The effect of serotonergic agents on haloperidol-induced striatal dopamine release in vivo: opposite role of 5-HT(2A) and 5-HT(2C) receptor subtypes and significance of the haloperidol dose used

Increasing dopamine synthesis in nigrostriatal circuits increases phasic dopamine release and alters dorsal striatal connectivity: implications for schizophrenia

One of the most robust neurochemical abnormalities reported in patients with schizophrenia is an increase in dopamine (DA) synthesis and release, restricted to the dorsal striatum (DS). This hyper functionality is strongly associated with psychotic symptoms and progresses in those who later transition to schizophrenia. To understand the implications of this progressive neurobiology on brain function, we have developed a model in rats which we refer to as EDiPs (Enhanced Dopamine in Prodromal schizophrenia). The EDiPs model features a virally mediated increase in dorsal striatal (DS) DA synthesis capacity across puberty and into adulthood. This protocol leads to progressive changes in behaviour and neurochemistry. Our aim in this study was to explore if increased DA synthesis capacity alters the physiology of DA release and DS connectivity. Using fast scan cyclic voltammetry to assess DA release we show that evoked/phasic DA release is increased in the DS of EDiPs rats, whereas tonic/background levels of DA remain unaffected. Using quantitative immunohistochemistry methods to quantify DS synaptic architecture we show a presynaptic marker for DA release sites (Bassoon) was elevated within TH axons specifically within the DS, consistent with the increased phasic DA release in this region. Alongside changes in DA systems, we also show increased density of vesicular glutamate transporter 1 (VGluT1) synapses in the EDiPs DS suggesting changes in cortical connectivity. Our data may prove relevant in understanding the long-term implications for DS function in response to the robust and prolonged increases in DA synthesis uptake and release reported in schizophrenia.

Efecto del compuesto N-2,6-dicloro-aralquil-2-Aminoindano en la conducta estereotipada de ratas. Acción dopaminérgica selectiva central sobre los ganglios basales más que en las estructuras límbicas

Dopamine 1 is involved in neurodegenerative disorders affect-ing the central nervous system (CNS), such as Parkinson’s disease. Despite the absence of some available drugs capable of preventing, stopping or curing the progression of such diseases, there are numerous compounds designed, synthesized, and pharmacologically tested which give rise to pharmacophoric generalizations about the dopaminergic receptor required for the search of a drug able to improve or cure those pathologies. N-aralkyl-2-aminoindane de-rivatives have shown selective activity in the central dopaminergic system. Both the N-[(2,4-dichlorophenyl)-1-methyl-ethyl]-2-aminoindane hydrochloride 2and N-[(3,4-dichlorophenyl)-1-methyl-ethyl]-2-aminoindane hydrochloride 3 showed an agonistic activity mediated by central dopaminergic mechanisms. To contribute to the search of new drugs able to re-establish homeostasis in the dopaminergic transmission in Parkinson’s disease, the compound N-2,6-dichloro-aralkyl-2-aminoindane 4 was designed through medicinal chemistry strategies that contain pharmacophoric approximations of prodrugs. The phar-macological evaluation of compound 4 in the stereotyped behavior of male Sprague Dawley rats showed agonistic activity through the activation of central dopaminergic mechanisms and a higher selectivity in the responses of stereo-typed behavior characteristic of the basal ganglia over the typical responses from limbic structures.

In Vivo Study of Monoamine Oxidases Using Multisite Intracerebral Microdialysis

The activity of monoamine oxidases (MAOs) in the brain is often associated with neurodegenerative diseases. The study of MAOs in vivo or ex vivo is generally performed using MAO inhibitors and rarely using substrates. We present a pharmacological approach using intracerebral microdialysis to study the activity of MAO in the striatum and the prefrontal cortex of rats. It consists of applying ascending concentrations of 3-methoxytyramine (3-MT) as a substrate via the probes and measuring the indirect product homovanillic acid generated by MAO activity. We present herein the methodologies comprising our in-house stereotaxic procedures in rats, the microdialysis perfusion system and the substrate application, and the neurochemical analysis of the samples.

Serotonin/dopamine interaction: Electrophysiological and neurochemical evidence

The interaction between serotonin (5-HT) and dopamine (DA) in the central nervous system (CNS) plays an important role in the adaptive properties of living animals to their environment. These are two modulatory, divergent systems shaping and regulating in a widespread manner the activity of neurobiological networks and their interaction. The concept of one interaction linking these two systems is rather elusive when looking at the mechanisms triggered by these two systems across the CNS. The great variety of their interacting mechanisms is in part due to the diversity of their neuronal origin, the density of their fibers in a given CNS region, the distinct expression of their numerous receptors in the CNS, the heterogeneity of their intracellular signaling pathway that depend on the cellular type expressing their receptors, and the state of activity of neurobiological networks, conditioning the outcome of their mutual influences. Thus, originally conceptualized as inhibition of 5-HT on DA neuron activity and DA neurotransmission, this interaction is nowadays considered as a multifaceted, mutual influence of these two systems in the regulation of CNS functions. These new ways of understanding this interaction are of utmost importance to envision the consequences of their dysfunctions underlined in several CNS diseases. It is also essential to conceive the mechanism of action of psychotropic drugs directly acting on their function including antipsychotic, antidepressant, antiparkinsonian, and drug of abuse together with the development of therapeutic strategies of Alzheimer's diseases, epilepsy, obsessional compulsive disorders. The 5-HT/DA interaction has a long history from the serendipitous discovery of antidepressants and antipsychotics to the future, rationalized treatments of CNS disorders.

Effect of 5-HT2A receptor antagonism on levels of D2/3 receptor occupancy and adverse behavioral side-effects induced by haloperidol: a SPECT imaging study in the rat

Several studies suggested that 5-HT_2A receptor (5-HT_2AR) blockade may provide a more favorable efficacy and side-effect profile to antipsychotic treatment. We hypothesized that a combined haloperidol (a D_2/3 receptor (D_2/3R) antagonist) and MDL-100,907 (a 5-HT_2AR antagonist) treatment would reverse the side effects and the neurochemical alterations induced by haloperidol alone and would potentialize its efficacy. We thus chronically treated male Mdr1a knock-out rats with several doses of haloperidol alone or in combination with a saturating dose of a MDL-100,907. Receptor occupancy at clinically relevant levels was validated with a dual-radiotracer in-vivo SPECT imaging of D_2/3R and 5-HT_2AR occupancy. Experimental tests of efficacy (dizocilpine-disrupted prepulse inhibition (PPI) of the startle reflex) and side effects (catalepsy, vacuous chewing movements) were performed. Finally, a second dual-radiotracer in-vivo SPECT scan assessed the neurochemical changes induced by the chronic treatments. Chronic haloperidol failed to reverse PPI disruption induced by dizocilpine, whilst administration of MDL-100,907 along with haloperidol was associated with a reversal of the effect of dizocilpine. Haloperidol at 0.5 mg/kg/day and at 1 mg/kg/day induced catalepsy that was significantly alleviated (by ~50%) by co-treatment with MDL-100,907 but only at 0.5 mg/kg/day dose of haloperidol. Chronic haloperidol treatment, event at doses as low as 0.1 mg/kg/day induced a significant upregulation of the D_2/3R in the striatum (by over 40% in the nucleus accumbens and over 20% in the caudate-putamen nuclei), that was not reversed by MDL-100,907. Finally, an upregulation of 5-HT_2AR after chronic haloperidol treatment at a moderate dose only (0.25 mg/kg/day) was demonstrated in frontal cortical regions and the ventral tegmental area. Overall, a partial contribution of a 5-HT_2AR antagonism to the efficacy and side-effect profile of antipsychotic agents is suggested.

International society of sports nutrition position stand: caffeine and exercise performance

Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: 1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions. 2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals. 3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3-6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect. 4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session. 5. Caffeine appears to improve physical performance in both trained and untrained individuals. 6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation. 7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals. 8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. 9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4-6 mg/kg, respectively. 10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise. 11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.

Chronic Administration of Fipronil Heterogeneously Alters the Neurochemistry of Monoaminergic Systems in the Rat Brain

Fipronil (FPN), a widely used pesticide for agricultural and non-agricultural pest control, is possibly neurotoxic for mammals. Brain monoaminergic systems, involved in virtually all brain functions, have been shown to be sensitive to numerous pesticides. Here, we addressed the hypothesis that chronic exposure to FPN could modify brain monoamine neurochemistry. FPN (10 mg/kg) was chronically administered for 21 days through oral gavage in rats. Thereafter, the tissue concentrations of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid; serotonin (5-HT) and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA); and noradrenaline (NA) were measured in 30 distinct brain regions. FPN significantly decreased DA and its metabolite levels in most striatal territories, including the nucleus accumbens and the substantia nigra (SN). FPN also diminished 5-HT levels in some striatal regions and the SN. The indirect index of the turnovers, DOPAC/DA and 5-HIAA/5-HT ratios, was increased in numerous brain regions. FPN reduced the NA content only in the nucleus accumbens core. Using the Bravais–Pearson test to study the neurochemical organization of monoamines through multiple correlative analyses across the brain, we found fewer correlations for NA, DOPAC/DA, and 5-HIAA/5-HT ratios, and an altered pattern of correlations within and between monoamine systems. We therefore conclude that the chronic administration of FPN in rats induces massive and inhomogeneous changes in the DA and 5-HT systems in the brain.

Lorcaserin Alters Serotonin and Noradrenaline Tissue Content and Their Interaction With Dopamine in the Rat Brain

Lorcaserin is a preferential serotonin2C receptor (5-HT_2CR) agonist effective to treat obesity that has also recently been proposed to treat addiction and epilepsy. Central dopamine (DA) mechanisms are likely involved in the lorcaserin mechanism of action, but other monoamines 5-HT and noradrenaline (NA) contents or their interaction with DA might account for its effects. Here we showed that lorcaserin at 3, but not 0.3 mg/kg enhanced 5-HT content in the insular cortex, the core of the nucleus accumbens, and ventral hypothalamus. Without affecting the metabolite 5-hydroxy indole acetic acid, lorcaserin reduced the indirect index of 5-HT turnover in the hippocampus, substantia nigra, and habenula. Lorcaserin at 3 mg/kg increased NA content in the orbitofrontal cortex, the central amygdala (also at 0.3 mg/kg), the ventral hypothalamus, and the shell of the nucleus accumbens. A correlative analysis of the tissue contents between pairs of brain regions revealed that 0.3 mg/kg lorcaserin enhanced the number of correlations for 5-HT, its metabolism, and NA to a lower extent. The correlation profiles were very different between saline, 0.3 and 3 mg/kg lorcaserin. Lorcaserin enhanced the correlations established between NA or 5-HT at 0.3 and 3 mg/kg and reduced the number of correlations established between the index of the turnover for DA and 5-HT. These results show that lorcaserin modulates the biochemistry of NA and 5-HT systems in a subset of brain regions. Qualitatively, they reveal, oppositely to the DA changes, that lorcaserin at 0.3, but not 3 mg/kg, enhanced the number of correlations of 5-HT content between brain regions.

Effect of Caffeine on Endurance Performance in Athletes May Depend on HTR2A and CYP1A2 Genotypes

Guest, NS, Corey, P, Tyrrell, PN, and El-Sohemy, A. Effect of caffeine on endurance performance in athletes may depend on HTR2A and CYP1A2 genotypes. J Strength Cond Res XX(X): 000-000, 2020-This investigation determined whether variation in the HTR2A (serotonin receptor) gene modifies the ergogenic effects of caffeine on endurance and further modifies performance by the CYP1A2 genotype. Male athletes (n = 100; 25 ± 4 years) completed 10-km cycling time trials under 3 conditions as follows: 0, 2, or 4 mg of caffeine per kg body mass. Using a randomized, double-blinded, placebo-controlled design, data were analyzed using analysis of covariance to compare changes in cycling time between placebo (0 mg·kg) and each caffeine dose and adjusted for the placebo trial and order of treatment. A significance of ρ ≤ 0.05 was used. Subjects were genotyped for HTR2A (rs6313) and CYP1A2 (rs762551). A significant caffeine-HTR2A interaction (p = 0.003) was observed; however, after adjustment for placebo trials, the interaction was no longer significant (p = 0.37). Because of the strong caffeine-CYP1A2 interaction (p < 0.0001) previously reported in these subjects, where the 4-mg dose resulted in divergent effects (slower and faster) on the 10-km cycling time, we conducted a simplified model to examine these same factors by the HTR2A genotype. The post hoc analysis excluded HTR2A CT heterozygotes and 2-mg·kg caffeine trials. Among CYP1A2 fast metabolizers alone, a significant difference (1.7 minutes; p = 0.006) was observed when comparing (4- vs. 0-mg·kg caffeine trials) between the HTR2A CC (n = 16; 2.4 minutes) and TT (n = 7; 0.7 minutes) genotypes. Our results show that 4-mg·kg caffeine improves performance in individuals with the HTR2A CC genotype but only in those who are also CYP1A2 AA fast metabolizers. This study was registered with clinicaltrials.gov (NCT02109783).

Differential control of dopamine ascending pathways by serotonin2B receptor antagonists: New opportunities for the treatment of schizophrenia

Recent studies suggest that the central serotonin2B receptor (5-HT2BR) could be an interesting pharmacological target for treating neuropsychiatric disorders related to dopamine (DA) dysfunction, such as schizophrenia. Thus, the present study was aimed at characterizing the role of 5-HT2BRs in the control of ascending DA pathway activity. Using neurochemical, electrophysiological and behavioral approaches, we assessed the effects of two selective 5-HT2BR antagonists, RS 127445 and LY 266097, on in vivo DA outflow in DA-innervated regions, on mesencephalic DA neuronal firing, as well as in behavioral tests predictive of antipsychotic efficacy and tolerability, such as phencyclidine (PCP)-induced deficit in novel object recognition (NOR) test, PCP-induced hyperlocomotion and catalepsy. Both RS 127445 (0.16 mg/kg, i.p.) and LY 266097 (0.63 mg/kg, i.p.) increased DA outflow in the medial prefrontal cortex (mPFC). RS 127445, devoid of effect in the striatum, decreased DA outflow in the nucleus accumbens, and potentiated haloperidol (0.1 mg/kg, s.c.)-induced increase in mPFC DA outflow. Also, RS 127445 decreased the firing rate of DA neurons in the ventral tegmental area, but had no effect in the substantia nigra pars compacta. Finally, both RS 127445 and LY 266097 reversed PCP-induced deficit in NOR test, and reduced PCP-induced hyperlocomotion, without inducing catalepsy. These results demonstrate that 5-HT2BRs exert a differential control on DA pathway activity, and suggest that 5-HT2BR antagonists could represent a new class of drugs for improved treatment of schizophrenia, with an ideal profile of effects expected to alleviate cognitive and positive symptoms, without eliciting extrapyramidal symptoms.

Serotonergic modulation of the activity of mesencephalic dopaminergic systems: Therapeutic implications

Since their discovery in the mammalian brain, it has been apparent that serotonin (5-HT) and dopamine (DA) interactions play a key role in normal and abnormal behavior. Therefore, disclosure of this interaction could reveal important insights into the pathogenesis of various neuropsychiatric diseases including schizophrenia, depression and drug addiction or neurological conditions such as Parkinson's disease and Tourette's syndrome. Unfortunately, this interaction remains difficult to study for many reasons, including the rich and widespread innervations of 5-HT and DA in the brain, the plethora of 5-HT receptors and the release of co-transmitters by 5-HT and DA neurons. The purpose of this review is to present electrophysiological and biochemical data showing that endogenous 5-HT and pharmacological 5-HT ligands modify the mesencephalic DA systems' activity. 5-HT receptors may control DA neuron activity in a state-dependent and region-dependent manner. 5-HT controls the activity of DA neurons in a phasic and excitatory manner, except for the control exerted by 5-HT_2C receptors which appears to also be tonically and/or constitutively inhibitory. The functional interaction between the two monoamines will also be discussed in view of the mechanism of action of antidepressants, antipsychotics, anti-Parkinsonians and drugs of abuse.

5-HT2 receptors modulate the expression of antipsychotic-induced dopamine supersensitivity

Antipsychotic treatment can produce supersensitivity to dopamine receptor stimulation. This compromises the efficacy of ongoing treatment and increases the risk of relapse to psychosis upon treatment cessation. Serotonin 5-HT2 receptors modulate dopamine function and thereby influence dopamine-dependent responses. Here we evaluated the hypothesis that 5-HT2 receptors modulate the behavioural expression of antipsychotic-induced dopamine supersensitivity. To this end, we first treated rats with the antipsychotic haloperidol using a clinically relevant treatment regimen. We then assessed the effects of a 5-HT2 receptor antagonist (ritanserin; 0.01 and 0.1mg/kg) and of a 5-HT2A receptor antagonist (MDL100,907; 0.025-0.1mg/kg) on amphetamine-induced psychomotor activity. Antipsychotic-treated rats showed increased amphetamine-induced locomotion relative to antipsychotic-naïve rats, indicating a dopamine supersensitive state. At the highest dose tested (0.1mg/kg for both antagonists), both ritanserin and MDL100,907 suppressed amphetamine-induced locomotion in antipsychotic-treated rats, while having no effect on this behaviour in control rats. In parallel, antipsychotic treatment decreased 5-HT2A receptor density in the prelimbic cortex and nucleus accumbens core and increased 5-HT2A receptor density in the caudate-putamen. Thus, activation of either 5-HT2 receptors or of 5-HT2A receptors selectively is required for the full expression of antipsychotic-induced dopamine supersensitivity. In addition, antipsychotic-induced dopamine supersensitivity enhances the ability of 5-HT2/5-HT2A receptors to modulate dopamine-dependent behaviours. These effects are potentially linked to changes in 5-HT2A receptor density in the prefrontal cortex and the striatum. These observations raise the possibility that blockade of 5-HT2A receptors might overcome some of the behavioural manifestations of antipsychotic-induced dopamine supersensitivity.

New therapeutic opportunities for 5-HT2C receptor ligands in neuropsychiatric disorders

The 5-HT2C receptor (R) displays a widespread distribution in the CNS and is involved in the action of 5-HT in all brain areas. Knowledge of its functional role in the CNS pathophysiology has been impaired for many years due to the lack of drugs capable of discriminating among 5-HT2R subtypes, and to a lesser extent to the 5-HT1B, 5-HT5, 5-HT6 and 5-HT7Rs. The situation has changed since the mid-90s due to the increased availability of new and selective synthesized compounds, the creation of 5-HT2C knock out mice, and the progress made in molecular biology. Many pharmacological classes of drugs including antipsychotics, antidepressants and anxiolytics display affinities toward 5-HT2CRs and new 5-HT2C ligands have been developed for various neuropsychiatric disorders. The 5-HT2CR is presumed to mediate tonic/constitutive and phasic controls on the activity of different central neurobiological networks. Preclinical data illustrate this complexity to a point that pharmaceutical companies developed either agonists or antagonists for the same disease. In order to better comprehend this complexity, this review will briefly describe the molecular pharmacology of 5-HT2CRs, as well as their cellular impacts in general, before addressing its central distribution in the mammalian brain. Thereafter, we review the preclinical efficacy of 5-HT2C ligands in numerous behavioral tests modeling human diseases, highlighting the multiple and competing actions of the 5-HT2CRs in neurobiological networks and monoaminergic systems. Notably, we will focus this evidence in the context of the physiopathology of psychiatric and neurological disorders including Parkinson's disease, levodopa-induced dyskinesia, and epilepsy.

The neurosteroid dehydroepiandrosterone sulfate, but not androsterone, enhances the antidepressant effect of cocaine examined in the forced swim test--Possible role of serotonergic neurotransmission

One of the mechanisms of cocaine's actions in the central nervous system is its antidepressant action. This effect might be responsible for increased usage of the drug by individuals with mood disorders. Higher endogenous levels of the excitatory neurosteroid dehydroepiandrosterone sulfate (DHEAS) were reported to correlate with successful abstinence from cocaine use in addicts, but a clinical trial showed that supplementation with a high dose of DHEA increased cocaine usage instead. Such ambiguous effects of DHEA(S) could potentially be linked to its influence on the antidepressant effect of cocaine. In this study we tested DHEAS and its metabolite, androsterone, for interactions with cocaine in animal model of depression (forced swim test) and examined the effects of both steroids and cocaine on serotoninergic neurotransmission. All substances were also tested for influence on locomotor activity. A cocaine dose of 5mg/kg, which had no significant effect on locomotor activity, was chosen for the forced swim test. Neither DHEAS nor androsterone showed any antidepressant action in this test, while cocaine manifested a clear antidepressant effect. Androsterone slightly reduced the antidepressant influence of cocaine while DHEAS markedly, dose-dependently enhanced it. Such an effect might be caused by the influence of DHEAS on serotonin neurotransmission, as this steroid decreased serotonin concentration and turnover in the striatum. When DHEAS and cocaine were administered together, the levels of serotonin in the striatum and hippocampus remained unchanged. This phenomenon may explain the additive antidepressant action of DHEAS and cocaine and why co-administration of DHEAS and cocaine increases drug use.

Daily rhythms of serotonin metabolism and the expression of clock genes in suprachiasmatic nucleus of rotenone-induced Parkinson's disease male Wistar rat model and effect of melatonin administration

The circadian system in suprachiasmatic nucleus (SCN) involves regulated serotonin levels and coordinated expression of various clock genes. To understand circadian disfunction in the age-related neurodegenerative disorder Parkinson's disease (PD), the rotenone-induced PD (RIPD) male Wistar rat model was used. The alterations in the rhythmic dynamic equilibrium of interactions between the various components of serotonin metabolism and the molecular clock were measured. There was significant decrease in the mean 24 h levels of tryptophan, 5-hydroxytryptophan (5-HTP), serotonin (5-HT), N-acetyl serotonin (NAS) and melatonin (MEL) by approximately 63, 51, 76 and 96% respectively ( p ≤ 0.05). However significant increase in 5-methoxy indole acetic acid (5-MIAA), 5-methoxy tryptophol (5-MTOH), 5-hydroxy tryptophol (5-HTOH) indicated increased serotonin catabolism with the abolition of daily rhythms of MEL, 5-HTP and 5-MIAA in RIPD. 24 h mean levels of rPer1, rCry1, rBmal1 reduced by about 0.5, 0.74 and 0.39-fold and increased for rPer2 by about 1.7-fold. The daily pulse of rPer2, rCry1, rCry2 and rBmal1 significantly decreased by 0.36, 0.6, 0.14, 0.1 and 0.2-fold. As melatonin, an antioxidant and an endogenous synchronizer of rhythm declined in RIPD male Wistar rat model, the effects of melatonin-administration on the rhythmic expression of various clock genes were studied. Interestingly, melatonin-administration resulted in restoration of the phase of rPer1 daily rhythm in RIPD indicating differential sensitivity of various clock components towards melatonin. The animals which were administered both rotenone and MEL for 48 days interestingly showed neuroprotective effects in dark phase on correlations between expression of various genes.

Multiple controls exerted by 5-HT2C receptors upon basal ganglia function: from physiology to pathophysiology

Serotonin2C (5-HT2C) receptors are expressed in the basal ganglia, a group of subcortical structures involved in the control of motor behaviour, mood and cognition. These receptors are mediating the effects of 5-HT throughout different brain areas via projections originating from midbrain raphe nuclei. A growing interest has been focusing on the function of 5-HT2C receptors in the basal ganglia because they may be involved in various diseases of basal ganglia function notably those associated with chronic impairment of dopaminergic transmission. 5-HT2C receptors act on numerous types of neurons in the basal ganglia, including dopaminergic, GABAergic, glutamatergic or cholinergic cells. Perhaps inherent to their peculiar molecular properties, the modality of controls exerted by 5-HT2C receptors over these cell populations can be phasic, tonic (dependent on the 5-HT tone) or constitutive (a spontaneous activity without the presence of the ligand). These controls are functionally organized in the basal ganglia: they are mainly localized in the input structures and preferentially distributed in the limbic/associative territories of the basal ganglia. The nature of these controls is modified in neuropsychiatric conditions such as Parkinson's disease, tardive dyskinesia or addiction. Most of the available data indicate that the function of 5-HT2C receptor is enhanced in cases of chronic alterations of dopamine neurotransmission. The review illustrates that 5-HT2C receptors play a role in maintaining continuous controls over the basal ganglia via multiple diverse actions. We will discuss their interest for treatments aimed at ameliorating current pharmacotherapies in schizophrenia, Parkinson's disease or drugs abuse.

Pharmacological and genetic interventions in serotonin (5-HT)(2C) receptors to alter drug abuse and dependence processes

The present review provides an overview on serotonin (5-hydroxytryptamine; 5-HT)(2C) receptors and their relationship to drug dependence. We have focused our discussion on the impact of 5-HT(2C) receptors on the effects of different classes of addictive drugs, illustrated by reference to data using pharmacological and genetic tools. The neurochemical mechanism of the interaction between 5-HT(2C) receptors, with focus on the mesocorticolimbic dopaminergic system, and drugs of abuse (using cocaine as an example) is discussed. Finally, we integrate recent nonclinical and clinical research and information with marketed products possessing 5-HT(2C) receptor binding affinities. Accordingly, available nonclinical data and some clinical observations targeting 5-HT(2C) receptors may offer innovative translational strategies for combating drug dependence.This article is part of a Special Issue entitled: Brain Integration.

Dorsal-striatal 5-HT₂A and 5-HT₂C receptors control impulsivity and perseverative responding in the 5-choice serial reaction time task

RATIONAL

Prefrontal cortex (PFC) and dorsal striatum are part of the neural circuit critical for executive attention. The relationship between 5-HT and aspects of attention and executive control is complex depending on experimental conditions and the level of activation of different 5-HT receptors within the nuclei of corticostriatal circuitry.

OBJECTIVE

The present study investigated which 5-HT(2A) and 5-HT(2C) receptors in the dorsomedial-striatum (dm-STR) contribute to executive attention deficit induced by blockade of NMDA receptors in the PFC.

MATERIALS AND RESULTS

Executive attention was assessed by the five-choice serial reaction time task (5-CSRTT), which provides indices of attention (accuracy) and those of executive control over performance such as premature (an index of impulsivity) and perseverative responding. The effects of targeted infusion in dm-STR of 100 and 300 ng/μl doses of the selective 5-HT(2A) antagonist M100907 and 1 and 3 μg/μl doses of 5-HT(2C) agonist Ro60-0175 was examined in animals injected with 50 ng/μl dose of a competitive NMDA receptor antagonist 3-(R)-2-carboxypiperazin-4-phosphonic acid (CPP) in the mPFC. Blockade of NMDA receptors impaired accuracy as well as executive control as shown by increased premature and perseverative responding. The CPP-induced premature and perseverative over-responding were dose-dependently prevented by both M100907 and Ro60-0175. Both drugs partially removed the CPP-induced accuracy deficit but only at the highest dose tested.

CONCLUSIONS

It is suggested that in the dorsal striatum, 5-HT by an action on 5-HT(2A) and 5-HT(2C) receptors may integrate the glutamate corticostriatal inputs critical for different aspects of the 5-CSRT task performance.

Presynaptic control of serotonin on striatal dopamine function

RATIONALE

The influences of the serotonergic system on dopamine (DA) neuron activity have received considerable attention during the last three decades due to the real opportunity to improve disorders related to central DA neuron dysfunctions such as Parkinson's disease, schizophrenia, or drug abuse with serotonergic drugs. Numerous biochemical and behavioral data indicate that serotonin (5-HT) affects dopaminergic terminal function in the striatum.

OBJECTIVE

The authors propose a thorough examination of data showing controversial effects induced by striatal 5-HT on dopaminergic activity.

RESULTS

Inhibitory and excitatory effects of exogenous 5-HT have been reported on DA release and synthesis, involving various striatal 5-HT receptors. 5-HT also promotes an efflux of DA through reversal of the direction of DA transport. By analogy with the mechanism of action described for amphetamine, the consequences of 5-HT entering DA terminals might explain both the excitatory and inhibitory effects of 5-HT on presynaptic DA terminal activity, but the physiological relevance of this mechanism is far from clear. The recent data suggest that the endogenous 5-HT system affects striatal DA release in a state-dependent manner associated with the conditional involvement of various 5-HT receptors such as 5-HT(2A), 5-HT(2C), 5-HT(3), and 5-HT(4) receptors.

CONCLUSION

Methodological and pharmacological issues have prevented a comprehensive overview of the influence of 5-HT on striatal DA activity. The distribution of striatal 5-HT receptors and their restricted influence on DA neuron activity suggest that the endogenous 5-HT system exerts multiple and subtle influences on DA-mediated behaviors.

The central serotonin 2B receptor: a new pharmacological target to modulate the mesoaccumbens dopaminergic pathway activity

The function of the serotonin(2B) receptor (5-HT(2B)R) in the mammalian brain is poorly characterized, especially with regard to its influence on dopamine (DA) neuron activity. Here, we assessed this issue by evaluating effects of 5-HT(2B)Rs ligands in the control of striatal and accumbal DA outflow, using in vivo microdialysis in halothane-anesthetized rats, and amphetamine-induced hyperlocomotion in vigil rats. The selective 5-HT(2B)R antagonist 1-[(2-chloro-3,4-dimethoxyphenyl)methyl]-2,3,4,9-tetrahydro-6-methyl-1H-pyrido[3,4-B]indole (LY 266097; 0.16 mg/kg, i.p.) had no influence on basal accumbal and striatal DA outflow but reduced significantly accumbal DA outflow when injected at 0.63 mg/kg. A significant reduction of basal DA outflow in the nucleus accumbens was also observed after i.p. administration of 0.16 mg/kg 2-amino-4-(4-fluoronaphth-1-yl)-6-isopropylpyrimidine, another selective 5-HT(2B)R antagonist. In contrast, the 5-HT(2B)R agonist alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine (3 mg/kg, s.c.) had no influence on basal DA outflow in either brain region. The increase in striatal and accumbal DA outflow induced by the 5-HT(2C)R inverse agonist 5-methyl-1-(3-pyridylcarbamoyl)-1,2,3,5-tetrahydropyrrolo[2,3-f] indole (5 mg/kg, i.p.) was unaltered by LY 266097 (0.63 mg/kg) pre-treatment. Conversely, LY 266097 (0.63 mg/kg) significantly diminished the increase in DA outflow induced by haloperidol (0.01 mg/kg, s.c.) or amphetamine (0.5 mg/kg, i.p.) in the nucleus accumbens, but not in the striatum. Amphetamine-induced hyperlocomotion (1 mg/kg) was also attenuated by LY 266097 (0.63 mg/kg). These findings demonstrate that 5-HT(2B)Rs exert a facilitatory control on mesoaccumbens DA pathway activity, and suggest that they may constitute a new target for improved treatment of DA-related neuropsychiatric disorders.

The use of an antagonist 5-HT2a/c for depression and motor function in Parkinson' disease

OBJECTIVE

To test the ability of a 5HT2a/c (trazodone) antagonist, to improve depression and motor function in Parkinson' disease (PD).

METHOD

Twenty PD patients with and without depression were randomly assigned to receive trazodone (group 1) or not (group 2). They were evaluated through UPDRS and Hamilton Depression Rating Scale (HAM-D).

RESULTS

For the UPDRS the mean score of group 2 was 33.1 +/- 19.7 and 37.1 +/- 18.0 at the end. For the group 1, the corresponding scores were 31.4 +/- 11.3 and 25.9 +/- 13.7. The variations in the Mann-Whitney test were 0.734 at the initial moment and 0.208 at the final moment. The variation in the comparison of the initial moment with the final moment was 0.005 providing statistical significance. For the HAM-D, the mean score went up 4 points in group 2, contrary to a 5.5 points decrease in group 1.

CONCLUSION

Data analysis shows that this agent significantly improves depression, but the motor function improved only in the depressed patients. Because of the known anti-dopaminergic property of the 5-HT2c receptors, a possible approach for depression in PD could be the use of 5-HT2c antagonists, similarly to the use of atypical neuroleptics in case of psychotic symptoms.

Electrophysiological studies in the rat brain on the basis for aripiprazole augmentation of antidepressants in major depressive disorder

RATIONALE

Aripiprazole (ARI) is an atypical antipsychotic approved by the Food and Drug Administration for use in major depressive disorder as an adjunct to antidepressants. However, the precise mechanisms responsible for the effectiveness of ARI augmentation are not fully understood.

OBJECTIVES

The current study was aimed at examining the effects of ARI administration alone and in combination with the selective serotonin reuptake inhibitors (SSRI) escitalopram (ESC) on the firing of serotonin (5-HT), norepinephrine (NE), and dopamine (DA) neurons.

METHODS

Electrophysiological experiments were carried out in anesthetized Sprague-Dawley rats. ESC was delivered via subcutaneously implanted osmotic minipumps at a dose of 10 mg/kg/day. ARI was subcutaneously injected daily at a dose of 2 mg/kg/day. Both drugs were administered for 2 and 14 days alone and in combination. Control rats received physiological saline in analogous regimens.

RESULTS

Two-day ESC administration resulted in a significant decrease in the firing rate of 5-HT, NE, and DA neurons. Following 14 days of ESC administration, 5-HT firing returned to the baseline. The firing rate of NE and DA neurons remained significantly decreased. ARI administered for 2 or 14 days significantly increased the firing rate of 5-HT neurons by 36% and 48%, respectively, but not those of DA and NE neurons. Desensitization of somatodendritic 5-HT autoreceptors was observed after 2 days of ARI administration. The combination of the two drugs reversed the inhibitory action of ESC on the firing rate of 5-HT, NE, and DA neurons.

CONCLUSION

The present study showed that addition of ARI to an SSRI regimen reverses the inhibitory action of the SSRI on monoaminergic neuronal firing.

Focus on HTR2C: A possible suggestion for genetic studies of complex disorders

HTR2C is one of the most relevant and investigated serotonin receptors. Its role in important brain structures such as the midbrain, the lateral septal complex, the hypothalamus, the olfactory bulb, the pons, the choroid plexus, the nucleus pallidus, the striatum and the amygdala, the nucleus accumbens and the anterior cingulated gyrus candidate it as a promising target for genetic association studies. The biological relevance of these brain structures is reviewed by way of the focus on HTR2C activity, with a special attention paid to psychiatric disorders. Evidence from the genetic association studies that dealt with HTR2C is reviewed and discussed alongside the findings derived from the neuronatmic investigations. The reasons for the discrepancies between these two sets of reports are discussed. As a result, HTR2C is shown to play a pivotal role in many different psychiatric behaviors or psychiatric related disrupted molecular balances, nevertheless, genetic association studies brought inconsistent results so far. The most replicated association involve the feeding behavior and antipsychotic induced side effects, both weight gain and motor related: Cys23Ser (rs6318) and -759C/T (rs3813929) report the most consistent results. The lack of association found in other independent studies dampens the clinical impact of these reports. Here, we report a possible explanation for discrepant findings that is poorly or not at all usually considered, that is that HTR2C may exert different or even opposite activities in the brain depending on the structure analyzed and that mRNA editing activity may compensate possible genetically controlled functional effects. The incomplete coverage of the HTR2C variants is proposed as the best cost-benefit ratio bias to fix. The evidence of brain area specific HTR2C mRNA editing opens a debate about how the brain can differently modulate stress events, and process antidepressant treatments, in different brain areas. The mRNA editing activity on HTR2C may play a major role for the negative association results.

Parkinson's disease: emerging pharmacotherapy

Parkinson's disease (PD) is the second most common neurodegenerative disease. The prevalence is increasing with age and averages approximately 0.3% in the entire population. The clinical picture is dominated by the cardinal motor symptoms such as tremor at rest, bradykinesia, muscular rigidity, stooped posture and postural instability. Psychiatric comorbidity is common, comprising dementia, depression, anxiety and psychosis. Although many drugs have been developed and introduced into the market to provide symptomatic treatment, there is still no cure for PD and not even solid evidence for disease-modifying strategies. In addition, motor complications in advanced stages of the disease, side effects of the dopaminergic therapy, and non-motor symptoms remain huge challenges during long-term therapy. Thus, new therapeutic agents are desperately needed. Here, we describe current therapies and possible future developments that we hope will contribute to sustaining quality of life in patients suffering from Parkinson's disease for many years.

Antipsychotic and antidepressant co-treatment: effects on transcripts of inducible postsynaptic density genes possibly implicated in behavioural disorders

Selective serotonin reuptake inhibitors (SSRIs) and antipsychotics co-administration is a widely used strategy to treat both psychotic depression and depressive symptoms in schizophrenia. Nonetheless, the molecular mechanisms involved in the therapeutic benefits of antidepressant-antipsychotic combination are still elusive. It has been suggested that co-administration of SSRIs and antipsychotics may result in molecular changes different from their individual effects. In the present study, we evaluated the acute effects of two SSRIs, citalopram and escitalopram, alone or in combination with haloperidol, on the expression of Homer1a together with its splice variant ania-3, and p11, two genes linked respectively to dopaminergic and serotonergic neurotransmission and involved in synaptic plasticity. Homer1a and ania-3 were induced in the striatum by haloperidol, alone and in combination with SSRIs, but not by SSRIs only. Haloperidol+citalopram co-administration induced a stronger Homer1a expression than haloperidol alone in the ventrolateral caudate-putamen. No signal was detected for p11 in striatum, while there were no significant differences among treatments in cortical subregions. Homer1a was significantly down-regulated in the parietal cortex by all treatments. These results demonstrated that haloperidol+citalopram combination exerts synergistic effects on Homer expression, suggesting that citalopram may influence the impact by haloperidol on the dopaminergic neurotransmission. Moreover, present findings confirm that Homer1a and ania-3 are strongly induced in striatum by haloperidol, while they are not influenced by citalopram or escitalopram in this region. Oppositely, in the cortex the two transcripts are modulated by both haloperidol and SSRIs, suggesting a possible role of both dopamine and serotonin in their cortical regulation.

Fine-tuning serotonin2c receptor function in the brain: molecular and functional implications

The serotonin(2C) receptor (5-HT(2C)R) is a member of the serotonin(2) family of 7-transmembrane-spanning (7-TMS) receptors, which possesses unique molecular and pharmacological properties such as constitutive activity and RNA editing. The 5-HT(2C)R is widely expressed within the central nervous system, where is thought to play a major role in the regulation of neuronal network excitability. In keeping with its ability to modulate dopamine (DA) neuron function in the brain, the 5-HT(2C)R is currently considered as a major target for improved treatments of neuropsychiatric disorders related to DA neuron dysfunction, such as depression, schizophrenia, Parkinson's disease or drug addiction. The aim of this review is to provide an update of the functional status of the central 5-HT(2C)R, covering molecular, cellular, anatomical, biochemical and behavioral aspects to highlight its distinctive regulatory properties, the emerging functional significance of constitutive activity and RNA editing in vivo, and the therapeutic potential of inverse agonism.

Clozapine and haloperidol differentially alter the constitutive activity of central serotonin2C receptors in vivo

BACKGROUND

Central serotonin2C (5-HT2C) receptors are known to play a role in the mechanism of action of the antipsychotic drugs (APDs) clozapine and haloperidol. However, evidence for the involvement of the constitutive activity of 5-HT2C receptors in the dopamine (DA)ergic effects of APDs is lacking in vivo.

METHODS

Using in vivo microdialysis in halothane-anesthetized rats, we assessed the ability of selective 5-HT2C compounds to modulate the release of DA induced by haloperidol and clozapine in the nucleus accumbens and striatum.

RESULTS

Both APDs induced a dose-dependent increase in accumbal and striatal DA extracellular levels. The effect of .01 mg/kg haloperidol was potentiated by the 5-HT2C inverse agonist SB 206553 (5 mg/kg) but unaltered by the 5-HT2C antagonists SB 243213 and SB 242084 (1 mg/kg). Conversely, the effect of 1 mg/kg clozapine, a dose able to reverse the decrease in DA outflow induced by the 5-HT2C agonist Ro 60-0175 (3 mg/kg), was unaffected by SB 206553 but blocked by SB 243213 (1 mg/kg) and SB 242084 (.3 and 1 mg/kg).

CONCLUSIONS

These results show that clozapine and haloperidol differentially alter the constitutive activity of 5-HT2C receptors and suggest that clozapine behaves as a 5-HT2C inverse agonist in vivo.

ACP-103, a 5-HT2A/2C inverse agonist, potentiates haloperidol-induced dopamine release in rat medial prefrontal cortex and nucleus accumbens

RATIONALE

Atypical antipsychotic drugs (APDs) such as clozapine, olanzapine, quetiapine, risperidone, and ziprasidone are serotonin (5-HT)(2A) antagonists and relatively weaker dopamine (DA) D(2) antagonists, with variable 5-HT(2C) antagonist properties. The ability of atypical APDs to preferentially increase DA release in the cortex compared to the limbic system is believed to be due in part to their antagonism of 5-HT(2A) and D(2) receptors and believed to contribute to their beneficial effects on cognition, negative, and psychotic symptoms. Previous studies from this laboratory using microdialysis have shown that pretreatment of the 5-HT(2A) antagonist M100907 with the typical APD and D(2) antagonist haloperidol produced an increase in the medial prefrontal cortex (mPFC), but not in the nucleus accumbens (NAC), DA release. However, pretreatment with the 5-HT(2A/2C) receptor antagonist SR46349-B with haloperidol increased both mPFC and NAC DA release, suggesting that both 5-HT(2A) and 5-HT(2C) properties may be important for atypical APD effects.

OBJECTIVE

The purpose of this study was to examine the effects of a novel putative atypical APD ACP-103 on mPFC and NAC DA release using in vivo microdialysis in freely moving rats that are awake. ACP-103 is an inverse agonist at both 5-HT(2A) and 5-HT(2C) receptors and has intermediate affinities for 5-HT(2C) receptors relative to their affinities for 5-HT(2A) receptors compared to M100907 and SR46349-B. In addition, the effects of ACP-103 were compared to M100907 and SR46349-B, and ACP-103 was also coadministered with haloperidol.

RESULTS

ACP-103 10.0 mg/kg, but not 3.0 mg/kg, increased DA release in the mPFC, while neither dose increased DA release in the NAC. Like M100907, ACP-103 (3.0 mg/kg) potentiated 0.1 mg/kg haloperidol-induced DA release in the mPFC while inhibiting that in the NAC. However, ACP-103 (3.0 mg/kg), similar to SR46349-B, potentiated a high dose of haloperidol (1.0 mg/kg)-induced DA release in both regions. The potent 5-HT(2C) antagonist SB242084 1.0 mg/kg significantly potentiated 0.1 mg/kg haloperidol-induced DA release in both the mPFC and NAC. However, SB242084, at 0.2 mg/kg, significantly potentiated DA release only in the NAC. Moreover, SB242084 0.2 mg/kg potentiated DA release in the NAC produced by the combination treatment of 3 mg/kg ACP-103 and 0.1 mg/kg haloperidol.

CONCLUSION

These data suggest that the relative extent of 5-HT(2A) and 5-HT(2C) antagonism, as well as the extent of D(2) receptor blockade, has a critical influence on DA release in the mPFC and NAC and may be a determining factor in the action of this class of atypical APDs on these two potentially clinically relevant parameters.

Serotonergic mechanisms in Parkinson’s disease: opposing results from preclinical and clinical data

Parkinson's disease (PD) is a neuropsychiatric disease affecting approximately 1-2% of the general population. The classical triad of symptoms, tremor, rigidity, and bradykinesia is mainly caused by degeneration of dopaminergic neurons from the substantia nigra. However, other neurotransmitter systems also show signs of degeneration, among which the serotonergic system. The exact role of serotonin in PD remains unclear. We present here a review about functional serotonergic interventions and serotonergic imaging studies in PD, and will go into the importance of combining preclinical and clinical research data in order to gain more insight into the role of serotonin in PD. More specifically, the present review is aimed at bridging the gap between data from animal models of PD and data from human research.

Regionally and functionally distinct serotonin3 receptors control in vivo dopamine outflow in the rat nucleus accumbens

Central serotonin(3) (5-HT(3)) receptors control the mesoaccumbens dopamine (DA) pathway. This control is thought to be conditional and might involve regionally distinct subpopulations of 5-HT(3) receptors. Here, using in vivo microdialysis in rats, we assessed the relative contribution of nucleus accumbens (Nacc) 5-HT(3) receptors to the overall influence exerted by 5-HT(3) receptors on accumbal DA release induced by different drugs or treatments. In freely moving rats, pre-treatment with 5-HT(3) antagonists (0.1 mg/kg ondansetron and/or 0.03 mg/kg MDL 72222, s.c.) reduced DA efflux enhanced by morphine (1-10 mg/kg, s.c.) and haloperidol (0.01 mg/kg, s.c.), but not amphetamine (1-2.5 mg/kg, i.p.) or cocaine (10-20 mg/kg, i.p.), the latter two drugs do not trigger depolarization-stimulated DA exocytosis. Intra-Nacc administration of ondansetron (1 microm) in freely moving rats reduced the DA effects elicited by 10 mg/kg morphine, but not 1 mg/kg morphine or haloperidol. The 5-HT(1A) agonist 8-OH-DPAT (0.1 mg/kg, s.c.), known to decrease central 5-HT tone, reduced 10 but not 1 mg/kg morphine-stimulated DA outflow in freely moving rats. In halothane-anaesthetized rats, intra-Nacc ondansetron (1 microm) application reduced dorsal raphe nucleus electrical stimulation (20Hz)-induced DA outflow. Our results show that regionally distinct populations of 5-HT(3) receptors control the depolarization-dependent exocytosis of DA and suggest that the involvement of Nacc 5-HT(3) receptors occurs only when central DA and 5-HT tones are concomitantly increased.

The effect of a 5-HT1A receptor agonist on striatal dopamine release

5-HT1A receptor agonists consistently reduce neuroleptic induced catalepsy in rats. A serotonin-dopamine interaction has been proposed to underlie this effect. Specifically, 5-HT1A receptor agonists may reduce the activity of serotonergic projections that inhibit dopaminergic nigrostriatal neurones, therefore increasing dorsal striatal dopamine levels and partially overcoming the neuroleptic blockade of D2 receptors. We tested the hypothesis that 5-HT1A receptor agonists increase striatal dopamine release in man using PET scanning with the selective D2 receptor radioligand [11C]raclopride, which is sensitive to endogenous dopamine levels. Six healthy volunteers received two PET scans, one after placebo, the other after 1 mg flesinoxan, a selective 5-HT1A receptor agonist. Binding potential values for striatal subdivisions were determined using a simplified reference tissue model. We did not find any difference in striatal [11C]raclopride binding between conditions, even though flesinoxan lead to typical 5-HT1A receptor agonist side effects and produced elevation of growth hormone in five of the six subjects. Our results suggest that the anticataleptic effect of 5-HT1A receptor agonists is not mediated by striatal dopamine release, and indicates a need for further research with other suitable 5-HT1A receptor agonists.

Sulpiride in combination with fluvoxamine increases in vivo dopamine release selectively in rat prefrontal cortex

Coadministration of atypical antipsychotics and selective serotonin reuptake inhibitors (SSRIs) enhances the release of monoamines such as dopamine (DA), norepinephrine (NE), and serotonin (5-HT) in the prefrontal cortex. To clarify the role of DA-D2/3 receptors in the combination effect, we examined the effects of coadministration of the selective DA-D2/3 antagonist sulpiride and the SSRI fluvoxamine on amine neurotransmitter release in rat prefrontal cortex. Sulpiride (10 mg/kg, i.p.) and fluvoxamine (10 mg/kg, i.p.) alone did not affect extracellular DA levels, while their coadministration caused a significant increase in DA levels. Sulpiride alone did not affect extracellular levels of 5-HT and NE in the prefrontal cortex, while fluvoxamine alone caused a marked increase in 5-HT levels and a slight increase in NE levels. Sulpiride did not affect the fluvoxamine-induced increases in extracellular levels of 5-HT and NE. The DA-D2/3 antagonist haloperidol (0.1 mg/kg) in combination with fluvoxamine also caused a selective increase in extracellular DA levels in the cortex. Coadministration of sulpiride and fluvoxamine did not affect extracellular DA levels in the striatum. Combination of systemic sulpiride and local fluvoxamine did not increase the DA levels, but that of systemic fluvoxamine with local sulpiride increased. The combination effect in increasing prefrontal DA levels was antagonized systemically, but not locally, by the 5-HT1A antagonist WAY100635 at a low dose. These findings suggest that the combination of prefrontal DA-D2/3 receptor blockade and 5-HT1A receptor activation in regions other than the cortex plays an important role in sulpiride and fluvoxamine-induced increase in prefrontal DA release.

Protein kinase C inhibition differentially affects 3,4-methylenedioxymethamphetamine-induced dopamine release in the striatum and prefrontal cortex of the rat

The acute administration of 3,4-methylenedioxymethamphetamine (MDMA) elevates extracellular concentrations of dopamine (DA) and serotonin (5-HT) in the rat striatum and medial prefrontal cortex (mPFC). The release of DA induced by MDMA is thought to involve both transporter and impulse-mediated processes. Furthermore, the impulse-dependent release of DA in the striatum elicited by MDMA appears to involve 5-HT2 receptor activation. Since 5-HT2 receptors are known to utilize protein kinase C (PKC) for intracellular signaling, we examined the effects of modulators of PKC activity on DA release stimulated by MDMA. Reverse dialysis of the PKC inhibitors bisindolylmaleimide I (BIM; 30 microM) or chelerythrine chloride (100 microM) through a microdialysis probe significantly attenuated the MDMA (10 mg/kg, i.p.)-induced increase in the extracellular concentration of DA in the striatum. In contrast, BIM did not significantly alter the increase in the extracellular concentration of DA in the striatum elicited by amphetamine (5 mg/kg, i.p.). Reverse dialysis of a PKC activator, phorbol 12,13-dibutyrate (PDBu) (0.5 microM), through the microdialysis probe into the striatum, significantly increased MDMA-induced DA release. In contrast to the inhibitory effects of the PKC inhibitors on MDMA-induced DA release in the striatum, intracortical infusion of BIM enhanced MDMA-induced release of DA in the mPFC. These data suggest that PKC-mediated signaling pathways differentially modulate MDMA-induced DA release from mesocorticolimbic and nigrostriatal neurons.

In vivo evidence that 5-HT2C receptor antagonist but not agonist modulates cocaine-induced dopamine outflow in the rat nucleus accumbens and striatum

During recent years, much attention has been devoted at investigating the modulatory role of central 5-HT(2C) receptors on dopamine (DA) neuron activity, and it has been proposed that these receptors modulate selectively DA exocytosis associated with increased firing of DA neurons. In the present study, using in vivo microdialysis in the nucleus accumbens (NAc) and the striatum of halothane-anesthetized rats, we addressed this hypothesis by assessing the ability of 5-HT(2C) agents to modulate the increase in DA outflow induced by haloperidol and cocaine, of which the effects on DA outflow are associated or not with an increase in DA neuron firing, respectively. The intraperitoneal administration of cocaine (10-30 mg/kg) induced a dose-dependent increase in DA extracellular levels in the NAc and the striatum. The effect of 15 mg/kg cocaine was potentiated by the mixed 5-HT(2C/2B) antagonist SB 206553 (5 mg/kg i.p.) and the selective 5-HT(2C) antagonist SB 242084 (1 mg/kg i.p.) in both brain regions. The mixed 5-HT(2C/2B) agonist, Ro 60-0175 (1 mg/kg i.p.), failed to affect cocaine-induced DA outflow, but reduced significantly the increase in DA outflow induced by the subcutaneous administration of 0.1 mg/kg haloperidol. The obtained results provide evidence that 5-HT(2C) receptors exert similar effects in both the NAc and the striatum, and they modulate DA exocytosis also when its increase occurs independently from an increase in DA neuron impulse activity. Furthermore, they show that 5-HT(2C) agonists, at variance with 5-HT(2C) antagonists, exert a preferential control on the impulse-stimulated release of DA.

Psychotic bipolar disorders: dimensionally similar to or categorically different from schizophrenia?

For over a century, clinicians have struggled with how to conceptualize the primary psychoses, which include psychotic mood disorders and schizophrenia. Indeed, the nature of the relationship between mood disorders and schizophrenia is an area of ongoing controversy. Psychotic bipolar disorders have characteristics such as phenomenology, biology, therapeutic response, and brain imaging findings, suggesting both commonalities with and dissociations from schizophrenia. Taken together, these characteristics are in some instances most consistent with a dimensional view, with psychotic bipolar disorders being intermediate between non-psychotic bipolar disorders and schizophrenia spectrum disorders. However, in other instances, a categorical approach appears useful. Although more research is clearly necessary to address the dimensional versus categorical controversy, it is feasible that at least in the interim, a mixed dimensional/categorical approach could provide additional insights into pathophysiology and management options, which would not be available utilizing only one of these models.

Preclinical and clinical pharmacology of cyamemazine: anxiolytic effects and prevention of alcohol and benzodiazepine withdrawal syndrome

Several studies have suggested that the antipsychotic compound, cyamemazine, possesses anxiolytic properties in humans. The original pharmacological profile of cyamemazine (D(2), 5-HT(2A), 5-HT(2C), and 5-HT(3) receptor antagonist), which was established by binding, microdialysis and behavioral studies, is consistent with these observations. In the light/dark exploration test, cyamemazine demonstrated anxiolytic-like activity by acute, but not chronic administration. By chronic administration, however, cyamemazine increased the time spent in the open arms of the elevated plus maze (EPM) test demonstrating anxiolytic-like activity. The discrepancy between the results obtained in these tests by acute and chronic administration, could be due to a combination of dopamine D(2) receptor antagonism with antagonism of the 5-HT(2C) and 5-HT(3) receptors. The action of cyamemazine on both the dopaminergic system and 5-HT(3) receptors could also explain the activity of cyamemazine in the management of alcohol withdrawal demonstrated in preclinical studies. This potential indication for cyamemazine and its activity in benzodiazepine withdrawal syndrome have recently been investigated in clinical trials and the results of these studies are presented in this review.

Conditional involvement of striatal serotonin3 receptors in the control of in vivo dopamine outflow in the rat striatum

Serotonin3 (5-HT3) receptors can affect motor control through an interaction with the nigrostriatal dopamine (DA) neurons, but the neurochemical basis for this interaction remains controversial. In this study, using in vivo microdialysis, we assessed the hypothesis that 5-HT3 receptor-dependent control of striatal DA release is conditioned by the degree of DA and/or 5-HT neuron activity and the means of DA release (impulse-dependent vs. impulse-independent). The different DA-releasing effects of morphine (1 and 10 mg/kg), haloperidol (0.01 mg/kg), amphetamine (1 and 2.5 mg/kg), and cocaine (10 and 20 mg/kg) were studied in the striatum of freely moving rats administered selective 5-HT3 antagonists ondansetron (0.1 mg/kg) or MDL 72222 (0.03 mg/kg). Neither of the 5-HT3 antagonists modified basal DA release by itself. Pretreatment with ondansetron or MDL 72222 reduced the increase in striatal DA release induced by 10 mg/kg morphine but not by 1 mg/kg morphine, haloperidol, amphetamine or cocaine. The effect of 10 mg/kg morphine was also prevented by intrastriatal ondansetron (1 microm) administration. Reverse dialysis with ondansetron also reduced the increase in DA release induced by the combination of haloperidol and the 5-HT reuptake inhibitor citalopram (1 mg/kg). Considering the different DA and 5-HT-releasing properties of the drugs used, our results demonstrate that striatal 5-HT3 receptors control selectively the depolarization-dependent exocytosis of DA only when central DA and 5-HT tones are increased concomitantly.

Central serotonin4 receptors selectively regulate the impulse-dependent exocytosis of dopamine in the rat striatum: in vivo studies with morphine, amphetamine and cocaine

In vivo microdialysis and single-cell extracellular recordings were used to assess the involvement of serotonin(4) (5-HT(4)) receptors in the effects induced by morphine, amphetamine and cocaine on nigrostriatal and mesoaccumbal dopaminergic (DA) pathway activity. The increase in striatal DA release induced by morphine (2.5 mg/kg, s.c.) was significantly reduced by the selective 5-HT(4) antagonists GR 125487 (0.1 and 1 mg/kg, i.p.) or SB 204070 (1 mg/kg, i.p.), and potentiated by the 5-HT(4) agonist prucalopride (5 mg/kg, i.p.). Neither of these compounds affected morphine-stimulated DA release in the nucleus accumbens. In both regions, amphetamine (2 mg/kg, i.p.) and cocaine (15 mg/kg, i.p.) induced DA release was affected neither by GR 125487 nor by prucalopride. None of the 5-HT agents used modified basal DA release in either brain region. Finally, GR 125487 (445 microg/kg, i.v.), whilst not affecting basal firing of DA neurons within either the substantia nigra pars compacta nor the ventral tegmental area, significantly reduced morphine (0.1-10 mg/kg, i.v.) stimulated firing of nigrostriatal DA neurons only. These results confirm that 5-HT(4) receptors exert a state-dependent facilitatory control restricted to the nigrostriatal DA pathway, and indicate that 5-HT(4) receptors selectively modulate DA exocytosis associated with increased DA neuron firing rate.

5-HT(2A) receptor antagonism potentiates haloperidol-induced dopamine release in rat medial prefrontal cortex and inhibits that in the nucleus accumbens in a dose-dependent manner

Combined serotonin (5-HT)(2A) and dopamine (DA) D(2) blockade has been shown to contribute to the ability of atypical antipsychotic drugs (APDs) to increase DA release in rat medial prefrontal cortex (mPFC). We provide additional support for this hypothesis by examining the effect of the selective 5-HT(2A) antagonist M100907 plus haloperidol, a potent D(2) antagonist APD, on DA release in the mPFC and nucleus accumbens (NAC). Haloperidol (0.01-1.0 mg/kg) produced an inverted U-shaped increase in DA release in the mPFC, with a significant increase only at 0.1 mg/kg. Haloperidol (0.1 and 1.0 mg/kg) significantly increased DA release in the NAC. M100907 (0.1 mg/kg) by itself had no effect on DA release in either region. This dose of M100907 potentiated the ability of low (0.01-0.1 mg/kg), but not high dose (0.3-1.0 mg/kg) haloperidol to increase mPFC DA release, whereas it abolished the effect of both 0.1 and 1.0 mg/kg haloperidol on NAC DA release. These results suggest that the relatively higher ratio of 5-HT(2A) to D(2) antagonism may contribute to the potentiation of haloperidol-induced mPFC DA release, whereas 5-HT(2A) antagonism can diminish haloperidol-induced NAC DA release, even when combined with extensive D(2) antagonism, which may not be synergistic with 5-HT(2A) antagonism in the mPFC.

Stimulation of 5-hydroxytryptamine (5-HT(2C) ) receptors in the ventrotegmental area inhibits stress-induced but not basal dopamine release in the rat prefrontal cortex

The present study investigated whether 5-HT(2C) receptors in the ventrotegmental area and prefrontal cortex regulate basal and stimulus-evoked dopamine release in the prefrontal cortex. Using the in vivo microdialysis technique in conscious rats, we studied the effect of a selective 5-HT(2C) receptor agonist, Ro60-0175, on basal and immobilization stress-induced dopamine release in the prefrontal cortex. Ro60-0175 intraperitoneally (2.5 mg/kg) and into the ventrotegmental area (10 microg/0.5 microL) completely antagonized the effect of stress on extracellular dopamine without altering basal levels. Infusion of 10 microm Ro60-0175 through the cortical probe had no significant effect on basal and stress-induced dopamine release. SB242084 (10 mg/kg), a selective antagonist of 5-HT(2C) receptors, significantly increased basal extracellular dopamine and completely prevented the effect of intraperitoneal and intraventrotegmental Ro60-0175 on the stress-induced rise of extracellular dopamine, but had no effect itself in stressed rats. The results show that Ro60-0175 suppresses cortical dopamine release induced by immobilization stress through the stimulation of 5-HT(2C) receptors in the ventrotegmental area. While confirming that endogenous 5-HT acting on 5-HT(2C) receptors tonically inhibit basal dopamine release in the prefrontal cortex, the present findings suggest that the stimulation of 5-HT(2C) receptors with an exogenous agonist preferentially inhibit stimulated release.

Neurochemical and electrophysiological evidence that 5-HT4 receptors exert a state-dependent facilitatory control in vivo on nigrostriatal, but not mesoaccumbal, dopaminergic function

In this study we investigated, using in vivo microdialysis and single unit recordings, the role of serotonin4 (5-HT4) receptors in the control of nigrostriatal and mesoaccumbal dopaminergic (DA) pathway activity. In freely moving rats, the 5-HT4 antagonist GR 125487 (1 mg/kg, i.p.), without effect on its own, significantly reduced the enhancement of striatal DA outflow induced by 0.01 (-35%) and 0.1 (-66%), but not 1 mg/kg, s.c. haloperidol (HAL). Intrastriatal infusion of GR 125487 (1 microM) had no influence on basal DA outflow, but attenuated (-49%) the effect of 0.01 mg/kg HAL. Systemic administration of GR 125487 modified neither basal nor 0.01 mg/kg HAL-stimulated accumbal DA outflow. In halothane-anaesthetized rats, 1 or 10 mg/kg GR 125487, without effect by itself, failed to modify the changes in accumbal and striatal DA outflow elicited by electrical stimulation (300 microA, 1 ms, 20 Hz, 15 min) of the dorsal raphe nucleus. Finally, GR 125487 (444 microg/kg, i.v.), whilst not affecting basal firing of DA neurons within either the substantia nigra or the ventral tegmental area, reduced HAL-stimulated (1--300 microg/kg, i.v.) impulse flow of nigrostriatal DA neurons only. These results indicate that 5-HT4 receptors exert a facilitatory control on both striatal DA release and nigral DA neuron impulse flow only when nigrostriatal DA transmission is under activated conditions. Furthermore, they indicate that the striatum constitutes a major site for the expression of the control exerted by 5-HT4 receptors on DA release. In contrast, 5-HT4 receptors have no influence on mesoaccumbal DA activity in either basal or activated conditions.

The reverse transport of DA, what physiological significance?

It is well established that midbrain dopamine neurons innervating the striatum, release their neurotransmitter through an exocytotic process triggered by the neural firing and involving a transient calcium entry in the terminals. Long ago, it had been proposed, however, that another mechanism of release could co-exist with classical exocytosis, involving the reverse-transport of the cytosolic amine by the carrier, ordinarily responsible for uptake function. This atypical mode of release could be evoked directly at the preterminal level by multiple environmental endogenous factors involving transient alterations of the sodium gradient. It cannot be excluded that this mode of release participates in the firing-induced release. In contrast with the classical exocytosis of a preformed DA pool, the reverse-transport of DA requires simultaneous alterations of intraterminal amine metabolism including synthesis and displacement from storage compartment. The concept of a reverse-transport of dopamine is coming from the observations that releasing substances, such as amphetamine-related molecules, actually induce this type of transport. A large set of arguments advocates that reverse-transport plays a role in the maintenance of basal extracellular DA concentration in striatum. It was also often evoked in physiopathological situations including ischemia, neurodegenerative processes, etc. The most recent studies suggest that this release could occur mainly outside the synapses, and thus could constitute a major feature in the paracrine transmission, sometimes evoked for DA.

The antidepressant activity of inositol in the forced swim test involves 5-HT(2) receptors

The effect of inositol as an antidepressant was previously demonstrated in both animal models of depression-like behavior and in clinical trials. Unlike most antidepressant drugs, inositol does not have a clear target in the synapse and was not demonstrated to alter monoamine levels in the brain. The present study attempted to draw a psychopharmacological profile of inositol's behavioral effects by exploring the interactions between the drug and specific receptor agonists and antagonists in the forced swim test. Rats received inositol treatment (or control) in combination with the serotonergic metabolism inhibitor PCPA or with the noradrenergic neurotoxin DSP-4. Results indicated that PCPA but not DSP-4 abolished the ability of inositol to cause a reduction in immobility time in the forced swim test. In mice, the specific 5-HT(2A)/5-HT(2C) antagonist ritanserin, but not the 5-HT(1A)/5-HT(1B)/beta adrenergic antagonist pindolol, abolished inositol's effect in the forced swim test. The 5-HT(2A)/5-HT(2C) agonist DOI and the 5-HT(1A) agonist 8-OH-DPAT did not have any significant effects on inositol's activity. The present data indicates that the antidepressant effect of inositol may involve 5-HT(2) receptors. It is thus possible that the effects of reuptake antidepressant drugs and the effects of inositol may have a common final pathway.