Effect of two non tricyclic antidepressant drugs on [14C]5-hydroxytryptamine uptake by rat platelets

Beyond Haemostasis and Thrombosis: Platelets in Depression and Its Co-Morbidities

Alongside their function in primary haemostasis and thrombo-inflammation, platelets are increasingly considered a bridge between mental, immunological and coagulation-related disorders. This review focuses on the link between platelets and the pathophysiology of major depressive disorder (MDD) and its most frequent comorbidities. Platelet- and neuron-shared proteins involved in MDD are functionally described. Platelet-related studies performed in the context of MDD, cardiovascular disease, and major neurodegenerative, neuropsychiatric and neurodevelopmental disorders are transversally presented from an epidemiological, genetic and functional point of view. To provide a complete scenario, we report the analysis of original data on the epidemiological link between platelets and depression symptoms suggesting moderating and interactive effects of sex on this association. Epidemiological and genetic studies discussed suggest that blood platelets might also be relevant biomarkers of MDD prediction and occurrence in the context of MDD comorbidities. Finally, this review has the ambition to formulate some directives and perspectives for future research on this topic.

Pharmacology of antidepressants

This review covers mechanisms of action, efficacy, side effects, and toxicity of various classes of antidepressants: tricyclic antidepressants, monoamine oxidase inhibitors, second-generation antidepressants including the selective inhibitors of serotonin reuptake, and novel drugs such as mirtazapine, nefazodone, and venlafaxine.

Simultaneous brain and blood microdialysis study with a new removable venous probe. Serotonin and 5-hydroxyindolacetic acid changes after D-norfenfluramine or fluoxetine

A removable intravenous microdialysis probe was developed and simultaneously used with a removable microdialysis probe placed in the lateral hypothalamus (LH). Serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) changes in blood and brain dialysates were measured by HPLC-EC after an i.p. injection of 5 mg/kg d-norfenfluramine (dNF) or 10 mg/kg fluoxetine (FLU) in freely moving rats. 5-HT in the LH significantly increased after both drugs, but the rise was larger and faster with dNF [F(7,28)=4.0 p<0.05] than with FLU [F(5,20)=5.0 p<0.01]. By contrast, in venous blood 5-HT increased after FLU [F(5,20)=2.96 p<0.05] but not after dNF. 5-HIAA after both drugs continued decreasing significantly in the LH [dNF F(7,28)=11.4 p<0.01; FLU F(5,20)=22.8 p<0.01], but it did not change in blood. Simultaneous dialysis in brain and blood allowed evaluation of the differential effects of dNF and FLU on 5-HT and 5-HIAA in the two places. Removable venous probes prevented the inflammatory reaction that may occur around permanently implanted probes, and the dialysis could be more efficient and with less risk of clogging.

Fluoxetine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in depressive illness

Fluoxetine is a new antidepressant which enhances serotoninergic neurotransmission through potent and selective inhibition of neuronal reuptake of serotonin. Metabolism by N-desmethylation occurs in man yielding desmethylfluoxetine, which also inhibits serotonin reuptake. Both the parent compound and metabolite possess elimination half-lives of several days facilitating the maintenance of steady-state plasma concentrations during long term treatment. Fluoxetine has overall therapeutic efficacy comparable with imipramine, amitriptyline and doxepin in patients with unipolar depression treated for 5 to 6 weeks, although it may be less effective than tricyclic antidepressants in relieving sleep disorders in depressed patients. Geriatric patients also responded as well to fluoxetine as to doxepin. The symptomatic improvement in patients with unipolar depression during short term fluoxetine treatment has been satisfactorily maintained when therapy was extended for at least 6 months: the relapse rate was low and similar to that of imipramine. Preliminary data have shown that patients with bipolar depression gained similar therapeutic benefit from fluoxetine or imipramine. Other preliminary trials have indicated that fluoxetine may be useful in obsessive-compulsive disorders. Usual doses of fluoxetine cause significantly fewer anticholinergic-type side effects than tricyclic antidepressants. Nausea, nervousness and insomnia are the most frequently reported fluoxetine-related adverse effects, but these have usually not been severe. Therapeutic doses of fluoxetine do not affect cardiac conduction intervals in patients without pre-existing cardiovascular disease and fluoxetine has been relatively safe in the small number of patients who have taken overdoses. It has not been clearly established whether some types of depression may respond more readily to fluoxetine than other antidepressants, and its overall therapeutic efficacy has not been compared with other second generation antidepressants. Thus, with its different and perhaps improved side effect profile compared with older tricyclic antidepressants, fluoxetine offers properties that could be used to advantage in many patients with depression.

Trazodone hydrochloride: a wide spectrum antidepressant with a unique pharmacological profile. A review of its neurochemical effects, pharmacology, clinical efficacy, and toxicology

Trazodone is a new antidepressant agent that was recently introduced in the United States. It has a unique pharmacological profile that is not typical of either tricyclic or monoamine oxidase inhibitor antidepressants. As such it represents a new class of antidepressant drugs. The efficacy of trazodone has been clearly established in comparative studies with imipramine and amitriptyline. Major depression is the principal indication for its use, but good results have been shown in a wide variety of depressive subtypes. Of particular importance is the low frequency of adverse reactions seen with this drug.

The effect of niaprazine on the turnover of 5-hydroxytryptamine in the rat brain

Niaprazine (60 mg/kg i.p.) increased rat brain 5-hydroxyindole acetic acid (5-HIAA) concentrations 30 min after treatment, and reduced them at 3-8 hr after treatment. Rat brain 5-hydroxytryptamine (5-HT) levels were unchanged. Niaprazine also produced a short-lasting depletion of rat brain noradrenaline (NA) and dopamine (DA). Pretreatment with alpha-phenyl-alpha-propyl-benzeneacetic acid, 2-(diethylamino) ethyl ester hydrochloride (SKF 525A) (75 mg/kg i.p.) potentiated the increase in 5-HIAA and depletion of catecholamines produced 1 hr after niaprazine, but abolished the reduction in 5-HIAA produced 8 hr after the drug. This suggested that a metabolite might be responsible for the delayed reduction in 5-HIAA levels. A potential metabolite, p-fluoro-phenylpiperazine (FPP) (5-40 mg/kg i.p.) reduced rat brain 5-HIAA and 3,4-dihydroxyphenyl acetic acid (DOPAC), and inhibited 5-HT and NA uptake in vitro. Unlike niaprazine, FPP produced no behavioural sedation, but in large doses produced a behavioural syndrome indicative of serotonergic stimulation. Studies of the metabolism of 14C-niaprazine in rats indicated the presence of a urinary metabolite with the same chromatographic characteristics as FPP. These results suggest that niaprazine itself depletes brain catecholamines and increases 5-HT turnover, while a metabolite, FPP, subsequently reduces the turnover of 5-HT and DA.

Du 24565, a quipazine derivative, a potent selective serotonin uptake inhibitor

Du 24565, 6-nitro,2-(1-piperazinyl)quinoline, is a potent and selective inhibitor of the synaptosomal uptake of serotonin (5-HT). At concentrations at least 10(3)-fold higher it affects the uptake of norepinephrine (NA) and dopamine (DA), The IC50 values are: 5-HT: 4 x 10(-8) M; NA: 6 x 10(-5) M and DA: 4 x 10(-5) M. Uptake of 5-HT by rat blood platelets is also strongly inhibited (Ki approximately 5 x 10(-8) M); the inhibition is probably noncompetitive. In vivo, DU 24565 is active at low oral doses: the 5-HT depletion in rat brain caused by p-chloroamphetamine is antagonized by DU 24565 (oral ED50 0.7 mg/kg). The decrease in the 5-HT content caused by 4, alpha-dimethyl-m-tyramine (H 77/77) is antagonized by DU 24565 at 1 mg/kg orally, without any effect on the depletion of catecholamines. 5-HT turnover, measured by the probenecid method, is reduced by the same dose of DU 24565. Other tests confirmed the activity and selectivity of DU 24565: it potentiated the behavioural affects of the 5-HT precursor 5-hydroxytryptophan (5-HTP) in mice (ED50 1.5 mg/kg orally); it potentiated the temperature increases caused by 5-HTP in the rabbit; it had low activity or no effect at all in NA potentiation tests. This new compound is more potent and selective than the known 5-HT uptake inhibitors. It is a potential antidepressant and can be useful as a pharmacological tool to study the role of 5-HT in the central nervous system.

Trazodone, a central serotonin antagonist and agonist

We examined the effect of trazodone (TR), a non-tricyclic antidepressant drug with an unknown mechanism of action, as well as its supposed metabolites beta-(3-oxo-s-triazolo-[4, 3 a]-pyridin-2-yl-propionic acid (OTPA) and 1-(m-chlorophenyl)-piperazine (CPP) on the serotonin (5-HT) -system in a model of the hind limb flexor reflex of the spinal rat. When given alone at low doses (1 mg/kg) TR does not change the flexor reflex but counteracts its serotonergic stimulation induced by LSD, quipazine or fenfluramine. At higher doses (6--8 mg/kg), after a period of latency, it enhances the reflex; this effect is antagonized by the 5-HT receptor blockers (cyproheptadine, WA-335 and metergoline) but not by imipramine. From the two TR metabolites studied only CPP exerts an effect in the flexor reflex model. It considerably enhances (0.05--1 mg/kg) the reflex, this effect being antagonized by cyproheptadine, WA-335 and metergoline, but not by imipramine. Our findings indicate that TR has a double effect on the central 5-HT system: at low doses it acts as a 5-HT antagonist, whereas at higher ones--as a 5-HT agonist. The latter effect may be connected with formation of a metabolite, CPP, or a compound chemically related to CPP.

Extrapyramidal side effects and increased serum prolactin following fluoxetine, a new antidepressant

Fluoxetine (Lilly 110140) is a potent, specific serotonin (5-HT) uptake blocker which is being tested in man for antidepressant activity. One of 9 depressed patients receiving this drug developed a dystonic reaction, parkinsonian rigidity, and increased serum prolactin levels, all signs of decreased dopaminergic activity. Homovanillic acid levels also decreased in the cerebrospinal fluid of this subject. We postulate that fluoxetine, via the increase in 5-HT activity resulting from 5-HT uptake blockade, inhibited both the nigro-striatal and tubero-infundibular dopaminergic neurons. These results provide additional evidence for a linkage between serotonergic and dopaminergic neurons in man.