Antiobsessive effect of fluoxetine

Sérotonine et capacité à différer une conduite un modèle psychobiologique

Des troubles du fonctionnement sérotoninergique ont été impliqués dans de nombreuses pathologies ou dysrégulations du système nerveux central: trouble dépressif, trouble anxieux, schizophrénie, psychopathie, agressivité, boulimie, éthylisme, etc.

Le rôle de cette amine dans l’inhibition de la survenue de certains comportements est décrit depuis longtemps. Chez l’animal, ce rôle semble organiser la capacité à différer une conduite et/ou à tolérer sans réponse comportementale une situation de contrainte. Chez l’homme, la sérotonine semble réguler une capacité à contrôler les réponses impulsives dans le cadre des troubles très différents tels que passage à l’acte suicidaire, conduite boulimique, compulsions itératives, conduite éthylique, etc. Les inhibiteurs du recaptage de la sérotonine semblent améliorer l’existence de ces troubles de façon transnosologique.

Nous faisons l’hypothèse que certains diagnostics pourraient être la conséquence d’un fonctionnement «limite» sur le plan biologique facilitant le passage à l’acte et des troubles de personnalité. Aucune des deux dimensions ne serait en soi pathologique. Le manque d’adaptabilité de certains fonctionnements mentaux (caractère, personnalité) ajoutée à un fonctionnement biologique «limite” (difficulté à différer sa réponse) seraient par leur coexistence responsables de la décompensation qui aboutit à ce qu’on appelle un diagnostic.

Urinary indoleamines in Tourette syndrome patients with obsessive-compulsive characteristics

Tourette syndrome patients with high levels of obsessive-compulsive symptoms were compared with patients without these symptoms on urinary measures of serotonin and its major metabolite, 5-hydroxyindoleacetic acid (5HIAA). Both groups were compared with normal controls, and it was hypothesized that patients with obsessive-compulsive symptoms would have lower levels of serotonin. Both groups of Tourette syndrome patients had lower levels than controls, but there was no difference between them. Obsessive symptoms were related to higher levels of 5HIAA and to a higher turnover of serotonin.

Neurobiology of obsessive compulsive disorder--a serotonergic basis of Freudian repression

Intrusive thoughts and images, often of a violent, horrific, or blasphemous nature are the hallmark of Obsessive Compulsive Disorder (OCD). OCD patients frequently also often have reductions in normal serotonergic (5-HT) function. This paper proposes a model of 5-HT function involving the routine filtering and suppression of violent or libidinal impulses. This model accounts for OCD as an instance of failed inhibition. The model also appears to resemble Freud's model of ego-id interactions at least in part, suggesting that it may be possible to psychobiologically substantiate a Freudian metaphor.

5-HT-related drugs and human experimental anxiety

Clinical observations and double-blind studies demonstrated an anxiolytic effect of drugs that facilitate serotonergic transmission on several anxiety disorders. There is a latency of several weeks for their anxiolytic effect to take place. There may be, in addition, a biphasic effect, i.e., an acute anxiogenic effect followed by an anxiolytic effect after chronic use. In addition, acute administration of m-chlorophenylpiperazine (MCPP), an agonist of 5-HT-1 receptors, increased anxiety in normal volunteers as well as in patients with panic or obsessive-compulsive disorders. Studies in health volunteers have been performed in our laboratory to explore the acute effect on human anxiety of drugs that selectively influence 5-HT neurotransmission. We observed that acute administration of chlorimipramine enhanced the rise in anxiety induced in healthy volunteers by speaking in front of a video camera. With a similar experimental design, we also demonstrated an anxiogenic effect of metergoline, a nonselective 5-HT receptor blocker. It is suggested that the proanxiogenic effect of acute administration of 5-HT uptake inhibitors may be due to impaired 5-HT neurotransmission.

Obsessive-compulsive disorder: psychobiological approaches to diagnosis, treatment, and pathophysiology

The diagnosis, treatment, and pathophysiology of obsessive-compulsive disorder (OCD) were examined in a series of studies utilizing psychobiological approaches. Putative biological markers previously reported in depression were studied in this disorder and revealed that on some measures [Dexamethasone Suppression Test and rapid eye movement (REM) latency on sleep electroencephalogram (EEG)], OCD patients resemble those with major depressive disorder (MDD), whereas on others [REM density, platelet serotonin uptake, probably platelet 3H-imipramine binding, and 5-hydroxy-indoleacetic acid (5-HIAA) in cerebral spinal fluid (CSF)] they do not. The relationship between OCD and MDD was further explored in a double-blind, randomized crossover study designed to compare the antiobsessional effects of two tricyclic antidepressants, clomipramine (CMI) and desipramine (DMI), in a nondepressed cohort of OCD patients. CMI was found to have significant antiobsessional effects in this group, whereas in the same patients, DMI lacked therapeutic effects. These results suggest that not all antidepressants are antiobsessive and that some property of CMI, such as its potent serotonergic effects, may be of pathophysiological relevance for OCD. The role of serotonin in this disorder was then tested using the pharmacological challenge strategy. A novel serotonin postsynaptic receptor (5HT-1) agonist, m-chlorophenylpiperazine (m-CPP), was administered orally (0.5 mg/kg) under double-blind, placebo-controlled conditions to OCD patients and controls. In addition, a serotonergic receptor antagonist, metergoline (4 mg), was given to a subset of OCD patients. Relative to healthy volunteers, the OCD patients became significantly more anxious, depressed, and dysphoric after m-CPP administration. Moreover, in the OCD patients, obsessive-compulsive symptoms increased markedly after m-CPP and decreased significantly following metergoline administration. These results demonstrate that agents that bind to the 5HT-1 receptor can acutely affect the symptoms of OCD patients. The striking behavioral effects of these direct postsynaptic receptor ligands and the relative specificity of clomipramine as an antiobsessional agent suggest that serotonergic neurons may play a role in the pathophysiology, as well as mediating the pharmacological reduction, of obsessional symptoms.

Fluoxetine: a serotonin-specific, second-generation antidepressant

Fluoxetine is a bicyclic antidepressant that is a specific and potent inhibitor of the presynaptic reuptake of serotonin. It has essentially no effect on the reuptake of norepinephrine or other neurotransmitters. Similarly, it has negligible binding affinity for neurotransmitter receptor sites. It is well absorbed after oral administration, with absolute bioavailability in dogs of approximately 72 +/- 27.6%. The mean Tmax is between 4 and 8 hours, and it is approximately 94% protein bound. After a single dose, the elimination half-life is 1-3 days. After long-term administration, the elimination half-life averages 4 days. Its pharmacokinetics appear nonlinear. It is metabolized to an active metabolite norfluoxetine, which is also specific for the inhibition of serotonin reuptake. Norfluoxetine's elimination half-life averaged 7 days after long-term administration. Little is known about potential drug interactions; however, fluoxetine appears to have minimal clinically relevant interactions. Fluoxetine is indicated in the treatment of major depression. Its efficacy is comparable to the tricyclics and it has a similar onset of action. Although doses as high as 80 mg/day have been used, the optimal dosage range appears to be 20-40 mg once daily. Fluoxetine has been used with success in obsessive-compulsive disorder and intention myoclonus, however, its use in these disorders remains investigational. The frequency of side effects is low and dose related; the most common effects are nausea, anxiety, insomnia, anorexia, diarrhea, nervousness, and headache. Eight reports of intentional overdose with fluoxetine alone resulted in no deaths and mild adverse effects. It will be marketed as 20-mg capsules under the brand name of Prozac. Although fluoxetine should be added to formularies, its use should be reserved for treatment of those who do not respond to or do not tolerate tricyclic agents.