Sex and age differences in the antidepressant-like effect of fluoxetine in the forced swim test.

This study compared in males and females of three representative ages: young adults (3-5months old), middle-aged (12-15months old) and senescent (23-25months old) the antidepressant-like effect of fluoxetine (FLX, 5.0 and 10mg/kg) in the forced swim test (FST). Intact (non gonadectomized) rats were evaluated. Young adult females were chosen in proestrus/estrus or in metestrus/diestrus, while middle-aged and senescent females were selected in metestrus/diestrus. Locomotion and motor coordination were also recorded. Under basal conditions (without FLX), young adult and middle-aged females showed less immobility than males. This sex difference disappeared at senescence because males diminished their levels of immobility. Thus, senescent males showed lower immobility than middle-aged and young males. FLX (5 and 10mg/kg) produced similar actions in young females irrespective of their estrous cycle phase, therefore, these subgroups were pooled in a single one. Young adult and middle aged females clearly responded to 5 and 10mg/kg of FLX with a reduction in immobility, while young adult and middle-aged males only did to 10mg/kg. In senescent females 10mg/kg FLX reduced immobility. Remarkably, in senescent males this FLX dose did not produce an antidepressant-like effect. FLX marginally affected locomotion; however, at its highest dose (10mg/kg), and only in senescent males, interfered with motor coordination tested in the rotarod. These data show that sex and aging influence behavioral despair without treatment and after FLX.

Age-related changes in the antidepressant-like effect of desipramine and fluoxetine in the rat forced-swim test.

Some reports suggest that older patients are less responsive to antidepressants than young adults, but this idea has not been fully supported. Here, we investigated the role of aging in the behavioral effects of the antidepressants, desipramine (DMI) (5, 10, and 20 mg/kg) and fluoxetine (FLX) (5, 10, and 20 mg/kg) in young adults (3-5 months), middle-aged (MA, 12-15 months), and senescent (SE, 23-25 months) male rats in the forced-swim test. In addition, locomotor activity and motor coordination were assessed as side-effects. DMI and fluoxetine produced an antidepressant-like effect in YA and MA animals, although in the latter group, a shift to the right in the dose-response curve was found for DMI. Importantly, neither drug was effective in SE animals. Motor side-effects were produced mainly by DMI in MA and SE rats. Therefore, a decrease in the antidepressant-like effect is associated strongly with senescence as well as an increased vulnerability to motor side-effects, particularly of tricyclics. This study is significant because SE animals are scarcely studied in pharmacological screening tests, and our findings might be useful for improving antidepressant treatments for the increasing aged population.

Participación de las hormonas gonadales en el efecto de los fármacos antidepresivos en la rata macho / Participation of gonadal hormones in the effect of antidepressant drugs in male rats

It has been proposed that gonadal hormones participate in regulation of mood and emotion in men as well as in the effect of psychoactive drugs, such as antidepressants. However, evaluation of this type of interactions has been poorly studied in clinic and basic studies. The objective of the present study was to determine the role of gonadal hormones, testosterone (T) and 17β-estradiol (E2), one of its main metabolites, in the effect of two antidepressant drugs: desipramine and fluoxetine. The former is a tricyclic antidepressant that inhibits noradrenaline reuptake in a preferential manner, while the second is a serotonin selective reup-take inhibitor (SSRI) and the most prescribed antidepressant. Behavioral evaluations were conducted in adult male rats, intact or orchidectomized (Orx), treated with T (0-2 mg/rata), E2 (0-40 µg/rata), desipramine (0-20 mg/kg), fluoxetine (0-20 mg/kg) and their combinations. Forced swimming test was used as an animal model to detect antidepressant-like effect induced by treatments, on the basis of its predictive validity. We found that desipramine and fluoxetine produced an anti-depressant-like effect in gonadally intact male rats. However, the antidepressant-like effect of both treatments was cancelled in Orx males. Treatment with E2, but not with T, produced antidepressant-like actions in Orx males. Interestingly, treatment with E2 restored the antidepressant-like effect of desipramine and fluoxetine, while supplementation with T only reestablished the antidepressant-like action of desipramine, evidencing that gonadal hormones have a differential participation in regulation of neurotransmitter systems involving in the antidepressant effect. In conclusion, the main testicular androgen T, participates in the expression of the effect of antidepressant drugs, mainly via conversion to its estrogenic metabolite E2. These results give support to the idea that a combined therapy of gonadal hormones and antidepressant drugs may be more convenient to treat depressive disorders in hypogonadal men resistant to conventional antidepressant drugs.

Se ha propuesto que las hormonas gonadales participan en la regulación del estado de ánimo en los varones, y en el efecto de los fármacos psicoactivos, tales como los antidepresivos. Sin embargo, la evaluación de este tipo de interacciones ha sido estudiada escasamente. El objetivo del presente trabajo fue determinar el papel que cumplen las hormonas testosterona (T) y 17β-estradiol (E2), uno de sus principales metabolitos, en el efecto de dos fármacos antidepresivos utilizados en la práctica clínica, desipramina y fluoxetina. El primero es un tricíclico con acciones sobre el sistema noradrenérgico, mientras que la fluoxetina es un inhibidor selectivo de la recaptura de serotonina. Las evaluaciones se llevaron a cabo utilizando ratas macho adultas jóvenes, gonadalmente intactas u orquidectomizadas (Orx), bajo tratamiento con T (0-1 mg/rata), E2 (0-40 µg/rata), desipramina (0-20 mg/kg), fluoxetina (0-20 mg/kg) y sus respectivas combinaciones. Se utilizó la prueba de nado forzado (PNF) para detectar las acciones antidepresivas de los tratamientos. Encontramos que desipramina y fluoxetina redujeron la conducta de depresión en los machos gonadalmente intactos; sin embargo, el efecto de ambos tratamientos fue abolido por la orquidectomía. El tratamiento de restitución hormonal con E2, pero no con T, indujo acciones antidepresivas en los machos Orx. A su vez, cuando los animales Orx recibieron la restitución con T se produjo la recuperación del efecto antidepresivo de la desipramina, mientras que el E2 restableció las acciones antidepresivas de ambos fármacos. En conclusión, el principal andrógeno de origen testicular, la T, participa en la expresión del efecto de los fármacos antidepresivos explorados en el presente estudio, principalmente a través de su metabolito estrogénico, el E2. Estos resultados apoyan la idea de que una terapia adjunta de tratamientos hormonales y antidepresivos sería de beneficio para varones hipogonadales que cursen con depresión resistente a los fármacos antidepresivos convencionales.