Interactions of fluoxetine with metabolism of dopamine and serotonin in rat brain regions

Effects of acute or repeated paroxetine and fluoxetine treatment on affective behavior in male and female adolescent rats

RATIONALE

The SSRI antidepressant fluoxetine is one of the few drugs that is effective at treating depression in adolescent humans. In contrast, the SSRI paroxetine has limited efficacy and is more at risk for inducing suicidal behavior.

OBJECTIVE

The purpose of the present study was to more fully characterize the differential actions of paroxetine and fluoxetine.

METHODS

In experiment 1, male and female rats were injected with paroxetine (2.5 or 10 mg/kg), fluoxetine (10 mg/kg), or vehicle for 10 days starting on postnatal day (PD) 35, and affective behaviors were assessed using sucrose preference and elevated plus maze tasks. A separate set of rats were used to examine monoamine levels. In experiment 2, rats were injected with paroxetine (2.5, 5, or 10 mg/kg), fluoxetine (5, 10, or 20 mg/kg), or vehicle during the same time frame as experiment 1, and anxiety-like behaviors were measured using elevated plus maze, light/dark box, and acoustic startle.

RESULTS

Repeated SSRI treatment failed to alter sucrose preference, although both paroxetine and fluoxetine reduced time spent in the open arms of the elevated plus maze and light compartment of the light/dark box. Paroxetine, but not fluoxetine, enhanced acoustic startle and interfered with habituation. Serotonin turnover was decreased by both acute and repeated fluoxetine treatment but unaltered by paroxetine administration.

DISCUSSION

These results show that repeated treatment with paroxetine and fluoxetine has dissociable actions in adolescent rats. In particular, paroxetine, but not fluoxetine, increases acoustic startle at low doses and may increase sensitivity to environmental stressors.

Behavioral disturbance in dementia

Behavioral disturbances are frequently the most challenging manifestations of dementia and are exhibited in almost all people with dementia. Common behavioral disturbances can be grouped into four categories: mood disorders (e.g., depression, apathy, euphoria); sleep disorders (insomnia, hypersomnia, night-day reversal); psychotic symptoms (delusions and hallucinations); and agitation (e.g., pacing, wandering, sexual disinhibition, aggression). They are often persistent, greatly diminish quality of life of patients and their family caregivers, cause premature institutionalization, and pose a high economic burden on the patient, family, and society. Behavioral disturbances can be prevented and treated with a multifaceted approach that supports dignity and promotes comfort and quality of life of persons with dementia and their family members. Management involves prompt treatment of reversible factors and management of symptoms using primarily individualized nonpharmacological interventions. Pharmacological interventions need to be restricted to behavioral emergencies and for short-term treatment of behavioral disturbances that pose imminent danger to self or others.

A case of needle fixation

Needle fixation is frequently missed and dismissed by clinicians and patients. However, ignoring this condition can have severe consequences, such as septicaemia, thrombosis, blood borne viruses, and is associated with an overall poor prognosis of drug dependence.Here we describe a 37-year-old man who presented with 20-year history of polydrug dependence, drug-induced psychosis and antisocial personality disorder. He was found to also have a 5-year history of intermittent needle fixation. His injecting behaviour and drug use improved significantly with fluoxetine while being on methadone maintenance.At present there is little evidence for any effective treatment strategies for needle fixation. The current recommended treatment consists of cognitive behavioural therapy and cue exposure. Whether fluoxetine constitutes an effective management strategy remains to be seen.

Multifunctional pharmacotherapy: what can we learn from study of selective serotonin reuptake inhibitor augmentation of antipsychotics in negative-symptom schizophrenia?

Many patients suffering from major psychiatric disorders do not respond adequately to monotherapy and require additional drugs. To date, there are no objective guidelines for deciding which combination may be effective, and the choice is based on previous clinical experience and on trial and error. Even when combination drugs are effective, the biochemical mechanisms responsible for the value-added effect are unknown. Understanding the mechanism of such synergism may provide a rational basis for choosing drug combinations and for developing more effective drugs. In schizophrenia, negative symptoms respond poorly to antipsychotics, but may improve when these are augmented with selective serotonin reuptake inhibitors (SSRI). This augmenting effect cannot be explained by summating the pharmacological effects of the individual drugs. We proposed that the study of SSRI augmentation can serve as a window to understanding the biochemical mechanisms of clinically effective drug synergism. In a series of studies we identified unique biochemical effects of the combination, different from each individual drug, and proposed that some of these are involved in mediating the clinical effect. Here we review some of the findings and propose that the mechanism of action involves regionally selective modulation of the GABA system. The evidence indicates that the SSRI antidepressant-antipsychotic combination may be a useful paradigm for studying therapeutically effective synergistic drug interactions in schizophrenia. Although as yet limited in scope, the findings of definable molecular targets for synergistic SSRI-antipsychotic interaction provide new directions to inform future research and provide novel bio-molecular targets for drug development.

Acute effects of combining citalopram and pindolol on regional brain serotonin synthesis in sham operated and olfactory bulbectomized rats

The olfactory bulbectomized (OBX) rat is considered to be a good model of the pathology of human depression and also of the functional actions of antidepressant drug therapy. It has been proposed that antidepressant effects of selective serotonin reuptake inhibitors (SSRIs) can be accelerated by blocking 5-HT(1A/B) autoreceptors with pindolol. The underlying mechanism is thought to involve acute unrestricting of 5-HT release and, consequently, relatively enhanced 5-HT turnover throughout the forebrain serotonergic networks. The effect of this combination on 5-HT turnover in sham operated or OBX rats can be assessed at the level of 5-HT synthesis, a very important presynaptic step in serotonergic neurotransmission, using the alpha-[(14)C]methyl-l-tryptophan autoradiography method. In sham rats, acute citalopram (20mg/kg) treatment increased synthesis at almost all serotonergic terminal regions but slightly decreased synthesis at serotonergic cell body regions (i.e. dorsal and median (not significant) raphe; approximately 16%). Combining pindolol (10mg/kg) with citalopram further increased synthesis at many regions in sham rats (relative to treatment with only citalopram). In OBX rats, citalopram decreased synthesis at a few terminal regions and greatly decreased synthesis at the dorsal and median raphe ( approximately 45%; relative to OBX rats treated with saline). Combining pindolol with citalopram greatly increased synthesis at almost all regions in OBX rats (relative to treatment with only citalopram). These results suggest that acute citalopram effects result in elevated terminal 5-HT synthesis, but these effects are restrained by 5-HT(1A/B) autoreceptor feedback to different degrees in sham and OBX rats. Moreover, 5-HT(1A/B) autoreceptor feedback is stronger in OBX rats and may underlie the delay of SSRI effects in OBX rats and, correspondingly, in human depression. Pindolol acceleration and augmentation of SSRI antidepressant therapy for human depression may be mediated by attenuation of 5-HT(1A/B) autoreceptor feedback, permitting unhindered SSRI effects on serotonergic terminals.

Up-regulation of tryptophan hydroxylase-2 mRNA in the rat brain by chronic fluoxetine treatment correlates with its antidepressant effect

Tryptophan hydroxylase-2 (TPH2), the rate-limiting enzyme in 5-HT synthesis in the brain, is a candidate for participation in a mechanism mediating the antidepressant effect of selective 5-HT reuptake inhibitors such as fluoxetine. Using real-time reverse transcription-polymerase chain reaction (RT-PCR) and semi-quantitative RT-PCR techniques, we have examined the effects of fluoxetine administration with drinking water (7.5 mg/kg/day) for 2, 4 and 8 weeks on TPH2 mRNA expression in the midbrain part of the dorsal raphe nucleus (DRN) and in the brainstem containing the rest of the raphe complex. Fluoxetine treatment for 4 and 8 weeks significantly increased basal TPH2 mRNA levels in the midbrain, an effect that was correlated with the appearance of antidepressant-like effects in the forced swim test. A significant induction of TPH2 and 5-HT transporter (5-HTT) mRNAs was detected in the midbrain of untreated rats 24 h after the swim test. In these animals, the swim test also produced a marked decrease in 5-HT metabolite (5-hydroxyindoleacetic acid (5-HIAA)) content in the amygdala. Fluoxetine treatment for 4 and 8, but not for 2 weeks, abolished these swim-induced changes in TPH2 and 5-HTT mRNAs levels in the midbrain and 5-HIAA content in the amygdala. The results of the present study suggest that TPH2 gene expression in the midbrain part of the DRN is implicated in depression and stress response, as well as in the antidepressant fluoxetine action.

Dopamine and serotonin metabolism in response to chronic administration of fluvoxamine and haloperidol combined treatment

Treating primary 'negative symptoms' of schizophrenia with a combination of a typical antipsychotic and a selective serotonin reuptake inhibitor, is more effective than with antipsychotic alone and is similar to the effect of the atypical antipsychotic, clozapine. The mechanism of this treatment combination is unknown and may involve changes in dopaminergic and serotonin systems. We studied dopamine and serotonin metabolism in different rat brain areas at 1.5 and 24 h after the last dosage of chronic treatment (30 days), with haloperidol plus fluvoxamine, each drug alone, and clozapine. Haloperidol-fluvoxamine combination, haloperidol, and clozapine treatments increased striatal and frontal cortex dopamine turnover and reduced striatal tyrosine hydroxylase activity at 1.5 h. At 24 h both dopamine turnover and tyrosine hydroxylase activity were reduced. Thus, in chronically treated animals, release of striatal dopamine increases following a drug pulse and returns to baseline by 24 h. Serotonin and 5-hydroxyindoleacetic acid concentrations were decreased at 1.5 h in haloperidol-fluvoxamine and clozapine groups and returned to normal levels by 24 h. A limited behavioral assessment showed that treatment with haloperidol plus fluvoxamine reduced motor activity compared to haloperidol, and increased sniffing compared to haloperidol, fluvoxamine and clozapine. These findings indicate that combining antipsychotic with SSRI results in specific changes in dopaminergic and serotonergic systems and in behavior. The possibility that these may be relevant to the mechanism underlying the clinical effectiveness of augmentation treatment warrant further study.

Serotonin decreases aggression via 5-HT1A receptors in the fighting fish Betta splendens

The role of the monoamine neurotransmitter serotonin (5-HT) in the modulation of conspecific aggression in the fighting fish (Betta splendens) was investigated using pharmacological manipulations. We used a fish's response to its mirror image as our index of aggressive behavior. We also investigated the effects of some manipulations on monoamine levels in the B. splendens brain. Acute treatment with 5-HT and with the 5-HT1A receptor agonist 8-OH-DPAT both decreased aggressive behavior; however, treatment with the 5-HT1A receptor antagonist WAY-100635 did not increase aggression. Chronic treatment with the selective serotonin reuptake inhibitor fluoxetine caused no significant changes in aggressive behavior and a significant decline in 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentrations. Treatment with the serotonin synthesis inhibitor p-chlorophenylalanine resulted in no change in aggression, yet serotonergic activity decreased significantly. Finally, a diet supplemented with L-tryptophan (Trp), the precursor to 5-HT, showed no consistent effects on aggressive behavior or brain monoamine concentrations. These results suggest a complex role for serotonin in the expression of aggression in teleost fishes, and that B. splendens may be a useful model organism in pharmacological and toxicological studies.

Start of a selective serotonin reuptake inhibitor (SSRI) and increase of antiparkinsonian drug treatment in patients on levodopa

AIMS

We determined whether the start of selective serotonin reuptake inhibitors (SSRI) in levodopa users was followed by a faster increase of antiparkinsonian drug treatment.

METHODS

Selected were all levodopa users of 55 years and older from the PHARMO prescription database. The rate of increase of antiparkinsonian drug treatment was compared using Cox's proportional hazard model for starters of SSRI (n = 15) with starters of tricyclic antidepressants (TCA) (n = 31) and with patients not using antidepressants (n = 304), and was adjusted for age, gender, and duration of levodopa use.

RESULTS

The hazard ratio for the SSRI group compared with the TCA group was 4.2 (95% confidence interval 1.4, 12.6) and compared with the second control group was 2.7 (1.2, 5.2).

CONCLUSIONS

The start of SSRI therapy in levodopa users is followed by a faster increase of antiparkinsonian drug treatment.

Long-term effects of St. John's wort and hypericin on monoamine levels in rat hypothalamus and hippocampus

Hypericum perforatum L. (St. John's wort) is one of the leading psychotherapeutic phytomedicines and, because of this, great effort has been devoted to clarifying its mechanism of action. Chronic effects of St. John's wort and hypericin, one of its major active compounds, on regional brain amine metabolism have not been reported yet. We used a high-performance liquid chromatography system to examine the effects of short-term (2 weeks) and long-term (8 weeks) administration of imipramine, Hypericum extract or hypericin on regional levels of serotonin (5-HT), norepinephrine, dopamine and their metabolites in the rat brain. We focused our interest on the hypothalamus and hippocampus, as these brain regions are thought to be involved in antidepressant drug action. Imipramine (15 mg/kg, p.o.), Hypericum extract (500 mg/kg, p.o.), and hypericin (0.2 mg/kg, p.o.) given daily for 8 weeks significantly increased 5-HT levels in the hypothalamus (P<0.05). The 5-HT turnover was significantly lowered in both brain regions after 8 weeks of daily treatment with the Hypericum extract (both P<0.05). Consistent changes in catecholamine levels were only detected in hypothalamic tissues after long-term treatment. Comparable to imipramine, Hypericum extract as well as hypericin significantly decreased 3,4-dihydroxyphenylacetic acid and homovanillic acid levels in the hypothalamus (P<0.01). Our data clearly show that long-term, but not short-term administration of St. John's wort and its active constituent hypericin modify levels of neurotransmitters in brain regions involved in the pathophysiology of depression.

The mechanisms involved in the long-lasting neuroprotective effect of fluoxetine against MDMA ('ecstasy')-induced degeneration of 5-HT nerve endings in rat brain

1. It has been reported that co-administration of fluoxetine with 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') prevents MDMA-induced degeneration of 5-HT nerve endings in rat brain. The mechanisms involved have now been investigated. 2. MDMA (15 mg kg(-1), i.p.) administration produced a neurotoxic loss of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in cortex, hippocampus and striatum and a reduction in cortical [3H]-paroxetine binding 7 days later. 3. Fluoxetine (10 mg kg(-1), i.p., x2, 60 min apart) administered concurrently with MDMA or given 2 and 4 days earlier provided complete protection, and significant protection when given 7 days earlier. Fluvoxamine (15 mg kg(-1), i.p., x2, 60 min apart) only produced neuroprotection when administered concurrently. Fluoxetine (10 mg kg(-1), x2) markedly increased the K(D) and reduced the B(max) of cortical [3H]-paroxetine binding 2 and 4 days later. The B(max) was still decreased 7 days later, but the K(D) was unchanged. [3H]-Paroxetine binding characteristics were unchanged 24 h after fluvoxamine (15 mg kg(-1), x2). 4. A significant cerebral concentration of fluoxetine plus norfluoxetine was detected over the 7 days following fluoxetine administration. The fluvoxamine concentration had decreased markedly by 24 h. 5. Pretreatment with fluoxetine (10 mg kg(-1), x2) failed to alter cerebral MDMA accumulation compared to saline pretreated controls. 6. Neither fluoxetine or fluvoxamine altered MDMA-induced acute hyperthermia. 7. These data demonstrate that fluoxetine produces long-lasting protection against MDMA-induced neurodegeneration, an effect apparently related to the presence of the drug and its active metabolite inhibiting the 5-HT transporter. Fluoxetine does not alter the metabolism of MDMA or its rate of cerebral accumulation.

Pharmacology of antidepressants

Presently in the United States, 21 compounds have been approved by the Food and Drug Administration as antidepressants. Two additional drugs marketed outside the United States as antidepressants have been approved for obsessive-compulsive disorder. Nearly one half of all these compounds became available within the past 12 years, whereas the first antidepressant was available more than 40 years ago. After the clinical aspects of depression are introduced in this article, the pharmacology of the newer generation drugs is reviewed in relationship to the older compounds. The information in this review will help clinicians treat acute depression with pharmacological agents.

The serotonin 5-HT(2A) receptor subtype does not mediate apomorphine-induced aggressive behaviour in male Wistar rats

We have studied the effect of the 5-HT(2A) receptor antagonists on apomorphine-induced aggressive behaviour in male Wistar rats. In acute behavioural experiments with apomorphine-pretreated (1.0 mg/kg, s.c., once daily, 2 weeks) animals, risperidone (0.5 and 1.0 mg/kg) inhibited aggressive behaviour, but ketanserin and ritanserin (0.5-5. 0 mg/kg) had no effect on the latency and intensity of aggressive behaviour. Concomitant risperidone (0.5 mg/kg) and haloperidol (0.03 and 0.3 mg/kg) administration blocked aggressive behaviour completely. In conclusion, our experiments confirm that inhibition of the apomorphine-induced aggressive behaviour is elicited by drugs with dopamine (DA) but not with 5-HT(2A) antagonistic activity. Moreover, it may be concluded that the serotonin 5-HT(2A) receptor subtype does not alter the DA-mediated behaviour.

Behavioral tolerance to and withdrawal from multiple fluoxetine administration

The objective of this study was to characterize the lasting effects of fluoxetine on the locomotor behavior of rats using a computerized activity-monitoring system. Challenge dosages (8, 16, and 24 mg/kg i.p.) of fluoxetine 2 h into the dark phase resulted in dose-dependent suppression of locomotor activity for 4 h following injection. Escalating (10-30 mg/kg i.p.) semidaily fluoxetine administration for the next five days resulted in decreasing locomotor activity during the multiple-administration period relative to saline control. Circadian activity patterns at the conclusion of the regimen were unchanged in shape, but featured uniform decreases in locomotor activity at every hour which were more significant during the phase. Upon discontinuation, fluoxetine-treated rats showed a significant increase in activity during the first 4 h following the first "missed" dose which was not seen in subsequent washout. Ninety-six h after the final maintenance dose, the initial three dosages were readministered, and the locomotor activity suppression in response to the rechallenge dose of fluoxetine was significantly lessened compared to initial challenge. These findings suggest that tolerance and withdrawal were obtained.

Treatment of behavioural disturbances in Parkinson's disease

Behavioural disorders in Parkinson's disease can grossly be subdivided in primary disturbances and those which are related to drug treatment. Depression and anxiety are a common feature in parkinsonian patients. Both occur independently of drug treatment. In general, most current antidepressive and anxiolytic drugs could be administered in Parkinson's disease with the same precautions as in the normal population. However, in single case reports modern serotonin reuptake blockers in Parkinson's disease have been accused to worsen parkinsonian motor condition. Combinations of serotonin reuptake inhibitors with MAO-inhibitors like selegiline should be used with caution. In the case of cognitive decline firstly an underlying depression should be disclosed or if existent be treated. Depression seems to be the single most important factor associated with the severity of dementia and early antidepressant treatment seems to decrease cognitive decline in depressed parkinsonian patients. Anticholinergic medications should be discontinued since they may cause mental side effects. Sleep disorders in Parkinson's disease are mainly caused by nocturnal akinesia, which causes sleep fragmentation or altered dreaming and nightmares, which might be a side-effect of dopaminergic treatment. In the first case the administration of a controlled release preparation of levodopa at bedtime may be indicated. If the sleep disorder is considered to be due to dopaminergic medication, a reduction of long-term acting agents like modern dopamine agonists and controlled-release levodopa should be considered. In severe psychotic states related to drug treatment antiparkinsonian therapy must be carefully analysed and, if possible, reduced. If motor condition worsens and/or psychiatric symptoms do not improve, initiation with "atypical" neuroleptics like clozapine is indicated. The pharmacological and clinical properties of new antipsychotic drugs that can be used in Parkinson's disease are revised.

Serotonergic regulation of neuropeptide and glutamic acid decarboxylase mRNA levels in the rat striatum and globus pallidus: studies with fluoxetine and DOI

The serotonergic regulation of neuropeptide and glutamic acid decarboxylase (GAD) mRNA level in the rat basal ganglia was investigated by determining the effects of chronic treatment with the serotonin uptake blocker fluoxetine and the serotonin 5-HT2 agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrobromide (DOI). Fluoxetine (10 mg/kg) induced a reduction of preproenkephalin and GAD65 mRNA levels in the caudate-putamen and nucleus accumbens core and shell after 5 days of treatment. In addition, GAD65 mRNA levels were reduced in the globus pallidus. These changes appeared to be transient as they were not found after 15 days of fluoxetine treatment. DOI (7 mg/kg), administered for 9 days, induced a decrease of preprodynorphin mRNA levels in the caudate-putamen and the nucleus accumbens core and shell. No regional differentiation in the effects of fluoxetine and DOI was observed. Based on the present results, we propose that an increased 5-HT tone may reduce enkephalin and GABA mRNA levels in striatal regions and in the globus pallidus. Our results further show that preproenkephalin mRNA is not affected by chronic 5-HT2 receptor stimulation, indicating that the fluoxetine-induced decrease in preproenkephalin mRNA levels involves other 5-HT receptors than the 5-HT2 receptor. Preprodynorphin mRNA levels, on the other hand, were found to be reduced after chronic 5-HT2 receptors than stimulation. This observation, together with our previous finding that the 5-HT2 antagonist ritanserin tends to increase preprodynorphin mRNA levels, suggests a 5-HT2-mediated tonic inhibition of preprodynorphin mRNA levels.

Paroxetine potentiates the central nervous system side effects of perphenazine: contribution of cytochrome P4502D6 inhibition in vivo

BACKGROUND

Paroxetine is a frequently used antidepressant and a potent inhibitor of the CYP2D6 isozyme in vitro (inhibition constant [Ki] = 0.15 micromol/L). Most classic antipsychotic agents such as perphenazine are metabolized by the CYP2D6 isozyme and are often coadministered with antidepressant agents. This study assessed the extent of changes in CYP2D6 isozyme activity in vivo after pretreatment with paroxetine and its consequences on perphenazine kinetics and central nervous system effects.

METHODS

Eight extensive metabolizers for CYP2D6 were administered a single dose of perphenazine (0.11 mg/kg orally) or placebo following a randomized double-blind design. Perphenazine plasma concentrations and effects were assessed for a period of 8 hours. Subsequently, subjects were treated with a standard therapeutic dose of paroxetine (20 mg/day orally) for 10 days and test sessions with perphenazine and placebo were repeated.

RESULTS

Paroxetine treatment resulted in a twofold to 21-fold decrease in CYP2D6 activity (p < 0.001). After pretreatment with paroxetine, perphenazine peak plasma concentrations increased twofold to 13-fold (p < 0.01). This was associated with a significant increase in central nervous system side effects of perphenazine, including oversedation, extrapyramidal symptoms, and impairment of psychomotor performance and memory (p < 0.05).

CONCLUSION

Coadministration of perphenazine after pretreatment with a standard therapeutic dose of paroxetine increased the plasma concentration and central nervous system side effects of perphenazine, primarily as a result of inhibition of the CYP2D6 isozyme. In patients who are at steady state with paroxetine, a reduction of perphenazine dose may be required to prevent central nervous system side effects.

Tricyclic antidepressant-induced extrapyramidal side effects

Two cases of tricyclic antidepressant-related extrapyramidal side effects are reported and, the authors review the literature describing these effects. Despite clear case reports, these side effects are not well known. Given the wide prescription of tricyclic antidepressants (TCA) and the low number of case reports, the prevalence of these side effects is indeed low, but clinical implications exist. The extrapyramidal symptoms induced by TCA alone are acute or tardive dyskinesia, akathisia, myoclonus, rabbit syndrome and dystonia. These symptoms seem to be non age-related, but often dose-related, and were responders to antiparkinsonian agents or propranolol. The factors that predispose an individual to the development of these side effects are not completely understood. Some risk factors such as prior exposure to neuroleptics and/or lithium or estrogens could facilitate the development of these side effects. In some cases, they can disappear even though the same dose of TCA is continued, and they do not seem to be a drug class reaction. The susceptibility of each individual patient to the development of these disorders may be limited to only one or a few of these agents.

Clinically significant interactions of psychotropic agents with antipsychotic drugs

Various psychotropic drugs are commonly combined with antipsychotic agents. Such combinations can induce pharmacodynamically based, presumably additive, beneficial (e.g. sedative or mood-altering) effects or adverse autonomic, cardiac depressant and CNS intoxicating effects. Clinically significant interactions also arise through competition with or induction of hepatic microsomal cytochrome P450 (CYP) enzymes, particularly the CYP1A2 and CYP2D6 isozymes by which most antipsychotics are oxidised. Such pharmacokinetic interactions can elevate circulating concentrations of antipsychotics (both typical agents and the atypical antipsychotic clozapine) to potentially toxic ranges, which may lead to increased risks of adverse effects. Such interactions occur particularly with serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor antidepressants. Metabolic interactions that lead to lesser increases in antipsychotic concentrations may arise in combining these drugs with other antidepressants, benzodiazepines or propranolol. In contrast, most anticonvulsants, except valproic acid (sodium valproate), induce the oxidative metabolism of antipsychotics and can lower their plasma concentrations to potentially subtherapeutic levels, with unpredictable increases after their discontinuation. Since simultaneous use of multiple psychotropic agents is increasingly common, special caution is required to avoid untoward consequences of interactive adverse effects due to drug interactions, which can sometimes be severe or life-threatening.

Freezing of gait in Parkinson's disease is improved by treatment with weak electromagnetic fields

Freezing, a symptom characterized by difficulty in the initiation and smooth pursuit of repetitive movements, is a unique and well known clinical feature of Parkinson's disease (PD). It usually occurs in patients with long duration and advanced stage of the disease and is a major cause of disability often resulting in falling. In PD patients freezing manifests most commonly as a sudden attack of immobility usually experienced during walking, attempts to turn while walking, or while approaching a destination. Less commonly it is expressed as arrest of speech or handwriting. The pathophysiology of Parkinsonian freezing, which is considered a distinct clinical feature independent of akinesia, is poorly understood and is believed to involve abnormalities in dopamine and norepinephrine neurotransmission in critical motor control areas including the frontal lobe, basal ganglia, locus coeruleus and spinal cord. In general, freezing is resistant to pharmacological therapy although in some patients reduction or increase in levodopa dose may improve this symptom. Three medicated PD patients exhibiting disabling episodes of freezing of gait are presented in whom brief, extracerebral applications of pulsed electromagnetic fields (EMFs) in the picotesla range improved freezing. Two patients had freezing both during "on" and "off" periods while the third patient experienced random episodes of freezing throughout the course of the day. The effect of each EMFs treatment lasted several days after which time freezing gradually reappeared, initially in association with "off" periods. These findings suggest that the neurochemical mechanisms underlying the development of freezing are sensitive to the effects of EMFs, which are believed to improve freezing primarily through the facilitation of serotonin (5-HT) neurotransmission at both junctional (synaptic) and nonjunctional neuronal target sites.

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.

Differential effects of acute and chronic fluoxetine administration on the spontaneous activity of dopaminergic neurones in the ventral tegmental area

1. Electrophysiological techniques were used to study the effects of fluoxetine and citalopram on the basal activity of dopaminergic neurones in the ventral tegmental area (VTA) and substantia nigra, pars compacta (SNc) of rats. 2. Acute i.v. injection of fluoxetine (20-1280 micrograms kg-1) caused a dose-dependent inhibition of the firing rate of VTA dopaminergic neurones, but did not affect the activity of dopaminergic cells in the SNc. Citalopram (20-1280 micrograms kg-1, i.v.) inhibited the firing rate of dopaminergic neurones in the VTA, but its effect (maximal inhibition: 14 +/- 7%) was less pronounced than that of fluoxetine (maximal inhibition: 34 +/- 7%). 3. Pretreatment with mesulergine (80 micrograms kg-1, i.v.), a 5-hydroxytryptamine2C/2B (5-HT2C/2B) receptor antagonist, blocked the inhibitory effect of fluoxetine on VTA dopaminergic cells. Selective lesions of 5-hydroxytryptaminergic neurones by the neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), abolished the fluoxetine-induced reduction of VTA dopaminergic activity. 4. In a series of experiments, fluoxetine (10 mg kg-1, i.p.) was administered once daily for 21 consecutive days. Acute i.v. administration of fluoxetine (20-1280 micrograms kg-1, 72 h after the last i.p. injection) did not cause any change in the basal firing rate of VTA dopaminergic neurones in treated rats, whereas it induced the typical inhibitory effect in control animals. A group of rats chronically treated with fluoxetine, received i.v. m-chlorophenylpiperazine (mCPP; 10-320 micrograms kg-1), a 5-HT2C/2B receptor agonist. This drug significantly inhibited VTA dopaminergic function in control rats, but did not modify the basal activity of dopaminergic cells in animals given chronic fluoxetine. 5 It is concluded that fluoxetine inhibits dopaminergic function in the VTA by enhancing the synaptic levels of 5-HT, which possibly acts through the 5-HT2C/2B receptor subtype. Repeated treatment with fluoxetine induces tolerance to its inhibitory effect on dopaminergic activity, possibly as a consequence of down-regulation of 5-HT2C/2B receptors. The effects of fluoxetine on VTA dopaminergic cell activity might be relevant for its therapeutic actions and may explain the origin of the reported cases of akathisia.

Comparative Effects of Sertraline and Nortriptyline on Body Sway in Older Depressed Patients

This study examined effects of nortriptyline and sertraline on the balance and stability of depressed geriatric inpatients. Body sway was measured with a stable force-platform at three timepoints: before starting antidepressant medication, 5-7 days after medication was initiated, and 1 week later. A group of healthy, unmedicated older volunteers was evaluated under the same conditions as patients. In sertraline-treated patients (n = 10), significant differences (P < 0.05) between baseline and the first week of treatment were found in the force-platform measurements of sway length (L) and area of the center of pressure (Ao), with patients' eyes both open and closed. This change in postural stability occurred in the absence of orthostatic hypotension. By the second week of treatment, neither variable was found to be significantly different from baseline. In the nonmedicated volunteers (n = 20) and in the group of patients receiving nortriptyline (n = 11), no significant changes in postural stability were found.

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.

Pharmacology of antidepressants--characteristics of the ideal drug

OBJECTIVE

To describe the clinical and basic pharmacologic properties of antidepressants and thus define the pharmacologic criteria for the ideal antidepressant.

DESIGN

A review of the pharmacologic characteristics of the newer second-generation antidepressants is presented in relationship to those of the older compounds.

MATERIAL AND METHODS

Clinical pharmacologic and in vitro data on the synaptic effects of antidepressants (inhibition of synaptosomal uptake and blockade of neurotransmitter receptors) were obtained for the older antidepressants and for the more recently marketed and approved drugs. The group of antidepressants includes six new antidepressants approved for marketing since 1988 and two additional drugs marketed outside the United States as antidepressants but approved for use in the United States for obsessive-compulsive disorder. Thus, 18 antidepressant drugs are discussed.

RESULTS

All antidepressants seem to be equally efficacious in treating depression, and no drug seems to work more rapidly than another. Nonetheless, antidepressant drugs differ substantially in pharmacokinetic variables (elimination half-lives); in their effects on the metabolism of other drugs (by inhibiting the cytochrome P450 system); in their potencies for blocking the reuptake of norepinephrine, serotonin, and dopamine; and in their affinities for blocking histamine H1, muscarinic acetylcholine, alpha 1-adrenergic, and dopamine D2 receptors. Most side effects of antidepressants can be explained by their effects on blocking uptake and on blocking neurotransmitter receptors.

CONCLUSION

The newer second-generation antidepressants have distinct pharmacologic advantages in comparison with the tricyclic antidepressants and the older second-generation compounds. These advantages are clearly seen from their synaptic effects, in which most newer second-generation antidepressants are practically devoid of blocking effects at neurotransmitter receptors. Although the newer second-generation antidepressants are much closer to being the ideal antidepressant than are the older compounds, none completely fulfills the criteria for being the ideal drug.

Changes in dopamine metabolism in rat forebrain regions after cessation of long-term fluoxetine treatment: relationship with brain concentrations of fluoxetine and norfluoxetine

We examined the effects of repeated administration of the selective serotonin uptake inhibitor (SSRI) fluoxetine (Flx) (5, 10, or 15 mg/kg i.p., twice daily for 21 days) on brain and plasma concentrations of the parent drug and its active desmethyl metabolite, norfluoxetine (NFlx), in rats during the 21-day regimen as well as after cessation of drug treatment. We also measured dopamine (DA) levels in 2 midbrain regions (the striatum, St and nucleus accumbens, NAc) in rats killed 1-14 days after the last dose. NFlx concentrations in plasma and brain were ten times higher than those of Flx during the period of drug treatment. Although Flx accumulated more markedly in the rat brain than NFlx, it disappeared completely from plasma and brain after treatment stopped, while NFlx persisted up to Day P7. Chronic Flx treatment caused a persistent decrease in brain DA levels of -60% to -70% in St and NAc; this lasted for 7-14 days after cessation of treatment, depending on the dose used. The levels of DA metabolites decreased by 20-40%, and, except for 3-MT, tended to overshoot during the recovery period. Our data suggest that the long-term inhibition of DA neurons after cessation of Flx treatment parallels the inhibition previously observed for 5-HT neurons. Thus, besides blocking 5-HT uptake, Flx is likely to also inhibit in vivo DA uptake in forebrain regions, following prolonged administration.

Fluoxetine: adverse effects and drug-drug interactions

This overview summarizes the major and minor side effects and drug interactions of fluoxetine. The adverse reactions include the "serotonin syndrome", cardiovascular complications, extrapyramidal side effects such as akathisia, dyskinesias, and parkinsonian-like syndromes and an apparently increased risk of suicidality. Fluoxetine-induced mania and hypomania, seizures and sexual disorders are evaluated along with minor symptoms of allergic reactions, stuttering, hematological changes, psoriasis, and inappropriate secretion of the antidiuretic hormone. The major fluoxetine-drug interactions involve the amino acids L-dopa and L-tryptophan, anorexiants, anticonvulsants, antidepressants, anxiolytics, calcium channel blockers, cyproheptadine, lithium salts, and drugs of abuse. The underlying mechanism and the paradoxical effects of fluoxetine are addressed.

Fluoxetine and suicidal behaviour. Some clinical and theoretical aspects of a controversy

“In the practical decisions of life it will scarcely ever be possible to go through all the arguments in favour of or against one possible decision, and one will therefore always have to act on insufficient evidence” Werner Heisenberg (1962).

The development of selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitors (SSRIs) has added a new dimension to the pharmacotherapy of depression. Their lack of sedative and anticholinergic effects together with relative safety in overdose, has led some authors to suggest that the older tricyclic antidepressants (TCAs) should not now be considered a first-line treatment (Montgomery, 1988). However, since a report by Teicher et al (1990) of suicidal preoccupation associated with fluoxetine treatment, there has been both intense media interest and animated correspondence in clinical and scientific journals (O'Donnell, 1991).