Behavioral aspects of serotonin-dopamine interaction in the monkey

A closer look to neural pathways and psychopharmacology of obsessive compulsive disorder

The intricate neural pathways involved in obsessive-compulsive disorder (OCD) affect areas of our brain that control executive functioning, organization, and planning. OCD is a chronic condition that can be debilitating, afflicting millions of people worldwide. The lifetime prevalence of OCD in the US is 2.3%. OCD is predominantly characterized by obsessions consisting of intrusive and unwanted thoughts, often with impulses that are strongly associated with anxiety. Compulsions with OCD encompass repetitive behaviors or mental acts to satisfy their afflicted obsessions or impulses. While these factors can be unique to each individual, it has been widely established that the etiology of OCD is complex as it relates to neuronal pathways, psychopharmacology, and brain chemistry involved and warrants further exploration.

Bilateral Globus Pallidus Externus Deep Brain Stimulation for the Treatment of Refractory Tourette Syndrome: An Open Clinical Trial

OBJECTIVES

We have previously proposed that Tourette syndrome (TS) is the clinical expression of the hyperactivity of globus pallidus externus (GPe) and various cortical areas. This study was designed to test this hypothesis by verifying the efficacy and safety of bilateral GPe deep brain stimulation (DBS) for treating refractory TS.

MATERIALS AND METHODS

In this open clinical trial, 13 patients were operated on. Target coordinates (center of GPe) were obtained by direct visualization. Physiological mapping was performed with macrostimulation and microrecording. Primary and secondary outcome measures were, respectively, responder and improvement rates of TS and comorbidities, according to pre- and postoperative scores on the following assessment instruments: Yale Global Tic Severity Scale, Yale-Brown Obsessive Compulsive Scale, Beck Depression Inventory/Hamilton Depression Rating Scale, Beck Anxiety Inventory/Hamilton Anxiety Rating Scale, and Concentrated Attention test.

RESULTS

Intraoperative stimulation (100 Hz/5.0V) did not produce any adverse effects or impact on tics. Microrecording revealed bursting cells discharging synchronously with tics in the central part of the dorsal half of GPe. Patients were followed up for a mean of 61.46±48.50 months. Responder rates were 76.9%, 75%, 71.4%, 71.4%, and 85.7%, respectively, for TS, obsessive-compulsive disorder (OCD), depression, anxiety, and attention deficit hyperactivity disorder. Mean improvements among responders in TS, OCD, depression, and anxiety were 77.4%, 74.7%, 89%, and 84.8%, respectively. After starting stimulation, tic improvement was usually delayed, taking up to ten days to manifest. Afterward, it increased over time, usually reaching its maximum at approximately one year postoperatively. The best stimulation parameters were 2.3V to 3.0V, 90 to 120 μsec, and 100 to 150 Hz, and the most effective contacts were the two dorsal ones. Two complications were registered: reversible impairment of previous depression and transient unilateral bradykinesia.

CONCLUSIONS

Bilateral GPe-DBS proved to be low risk and quite effective for treating TS and comorbidities, ratifying the pathophysiological hypothesis that led to this study. Moreover, it compared favorably with DBS of other targets currently in use.

Induction of Ticlike Involuntary Movements in Rats by Striatotomy and Subsequent Neurochemical Sensitization

OBJECTIVE

It has been proposed that Tourette syndrome is associated with dysfunction in widespread cortical areas and globus pallidus externus hyperactivity secondary to dopaminergic hyperactivity and serotonergic/dynorphinergic hypoactivity. The main objective of this study was to test this hypothesis by developing an animal model of Tourette syndrome via striatotomy, followed by administration of drugs that mimic the neurotransmitter environment, so as to induce globus pallidus externus hyperactivity.

METHODS

Rats were assigned to 3 groups: stereotactic striatotomy (STT) and striatal sham -lesion (SHAM) groups, treated with anterior and posterior striatum procedures in both hemispheres, and a group of nonoperated animals (NAIVE). Postoperatively, all rodents were blindly administered 3 drug protocols: levodopa/benserazide; levodopa/benserazide/ergotamine/naloxone (MIX); and saline. The animals were filmed at the peak action of these drugs. The videos were evaluated by a single blinded researcher.

RESULTS

Six types of involuntary movements (IMs) were observed: cephalic, trunk jerks, oromandibular, forepaw jerks, dystonic, and locomotive. The number of animals with IM and the mean number of IM after both levodopa/benserazide and MIX was significantly higher in the STT compared with the SHAM and NAIVE groups. In the SHAM and NAIVE, MIX was superior to levodopa/benserazide in the induction of IM. In the STT, MIX was superior to levodopa/benserazide in the induction of trunk jerks. Appendicular IM were more common after posterior than after anterior striatotomy.

CONCLUSIONS

These results show that striatotomy, followed by administration of levodopa/benserazide alone or associated with ergotamine and naloxone, is efficacious in inducing IM, supporting the hypothesis that led to this study.

Intra-subject consistency of spontaneous eye blink rate in young women across the menstrual cycle

The spontaneous eye blink rate (EBR) has been linked to different cognitive processes and neurobiological factors. It has also been proposed as a putative index for striatal dopaminergic function. While estradiol is well-known to increase dopamine levels through multiple mechanisms, no study up to date has investigated whether the EBR changes across the menstrual cycle. This question is imperative however, as women have sometimes been excluded from studies using the EBR due to potential effects of their hormonal profile. Fifty-four women were tested for spontaneous EBR at rest in three different phases of their menstrual cycle: during menses (low progesterone and estradiol), in the pre-ovulatory phase (when estradiol levels peak and progesterone is still low), and during the luteal phase (high progesterone and estradiol). No significant differences were observed across the menstrual cycle and Bayes factors show strong support for the null hypothesis. Instead, we observed high intra-individual consistency of the EBR in our female sample. Accordingly, we strongly encourage including female participants in EBR studies, regardless of their cycle phase.

Buspirone-associated Movement Disorder: A Literature Review

Buspirone (BUS) belongs to the azapirone chemical class. The aim of this literature review is to evaluate the clinical epidemiological profile, pathological mechanisms, and management of BUS-associated movement disorders (MD). Relevant reports in six databases were identified and assessed by two reviewers without language restriction. A total of 25 reports containing 65 cases were assessed. The MD associated with BUS were: dyskinesia in 14 cases, 10 of akathisia, 8 of myoclonus, 6 of Parkinsonism, and 6 of dystonia. The cases not clearly defined were 7 tension, 14 incoordination, and the undefined number of dyskinesia, tics, and Parkinsonism. The mean age was 45.23 years (range: 15-74). The male was the predominant sex in 60.86% and the most common BUS-indication was anxiety disorder. The mean BUS-dose was 42.16 mg (range: 5-100). The time from the beginning of BUS administration to the MD onset was one month or less in 76%. The time from BUS withdrawal to complete recovery was within one month in 87.5%. The most common management was BUS withdrawal. In 16 patients the follow-up was reported: 14 had a full recovery, but in two (1 dyskinesia + 1 dystonia) the symptoms continued after the BUS withdrawal. MD associated with BUS were scarcely reported in the literature. Moreover, in the majority of cases, no clear description of the clinical profile, neurological examination, or the time data of the movement disorder onset and recovery were given.

Biological correlates of personality: considerations on the possible usefulness of central nervous system peripheral markers

Although a great deal of biological research has been carried out on several psychiatric disorders, it is disappointing to see how little progress has been made in the field of the biology of personality. The authors underline the methodological problems that arise in the investigation of biological substrates of human personality and review both currently available and putative peripheral markers of the central nervous system that might be used in further human studies.

Breaking Away: The Role of Homeostatic Drive in Perpetuating Depression

We propose that the complexity of regulatory interactions modulating brain neurochemistry and behavior is such that multiple stable responses may be supported, and that some of these alternate regulatory programs may play a role in perpetuating persistent psychological dysfunction. To explore this, we constructed a model network representing major neurotransmission and behavioral mechanisms reported in literature as discrete logic circuits. Connectivity and information flow through this biobehavioral circuitry supported two distinct and stable regulatory programs. One such program perpetuated a depressive state with a characteristic neurochemical signature including low serotonin. Further analysis suggested that small irregularities in glutamate levels may render this pathology more directly accessible. Computer simulations mimicking selective serotonin reuptake inhibitor (SSRI) therapy in the presence of everyday stressors predicted recidivism rates similar to those reported clinically and highlighted the potentially significant benefit of concurrent behavioral stress management therapy.

Increasing Resilience to Traumatic Stress: Understanding the Protective Role of Well-Being

The brain maintains homeostasis in part through a network of feedback and feed-forward mechanisms, where neurochemicals and immune markers act as mediators. Using a previously constructed model of biobehavioral feedback, we found that in addition to healthy equilibrium another stable regulatory program supported chronic depression and anxiety. Exploring mechanisms that might underlie the contributions of subjective well-being to improved therapeutic outcomes in depression, we iteratively screened 288 candidate feedback patterns linking well-being to molecular signaling networks for those that maintained the original homeostatic regimes. Simulating stressful trigger events on each candidate network while maintaining high levels of subjective well-being isolated a specific feedback network where well-being was promoted by dopamine and acetylcholine, and itself promoted norepinephrine while inhibiting cortisol expression. This biobehavioral feedback mechanism was especially effective in reproducing well-being's clinically documented ability to promote resilience and protect against onset of depression and anxiety.

Interactive Effects of Dopamine Baseline Levels and Cycle Phase on Executive Functions: The Role of Progesterone

Estradiol and progesterone levels vary along the menstrual cycle and have multiple neuroactive effects, including on the dopaminergic system. Dopamine relates to executive functions in an “inverted U-shaped” manner and its levels are increased by estradiol. Accordingly, dopamine dependent changes in executive functions along the menstrual cycle have been previously studied in the pre-ovulatory phase, when estradiol levels peak. Specifically it has been demonstrated that working memory is enhanced during the pre-ovulatory phase in women with low dopamine baseline levels, but impaired in women with high dopamine baseline levels. However, the role of progesterone, which peaks in the luteal cycle phase, has not been taken into account previously. Therefore, the main goals of the present study were to extend these findings (i) to the luteal cycle phase and (ii) to other executive functions. Furthermore, the usefulness of the eye blink rate (EBR) as an indicator of dopamine baseline levels in menstrual cycle research was explored. 36 naturally cycling women were tested during three cycle phases (menses–low sex hormones; pre-ovulatory–high estradiol; luteal–high progesterone and estradiol). During each session, women performed a verbal N-back task, as measure of working memory, and a single trial version of the Stroop task, as measure of response inhibition and cognitive flexibility. Hormone levels were assessed from saliva samples and spontaneous eye blink rate was recorded during menses. In the N-back task, women were faster during the luteal phase the higher their progesterone levels, irrespective of their dopamine baseline levels. In the Stroop task, we found a dopamine-cycle interaction, which was also driven by the luteal phase and progesterone levels. For women with higher EBR performance decreased during the luteal phase, whereas for women with lower EBR performance improved during the luteal phase. These findings suggest an important role of progesterone in modulating dopamine-cycle interactions. Additionally, we identified the eye blink rate as a non-invasive indicator of baseline dopamine function in menstrual cycle research.

Differential regulation of observational fear and neural oscillations by serotonin and dopamine in the mouse anterior cingulate cortex

RATIONALE

The aberrant regulation of serotonin (5-HT) and dopamine (DA) in the brain has been implicated in neuropsychiatric disorders associated with marked impairments in empathy, such as schizophrenia and autism. Many psychiatric drugs bind to both types of receptors, and the anterior cingulate cortex (ACC) is known to be centrally involved with empathy. However, the relationship between the 5-HT/DA system in the ACC and empathic behavior is not yet well known.

OBJECTIVES

We investigated the role of 5-HT/DA in empathy-like behavior and in the regulation of ACC neural activity.

METHODS

An observational fear learning task was conducted following microinjections of 5-HT, DA, 5-HT and DA, methysergide (5-HT receptor antagonist), SCH-23390 (DA D1 receptor antagonist), or haloperidol (DA D2 receptor antagonist) into the mouse ACC. The ACC neural activity influenced by 5-HT and DA was electrophysiologically characterized in vitro and in vivo.

RESULTS

The microinjection of haloperidol, but not methysergide or SCH-23390, decreased the fear response of observing mice. The administration of 5-HT and 5-HT and DA together, but not DA alone, reduced the freezing response of observing mice. 5-HT enhanced delta-band activity and reduced alpha- and gamma-band activities in the ACC, whereas DA reduced only alpha-band activity. Based on entropy, reduced complexity of ACC neural activity was observed with 5-HT treatment.

CONCLUSIONS

The current results demonstrated that DA D2 receptors in the ACC are required for observational fear learning, whereas increased 5-HT levels disrupt observational fear and alter the regularity of ACC neural oscillations.

Effects of dopamine D2 receptor partial agonist antipsychotic aripiprazole on dopamine synthesis in human brain measured by PET with L-[β-11C]DOPA

Dopamine D₂ receptor partial agonist antipsychotic drugs can modulate dopaminergic neurotransmission as functional agonists or functional antagonists. The effects of antipsychotics on presynaptic dopaminergic functions, such as dopamine synthesis capacity, might also be related to their therapeutic efficacy. Positron emission tomography (PET) was used to examine the effects of the partial agonist antipsychotic drug aripiprazole on presynaptic dopamine synthesis in relation to dopamine D₂ receptor occupancy and the resulting changes in dopamine synthesis capacity in healthy men. On separate days, PET studies with [¹¹C]raclopride and L-[β-¹¹C]DOPA were performed under resting condition and with single doses of aripiprazole given orally. Occupancy of dopamine D₂ receptors corresponded to the doses of aripiprazole, but the changes in dopamine synthesis capacity were not significant, nor was the relation between dopamine D₂ receptor occupancy and these changes. A significant negative correlation was observed between baseline dopamine synthesis capacity and changes in dopamine synthesis capacity by aripiprazole, indicating that this antipsychotic appears to stabilize dopamine synthesis capacity. The therapeutic effects of aripiprazole in schizophrenia might be related to such stabilizing effects on dopaminergic neurotransmission responsivity.

REVIEW: Apathy diagnosis, assessment, and treatment in Alzheimer's disease

Apathy is defined as a disorder of motivation. There is wide acknowledgement that apathy is an important behavioral syndrome in Alzheimer's disease and in various neuropsychiatric disorders. In light of recent research and the renewed interest in the correlates and impacts of apathy and in its treatments, it is important to develop criteria for apathy that will be widely accepted, have clear operational steps, and be easy to apply in clinical practice and in research settings. Meeting these needs was the focus for a task force that included members of the European Psychiatric Association, the European Alzheimer's Disease Consortium and experts from Europe, Australia and North America.

Role of cortical and striatal 5-HT1A receptors in alleviating antipsychotic-induced extrapyramidal disorders

Previous studies have revealed that 5-HT(1A) agonists ameliorate antipsychotic-induced extrapyramidal symptoms (EPS) through postsynaptic 5-HT(1A) receptors. Here, we conducted an intracerebral microinjection study of (+/-)-8-hydroxy-2-(di-n-propylamino)-tetralin ((+/-)8-OH-DPAT) to determine the action site of the 5-HT(1A) agonist in alleviating EPS. Bilateral microinjection of(+/-)8-OH-DPAT (5 microg/1microL per side) either into the primary motor cortex (MC) or the dorsolateral striatum (dlST) significantly attenuated haloperidol-induced catalepsy in rats. The anticataleptic action of (+/-)8-OH-DPAT was more prominent with the MC injection than with the dlST injection. WAY-100135 (a selective 5-HT(1A) antagonist) completely antagonized the reversal of haloperidol-induced catalepsy both by intracortical and intrastriatal (+/-)8-OH-DPAT. Furthermore, lesioning of dopamine neurons with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (30 mg/kg/day, i.p., for 4 days) did not alter the anti-EPS actions of (+/-)8-OH-DPAT in a mouse pole test. The present results strongly suggest that 5-HT(1A) agonist alleviates antipsychotic-induced EPS by activating postsynaptic 5-HT(1A) receptors in the MC and dlST, probably through non-dopaminergic mechanisms.

Blockade of dopamine, but not noradrenaline, transporters produces hyperthermia in rats that lack serotonin transporters

To investigate whether life-long disturbed serotonin neurotransmission may result in adaptive changes of dopaminergic and noradrenergic systems, effects of drugs on stress-induced hyperthermia were studied in serotonin transporter knockout rats. The noradrenalin transporter blocker atomoxetine was more effective in reducing stress-induced hyperthermia, induced by an injection, in serotonin transporter (SERT) knockout (SERT(-/-)) rats compared to SERT(+/+) rats. The dopamine transporter blocker GBR12909 increased the core body temperature in SERT(-/-) rats, and had no effect on the SERT(+/+) rats. Finally, the noradrenalin transporter together with dopamine transporter blocker bupropion was more effective in decreasing the stress of an injection in SERT(-/-) rats than in SERT(+/+) rats. These data suggest that the sensitivity of dopamine and noradrenalin receptors is changed in serotonin transporter knockout rats. The lack of the serotonin transporter in SERT(-/-) rats might reflect humans with a life-long disturbed serotonin system, making this rat a good model to study possible changes in dopaminergic and noradrenergic systems in psychiatric disorders.

Effects of the antipsychotic risperidone on dopamine synthesis in human brain measured by positron emission tomography with L-[beta-11C]DOPA: a stabilizing effect for dopaminergic neurotransmission?

Effects of antipsychotic drugs have widely been considered to be mediated by blockade of postsynaptic dopamine D(2) receptors. Effects of antipsychotics on presynaptic functions of dopaminergic neurotransmission might also be related to therapeutic effects of antipsychotics. To investigate the effects of antipsychotics on presynaptic functions of dopaminergic neurotransmission in relation with occupancy of dopamine D(2) receptors, changes in dopamine synthesis capacity by antipsychotics and occupancy of dopamine D(2) receptors were measured by positron emission tomography (PET) in healthy men. PET studies using [(11)C]raclopride and L-[beta-(11)C]DOPA were performed under resting condition and oral administration of single dose of the antipsychotic drug risperidone on separate days. Although occupancy of dopamine D(2) receptors corresponding dose of risperidone was observed, the changes in dopamine synthesis capacity by the administration of risperidone were not significant, nor was the relation between the occupancy of dopamine D(2) receptors and these changes. A significant negative correlation was observed between the baseline dopamine synthesis capacity and the changes in dopamine synthesis capacity by risperidone, indicating that this antipsychotic can be assumed to stabilize the dopamine synthesis capacity. The therapeutic effects of risperidone in schizophrenia might be related to such stabilizing effects on dopaminergic neurotransmission responsivity.

The relationship of pineal calcification and melatonin secretion to the pathophysiology of tardive dyskinesia and tourette's syndrome

Despite current intensive research, the pathophysiology of tardive dyskinesia (TD), a serious neurological side effect of neuroleptic treatment, is poorly understood. Prompted by the observation of an increased incidence and severity of abnormal perioral movements in neuroleptic-treated pinealectomized, as compared to intact rats, we suggested that the pineal gland exerts a protective effect which mitigates against the development of TD and, by inference, that reduced melatonin secretion may be related to the pathophysiology of TD. To investigate this proposition further, we studied the association of TD with pineal calcification (PC) on CT scan in chronic schizophrenic patients. Our findings revealed a significant association between TD and PC and suggest, furthermore, that PC may be a neuroradiological marker of TD. Since PC may reflect diminished secretory activity of the gland, these findings support the hypothesis that the pathophysiology of TD is linked to disturbances of melatonin secretion. The clinical and therapeutic implications of these novel findings are discussed. In the following communication, in which we introduce the hypothesis that disturbances of 5-HT and melatonin secretion are related to the pathophysiology of TD. Subsequently, we present a series of studies which relate to the association of TD with PC. We conclude by presenting the hypothesis that disturbances in melatonin secretion may also be relevant to the pathophysiology of Tourette's syndrome.

No regional difference in dopamine D2 receptor occupancy by the second-generation antipsychotic drug risperidone in humans: a positron emission tomography study

The effects of antipsychotic drugs have generally been considered to be mediated by blockade of dopamine D2 receptors. The concept of limbic and cortical selectivity of second-generation antipsychotics, i.e. higher dopamine D2 receptor occupancy in the cerebral cortices than in the striatum, has been suggested to explain their clinical efficacy with lower incidence of extrapyramidal side-effects. In this study, regional distribution of dopamine D2 receptor occupancy by risperidone was determined in order to elucidate the limbic and cortical selectivity of second-generation antipsychotics. Striatal and extrastriatal dopamine D2 receptor binding at baseline and after oral administration of 2 mg risperidone were measured in ten healthy men by positron emission tomography (PET) using different tracers with different affinity for the receptors, [11C]raclopride and [11C]FLB 457, respectively. Striatal and extrastriatal occupancies of dopamine D2 receptors were calculated for each brain region. Occupancies of dopamine D2 receptors were about 70% and 60% in the striatum and extrastriatum, respectively. A simulation study showed that non-negligible specific binding in the reference region (cerebellum), could cause systemic underestimation of occupancy in [11C]FLB 457 PET studies, indicating that occupancies in both the striatum and extrastriatum may not have differed. Among the extrastriatal regions including limbic and neocortical regions, no significant regional differences in dopamine D2 receptor occupancy were observed. Thus, limbic and cortical selectivity was not observed by one of the second-generation antipsychotics, risperidone.

Evaluation of the antibradykinetic actions of 5-HT1A agonists using the mouse pole test

To clarify the role and mechanism of the 5-HT1A receptor in modulating extrapyramidal motor disorders, we studied the actions of 5-HT1A agonists in the mouse pole test, a valid model of parkinsonian bradykinesia. Haloperidol markedly delayed pole-descending behavior of mice in the pole test, and this effect was alleviated by the antiparkinsonian agent trihexyphenidyl (a muscarinic antagonist). The selective 5-HT1A agonists, 8-hydroxydipropylaminotetraline (8-OH-DPAT) and tandospirone, significantly attenuated haloperidol-induced bradykinesia in a dose-dependent manner. The alleviation of haloperidol-induced bradykinesia by 8-OH-DPAT was completely antagonized by WAY-100135 (a selective 5-HT1A antagonist), but was unaffected by cerebral 5-HT depletion with p-chlorophenylalanine (PCPA) treatment (300 mg/kg, i.p. for 3 days). These results suggest that 5-HT1A agonists improve extrapyramidal motor disorders associated with antipsychotic treatments by stimulating the postsynaptic 5-HT1A receptor.

Fluoxetine, smoking, and history of major depression: A randomized controlled trial

The study was a randomized placebo-controlled trial testing whether fluoxetine selectively enhances cessation for smokers with a history of depression. Euthymic smokers with (H+, n = 109) or without (H-, n = 138) a history of major depression received 60 mg fluoxetine or placebo plus group behavioral quit-smoking treatment for 12 weeks. Fluoxetine initially enhanced cessation for H+ smokers (p = .02) but subsequently impaired cessation regardless of depressive history. Six months after quit date, fluoxetine-treated participants were 3.3 times more likely to be smoking (p = .02). Further research is warranted to determine why high-dose fluoxetine produces continuing effects that oppose tobacco abstinence.

Contribution of the serotonin 5-HT1A receptor agonism of 8-OH-DPAT and EMD 128130 to the regulation of haloperidol-induced muscle rigidity in rats

The aim of the present study was to find out whether (+/-)-8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), a prototypical 5-HT1A agonist, and (R)-(-)-2-[5-(4-fluorophenyl)-3-pyridylmethylaminomethyl]-chromane HCl (EMD 128130), a compound with serotonin 5-HT1A-agonist and dopamine D2-like antagonist properties, are able to attenuate the haloperidol-induced (1 mg/kg) muscle rigidity in rats. Muscle tone was examined using a combined mechano- and electromyographic (EMG) method that simultaneously measured the mechanical muscle resistance (MMG) of the rat's hind foot to passive movements in the ankle joint, and the EMG activity of two antagonist muscles. Both 8-OH-DPAT (0.125-0.5 mg/kg i.p.) and EMD 128130 (1-10 mg/kg i.p.) dose-dependently decreased the haloperidol-enhanced MMG to passive movements, as well as the tonic and the long-latency reflex EMG activities. Provided these results can be extrapolated to humans, the efficacy of EMD 128130 in relieving the haloperidol-induced muscle rigidity supports the concept that novel antipsychotics with 5-HT1A agonist and dopamine D2 antagonist activities should have a favourable extrapyramidal side-effect profile.

SSR181507, a dopamine D2 receptor antagonist and 5-HT1A receptor agonist. II: Behavioral profile predictive of an atypical antipsychotic activity

SSR181507 ((3-exo)-8-benzoyl-N-(((2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl)methyl)-8-azabicyclo(3.2.1)octane-3-methanamine monohydrochloride) is a novel tropanemethanamine benzodioxane that displays antagonist activity at dopamine D(2) receptors and agonist activity at 5-HT(1A) receptors. SSR181507 antagonized apomorphine-induced climbing in mice and stereotypies in rats (ED(50) of 2 and 3.4 mg/kg i.p., respectively) and blocked D-amphetamine-induced hyperlocomotion in rats at lower doses (0.3-1 mg/kg i.p.). At 1-10 mg/kg, it was found to disrupt active avoidance in mice. SSR181507 did not induce catalepsy in rats (MED>60 mg/kg i.p.) and antagonized (3-10 mg/kg i.p.) haloperidol-induced catalepsy. SSR181507 was also active in two models sensitive to antidepressant/anxiolytic drugs: in a guinea-pig pup/mother separation test, it decreased (1-3 mg/kg i.p.) the time spent vocalizing during the separation episode, and in a lithium-induced taste aversion procedure in rats, it partially reversed (3 mg/kg i.p.) the decrease of intake of a saccharin solution. Furthermore, SSR181507 increased (3 mg/kg i.p.) the latency time to paradoxical sleep in rats, an effect commonly observed with antidepressants. Coadministration of the selective 5-HT(1A) blocker SL88.0338 produced catalepsy and antagonized the effects of SSR181507 in the depression/anxiety tests, confirming the view that activation of 5-HT(1A) receptors confers an atypical profile on SSR181507, and is responsible for its antidepressant/anxiolytic properties. Finally, SSR181507 (1-3 mg/kg) did not affect memory performance in a Morris water maze task in rats. The pharmacological profile of SSR181507 suggests that it should control the symptoms of schizophrenia, in the absence of extrapyramidal signs and cognitive deficits, with the additional benefit of antidepressant/anxiolytic activities.

Effects of melatonin on behavioral dopaminergic supersensitivity

This study examines the effects of melatonin on dopaminergic supersensitivity induced by long-term treatment with haloperidol in rats. Enhancements of spontaneous general activity in an open-field and of stereotyped behavior induced by apomorphine after abrupt withdrawal from long-term treatment with haloperidol were used as experimental parameters for dopaminergic supersensitivity. Experiment 1 was conducted to investigate the effects of melatonin on the development of dopaminergic supersensitivity, and experiment 2 was conducted to investigate the effects of melatonin on the development as well as on expression of dopaminergic supersensitivity. Rats of both experiments were long-term treated with saline or haloperidol concomitant to saline or melatonin. In experiment 1 behavioral observations were performed after abrupt withdrawal from long-term treatment. In experiment 2 behavioral observations were performed 1 hour after an acute injection of saline or melatonin, administered after the abrupt withdrawal from long-term treatment. Both behavioral parameters used showed the development of central dopaminergic supersensitivity in rats treated with haloperidol since 24 hours after abrupt withdrawal. Concomitant treatment with melatonin intensified haloperidol-induced dopaminergic supersensitivity, observed 72 hours after withdrawal. Melatonin treatment per se also induced behavioral supersensitivity evaluated by both open-field and stereotyped behaviors, although it was more fugacious than that presented by haloperidol. Acute treatment with melatonin reverted the enhancement of the haloperidol-induced dopaminergic supersensitivity produced by concomitant long-term treatment with melatonin, as well as melatonin-induced dopaminergic supersensitivity per se. Our results support previous evidence of antidopaminergic effects of melatonin and demonstrate that repeated administration of this hormone modifies the plasticity of behaviors mediated by central dopaminergic systems.

Differential serotonergic inhibition of in vitro striatal [3H]acetylcholine release in prenatally cocaine-exposed male and female rats

Previous research indicates that prenatal cocaine (pCOC)-exposure results in greater 5-HT3 agonist-induced inhibition of electrically evoked [3H]acetylcholine (ACh) overflow in rat striatal slices. The present study examines the effects of fluoxetine (FLU)-induced and exogenous serotonin (5-HT) on electrically evoked ACh release from striatal slices prepared from adult male and female (in periods of diestrus or proestrus) rats exposed to saline or cocaine in utero. Additionally, we assessed the impact of monoaminergic receptor stimulation on evoked ACh release by superfusion with selective 5-HT2, 5-HT3 and D2 receptor antagonists in the presence of FLU-induced and exogenous 5-HT and measuring the capacity of these drugs to reverse inhibitory effects of 5-HT. Given our previous findings of accentuated inhibition of ACh release by 5-HT3 agonism in striata of pCOC-exposed adult rats, we hypothesized that superfusion of endogenous and exogenous 5-HT would lead to greater suppression of evoked ACh release in this group of animals. Our results indicated that ACh release from slices of all prenatal saline (pSAL) rats was inhibited comparably by FLU (10 microM)-elicited increases in endogenous 5-HT or by increases elicited with application of exogenous 5-HT (5 microM). Robust FLU-mediated inhibition of ACh release was evident in slices from pCOC male and pCOC diestrus female rats vs. their respective PSAL control groups. Superfusion of striatal slices with 5-HT (5 microM) produced a pattern of ACh inhibition similar to that produced by FLU; however, the magnitude of ACh inhibition was consistently greater than that observed with FLU. Inhibition of ACh overflow by FLU was blocked by co-superfusion with ketanserin, a 5-HT2 receptor antagonist. ICS-205,930, a 5-HT3 receptor antagonist or sulpiride, a D2 receptor antagonist. Conversely, serotonergic inhibition of ACh overflow was only blocked by a high concentration of ICS-205,930 (5 microM) and was completely reversed by sulpiride (1 microM). Collectively, these findings demonstrate serotonergic modulation of cholinergic neurons varying as a function of prenatal treatment, sex and, for females, phase of estrous. Inhibition of ACh release by 5-HT appears to be mediated by a complex relationship between 5-HT2, 5-HT3 and D2 receptor regulation, as the blockade of any of these receptors reversed the inhibitory effects of FLU on ACh release. Conversely, in the case of exogenous 5-HT-induced inhibition, only blockade of D2 receptors and high concentrations of the 5-HT3 receptor antagonists were capable of reversing monoaminergic inhibition. These data support the hypothesis that the enhanced serotonergic modulation of ACh neurons in pCOC-exposed animals is largely mediated by dopamine (DA) and reflect a major biochemical persistence of neurodevelopmental adaptations elicited by early cocaine exposure.

Dopamine, but not norepinephrine or serotonin, reuptake inhibition reverses motor deficits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primates

Monoamine reuptake inhibitors that do not discriminate between the transporters for dopamine (DA), norepinephrine (NE), or 5-hydroxytryptamine (5-HT, serotonin) can reverse locomotor deficits and motor disability in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets. DA reuptake inhibition is presumed to be primarily responsible, but the role played by inhibition of NE and 5-HT reuptake is unknown. We now evaluate the efficacy of a range of monoamine reuptake inhibitors either alone or in combination in MPTP-treated common marmosets to determine the actions required for effective antiparkinsonian activity. Monoamine reuptake inhibitors not discriminating between the DA, NE, and 5-HT transporters [1-[1-(3,4-dichlororphenyl)cyclobutyl]-2-(3-diaminethylaminopropylthio)ethanone monocitrate (BTS 74 398) and nomifensine] reversed locomotor deficits and motor disability in MPTP-treated marmosets but bupropion was without effect. The selective DA reuptake inhibitor 1-(2-(bis-(4-fluorophenyl)-methoxy)ethyl)-4-(3-phenylpropyl) piperazine) dihydrochloride (GBR 12909) also reversed these motor deficits. The relative efficacy of the compounds (BTS 74 398 > GBR 12909 > nomifensine >> bupropion) paralleled their potency in inhibiting DA uptake in vitro and in vivo. In contrast, the selective NE reuptake inhibitor nisoxetine and the 5-HT reuptake inhibitor sertraline administered alone failed to improve motor function and tended to worsen the deficits. Coadministration of nisoxetine attenuated the improvement in motor deficits produced by GBR 12909. Coadministration of sertraline also abolished the reversal of motor deficits produced by GBR 12909. Coadministration of both sertraline and nisoxetine similarly abolished the improvement of motor deficits produced by GBR 12909. Molecules possessing potent DA reuptake inhibitory activity may be useful in the treatment of the motor symptoms of Parkinson's disease. In contrast, there seems to be no role for NE or 5-HT reuptake inhibitors, and they may impair antiparkinsonian activity mediated through dopaminergic mechanisms.

Effect of acute and chronic administration of 1,2,3,4-tetrahydroisoquinoline on muscle tone, metabolism of dopamine in the striatum and tyrosine hydroxylase immunocytochemistry in the substantia nigra, in rats

The effects of acute and chronic administration of 1,2,3,4-tetrahydroisoquinoline, an endogenous substance suspected of producing parkinsonism in humans, on the muscle tone and metabolism of dopamine in the striatum, and on the number of tyrosine hydroxylase-immunoreactive cells in the substantia nigra were investigated in rats. Muscle tone was examined using a combined mechanomyographic and electromyographic method which measured simultaneously the muscle resistance of the rat's hind foot to passive extension and flexion in the ankle joint and electromyographic activity of the antagonistic muscles of that joint: gastrocnemius and tibialis anterior. 1,2,3,4-Tetrahydroisoquinoline administered at doses of 50 and 100 mg/kg intraperitoneally for 19 days increased muscle resistance 1 h after the first injection (acute treatment), 1 h after the last injection (chronic treatment) and three days after compound withdrawal. Rigidity observed on the third day of 1,2,3,4-tetrahydroisoquinoline withdrawal was accompanied by an increased tonic (resting) electromyographic activity of the gastrocnemius and tibialis anterior muscles. At the same time, a significant reduction in the number of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra and a decrease in the dopamine level in the striatum were also found. A declining number of tyrosine hydroxylase-immunoreactive neurons in the whole substantia nigra showed a significant negative correlation with the enhanced muscle resistance, as well as with the tonic electromyographic activity recorded at rest, i.e. before the start of movements, from the gastrocnemius and tibialis anterior muscles. Our results suggest that 1,2,3,4-tetrahydroisoquinoline may be one of the endogenous substances involved in the progress of Parkinson's disease.

SSRI-induced extrapyramidal side-effects and akathisia: implications for treatment

The selective serotonin reuptake inhibitors (SSRIs) may occasionally induce extrapyramidal side-effects (EPS) and/or akathisia. This may be a consequence of serotonergically-mediated inhibition of the dopaminergic system. Manifestations of these effects in patients may depend on predisposing factors such as the presence of psychomotor disturbance, a previous history of drug-induced akathisia and/or EPS, concurrent antidopaminergic and/or serotonergic therapy, recent monoamine oxidase inhibitor discontinuation, comorbid Parkinson's disease and possibly deficient cytochrome P450 (CYP) isoenzyme status. There is increasing awareness that there may be a distinct form of melancholic or endogenous depression with neurobiological underpinnings similar to those of disorders of the basal ganglia such as Parkinson's disease. Thus, it is not surprising that some individuals with depressive disorders appear to be susceptible to developing drug-induced EPS and/or akathisia. In addition, the propensity for the SSRIs to induce these effects in individual patients may vary within the drug class depending, for example, on their selectivity for serotonin relative to other monoamines, affinity for the 5-HT2C receptor, pharmacokinetic drug interaction potential with concomitantly administered neuroleptics and potential for accumulation due to a long half-life. The relative risk of EPS and akathisia associated with SSRIs have yet to be clearly established. The potential risks may be reduced by avoiding rapid and unnecessary dose titration. Furthermore, early recognition and appropriate management of EPS and/or akathisia is required to prevent the impact of these effects on patient compliance and subjective well-being. It is important that the rare occurrence of EPS in patients receiving SSRIs does not preclude their use in Parkinson's disease where their potentially significant role requires more systematic evaluation.

A.E. Bennett Research Award. Toward a neurodevelopmental model of of obsessive--compulsive disorder

BACKGROUND

Neurobiological models for obsessive-compulsive disorder (OCD) have consistently implicated ventral prefrontal cortical and striatal circuits in the pathophysiology of this disorder, but typically have not utilized a developmental framework for conceptualizing the illness.

METHODS

We describe an integrated series of neurobiologic studies aimed at testing the hypothesis that neurodevelopmental abnormalities of ventral prefrontal-striatal circuits may be involved in and contribute to the etiology and presentation of the illness.

RESULTS

Using studies of oculomotor physiology, we have identified a selective deficit in neurobehavioral response suppression in OCD that may be related to failures in the developmental maturation of frontostriatal circuitry. Magnetic resonance imaging studies showed that treatment-naive pediatric OCD patients had significant volumetric abnormalities in ventral prefrontal cortical and striatal regions but no abnormalities in dorsolateral prefrontal cortex. Severity of OCD symptoms but not illness duration was related to ventral prefrontal cortical and striatal volumes.

CONCLUSIONS

Critical neurodevelopmental changes in ventral prefrontal-striatal circuitry may be associated with the initial presentation of OCD, and a developmentally mediated network dysplasia may underlie OCD. Such dysplasia in ventral prefrontal cortical circuits could manifest clinically by disrupting brain functions that mediate ongoing purposive behaviors.

D3 dopamine receptor mRNA is widely expressed in the human brain

Considerable attention has been given to the association of the D3 dopamine receptor subtype and limbic function based on the abundant localization of D3 receptor sites and mRNA expression in the islands of Calleja and nucleus accumbens in experimental animals. Though most human anatomical studies have focused on the role of D3 receptors in limited brain structures, detailed information about the overall anatomical organization of the D3 receptor in the human brain is still, however, not available. In the current study, we examined the anatomical distribution of D3 receptor mRNA expression at different levels of the human brain in whole hemisphere horizontal cryosections using in situ hybridization. This approach made it possible to establish for the first time the wide and heterogenous expression of the D3 receptor gene throughout the human brain. As expected, the most abundant D3 mRNA expression levels were found in the islands of Calleja and discrete cell cluster populations within the ventral striatum/nucleus accumbens region. High levels were also evident within the dentate gyrus and striate cortex. Low to moderate D3 mRNA expression levels were apparent in most brain areas including all other cortical regions (highest in the anterior cingulate/subcallosal gyrus), caudate nucleus, putamen, anterior and medial thalamic nucleus, mammillary body, amygdala, hippocampal CA region, lateral geniculate body, substantia nigra pars compacta, locus coeruleus, and raphe nuclei. While the current anatomical map of D3 receptor mRNA expression in the human brain does confirm previous reports that D3 receptors may play important roles in limbic-related functions such as emotion and cognition, the findings also suggest other non-limbic functions for D3 mRNA-expressing cell populations such as processing of motor and sensory information.

Effects of perospirone (SM-9018), a potential atypical neuroleptic, on dopamine D1 receptor-mediated vacuous chewing movement in rats: a role of 5-HT2 receptor blocking activity

We compared the acute and subacute effects of perospirone (SM-9018), a novel neuroleptic with potent 5-HT2 and D2 blocking actions, and of haloperidol (HAL) on dopamine D1 receptor-mediated vacuous chewing movement (VCM) in rats. A selective D1 agonist, SKF 38393 (SKF), markedly increased the incidence of VCM, which was blocked by SCH 23390 (a D1 antagonist) but not by sulpiride (a D2 antagonist). Perospirone and HAL inhibited the SKF-induced VCM in a dose-dependent manner. The potency of the inhibitory actions of perospirone was considerably weaker (about 30 times) than that of HAL despite their similar affinities for D1 receptors. Subacute treatment with perospirone for 2 weeks failed to affect the behavioral sensitivity of rats to SKF. However, the HAL treatment markedly enhanced the incidence of the SKF-induced VCM. On the other hand, the selective 5-HT2 antagonists ritanserin and ketanserin significantly reduced the inhibitory actions of HAL and SCH 23390 on the SKF-induced VCM. In addition, combined treatment of ritanserin with HAL for 2 weeks abolished the enhancement of SKF-induced VCM by HAL treatment. These findings suggest that perospirone is weaker than HAL in altering the behavioral sensitivity of D1 receptor-mediated VCM under repeated administration, which may be related to the 5-HT2 blocking activity of perospirone.

Serotonin-2 and dopamine-1 binding components of clozapine in frontal cortex and striatum in the human brain visualized by positron emission tomography

The specific binding of N-methyl-11C-clozapine in the human brain was studied in five healthy volunteers with positron emission tomography (PET). Four of the volunteers were reexamined after treatment with the dopamine D1 and D2 receptor antagonist flupenthixol, and all five volunteers were reexamined after pretreatment with the serotonin2 receptor antagonist ritanserin. The examinations after flupenthixol and ritanserin treatment were performed on different occasions. In the flupenthixol part of the study, two of the subjects were given an oral dose of 1 mg flupenthixol 2-3 h before the posttreatment study with PET. The other two subjects received 0.5 mg orally three times during the 24 h preceding the posttreatment PET study, with the last dose being administered < or = 4 h before the scan. All five ritanserin-treated subjects followed the same dosing regimen. During the 5 days preceding the posttreatment PET study, they were given a 10-mg tablet of ritanserin in the evening. The last dose was administered 2-1/2 hours before the study. Both flupenthixol and ritanserin pretreatment were associated with decreased binding of N-methyl-11C-clozapine in dorsolateral and medial frontal cortical regions. These results support previous findings that clozapine has affinity for both dopamine D1 and serotonin 5-HT2 receptors in the human frontal cortex. No consistent change of binding was observed in striatal regions following flupenthixol or ritanserin pretreatment. The clinical aspects of this feature are discussed, both with respect to efficacy and side effects.

A role for the subthalamic nucleus in 5-HT2C-induced oral dyskinesia

The 5-hydroxytryptamine2C serotonin receptor is broadly distributed in brain, however, its functional role is unknown. Peripheral administration of drugs acting at the 5-hydroxytryptamine2C receptor induces abnormal oral dyskinesias, hyperkinetic motor disorders that often result from dysfunction of the basal ganglia. The subthalamic nucleus, a brain region anatomically and functionally related to the basal ganglia, has been implicated in oral dyskinesia. The subthalamic nucleus contains messenger RNA encoding 5-hydroxytryptamine2C receptors, suggesting its potential role in 5-hydroxytryptamine2C-mediated oral dyskinesia. Both systemic administration and local unilateral infusion of the 5-hydroxytryptamine2C/1B agonist, 1-(m-chlorophenyl)piperazine into the subthalamic nucleus increased orofacial movements. Oral movements following subthalamic infusion of 1-(m-chlorophenyl)piperazine were blocked by systemic administration of the 5-hydroxytryptamine2C/2A antagonists mianserin, ketanserin and mesulergine but were not altered by systemic pretreatment with either the 5-hydroxytryptamine1A/2A and dopamine antagonist spiperone or the 5-hydroxytryptamine1A/1B antagonist pindolol. Co-infusion of mesulergine with 1-(m-chlorophenyl)piperazine into the subthalamic nucleus blocked 1-(m-chlorophenyl)piperazine-stimulated oral movements. Oral bouts following systemically administered 1-(m-chlorophenyl)piperazine were markedly reduced following bilateral subthalamic infusion of either mesulergine or the selective 5-hydroxytryptamine2C antagonist SDZ SER 082. The findings indicate that stimulating 5-hydroxytryptamine2C receptors in the subthalamic nucleus elicits orofacial dyskinesia in the rat. These data are novel in providing a behavioral model for central 5-hydroxytryptamine2C receptor stimulation attributed to a specific anatomical location, and suggest that antagonists at the 5-hydroxytryptamine2C receptor could be useful in treating hyperkinetic motor disorders.

5-HT2 antagonism and EPS benefits: is there a causal connection?

This article examines the hypothesis that 5-HT2 antagonism ameliorates extrapyramidal side effects (EPS) induced by the blockade of D2 dopamine receptors by antipsychotics. Neuroanatomical and neurophysiological data confirm the existence of pathways whereby 5-HT2 antagonism may influence EPS. The experimental data in rodents is marginally positive, but shows that the net effect of 5-HT2 antagonism is dependent upon the precise conditions under which catalepsy is induced. The data in monkeys are mainly negative. Studies in patients who have received adjunct 5-HT2 antagonists in addition to typical neuroleptics lend some support the the hypothesis, but are not conclusive. It is reasoned that 5-HT2 antagonism plays no role in clozapine's freedom from EPS, but it may be responsible for risperidone's decreased propensity to cause EPS. The article concludes that there is support for a conditional role of 5-HT2 in decreasing EPS: 5-HT2 antagonists may delay the onset and decrease the severity of EPS but cannot totally eliminate its occurrence. The implications of these findings for the next generation of combined 5-HT2/D2 antagonists are discussed.

Mechanisms of action of atypical antipsychotic drugs: a critical analysis

Various criteria used to define atypical antipsychotic drugs include: 1) decrease, or absence, of the capacity to cause acute extrapyramidal motor side effects (acute EPSE) and tardive dyskinesia (TD); 2) increased therapeutic efficacy reflected by improvement in positive, negative, or cognitive symptoms; 3) and a decrease, or absence, of the capacity to increase prolactin levels. The pharmacologic basis of atypical antipsychotic drug activity has been the target of intensive study since the significance of clozapine was first appreciated. Three notions have been utilized conceptually to explain the distinction between atypical versus typical antipsychotic drugs: 1) dose-response separation between particular pharmacologic functions; 2) anatomic specificity of particular pharmacologic activities; 3) neurotransmitter receptor interactions and pharmacodynamics. These conceptual bases are not mutually exclusive, and the demonstration of limbic versus extrapyramidal motor functional selectivity is apparent within each arbitrary theoretical base. This review discusses salient distinctions predominantly between prototypic atypical and typical antipsychotic drugs such as clozapine and haloperidol, respectively. In addition, areas of common function between atypical and typical antipsychotic drug action may also be crucial to our identification of pathophysiological foci of the different dimensions of schizophrenia, including positive symptoms, negative symptoms, and neurocognitive deficits.

Serotonergic stimulation of the ventrolateral striatum induces orofacial stereotypy

Dopaminergic (DA) stimulation of the ventrolateral striatum produces a syndrome of intense orofacial stereotypies. In addition to dopaminergic projections from the substantia nigra, the striatum receives serotonergic (5-HT) inputs arising from the raphe nuclei. To assess the putative role of striatal 5-HT in orofacial movements, serotonin (0, 0.2, 2, 10, 20 micrograms/1.0 microliters) was infused into the ventrolateral striatum and behaviors were recorded using a time-sampling procedure. Serotonin produced a dose-dependent, site-specific increase in stereotyped orofacial behaviors. Infusion of selective 5-HT receptor agonists or uptake inhibitors did not produce the orofacial syndrome and pretreatment with either selective or nonselective 5-HT receptor antagonists did not block the 5-HT induced stereotypy. In contrast, pretreatment with DA receptor antagonists completely abolished the 5-HT induced repetitive orofacial movements, providing evidence for a 5-HT/DA interaction at this site. Moreover, depletion of DA with a combination of reserpine and alpha-methyl-p-tyrosine markedly decreased the stereotyped behaviors induced by 5-HT microinfusion. These data provide evidence for an interaction between 5-HT and DA in the striatum at presynaptic DA terminals. It is hypothesized that 5-HT may cause release of DA via reversal of the DA transporter. This syndrome may provide an animal model for some aspects of obsessive-compulsive disorder, because current theories of this disorder implicate 5-HT dysfunction in the basal ganglia.

Effect of antidepressants on striatal and accumbens extracellular dopamine levels

The effect of the selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor, fluoxetine (10 mg/kg s.c.), two tricyclic antidepressants, clomipramine (10 mg/kg s.c.) and imipramine (10 mg/kg s.c.), and vehicle on extracellular dopamine levels was studied in rat nucleus accumbens and striatum by in vivo microdialysis. Fluoxetine produced significant decreases in extracellular dopamine levels in both the nucleus accumbens and striatum (mean maximum percentage decrease: 58% and 57% of pre-drug baseline, respectively). In contrast, imipramine and clomipramine significantly increased extracellular dopamine in the striatum (148% and 150%, respectively) compared to the effect of vehicle alone (118%). These results suggest that the selective serotonin reuptake inhibitor, fluoxetine, and the tricyclic antidepressants, clomipramine and imipramine, affect dopaminergic activity in diverse ways and in a region-specific manner. Thus, the antidepressant effect of these drugs is unlikely to be related to their acute effects on dopaminergic neurotransmission. The differential effects of the selective serotonin reuptake inhibitor and tricyclic antidepressants on extracellular dopamine could account for other differences in their clinical and side effect profiles. Further studies of the chronic effects of the selective serotonin reuptake inhibitor and the tricyclic antidepressants on dopaminergic activity are required to elucidate the role of dopamine in the antidepressant effect.

Effects of chronic treatments with SM-9018, a potential atypical neuroleptic, on behavioral dopaminergic and serotonergic sensitivities in rats

1. Changes in behavioral dopaminergic and serotonergic sensitivities were studied in rats after withdrawal of the chronic treatments with SM-9018 (0.1 mg/kg/day), a potential atypical neuroleptic, and with haloperidol (0.3 mg/kg/day) using continuous infusion pumps. 2. Administration of SM-9018 inhibited the rat locomotor activities to an extent similar to that of haloperidol during the course of the 2 weeks treatment. 3. The incidence of the apomorphine-induced stereotyped behaviors (e.g., sniffing, chewing, licking and biting) was negligibly affected by SM-9018 treatment, but was markedly enhanced by haloperidol treatment. 4. The incidence of the 5-hydroxytryptophan-induced wet dog shakes and 8-hydroxy-2-(di-n-propyl-amino)tetralin-induced flat body posture was unaffected by either treatment with SM-9018 or haloperidol. 5. These findings suggest that SM-9018 is weaker than haloperidol in inducing the behavioral dopaminergic hypersensitivity after its chronic treatment and has a lower propensity to cause tardive dyskinesia.

A placebo-controlled trial of fluoxetine added to neuroleptic in patients with schizophrenia

Following a 2-week placebo lead-in, schizophrenic patients were randomly assigned to fluoxetine 20 mg/day or placebo added to depot neuroleptic for a 6-week, double blind trial. All patients had received a stable dose of depot neuroleptic for at least 6 months and did not meet criteria for depression. Serum samples were obtained at baseline and at weeks 4 and 6. Scores on the negative symptom subscale of the Brief Psychiatric Rating Scale (BPRS) were significantly lower at week 6, controlling for baseline scores, in patients receiving fluoxetine (n = 20) compared to patients receiving placebo (n = 21). Measures of psychosis, depression, global functioning and extrapyramidal symptoms (EPS) did not differ between groups at week 6. Fluoxetine administration was associated with a mean 65% increase in serum fluphenazine concentrations in 15 patients and a mean 20% increase in serum haloperidol concentrations in three patients. The change in negative symptoms at week 6 did not correlate with serum concentrations of fluoxetine or norfluoxetine, but did inversely correlate with S-norfluoxetine, an active stereoisomer of fluoxetine. For these chronically ill patients, fluoxetine significantly improved negative symptoms and did not worsen EPS, despite causing substantial elevation in serum concentrations of neuroleptics.

Extrapyramidal symptoms with selective serotonin reuptake inhibitors

BACKGROUND

Several case reports in the literature suggest that selective serotonin reuptake inhibitors can produce extrapyramidal symptoms.

METHODS

Computerised literature searches were used to identify reports on extrapyramidal symptoms and serotonin reuptake inhibitors. Subsequently, manual searches were made for articles in which there was any indication of the mechanisms responsible for these extrapyramidal symptoms.

RESULTS

Only a few reports could be identified in which serotonin reuptake inhibitors were implicated in extrapyramidal symptoms in some patients.

CONCLUSIONS

Evidence is discussed from preclinical and clinical studies suggesting the interaction between serotoninergic and dopaminergic neurotransmitter system, as a possible mechanism for production of extrapyramidal symptoms.

Evaluation of bradykinesia induction by SM-9018, a novel 5-HT2 and D2 receptor antagonist, using the mouse pole test

Induction of bradykinesia by SM-9018, a novel 5-HT2 and D2 antagonist, was compared with that of other neuroleptics using the pole test in mice. Neuroleptics including SM-9018, haloperidol, chlorpromazine, and thioridazine dose dependently induced bradykinesia in the pole-descending behavior of mice with relative potencies consistent with those for catalepsy induction. SM-9018 was about 70 times weaker than haloperidol and twice as weak as thioridazine in inducing bradykinesia. Other CNS drugs such as barbiturates and antidepressants had no effects. Haloperidol-induced bradykinesia was significantly attenuated by a cholinergic muscarinic antagonist (i.e., trihexyphenidyl) and 5-HT2 antagonists (i.e., ritanserin and cyproheptadine) whereas that caused by SM-9018 was relatively resistant to the 5-HT2 antagonists. These findings suggest that SM-9018 is weaker than other neuroleptics in inducing extrapyramidal side effects and that the 5-HT2 blocking activity of SM-9018 may contribute to its atypical neuroleptic property.

Motor and mental aspects of acute extrapyramidal syndromes

Acute extrapyramidal syndromes (EPS) are one of the major limitations to effective neuroleptic treatment. These disorders have both motor (objective) and mental (subjective) aspects, which must be considered in any evaluation and differential diagnosis of treatment-related side effects. The disorders of akathisia, acute dystonia and parkinsonism have unique features that are best understood in the context of a careful assessment of patient characteristics, drug factors and temporal aspects. Though acute EPS are commonly explained on the basis of dopamine D2 receptor antagonism, data from several lines of study raise important questions about this hypothesis. The roles of receptor subtype specificity, brain region selectivity and ratios of different receptor subtype antagonism are discussed. New and novel antipsychotic drugs with low rates of EPS are important clinical advancements that will increase patients' ability to participate in therapy and rehabilitation and thus improve their quality of life.

Tryptophan depletion in normal volunteers produces selective impairments in learning and memory

The amino-acid L-tryptophan is essential in the synthesis of brain serotonin, and its depletion can lead to a widespread reduction in central serotonergic activity. A placebo-controlled cross-over within-subjects design (n = 12) examined the effects of tryptophan depletion on human cognitive performance. A low-tryptophan (low-TRP) drink successfully reduced the levels of plasma and total free tryptophan. Computerized tests of memory, learning and executive function revealed selective and non-sedative impairments on cognitive performance following the active drink. Specifically, low-TRP impaired learning as seen in tests of visual discrimination and paired associates. Furthermore, low-TRP lengthened thinking times during the Tower of London planning task, but only in subjects already familiar with the task, suggesting a retrieval deficit. No evidence was found for an effect of the low-TRP drink on measures sensitive to frontal lobe dysfunction, supporting instead a specific role for the serotonergic system in the processes of memory and learning not directly implicated in frontal lobe function.

Survey on the pharmacodynamics of the new antipsychotic risperidone

This review reports on the pharmacodynamics of the new antipsychotic risperidone. The primary action of risperidone is serotonin 5-HT2 receptor blockade as shown by displacement of radioligand binding (Ki: 0.16 nM), activity on isolated tissues (EC50: 0.5 nM), and antagonism of peripherally (ED50: 0.0011 mg/kg) and centrally (ED50: 0.014 mg/kg) acting 5-HT2 receptor agonists in rats. Risperidone is at least as potent as the specific 5-HT2 receptor antagonist ritanserin in these tests. Risperidone is also a potent dopamine D2 receptor antagonist as indicated by displacement of radioligand binding (Ki: 1.4 nM), activity in isolated striatal slices (IC50: 0.89 nM), and antagonism of peripherally (ED50: 0.0057 mg/kg in dogs) and centrally acting D2 receptor agonists (ED50: 0.056-0.15 mg/kg in rats). Risperidone shows all effects common to D2 antagonists, including enhancement of prolactin release. However, some central effects such as catalepsy and blockade of motor activity occur at high doses only. Risperidone is 4-10 times less potent than haloperidol as a central D2 antagonist in rats and it differs from haloperidol by the following characteristics: predominant 5-HT2 antagonism; LSD antagonism; effects on sleep; smooth dose-response curves for D2 antagonism; synergism of combined 5-HT2/D2 antagonism; pronounced effects on amphetamine-induced oxygen consumption; increased social interaction; and pronounced effects on dopamine (DA) turnover. Risperidone displays similar activity at pre- and postsynaptic D2 receptors and at D2 receptors from various rat brain regions. The binding affinity for D4 and D3 receptors is 5 and 9 times weaker, respectively, than for D2 receptors; interaction with D1 receptors occurs only at very high concentrations. The pharmacological profile of risperidone includes interaction with histamine H1 and alpha-adrenergic receptors but the compound is devoid of significant interaction with cholinergic and a variety of other types of receptors. Risperidone has excellent oral activity, a rapid onset, and a 24-h duration of action. Its major metabolite, 9-hydroxyrisperidone, closely mimics risperidone in pharmacodynamics. Risperidone can be characterized as a potent D2 antagonist with predominant 5HT2 antagonistic activity and optimal pharmacokinetic properties.

Brain monoamines in progressive supranuclear palsy--comparison with idiopathic Parkinson's disease

Like idiopathic Parkinson's disease (iPD), Progressive Supranuclear Palsy (PSP) is characterized, inter alia, by a pronounced non-overlapping loss of dopamine (DA) in caudate, putamen and substantia nigra. Unlike iPD, in PSP the striatal DA loss is more severe in the caudate than in the putamen; this may contribute to the higher frequency of cognitive deficits in PSP. In contrast to iPD, in patients with PSP the serotonin (5-HT) levels in the basal ganglia are not significantly reduced, thus resulting in a relative predominance of the inhibitory serotonergic influences on the motor behaviour in these patients. It is suggested that combination of levodopa with a 5-HT receptor blocker may substantially improve the (poor) responsiveness of patients with PSP to DA substitution therapy.