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Several recent studies have demonstrated that 5-HT 1A , 5-HT 1B and 5-HT 3 receptors were implicated in the mechanism of action of antidepressants in the mouse forced swimming test. Despite extensive evidence for a role of 5-HT 2C receptors in depression, the precise role of these receptors in the effects of clinically established antidepressants was not directly investigated in the mouse forced swimming test. This work was aimed at exploring interactions between several doses of Ro 60-0175, a recently available, full and selective 5-HT 2C agonist, and antidepressant drugs in the mouse forced swimming test. Spontaneous locomotor activity was measured as an index of intact sensorimotor functions and the dose–effect of Ro 60-0175 alone, as well as interactions with several antidepressants, such as tricyclic antidepressants (imipramine, desipramine and maprotiline) and selective serotonin reuptake inhibitors (paroxetine, citalopram, fluoxetine, fluvoxamine and sertraline), were studied in the mouse forced swimming test. There was no intrinsic antidepressant-like effect of Ro 60-0175, but an impairment in locomotor function was detected when using doses higher than 4 mg/kg in the mouse. There was a synergistic effect of low doses of Ro 60-0175 with sub-active doses of imipramine, paroxetine, citalopram and fluvoxamine; an antagonism between the highest dose of Ro 60-0175 and the active doses of paroxetine and fluoxetine was also detected. There is evidence that 5-HT 2C receptors may be involved in the action of antidepressants which are able to boost the concentration of serotonin in the synapse, i.e. SSRIs and imipramine

We examined the relationship between plasma concentrations of specific acting antidepressants (fluvoxamine/maprotiline) and clinical improvement as well as the impact of the magnitude of the plasma concentration of these antidepressants on side effects. Patients (32 patients with major depression) were treated within a double-blind parallel trial for four weeks and plasma concentrations were obtained before, on days 8 and 28 of the trial. Although there was a fixed-flexible dosage design it was apparent that 16 patients (89%) of the fluvoxamine group and all patients of the maprotiline group received a dosage between 200 and 300 mg/day in the last week of the trial. Plasma concentrations (mean +/- SD micrograms/l) of fluvoxamine were 125 +/- 91 and 142 +/- 108 on days 8 and 28, respectively and the range of fluvoxamine plasma concentrations on day 28 was from 20 to 417 micrograms/l. Plasma concentrations (mean +/- SD micrograms/l) of maprotiline were 146 +/- 62 and 202 +/- 134 on days 8 and 28, respectively and the range of maprotiline plasma concentration on day 28 was from 12 to 428 micrograms/l. There was no linear relationship between plasma concentrations of both antidepressants (fluvoxamine/maprotiline) and oral dosage. Whereas there was no correlation between fluvoxamine concentration and clinical response there was a tendency that higher maprotiline concentrations were associated with a better antidepressive efficacy at the end of the trial. Higher concentrations of fluvoxamine as well as of maprotiline were significantly (P0.05) associated with more side effects.

Many antidepressants reverse arylpiperazine-induced hypothermia after acute treatment by a mechanism that does not seem to implicate monoamine uptake inhibition. Activity is found in reversing 1-( m -trifluoromethylphenyl)piperazine (TFMPP)-induced hypothermia by desipramine 5 and 10 mg/kg and not by maprotiline 10 and 20 mg/kg. Clomipramine and fluoxetine with comparable serotonin uptake blocking potential do not have comparable TFMPP-reversing effects. A dibenzothiadiazepine compound (IM/P/3/4), hypothesized to have antidepressant activity though devoid of uptake blocking properties, was active at 10 and 20 mg/kg. Other classes of tricyclics such as neuroleptics (clozapine 5 and 10 mg/kg) and chlorpromazine (2 and 10 mg/kg) and the H 1 antihistamines, promethazine (20 mg/kg) and cyproheptadine (10 mg/kg) are active, as well as the calcium antagonists nifedipine (10 mg/kg) and verapamil (10 mg/kg). We hypothesize that properties other than monoamine-uptake block which these compounds share (such as calcium-uptake inhibition) could be involved. Activity was also seen with the 5-HT 1A agonists 8-hydroxy-2- (di- n -propylamino)tetralin (8-OH-DPAT, at 0.05 and 0.25 mg/kg), and 5-methoxy- N - N -dimethyltryptamine (5-MeODMT at 3 mg/kg) as well as the muscarinic agonist oxotremorine (0.1 mg/kg).