least during stage IV sleep and greatest during REM. The correlation dimension for the original data also differed from that for surrogate data, confirming nonlinearity in original data. The results suggest that the nonlinear dynamics of respiratory movement in sleep changes with sleep stage, presumably due to the information processing by the cerebral cortex. The increased correlation dimension for respiratory movement in REM sleep may be related to increased cortical information processing associated with dreaming. (Chronobiology International, 18(1), 71–83, 2001)     

A Physiologic Role for Serotonergic Transmission in Adult Rat Taste Buds

Of the multiple neurotransmitters and neuropeptides expressed in the mammalian taste bud, serotonin remains both the most studied and least understood. Serotonin is expressed in a subset of taste receptor cells that form synapses with afferent nerve fibers (type III cells) and was once thought to be essential to neurotransmission (now understood as purinergic). However, the discovery of the 5-HT_1A serotonin receptor in a subset of taste receptor cells paracrine to type III cell suggested a role in cell-to-cell communication during the processing of taste information. Functional data describing this role are lacking. Using anatomical and neurophysiological techniques, this study proposes a modulatory role for serotonin during the processing of taste information. Double labeling immunocytochemical and single cell RT-PCR technique experiments documented that 5-HT_1A-expressing cells co-expressed markers for type II cells, cells which express T1R or T2R receptors and release ATP. These cells did not co-express type III cells markers. Neurophysiological recordings from the chorda tympani nerve, which innervates anterior taste buds, were performed prior to and during intravenous injection of a 5-HT_1A receptor antagonist. These experiments revealed that serotonin facilitates processing of taste information for tastants representing sweet, sour, salty, and bitter taste qualities. On the other hand, injection of ondansetron, a 5-HT₃ receptor antagonist, was without effect. Collectively, these data support the hypothesis that serotonin is a crucial element in a finely-tuned feedback loop involving the 5-HT_1A receptor, ATP, and purinoceptors. It is hypothesized that serotonin facilitates gustatory signals by regulating the release of ATP through ATP-release channels possibly through phosphatidylinositol 4,5-bisphosphate resynthesis. By doing so, 5-HT_1A activation prevents desensitization of post-synaptic purinergic receptors expressed on afferent nerve fibers and enhances the afferent signal. Serotonin may thus play a major modulatory role within peripheral taste in shaping the afferent taste signals prior to their transmission across gustatory nerves.     

Involvement of 5-HT<Subscript>2A</Subscript> receptors in genetic mechanisms of autoregulation of brain 5-HT system

The brain serotonin (5-HT) system has been implicated in the pathophysiology of anxiety, depression, drug addiction, and schizophrenia. 5-HT_2A receptors are involved in the mechanisms of stressinduced psychopathology and impulsive behavior. In this work, we investigated the role of 5-HT_2A receptors in the autoregulation of the brain 5-HT system. Chronic treatment with DOI, a 5-HT_2A receptor agonist (1.0 mg/kg, i.p./14 days), produced a considerable decrease in the number of 5-HT_2A receptor-mediated head twitches in AKR/J mice, indicating the desensitization of 5-HT_2A receptors. Chronic DOI treatment did not affect the expression of the 5-HT_2A receptor gene in the midbrain, hippocampus and frontal cortex. At the same time, an increase in the expression of the gene encoding a key enzyme of 5-HT synthesis, tryptophan hydroxylase-2 (TPH-2), accompanied with an increase in TPH-2 activity and 5-HT levels, and decreased expression of the serotonin transporter (5-HTT) gene were observed in the midbrain of DOI-treated mice. These results provide new evidence of receptor-gene cross-talk in the brain 5-HT system and implication 5-HT_2A receptors in the autoregulation of the brain 5-HT system.     

The central serotonergic system mediates the analgesic effect of electroacupuncture on<Emphasis Type="Italic">Zusanli</Emphasis> (ST36) acupoints

Evidence in the past decade indicates that the mechanisms of anti-nociception of electroacupuncture (EAc) involve actions of neuropeptides (i.e., enkephalin and endorphin) and monoamines (i.e., serotonin and norepinephrine) in the central nervous system. Our present results using a subcutaneous injection of formalin to test pain sensation in mice provide further understanding of the involvement of serotonin in the actions of EAc-induced analgesia. Our observations show that (1) EAc at three different frequencies (2, 10 and 100 Hz) elicited an anti-nociceptive effect as determined by behavioral observations of reduced hindpaw licking; (2) exogenously intracerebroventricular administration of 5-hydroxy-tryptamine (5-HT) exhibited an analgesic effect, which partially mimicked the analgesic actions of EAc; (3) the anti-nociception of EAc at different frequencies was attenuated after reduced biosynthesis of serotonin by the administration of the tryptophan hydroxylase inhibitor,p-chlorophenylalanine, and (4) the 5-HT_1A and 5-HT₃ receptor antagonists, pindobind-5-HT_1A and LY-278584, respectively, blocked three different frequencies of EAc-induced analgesic effects, but the anti-nociceptive effect of 100 Hz EAc was potentiated by the 5-HT₂ receptor antagonist, ketanserin. These observations suggest that 5-HT_1A and 5-HT₃ receptors partially mediate the analgesic effects of EAc, but that the 5-HT₂ receptor is conversely involved in the nociceptive response.     

Anxiolytic effect of the GPR103 receptor agonist peptide P550 (homolog of neuropeptide 26RFa) in mice. Involvement of neurotransmitters

The GPR103 receptor is a G protein-coupled receptor, which plays a role in several physiological functions. However, the role of the GPR103 receptor in anxiety has not been clarified. The first aim of our study was to elucidate the involvement of the GPR103 receptor in anxious behavior. Mice were treated with peptide P550, which is the mouse homolog of neuropeptide 26RFa and has similar activity for the GPR103 receptor as neuropeptide 26RFa. The anxious behavior was investigated using an elevated plus-maze paradigm. The second aim of our study was to investigate the underlying neurotransmissions. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a γ-aminobutyric acid subunit A (GABA_A) receptor antagonist, bicuculline, a non-selective 5-HT₂ serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT₁/5-HT₂ serotonergic receptor antagonist, methysergide, a D₂, D₃, D₄ dopamine receptor antagonist, haloperidol, a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a nonselective β-adrenergic receptor antagonist, propranolol. Our results demonstrated that peptide P550 reduces anxious behavior in elevated plus maze test in mice. Our study shows also that GABA_A-ergic, α- and β-adrenergic transmissions are all involved in this action, whereas 5-HT₁ and 5-HT₂ serotonergic, muscarinic cholinergic and D₂, D₃, D₄ dopaminergic mechanisms may not be implicated.     

The Cardiac Ventricular 5-HT4 Receptor Is Functional in Late Foetal Development and Is Reactivated in Heart Failure

A positive inotropic responsiveness to serotonin, mediated by 5-HT₄ and 5-HT_2A receptors, appears in the ventricle of rats with post-infarction congestive heart failure (HF) and pressure overload-induced hypertrophy. A hallmark of HF is a transition towards a foetal genotype which correlates with loss of cardiac functions. Thus, we wanted to investigate whether the foetal and neonatal cardiac ventricle displays serotonin responsiveness. Wistar rat hearts were collected day 3 and 1 before expected birth (days -3 and -1), as well as day 1, 3, 5 and 113 (age matched with Sham and HF) after birth. Hearts from post-infarction HF and sham-operated animals (Sham) were also collected. Heart tissue was examined for mRNA expression of 5-HT₄, 5-HT_2A and 5-HT_2B serotonin receptors, 5-HT transporter, atrial natriuretic peptide (ANP) and myosin heavy chain (MHC)-α and MHC-β (real-time quantitative RT-PCR) as well as 5-HT-receptor-mediated increase in contractile function ex vivo (electrical field stimulation of ventricular strips from foetal and neonatal rats and left ventricular papillary muscle from adult rats in organ bath). Both 5-HT₄ mRNA expression and functional responses were highest at day -3 and decreased gradually to day 5, with a further decrease to adult levels. In HF, receptor mRNA levels and functional responses reappeared, but to lower levels than in the foetal ventricle. The 5-HT_2A and 5-HT_2B receptor mRNA levels increased to a maximum immediately after birth, but of these, only the 5-HT_2A receptor mediated a positive inotropic response. We suggest that the 5-HT₄ receptor is a representative of a foetal cardiac gene program, functional in late foetal development and reactivated in heart failure.     

Effect of chronic l-DOPA treatment on 5-HT1A receptors in parkinsonian monkey brain

After chronic use of l-3,4-dihydroxyphenylalanine (l-DOPA), most Parkinson’s disease (PD) patients suffer from its side effects, especially motor complications called l-DOPA-induced dyskinesia (LID). 5-HT_1A agonists were tested to treat LID but many were reported to worsen parkinsonism. In this study, we evaluated changes in concentration of serotonin and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) and of 5-HT_1A receptors in control monkeys, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys, dyskinetic MPTP monkeys treated chronically with l-DOPA, low dyskinetic MPTP monkeys treated with l-DOPA and drugs of various pharmacological activities: Ro 61-8048 (an inhibitor of kynurenine hydroxylase) or docosahexaenoic acid (DHA) and dyskinetic MPTP monkeys treated with l-DOPA + naltrexone (an opioid receptor antagonist). Striatal serotonin concentrations were reduced in MPTP monkeys compared to controls. Higher striatal 5-HIAA/serotonin concentration ratios in l-DOPA-treated monkeys compared to untreated monkeys suggest an intense activity of serotonin axon terminals but this value was similar in dyskinetic and nondyskinetic animals treated with or without adjunct treatment with l-DOPA. As measured by autoradiography with [³H]8-hydroxy-2-(di-n-propyl) aminotetralin (8-OH-DPAT), a decrease of 5-HT_1A receptor specific binding was observed in the posterior/dorsal region of the anterior cingulate gyrus and posterior/ventral area of the superior frontal gyrus of MPTP monkeys compared to controls. An increase of 5-HT_1A receptor specific binding was observed in the hippocampus of MPTP monkeys treated with l-DOPA regardless to their adjunct treatment. Cortical 5-HT_1A receptor specific binding was increased in the l-DOPA-treated MPTP monkeys alone or with DHA or naltrexone and this increase was prevented in low dyskinetic MPTP monkeys treated with l-DOPA and Ro 61-8048. These results highlight the importance of 5-HT_1A receptor alterations in treatment of PD with l-DOPA.     

Synthesis and evaluation of a series of 2-substituted-5-thiopropylpiperazine (piperidine)-1,3,4-oxadiazoles derivatives as atypical antipsychotics

Background

It is important to develop novel antipsychotics that can effectively treat schizophrenia with minor side-effects. The aim of our work is to develop novel antipsychotics that act on dopamine D₂ and D₃, serotonin 5-HT_1A and 5-HT_2A receptors with low affinity for the serotonin 5-HT_2C and H₁ receptors, which can effectively cure positive symptoms, negative symptoms and cognitive impairment without the weight gain side-effect.

Methodology/Principal Findings

A series of 2-substituted-5-thiopropylpiperazine (piperidine) -1,3,4-oxadiazoles derivatives have been synthesized and the target compounds were evaluated for binding affinities to D₂, 5-HT_1A and 5-HT_2A receptors. Preliminary results indicated that compounds 14, 16 and 22 exhibited high affinities to D₂, 5-HT_1A and 5-HT_2A receptors among these compounds. Further binding tests showed that compound 22 had high affinity for D₃ receptor, and low affinity for serotonin 5-HT_2C and H₁ receptors. In addition, compound 22 inhibited apomorphine-induced climbing behavior and MK-801-induced hyperactivity with no extrapyramidal symptoms liability in mice. Moreover, compound 22 exhibited acceptable pharmacokinetic properties.

Conclusions/Significance

Compound 22 showed an atypical antipsychotic activity without liability for extrapyramidal symptoms. We anticipate compound 22 to be useful for developing a novel class of drug for the treatment of schizophrenia.